Re: Taxiing before first flight. (long editorial)


Mike Perry <dmperry1012@...>
 

I would like to point out something I think people loose sight of regarding
the Jim-Bob 6-Pack: The bellcrank mod allows the builder to reduce the
pivot arc (travel) of the tail wheel relative to the rudder travel. That
makes the plane much less susceptible to sudden swerves at high speed, and
thus easier to control during takeoff and landing. The tail wheel springs
also desensitize the tail wheel.

(You could achieve the same thing using split cables and changing the
lengths of the control horns on the rudder and tail wheel, but the bell
crank is an easy place to change the relative travel.)

I understand the tail wheels of some WW II fighters had very little travel,
but I can't seem to document that right now. My opinion is that tail
draggers that land at high speeds need tail wheels that are "desensitized"
with a reduced pivot arc and tail wheel springs.

I understand the Q-2 plans from QAC used a tail wheel with a wide pivot arc
in order to negotiate tighter corners on airports. This design worked OK
on the Quickie, which lands at a lower speed, but has been problematic on
the Q-2 and Q-200. The 6-Pack has full pivoting tail wheel and
differential brakes to allow you to negotiate tight corners, and a reduced
pivot arc and springs to desensitize the tail wheel at high speeds.

Jim, I think this is what you meant when you said: "With just splitting the
cables, Wes has no way to differentiate (detune)the angle of the tail wheel
from the rudder." I just wanted to say it more clearly.

Mike Perry

At 06:33 PM 10/19/2006 +0000, Jim Patillo wrote:


Fellas,

I had the opportunity to high speed taxi Wes Isbergs' Q200 Saturday
before his first flight and would like to share some info. Even
though he did a fair job of controlling the plane down the runway, I
found it very difficult to handle. I could not keep it straight
either with rudder or his braking system or the combination. Wind
was about 12K - 10-15 degrees off the nose. (Note: he has no
bellcrank but has split the cables internally to rudder and tail
wheel and has a modified dual differential finger brake system).
Guess he didn't buy the Jim/Bob Six Pack Mod concept. My immediate
response to him was to park the plane before he got hurt and fix the
problem!

Now for the details. With just splitting the cables, Wes has no way
to differentiate (detune)the angle of the tail wheel from the
rudder. He's installed a modified dual finger brake that has a
single stick that slides sideways to apply pressure to one master
cylinder or the other or both. That is not good because its way to
sensitive and hard to get positive results from known inputs.
Further exacerabating the situation is his hand is on the brake and
not the throttle when taking off or landing. Not a good thing! How
many serious tail draggers have anything other than toe brakes or
heel brakes? Its just not natural to have finger brakes on a tail
dragger and is to dangerous in my opinion. There are way to many
things going on to be doing this additional "dance".

This leads me to a conclusion. The Q's with sixpack mods installed
are really quite tame, ask anyone who has them. I cannot for the
life of me understand why anyone would want to do anything
different. Yet we see it all the time. Most new Q pilots have a very
difficult time handling their planes initially and often crack them
up or have an incident even before the first flight. Because you
didn't invent it, doesn't mean you can't copy it! The situation with
Wes; here's a very intellignet fella sitting on a field with
sucessuful Q's all around, yet he chooses to do his own thing. Why?
To much additional cost? To much additional labor? Doesn't have a
clear undrstanding of the problem? Doesn't know how to fix it - NOT!
What? I do not understand this.

This leads me to another conclusion. If Wes, sitting in the middle
of LVK with sucessful planes all aroud, chooses to go a different
route, what does that tell you about builders working on their own,
isolated and out of touch? I now understand why this is not so
simple and brace yourself fellas, we're in for more!

These comments are in no way intended to bring heat on Wes but to
simply make a couple of points as to why Q pilots are still smacking
up their planes. Hopefully this turns on the lights for someoen who
don't want to get hurt.

Regards,
Jim Patillo N46JP Q200 800 hours in type. So far, even in severe
crosswinds, this plane has never deviated from the center line.
Bingo! There's a reason.

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