Need Help on Landing Gear Calculations

"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

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

"Dick" wrote

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.

True, the G rating for an airplane is for the airframe, but how many G's would a
drop from 19" develop?

I don't have the slightest idea. I'm not a wiz on math problems.

If a drop from 19" does not stress the plane to more than 3 G's, that would be a
wimpy test, in my opinion. A plane dropping in on a blown landing hits with a
real whack. How about it, you out there with G meters? How high of a reading
have you seen on a really blown landing?

It should not be that tough, for a wiz at math to figure out how hard of a whack
a 19" drop generates. Take the speed generated, and divide that result out into
the amount of suspension travel, I would think.

The whole key in the difference is that the G rating for an airframe is
generated and suspended by the wings, and the G rating for the landing gear is
generated by changing velocity into a stop by the landing gear.
--
Jim in NC