So, as I sand on my Champ my mind starts to wander and think about the next project.
I have been thinking for quite a while that a long travel, self contained gear leg, with a smaller lighter wheel and tire combination would work well for off airport landings and not have the drag associtaed with big bush tires.

If any of you are into current model high performance off road bikes, you have probably held a fork leg in your hand recently. What I am thinking is a clamp in the gearbox of the fuselage machined from a bilet or a welded steel clamp that holds the gear legs, which would very closley resemble motorcycle fork legs.
With this type of design, there would be about 14 or so inches of travel. The travel would also be controlled interally to limit bounce and adjust firmness (just like a bike)
The old Nazi Storch had simular gear, just not with the mordern touch like this would have. If it worked, it would allow the use of much smaller and lighter tires and wheels.
I am not an aircraft engineer, just a guy who thinks too much while sanding, so this may not work at all, but might be fun to discuss. My thoughts are that this would work on something like a Rans, Kitfox, or Highlander.

D.

Im not expert but I like the larger tires so I go over the little gopher holes, not through them. Im just guessing but going over probably helps get to takeoff speed faster. But Im not an engineer.

Maybe you could use lighter less balloony tires but I think they would still have to be pretty big around just like a bike tire to work well.

Big tires don't just absorb bumps while landing off airport but they also add a lot of flotation on soft surfaces such as sand. Landing gear like you suggest might work on some rough strips, but land in soft sand and you will risk flipping the plane on its back due to the small tires digging in.

How about this angle to the problem---A taller tire adds floatation in the form of bridging the gap between ridges.rocks and gopher holes--instead of wider maybe taller with still room for inflation variences. This would also leave room for pants for streamlining purposes.Longer legs and prop clearance....Form Follows Function(Maybe Not?)

David, just keep sanding and get big tires!

I was picturing it with a 21" wheel and a 3 or 4 inch wide, and smooth tire. I see the advantage to wide tires in soft surfaces, but diameter is almost as good if the weight they are carrying is low enough. Like I said, it is just and idea. I suppose if an advanced suspension system is a desirable thing for landing gear, then it wouldn't really make it not work by using it with larger tires.
Looking at the parts ilustration of my 1946 Aeronca "no bounce" gear, there is not much in it. What I am thinking of is the same idea, but with compression and rebound shim stacks, progressive springs, urethane bottoming cushions, and friction sufaces that are TiNitride on Teflon. These components wouldn't add weight or drag, and are proven.

patrol guy wrote:David, just keep sanding and get big tires!

Already has learger tires and wheels on it from the previous owner. It has also been flown to every out of the way strip within it's range of Wenatche and Spokane. I am sure it will suit me just fine. I am looking forwards to a future project, and just thinking out loud. But you are right, I need to keep sanding.

Hey David,

If you're crazy, then maybe I am too. I have had similar thoughts about how to make an inexpensive backcountry monster. I have thought about modifying a Sky Raider or an Ultra Pup with a Rotax 912 or Jabiru. I would like and overpowered(?) lightweight rock-pounding-STOL personal bush plane. Take a look at the Butterfly Gyroplane gear. http://www.thebutterflyllc.com/video/videos_gflg.htm Might be able to design something similar for a fixed wing aircraft.

Aviation is pretty conservative and I think there is a fair bit of room to think outside of the box.
Cheers,
Joe

I am definitely impressed with that video on the suspension gear. I think the limiting factor for using that gear on standard aircraft is the forward speed at touchdown. Most of the planes used in backcountry flying are going to have a need for more forward speed or rolling shock absorption and less need for vertical shock absorption. (Honey I shrunk the prop clearance.) Although I will make an exception in the case of the Fiessler Storch and the lines of aircraft that evolved from it.

You're talking about two or three separate factors, which IMHO require two separate solutions. Large and wide tires solve two problems... the gopher holes and the flotation as mentioned.

The long-stroke suspension provides shock absorption from vertical impact, not flotation or bridging ruts.

Although a comparison in the field will likely never be done, I would bet that the Fieseler Storch cannot land on the rocks and the rough ground like a big-tire Cub can. The Storch would be over on its nose. But the Cub could not be stalled at 10 feet AGL and come down without damaging the aircraft or hitting the propeller like the Storch could.

So the solution for a back country monster airplane is likely BOTH large tires for flotation and ruts... AND a long-stroke shock absorbing system for the Navy arrivals.

This kind of airplane would be even slower than the standard big-tire Cub, since a longer stroke gear puts the tire further below the aircraft, making more nose-down pitching force, requiring more nose-up trim for level flight, making more drag.

Having built several off road cars, including a sandrail with over 24" of travel on each corner, I always thought this would be a cool idea... and then a few doses of reality hit me.

First and foremost, light weight and long travel do not go hand in hand... It just simply doesn't exist. Add complex dampening and the weight goes up even more. The difference in weight between a really fast sand car, and a long travel sand car is 500#s... I used sand cars, instead of motorcycles because they tend to weigh about the same as an airplane, I don't know anyone flying an airplane that weighs the same as a motocross bike....

Next, Why do we go long travel in the off road community? : So we can go fast! It is the ONLY reason... It is also the opposite of the STOL goal... At cub speeds and less you simply don't need suspension... PERIOD... A J3 (no hydrasorbs) on bushwheels will get into some astonishing places... getting in is not the problem, getting out is!

And lastly, in the motorcycle, or automotive suspension industry, the very first question they are going to ask is "what's it weigh?" and "it" always weighs the same, because "it" doesn't have wings that produce various amounts of lift at the flick of a control... in other words... suspension for bikes and cars (as technical as they can be) are wayyy simpler to come up with than suspension for an airplane that not only "changes weight" but doesn't necessarily do so in a linear fashion!

It's a really cool idea, but I'd have to agree with patrolguy:

patrol guy wrote:David, just keep sanding and get big tires!

So far all of the discussion has focused on using the shocks for travel in compression like a motorcycle fork. It would be possible to use the same technology in extention as a replacement for a bunjie system. That way the loads would be carried by the mains and the shocks would only serve to control the rate and distance of travel. It would be easy to set up a variable rate system to allow the small bumps to be absorbed softly while the navy style hits would be dampened. Easy to make it air adjustable for loads and temperature changes.
X-Air has used a spring-over-oil shock on their mains for years.

I've heard these work good, but I think there pretty spendy.

http://www.aoss.net/

All really valid points for and against this type of system. Every change you make to something, especially something that already works well, will require several other things to change so the first thing that was changed does not negativly effect other performance aspects of whatever it is you are trying to change.

I was going to multi-quote reply, but I am too lazy at the moment and need to get going to the gym, and then the hangar. As far as weight, modern motorcross stuff is light, lighter that old airplane stuff. As far as not having a consistant weight, that does not matter that much for what this is. When the weight is off the suspension in this use, does it matter if the suspension works perfectly at that moment?

As far as needing large tires to bridge gaps and float soft terrain. There is no way around that, it is what works. So, I would agree, all this would help with is aircraft that preform a "carrier" landing. Also, since prop clearance would be reduced at full compression, it would be better to just get tossed around a bit by that lack of suspension rather than bend the prop.
The system that Coyote Ugly linked to looks neat. I says it only adds one pound. I guess with even one additional pound of weight, you would need to ask yourself if it is really necessary, or do the trust old bungies that have been used for years work well enough?
Enough said, I'll go sand my Champ some more.

What about a Wilga with big tires? This plane has been on barnstormers for a while now.

DavidB. wrote:
it would be better to just get tossed around a bit by that lack of suspension rather than bend the prop.

"Tossed around" can also mean that you are wearing out your airplane to one degree or another. Spar fitting bolts can get worn, strut fitting bolts can get worn, engine mounts can develop cracks, firewalls can develop cracks... some of that crap can get dangerous too.

Flying off-road has its requirements and its safety factors just like instrument flying or flying in icing conditions. Every specialized modification or feature comes with some cost in weight, money, complexity, etc. Landing on boulders or sandbars or across ruts means you will have to adjust your airplane... the same way as you would lose money, useful load, and simplicity when you outfit an airplane for IFR work.

Experimental Maule suspension

http://www.supercub.org/forum/showthrea ... nken+maule

This kind of airplane would be even slower than the standard big-tire Cub, since a longer stroke gear puts the tire further below the aircraft, making more nose-down pitching force, requiring more nose-up trim for level flight, making more drag.

Exactly the reason why I decided to keep the standard length gear on the new RR being made right now.

What about the old style tandem gear they used to use on cubs? double the flotation without any increase in frontal drag area. Of course this did nothing to help suspension wise and doubled the weight. Having ridden dirt bikes a lot I sort of like the idea of a tall wheel, as stated, a tall narrow tire can have the same square inches of foot print as a short fat one and would roll across the gopher holes better while having less weight. Of course a tall, fat tire filled with helium might be the best bet>