"Exponential" differential via mechanics


David J. Gall
 

Bob,

Larry Hamm's suggestion is good but it requires significant angular
displacement of the belcrank to get any substantial differential.

Consider this alternative: Make your tailcone belcrank in the shape of the
letter 'K' with the angled legs pointing forward. The rudder pedal cables
connect to the angled legs, but the rudder and tailwheel cables connect to
the straight leg. This gives a differential since the angular displacement
of the belcrank is increased for any given linear displacement of the cable
the more the angled belcrank leg moves forward in its arc [d-theta/d-x goes
as 1/cos(theta)].

Similarly, move the cable attachment points on the rudder pedals aft of the
plane of the rudder pedal pivot so that as the rudder pedal is pressed
forward, the attachment point arm becomes more perpendicular to the line of
travel of the cable.

Either of these geometries will induce a differential movement in the
belcrank; both together will give even more differential.

The resulting angular differential can be amplified or reduced by varying
the ratio between the length of the angled legs of the belcrank and the
effective lengths of the rudder pedal arms (and the desired throw of the
pedals forward of neutral). The ratio of the length of the angled legs of
the belcrank to the straight legs and, finally, to the length of the rudder
and tailwheel belhorns will control the total angle of the rudder and
tailwheel deflections with rudder pedal displacement.


David J. Gall
P.S. Larry's suggestion does not have to be fabricated as an oval or
ellipse; a simple diamond or even a rectangle will work.

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of Bob Farnam
Sent: Friday, October 20, 2006 10:08 AM
To: Q-LIST@...
Subject: RE: [Q-LIST] Taxiing before first flight. (long editorial)

My ratio is not as much as I would like, but is limited by my
own requirement that I be able to reach the unlock detent on
the full swivelling tailwheel at full rudder. This so I can
pivot around a wheel on the ground.
The result is that my airplane is less sensitive than the
original design - enough that I can fairly easily steer it
straight at takeoff speed, but still sensitive. I would
really like to have what the RC guys refer to as
"exponential" control, where the response is low in the
center part of the travel, but increases at full rudder
input. Easy to do with an RC transmitter which has it
builtin, but I haven't yet figured out a simple and durable
mechanical way to make it happen. Anyone have a sudden flash
of insight?

Bob F
EAA Flight Advisor


quickieaircraft
 

Just remember that the torque you can apply will vary
inversely with the displacement ratio--not that your
feet are torque-limited.

Imraan
UAV systems engineer and pilot in Washington DC
still looking for Q2/Q200

--- "David J. Gall" <David@...> wrote:

Bob,

Larry Hamm's suggestion is good but it requires
significant angular
displacement of the belcrank to get any substantial
differential.

Consider this alternative: Make your tailcone
belcrank in the shape of the
letter 'K' with the angled legs pointing forward.
The rudder pedal cables
connect to the angled legs, but the rudder and
tailwheel cables connect to
the straight leg. This gives a differential since
the angular displacement
of the belcrank is increased for any given linear
displacement of the cable
the more the angled belcrank leg moves forward in
its arc [d-theta/d-x goes
as 1/cos(theta)].

Similarly, move the cable attachment points on the
rudder pedals aft of the
plane of the rudder pedal pivot so that as the
rudder pedal is pressed
forward, the attachment point arm becomes more
perpendicular to the line of
travel of the cable.

Either of these geometries will induce a
differential movement in the
belcrank; both together will give even more
differential.

The resulting angular differential can be amplified
or reduced by varying
the ratio between the length of the angled legs of
the belcrank and the
effective lengths of the rudder pedal arms (and the
desired throw of the
pedals forward of neutral). The ratio of the length
of the angled legs of
the belcrank to the straight legs and, finally, to
the length of the rudder
and tailwheel belhorns will control the total angle
of the rudder and
tailwheel deflections with rudder pedal
displacement.


David J. Gall
P.S. Larry's suggestion does not have to be
fabricated as an oval or
ellipse; a simple diamond or even a rectangle will
work.

-----Original Message-----
From: Q-LIST@...
[mailto:Q-LIST@...]
On Behalf Of Bob Farnam
Sent: Friday, October 20, 2006 10:08 AM
To: Q-LIST@...
Subject: RE: [Q-LIST] Taxiing before first flight.
(long editorial)

My ratio is not as much as I would like, but is
limited by my
own requirement that I be able to reach the unlock
detent on
the full swivelling tailwheel at full rudder. This
so I can
pivot around a wheel on the ground.
The result is that my airplane is less sensitive
than the
original design - enough that I can fairly easily
steer it
straight at takeoff speed, but still sensitive. I
would
really like to have what the RC guys refer to as
"exponential" control, where the response is low
in the
center part of the travel, but increases at full
rudder
input. Easy to do with an RC transmitter which has
it
builtin, but I haven't yet figured out a simple
and durable
mechanical way to make it happen. Anyone have a
sudden flash
of insight?

Bob F
EAA Flight Advisor

__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com


Larry Hamm <LDHAMM@...>
 

David,
So, how does one achieve a smoothly increasing radius, and hence the exponential control effect, with a diamond or a rectangle?? I'm not real clear on that!
Larry Hamm

David J. Gall wrote:

P.S. Larry's suggestion does not have to be fabricated as an oval or
ellipse; a simple diamond or even a rectangle will work.


David J. Gall
 

Larry,

One does not need a "smoothly increasing radius" to get a smoothly
increasing differential control effect. Nor do we need a "smoothly"
increasing differential effect, just one that is not discontinuous or too
abrupt (no sudden "shifting gears" to unnerve the pilot). The diamond and
rectangle each meet this criterion. Consider:

The effect of your oval cam comes from the increasing arm length
perpendicular to the cable as the angular deflection moves away from
neutral. Rhetorical question: Were we to use your "oval" as a mathematical
ellipse, what aspect ratio would you advise? In the limit, the aspect ratio
could go to zero (minor axis length divided by major axis length) and we
would have a "bar" oriented parallel to the rudder cables, with said rudder
cables attached at the fore end (farthest from the rudder).

As the belcrank rotates this "bar," initially the infinitesimal motion
transmitted to the tailwheel belhorn is zero (yes, that's a problem we'll
deal with in just a moment). Then the aft end of the ellipse ("bar") "picks
up" the cable and starts to move it laterally away from the belcrank pivot,
giving an increasing arm perpendicular to the cable and starting to pull on
the cable. You'll notice that the effective arm length increases gradually
with rotation of the belcrank, not suddenly, so it gives a progressive
increase in effectiveness, just like your ellipse would give; it IS an
ellipse (okay, a degenerate ellipse if you must). Hence, the "bar" is
equivalent to the ellipse in providing a progressive differential at
increasing deflections from neutral. Using the "bar" with the rudder cables
attached at the fore end, the opposite cable moves with the fore end of the
bar giving just enough slack to let the tailwheel belhorn pivot without
letting the cables actually go slack, just like your ellipse.

What you achieve with your ellipse is that you control the "minimum" ratio
between belcrank and belhorn by choosing a minor axis length of the ellipse
that is greater than zero. The "bar" version of the ellipse has the
disadvantage that control near neutral is non-existent. In both cases, the
major axis of the ellipse/length of the bar sets the maximum ratio of
belcrank to belhorn. (The amount of differential is the ratio between the
minimum and maximum described above.)

So, the drawback to the "bar" is that it is not wide enough near neutral,
resulting in not enough control deflection, so the remedy is to make the bar
wider. Whether the long end of the bar "picks up" the cable in a perfectly
elliptical manner or not is such a minor difference that my fat feet will
never notice it. Make the "bar" wider by making it a rectangle and the
differential effect will start immediately on deflection away from neutral;
make the bar a diamond and you can enforce a small region near neutral where
the ratio stays low, then increases after the aft portion of the diamond
"picks up" the cable and starts to move it laterally, mimicking your perfect
ellipse with much simpler manufacturing effort. The only real limitation to
the shape of the ellipse/bar/diamond/rectangle cam is that it must force the
cables into convex symmetry about the forward part of the device at all
anticipated deflections so that the cables don't go slack.

Work it out in your favorite modelling software, or go prototype it in
cardboard and thumbtacks and string and convince yourself that it works just
as well with less fabrication effort than machining an elliptical plate with
a groove along its edge (that would be a pricey part indeed!)


David J. Gall

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of Larry Hamm
Sent: Sunday, October 22, 2006 8:57 PM
To: Q-LIST@...
Subject: Re: [Q-LIST] "Exponential" differential via mechanics

David,
So, how does one achieve a smoothly increasing radius, and
hence the exponential control effect, with a diamond or a
rectangle?? I'm not real clear on that!
Larry Hamm

David J. Gall wrote:

P.S. Larry's suggestion does not have to be fabricated as
an oval or
ellipse; a simple diamond or even a rectangle will work.


Larry Hamm <LDHAMM@...>
 

David,
OK, I see what you're getting at. The only practical drawback I envision with hard geometric shapes is the possibility of wear on the cables as they cross the corners. As far as expense, well, that train left the station a long time ago, and I'm not even half finished! Less than the price of a Continental exhaust valve, I'd guess.
Larry

David J. Gall wrote:

Larry,
One does not need a "smoothly increasing radius" to get a smoothly
increasing differential control effect. Nor do we need a "smoothly"
increasing differential effect, just one that is not discontinuous or too
abrupt (no sudden "shifting gears" to unnerve the pilot). The diamond and
rectangle each meet this criterion. Consider:
The effect of your oval cam comes from the increasing arm length
perpendicular to the cable as the angular deflection moves away from
neutral. Rhetorical question: Were we to use your "oval" as a mathematical
ellipse, what aspect ratio would you advise? In the limit, the aspect ratio
could go to zero (minor axis length divided by major axis length) and we
would have a "bar" oriented parallel to the rudder cables, with said rudder
cables attached at the fore end (farthest from the rudder). As the belcrank rotates this "bar," initially the infinitesimal motion
transmitted to the tailwheel belhorn is zero (yes, that's a problem we'll
deal with in just a moment). Then the aft end of the ellipse ("bar") "picks
up" the cable and starts to move it laterally away from the belcrank pivot,
giving an increasing arm perpendicular to the cable and starting to pull on
the cable. You'll notice that the effective arm length increases gradually
with rotation of the belcrank, not suddenly, so it gives a progressive
increase in effectiveness, just like your ellipse would give; it IS an
ellipse (okay, a degenerate ellipse if you must). Hence, the "bar" is
equivalent to the ellipse in providing a progressive differential at
increasing deflections from neutral. Using the "bar" with the rudder cables
attached at the fore end, the opposite cable moves with the fore end of the
bar giving just enough slack to let the tailwheel belhorn pivot without
letting the cables actually go slack, just like your ellipse.
What you achieve with your ellipse is that you control the "minimum" ratio
between belcrank and belhorn by choosing a minor axis length of the ellipse
that is greater than zero. The "bar" version of the ellipse has the
disadvantage that control near neutral is non-existent. In both cases, the
major axis of the ellipse/length of the bar sets the maximum ratio of
belcrank to belhorn. (The amount of differential is the ratio between the
minimum and maximum described above.)
So, the drawback to the "bar" is that it is not wide enough near neutral,
resulting in not enough control deflection, so the remedy is to make the bar
wider. Whether the long end of the bar "picks up" the cable in a perfectly
elliptical manner or not is such a minor difference that my fat feet will
never notice it. Make the "bar" wider by making it a rectangle and the
differential effect will start immediately on deflection away from neutral;
make the bar a diamond and you can enforce a small region near neutral where
the ratio stays low, then increases after the aft portion of the diamond
"picks up" the cable and starts to move it laterally, mimicking your perfect
ellipse with much simpler manufacturing effort. The only real limitation to
the shape of the ellipse/bar/diamond/rectangle cam is that it must force the
cables into convex symmetry about the forward part of the device at all
anticipated deflections so that the cables don't go slack.
Work it out in your favorite modelling software, or go prototype it in
cardboard and thumbtacks and string and convince yourself that it works just
as well with less fabrication effort than machining an elliptical plate with
a groove along its edge (that would be a pricey part indeed!)
David J. Gall

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of Larry Hamm
Sent: Sunday, October 22, 2006 8:57 PM
To: Q-LIST@...
Subject: Re: [Q-LIST] "Exponential" differential via mechanics

David,
So, how does one achieve a smoothly increasing radius, and hence the exponential control effect, with a diamond or a rectangle?? I'm not real clear on that!
Larry Hamm

David J. Gall wrote:


P.S. Larry's suggestion does not have to be fabricated as
an oval or
ellipse; a simple diamond or even a rectangle will work.
Quickie Builders Association WEB site
http://www.quickiebuilders.org
Yahoo! Groups Links


David J. Gall
 

Larry,

Yah, round corners. Since price is no object, you could use some of your
surplus $5 gold pieces for radiussed corners. The gold will wear instead of
the steel cables. Probably cost less than using some of those phenolic
aircraft-grade pulleys for round corners, eh? :)

Actually, you've got me thinking more and more about your/our approach. We'd
need some way to "keep" the cables so that they'd be sure to engage the
groove on your ellipse or any of my oddball shapes. It could be so simple to
make the diamond shape by using a couple of plates held apart by spacers,
with the cables running between the plates and attached to one of the
spacers at the fore end, the narrow axis of the diamond established by a
couple more spaceers, and the other end of the diamond by another spacer.
Two plates, four sets of bolts/spacers, and some cotter pins outside the
cable runs to act as cable keepers. The bottom plate could double as the JB
belcrank....

I'm opposed to the idea of modifying the Air Products tailwheel for the cost
of it, so maybe this is a cheaper approach. We'll see.

End of thread.


David J. Gall

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of Larry Hamm
Sent: Monday, October 23, 2006 8:37 AM
To: Q-LIST@...
Subject: Re: [Q-LIST] "Exponential" differential via mechanics

David,
OK, I see what you're getting at. The only practical drawback
I envision with hard geometric shapes is the possibility of
wear on the cables as they cross the corners. As far as
expense, well, that train left the station a long time ago,
and I'm not even half finished! Less than the price of a
Continental exhaust valve, I'd guess.
Larry


Bob Farnam <bfarnam@...>
 

Good suggestions, David. The "K" belcrank would also provide stronger
centering action from the pedal return springs - not a bad thing. Might make
a good winter project.

Bob F.

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]On Behalf Of
David J. Gall
Sent: Sunday, October 22, 2006 3:33 PM
To: Q-LIST@...
Subject: [Q-LIST] "Exponential" differential via mechanics


Bob,

Larry Hamm's suggestion is good but it requires significant angular
displacement of the belcrank to get any substantial differential.

Consider this alternative: Make your tailcone belcrank in the shape of the
letter 'K' with the angled legs pointing forward. The rudder pedal cables
connect to the angled legs, but the rudder and tailwheel cables connect to
the straight leg. This gives a differential since the angular displacement
of the belcrank is increased for any given linear displacement of the
cable
the more the angled belcrank leg moves forward in its arc [d-theta/d-x
goes
as 1/cos(theta)].

Similarly, move the cable attachment points on the rudder pedals aft of
the
plane of the rudder pedal pivot so that as the rudder pedal is pressed
forward, the attachment point arm becomes more perpendicular to the line
of
travel of the cable.

Either of these geometries will induce a differential movement in the
belcrank; both together will give even more differential.

The resulting angular differential can be amplified or reduced by varying
the ratio between the length of the angled legs of the belcrank and the
effective lengths of the rudder pedal arms (and the desired throw of the
pedals forward of neutral). The ratio of the length of the angled legs of
the belcrank to the straight legs and, finally, to the length of the
rudder
and tailwheel belhorns will control the total angle of the rudder and
tailwheel deflections with rudder pedal displacement.

David J. Gall
P.S. Larry's suggestion does not have to be fabricated as an oval or
ellipse; a simple diamond or even a rectangle will work.

> -----Original Message-----
> From: Q-LIST@... [mailto:Q-LIST@...]
> On Behalf Of Bob Farnam
> Sent: Friday, October 20, 2006 10:08 AM
> To: Q-LIST@...
> Subject: RE: [Q-LIST] Taxiing before first flight. (long editorial)
>
> My ratio is not as much as I would like, but is limited by my
> own requirement that I be able to reach the unlock detent on
> the full swivelling tailwheel at full rudder. This so I can
> pivot around a wheel on the ground.
> The result is that my airplane is less sensitive than the
> original design - enough that I can fairly easily steer it
> straight at takeoff speed, but still sensitive. I would
> really like to have what the RC guys refer to as
> "exponential" control, where the response is low in the
> center part of the travel, but increases at full rudder
> input. Easy to do with an RC transmitter which has it
> builtin, but I haven't yet figured out a simple and durable
> mechanical way to make it happen. Anyone have a sudden flash
> of insight?
>
> Bob F
> EAA Flight Advisor


Larry Hamm <LDHAMM@...>
 

David,
Works for me. I'd envisioned two plates with beveled edges to form a groove, but your plan would hold the cables more securely.
Besides, I'm quickly running out of the half Eagles!
Larry Hamm

David J. Gall wrote:

Actually, you've got me thinking more and more about your/our approach. We'd
need some way to "keep" the cables so that they'd be sure to engage the
groove on your ellipse or any of my oddball shapes. It could be so simple to
make the diamond shape by using a couple of plates held apart by spacers,
with the cables running between the plates and attached to one of the
spacers at the fore end, the narrow axis of the diamond established by a
couple more spaceers, and the other end of the diamond by another spacer.
Two plates, four sets of bolts/spacers, and some cotter pins outside the
cable runs to act as cable keepers. The bottom plate could double as the JB
belcrank....


Peter Harris <peterjfharris@...>
 

Fellers,

Are you really doing all this so you get more rudder authority in rollout?

Peter



_____

From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
Bob Farnam
Sent: Tuesday, 24 October 2006 4:47 AM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics



Good suggestions, David. The "K" belcrank would also provide stronger
centering action from the pedal return springs - not a bad thing. Might make
a good winter project.

Bob F.

-----Original Message-----
From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]On Behalf
Of
David J. Gall
Sent: Sunday, October 22, 2006 3:33 PM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: [Q-LIST] "Exponential" differential via mechanics

Bob,

Larry Hamm's suggestion is good but it requires significant angular
displacement of the belcrank to get any substantial differential.

Consider this alternative: Make your tailcone belcrank in the shape of the
letter 'K' with the angled legs pointing forward. The rudder pedal cables
connect to the angled legs, but the rudder and tailwheel cables connect to
the straight leg. This gives a differential since the angular displacement
of the belcrank is increased for any given linear displacement of the
cable
the more the angled belcrank leg moves forward in its arc [d-theta/d-x
goes
as 1/cos(theta)].

Similarly, move the cable attachment points on the rudder pedals aft of
the
plane of the rudder pedal pivot so that as the rudder pedal is pressed
forward, the attachment point arm becomes more perpendicular to the line
of
travel of the cable.

Either of these geometries will induce a differential movement in the
belcrank; both together will give even more differential.

The resulting angular differential can be amplified or reduced by varying
the ratio between the length of the angled legs of the belcrank and the
effective lengths of the rudder pedal arms (and the desired throw of the
pedals forward of neutral). The ratio of the length of the angled legs of
the belcrank to the straight legs and, finally, to the length of the
rudder
and tailwheel belhorns will control the total angle of the rudder and
tailwheel deflections with rudder pedal displacement.

David J. Gall
P.S. Larry's suggestion does not have to be fabricated as an oval or
ellipse; a simple diamond or even a rectangle will work.

-----Original Message-----
From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]
On Behalf Of Bob Farnam
Sent: Friday, October 20, 2006 10:08 AM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: RE: [Q-LIST] Taxiing before first flight. (long editorial)

My ratio is not as much as I would like, but is limited by my
own requirement that I be able to reach the unlock detent on
the full swivelling tailwheel at full rudder. This so I can
pivot around a wheel on the ground.
The result is that my airplane is less sensitive than the
original design - enough that I can fairly easily steer it
straight at takeoff speed, but still sensitive. I would
really like to have what the RC guys refer to as
"exponential" control, where the response is low in the
center part of the travel, but increases at full rudder
input. Easy to do with an RC transmitter which has it
builtin, but I haven't yet figured out a simple and durable
mechanical way to make it happen. Anyone have a sudden flash
of insight?

Bob F
EAA Flight Advisor


Larry Hamm <LDHAMM@...>
 

Peter,
No, Bob Farnum wanted a tailwheel which turned faster as more pedal was applied. Less twitchy when centered or nearly so, strong response toward the limits.
Larry Hamm

Peter Harris wrote:

Fellers,
Are you really doing all this so you get more rudder authority in rollout?
Peter


Peter Harris <peterjfharris@...>
 

Thanks Larry.

To me it seems like an awful lot of complication for a dubious result. The
sensitivity of the tailwheel steering increases as the speed reduces. At
first touchdown the aircraft momentum and tail makes it stay straight and
any attempt to deflect it is limited by the flex of the tailspring and the
grip of the tyre, so at first it will skid rather than deflect the tail.
Later in the ground roll the plans ratio seems right for the job to me. I
think it is just something we learn to do and get the feel with familiarity.

But I am in favour of most ideas as long as they are not compulsory.

Cheers

Peter



_____

From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
Larry Hamm
Sent: Tuesday, 24 October 2006 9:32 AM
To: Q-LIST@...
Subject: Re: [Q-LIST] "Exponential" differential via mechanics



Peter,
No, Bob Farnum wanted a tailwheel which turned faster as more pedal was
applied. Less twitchy when centered or nearly so, strong response toward
the limits.
Larry Hamm

Peter Harris wrote:

Fellers,

Are you really doing all this so you get more rudder authority in rollout?

Peter


David J. Gall
 

Peter,

Allow me to rebut:

Part of the reason it skids is that the plans ratio moves it too much. At
higher speeds, the tailwheel is quickly and easily pushed past the limiting
slip angle and it begins to skid. Like an all-flying tailplane that has too
much throw, the pilot can push it right past "stall" and it becomes less
effective than it could be were it not stalled. Likewise, the plans ratio
allows the rudder control system to push the tailwheel right on past the
skid limit of the tire (between 3 and 7 degrees, depending on tire type)
when the pilot applies "a little" rudder pressure.

At lower speeds, when the tail can respond and a turning radius can be
accomodated, the amount of deflection can be more without exceeding the
limiting slip angle. So it makes sense to have a differential system. At
higher speeds the smaller throw near center helps to keep from skidding the
tailwheel, actually increasing effectiveness, and at lower speeds the large
throw needed for ramp maneuvering is still available.

If you think it is a lot of complication, consider that your airplane
actually has the opposite, a DEcreasing differential, due to the installed
angle of the rudder pedals and the absence of any thought given to the
design. The cables simply attach to the sides of the rudder pedals, so as
the rudder pedal is pressed forward the amount of linear pull on the cable
actually diminishes for increasing angular displacement of the rudder pedal.


Lack of thought does not imply simplicity; more thoughtful design does not
imply increased complication. I gave a perfectly valid suggestion that
increases the "fail point" count by exactly ZERO while reversing the
bass-ackwards differential that the fine folks at QAC gave you. Simply
change the shape of the one-piece rudder pedal so that the cable attach
point is aft of the hinge axis. This one change will give INcreasing
differential without all the monkey-motion of a belcrank, if you wish, while
still addressing the fundamental issue of an ill-executed design.

I'd wager that there aren't many airplane designers who actually take the
time to think about the linkages they create in their control systems, and
we consumers/pilots pay the price every day. Burt Rutan is not immune from
mess-ups in his designs, and having Tom Jewett do the detail design work on
the Quickie was no guarantee of error detection and correction. Gary LeGare
(the plumber) scaling up the design to two-place certainly didn't add any
particular expertise in the realm of control system design and the ensuing
redesign for mass production was not about refinement, either. So you have a
minimalist system that had no real thought given to it adopted in toto and
you now wish to defend it on the basis of its "simplicity" and limited
number of "fail points"? Hello? It doesn't work right, what about that?

The design itself IS a fail point, witness its failure to prevent the
tailwheel from skidding during the fast part of the ground run. Were it not
for the many, more serious design issues missed by the QAC, we would have
been on about this one, say, twenty years ago, but it has taken us this long
to synthesize a consensus on the JB6Pack to where we can actually start to
talk about fine-tuning. If that warrants poo-pooing, then so be it. Some
things truly aren't worth persuing; this one is, and I knew it in 1997 when
I first published my thoughts on the matter.

Carry on, O gravel-runway reflexor-less single-data-point friend....


David J. Gall
P.S. And your Norton Rotary wasn't a lot of complication for dubious
results...?
P.P.S. When are Jabiru going to finally hire an internal-flow consultant to
design proper cooling for their engines instead of telling owners to burn
'em in for 50-100 hrs until they "loosen up"? Some of the nicest engines,
some of the most pitiful cowls.... :(

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of Peter Harris
Sent: Tuesday, October 24, 2006 12:07 AM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics

Thanks Larry.

To me it seems like an awful lot of complication for a
dubious result. The sensitivity of the tailwheel steering
increases as the speed reduces. At first touchdown the
aircraft momentum and tail makes it stay straight and any
attempt to deflect it is limited by the flex of the
tailspring and the grip of the tyre, so at first it will skid
rather than deflect the tail.
Later in the ground roll the plans ratio seems right for the
job to me. I think it is just something we learn to do and
get the feel with familiarity.

But I am in favour of most ideas as long as they are not compulsory.

Cheers

Peter


wesisberg <wes@...>
 

I've been experimenting with graduated-effectiveness since Jim rated
57RM's taxi a 5. I'm targetting toe-travel for the runway and
leg-travel for taxiway, so I have a clear rule for staying out of
trouble on the runway. For my toes/legs, it came out to about 21 and
35 degrees pedal rotation, aiming for 10-12 degrees max runway turn,
(probably too high) and the 30-degree tailwheel detente.

I've tried pulleys on the pedal to make the cable travel 1:n with
rotation; the effect at the rudder horn is to increase the angular
speed at large displacements, enabling me to detune the lower
displacements for the runway. That worked nicely, but it didn't get
me the turns I wanted at taxi.

So then I tried increasing radius. I couldn't figure out a good way
to make a true increasing-radius spiral, so I instead made a large
pulley (4.25" radius) but mounted only a 75-degree arc on a 2.25"
pedal center, resulting in 2.25 to 3.0" radius, to get the target
22/35 degree rotation. (Works, but bulkhead interference.)

(Re: the suggestion to put the cable attach forward on the pedal:
resulted in even more pull on the other pedal - e.g., a 30-degree push
could result in a 40+-degree pull. For me, my off/pull leg was
knocking the panel, which was distracting. Doing it at the bellcrank
would sort this out.)

Testing soon...
Wes

--- In Q-LIST@..., "Bob Farnam" <bfarnam@...> wrote:

Good suggestions, David. The "K" belcrank would also provide stronger
centering action from the pedal return springs - not a bad thing.
Might make
a good winter project.

Bob F.
-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]On
Behalf Of
David J. Gall
Sent: Sunday, October 22, 2006 3:33 PM
To: Q-LIST@...
Subject: [Q-LIST] "Exponential" differential via mechanics


Bob,

Larry Hamm's suggestion is good but it requires significant angular
displacement of the belcrank to get any substantial differential.

Consider this alternative: Make your tailcone belcrank in the
shape of the
letter 'K' with the angled legs pointing forward. The rudder pedal
cables
connect to the angled legs, but the rudder and tailwheel cables
connect to
the straight leg. This gives a differential since the angular
displacement
of the belcrank is increased for any given linear displacement of the
cable
the more the angled belcrank leg moves forward in its arc [d-theta/d-x
goes
as 1/cos(theta)].

Similarly, move the cable attachment points on the rudder pedals
aft of
the
plane of the rudder pedal pivot so that as the rudder pedal is pressed
forward, the attachment point arm becomes more perpendicular to
the line
of
travel of the cable.

Either of these geometries will induce a differential movement in the
belcrank; both together will give even more differential.

The resulting angular differential can be amplified or reduced by
varying
the ratio between the length of the angled legs of the belcrank
and the
effective lengths of the rudder pedal arms (and the desired throw
of the
pedals forward of neutral). The ratio of the length of the angled
legs of
the belcrank to the straight legs and, finally, to the length of the
rudder
and tailwheel belhorns will control the total angle of the rudder and
tailwheel deflections with rudder pedal displacement.

David J. Gall
P.S. Larry's suggestion does not have to be fabricated as an oval or
ellipse; a simple diamond or even a rectangle will work.

> -----Original Message-----
> From: Q-LIST@... [mailto:Q-LIST@...]
> On Behalf Of Bob Farnam
> Sent: Friday, October 20, 2006 10:08 AM
> To: Q-LIST@...
> Subject: RE: [Q-LIST] Taxiing before first flight. (long editorial)
>
> My ratio is not as much as I would like, but is limited by my
> own requirement that I be able to reach the unlock detent on
> the full swivelling tailwheel at full rudder. This so I can
> pivot around a wheel on the ground.
> The result is that my airplane is less sensitive than the
> original design - enough that I can fairly easily steer it
> straight at takeoff speed, but still sensitive. I would
> really like to have what the RC guys refer to as
> "exponential" control, where the response is low in the
> center part of the travel, but increases at full rudder
> input. Easy to do with an RC transmitter which has it
> builtin, but I haven't yet figured out a simple and durable
> mechanical way to make it happen. Anyone have a sudden flash
> of insight?
>
> Bob F
> EAA Flight Advisor






[Non-text portions of this message have been removed]


Peter Harris <peterjfharris@...>
 

Hi David,

I apologise if my posts on this subject have seemed a bit negative. I should
be the last one to discourage experiment and design as it is my main
interest and

I am always impressed by the thorough and highly informed approach you take,
and the mod to the pedals is a simpler design. But it is just this
additional pivoting bellcrank differential thingo that you are on about that
makes me have to raise my hand to present a different point of view.



1. At high speed on touchdown any missaplication of rudder/tailwheel
steering is accommodated by flex and skid. Crude but very simple and
effective.

2. At intermediate to low speed the plans steering ratio works fine
(for me )



With a limited amount of experience all of this is imprinted in the brain
stem, just like riding a bike. It is automatic and cannot be described.



My message is simplificate, simplificate. !



I am not sure if you have flown, landed or fast taxied a Q on gravel, tarmac
or concrete?. It is very good exercise for the brain stem.

Trouble is now a whole bunch of people are out on a diverting tedious,
complex hair splitting exercise when I really do think that it is
unnecessary.

Just my humble opinion David, but from my experience the simplest way is
usually the best.



My experience with the Norton taught me very nicely how to simplificate

And if you are going to start throwing stones at Jabiru I think you should
join their list at jabiruengines@yahoogroups so you will be better informed.


It would be better not to resort to personal attacks.



Peter

_____

From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
David J. Gall
Sent: Tuesday, 24 October 2006 7:42 PM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics



Peter,

Allow me to rebut:

Part of the reason it skids is that the plans ratio moves it too much. At
higher speeds, the tailwheel is quickly and easily pushed past the limiting
slip angle and it begins to skid. Like an all-flying tailplane that has too
much throw, the pilot can push it right past "stall" and it becomes less
effective than it could be were it not stalled. Likewise, the plans ratio
allows the rudder control system to push the tailwheel right on past the
skid limit of the tire (between 3 and 7 degrees, depending on tire type)
when the pilot applies "a little" rudder pressure.

At lower speeds, when the tail can respond and a turning radius can be
accomodated, the amount of deflection can be more without exceeding the
limiting slip angle. So it makes sense to have a differential system. At
higher speeds the smaller throw near center helps to keep from skidding the
tailwheel, actually increasing effectiveness, and at lower speeds the large
throw needed for ramp maneuvering is still available.

If you think it is a lot of complication, consider that your airplane
actually has the opposite, a DEcreasing differential, due to the installed
angle of the rudder pedals and the absence of any thought given to the
design. The cables simply attach to the sides of the rudder pedals, so as
the rudder pedal is pressed forward the amount of linear pull on the cable
actually diminishes for increasing angular displacement of the rudder pedal.

Lack of thought does not imply simplicity; more thoughtful design does not
imply increased complication. I gave a perfectly valid suggestion that
increases the "fail point" count by exactly ZERO while reversing the
bass-ackwards differential that the fine folks at QAC gave you. Simply
change the shape of the one-piece rudder pedal so that the cable attach
point is aft of the hinge axis. This one change will give INcreasing
differential without all the monkey-motion of a belcrank, if you wish, while
still addressing the fundamental issue of an ill-executed design.

I'd wager that there aren't many airplane designers who actually take the
time to think about the linkages they create in their control systems, and
we consumers/pilots pay the price every day. Burt Rutan is not immune from
mess-ups in his designs, and having Tom Jewett do the detail design work on
the Quickie was no guarantee of error detection and correction. Gary LeGare
(the plumber) scaling up the design to two-place certainly didn't add any
particular expertise in the realm of control system design and the ensuing
redesign for mass production was not about refinement, either. So you have a
minimalist system that had no real thought given to it adopted in toto and
you now wish to defend it on the basis of its "simplicity" and limited
number of "fail points"? Hello? It doesn't work right, what about that?

The design itself IS a fail point, witness its failure to prevent the
tailwheel from skidding during the fast part of the ground run. Were it not
for the many, more serious design issues missed by the QAC, we would have
been on about this one, say, twenty years ago, but it has taken us this long
to synthesize a consensus on the JB6Pack to where we can actually start to
talk about fine-tuning. If that warrants poo-pooing, then so be it. Some
things truly aren't worth persuing; this one is, and I knew it in 1997 when
I first published my thoughts on the matter.

Carry on, O gravel-runway reflexor-less single-data-point friend....

David J. Gall
P.S. And your Norton Rotary wasn't a lot of complication for dubious
results...?
P.P.S. When are Jabiru going to finally hire an internal-flow consultant to
design proper cooling for their engines instead of telling owners to burn
'em in for 50-100 hrs until they "loosen up"? Some of the nicest engines,
some of the most pitiful cowls.... :(

-----Original Message-----
From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]
On Behalf Of Peter Harris
Sent: Tuesday, October 24, 2006 12:07 AM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: RE: [Q-LIST] "Exponential" differential via mechanics

Thanks Larry.

To me it seems like an awful lot of complication for a
dubious result. The sensitivity of the tailwheel steering
increases as the speed reduces. At first touchdown the
aircraft momentum and tail makes it stay straight and any
attempt to deflect it is limited by the flex of the
tailspring and the grip of the tyre, so at first it will skid
rather than deflect the tail.
Later in the ground roll the plans ratio seems right for the
job to me. I think it is just something we learn to do and
get the feel with familiarity.

But I am in favour of most ideas as long as they are not compulsory.

Cheers

Peter


Mike Perry <dmperry1012@...>
 

To Peter Harris, but also for anyone overseas: Why do you say "But I am in
favour of most ideas as long as they are not compulsory." What do you
mean? These are EXPERIMENTAL aircraft. In the USA we can do almost
anything we can talk the inspector into, which is almost anything except
hardware store bolts without safety wire. The word "compulsory" just
doesn't make sense -- how could it be compulsory, or who could make it
so? Is this some legal or licensing issue in your country?

Otherwise, Peter, I don't understand the vehemence with which you oppose
the six-pack. There is now a lot of experience with these airplanes and a
lot of it is bad. You should have heard the reaction at my local EAA
chapter when I said I was building a Q-200. The general reaction is "how
do you land something that lands so fast and is so squirrely on the
runway?" These guys have seen a Q-2 land and they are not impressed. The
fact that a few people have mastered landing bird doesn't mean the design
is reasonable.

Mike Perry



At 05:07 PM 10/24/2006 +1000, Peter Harris wrote:

Thanks Larry.

To me it seems like an awful lot of complication for a dubious result. The
sensitivity of the tailwheel steering increases as the speed reduces. At
first touchdown the aircraft momentum and tail makes it stay straight and
any attempt to deflect it is limited by the flex of the tailspring and the
grip of the tyre, so at first it will skid rather than deflect the tail.
Later in the ground roll the plans ratio seems right for the job to me. I
think it is just something we learn to do and get the feel with familiarity.

But I am in favour of most ideas as long as they are not compulsory.

Cheers

Peter
At 25 Oct 2006 11:29:44 +1000 Peter Harris wrote


Trouble is now a whole bunch of people are out on a diverting tedious,
complex hair splitting exercise when I really do think that it is
unnecessary.


David J. Gall
 

Peter,

I never meant to launch a personal attack against you. In my world view,
disagreeing with you does not constitute such, but challenging your
character does. I do not believe that I maligned your character, but if I
did, I apologize and welcome instruction in that which crossed over into
offense.

To clarify: My position on the tailcone belcrank is that it is a better
solution than merely splitting the cables somewhere mid-fuselage. Granted,
ideally the rudder belhorn IS the tailcone belcrank, but that puts all the
connecting goodies out in the airstream (=slowness). Besides, the QAC folks
got it exactly backwards by running the cables FIRST to the tailwheel and
then FORWARD to the rudder. Tailspring breaks and all directional control is
lost.

So, in order of evolution:

1) Use the rudder belcrank as the terminus for the rudder cables, then run
separate cables to the tailwheel. Much better (as you have done). However,
the geometry is not favorable for the tailwheel cables/springs and as I
said, all the slowness leaks out of the fuselage. (Though I do believe that
the lower rudder hinge IS sufficiently robust for such duty.)

2) Put the slowness inside the fuselage where it belongs. But there's the
rub; simply splitting the cables and running one part to the rudder and one
part to the tailwheel invites various minor and major catastrophes, from
rudder flutter to inability to separate the ratios of the control inputs to
each (wheel vs. rudder) to loss of directional control if the tailspring
breaks (yes, it could happen depending on how the whole thing is arranged).

3) A solution to the problems in 2) is to run separate cables all the way
from the rudder pedals to the rudder and tailwheel. Different attach points
on the rudder pedals can accommodate the need for different ratios, the
tailwheel springs can go anywhere, all is good in the world. This might be
the simplest, most austere, most elegant solution available (how come nobody
promotes this one???!)...

HOWEVER,

4) There are people who already HAVE a tailcone belcrank. These people are
in the forefront of defining a pseudo-standard for what constitutes an
acceptable Quickie vis-a-vis the JB6Pack. I've fought good and hard to get
my alignment suggestions recognized as psrt of the 6-Pack because I
recognize that you can never win in a contest against superior marketing
savvy. Not to mention that they are RIGHT (for the most part). Likewise, why
fight success by arguing against the tailcone belcrank. These people HAVE
the belcrank, they BELIEVE in it, and it is part of the GOSPEL of how to
make an acceptable airplane. And it works. You might disagree on engineering
grounds, but the marketing machine is what will eventually lift these planes
out of the dustbin of history and bring the resale value up to something
above sub-par. So what if the solution isn't the most pure one possible? In
fact, that might be an advantage because it is IDENTIFIABLE as so VERY
different from the original. As an engineer you know that there is no
optimum solution, only solutions (PLURAL), so pick one. So long as the
solution has been decreed by the marketing department and is justifiably a
bona fide solution, then allow the engineers to massage it into a more
useful, more elegant, more functional solution than the rudimentary initial
device may have been. What's the harm?

5) These planes were meant to be built by avarage guys with little more than
a high school education. The subtleties of design may escape them, but they
can identify that a part is or is not built in accordance with "the
drawing." Sometimes "complicating" the design actually makes it simpler to
build or just to understand. Sometimes maybe people don't want to dig under
the panel to extract their rudder pedals and get new parts welded to them,
so they find it easier to just add a new belcrank and cut the cables to
suit.

6) Since you don't have a fuselage split, you may not appreciate the
perceived benefit of having the rudder and tailwheel cables all captured
right there in the mouth of the tailcone. It may not actually be a benefit,
but it is perceived as one.

So, Peter, you see, I'm not at all opposed to what you've done or your
opposition to what others are doing. I'm just greatly in favor of some kind
of standardization such as we would have had if a man of Burt Rutan's
stature had been at the helm of the Quickie Aircraft Corporation. Absent
that leadership, I'll take the JB6Pack Cheerleaders Council as defacto
leadership if only through sheer vocal determination (not that they're wide
of the mark, either) in order to establish some sort of recognizable parity
to yank this fine airplane design out of the doldrums of its well-deserved
reputation. There's no reason for the general consensus among homebuilders
to be to sneer at the world's most efficient two seat airplane just because
it lands like snot on sandpaper. Give it a Kleenex and forget the quibbles
over design economy and eloquence. Fix it, put a happy face on it, and make
it friendly again.

As for your Norton, I was only trying to draw a parallel, noting that you
have "abandoned" the elegance of few moving parts and rotary motion in favor
of a well-polished but old-school design with lots of reciprocating bits, in
analogy to the high parts count and "fail point" count of the "un-needed"
belcrank that we continue to try to refine....

As for Jabiru, well, I've spent enough time under their hood already to know
that that little jewel of an engine is being mistreated by the factory
personnel, whoever they are, who are "advising" the design of cowlings for
the various airplanes, including Jabiru's own, that house the sweet little
engines. The plenum design they've recommended is poorly executed, leaks,
and leaves the crankcase soaking in uncirculated cylinder waste heat. If
you've copied anything like the factory cowl on a Jabiru or Thorpedo, then I
think you'll be buying new crankshaft and camshaft bearings sooner than you
should have to. Evidence: the "loosening up" period recommended by the
factory. Evidence: Five minutes at full throttle in a J230 leads to
excessive oil temps in level flight. Evidence: ground operations lead to
high cylinder head temps on #6 under the stock plenums. Evidence: what the
heck are all those cooling outlets for on a Thorpedo??! I won't join the
battle, though, because they have marketing muscle and market penetration on
their side. And I don't have time. But for you, friend, I'll make time to
hint that perhaps you should investigate the possibility that you could be
cooking your expensive investment into scrap aluminum under the factory's
advice.

Cheers, Peter, and carry on. Never mind all this ruckus Stateside.


David J. Gall
P.S. No, I haven't taxied a Q and I don't think I need to. I joined this
discussion because another pilot/engineer had already determined that the
problem existed and had identified the correct solution. His was a question
of implementation. You, however, have questioned the original assertion that
there is even a problem to address. Granted, questioning the assumptions is
what good engineers and armchair quarterbacks do, but all this "diverting
tedious, complex splitting of hairs" has actually been by request. The
necessity thereof was never at issue.

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of Peter Harris
Sent: Tuesday, October 24, 2006 6:30 PM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics

Hi David,

I apologise if my posts on this subject have seemed a bit
negative. I should be the last one to discourage experiment
and design as it is my main interest and

I am always impressed by the thorough and highly informed
approach you take, and the mod to the pedals is a simpler
design. But it is just this additional pivoting bellcrank
differential thingo that you are on about that makes me have
to raise my hand to present a different point of view.



1. At high speed on touchdown any missaplication of
rudder/tailwheel
steering is accommodated by flex and skid. Crude but very
simple and effective.

2. At intermediate to low speed the plans steering
ratio works fine
(for me )



With a limited amount of experience all of this is imprinted
in the brain stem, just like riding a bike. It is automatic
and cannot be described.



My message is simplificate, simplificate. !



I am not sure if you have flown, landed or fast taxied a Q on
gravel, tarmac or concrete?. It is very good exercise for the
brain stem.

Trouble is now a whole bunch of people are out on a diverting
tedious, complex hair splitting exercise when I really do
think that it is unnecessary.

Just my humble opinion David, but from my experience the
simplest way is usually the best.



My experience with the Norton taught me very nicely how to
simplificate

And if you are going to start throwing stones at Jabiru I
think you should join their list at jabiruengines@yahoogroups
so you will be better informed.


It would be better not to resort to personal attacks.



Peter

_____

From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of David J. Gall
Sent: Tuesday, 24 October 2006 7:42 PM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics



Peter,

Allow me to rebut:

Part of the reason it skids is that the plans ratio moves it
too much. At higher speeds, the tailwheel is quickly and
easily pushed past the limiting slip angle and it begins to
skid. Like an all-flying tailplane that has too much throw,
the pilot can push it right past "stall" and it becomes less
effective than it could be were it not stalled. Likewise, the
plans ratio allows the rudder control system to push the
tailwheel right on past the skid limit of the tire (between 3
and 7 degrees, depending on tire type) when the pilot applies
"a little" rudder pressure.

At lower speeds, when the tail can respond and a turning
radius can be accomodated, the amount of deflection can be
more without exceeding the limiting slip angle. So it makes
sense to have a differential system. At higher speeds the
smaller throw near center helps to keep from skidding the
tailwheel, actually increasing effectiveness, and at lower
speeds the large throw needed for ramp maneuvering is still available.

If you think it is a lot of complication, consider that your
airplane actually has the opposite, a DEcreasing
differential, due to the installed angle of the rudder pedals
and the absence of any thought given to the design. The
cables simply attach to the sides of the rudder pedals, so as
the rudder pedal is pressed forward the amount of linear pull
on the cable actually diminishes for increasing angular
displacement of the rudder pedal.

Lack of thought does not imply simplicity; more thoughtful
design does not imply increased complication. I gave a
perfectly valid suggestion that increases the "fail point"
count by exactly ZERO while reversing the bass-ackwards
differential that the fine folks at QAC gave you. Simply
change the shape of the one-piece rudder pedal so that the
cable attach point is aft of the hinge axis. This one change
will give INcreasing differential without all the
monkey-motion of a belcrank, if you wish, while still
addressing the fundamental issue of an ill-executed design.

I'd wager that there aren't many airplane designers who
actually take the time to think about the linkages they
create in their control systems, and we consumers/pilots pay
the price every day. Burt Rutan is not immune from mess-ups
in his designs, and having Tom Jewett do the detail design
work on the Quickie was no guarantee of error detection and
correction. Gary LeGare (the plumber) scaling up the design
to two-place certainly didn't add any particular expertise in
the realm of control system design and the ensuing redesign
for mass production was not about refinement, either. So you
have a minimalist system that had no real thought given to it
adopted in toto and you now wish to defend it on the basis of
its "simplicity" and limited number of "fail points"? Hello?
It doesn't work right, what about that?

The design itself IS a fail point, witness its failure to
prevent the tailwheel from skidding during the fast part of
the ground run. Were it not for the many, more serious design
issues missed by the QAC, we would have been on about this
one, say, twenty years ago, but it has taken us this long to
synthesize a consensus on the JB6Pack to where we can
actually start to talk about fine-tuning. If that warrants
poo-pooing, then so be it. Some things truly aren't worth
persuing; this one is, and I knew it in 1997 when I first
published my thoughts on the matter.

Carry on, O gravel-runway reflexor-less single-data-point friend....

David J. Gall
P.S. And your Norton Rotary wasn't a lot of complication for
dubious results...?
P.P.S. When are Jabiru going to finally hire an internal-flow
consultant to design proper cooling for their engines instead
of telling owners to burn 'em in for 50-100 hrs until they
"loosen up"? Some of the nicest engines, some of the most
pitiful cowls.... :(


Ron Triano <rondefly@...>
 

David and Peter, I sincerely hope my ramblings on the way I went about my
tailwheel control and wheel alignment has not offended anyone, I simply was
not pleased with the way others have attacked the problems. I have been a
building contractor for over 40 years and have worked very close with
engineers of all types so I possibly understand much more than the average Q
builder as far as structural items are concerned. Each time I do something
that is not per plans or what everyone else is doing I spend much time in
research until I accept something or abandon it.

I do agree with your points of the rudder bellcrank or horn as you call it.
I also think the two cables you stated would solve any questions and could
have the springs inside out of the airstream. Also I feel the rudder horn is
plenty stout for the use it will get. I would like to insert other
questions for your suggestions if I may.

Since most agree that the high speed taxi at landing or takeoff seams to be
where less tailwheel would be better, why not a larger rudder as I have
heard on this list by several. Due to the elevators on the canard I can see
why a 3 point is the way for takeoff and landing, not being able to lift the
tail. These are the areas I would like to hear others chat about.

With you two being engineers, I would like to hear any remarks about the way
I have done my wheel alignment. I really feel very strongly about being able
to adjust the wheels for alignment rather than a fixed point alignment,
because no two Q's are the same. Please state exactly what you think, I will
not be offended. We all need to work together to improve the design.



Ron Triano

South Lake Tahoe, CA

The Sonerai is finished and flying

finishing the Q200

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
David J. Gall
Sent: Wednesday, October 25, 2006 2:26 AM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics



Peter,

I never meant to launch a personal attack against you. In my world view,
disagreeing with you does not constitute such, but challenging your
character does. I do not believe that I maligned your character, but if I
did, I apologize and welcome instruction in that which crossed over into
offense.

To clarify: My position on the tailcone belcrank is that it is a better
solution than merely splitting the cables somewhere mid-fuselage. Granted,
ideally the rudder belhorn IS the tailcone belcrank, but that puts all the
connecting goodies out in the airstream (=slowness). Besides, the QAC folks
got it exactly backwards by running the cables FIRST to the tailwheel and
then FORWARD to the rudder. Tailspring breaks and all directional control is
lost.

So, in order of evolution:

1) Use the rudder belcrank as the terminus for the rudder cables, then run
separate cables to the tailwheel. Much better (as you have done). However,
the geometry is not favorable for the tailwheel cables/springs and as I
said, all the slowness leaks out of the fuselage. (Though I do believe that
the lower rudder hinge IS sufficiently robust for such duty.)

2) Put the slowness inside the fuselage where it belongs. But there's the
rub; simply splitting the cables and running one part to the rudder and one
part to the tailwheel invites various minor and major catastrophes, from
rudder flutter to inability to separate the ratios of the control inputs to
each (wheel vs. rudder) to loss of directional control if the tailspring
breaks (yes, it could happen depending on how the whole thing is arranged).

3) A solution to the problems in 2) is to run separate cables all the way
from the rudder pedals to the rudder and tailwheel. Different attach points
on the rudder pedals can accommodate the need for different ratios, the
tailwheel springs can go anywhere, all is good in the world. This might be
the simplest, most austere, most elegant solution available (how come nobody
promotes this one???!)...

HOWEVER,

4) There are people who already HAVE a tailcone belcrank. These people are
in the forefront of defining a pseudo-standard for what constitutes an
acceptable Quickie vis-a-vis the JB6Pack. I've fought good and hard to get
my alignment suggestions recognized as psrt of the 6-Pack because I
recognize that you can never win in a contest against superior marketing
savvy. Not to mention that they are RIGHT (for the most part). Likewise, why
fight success by arguing against the tailcone belcrank. These people HAVE
the belcrank, they BELIEVE in it, and it is part of the GOSPEL of how to
make an acceptable airplane. And it works. You might disagree on engineering
grounds, but the marketing machine is what will eventually lift these planes
out of the dustbin of history and bring the resale value up to something
above sub-par. So what if the solution isn't the most pure one possible? In
fact, that might be an advantage because it is IDENTIFIABLE as so VERY
different from the original. As an engineer you know that there is no
optimum solution, only solutions (PLURAL), so pick one. So long as the
solution has been decreed by the marketing department and is justifiably a
bona fide solution, then allow the engineers to massage it into a more
useful, more elegant, more functional solution than the rudimentary initial
device may have been. What's the harm?

5) These planes were meant to be built by avarage guys with little more than
a high school education. The subtleties of design may escape them, but they
can identify that a part is or is not built in accordance with "the
drawing." Sometimes "complicating" the design actually makes it simpler to
build or just to understand. Sometimes maybe people don't want to dig under
the panel to extract their rudder pedals and get new parts welded to them,
so they find it easier to just add a new belcrank and cut the cables to
suit.

6) Since you don't have a fuselage split, you may not appreciate the
perceived benefit of having the rudder and tailwheel cables all captured
right there in the mouth of the tailcone. It may not actually be a benefit,
but it is perceived as one.

So, Peter, you see, I'm not at all opposed to what you've done or your
opposition to what others are doing. I'm just greatly in favor of some kind
of standardization such as we would have had if a man of Burt Rutan's
stature had been at the helm of the Quickie Aircraft Corporation. Absent
that leadership, I'll take the JB6Pack Cheerleaders Council as defacto
leadership if only through sheer vocal determination (not that they're wide
of the mark, either) in order to establish some sort of recognizable parity
to yank this fine airplane design out of the doldrums of its well-deserved
reputation. There's no reason for the general consensus among homebuilders
to be to sneer at the world's most efficient two seat airplane just because
it lands like snot on sandpaper. Give it a Kleenex and forget the quibbles
over design economy and eloquence. Fix it, put a happy face on it, and make
it friendly again.

As for your Norton, I was only trying to draw a parallel, noting that you
have "abandoned" the elegance of few moving parts and rotary motion in favor
of a well-polished but old-school design with lots of reciprocating bits, in
analogy to the high parts count and "fail point" count of the "un-needed"
belcrank that we continue to try to refine....

As for Jabiru, well, I've spent enough time under their hood already to know
that that little jewel of an engine is being mistreated by the factory
personnel, whoever they are, who are "advising" the design of cowlings for
the various airplanes, including Jabiru's own, that house the sweet little
engines. The plenum design they've recommended is poorly executed, leaks,
and leaves the crankcase soaking in uncirculated cylinder waste heat. If
you've copied anything like the factory cowl on a Jabiru or Thorpedo, then I
think you'll be buying new crankshaft and camshaft bearings sooner than you
should have to. Evidence: the "loosening up" period recommended by the
factory. Evidence: Five minutes at full throttle in a J230 leads to
excessive oil temps in level flight. Evidence: ground operations lead to
high cylinder head temps on #6 under the stock plenums. Evidence: what the
heck are all those cooling outlets for on a Thorpedo??! I won't join the
battle, though, because they have marketing muscle and market penetration on
their side. And I don't have time. But for you, friend, I'll make time to
hint that perhaps you should investigate the possibility that you could be
cooking your expensive investment into scrap aluminum under the factory's
advice.

Cheers, Peter, and carry on. Never mind all this ruckus Stateside.

David J. Gall
P.S. No, I haven't taxied a Q and I don't think I need to. I joined this
discussion because another pilot/engineer had already determined that the
problem existed and had identified the correct solution. His was a question
of implementation. You, however, have questioned the original assertion that
there is even a problem to address. Granted, questioning the assumptions is
what good engineers and armchair quarterbacks do, but all this "diverting
tedious, complex splitting of hairs" has actually been by request. The
necessity thereof was never at issue.

-----Original Message-----
From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]
On Behalf Of Peter Harris
Sent: Tuesday, October 24, 2006 6:30 PM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: RE: [Q-LIST] "Exponential" differential via mechanics

Hi David,

I apologise if my posts on this subject have seemed a bit
negative. I should be the last one to discourage experiment
and design as it is my main interest and

I am always impressed by the thorough and highly informed
approach you take, and the mod to the pedals is a simpler
design. But it is just this additional pivoting bellcrank
differential thingo that you are on about that makes me have
to raise my hand to present a different point of view.



1. At high speed on touchdown any missaplication of
rudder/tailwheel
steering is accommodated by flex and skid. Crude but very
simple and effective.

2. At intermediate to low speed the plans steering
ratio works fine
(for me )



With a limited amount of experience all of this is imprinted
in the brain stem, just like riding a bike. It is automatic
and cannot be described.



My message is simplificate, simplificate. !



I am not sure if you have flown, landed or fast taxied a Q on
gravel, tarmac or concrete?. It is very good exercise for the
brain stem.

Trouble is now a whole bunch of people are out on a diverting
tedious, complex hair splitting exercise when I really do
think that it is unnecessary.

Just my humble opinion David, but from my experience the
simplest way is usually the best.



My experience with the Norton taught me very nicely how to
simplificate

And if you are going to start throwing stones at Jabiru I
think you should join their list at jabiruengines@yahoogroups
so you will be better informed.


It would be better not to resort to personal attacks.



Peter

_____

From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]
On Behalf Of David J. Gall
Sent: Tuesday, 24 October 2006 7:42 PM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: RE: [Q-LIST] "Exponential" differential via mechanics



Peter,

Allow me to rebut:

Part of the reason it skids is that the plans ratio moves it
too much. At higher speeds, the tailwheel is quickly and
easily pushed past the limiting slip angle and it begins to
skid. Like an all-flying tailplane that has too much throw,
the pilot can push it right past "stall" and it becomes less
effective than it could be were it not stalled. Likewise, the
plans ratio allows the rudder control system to push the
tailwheel right on past the skid limit of the tire (between 3
and 7 degrees, depending on tire type) when the pilot applies
"a little" rudder pressure.

At lower speeds, when the tail can respond and a turning
radius can be accomodated, the amount of deflection can be
more without exceeding the limiting slip angle. So it makes
sense to have a differential system. At higher speeds the
smaller throw near center helps to keep from skidding the
tailwheel, actually increasing effectiveness, and at lower
speeds the large throw needed for ramp maneuvering is still available.

If you think it is a lot of complication, consider that your
airplane actually has the opposite, a DEcreasing
differential, due to the installed angle of the rudder pedals
and the absence of any thought given to the design. The
cables simply attach to the sides of the rudder pedals, so as
the rudder pedal is pressed forward the amount of linear pull
on the cable actually diminishes for increasing angular
displacement of the rudder pedal.

Lack of thought does not imply simplicity; more thoughtful
design does not imply increased complication. I gave a
perfectly valid suggestion that increases the "fail point"
count by exactly ZERO while reversing the bass-ackwards
differential that the fine folks at QAC gave you. Simply
change the shape of the one-piece rudder pedal so that the
cable attach point is aft of the hinge axis. This one change
will give INcreasing differential without all the
monkey-motion of a belcrank, if you wish, while still
addressing the fundamental issue of an ill-executed design.

I'd wager that there aren't many airplane designers who
actually take the time to think about the linkages they
create in their control systems, and we consumers/pilots pay
the price every day. Burt Rutan is not immune from mess-ups
in his designs, and having Tom Jewett do the detail design
work on the Quickie was no guarantee of error detection and
correction. Gary LeGare (the plumber) scaling up the design
to two-place certainly didn't add any particular expertise in
the realm of control system design and the ensuing redesign
for mass production was not about refinement, either. So you
have a minimalist system that had no real thought given to it
adopted in toto and you now wish to defend it on the basis of
its "simplicity" and limited number of "fail points"? Hello?
It doesn't work right, what about that?

The design itself IS a fail point, witness its failure to
prevent the tailwheel from skidding during the fast part of
the ground run. Were it not for the many, more serious design
issues missed by the QAC, we would have been on about this
one, say, twenty years ago, but it has taken us this long to
synthesize a consensus on the JB6Pack to where we can
actually start to talk about fine-tuning. If that warrants
poo-pooing, then so be it. Some things truly aren't worth
persuing; this one is, and I knew it in 1997 when I first
published my thoughts on the matter.

Carry on, O gravel-runway reflexor-less single-data-point friend....

David J. Gall
P.S. And your Norton Rotary wasn't a lot of complication for
dubious results...?
P.P.S. When are Jabiru going to finally hire an internal-flow
consultant to design proper cooling for their engines instead
of telling owners to burn 'em in for 50-100 hrs until they
"loosen up"? Some of the nicest engines, some of the most
pitiful cowls.... :(


David J. Gall
 

Ron,

I think the ability to adjust camber and toe as you have done is nice, but
overkill. The only real requirement is that the worst-case scenario -- max
weight, forward CG, steeply crowned runway -- be met with positive camber
and toe. Even slightly negative camber has proved to be manageable, but
more-positive camber and toe is not an issue. If you get zero-zero at max
gross weight, there's nothing wrong with three degrees positive camber at
lighter weight. (The inverse is not true, however.) The tire serviceabilty
that your change provides is definitely convenient, but at what weight
penalty? And how often - really - do you expect that you'll actually adjust
your camber for any particular flight once the airplane is in daily service?
I'm sure you know the term "drill on assembly."

Regarding a larger rudder, no need, but "no harm-no foul" if you do it. Just
keep in mind that putting on a larger rudder is not addressing the problem
of an ineffective tailwheel. You can choose to make the tailwheel effective
or not and still overpower it with a bigger rudder. If you're gonna make a
bigger rudder, you might as well just get a locking tailwheel and be done
with all the complexities of a steerable one. Line it up, lock the
tailwheel, and go. Lock the tailwheel, land, then unlock and use rudder and
differential brakes to steer the castering thing. No more belcranks and
springs and such, just one cable to pull the lock lever. Better not forget
it on landing, though! :)

JMHO,


David J. Gall

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...]
On Behalf Of Ron Triano
Sent: Wednesday, October 25, 2006 7:54 AM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics

David and Peter, I sincerely hope my ramblings on the way I
went about my tailwheel control and wheel alignment has not
offended anyone, I simply was not pleased with the way others
have attacked the problems. I have been a building contractor
for over 40 years and have worked very close with engineers
of all types so I possibly understand much more than the
average Q builder as far as structural items are concerned.
Each time I do something that is not per plans or what
everyone else is doing I spend much time in research until I
accept something or abandon it.

I do agree with your points of the rudder bellcrank or horn
as you call it.
I also think the two cables you stated would solve any
questions and could have the springs inside out of the
airstream. Also I feel the rudder horn is plenty stout for
the use it will get. I would like to insert other questions
for your suggestions if I may.

Since most agree that the high speed taxi at landing or
takeoff seams to be where less tailwheel would be better, why
not a larger rudder as I have heard on this list by several.
Due to the elevators on the canard I can see why a 3 point is
the way for takeoff and landing, not being able to lift the
tail. These are the areas I would like to hear others chat about.

With you two being engineers, I would like to hear any
remarks about the way I have done my wheel alignment. I
really feel very strongly about being able to adjust the
wheels for alignment rather than a fixed point alignment,
because no two Q's are the same. Please state exactly what
you think, I will not be offended. We all need to work
together to improve the design.



Ron Triano

South Lake Tahoe, CA

The Sonerai is finished and flying

finishing the Q200


Peter Harris <peterjfharris@...>
 

David ,



If your derogatory comments about the Jabiru and the Norton and my lack of a
reflexor were NOT meant to suggest that I have poor judgement, then those
comments are irrelevant, besides being uninformed, misleading and
gratuitous. If you cannot debate the merits of your design without
resorting to that kind of response it shows a lack of maturity.

<To clarify: My position on the tailcone belcrank is that it is a better
solution than merely splitting the cables somewhere mid-fuselage. Granted,
ideally the rudder belhorn IS the tailcone belcrank, but that puts all the
connecting goodies out in the airstream (=slowness). Besides, the QAC folks
got it exactly backwards by running the cables FIRST to the tailwheel and
then FORWARD to the rudder. Tailspring breaks and all directional control is
lost. >

The tailspring supplied by QAC may well break. It is full of resin. I am
using a tailspring properly designed by John Tenhave and made by a
professional spar maker. Sam also has one of these. It is flexible but very
much stronger than the original. I don't expect it to break in normal use
including the occasional heavy landing. A better tailspring and no unwanted
complication in bellcranks. At worst a broken tailspring = a lazy
groundloop which is allowed in planned operations anyway and should be
practiced occasionally.

<1) Use the rudder belcrank as the terminus for the rudder cables, then run
separate cables to the tailwheel. Much better (as you have done). However,
the geometry is not favorable for the tailwheel cables/springs and as I
said, all the slowness leaks out of the fuselage. (Though I do believe that
the lower rudder hinge IS sufficiently robust for such duty.) >

I have not done that. My rudder drives from the tailwheel belcrank as
originally planned and I would not be happy to load the rudder hinge that
way.

You assert there is a problem with the geometry but you have never taxied a
Quickie ! I find no problem with it on gravel, tarmac , concrete and wet
grass.

<2) Put the slowness inside the fuselage where it belongs. But there's the
rub; simply splitting the cables and running one part to the rudder and one
part to the tailwheel invites various minor and major catastrophes, from
rudder flutter to inability to separate the ratios of the control inputs to
each (wheel vs. rudder) to loss of directional control if the tailspring
breaks (yes, it could happen depending on how the whole thing is arranged).


Rudder vs tailwheel authority is irrelevant . Tailwheel rules on the ground.
Follow the POH landing technique and get it grounded from the beginning. Get
a properly designed tail spring. Rudder flutter identified to this
configuration??


<3) A solution to the problems in 2) is to run separate cables all the way
from the rudder pedals to the rudder and tailwheel. Different attach points
on the rudder pedals can accommodate the need for different ratios, the
tailwheel springs can go anywhere, all is good in the world. This might be
the simplest, most austere, most elegant solution available (how come nobody
promotes this one???!) >...

Because almost 50% of the group has been sold an extra belcrank.


<4) There are people who already HAVE a tailcone belcrank. These people are
in the forefront of defining a pseudo-standard for what constitutes an
acceptable Quickie vis-a-vis the JB6Pack. I've fought good and hard to get
my alignment suggestions recognized as psrt of the 6-Pack because I
recognize that you can never win in a contest against superior marketing
savvy. Not to mention that they are RIGHT (for the most part). Likewise, why
fight success by arguing against the tailcone belcrank. These people HAVE
the belcrank, they BELIEVE in it, and it is part of the GOSPEL of how to
make an acceptable airplane. And it works. You might disagree on engineering
grounds, but the marketing machine is what will eventually lift these planes
out of the dustbin of history and bring the resale value up to something
above sub-par. So what if the solution isn't the most pure one possible? In
fact, that might be an advantage because it is IDENTIFIABLE as so VERY
different from the original. As an engineer you know that there is no
optimum solution, only solutions (PLURAL), so pick one. So long as the
solution has been decreed by the marketing department and is justifiably a
bona fide solution, then allow the engineers to massage it into a more
useful, more elegant, more functional solution than the rudimentary initial
device may have been. What's the harm? >

David that it is just not good enough to go along with something that is not
well engineered just because of superior advertising. That is behaving like
a bunch of Lemmings.

You have the training and the responsibility to show the right way.

<5) These planes were meant to be built by avarage guys with little more
than
a high school education. The subtleties of design may escape them, but they
can identify that a part is or is not built in accordance with "the
drawing." Sometimes "complicating" the design actually makes it simpler to
build or just to understand. Sometimes maybe people don't want to dig under
the panel to extract their rudder pedals and get new parts welded to them,
so they find it easier to just add a new belcrank and cut the cables to
suit. >

This paragraph is not making a lot of sense.

6) Since you don't have a fuselage split, you may not appreciate the
perceived benefit of having the rudder and tailwheel cables all captured
right there in the mouth of the tailcone. It may not actually be a benefit,
but it is perceived as one.



David what are you smoking ?? If it is not right get it unperceived


<So, Peter, you see, I'm not at all opposed to what you've done or your
opposition to what others are doing. I'm just greatly in favor of some kind
of standardization such as we would have had if a man of Burt Rutan's
stature had been at the helm of the Quickie Aircraft Corporation. Absent
that leadership, I'll take the JB6Pack Cheerleaders Council as defacto
leadership if only through sheer vocal determination (not that they're wide
of the mark, either) in order to establish some sort of recognizable parity
to yank this fine airplane design out of the doldrums of its well-deserved
reputation. There's no reason for the general consensus among homebuilders
to be to sneer at the world's most efficient two seat airplane just because
it lands like snot on sandpaper. Give it a Kleenex and forget the quibbles
over design economy and eloquence. Fix it, put a happy face on it, and make
it friendly again >.

Instead of accepting hype and rolling over I think we should get hard facts
for good and only good, properly justified design amendments, approve them
and put the details in the website resources link . That would include your
wheel alignment . There should definitely be some safety limits set for
operation of the reflexor , I have experienced unsafe operation with zero
reflex and I confirmed it again this week.

Whatever you have to say about Jabiru is uninformed and may even be
libelous. Try writing that stuff to the jabiruengines@yahoogroups if you
really think it's true.

<David J. Gall
<P.S. No, I haven't taxied a Q and I don't think I need to. I joined this
discussion because another pilot/engineer had already determined that the
problem existed and had identified the correct solution. His was a question
of implementation. You, however, have questioned the original assertion that
there is even a problem to address. Granted, questioning the assumptions is
what good engineers and armchair quarterbacks do, but all this "diverting
tedious, complex splitting of hairs" has actually been by request. The
necessity thereof was never at issue >.

David It is long overdue, you need to give your brainstem a run. Get in a
Quickie and fast taxi to 50KTS. Try a ground loop or two. Then you will be
better qualified to offer design advice.

Peter Harris

-----Original Message-----
From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]
On Behalf Of Peter Harris
Sent: Tuesday, October 24, 2006 6:30 PM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: RE: [Q-LIST] "Exponential" differential via mechanics

Hi David,

I apologise if my posts on this subject have seemed a bit
negative. I should be the last one to discourage experiment
and design as it is my main interest and

I am always impressed by the thorough and highly informed
approach you take, and the mod to the pedals is a simpler
design. But it is just this additional pivoting bellcrank
differential thingo that you are on about that makes me have
to raise my hand to present a different point of view.



1. At high speed on touchdown any missaplication of
rudder/tailwheel
steering is accommodated by flex and skid. Crude but very
simple and effective.

2. At intermediate to low speed the plans steering
ratio works fine
(for me )



With a limited amount of experience all of this is imprinted
in the brain stem, just like riding a bike. It is automatic
and cannot be described.



My message is simplificate, simplificate. !



I am not sure if you have flown, landed or fast taxied a Q on
gravel, tarmac or concrete?. It is very good exercise for the
brain stem.

Trouble is now a whole bunch of people are out on a diverting
tedious, complex hair splitting exercise when I really do
think that it is unnecessary.

Just my humble opinion David, but from my experience the
simplest way is usually the best.



My experience with the Norton taught me very nicely how to
simplificate

And if you are going to start throwing stones at Jabiru I
think you should join their list at jabiruengines@yahoogroups
so you will be better informed.


It would be better not to resort to personal attacks.



Peter

_____

From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]
On Behalf Of David J. Gall
Sent: Tuesday, 24 October 2006 7:42 PM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: RE: [Q-LIST] "Exponential" differential via mechanics



Peter,

Allow me to rebut:

Part of the reason it skids is that the plans ratio moves it
too much. At higher speeds, the tailwheel is quickly and
easily pushed past the limiting slip angle and it begins to
skid. Like an all-flying tailplane that has too much throw,
the pilot can push it right past "stall" and it becomes less
effective than it could be were it not stalled. Likewise, the
plans ratio allows the rudder control system to push the
tailwheel right on past the skid limit of the tire (between 3
and 7 degrees, depending on tire type) when the pilot applies
"a little" rudder pressure.

At lower speeds, when the tail can respond and a turning
radius can be accomodated, the amount of deflection can be
more without exceeding the limiting slip angle. So it makes
sense to have a differential system. At higher speeds the
smaller throw near center helps to keep from skidding the
tailwheel, actually increasing effectiveness, and at lower
speeds the large throw needed for ramp maneuvering is still available.

If you think it is a lot of complication, consider that your
airplane actually has the opposite, a DEcreasing
differential, due to the installed angle of the rudder pedals
and the absence of any thought given to the design. The
cables simply attach to the sides of the rudder pedals, so as
the rudder pedal is pressed forward the amount of linear pull
on the cable actually diminishes for increasing angular
displacement of the rudder pedal.

Lack of thought does not imply simplicity; more thoughtful
design does not imply increased complication. I gave a
perfectly valid suggestion that increases the "fail point"
count by exactly ZERO while reversing the bass-ackwards
differential that the fine folks at QAC gave you. Simply
change the shape of the one-piece rudder pedal so that the
cable attach point is aft of the hinge axis. This one change
will give INcreasing differential without all the
monkey-motion of a belcrank, if you wish, while still
addressing the fundamental issue of an ill-executed design.

I'd wager that there aren't many airplane designers who
actually take the time to think about the linkages they
create in their control systems, and we consumers/pilots pay
the price every day. Burt Rutan is not immune from mess-ups
in his designs, and having Tom Jewett do the detail design
work on the Quickie was no guarantee of error detection and
correction. Gary LeGare (the plumber) scaling up the design
to two-place certainly didn't add any particular expertise in
the realm of control system design and the ensuing redesign
for mass production was not about refinement, either. So you
have a minimalist system that had no real thought given to it
adopted in toto and you now wish to defend it on the basis of
its "simplicity" and limited number of "fail points"? Hello?
It doesn't work right, what about that?

The design itself IS a fail point, witness its failure to
prevent the tailwheel from skidding during the fast part of
the ground run. Were it not for the many, more serious design
issues missed by the QAC, we would have been on about this
one, say, twenty years ago, but it has taken us this long to
synthesize a consensus on the JB6Pack to where we can
actually start to talk about fine-tuning. If that warrants
poo-pooing, then so be it. Some things truly aren't worth
persuing; this one is, and I knew it in 1997 when I first
published my thoughts on the matter.

Carry on, O gravel-runway reflexor-less single-data-point friend....

David J. Gall
P.S. And your Norton Rotary wasn't a lot of complication for
dubious results...?
P.P.S. When are Jabiru going to finally hire an internal-flow
consultant to design proper cooling for their engines instead
of telling owners to burn 'em in for 50-100 hrs until they
"loosen up"? Some of the nicest engines, some of the most
pitiful cowls.... :(


Ron Triano <rondefly@...>
 

Thanks David, I appreciate your views, I will stick by what I have done on
my Q and feel great about the changes. I guess I differ from some others on
this list trying to cram certain changes, (the 6pack) down new builder
throats, there are many ways to a safer build. I really think we all should
let new builders know the problems with the original design and that there
are many ways to correct the problems. Anyone considering construction of a
Q should have some mechanical ability or they should not attempt doing it
themselves but hire competent help. I have always been an experimenter, like
to search for better ways to an end and do it with every project in real
life or building my toys. With all the knowledge available I get great
satisfaction in researching new ideas.



I don't think the 1-1/4" axle and several plys of cloth on each side will
add much to the weight of my installation, but see, I don't have all those
extra bellcranks and cables. Ha Ha. When I do the final toe/camber adjust I
will do it for only one person aboard as that is 98% of my flying. However I
will set it for additional weight since there are two seats available. The
only time I see a need to re-adjust is the event of adverse tire wear.

I really don't see the need for a larger rudder, it was not suggested by me
but by others on this list, Just wanted your views on it. On my computerized
view of my finished Q it shows a tailwheel fairing, that should take care of
any extra drag from the springs. I am presently working on major changes in
the engine compartment, and as usual only implemented by much research.

Thank you again



Ron Triano

South Lake Tahoe, CA

The Sonerai is finished and flying

finishing the Q200

-----Original Message-----
From: Q-LIST@... [mailto:Q-LIST@...] On Behalf Of
David J. Gall
Sent: Wednesday, October 25, 2006 7:58 PM
To: Q-LIST@...
Subject: RE: [Q-LIST] "Exponential" differential via mechanics



Ron,

I think the ability to adjust camber and toe as you have done is nice, but
overkill. The only real requirement is that the worst-case scenario -- max
weight, forward CG, steeply crowned runway -- be met with positive camber
and toe. Even slightly negative camber has proved to be manageable, but
more-positive camber and toe is not an issue. If you get zero-zero at max
gross weight, there's nothing wrong with three degrees positive camber at
lighter weight. (The inverse is not true, however.) The tire serviceabilty
that your change provides is definitely convenient, but at what weight
penalty? And how often - really - do you expect that you'll actually adjust
your camber for any particular flight once the airplane is in daily service?
I'm sure you know the term "drill on assembly."

Regarding a larger rudder, no need, but "no harm-no foul" if you do it. Just
keep in mind that putting on a larger rudder is not addressing the problem
of an ineffective tailwheel. You can choose to make the tailwheel effective
or not and still overpower it with a bigger rudder. If you're gonna make a
bigger rudder, you might as well just get a locking tailwheel and be done
with all the complexities of a steerable one. Line it up, lock the
tailwheel, and go. Lock the tailwheel, land, then unlock and use rudder and
differential brakes to steer the castering thing. No more belcranks and
springs and such, just one cable to pull the lock lever. Better not forget
it on landing, though! :)

JMHO,

David J. Gall

-----Original Message-----
From: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
[mailto:Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com]
On Behalf Of Ron Triano
Sent: Wednesday, October 25, 2006 7:54 AM
To: Q-LIST@yahoogroups. <mailto:Q-LIST%40yahoogroups.com> com
Subject: RE: [Q-LIST] "Exponential" differential via mechanics

David and Peter, I sincerely hope my ramblings on the way I
went about my tailwheel control and wheel alignment has not
offended anyone, I simply was not pleased with the way others
have attacked the problems. I have been a building contractor
for over 40 years and have worked very close with engineers
of all types so I possibly understand much more than the
average Q builder as far as structural items are concerned.
Each time I do something that is not per plans or what
everyone else is doing I spend much time in research until I
accept something or abandon it.

I do agree with your points of the rudder bellcrank or horn
as you call it.
I also think the two cables you stated would solve any
questions and could have the springs inside out of the
airstream. Also I feel the rudder horn is plenty stout for
the use it will get. I would like to insert other questions
for your suggestions if I may.

Since most agree that the high speed taxi at landing or
takeoff seams to be where less tailwheel would be better, why
not a larger rudder as I have heard on this list by several.
Due to the elevators on the canard I can see why a 3 point is
the way for takeoff and landing, not being able to lift the
tail. These are the areas I would like to hear others chat about.

With you two being engineers, I would like to hear any
remarks about the way I have done my wheel alignment. I
really feel very strongly about being able to adjust the
wheels for alignment rather than a fixed point alignment,
because no two Q's are the same. Please state exactly what
you think, I will not be offended. We all need to work
together to improve the design.



Ron Triano

South Lake Tahoe, CA

The Sonerai is finished and flying

finishing the Q200