Testing On The Cheap

[Veeduber[_2_]]

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

[rattlesnake]

Static load testing this way is a big nonsense. Why?
Firstly you support the spar center section. So you do NOT test the
wingbolts and the airframe attachments, but these are the locations where
things can go terribly wrong.

Secondly even if you support your airframe (maybe at the seats, the
sidewalls etc) then you do NOT simulate real load situations during flight.
Still worse you may damage some structures which werde designed for flight
loads but NOT for sandbags.

I'ts just a silly idea (which has to be carried out anway in some countries
for -each- new experimental to be registered). I know what I say because I
have to do it this Saturday and the heaps of bricks are already stacked up
ready to break my lovely aircraft :-(((


"Veeduber" > schrieb im Newsbeitrag
...
> 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

[bildan]

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.

[Brian Whatcott]

Be brave! If you want a shotgun, a rifle or a pistol that won't blow
up in your face, the first thing you do is stuff that modern saying "You
can't test quality into a product" where it belongs, and submit the
weapon to a proof load, greater than the user will thereafter apply.

And whaddaya know: a small proportion of weapons fail with bursts and
cracks. Too bad! Better in a proof-house, than up against your face.

And it is much the same with airframes: you know where the heavy point
loads are applied, [engine mount, seats??] so if you support at those
points, and load the wing,
then you are going to live a long happy life.
It's not just experimentals - when the big boys get serious, they shake
airframe panels through a forest of swingle-trees or the like, to check
fatigue life etc.

Brian W

rattlesnake wrote:
> Static load testing this way is a big nonsense. Why?
> Firstly you support the spar center section. So you do NOT test the
> wingbolts and the airframe attachments, but these are the locations where
> things can go terribly wrong.
>
> Secondly even if you support your airframe (maybe at the seats, the
> sidewalls etc) then you do NOT simulate real load situations during flight.
> Still worse you may damage some structures which werde designed for flight
> loads but NOT for sandbags.
>
> I'ts just a silly idea (which has to be carried out anway in some countries
> for -each- new experimental to be registered). I know what I say because I
> have to do it this Saturday and the heaps of bricks are already stacked up
> ready to break my lovely aircraft :-(((
>
>
> "Veeduber" > schrieb im Newsbeitrag
> ...
>> 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
>
>

[Brian Whatcott]

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

[cavelamb[_2_]]

Brian Whatcott wrote:
>
> 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


I've seen them do that in a 747.

[bildan]

On Jul 2, 5:11*pm, Brian Whatcott > wrote:
> bildan wrote:
> > On Jul 2, 1:37 am, Veeduber > wrote:[i]
> >> 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
> 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

Nope. A 10'+ tip deflection meant the aileron push rods wouldn't
work. Then there was the worry about flutter. The 1st generation
glass sailplanes were built to ~ +-20G just so they would be stiff
enough to avoid flutter. It took the introduction of carbon fiber
composite to finally make the strength and stiffness come out right.

[rattlesnake]

"Brian Whatcott" > schrieb im Newsbeitrag
...
.....
> And it is much the same with airframes: you know where the heavy point
> loads are applied, [engine mount, seats??] so if you support at those
> points, and load the wing,
> then you are going to live a long happy life.

absolutely not so! the seats are designed to carry max passenger weight
times safe G-load times 1.5 (usually). This is way less than the 2 tons you
will pack on the wings. Same with the engine mount. I don't like to know how
many guys flying around in a pre-damaged structure caused by stupid static
load testing.

[Brian Whatcott]

rattlesnake wrote:

>> And it is much the same with airframes: you know where the heavy point
>> loads are applied, [engine mount, seats??] so if you support at those
>> points, and load the wing,
>> then you are going to live a long happy life.
>
> absolutely not so! the seats are designed to carry max passenger weight
> times safe G-load times 1.5 (usually).

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

:-)

Brian W

[rattlesnake]

"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?

[Brian Whatcott]

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

[rattlesnake]

"Brian Whatcott" > schrieb im Newsbeitrag
...
.....
> 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.

[jerry wass]

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

[Brian Whatcott]

Jerry Wass wrote:
> rattlesnake wrote:
>> "Brian Whatcott" > schrieb im Newsbeitrag
>> ...
>> ....
>>> 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

[rattlesnake]

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

EOD

[Morgans[_7_]]

"rattlesnake" > wrote in message
...
>
> "Jerry Wass" > schrieb im Newsbeitrag
> . ..
> ....
>> And the moment legs, moment feet, etc....
>
> EOD

EOD ???
--
Jim in NC

[Charlie[_2_]]

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

[gorgon]

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]

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

[jan olieslagers[_2_]]

rattlesnake schreef:
(§&%!?$

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

[rattlesnake]

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...?

[Dan[_12_]]

Brian Whatcott wrote:
> bildan wrote:
>> On Jul 2, 1:37 am, Veeduber > wrote:[i]
>>> 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
> 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

[Dan[_12_]]

Jerry Wass wrote:
> rattlesnake wrote:
>> "Brian Whatcott" > schrieb im Newsbeitrag
>> ...
>> ....
>>> 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

[Dan[_12_]]

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

[jan olieslagers[_2_]]

Dan schreef:
B-707 wig tips

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

[jan olieslagers[_2_]]

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

[Dan[_12_]]

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

[Dan[_12_]]

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

[Brian Whatcott]

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
>
>
>
>

[rattlesnake]

"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.....

[Brian Whatcott]

rattlesnake wrote:
> "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.....
>
>
I'm thinking it would be stupid, or at least careless, if the load
were reacted through just one or two mount fixings.
Is that how the test was rigged?
(I noticed there seemed to be a steel strip
perhaps 3/16 X 1 inch welded into the cluster which seemed to
provide a rather abrupt section change.) Is that the way the plans
were drawn?

Brian W

[rattlesnake]

"Brian Whatcott" > schrieb im Newsbeitrag
...
....
> I'm thinking it would be stupid, or at least careless, if the load
> were reacted through just one or two mount fixings.
> Is that how the test was rigged?

roughly the setup was like this:
- plane upright
- tail and elevator loaded by about 430 lbs of bricks
- ailerons and flaps loaded by about 290 lbs of bricks
- both wings supported by 1.5 ton car jacks
- engine pushed down by about 1.100 lbs at position of the four attachment
points

I got a bad feeling before the test, but I have only two choices in my
country:
1: do this silly static test
2: reject it and never receive the permit to fly

I think the lower attach points can be repaired. Probably solid 3/4" rond
bars will be welded into the remaining tubes. However I lost some of my
confidence in this flying machine because I don't know what (invisible)
secondary damage may have occured.

[Peter Dohm]

"rattlesnake" > wrote in message
...
>
> "Brian Whatcott" > schrieb im Newsbeitrag
> ...
> ...
>> I'm thinking it would be stupid, or at least careless, if the load
>> were reacted through just one or two mount fixings.
>> Is that how the test was rigged?
>
> roughly the setup was like this:
> - plane upright
> - tail and elevator loaded by about 430 lbs of bricks
> - ailerons and flaps loaded by about 290 lbs of bricks
> - both wings supported by 1.5 ton car jacks
> - engine pushed down by about 1.100 lbs at position of the four attachment
> points
>
> I got a bad feeling before the test, but I have only two choices in my
> country:
> 1: do this silly static test
> 2: reject it and never receive the permit to fly
>
> I think the lower attach points can be repaired. Probably solid 3/4" rond
> bars will be welded into the remaining tubes. However I lost some of my
> confidence in this flying machine because I don't know what (invisible)
> secondary damage may have occured.
>
>
While it is really tempting to brag about my father's prescience, in his
decision to leave your country many decades ago, this really does not sound
like it should be an outrageous or damaging test it done correctly.

Assuming that the "engine" was simulated with a rigid fixture that mounted
is essentially the same manner as the engine and about 4 time the weight of
the engine was suspended from the CG point of the engine, or alternatively
that the engine was mounted and that about 3 more time the weight of the
engine was suspended below the CG point of the engine, it would appear that
you simply need a new engine mount which is free of defect. In that case,
the test was well designed and appears to have accomplished its purpose.

OTOH, if this was a "dynafocal" mount, and also if the test procedure failed
to maintain the relative orientation of the four engine mounting points,
then the test procedure would appear to be at fault. It that case, you will
probably ned to perform the test again with a new engine mount.

Peter (Damm)

[Brian Whatcott]

rattlesnake wrote:
....
> roughly the setup was like this:
> - plane upright
> - tail and elevator loaded by about 430 lbs of bricks
> - ailerons and flaps loaded by about 290 lbs of bricks
> - both wings supported by 1.5 ton car jacks
> - engine pushed down by about 1.100 lbs at position of the four attachment
> points
>
> I got a bad feeling before the test, but I have only two choices in my
> country:
> 1: do this silly static test
> 2: reject it and never receive the permit to fly
>
> I think the lower attach points can be repaired. Probably solid 3/4" rond
> bars will be welded into the remaining tubes. However I lost some of my
> confidence in this flying machine because I don't know what (invisible)
> secondary damage may have occurred.
>
>
Let me ask you this: how do feel about a tube that was loaded with 275
lb (if the loading was equal and local) that failed?
Pulling numbers out of the air, lets say the failing tube was 3/4 inch
diameter and the material was 30 ton steel - how thick would it be?
There's something evidently very wrong with my numbers, or your loading
conditions: the tube wall thickness would have been
(using 30 ton sq in = 60000 psi steel)
275 lb force = 60000 X pi X 0.75 X wall thickness
So wall thickness = 275 / (60000 X pi X 0.75 ) = about 2 thousandth
inch??
Certainly not! Perhaps it was light alloy tube rated at 20000 psi?
That leads to a wall thickness of 6 thousandth inch? Certainly not!

So maybe they loaded the engine itself though its centroid.
The tube did not fail in crushing, it looked like it failed in shear??
That's the weakest modulus - but not THAT weak - so I am missing
something about the geometry: a long long engine mount over a narrow
area bulkhead?? I just don't get it!

It should not be possible to weld up an engine mount WEAK enough to fail
at the load you mentioned.....
But inserting a solid rod into a thin tube is an unfavorable fix - the
stress concentration is inviting another failure just past the end of
the rod insert.....

Perhaps you might let someone look at the engine mount drawing. There's
something strange about it. At the very least, there was no post weld
heat treat ?? Critical structure should ALWAYS yield (if its metal)
not crack destructively.

Good luck

Brian W
p.s. If the designer was an absolute genius, and the materials all
produced exactly on specification, at the load test, if the engine mount
was just 2% stronger, then one or several other parts would have yielded
(but NEVER cracked) before the engine mount YIELDED.
You can take it for granted that nobody is that good!

[rattlesnake]

Peter, Brian,

thanks for the bright thoughts. Think I know what caused the problem. Per
the plans my engine requires about 1.5" long spacers between the mount's
attach points and the engine itself. This creates an extra bending moment
which may have triggered the failure.

The mount is made of 3/4" 4130 tube with 0.035" wall thickness.

My current idea of repair is to weld a short round bar into the remaining
tube and so rebuilding the attach points. Maybe I'll shorten the spacers a
bit and bring some ballast further forward instead (battery).

[Brian Whatcott]

rattlesnake wrote:
> Peter, Brian,
>
> thanks for the bright thoughts. Think I know what caused the problem. Per
> the plans my engine requires about 1.5" long spacers between the mount's
> attach points and the engine itself. This creates an extra bending moment
> which may have triggered the failure.
>
> The mount is made of 3/4" 4130 tube with 0.035" wall thickness.
>
> My current idea of repair is to weld a short round bar into the remaining
> tube and so rebuilding the attach points. Maybe I'll shorten the spacers a
> bit and bring some ballast further forward instead (battery).
>
>
See if you can find some tube that will fit inside or outside the failed
tube. perhaps 50 thou wall. fish mouth the ends. Rossette and end weld.
Take a look at CAM18. It gives specific instructions on repairing tubes.

Brian W

[rattlesnake]

hmmm....

found a tube which fits inside the faild tube, but how can I weld it in
then - just asking


"Brian Whatcott" > schrieb im Newsbeitrag
...
> rattlesnake wrote:
>> Peter, Brian,
>>
>> thanks for the bright thoughts. Think I know what caused the problem. Per
>> the plans my engine requires about 1.5" long spacers between the mount's
>> attach points and the engine itself. This creates an extra bending moment
>> which may have triggered the failure.
>>
>> The mount is made of 3/4" 4130 tube with 0.035" wall thickness.
>>
>> My current idea of repair is to weld a short round bar into the remaining
>> tube and so rebuilding the attach points. Maybe I'll shorten the spacers
>> a bit and bring some ballast further forward instead (battery).
>>
>>
> See if you can find some tube that will fit inside or outside the failed
> tube. perhaps 50 thou wall. fish mouth the ends. Rossette and end weld.
> Take a look at CAM18. It gives specific instructions on repairing tubes.
>
> Brian W

[rattlesnake]

oh, think I got it now with rossettes and fishmouths :-))


"Brian Whatcott" > schrieb im Newsbeitrag
...
> rattlesnake wrote:
>> Peter, Brian,
>>
>> thanks for the bright thoughts. Think I know what caused the problem. Per
>> the plans my engine requires about 1.5" long spacers between the mount's
>> attach points and the engine itself. This creates an extra bending moment
>> which may have triggered the failure.
>>
>> The mount is made of 3/4" 4130 tube with 0.035" wall thickness.
>>
>> My current idea of repair is to weld a short round bar into the remaining
>> tube and so rebuilding the attach points. Maybe I'll shorten the spacers
>> a bit and bring some ballast further forward instead (battery).
>>
>>
> See if you can find some tube that will fit inside or outside the failed
> tube. perhaps 50 thou wall. fish mouth the ends. Rossette and end weld.
> Take a look at CAM18. It gives specific instructions on repairing tubes.
>
> Brian W

[Brian Whatcott]

rattlesnake wrote:
> hmmm....
>
> found a tube which fits inside the failed tube, but how can I weld it in
> then - just asking
>
>
....
The ends of the insert are tapered. Holes are drilled in the failed tube
to allow rosette welds of the interior tube, which have much the same
effect as through bolts, but rather lighter and stronger, if well done.

Brian W

[rattlesnake]

hmmm.....

my idea was to take out about 1" of the failed tube and fishmouth(spelling?)
both open ends. Inserted tube (with about twice wall thickness) is visible
and can be welded in. How's about this?

"Brian Whatcott" > schrieb im Newsbeitrag
...
> rattlesnake wrote:
>> hmmm....
>>
>> found a tube which fits inside the failed tube, but how can I weld it in
>> then - just asking
>>
>>
> ...
> The ends of the insert are tapered. Holes are drilled in the failed tube
> to allow rosette welds of the interior tube, which have much the same
> effect as through bolts, but rather lighter and stronger, if well done.
>
> Brian W

[Bob]

On Jul 6, 5:52*pm, "Peter Dohm" > wrote:

(Lotsa stuff clipped)

Dear Peter (and the Group)

I guess I'm just a sissy but I would never use .035 for an engine
mount. In fact, I'd be leery of .049.

This isn't about calculations on a sheet of paper, it's about
incidental damage that can occur to the tubing over heaven knows how
many years of service. I'm talking about dropped wrenches and the
like -- falls down, DINGS the lower mount on its way to the bottom of
the nacelle or even clear to the ground, if you're lucky ( ...but you
seldom are, right? :-) So we fish it out and since there's no
apparent damage we assume everything is okay. But gravity sucks and
sure as the potential student always barfs on the new upholstery
(never on the old), Murphy's Law is ALWAYS waiting in the wings. Ding
round tubing and you may as well cut it out and start over; its specs
no longer apply and in nine cases out of ten the repair will cost more
than the replacement.

3/4 x .035 gottem internal dia, of ,680. Closest match is going to be
5/8ths but using it -- or even making the repair instead of doing a
replacement -- is going to depend on where the tube departed from
spec. Adjacent to a weld? Or a gradual bend across the entire length
of the member... because about the ONLY location where the repair
(using an internal sleeve of .5/8) is practical is right in the
middle of the member. Any where else, the REPLACEMENT is going to be
more practical... except for the engineering.

If you replace the failed member with the SAME SIZE tubing, you know
it's going to happen again. Indeed, the static test has done it's
job; it is telling you to use a sturdier member. But not just there,
EVERYWHERE. Because you have to assume there will be occasions when
gravity is going to be coming at you from different directions. So
that while those upper members may have done fine in the static test,
when they are being subjected to TENSION, there is a high probability
they will fail when the attitude of the aircraft makes them bear the
load in COMPRESSION... or visa versa. Indeed, the static test has
already told you so.

Are you familiar with the 'Jesus Factor'? That is the uncalculable
amount you ADD to every structure -- when ever you can -- so as to
cover the realities of serial production, Monday morning hang-overs,
Friday afternoon hurry-ups and every other thing you can thing of that
might cause the as-fabricated version to depart from the as-calculated
version. In a welded steel tube structure we're generally safe with a
Jesus Factor of 1.5 for the fuselage, 3.0 for a control surface and
5.0 for the landing gear AND ENGINE MOUNT.

Mention the Jesus Factor today and they're liable to start looking for
where you parked your bicycle. Perhaps a better tag would be the ****
Happens Factor. Call it what you will, there are those who upon
learning their engine mount is capable of withstanding 30g's when the
specs only call for six, commence to run in circles, waving their
hands and emitting tiny shrieks. And perhaps with good reason, if
we're talking about a home-built, where the builder is also the test
pilot as well as Line Captain. If the calculations call for .049 then
you can safely assume it won't be something thinner... although
thicker might appear now & then. But whatever you call it and no
matter where it is applied, from Farmington, Long Island to a garage
in San Diego, you can bet your bolly hooly it DOES exist -- and does
so for a purpose.

-R.S.Hoover

[Tim[_8_]]

"Dan" > wrote in message
...
>
> 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.
>

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

[cavelamb[_2_]]

rattlesnake wrote:
> hmmm.....
>
> my idea was to take out about 1" of the failed tube and fishmouth(spelling?)
> both open ends. Inserted tube (with about twice wall thickness) is visible
> and can be welded in. How's about this?
>


I wouldn't even consider it, snake.

This mount BROKE.

It's either too light, or has a stress riser at the break - or both.
(I'm guessing both from the pic)

Consider yourself lucky (you dodged a big bad bullet) and build it again.

Better this time.




Richard

PS: Read Bob's Jesus Factor post again.
And take it to heart...

[Brian Whatcott]

cavelamb wrote:
> rattlesnake wrote:
>> hmmm.....
>>
>> my idea was to take out about 1" of the failed tube and
>> fishmouth(spelling?) both open ends. Inserted tube (with about twice
>> wall thickness) is visible and can be welded in. How's about this?
>>
>
>
> I wouldn't even consider it, snake.
>
> This mount BROKE.
>
> It's either too light, or has a stress riser at the break - or both.
> (I'm guessing both from the pic)
>
> Consider yourself lucky (you dodged a big bad bullet) and build it again.
>
> Better this time.
>
>
>
>
> Richard
>
> PS: Read Bob's Jesus Factor post again.
> And take it to heart...


It would be helpful to know if there are any more samples of this
airplane design flying, and in particular, are there any more examples
of this engine mount in existence?
If there ARE, then that would focus the debate onto material defect or
construction defect or test rig defect.
Richard reminds us that you didn't see a permanent distortion of the
mount - which is the desired failure mode (supposing that any failure is
desirable) but a clean break - presumably two clean breaks. That should
not happen, ever on a test.

Brian W

[rattlesnake]

"Brian Whatcott" > schrieb im Newsbeitrag
...
....
> It would be helpful to know if there are any more samples of this airplane
> design flying,

yes there are and no engine mounts broke (in normal flight) until now (as
far as I know)

> and in particular, are there any more examples of this engine mount in
> existence?

yes, several

> If there ARE, then that would focus the debate onto material defect or
> construction defect or test rig defect.

I suppose a testrig issue. Load concentrations build up which do -not-
happen in real flight scenarios (my various previous posts about static load
testing)

> Richard reminds us that you didn't see a permanent distortion of the
> mount - which is the desired failure mode (supposing that any failure is
> desirable) but a clean break - presumably two clean breaks. That should
> not happen, ever on a test.

interesting aspect.

Note: because of legal coniderations I will not mention company names,
people's names or types or designations of aircraft here.

--
P.S.
what me -really-surprised is the fact that for about a minute the mount held
the engine more or less in place even with this two severe cracks! 4130 is
really good stuff...

[Brian Whatcott]

rattlesnake wrote:
>>...are there any more examples of this engine mount in
>> existence?
>
> yes, several
>
>> If there ARE, then that would focus the debate onto material defect or
>> construction defect or test rig defect.
>
> I suppose a testrig issue. Load concentrations build up which do -not-
> happen in real flight scenarios (my various previous posts about static load
> testing)...
> P.S.
> what me -really-surprised is the fact that for about a minute the mount held
> the engine more or less in place even with this two severe cracks! 4130 is
> really good stuff...
>
>

- -
4130 low alloy chrome molybdenum steel is preferred for engine mounts,
for its strength as annealed (not just 30 ton but 45 ton ) and extended
tenacity in yield.

Some ways I can think of, to break this excellent alloy:

1) chrome-plate it carelessly (or cadmium, nickel, some others too)
or
2) quench it rapidly from bright yellow, to get that brittle 90 ton
strength.
or
3) Decide that it's OK to MIG weld it on a cold day, and there's no need
to normalize or anneal afterwards.
or
4) Buy an engine mount, then leave it standing in the garage for 15
years while the project goes together - without an internal coat of
linseed or waxy film like Boeshield somethingorother. Oh, let the rain
get in it a time or two
or
5) decide that those tubes look really really thin and weedy, and add a
bar or two to "beef it up".
or
6) Decide you will mount a nice powerful 110 HP Subaru up front, with
engine controller, fuel injection, water cooling with the original
radiator etc.

THEN,
load it to the worst case design load, but allow untriangulated tubes of
the mount to load up in bending.

(If there are other similarly equipped examples flying, then you can be
pretty sure they HAVE passed a load test.)

Hope this is food for thought anyway though I am aware that what I am
doing here, is just one step better than making pronouncements on
exactly why the AirFrance liner went down recently....

Good Luck
Brian W

[rattlesnake]

thanks, Brian
your comments are much appreciated

"Brian Whatcott" > schrieb im Newsbeitrag
...
> rattlesnake wrote:
>>>...are there any more examples of this engine mount in existence?
>>
>> yes, several
>>
>>> If there ARE, then that would focus the debate onto material defect or
>>> construction defect or test rig defect.
>>
>> I suppose a testrig issue. Load concentrations build up which do -not-
>> happen in real flight scenarios (my various previous posts about static
>> load testing)...
>> P.S.
>> what me -really-surprised is the fact that for about a minute the mount
>> held the engine more or less in place even with this two severe cracks!
>> 4130 is really good stuff...
>
> - -
> 4130 low alloy chrome molybdenum steel is preferred for engine mounts, for
> its strength as annealed (not just 30 ton but 45 ton ) and extended
> tenacity in yield.
>
> Some ways I can think of, to break this excellent alloy:
>
> 1) chrome-plate it carelessly (or cadmium, nickel, some others too)
> or
> 2) quench it rapidly from bright yellow, to get that brittle 90 ton
> strength.
> or
> 3) Decide that it's OK to MIG weld it on a cold day, and there's no need
> to normalize or anneal afterwards.
> or
> 4) Buy an engine mount, then leave it standing in the garage for 15 years
> while the project goes together - without an internal coat of linseed or
> waxy film like Boeshield somethingorother. Oh, let the rain get in it a
> time or two
> or
> 5) decide that those tubes look really really thin and weedy, and add a
> bar or two to "beef it up".
> or
> 6) Decide you will mount a nice powerful 110 HP Subaru up front, with
> engine controller, fuel injection, water cooling with the original
> radiator etc.
>
> THEN,
> load it to the worst case design load, but allow untriangulated tubes of
> the mount to load up in bending.
>
> (If there are other similarly equipped examples flying, then you can be
> pretty sure they HAVE passed a load test.)
>
> Hope this is food for thought anyway though I am aware that what I am
> doing here, is just one step better than making pronouncements on
> exactly why the AirFrance liner went down recently....
>
> Good Luck
> Brian W

[Stealth Pilot[_2_]]

On Sat, 4 Jul 2009 08:47:51 +0200, "rattlesnake" >
wrote:

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

for what it is worth I think rattlesnake was correct in his comments.
he was talking about point loads between the test supports and the
structure being a problem but not really demonstrating anything.

Stealth Pilot

[Stealth Pilot[_2_]]

On Thu, 02 Jul 2009 18:36:18 -0500, cavelamb >
wrote:

>Brian Whatcott wrote:
>>
>> 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
>
>
>I've seen them do that in a 747.

....and here I was expecting you to post "I've seen them do that in the
texas taildragger"

Stealth :-) Pilot

[RST Engineering - JIm]

>>> 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....]


When I went through 727 fixit school, they showed us a video of the static
test of that bird. THe wingtips came within about a yard of each other
before the whole thing let go, but when it did it looked like an aluminum
blizzard.

Jim