Experimental Landing Gear Design Question

[Dick[_1_]]

Having almost worn out my Pazmany "Landing Gear Design for Light Aircraft"
while trying to resolve available materials and my fabrication abilities
regarding the main legs, a little help is requested..

Not having access to heat treating and basically being too cheap to purchase
HT'd, solid rod or leaf legs , the main gear leg ended up being a 4130 tube
sliding inside another, compressing an external Die Spring under landing
loads. This has tricycle gear with mains angled slightly aft of main spar
and maybe 30 degrees outboard. Gross is anticipated at 950 lbs.

Now in a fit of "amateur designer remorse "<G>, my concern is the "slot" cut
lengthwise into the one tube possibly weakening the leg too much considering
the "outboard alignment" ?? Additionally visual inspection of any "slot"
cracking or through bolt wear would be difficult with external spring and
outer tube .

Presently considering eliminating the Die Spring approach since a nearby
Sonex has a solid 1-1/2" Titanium rod leg and a T-18 grossing at 1500 lbs
has concentric heavy wall 4130 legs. To me, both appear to have no shock
absorption except in tire deflection.

Please feel free to muddy my mental waters <G>.

Thanks, Dick

[Ernest Christley]

Dick wrote:
> Having almost worn out my Pazmany "Landing Gear Design for Light Aircraft"
> while trying to resolve available materials and my fabrication abilities
> regarding the main legs, a little help is requested..
>
> Not having access to heat treating and basically being too cheap to purchase
> HT'd, solid rod or leaf legs , the main gear leg ended up being a 4130 tube
> sliding inside another, compressing an external Die Spring under landing
> loads. This has tricycle gear with mains angled slightly aft of main spar
> and maybe 30 degrees outboard. Gross is anticipated at 950 lbs.
>
> Now in a fit of "amateur designer remorse "<G>, my concern is the "slot" cut
> lengthwise into the one tube possibly weakening the leg too much considering
> the "outboard alignment" ?? Additionally visual inspection of any "slot"
> cracking or through bolt wear would be difficult with external spring and
> outer tube .
>
> Presently considering eliminating the Die Spring approach since a nearby
> Sonex has a solid 1-1/2" Titanium rod leg and a T-18 grossing at 1500 lbs
> has concentric heavy wall 4130 legs. To me, both appear to have no shock
> absorption except in tire deflection.
>
> Please feel free to muddy my mental waters <G>.
>
> Thanks, Dick
>
>
>

I got my Delta gear legs heat treated (6150 steel hardened to C41). I
think it was something like $40, plus the shipping to somewhere up
around Pittsburgh, PA.

[flybynightkarmarepair]

Dick wrote:
>
> the main gear leg ended up being a 4130 tube
> sliding inside another, compressing an external Die Spring under landing
> loads.
>
> Now in a fit of "amateur designer remorse "<G>, my concern is the "slot" cut
> lengthwise into the one tube possibly weakening the leg too much considering
> the "outboard alignment" ?? Additionally visual inspection of any "slot"
> cracking or through bolt wear would be difficult with external spring and
> outer tube .

This the use of a slot and a bolt to align and travel limit the gear is
a loser in any plane heavier than an ultralight. The Teenie Two used
such an approach, and the landing gear is by far the worst aspect of
that design.

> Presently considering eliminating the Die Spring approach since a nearby
> Sonex has a solid 1-1/2" Titanium rod leg and a T-18 grossing at 1500 lbs
> has concentric heavy wall 4130 legs. To me, both appear to have no shock
> absorption except in tire deflection.

Let's distinguish between "shock absorption" and "Dampening" first.
Contrary to the terminology used in the US, "shock absorption" is a
functon of SPRINGS. Contrary to first appearances, both the titanium
rod and the 4130 gear legs examples cited are just that, springs.
You'll be surprised, once you actually start selecting die springs,
just how stiff a spring you need.

But springs just STORE energy, you need DAMPENING to destroy it by
turning it into heat. Wittman style spring landing gear (which both
the T-18 and Sonex are examples of) use the FRICTION of the tires
SCRUBBING on the pavement as the damping. The type of spring gear you
are proposing actually has VERY LITTLE damping. Certainly less than an
oleo or a Wittman style gear.

That doesn't mean it's bad. My airplane will have a similar gear ;-)
It's just a little less forgiving than gear with effective damping. But
the problem of keeping the main gear aligned remains. Here are two
approachs for you to think about.

The first is nesting SQUARE tubing. You'll have to figure out some
external way of limiting travel up and down. This is the way I'm
going.

The second approach is to retain the round tube and use a scissors.
Tony Bingelis' books have some examples of home built scissors (as does
Pazmany's), or you can swipe one off a junk C150 nose gear, or P140
nose or main gear. I've seen them chewed out of aluminum plate with
not much more than Drill Press technology, or bent up out of 4130.
Hummelbirds use this approach.

[Jim Carriere]

flybynightkarmarepair wrote:
> the T-18 and Sonex are examples of) use the FRICTION of the tires
> SCRUBBING on the pavement as the damping. The type of spring gear you

The friction in the mounting hardware also provides some damping.

I say that because on an old car I used to own (I know, here we go...)
the rear shocks absorbers (properly referred to as dampers) were totally
worn out (they fell apart in my hands), but the car's motion was still
damped (it would just bounce several times first). This was almost
totally due to the friction in the suspension bushings.

[GeorgeB]

On 14 Oct 2006 09:41:10 -0700, "flybynightkarmarepair"
> wrote:

>Let's distinguish between "shock absorption" and "Dampening" first.

>But springs just STORE energy, you need DAMPENING to destroy it by

OUCH is my instructor in systems rolling over in his grave. If we
said dampen, he threw a cup of water on us. One DAMPS or uses a
DAMPING material ...

[Paul Tomblin]

In a previous article, GeorgeB > said:
>On 14 Oct 2006 09:41:10 -0700, "flybynightkarmarepair"
> wrote:
>>Let's distinguish between "shock absorption" and "Dampening" first.
>
>>But springs just STORE energy, you need DAMPENING to destroy it by
>
>OUCH is my instructor in systems rolling over in his grave. If we
>said dampen, he threw a cup of water on us. One DAMPS or uses a
>DAMPING material ...

I blame Star Trek: The Next Generation. They used "dampen" incorrectly
all the time.


--
Paul Tomblin > http://blog.xcski.com/
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