Landing gear, springs, wheels etc

[Murray Randall]

Attached are pics of the landing gear for my cabin mod of the XL. There is a shot of the AS Raymond stock 90 durometer .75 in urethane spring. Five or six of these, with 5 .020 alum spacer twix, in series yields 800 to 1000 lb per inch.  five springs weigh .25 oz. In the range of the speced steel spring eh? To facilitate changing the preload I slotted the lower tube for an AN3 bolt. Slotting allows changes to the spring length and preload without grinding and rewelding. You slotted the upper end of the tube, that was fun, why not the bottom. To evaluate the spring rate and preload I computed the tube loads in my finite element model and these are shown on a PDF file of the gear area of the model with the forces and moments added in red from the analysis. I ran the computation at 100 lb vertical load but the results scale linearly. I did not add the stresses as my axle is a .75 X .090 to accommodate a Tuff 16 inch wheel and Avid brake. The total weight of the gear, wheels, springs, brakes is 11 lb. If cooler heads see danger lurking in all this foolishness please shout out very loud! And yes this cabin mod will finish out at 254 lb. Murray Randall

[Murray Randall]

Looks like the system won't show a PDF file. Here I added a JPG of the file that I tried to submit as a PDF. Sorry Murray

[Steve]

Murray:

Hurry, I can't wait to see this stuff with "air under the wheels" - am amazed with the innovation you are putting into a simple design - keep your heath and momentum up ! ! ! Leave a little for the first "over the winter" rebuild...

Steve

[rockiedog2]

looks super Murray
more pics please
Spencer

[s johnson]

Murry, Looks great. Do you have any pictures of the fuselage cabin yet?

Thanks
Scott J.
Oshkosh

[Tom H]

Murray, regarding the urethane donuts, a couple things come to mind:

- a coil compression spring has a hard limit when it closes completely, "coil bound".  On the gear, if this limit is hit, the forces on the gear components increase quickly.  We saw this happen on our LEU, and the upper main gear leg got bent.  The center of the leg bent in the up direction.

- will the urethane donuts allow as much compression as compared to a compression spring?  Is there a linear spring rate, or something else.

Having a method to pre-load easily is good.

Just some thoughts.
Tom H

[Murray Randall]

Attached is a page from the Raymond Manual showing spring rate data for their urethane springs. The springs suitable for the Eagle gear is the .75 spring shown on the bottom left corner of the page. Note that it is not linear at all thus complicating things a bit. On the bottoming issue. I remembered that you had the bottoming problem and made my slots 1.5 in long rather than the 1.0 in in the plans for a bit more travel. I am using six of the .75 in long urethane springs.  
 
I get going on some of these esoteric little changes but sure hope that everyone thinks build to the plans for these wonderful planes. Quick, low cost fun builds and great lo and slo flying. These are experimentals, so pick and choose any of the mods shown on the site with skepticism! My motivation is to create cabin protection for the cold New England temps but stay at 254 lb. From time to time I refer to finite element analysis for S and Gs and offer this help to Eaglers doing mods but not scare. I build with a tape measure and a fat felt tip marker not a computer.   

[Murray Randall]

Here's a pic of the fuse with the door and windows in. They clam shell like a Cub, .625 X .020, weigh 3.22 lb. Gotta get that back.

[rockiedog2]

Tom H
I never have preloaded anything...just set the wheels out a little extra at the top and it's preloaded when u get in it
I never did figure that preload business out
Spencer

[Tom H]

Murray, never fooled with urethane springs.  But, once they are slightly loaded they seem to be fairly linear.  Should not be a big deal.  I wonder what happens to them if they continue to get squished past what the carts show?

Joe, without preload of the spring, some spring movement occurs when you put the airplane on the ground, and some of the available slot is used up.  With spring preload, the spring is already compressed to support the load when the airplane is put on the ground, and no slot us used up, so there is more slot available for landing loads.  If, of course, the spring does not get coil bound before the slot length is used up.

Obviously, it works great for you, but your landings are always grease jobs.  Why do you even have a spring?  Somebody else on here has a wire braced rigid gear, another show off!

Tom H

[rockiedog2]

hey Murray I always liked my shop trashed. I'd feel right at home in yours

[Murray Randall]

I wondered what happened if you max loaded the urethane springs and your asking prompted action. I cranked down on one in my 6" bench vise with a 10" extra arm as much torque as I dare to put into the vise. I used a .70 OD urethane that I MIGHT use for a tail wheel spring, flattened it down to .100 inch in the vise, it didn't visibly fail. Immediately out of the vise it was compressed to .490, it was initially .500 but it has returning to .500 say ten min after the little test. It looks like the things would behave like a bottomed steel. I have a X-country ski from the transfer station that I might use for the tail. I hope the ski or the urethanes can work out at the tail, be a bit lighter than the steel.

Yeah I try to keep the shop clutter kinda private Joe. Most parts of the plane remain in process waiting material or some cleaver idea to jump up. So I drop the tools and go on to another aspect of the build. I neaten up when I can't find something, eventually making the find and stop cleaning. There should be a compromise, too much cleaning yields no work, too much clutter also zero work. 

[rfeenstra]

Trashed shop? have you seen my pics?  I can't work in a clean shop - I find things too quickly and then I don't know how to act!

[rockiedog2]

I spend more time lookin for stuff than working. Today's lost items, the ones that I remember are a 250 ft roll of romex, the crowbar and a NIB 400$ prop xtension. There was somethin else but I can't remember what it was. I bought a new prop outa Russia a while back and got disturbed when couldn't remember what the name of it was. I'm over it now tho. Had just about forgot it happened
Seems like I used to get a lot more done

[bill utt]

My "work" bench is used more for storage than work.
Put a tool down and and can't find it five minutes later. Does it get worse? how did I get here? some of my tools are
disappearing. Don't know if I lent them or lost them. Maybe they just grew feet.
At least I feel as though I have company. Not so lonely . I feel better.