Need Help on Landing Gear Calculations

Thinking about load testing one main gear assembly off the plane project
anticipated for 1000 # gross and have two question areas.

FIRST: FAR 23.725 provides a drop height range from 9.2 " to 18.7". With a
1000# gross plane, I think this calculates as 797 and 882# respectively on
each main..........Correct??
IE: I was going to apply 797# minus the actual gear weight at 9.2" height.

Ground Load Dynamic tests in 23.726(a)(1) also requires a test at 2.25 x
height in above 23.725. This raises the drop heights to 20.7" and 42" with
weights at 892# and 942# if calc'ed correctly.

In a previous project a long while ago, I merely used a 3G load divided by
mains to size the structural members. Then with the aforementioned 1000#
gross, it would have be 1500# on each gear. My rational for the 3G was
23.561(b)(2) for emergency landing upward conditions on a normal category
airplane structure.

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the load??

Maybe along the lines of a built up 2x4 beam lever approach.......Any
suggestions?? Am I thoroughly confused G?

Thanks, Dick
ps Although RAH has been very helpful in the past, if there is a better
website for this kind of discussion, I would appreciate knowing it.

Dick wrote:

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the load??

I vote for a drop, so it rings like a bell. A steady load won't be the same.

"Lamellae" wrote in message
link.net...
Dick wrote:

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the load??

I vote for a drop, so it rings like a bell. A steady load won't be the same.

Untrue. Force is force. If you can calculate how much pressure is put on the
gear, by taking into account the weight of the craft, and the height at which it
is dropped, a steady load is the same. It could be even more stress on the
gear, because factors such as tire deflection will not be taken into account
with a steady force test, and it would actually decrease the amount of force put
on the gear in the drop test. Bear in mind that it will be a very sizable
load, though! g

I myself, would rather do the drop test. Less sandbags to fill and place, and
the drop would make a really good video, too! :-)
--
Jim in NC

I'd rather not drop my plane with engine G but am looking for a way to
just test the gear assembly. Was thinking ; restrain the top connection of
the gear leg and apply a uplifting force on wheel via some sort of lever
setup.

Can't get my mind around any method of dropping the gear assembly and would
appreciate some thoughts..
"Morgans" wrote in message
...

"Lamellae" wrote in message
link.net...
Dick wrote:

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the load??

I vote for a drop, so it rings like a bell. A steady load won't be the
same.

Untrue. Force is force. If you can calculate how much pressure is put on
the gear, by taking into account the weight of the craft, and the height
at which it is dropped, a steady load is the same. It could be even more
stress on the gear, because factors such as tire deflection will not be
taken into account with a steady force test, and it would actually
decrease the amount of force put on the gear in the drop test. Bear in
mind that it will be a very sizable load, though! g

I myself, would rather do the drop test. Less sandbags to fill and place,
and the drop would make a really good video, too! :-)
--
Jim in NC

Morgans wrote:
"Lamellae" wrote in message
link.net...
Dick wrote:

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the load??

I vote for a drop, so it rings like a bell. A steady load won't be the same.

Untrue. Force is force.

Force is force but impact loading and repeated loading cause
failures that are not observed under static loading condiitons.

It takes a finite amount of time for force to distribute itself
through the material. An impact can apply the force faster
than it is distributed, thus concentrating it, especially at
stress risers (e.g. notches). There may also be rebound
effects that will impart a load onto parts that would see none
at all in a static test.

As far as impacts go, dropping a landing gear is not terribly
extreme. But its not the same as a static load.

--

FF

I still haven't devised a method to drop test the gear leg off of the plane.
Anything practical come to mind? Thanks, Dick
wrote in message
ups.com...

Morgans wrote:
"Lamellae" wrote in message
link.net...
Dick wrote:

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the
load??

I vote for a drop, so it rings like a bell. A steady load won't be the
same.

Untrue. Force is force.

Force is force but impact loading and repeated loading cause
failures that are not observed under static loading condiitons.

It takes a finite amount of time for force to distribute itself
through the material. An impact can apply the force faster
than it is distributed, thus concentrating it, especially at
stress risers (e.g. notches). There may also be rebound
effects that will impart a load onto parts that would see none
at all in a static test.

As far as impacts go, dropping a landing gear is not terribly
extreme. But its not the same as a static load.

--

FF

This may or may not be of interest but here is a short video (6 seconds)of
Zenith Aircraft drop testing the gear for the 601XL.

http://www.zenithair.com/video/gear_drop_test.mpeg


"Dick" wrote in message
news:lC%dh.4851$Jg.178@trnddc08...
I still haven't devised a method to drop test the gear leg off of the
plane. Anything practical come to mind? Thanks, Dick
wrote in message
ups.com...

Morgans wrote:
"Lamellae" wrote in message
link.net...
Dick wrote:

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the
load??

I vote for a drop, so it rings like a bell. A steady load won't be the
same.

Untrue. Force is force.

Force is force but impact loading and repeated loading cause
failures that are not observed under static loading condiitons.

It takes a finite amount of time for force to distribute itself
through the material. An impact can apply the force faster
than it is distributed, thus concentrating it, especially at
stress risers (e.g. notches). There may also be rebound
effects that will impart a load onto parts that would see none
at all in a static test.

As far as impacts go, dropping a landing gear is not terribly
extreme. But its not the same as a static load.

--

FF

"Dick" wrote

I'd rather not drop my plane with engine G but am looking for a way to just
test the gear assembly. Was thinking ; restrain the top connection of the
gear leg and apply a uplifting force on wheel via some sort of lever setup.

The drop test points out possible shortcomings in the landing gear, but also
weaknesses in other critical areas.

An engine being dropped and suddenly stopping when the landing gear stops the
plane, will put a lot of force on the engine mount and firewall. The wing spar
will experience a very high load, if the gear is wing mounted.

The aft fuselage will try to bend downward, as the front of the fuselage is also
bending downward, so will the fuselage experience too much tension on the top,
and too much compression on the bottom?

I would propose putting the landing gear on separate roller platforms, so it can
experience whatever splaying may result when the gear is highly loaded. Then
load the areas with sandbags at the multiple of G's for whatever that part or
system weighs.

For example, if the drop test is expected to put a 10 G load on the plane, and
the engine weighs 200 pounds, you need to stack 2,000 pounds on and around the
center of gravity of the engine. Do the same thing for every area of the plane,
such as on each wing, and area of the fuselage, and don't forget, that much
weight needs to go in the driver's seats, too. g

Wow! Typing that out, it is suddenly very clear why people do drop tests,
instead of static tests.
--
Jim in NC

very interesting. good food for thought. thanks
"Gig 601XL Builder" wrDOTgiaconaATcox.net wrote in message
...
This may or may not be of interest but here is a short video (6 seconds)of
Zenith Aircraft drop testing the gear for the 601XL.

http://www.zenithair.com/video/gear_drop_test.mpeg


"Dick" wrote in message
news:lC%dh.4851$Jg.178@trnddc08...
I still haven't devised a method to drop test the gear leg off of the
plane. Anything practical come to mind? Thanks, Dick
wrote in message
ups.com...

Morgans wrote:
"Lamellae" wrote in message
link.net...
Dick wrote:

SECOND: What setup could be used to do such a load test??
Is it mandatory to actual freefall drop or somehow just apply the
load??

I vote for a drop, so it rings like a bell. A steady load won't be
the same.

Untrue. Force is force.

Force is force but impact loading and repeated loading cause
failures that are not observed under static loading condiitons.

It takes a finite amount of time for force to distribute itself
through the material. An impact can apply the force faster
than it is distributed, thus concentrating it, especially at
stress risers (e.g. notches). There may also be rebound
effects that will impart a load onto parts that would see none
at all in a static test.

As far as impacts go, dropping a landing gear is not terribly
extreme. But its not the same as a static load.

--

FF

Just thinking out loud here but thought the +/- 6 G was for airframe, etc
in flight while the landing gear get subjected to considerably less. Vaguely
remembering the FAA requirements as 3 times static wheel load dropped 19".
I'm thinking 300# on one mains times 3.

On the other hand, I could be confused once again G. Comments.
Dick

"Morgans" wrote in message
...

"Dick" wrote

I'd rather not drop my plane with engine G but am looking for a way to
just test the gear assembly. Was thinking ; restrain the top connection
of the gear leg and apply a uplifting force on wheel via some sort of
lever setup.

The drop test points out possible shortcomings in the landing gear, but
also weaknesses in other critical areas.

An engine being dropped and suddenly stopping when the landing gear stops
the plane, will put a lot of force on the engine mount and firewall. The
wing spar will experience a very high load, if the gear is wing mounted.

The aft fuselage will try to bend downward, as the front of the fuselage
is also bending downward, so will the fuselage experience too much tension
on the top, and too much compression on the bottom?

I would propose putting the landing gear on separate roller platforms, so
it can experience whatever splaying may result when the gear is highly
loaded. Then load the areas with sandbags at the multiple of G's for
whatever that part or system weighs.

For example, if the drop test is expected to put a 10 G load on the plane,
and the engine weighs 200 pounds, you need to stack 2,000 pounds on and
around the center of gravity of the engine. Do the same thing for every
area of the plane, such as on each wing, and area of the fuselage, and
don't forget, that much weight needs to go in the driver's seats, too. g

Wow! Typing that out, it is suddenly very clear why people do drop tests,
instead of static tests.
--
Jim in NC