Testing On The Cheap

rattlesnake wrote:
"Brian Whatcott" schrieb im Newsbeitrag
...
.....

Well, how about that!
And I thought seat belts were often specified at 29 g's. Silly me!

we talk about seats, not seat belts. How many G's do you think will your
C-150, -172 **seats** be good for?



Well, anonymous poster, you don't need my opinion. And I don't have a
demonstrated load case on those seats.
But take a look at that test case you mentioned: 2 tons on the wings.
Let's say you were demonstrating a 4 g load capability. That would imply
the gross wt is 1000 lbs.
If the engine weighs 220 lb (for a 100 HP) and the two seats can carry
200 lb wetware each - that would amount to 620 lb. Then the airframe
would weigh say 380 lb.

If you were a clueful designer interested in proving a test article, you
might want to ENSURE that a support on the seats, the engine mount and a
the empennage could react the wing proof loads. That would be a smart
thing to do, don't you think?

Do you really, really think an airframe designer hasn't thought it through?
Shouldn't you?

Brian W

"Brian Whatcott" schrieb im Newsbeitrag
news .....
Do you really, really think an airframe designer hasn't thought it
through?
Shouldn't you?

The airframe designer hasn't thought it through, at least of my plans-build
'kitplane'. This aircraft was designed to fly nicely and it shows it really
does. But it absolutely was not designed for static load testing (which in
my view was a smart decision, because designing-in hardpoints which are
completely useless in flight is just adding dead weight). Besides - you
can't just add up the support capability of seats and engine mount by
ignoring the moment arms of your construction.

rattlesnake wrote:
"Brian Whatcott" schrieb im Newsbeitrag
news ....
Do you really, really think an airframe designer hasn't thought it
through?
Shouldn't you?

The airframe designer hasn't thought it through, at least of my plans-build
'kitplane'. This aircraft was designed to fly nicely and it shows it really
does. But it absolutely was not designed for static load testing (which in
my view was a smart decision, because designing-in hardpoints which are
completely useless in flight is just adding dead weight). Besides - you
can't just add up the support capability of seats and engine mount by
ignoring the moment arms of your construction.


And the moment legs, moment feet, etc....

Jerry Wass wrote:
rattlesnake wrote:
"Brian Whatcott" schrieb im Newsbeitrag
news ....
Do you really, really think an airframe designer hasn't thought it
through?
Shouldn't you?

The airframe designer hasn't thought it through, at least of my
plans-build 'kitplane'. This aircraft was designed to fly nicely and
it shows it really does. But it absolutely was not designed for static
load testing (which in my view was a smart decision, because
designing-in hardpoints which are completely useless in flight is just
adding dead weight). Besides - you can't just add up the support
capability of seats and engine mount by ignoring the moment arms of
your construction.

And the moment legs, moment feet, etc....


Hehe....yes, indeed.
But hopefully in a static test (if it IS a static test) the clockwise
moments equal the anticlock moments.
Guess what? If they don't add to zero, the thing rotates.
No special hardpoints called for - just spread the reaction for test
loads proportionate to the mass involved. The design MUST be able to
react the loads due to the limit stresses on the aircraft mass as is,
else it's not a load test!
And a last thought for the anonymous poster: if an experimental design
has not been static tested at least once, you take your life in your hands.
And that's the great beauty of this free society - if you want to risk
killing yourself, you can. (But not in Germany under German rules, only
FAA rules)

Brian W

"Jerry Wass" schrieb im Newsbeitrag
. ..
.....
And the moment legs, moment feet, etc....

EOD

"rattlesnake" wrote in message
...

"Jerry Wass" schrieb im Newsbeitrag
. ..
....
And the moment legs, moment feet, etc....

EOD

EOD ???
--
Jim in NC

Veeduber wrote:
So... how strong is your wing?

The only sure way to know is to TEST it.

How do we do that? We roll the airframe over on it's nose, support
the main spar with a structure of some sort... Douglas Fir 2x4's works
okay... then we stack a known weight onto the wing.

Still confused? No problem; just follow me through. We already know
what the bird weighs., thanks to all those imaginary flights out to
Catalina and back. Empty weight is 318 pounds.. Nine gallons of
gasoline is 54 pounds and one sorta-skinny pilot is 155 pounds, so
we've got 318 + 54 + 155 = 527 pounds... and we wanna see if the wing
will support 527 pounds. (Yeah, I know... lemme work up to it.)

Start by removing the spinner and the prop, then bolt-on a wooden
bolster that weighs exactly the same as the spinner & prop. Now we
whistle-up some help and we ever to gently roll the plane forward,
first onto the bolster and then onto the support structure that pokes
up into the cockpit and bears against the main spar about where my
legs would go. The structure is kinda high because we dont want the
vertical stabilizer to touch the driveway. But we finally get it
rolled over and supported on the structure we've made (now THERE was a
fun project). Is it level? We check it out. Then we position a
couple of yard-sticks just off each wing tip. Now we cover the wing
with cardboard and start stacking on the weight.

What kinda weight?

Well... back in the Good Ol' Days, whenever that was, our local EAA
chapter would have a couple thousand pounds of lead weights all neatly
marked in matching pairs, and they'd deliver it and bust their backs
helping you do the Static Test (which doesn't have anything to do with
radio). Nowadays your best bet is probably bags of Portland cement or
other building material ( ...such as Plaster Sand... ) available in
bags, each marked with the weight of the contents. ( Anywhere outside
of the USA it'll probably be marked in kilograms instead of pounds.
Not a probelm; just work it out. )

Now you lay the weights onto the protected surface of the upside-down
wing, starting in the middle and working your way out toward the
tips. Five hundred and twenty-seven pounds is about six bags of
Portland cement so you'd have three bags per side.

Out at the wing tips, the marker aligned with your yard-sticks (meter
sticks across the pond) probably won't show any deflection at all.
Five hundred and sixty-four pounds ( that is, six times 94 ) equals
one g, which means you are cruizing along in level flight.

So what's your plane rated for? If it's non-aerobatic it's probably
rated for Utility Class, which is about 3.3g, Which means 3.3 times
517 or about 1706 pounds. Which happens to be about 18 bags of
Portland cement, so that's what you stack on, starting at the middle
and working your way out toward the tips, keeping an eye on those yard
sticks.

Odds are, you won't have any problem at 3.3g's -- the wing probably
won't deflect at all. Now all you've got to do is take a buncha
pictures and get everyone to sign the log. Or you could keep piling
on the weight until something breaks. That would indicate the
Ultimate Load for that particular structure but you gotta be careful
dealing with that amount of weight, especially if you're working in
somebody elses hangar, because when something fails it's liable to
flip those bags of cement around like a frisbee.
---------------------------------------------------------------------------

A lot of times you aren't working with a finished airframe; lots of
times you'll only be working with a part of an airplane, such as it's
horizontal stabilizer, or perhaps an engine mount., That's when
things can get interesting, because you may be trying to achieve 8 or
9 g's. That's when you'll want to have a couple of video cameras
running, because when the failure occurs it's liable to happen fast.

Sometimes you may be testing nothing more than a main spar, probably
bolted to a fixture you've designed to support it. If the main spar
is made of wood there's a good chance that you've fabricated this
sample out of something less expensive than Sitka Spruce and aviation
plywood.

Or you could be testing the strength of a part with the wood at a
different orientation. (Which is what this message was all about to
begin with.) :-)

Gravity and persistence can teach you a good deal about aeronautics
without ever leaving the ground. You'll have to fabricate your
supporting structure and line-up a suitable supply of weight, but
having done so you may find there is more to aeronautics than you
realized...

I'll leave the next step up to you because when you get right down to
it, YOU are the mechanic-in-charge.

-R.S.Hoover
Load testing a new design is a good thing, but simply stacking the load
across the wing evenly will likely break even a properly designed &
built wing. The load needs to be distributed to match the lift
distribution, which isn't linear. The wing should also be tilted to
match its angle of attack near stall so the load is angled toward the
leading edge, because the loaded wing is actually trying to swing up and
forward (relative to the fuselage) under load.

The next thing is that if something breaks, it can cause a lot of
shrapnel, and the multi-ton load/wing can head in who knows which
direction. If you look at the procedures used by manufacturers &
reputable kit makers, at each step in loading they support the wing,
load it up, slowly release the supports for the specified number of
seconds and immediately re-support the wing.

I did it once the way you describe on a Dragonfly canard I didn't trust
(previously repaired damage) but in retrospect, I could have killed
myself just testing the wing.

Here are a couple of links to Van's A/C testing that hint at what I'm
trying to describe.

http://vansaircraft.com/public/rv-10int3.htm

http://vansaircraft.com/pdf/12_NOVEMBER_UPDATE.pdf

Charlie

On Jul 3, 10:49*am, "rattlesnake" wrote:


Destruct static testing done in a non-silly and relevant manner. Kind
of cool to see that they predicted the failure mode and location. The
wing was designed within a couple of percent of the goal. No weight
sacrificed here.


http://www.youtube.com/watch?v=pe9PVaFGl3o

performed static testing on Saturday. Went well except engine mount broke
(§&%!?$ one of the few parts I didn't fabricate by myself) So far about
testing.....

www.ph21.de/guest/Pict0035.jpg



"gorgon" schrieb im Newsbeitrag
...
On Jul 3, 10:49 am, "rattlesnake" wrote:


Destruct static testing done in a non-silly and relevant manner. Kind
of cool to see that they predicted the failure mode and location. The
wing was designed within a couple of percent of the goal. No weight
sacrificed here.


http://www.youtube.com/watch?v=pe9PVaFGl3o

rattlesnake schreef:
(§&%!?$

You are strong at foreign languages, mein lieber Herr! Bravo!
But then, cursing is always learnt first, isnt'it...?