Rubber Discs for Shock Strut

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

challenger_II

Well-Known Member
Joined
Jul 15, 2009
Messages
610
Location
Fisher County, Tx. USA
I have one for each for the nose gear, of the two serial number blocks coming from Univair, to see how well they fit my application. Time will tell...

But, good suggestion! :)

Anybody looked at the MLG on the Ercoupe lately?
 

challenger_II

Well-Known Member
Joined
Jul 15, 2009
Messages
610
Location
Fisher County, Tx. USA
Ok, to streamline the responses, and ideas, for this thread:

I am using an existing strut. Unloaded, the area the die spring, or rubber doughnut assembly, will be installed is 6 1/4", and has a 7/8" center tube. At rest, empty, the gap is 5 5/8", and I do not know what the compressed (Loaded aircraft, and thumping the runway) gap is, at present. The gross weight of the airplane is 750#.

I intend to use the existing strut, not fabricate a new one.
The existing strut was originally designed to use 1/2" x 2 1/2" rubber disks. The builder of this particular airframe opted to use die springs, instead. The die springs from Aircraft Spruce proved to be too soft for the OB's liking, and he installed a spring from another source (a cut down oilfield down-hole service tool).
When the aircraft is at rest, and empty, there is very little compression left in the spring, and she bottoms-out rather easily. I wish to change this.
 

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
677
Location
United States
Ok, to streamline the responses, and ideas, for this thread:

I am using an existing strut. Unloaded, the area the die spring, or rubber doughnut assembly, will be installed is 6 1/4", and has a 7/8" center tube. At rest, empty, the gap is 5 5/8", and I do not know what the compressed (Loaded aircraft, and thumping the runway) gap is, at present. The gross weight of the airplane is 750#.

I intend to use the existing strut, not fabricate a new one.
The existing strut was originally designed to use 1/2" x 2 1/2" rubber disks. The builder of this particular airframe opted to use die springs, instead. The die springs from Aircraft Spruce proved to be too soft for the OB's liking, and he installed a spring from another source (a cut down oilfield down-hole service tool).
When the aircraft is at rest, and empty, there is very little compression left in the spring, and she bottoms-out rather easily. I wish to change this.
I get that you want rubber, but McMaster Carr and others have a whole variety of die springs with varying spring rates
McMaster-Carr 6 inch long, would give you a little gap when completely unloaded, which you COULD pack out with a spacer - a LITTLE pre-load is a good thing, a LOT makes assembly a fight like getting a wet cat into a paper bag. Or you can get cut to length, but cutting this stuff down and grinding the ends is a Bee-Yatch you might best leave to a Spring Shop, if any such still exist in your area. McMaster-Carr only one rate per shaft size, and it looks a little low to me.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,977
Location
US
I get that you want rubber, but McMaster Carr and others have a whole variety of die springs with varying spring rates
McMaster-Carr 6 inch long, would give you a little gap when completely unloaded, which you COULD pack out with a spacer - a LITTLE pre-load is a good thing, a LOT makes assembly a fight like getting a wet cat into a paper bag. Or you can get cut to length, but cutting this stuff down and grinding the ends is a Bee-Yatch you might best leave to a Spring Shop, if any such still exist in your area. McMaster-Carr only one rate per shaft size, and it looks a little low to me.
But, if using springs, the strut will still need some sort of damping.
 

challenger_II

Well-Known Member
Joined
Jul 15, 2009
Messages
610
Location
Fisher County, Tx. USA
If I go the spring route, I will use Belleville spring discs. This will give a much better adjustment range, by the cup arrangement, and individual spring compressibility. Mc Master has only three choices, in plain steel, in the ID I require.
I have also considered a combination of Bellville spring, and rubber disc. The kicker still remains the availability of 30-50 duro discs in 1/2" x 2-21/2" x 7/8" id.
 

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
677
Location
United States
But, if using springs, the strut will still need some sort of damping.
You're not wrong. But if the shock strut is splayed away from the fuselage at an angle, you'll get some damping from the scrubbing of the tire sideways as the gear deflects. This is the ONLY damping in a Wittman style landing gear, whether bar or rod. Trailing link gear, all bets are off, and you'll have to find some other source of damping.
 

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
677
Location
United States
The existing strut was originally designed to use 1/2" x 2 1/2" rubber disks.
McMaster-Carr Polyurethane rod in the right OD. Punch the center holes as previously described. 40A or 60A durometer to start? A bandsaw with metal cutting blade without much tooth set should turn this bar into disks with little difficulty, but I'd freeze it first.
 

challenger_II

Well-Known Member
Joined
Jul 15, 2009
Messages
610
Location
Fisher County, Tx. USA
And add polishing the "cut" edges. Must get rid of the stress risers.
This is, also, an area I have explored, and is in the running.

McMaster-Carr Polyurethane rod in the right OD. Punch the center holes as previously described. 40A or 60A durometer to start? A bandsaw with metal cutting blade without much tooth set should turn this bar into disks with little difficulty, but I'd freeze it first.
 

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
677
Location
United States
And add polishing the "cut" edges. Must get rid of the stress risers.
This is, also, an area I have explored, and is in the running.
That's a very good point, and I think is a good argument for molding them.

There are several brands of two part urethane molding liquids; Smooth-On gets good reviews, and there is a distributor in Dallas Reynolds Advanced Materials, Dallas Econ 60? Econ 40?
 

Geraldc

Well-Known Member
Joined
Nov 12, 2011
Messages
705
Location
nz
Just an interesting note.
One original drawing for the Jodel d9 shows undercarriage rubbers of 30mm x 30mm cut from truck tyres.
10 each leg with steel washers between each one.
 

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
677
Location
United States
One original drawing for the Jodel d9 shows undercarriage rubbers of 30mm x 30mm cut from truck tyres.
Probably durometer about Shore A 70. Pretty stiff, and the cord makes them more so, but stack stiff springs on top of each other (in "series") and you get a soft spring, so...
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
8,699
Location
World traveler
I would love to see just a phone pic of that drawing.

Just an interesting note.
One original drawing for the Jodel d9 shows undercarriage rubbers of 30mm x 30mm cut from truck tyres.
10 each leg with steel washers between each one.
 

GeeBee3

Member
Joined
Mar 20, 2016
Messages
16
Location
Canada
this should cut round rubber washers cleanly....


lots of various rubber sheet materials from the same source also... search 'rubber sheet and strip'

GB3
 

challenger_II

Well-Known Member
Joined
Jul 15, 2009
Messages
610
Location
Fisher County, Tx. USA
I have seen the wares at Mc Master: I am still trying to get my breath back, after the sticker shock on their rubber prices! But, it is an option

Between the cost of the rubber materials, and the cost of a good, reliable cutting tool, this is why I have been seeking a ready-made doughnut ring. Each are expensive.


this should cut round rubber washers cleanly....


lots of various rubber sheet materials from the same source also... search 'rubber sheet and strip'

GB3
 
Top