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Custom landing gear engineering question

Old 04-24-2012, 07:15 AM
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davidgeorge212
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Default Custom landing gear engineering question

Ok, I have an engineering challenge, I just need some suggestions about how to engineer a custom landing gear. I have a kit of the plane that I posted a picture of below. It is a really old free flight design and I will eventually convert it into R/C. The landing gear that it shows drawn on the plans is a 100% manual retract. I believe it is like a "U" shaped wire with only one wheel at the bottom. You have to initially pull the landing gear out by hand and set the plane on the ground. The weight of the plane keeps the retract gear and wheel from sliding back up into the fuselage. But, as soon as the plane leaves the ground, the weight is removed from the landing gear and a rubber band pulls the entire gear up inside the fuselage. It does not come out again for landing so it just bellies in on the grass. The way the landing gear retracts though is straight up in a straight path. It does not pivot or rotate or fold up like modern day retracts.

So, I was wondering if there is any way to engineer this landing gear so I could retract it down and back up from my transmitter? I think one issue is that the travel distance the wire gear will have to go is going to be much further than a standard servo will be albe to extend it. Another issue would be, once the retract gear is extended, how can I ensure it is solid enough to land on and not accidently collapse back up inside the plane? It will need some kind of lock when fully extended but be able to unlock and retract.

I dont think the gear has to be something super substantial but not weak either. Im guessing the AUW of this plane should be around 3 to 5 pounds ready to fly.

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Old 04-24-2012, 12:59 PM
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fledermaus
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Default RE: Custom landing gear engineering question

Just from the look of that plane, I think you should go with a fixed undercarriage. The plane sort of looks like the Polish PZL 11 fighter, or other 1930s designs. It would be easy to make a music wire undercarriage anchored into the wing support structures, and fair the wires with balsa.
Old 04-24-2012, 02:50 PM
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WaffleMan
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Default RE: Custom landing gear engineering question

Easy. You can buy nosegear retracts desinged for aircraft with tricicle gear, wich would be perfect for your needs. It won't look exacly the same, but it will do the purpose.
Old 04-24-2012, 05:22 PM
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davidgeorge212
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Default RE: Custom landing gear engineering question

I was looking at nose wheel retracts and that would be an easy way to pivot it back up. I just threw this out there though because I wanted to try and figure out a way to engineer the original landing gear to be able to extend and retract. I wanted to see if I could keep the landing gear looking authentic to the original design.

The plans show how to make the mechanical retract. For those that did not want to mess with the mechanical retract, though, the kit also came with a pre bend wire gear. I will keep thinking about my different options. On the one hand, I probably wont be doing stuff like touch and goes with one wheel and all, but on the other hand I thought it might be cool to have the wheel be able to retract and extend back out for the initial take off and landing.
Old 04-24-2012, 05:50 PM
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Default RE: Custom landing gear engineering question

Maybe retract units attatched to boh tips of the "u" wire? 
Old 04-24-2012, 06:02 PM
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Default RE: Custom landing gear engineering question

I'll sketch you up a possible fix tomorrow. A main wheel that moves vertically only.
Old 04-24-2012, 08:36 PM
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Default RE: Custom landing gear engineering question


ORIGINAL: MajorTomski

I'll sketch you up a possible fix tomorrow. A main wheel that moves vertically only.
that would be great, Ill take any ideas you have.
Old 04-24-2012, 09:18 PM
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Default RE: Custom landing gear engineering question

here is another photo I was finally able to take. It shows how to build the mechanical gear. To tell you the truth, it took me a while to figure out just how this works but its pretty simple once you understand it.
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Old 04-25-2012, 02:13 AM
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Default RE: Custom landing gear engineering question

That is a VERY beautiful aeroplane!
I believe there'd be a great amount of pleasure building it stock, at lease to the point of how the gear actuates etc.
Also covering/engine choice... stay in the retro groove.
I fellow brought a vintage RC model down to the strip last year. With a diesel motor. It ran SUPERBLY and was remarkably quiet during operation.
A real head turner, that left us all wondering what on earth are we doing with all our expensive equipment and stash... and here's an old man, with an old model that performs so well, sounds orgasmic and smells marvelous.
Good luck with the model.
Old 04-26-2012, 04:17 AM
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Default RE: Custom landing gear engineering question

Ok I have your sketch:

To get you the vertical linear mono-wheel retract you want to duplicate we’re going to use a 90degree main landing gear retract. I think the new e-flite 15 size main retract would work well for this. We’re going to mount it upside down and at a forty-five degree angle so that “up” becomes the down lock and “down” raises the gear. We’re going to use the linear distance the gear end travels to get the travel we need to get your gear up and down.

Mount the retract on a plate aft of the struts in your model, just about the same area that was originally used by the rubber band down lock.

Build the original model landing gear struts so that they freely travel in up and down in slots built in to the inside fuselage sides. The hardest part here will be leaving enough strut inside the slot to keep the wheel from bending backwards or breaking the slot it rides in from aft loads if you hit too hard.

Now all you need to add to the struts is a plate with a slot in it that will provide the space needed the axle part of the retract unit to travel through its normal arc. To adjust the amount of travel, move the axle in our out on the retract strut.
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Old 04-26-2012, 06:37 AM
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Default RE: Custom landing gear engineering question

Check out e-flites electronic retracts. You can probably use the nose gear retract. It's one piece - servo built in. You can either cover the landing gear wire with Robart strut covers, or get an aftermarket strut to keep the scale appearance.

I was thinking of ways to create what you asked for, but my solutions were involving screw drives or bell cranks, taking up a lot of money or space.

I agree that it looks fairly easy to make room in the belly for a folding gear. I also think it would be more robust than an axial-motion device.

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