landing gear

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arcticserv

Active Member
Joined
Nov 26, 2005
Messages
29
Hi all, things have been moving slowly though the spar is now half completed.
Have been doing a lot of experimenting with urathane disc's for the landing gear suspension, I got the idea from this forum and on investigating found that the Chipmunk and the Mosquito used this method of supension.
I have tested many different types of urathane made here in Australia, but with not much success.
Some had suggested fibroflex in one of the threads I had read here, so
I pursued this company which I found in Germany, the have very comprehensive data on their products which turned out would have saved me a lot of time and expense if I had went to them first.
Any how we have successfully designed and tested a leg (as attached j-peg)
to give 135mm of travel under 1250kgs per leg.
This is sufficient for a 950 kg aircraft to have up to a 3.5 g landing, (including tyre crush).
If your looking for urathane rubbers you cant go past Fibroflex
http://www.fibro.com/xdesk_neu/ximages/265/1145_b2hkgb2006.pdf
Have also put a picture of setting up the outer wing spar jig just for interest.

Shane
 

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PTAirco

Well-Known Member
Joined
Sep 20, 2003
Messages
3,507
Location
Corona CA
Rubber discs in compression were very common in British aircraft of the 30's and 40's. In compression it tends to be more effective as a shock absorber than ibn tension such as bungees. I believe even aircraft as large as the Mosquito used them. It was recomennded not to to stress the rubber much over 200lbs/sq.in though to get a good service life out of it. Urethane sounds good, but can you get it as soft as typical neoprene rubber?
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
8,959
Location
CT, USA
Polyurethane is available in a wide range of hardnesses, from around 10 Shore A (very soft) up to 85 Shore D (like hard plastic):

Of course those earlier aircraft probably used natural rubber or neoprene as I don't think polyurethane existed then.

-Dana

You do not need a parachute to skydive. You only need a parachute to skydive twice.
 

Falco Rob

Well-Known Member
Joined
Apr 8, 2004
Messages
185
Location
Perth, Western Australia
Shane,

Can I ask what model no. discs you used and if these guys have an Australian distributor?

I played with making replacements for the gas struts on my Falco using urethane do-nuts but the ones I eventually bought were super hard.

I finally bit the bullet and had hydraulic struts fabricated as per the plans, but they do have a reputation of leaking oil and deflating, so having an alternate would always be a good thing.

Rob
 

arcticserv

Active Member
Joined
Nov 26, 2005
Messages
29
Rob, I purchased the fibroflex spring through Bruderer Australia,
Model No 246.6.040.040 which is a 90 shore A 40mm dia and 40mm long,
I used 13 of these per leg with .5mm stainless disc's and a 3mm disc in the centre to aliviate the tendency to bow.
Speak with Rudi on 0419400995.
I pre compressed to 494 mm in length which gives a pre-loading of 220 kgs.
Iam not sure if will suit your needs because to get the results I have the total leg length not counting the wheel or the fork ended up at 770mm which suited the p51 scale I am using.
If you look at the site I listed at around page 50 through to 65 you will be able to design of these figure as they are quiet accurate.

Shane
 
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