Re: Load Limits: Confessions of an Obsessive Compulsive Nerd


John ten
 

Mark,

Unfortunately your posting is riddled with error as well.

You need to get to grips with structural analysis before you post.

This is just plain (and plane) nonsense.

After
figuring the numbers of Carbon fiber plys, LS1 design by W X L X
Cord. The
LS1 wing loading came out to an acceptable safety margin wing loading of
1340 lbs.

LS1 design by W x L x cord ? Huh?

"wing loading of 1340 lbs" is absurd and meaningless. Rutan is known
as one of the most adept composite engineers around, he is well known
for being unbeatable for his speed and accuracy of calculation. The
engobabble you are offering is the opposite.

You are also completely wrong about the behaviour of fiberglass it is
repeatable and well known. The fact that you do not know it should
sound loud warning bells that you need to find out, not make
engineering decisions based on an absence of information.

ten times stronger in what? tension, compression, shear?

If this is the depth of your knowledge and this what you have based
your decision upon to raise the MAUW to 1300 lbs, change your decision
before you kill yourself and others.

John








--- In Q-LIST@..., "Mark Alexander" <6oclockhigh@...> wrote:

Mike,


I just want to say thank you for providing some helpful information
on Q200
Gross Weight. A few months ago I asked for the Max Gross Weight for a
Tri-Q200 with an LS1 Canard. The conversation went from bad to
worst. I
think I was part of the problem because I expected the data to be
ready and
available. My rule of thumb is I have to have supporting data to
believe
what is being stated. Unless the data is from a owner, builder,
operator
who has done the home work to prove their clam in which they are
more then
happy to provide. I usually don't believe them. So in having said
that I'm
going to break my own rule of thumb.



After the let down with the Website conversation. I went back to
some of my
friends who are aeronautical engineers and love to crunch numbers.
After
figuring the numbers of Carbon fiber plys, LS1 design by W X L X
Cord. The
LS1 wing loading came out to an acceptable safety margin wing loading of
1340 lbs. I wanted to publish the data on the web but my friends
asked me
not to because these were not hard facts but based on soft data. We
need
more engineer data to build a data predicable simulation. Which
really means
IF AND BUT were not calculated in to the math. My friend affectionately
called it; Rutan math.



Because no one knows how fiberglass will react under certain conditions.
It's not repeatable. I mean that we have data to tell when 4130 steel
will start to bend, temperature, shear factors and tensile strength
just to
name a few. Metal will shear or show signs that its going to or ductile
overload. Metal is repeatable but fiberglass still has a lot of
unknowns.
If I build a metal airplane in my Hangar in the winter (30 *) the metal
still has the same repeatable calculated stress load limits. Same
conditions; Fiberglass not so much. Pound for pound fiberglass is
ten times
stronger than metal, if properly manufactured. But you just can't
tell when
it's going to break, it just doesn't tell you and there is the
dilemma in
calculating fiberglass load limits.



So after all that I guess I'm supporting your findings. I'm still
building
on Tri Q200 and I'm still just about done. Just one more thing to
finish up
and I'll be flying. BTW I'm listing my Max Gross Weight at 1300 lbs.



Mark

On Tue, Jun 3, 2008 at 12:00 PM, Mike Perry <dmperry1012@...> wrote:

Recently I produced a set of files designed to help people using
Q200s
at
gross weight over 1100 lbs. (Now posted on Jon Finley's website as
Q200_POH_supplement.zip) That drew questions on and off list about
Marc
Waddelow's analysis of the wing and the allegedly marginal
strength of the
main wing. Meanwhile Larry Severson keeps posting a claim that the Q2
canard was designed to 30Gs. Last nite and this AM I re-read
everything I
can find on Waddelow's analysis and all the old materials I have
on the
Q2xx from QAC and others. Here is my summary:

I did locate one statement supporting the 30G design of the
canard, along
with some other interesting information:

Lightweight does not, however, imply low structural margins; at
the drawing

board stage, the Q2 rear wing was designed for a positive 12G
limit load
and the canard, since it doubles as the main landing gear is
required to
withstand over 30G's of positive inflight loads and a 500 ft./min.
landing
impact. (Sport Aviation, May 1981, as reprinted by QAC for
distribution as
advertising)

The only documentation I have of Marc Waddelow's analysis of the
wing is in

Quicktalk # 28, pp 9-10. This is a summary of an exchange of letters
between Marc and Gene Sheehan. To summarize two pages of material, the
more detailed Marc's analysis, the closer he got to Sheehan's
numbers. I
have no doubt Marc had a better design, but I think it was only
slightly
better. If anyone has more information I am interested. Read the
newsletter, it's too long to reproduce here.

One quote from Sheehan: "As to your [Waddelow's] suggested
modifications I
can't see anything wrong with them other than an increase in
weight. This
may seem to be a small matter to you but my experience has shown
that the
typical homebuilder who doesn't trust the designer and adds a
little beef
here and there usually ends up with a very heavy airplane. He also
insists
on flying over gross weight. So instead of having a stronger
airplane he
may actually have less margin. . . "

Furthermore, Sheehan reported non-destructive testing to 8Gs, and
recommended any modification of the main wing or canard be tested
to "at
least 50% above what you wish to use as your limit G loading."

I did not find any documentation of testing to actual limits; that
is, no
one built a wing and loaded it until it broke. I think QAC should
have,
but they didn't.

We do have other data: there are some amazingly heavy Quickies
flying. Some Q2xxs were built with O235s, full panels, design mods
and the
kitchen sink. I have Larry Koutz's listing of flying Qs in the USA,
probably from about year 2000. There are several planes with empty
weights
over 825 lbs! Charlie Harris of Littleton Colorado has a Q200
weighing 832
lbs with 1000 hours.

Then we have the Weight and Balance info sent with my kit, showing
a gross
of 1300. There is no testing or engineering documentation to
support this
that I am aware of.

All this suggests to me the wing structure is safe at gross above 1100
lbs. I only remember two wing failures. One was an improper
repair; one
plane had a secondary gas tank above the main wing and a fuel leak
eroded
the foam.

Conclusions: I think the Q2xx main wing is safe up to a gross of 1300
lbs., but anyone flying at gross weights over 1100 lbs should read the
discussion in Quicktalk 28.

I still get angry with people who post "information" like "designed to
30Gs" but don't provide documentation. Then I end up doing the
research. See Title. Monk is my friend. I prefer sleep to research.

Mike Perry

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