Testing On The Cheap

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

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

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.

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

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

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.

On Jul 2, 5:11*pm, 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

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.

"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.

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

"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?