Testing On The Cheap

if you just scrapped a $1000 item wouldn't you, mon ami?


"jan olieslagers" schrieb im Newsbeitrag
...
rattlesnake schreef:
(§&%!?$

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

Brian Whatcott wrote:
bildan wrote:
On Jul 2, 1:37 am, 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

Been there, done that. It answers a lot of nagging questions.

Story:

Brand new (at the time) fiberglass sailplane wing design gets bolted
to the massive hangar corner I-beam where special root fitting adapter
has been welded. Wing extends horizontally at shoulder height with
the lower surface up. Shot bags are added spaced according to the
span-wise lift distribution. Wing tip touches ground at 1.8G Crap!

No room for back hoe so dig pit by hand with shovels. Pit under wing
tip now at grade - 2'. Add shot bags to 2.6G when tip touches bottom
of pit. Crap!

Four more hours of digging and pit is grade - 5'. Shot bags to 3.9G.
Tip touches pit bottom Crap!

It starts raining. Must remove shot bags and wing to interior of
hangar. Removing wing in the rain is BIG problem since there is now a
pit where the tip man would have to stand. Rain continues - pit is
under roof drain so it fills with water. Crap!

Rethink. It may be strong enough but is it stiff enough? Decision -
wing needs to be stiffer. Project dies. Better it than the test
pilot.


A striking comment in a wonderful book on engineering design disasters
mentioned casually that the proof load on a particular aluminum airliner
wing would bend it to the vertical at the tips [if buckling did not
occur long before....]
Perhaps you were too hasty to scrub the project?? I have looked out the
window in bumpy conditions to see wingtips flapping a yard or two....

Brian W

If memory serves the B-707 wig tips had something on the order of 14
feet of flex designed in. I wonder how much flex a B-777 has.

Dan, U.S. Air Force, retired

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....

But just momentarily.

Dan, U.S. Air Force, retired

Morgans wrote:


"rattlesnake" wrote in message
...

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

EOD

EOD ???

Explosive ordinance disposal?

Dan, U.S. Air Force, retired

Dan schreef:
B-707 wig tips

Hm. Tad out of period, no? Gay parades only since 1980's or thereabout?

Dan schreef:
Morgans wrote:


"rattlesnake" wrote in message
...

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

EOD

EOD ???

Explosive ordinance disposal?


To simple-minded IT'ers like yours truly, it only means End Of Data

jan olieslagers wrote:
Dan schreef:
B-707 wig tips

Hm. Tad out of period, no? Gay parades only since 1980's or thereabout?

I know how old B-707 is, but it was the only figure I could think of
off the top of my head. Senility, nicht wahr?

Dan, U.S. Air Force, retired

jan olieslagers wrote:
Dan schreef:
Morgans wrote:


"rattlesnake" wrote in message
...

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

EOD

EOD ???

Explosive ordinance disposal?


To simple-minded IT'ers like yours truly, it only means End Of Data

I have also seen it used as end of discussion.

Dan, U.S. Air Force, retired

Ouch,
glad THAT didn't happen in the air.


Seeing an engine depart must be on about the same excitement level as
seeing aeroelastic vibration in the wing tips.
Makes me think of a reason why I sometimes see a wire cable tether round
a couple of engine fixings back to a bulkhead. A loose engine has a
better CofG that a missing engine, no doubt!

Brian W


rattlesnake wrote:
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

"Brian Whatcott" schrieb im Newsbeitrag
...
Ouch,
glad THAT didn't happen in the air.

wouldn't happen in the air. Was caused by stupid static load testing.....