New Super Cub suspension system

[ksecub]

I will try to contact Race Runner tomorrow. If we could get them to design a unit that simply replaces the hyrosorb/bungee system, I think that would be best. How much do these things cost? If it is simply a nitrogen and oil piston system, it should be fairly easy to design it to handle tension loads rather than compressive. The only thing that comes to mind in changing the direction is the difference in piston area. In the compression mode, the piston area is simple (Pi * r^2). In the tension mode the effective piston area is reduced by the area of the rod. If Race Runner will not build us a unit, I might buy one and cut it open (after I check to see if I would not be violating any patent infringment laws first of course). I could reverse engineer it and have a good starting point. My guess is that the stops (end of travel) on these units would not be capable of meeting our needs. We need something that once the end of travel (in either direction is made) the whole unit stays intact and does not fail. I don't know anything about the internal workings of these unit so some investigation is required.

I like the old Ford I beam idea, but there are structural consequences. The longer the gear legs, the more moment load the fuselage has to handle. As the gear legs grow in length the lever arm grows and produces more stress on the airframe. This is the same argument posed by many supercub.org people with 6" gear, but in this case we are extending the gear more like 24". I don't want to stifle peoples ideas, it is great that everyone is thinking out side the box.

I ordered a couple of technical books on aircraft landing gear and will start pouring through the material. Everyone is doing a great job of keeping this thread alive and contributing ideas!

Doug

 

[jay cross]

I worked for 18 years on hydraulic and landing gear systems. The comments in this thread and the fix by the AOSS involves the rebound of the spring or the bungee. The two systems, spring and hydraulic metered shock absorber both work. The idea of keeping this as simple as possible makes sense. How about some sort of friction device working in one direction. Perhaps with an adjustment. Think of the skins they used to use on cross country skis to climb hills. The spring would take the shock and the friction limiter would dampen the rebound. Scrapers on shock struts perform a function sort of like this but they work both ways. A chevron type of wear strip could work. I don't have time to fiddle with it right now. But it is something to think about.

 

[Dave Calkins]

AOSS is actually quite an elegant solution.

There is good damping in both initial load and rebound (In other fields we'd call it 'compression' and 'rebound', of course).

I believe improving upon it's simplicity and easy retrofit features will involve some investment in designing an oleo that has seals and valving that work well with the initial load not being in compression like we (and shock absorber desingers in other fields) are used to.

Definitely a solvable problem, but it'll cost $.

I'll be interested in what Jay has to say.

 

[palhal]

Doug------When I owned the German Storch, it could be dropped in from any height and it would not bounce. It had a simple oleo with no valves or nitrogen.

It had a thin steel liner in a aluminum housing with an aluminum piston with holes in the top of piston and one thick single piston ring about 3/16" thick as far as I can remember. There was a coil spring loose inside the cylinder that the piston would rest on when on the ground.

On take off the weight of the gear, wheels, tires, brakes would retract the piston to the other end of the cylinder.

On landing the movement of the oleo was a slow, dropping, squishing feeling. (remember the Storch is a very heavy aircraft)

The gear on the Cub could be adjusted by the length of the oleo to hang down further than stock for more travel in this system. There was also a plug in the side of the cylinder for fill of 5606. This simple oleo was done in the 30s! This would meet the KISS requirement! -----PALHAL

 

[islandmonkey]

Hi Guys, This my first post on this site and I must say that it is of the most informative sites I have come across on the Super Cub. I have a German registered Super Cub 150. Its been in Germany for the last 40 years mostly towing gliders and banners. It has 4000 hours on the airframe and another 350hrs to TBO on the O320A2B. I have just bought a set of Grove Brakes to replace the origonal drums. I found out about Grove through this site so I want to thank you Guys. I enquired about the AOSS system but the owner will not sell into Europe. His loss not mine as there is at least 1000 Cubs and derivatives here in Europe all getting older by the day. I will stick to the rubber bands for now. I am contemplating developing my own suspension system with European STCs and patents. I will probably be at Osh later this year so I may see some of you there.
Tony

 

[Grant]

Skip on over to New Holstien that very same week. Thats where everyone who matters will be anyway!

 

[ksecub]

This thread seems to have died off. I think there were some good ideas presented. I don't have the time to try to develop any of them at this point. I may come back to it in the future, but for now, I will buy a set of AOSS from Burl. His system seems to be the best solution currently available.

 

[kase]

 

[behindpropellers]

L-14?

 

[Steve Pierce]

No, I think the L14 had an airfoil shaped tail that was pretty wide.

 

[behindpropellers]

found one...

 

[Steve Pierce]

I thought Clyde showed a picture of one in his seminar with an airfoil shaped stab. I must be thinking of something else. What about the wing? I though that was the same wing Dakota builds.

 

[kase]

The cub on skis is a PA18-135.

 

[centmont]

There is only one L-14 left in the US (another in Europe). It is in Kearney, Nebraska...., The owner is a friend and I have some photos...Yes it does have the Dakota wing...in fact, that Nebraska airplane was the one the Dakota guys took the measurements from for the wing. It is a neat plane with the extended glass bubble for the stretcher placement. Most of them went to the Philippines during the war and never returned. It was fascinating reading the book on the Nebraska plane. Ralph

 

[Crash]

This thread seems to have died off. I think there were some good ideas presented. I don't have the time to try to develop any of them at this point. I may come back to it in the future, but for now, I will buy a set of AOSS from Burl. His system seems to be the best solution currently available.

When you lay out all the parameters we want these things to perform in without installation or service hassles, the AOSS is still the best choice in my opinion as well.

In talking with Burl, he wanted to at first make a scale size replacement for the original Piper PA-18 hydrasorb that would not bounce during a hard landing, not have bungees to constantly replace and not have fluid or pressurized gas to leak or get thick at -40 below.

His first unit was the same size (length) as a stock hydrasorb and used stock PA-18 short legs. This design proved too short to give a long enough stroke to dampen properly in compression and rebound.

He then tried a longer unit that was about 2" in diameter. The compression disks (flubber) didn't compress or rebound right, too small.

He then tried a larger (current) size canister but the compression disks were still not right. They changed properties too much in cold and hot environments and just didn't perform right.

He shelved the project for a time and searched the world over to find a company that made compression disks that were unaffected by temperature change and had the right compression and rebound performance. At a point, he finally found the right combination of size and performance in a certain disk.

It (AOSS) then weighed too much so he turned the canister down by .063 up to the assembly ring and went to titanium on the short leg, shaft and turnbuckle.

He then went through years of testing and jumping through the FAA's hoops to get the product certified.

I would some times go over to his shop to visit or get a part machined and he would be like a kid at Christmas when he had another breakthrough on the AOSS project. After leaving I would think to myself "I wonder if this thing will ever be a success and will Burl ever get his investment back"?

I was glad but concerned when I saw him and his wife working a booth at the Alaskan Airmans show in 2004 trying to launch the AOSS. It seemed a lot of guys looked but few were buying. Finally a few sets got out there and word spread. Now the last couple of years the product has really taken off.

I don't think a lot of people can appreciate how much work goes into bringing a product like the AOSS or Mark's Thrustline mod to market this day and age.

My hat off to all the guys that bring new products out for our certified Cubs or entire airplanes for that matter (Cub Crafters, Legend, Super 18 etc).

Take care.

Crash

 

[jimboflying]

Previously I posted pictures of my PA12 with Fairchild style gear. I have since purchased 2" Air shocks from Race Runner (Sway Away) that are filled with 215 ml of oil and Nitrogen. The struts seem to be made very well as far as machining quality. I had to make some special adapters to fit my landing strut fittings. I found that with my angulation of the shock struts I needed 500 psi of nitrogen in the unloaded extended position to provide the ride height I wanted in the loaded position and to keep the wheels aligned vertically. I also found that the 12" of travel allowed the wheels to droop down a little too far in the unloaded flying condition. I called the company and the engineers were quite helpful and found some internal spacers that could be added in 1" increments to block the down travel of the piston. Those blocks are put inside after disassembling the strut. One of the nice features is that the compression and rebound rates are adjustable. The "dead weight of the mechanic hanging from the tie down fitting on the strut test" has been favorably passed and the anticipated ride looks good. Taxi and flights tests should occur fairly soon.

 

[ksecub]

Jimboflying,

Can you tell us how much the 2" Race Runners weigh and cost? Do the manufactures provide and force vs. deflection data at different nitrogen pressures with their units? Can you post some pictures?

Doug

 

[jimboflying]

My 2" diameter x 31.5" long Air shocks weigh about 8 pounds each. They have steel barrels and aluminum ends and pistons. The technical support said they are about as light as can be made however he said exotic metals could be used to make them even lighter at higher costs of course. These struts were $250 each. They have several models, lengths, and sizes with various prices. http://www.racerunnershocks.com/

On these air shocks the piston diameter is 1.83 inches so if you put 100psi it would hold 183 pounds etc. The max is reported to be 500psi. The air or recommended nitrogen is put in through a Schraeder valve just like a nose wheel strut. They are filled in the extended, non loaded condition. When the weight is lowered onto the wheels then the piston moves and compresses the internal gas. This compression of course increases the pressure inside more. So, one of the beauties of the system is that you can adjust the ride height by increasing the pressure to make the plane taller or decrease the pressure to bring the nose down. You could also change one side more than another if you needed to for some reason. The displacement curves would depend on how much weight is being supported and how much pressure is being put into them.

If for some reason the pressure should go away from inside, then the strut would of course lower to a dead stop so you should make certain the prop clearance is still OK should that occur.

Jim

 

[jimboflying]

Here are pictures of my PA12 with the 31.5" long 2" diameter Racerunner air shocks.

 

[ksecub]

Hello Jimbo,

Very cool! I like it.

FYI: pressure = force / area

In your case: A = Pi * r^2 which equals 2.628in^2 for your cylinders

 

[ksecub]

So Force = Pressure * Area = Pressure (psi) * 2.628 in^2

 

[jimboflying]

thanks for the reminder about our friend Pi. I was thinking surface area and quoted the ID of the tube. Tech support has a spread sheet that will tell you what loads are being carried. In my case I have 500psi with 7" of shaft exposed and 5" inside on a 12" travel. Their calculations show that strut with standard 115ml of oil is holding 1080 pounds. That seems high for the GVW but there is some geometry involved because the strut is not perfectly vertical.

 

[jimboflying]

I did the test taxi and gopher hole tests today. The 2" Racerunner air shocks worked very well. The flight tests with variable degrees of smoothness to the landings went well. Cross winds were handled fine. No complaints. I will put the same system on my new experimental 14 project.

 

[Dave Calkins]

Jimbo, does that gear take anything off the top speed of the -12.

I'd guess it does, but would love to hear from you.

Thanks. DAVE

 

[jimboflying]

Dave,

You might remember this plane as having been in the Wasilla, Eagle River area for a number of years. It is the Faust PA12 which has Fairchild style landing gear and the Warner 165 7 cylinder Radial Engine up front. The previous suspension was external bungees encased in a streamlined cover so this strut actually has less drag than the previous setup. So to answer your question it doesn't slow it down any more. The whole setup seems to work pretty well. I usually show about 100 +/- 5mph GPS speed at about 6500 msl.

Best wishes,

Jim

 

[Dave Calkins]

Thanks Jim.

I was not around the airplane at all, though I have seen photos somewhere.

What's the EW of the a/c?

You obviously love the set-up, as you're putting it on your new -14. Any other benefits that we-(me)-uninformed might like to hear??

Thanks again. DAVE

 

[jimboflying]

Dave,

It has a really wide stance which seems to help prevent the tail from swapping ends. It also is taller which gives more ground clearance for the 86" prop. One of the supporting struts comes forward from the upper end cluster to the firewall which makes a great refueling step.

Jim

 

[Rob]

Trailing link Wilga gear anyone?

I know this thread is about investigating new concepts... but this thing does look very cool in person

 

[drew]

Leading Link suspensions are "da bomb" for rough field landing. The CRJ, Wilga, L39 and a bunch of others make use of the leading link.

I once owned a Russian URAL motorcycle sidecar rig that had a leading link front end (aka Earles).

 

[Nathan K. Hammond]

I saw this yesterday and thought this was a neat idea.

nkh