wsmalley

My Feedback: (6)

Got a rather heavy .60 size Pilatus Porter with fixed L.G. Wondering if building scale sprung gear would improve handling-likes to bounce a bit on landing. Doesn't have much clearance between the prop and Mother Earth? Any opinions on sprung gear?

gjs

What you want in my humble opinion is shocks. Shocks absorb energy. Springs absorb energy and then return it,( bounce). In physics I learned you can't really consume energy, you use it or more exact, you convert it. Car brakes take the energy of the moving car and actually convert it to heat. Shocks force the oil through tiny holes at high velocity which makes the oil hot, converted to heat.
I plan, some day, on trying to make a shock out of a Polypropelene tube type material. When you stretch this stuff repeatedly it gets hot then slowly returns to original length (energy absorbing). like the Cub landing gear it would be where that chunk of black is between the stutts. The struts would need some spring to raise the model back up to standing tall while the energy absorbing material slowly returns for the next hit. I say hit because it should not be so weak that it sags or stretches enough to let the prop hit and not so stiff as to let something else absorb the energy like balsa. I'm assuming you felt the landings were "HARD". Gear too stiff. Need more info. Hope this helped.
Any engineers comments on my analysis are appreciated. gjs

wsmalley

My Feedback: (6)

Actually that would have been a better choice of words in this instance. The full scale Porter used shocks going from the wheel/axle area up to the side of the fuse. I bought an RC car shock with the idea of incorporating that. It seems a bit too big around to be very scale, but I think the principle is sound. The full scale Cub, did those black things enclose springs or shocks?

3 Channel Brain

If I remember those black things were Oilcloth to hide / protect
shock cords --Cubs were light didn't need much.

linclogs

Quote:
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The full scale Cub, did those black things enclose springs or shocks?
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Those black things on full scale Cubs enclose bungees.

I recently bought some 1/4 scale Cub gear for a project I'm working on which will be modeled after a full scale Super Cub my dad used to fly for a company called Union Flights out of Sacramento Executive Airport. They contracted to what used to be Pacific Bell for "telephone patrol" work and my dad had the route out of Reno, Nevada for awhile, then later through the wine country of Northern California and along the Northern California coast.

While Robart makes scale Cub landing gear in 3 sizes (1/5, 1/4 and 1/3 scale), I found another gentleman that makes some that I like a whole lot better. Bill Wallace from Dixie, Idaho is making a great set (but only in 1/5 and 1/4 scale). Both Robart and Mr. Wallace are building their gear from 4130 chrome molly welded tubing so I don't believe there's any difference in the strength, however the ones that Mr. Wallace make includes the bungee covers and he has provided an attachment point for mounting wing struts at the fuselage. Plus his are about 20% cheaper, which doesn't hurt! Check out his website at www.J3gear.com and also see what they look like in the photo I've attached.

gjs

I wish someone would clarify the difference between shock and spring. to my way of thinking a spring is a shock but it returns the energy quicker. In the case of your Pilatus since its close to the ground, your choice should be a FIRM shock Maybe rubber put in line somewhere to give a little. Whatever it takes I see it as a FINE TUNE thing. SOFTER TIRES, FIRMMER?
I think I remember custom made scale shock made with the inside tube pushing (with capped ends) or compressing silicone tubing inside the other tube.

Borzak

My Feedback: (2)

A spring does nothing to dampen the return of energy in the opposite direction - what you put in you get out.

A shock absorber - absorbs the "shock". If you've dealt with high performance cars you can adjust the rebound and spring rate on a coil over shock.

wsmalley

My Feedback: (6)

It seems the shocks seem to have the edge in the opinion polls. The question then becomes are there any model type(s) to recommend that are 'aircraft' type, or, how could you make them? That is, without a full blown machine shop. Seems the passages would be hard to do. I don't know how well my RC Car shock would perform, guess you'd just have to try it. Don't know how you would calculate the 'force'- you tell the auto parts guy the kind of car you have and the factory has worked it out. Does the big jet gear use shocks or some internal spring 'model' shock?

thebluemax

My Feedback: (151)

Here is what I did to my Altech Turbo Porter as I had big time problems with the fuse sides getting torn up from the shock of my landings. It wasn't cheap about $75 but it was easy to do and it works great!!! I bought Robart's Robo-struts, number 650 for another project which I hadn't built yet. So I used it for this instead. Look at the attached picture and I think you can see what I did.

thebluemax

My Feedback: (151)

here is another picture. The blue tape at the top was only there while lining things up until I tighten it down.

thebluemax

My Feedback: (151)

final results from another angle

egor

Interesting subject working through this sort of thing in my mind for a plane I'm butchering right now. on the carl goldberg tiger II the main gear is attached to the wing in a fairly flimsy manner ( my opinion) working out what I hope will be a better -heavier- Mount on my own and was thinking about using wire nose gear with the coil spring in the center. Of course all of this would have to be bent to fit , but I am curious as to your opinions as to the coil spring.

egor

FunXtra

Here's a tip:
For the Tiger II don't worry about how strong the main gear is. Just throw in some mechanical retracts and put sponge wheels on and voila. to solve your landing worries just make sure you give it REALLY nice landings
in case one of the wheels wont come down chop the engine off and do a belly landing. just install a belly guard [>:]