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Retractable gear on an RV

riobison

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

Thanks

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

Thanks

Tim


Germans :D



retract1.jpg



retract2.jpg
 
Retractable gear on an RV, for reliability and simplicity if a person was going to try and reverse engineer a system into the RV?s who?s 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.
 
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.
 
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.
 
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
 
Why?

Retractable gear on an RV, for reliability and simplicity if a person was going to try and reverse engineer a system into the RV?s who?s 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.
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
 
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!
 
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 ;)
 
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!

Dave built that airplane on the Hillsboro airport in OR (HIO) I checked in on his operation a couple of times back in those days with Lee McDaniel, Dave flew that airplane into Lee?s place on LA Center View airport some 20 years ago, it?s a private grass strip and the tail was bobbing on and off the ground, I picked the tail up, ya it was light. It was a cool looking airplane and it was a fun day, I remember watching Dave fly past several times looking for the airstrip before he spotted it, in his defense, no GPS, everyone seemed to get lost out there back then.
 
The German RV-4 pictured in this thread was the subject of a SA article years ago. The following is from memory, so please correct me, if I?m wrong.

This was the second RV-4 from this builder, the first being ?stock?. The German authorities made him perform a complete engineering analysis on the changes, no surprise there. So it was not some hack job. The article went into great detail regarding the modifications required. How the spar was strengthened to accommodate the loads; both landing and twisting.

In the end, it was only 4 knots faster than his ?stock? RV-4 and weighed 80 pounds more.

While it looks really cool, it was not a particle modification. I guess he proved that Van got the RV-4 right the first time. (OK, the 4th time.)
 
What about

I think something else you need consider when you start swinging gear, is more maintenance, more opportunity to screw up, and in turn more insurance premium.

Other than the cool factor, it seems that the extra expense and effort is a moot point, for the speed/economy gains.

It is good looking though!
 
Here's three reasons I can think of to go retractable:

1) You need to go over 300mph
2) You have a heavy airplane that requires large, complicated, shock absorbing struts and possibly big tires that have a lot of drag even if they have fairings.
3) You like spending time and money on maintenance and look for ways to do so.

None of these apply to an RV. Why put up with the horrendous complication and weight gain for, at best, 6-7 mph?

It would look cool though...

Tim
 
Nuff Said...

Here's three reasons I can think of to go retractable:

1) You need to go over 300mph
2) You have a heavy airplane that requires large, complicated, shock absorbing struts and possibly big tires that have a lot of drag even if they have fairings.
3) You like spending time and money on maintenance and look for ways to do so.

None of these apply to an RV. Why put up with the horrendous complication and weight gain for, at best, 6-7 mph?

It would look cool though...

Tim

Tim,
Well said. However comma, Having shared a hangar and extensively flown both of the aircraft below I would add a #4.

4.) You like EZ's or KR retracts...(no electrics/hydraulics)

:)

V/R
Smokey


KR-1


EZ at rest..
 
Tim,
Well said. However comma, Having shared a hangar and extensively flown both of the aircraft below I would add a #4.

4.) You like EZ's or KR retracts...(no electrics/hydraulics)

:)

V/R
SmokeyQUOTE]

Could this possibly be #5? "You like to pay higher insurance costs"?

At least I've always read that insurance is quite a bit more costly with a retract vs. fixed gear... :)
 
saw a 7 at Oshkosh

I was checking out an RV 7 at Oshkosh this year. Custom wings and retractable gear. Very cool looking airplane. Never asked if it had a standard tail or not.
 
IMG_0983.JPG


Here's the 7 at OSH. I don't remember the gentleman's name that built it, but it sure is pretty. I personally don't like retracts, but I do admire people like this that take on such a challenge and win.
 
RV-7 retract owner

Then RV-7 retract at OSH had the following on the prop card: N935MB, Marc Brewer, Churubusco, IN. I applaud Marc for his work and understand any new design will have issues that have to be addressed. One that I noticed is that the top skins above the landing gear did show signs of wrinkling while on the ground. It would be interesting to hear from him on the analysis he has done and what effort it has taken to achieve what he has. Does anyone know if Marc gets on VAF?
 
If anyone has more photos of Marc's -7 from other angles, please post or contact me and i'll give you an email address to send them to. I'd love more info!
 
He lives on a grass strip not too far from me near Ft. Wayne, IN. I have a mutual friend who has been wanting to arrange a visit and has been telling me about the progress of this airplane for a couple of years now.
 
How does it handle landings and roll out?
I bet it's a sweetheart. Wide track gear with oleo...less bounce & jounce, less swerve, what's not to like?
Although I prefer "Down & Welded", I think the oleo main gear attached to the wing spar has merit.
 
I hangared in Dave Lewis Sr's hangar in Hillsboro for many years. His opinion was that it was simply not worth it for the modest increase in performance against the increase in weight.
He had all of the rib molds sitting on a shelf gathering dust. I know the current hangar resident and will see if the molds are still hanging around but Dave Sr. past some time ago and I suspect they have been lost to time.
 
RV-7 r

Sure looks cool i always wondered what preformance would be with skinny wing and retrack anyone got the #'s
 
It's not worth it from the standpoint of performance versus weight/maintenance/insurance hassle (in my opinion) but the cool factor is up there pretty good!
 
Sure looks cool i always wondered what preformance would be with skinny wing and retrack anyone got the #'s

I talked with him shortly after he landed and asked him how it performed. From my conversation with him, he said he had very limited testing on it for pure performance, but it was doing a little better than a stock RV so far.

My guess is that once he gets all the little details worked out it will do better.

It was fun to see though!!
 
I liked Danny's retracts so much I did the same to Smokey. :D

P1020936_retract.jpg


Now I can finally keep up with the checkered-tail RVs.
 
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.

Not only has Bryan put in retractable mains, but his tail gear retracts as well. Better yet, it's taken him less than 4 years, start to finish on this aircraft which is ready for its first flight as soon as the paperwork arrives.

Fuselage is based on an RV-4, but Bryan stretched it by a few inches (4?) and is using an O-375 from Aero Sport. He calls it a Rocket because that simplifies the paperwork. I'm pretty sure some pics will appear in a few weeks.
 
Now I can finally keep up with the checkered-tail RVs.

That Jolly Roger tail has got to be at least as fast as a checkerboard tail or checkerboard nose. Might want to consider adding chrome valve covers to the engine if you haven't already got them. That'll be one of my next speed mods ;)
 
Fuselage is based on an RV-4, but Bryan stretched it by a few inches (4?) and is using an O-375 from Aero Sport. He calls it a Rocket because that simplifies the paperwork. I'm pretty sure some pics will appear in a few weeks.
I mocked up a couple of paint schemes for the Pocket Rocket, but in the end the amount of metal flake paint was deemed to be too expensive. Here's what I had so far.
RV-4%2520Pocket%2520Rocket_Swoosh.png
 
The wrinkles are from the gear. I originally had the torque tube that it pivots on when retracting end there. I extended it to the rear spar to correct it. It tracks very good with the wide gear and is a blast to fly. I just got the gear doors on and will let you know how the performance is. I went on vacation before I got a chance to fly it. To learn more about it you can visit www.tropria.net/rv Marcus
 
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Not only has Bryan put in retractable mains, but his tail gear retracts as well. Better yet, it's taken him less than 4 years, start to finish on this aircraft which is ready for its first flight as soon as the paperwork arrives.

Fuselage is based on an RV-4, but Bryan stretched it by a few inches (4?) and is using an O-375 from Aero Sport. He calls it a Rocket because that simplifies the paperwork. I'm pretty sure some pics will appear in a few weeks.

If I were him I would not call the aircraft a rocket. It will cost him come insurance time. Because a lot of HR rockets have been on their nose insurance Is 3 times what you pay for a RV. F1 rockets don't have the issue but the insurance companies don't care and charge the same. There are a couple of rockets registered as io540 RV-4's and they enjoy much lower insurance rates.

George
 
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The wrinkles are from the gear. I originally had the torque tube that it pivots on when retracting end there. I extended it to the rear spar to correct it. It tracks very good with the wide gear and is a blast to fly. I just got the gear doors on and will let you know how the performance is. I went on vacation before I got a chance to fly it. To learn more about it you can visit www.tropria.net/rv Marcus

Never mind the gear... I want to know more about that beautiful wing! :)
 
Yes, a beautiful wing.

Wow! True experimenting..congratulations and welcome to VAF.

Would you kindly share some performance numbers?

Thanks,
 
Bryan Carr's Rocket RG?

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.

Not only has Bryan put in retractable mains, but his tail gear retracts as well. ... Fuselage is based on an RV-4, but Bryan stretched it by a few inches (4?) and is using an O-375 from Aero Sport. He calls it a Rocket because that simplifies the paperwork.

A fellow aviation photographer from my area recently posted the following picture on a discussion forum that we frequent. I wonder if it's the new airplane or the previous one. Very cool, one way or the other.

9503_10151445105061654_1325886029_n.jpg




PS: I think it's interesting that, when one contemplates the slick look of most RVs, a natural thought is "It would look even cooler with retractable gear". I'm sure that most people who even think about it, think about it due to looks and the engineering challenge (and the pride of having made something unique), not to gain a couple knots. It's funny how often the question comes up, e.g. here and here and here (including even a discussion about the possibility of only retracting the nosewheel). Only rarely do we get actual evidence of people doing it, like Marcus' beautiful RV-7RG here with its unique wing, and Bob Gallagher's RV-4RG in Memphis, and that RV-4RG in Germany. By the way, how much RV is in the Radial Rocket? I don't know about the history of the design, but the name (and its general look) implies that it's an RV derivative to some extent (but I could be totally wrong about that. It's significantly heavier and more powerful than 2-seater RVs).
 
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Retract RV-4

The good thing about doing a retract mod is the ability to keep up with Lancairs with no trouble.

2hibb5g.jpg
 
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RV-7 RG Operational experiance

Hi there gents. Has anyone heard from Marc with respect to how things are coming along with the RG? any performance numbers and final weights?

Regards,

Tom.
 
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