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  #1  
Old 03-02-2012, 09:20 PM
riobison riobison is offline
 
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Default Retractable gear on an RV

Retractable gear on an RV, for reliability and simplicity if a person was going to try and reverse engineer a system into the RVs whos has the best design to start with?

Thanks

Tim
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  #2  
Old 03-02-2012, 09:36 PM
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Quote:
Originally Posted by riobison View Post
Retractable gear on an RV, for reliability and simplicity if a person was going to try and reverse engineer a system into the RVs whos has the best design to start with?

Thanks

Tim

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  #3  
Old 03-02-2012, 10:23 PM
riobison riobison is offline
 
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looks neat, a little too much camber on the gear on the port wing

Last edited by riobison : 03-02-2012 at 10:25 PM. Reason: grammer
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  #4  
Old 03-02-2012, 10:36 PM
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Bob Kuykendall Bob Kuykendall is offline
 
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Quote:
Originally Posted by riobison View Post
Retractable gear on an RV, for reliability and simplicity if a person was going to try and reverse engineer a system into the RVs whos has the best design to start with?
First off, I'm not an engineer, and within reason I defer to those who can demonstrate that they are. But, that said:

Boy, there's a bunch of different ways to skin that cat. My primary suggestion would be to look mostly at the systems in taildraggers. The systems in nosewheel airplanes like Cherokee Arrow, Mooney, and Bonanza all have the advantage of being able to mount trunnions in both the main spar and the drag spar, with the gear leg between them. And that is not necessarily practical for a taildragger.

The one that comes to mind as a good exemplar is Globe Swift. It has similar wing geometry to the RVs, so the packaging would be similar. In specific, pay attention to how wing torsion from braking or 3-point touchdown are resisted.

The main concern would be that putting the landing gear in the wing subjects the wing to all sorts of loads for which it was not originally designed. That doesn't mean it couldn't handle those loads or that it could not be modified to handle them. But it is something that ought to be subjected to a basic static analysis.

Since the leading edge where the gear legs stow (the place where the fuel tanks are in the stock wing) has to be open, it cannot contribute nearly as much torsional stiffness to the wing. So the wing box between the main and drag spars sees not only all the torsion that might have been reacted through the closed box of the fuel tank, but also the added torsional loads (breaking or 3-point touchdown) introduced by the landing gear.

My guess is that a relatively coarse analysis would show that the box that is there would need some reinforcement in order to do the job adequately. I'm thinking .040 skins aft of the spar, tightened rivet spacing, and maybe doublers in the area of the gear trunnions, stuff like that. Nothing major, but all stuff you have to account for in the detail design.

That aside, I have written before that retractable gear would make an RV a much more serious and less fun airplane, and I think would detract a lot from the overall happy experience of most RV flying. But I guess that if speed is your thing, you would have a legitimate reason to want retracts.

Thanks, Bob K.
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  #5  
Old 03-02-2012, 11:17 PM
SHIPCHIEF SHIPCHIEF is offline
 
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OK, I'll bite.
I have a Bellanca Cruisemaster. (makes me feel sad for the rest )
The point I'm trying to make, is that the gear can retract straight back.
Not as P-51 looking. Looks more P-40.
Or it could retract outward ala Spitfire or Me109.
I like straight back. Although it wouldn't fit entirely flush, the spanwise disruption of airflow is much less, and I think the simplicity of straight back retraction along with less disruption of the original wing structure could be a winner.
On my plane, the gear trunion is mounted to the front face of the front spar, so when the gear is retracted, it lays along the bottom of the wing, like a P-40. Unlike a P-40, the wheel does not rotate and lay flush to the wing.
That would be nice.
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  #6  
Old 03-03-2012, 04:59 AM
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Kevin Horton Kevin Horton is offline
 
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If I wanted an RV with retractable landing gear I would track down Bryan Carr in Langley, BC. He's currently working on what I think is his tenth RV or Rocket, and it will have retractable gear (it's an RV-4, IIRC). One of his earlier creations was an RV-4 with retractable gear.
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  #7  
Old 03-03-2012, 05:10 AM
sailvi767 sailvi767 is offline
 
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Since a clean RV can get near VNE in level flight with the larger engines would you not also have to consider flutter margins and possible changes to the tail?

George
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  #8  
Old 03-03-2012, 05:33 AM
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plehrke plehrke is offline
 
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Quote:
Originally Posted by riobison View Post
Retractable gear on an RV, for reliability and simplicity if a person was going to try and reverse engineer a system into the RVs whos has the best design to start with?
first question is why do you want retractable gear? I can only think of three reasons: looks cool and different, it is a challenge and learning experience, and to go faster. For the first two, go for it. For the speed how much speed do you think you will get for all the trouble? Maybe 15-20 kts? What ever it is please see quote below.
Quote:
Originally Posted by sailvi767 View Post
Since a clean RV can get near VNE in level flight with the larger engines would you not also have to consider flutter margins and possible changes to the tail?

George
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  #9  
Old 03-03-2012, 06:00 AM
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jthocker jthocker is offline
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FWIW, I have flown the retractable gear RV4 that has been pictured on these forums in the past. It was built by my friend David Lewis and his father some 23 years ago. The landing gear was adapted from the Celerity kit plane. The fuel tanks were moved outboard to make room for the gear. The engine is an angle valve 200hp. When the plane was completed and weighed, the tail wheel only weighed 12 POUNDS!!!! Can't remember the empty weight. For all the engineering and complexity the plane was only 7 MPH faster than a stock RV4 with a then non stock 180hp with a CS prop. I flew in formation with it all the way to Sun n Fun one time and have to admit that it looked really cool in flight.
I had the drawings and was going to build one, but the complete unstarted kit I bought had Phlogiston prebuilt spars and that ended that idea.
The airplane did slow down much faster than a stock RV4 though!
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  #10  
Old 03-03-2012, 07:27 AM
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Quote:
Originally Posted by jthocker View Post
FWIW, I have flown the retractable gear RV4 that has been pictured on these forums in the past. It was built by my friend David Lewis and his father some 23 years ago. The landing gear was adapted from the Celerity kit plane. The fuel tanks were moved outboard to make room for the gear. The engine is an angle valve 200hp. When the plane was completed and weighed, the tail wheel only weighed 12 POUNDS!!!! Can't remember the empty weight. For all the engineering and complexity the plane was only 7 MPH faster than a stock RV4 with a then non stock 180hp with a CS prop. I flew in formation with it all the way to Sun n Fun one time and have to admit that it looked really cool in flight.
I had the drawings and was going to build one, but the complete unstarted kit I bought had Phlogiston prebuilt spars and that ended that idea.
The airplane did slow down much faster than a stock RV4 though!

Years ago, that airplane had a prop strike (difficult hot start, revved up, and pivoted around main wheels). It was repropped with a whirlwind 151 and the battery was moved to the aft fuselage, which completely fixed the cg issues.

It is now a reliable airplane that flies a couple of times a week, mostly formation with an occasional cross country.

The airplane climbs well, and is faster than 160-180hp rvs, but my -8 with the same engine and prop will easily walk away from it in level flight.

I haven't flown it, but it is reportedly very easy to land, with the wide-spaced oleo strut gear.

It looks -way- cool both in flight and on the ground
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