Automotive shocks in aircraft

The Wittman gear is the flat or tubular main gear used on Cessnas and
Tailwinds.

--
Cy Galley, TC - Chair, Emergency Aircraft Repair, Oshkosh

Editor, EAA Safety Programs
or

Always looking for articles for the Experimenter

"Corrie" wrote in message
om...
"Rich S." wrote
It may have something to do with the rebound spring.

I think you're probably right. From what I can see of the pictures
and drawings, it's probably sized to damp the natural frequency of the
big spring, which is sized to damp the natural freq. of the small one.

It might be possible to screw up the gear with differently-massed
struts, wheels, brakes, tires, etc. so that the resulting natural
freqs synch up, yielding undamped divergent feedback. (Remember the
films of Galloping Gertie, the Tacoma Narrows bridge?) We had those
kinds of problems in my Statics and Dynamics classes back in college.
But they always made my head hurt. ;-)

Rich, in the Emeraude plans, how specifically are the springs called
out? Do they specify the stiffness (or the spring constant, may be
the same thing), as well as the dimensions? (By way of contrast, the
gear-retraction system of the CA-65 uses a garage-door spring , hardly
a tight specification. But there's not likely to be much occillation,
as the spring is just a mechanical assist while cranking up the gear.

BTW, a newbie question. What's a Wittman undercarriage? I know Steve
Wittman's name and that he was a major contributor to the field, and
I've seen lots of references to "Wittman undercarriage" but what
exactly IS this wonder-invention?

Corrie

Corrie wrote:
"Rich S." wrote

It may have something to do with the rebound spring.


I think you're probably right. From what I can see of the pictures
and drawings, it's probably sized to damp the natural frequency of the
big spring, which is sized to damp the natural freq. of the small one.

It might be possible to screw up the gear with differently-massed
struts, wheels, brakes, tires, etc. so that the resulting natural
freqs synch up, yielding undamped divergent feedback. (Remember the
films of Galloping Gertie, the Tacoma Narrows bridge?) We had those
kinds of problems in my Statics and Dynamics classes back in college.
But they always made my head hurt. ;-)

Rich, in the Emeraude plans, how specifically are the springs called
out? Do they specify the stiffness (or the spring constant, may be
the same thing), as well as the dimensions? (By way of contrast, the
gear-retraction system of the CA-65 uses a garage-door spring , hardly
a tight specification. But there's not likely to be much occillation,
as the spring is just a mechanical assist while cranking up the gear.

The gear in the Delta is a solid 1" round bar of 6150 spring steel. As
I understand it, it gets a lot of spring from twisting the bar.

The gear retraction is also spring assisted. Except John Dyke specified
a Chevy hood spring.


--
----Because I can----
http://www.ernest.isa-geek.org/
------------------------

"Corrie" wrote in message
om...

It might be possible to screw up the gear with differently-massed
struts, wheels, brakes, tires, etc. so that the resulting natural
freqs synch up, yielding undamped divergent feedback. (Remember the
films of Galloping Gertie, the Tacoma Narrows bridge?) We had those
kinds of problems in my Statics and Dynamics classes back in college.
But they always made my head hurt. ;-)

Remember it? Heck I drive over it several times a week. It's still down
there - under the new bridge.

Rich, in the Emeraude plans, how specifically are the springs called
out? Do they specify the stiffness (or the spring constant, may be
the same thing), as well as the dimensions?

On the plans, the coil springs are dimensioned by size and material, i.e.
wire diameter, coil diameter, length & # of turns. The kicker is they call
out 4130 steel as the material - entirely inappropriate for gear springs.

Rich S.

Have you ever looked at a Piper TriPacer (and other Piper models)? They use
bungee cords stretched over ears on what was originally an automotive shock
(off an old Buick I think). The bungees provided "boing" and the shock
smoothed the ground ride.

Bruce A. Frank

"B2431" wrote in message
...
Can automotive shocks or McPhereson struts be used in landing gear struts?
If
so how would one determine which ones to use?

Dan, U. S. Air Force, retired

On 15 Jul 2003 16:43:15 -0700, (Dan
Thomas) wrote:


The Aeronca Champ had spring oleos without any shock fluid or
whatever, and wasn't boingy. It had a somewhat leaky cylinder
arrangement, and I suppose the air flowing in and out probably damped
things a bit. It had a lot of travel and was too soft, making
crosswind operations hairy.

Not true.

The Champ came with two different oloes, both are conventional oil
damped units. The ones you are describing sound like the "lo-bounce"
oloes which had longer travel.

Rob
1946 7AC Champ

Don't forget the damping effect of the wings either. I don't think
designers bother much with damping on light aircraft. Too much weight
and complexity for a function thats secondary in a flying machine.

"B2431" wrote in message
...
Can automotive shocks or McPhereson struts be used in landing gear struts?
If
so how would one determine which ones to use?

Dan, U. S. Air Force, retired

Ah So--velly good reasoning.

Jay wrote:

Don't forget the damping effect of the wings either. I don't think
designers bother much with damping on light aircraft. Too much weight
and complexity for a function thats secondary in a flying machine.

"B2431" wrote in message
...
Can automotive shocks or McPhereson struts be used in landing gear struts?
If
so how would one determine which ones to use?

Dan, U. S. Air Force, retired