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Folding Wing RV-4

WingsOnWheels

Well Known Member
I just saw this on Barnstormers. Has anyone seen this plane in person, I wonder what mods were done to work this out. Reminds me of the Mustang II.

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interesting

Wow, that is interesting. I hope whoever did this has some engineering and test flying background - in my mind that is a pretty substantial modification/deviation from the plans.

It is cool though...
 
"just"

Wouldn't you "just" have to make the break in the spar stronger than the original? In college we had a lab where we had to redesign the wing attach bolts for a T-34 and perform testing in the lab to prove it...my group used, and PROVED that you could make zip ties work for up to utility category strength! :eek:
 
wing attach

In college we had a lab where we had to redesign the wing attach bolts for a T-34 and perform testing in the lab to prove it...my group used, and PROVED that you could make zip ties work for up to utility category strength! :eek:

How many zip ties did you have to use and what size and quality ???

Ed Booth, Trenton, SC
 
That is soooooo cool. I wish we could convince vans to come out with this mod. You could fit 3-4 rvs in one hangar. It would look like an old aircraft carrier.

Of course I would only trust vans to come out with it. Or maybe a bunch of people with a bunch of testing hours. That guy has a lot of guts.

So cool
 
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Odd!

I wonder if its still aerobatic?

Also there is something odd in the rear canopy.

Do you have a link for where this is, I could not find it on BStormers.
 
Did he split the flap as well or does the -4 flap stop short of the ailerons where he folds the wing? What about the fuel tank?
 
Just doesn't look like it will fit back into that hangar.

That was my first thought too.

Wing folding mechanisms aren't really all that difficult... They do always add weight, though.

Here's the link to the ad, with more photos.

Look like the owner has used Sika or Proseal to bond in a plexi panel behind the passenger's head... Maybe stopping drafts?
 
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It would be great if Vans could off a mod to make the RV with folding wings like the Mustang II. I like the RV better, but the folding wings on the mustange are very cool.
 
Only one wing?

The photo that's shot from the front shows that the flap on the folded wing is shorter than the one on the other wing.

I wonder if both wings fold, or only the port-side wing?

I also wonder if it has flown since the folding mod was performed. :D

- mark
 
It looks to me like only one wing folds and the flaps are definitely split, an unfinished project maybe, maybe the design intention was for both wings to fold but something interupted the project.:confused:
 
The cool factor is high on folding wings. As with it all there will be a trade off.

Extra weight, out bound on wings.

My first thoughts: RV4 folding wings?? It only has a 23' wingspan! Why fold them?

Fun to see the photo. Very cool.
 
It looks to me like both wings might fold. From the front photo you can see that there is a break in the right flap at the same station as the break in the left flap. There also appears to be some kind of a seam in the underside of the wing at that same station. On the other hand, I don't see any seam in the leading edge...
 
Just doesn't look like it will fit back into that hangar.

It would not help fit it in very many hangers I know (and especially in my hanger). Would only help in hangers with all low wing aircraft. Mine has 2 high wing airplanes so the low wing RVs fit under them.

In my opinion, no way does the precieved "cool factor" ever buy its way on an airplane espeicially for something already as cool as and RV but i do love the rules in E-AB that let people try these kind of things. Makes going to OSH fun to see what others have tried (do not get to see much at OSH what others have failed trying)
 
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In my opinion, no way does the precieved "cool factor" ever buy its way on an airplane espeicially for something already as cool as and RV but i do love the rules in E-AB that let people try these kind of things. Makes going to OSH fun to see what others have tried (do not get to see much at OSH what others have failed trying)

The Cool Factor is added to aircraft for mission specific use in the military. It sometimes takes an unlimited check book, (Gov,) to accomplish the Cool Factor.
 
I wonder if its still aerobatic?...
Good question. The folding Mustang II referenced in some of these posts is not aerobatic.

Although I couldn't find it on their site, one of our chapter members is building one and he said that was the only drawback to the folding option.
 
I wonder if that's true, or if it's "Common Knowledge"?
The final Thorp T-18 model, the S-18, is folding wing, and the aerobatic gross weight is 1500 pounds. The 'older' T-18 aerobatic gross weight is 1250 lbs.
The folding mechanism is said to be the same for the S-18 and the Mustang II.
I just flew out with the wife to look at an S-18 folder, on a trailer in a garage.
It was a great day trip with wonderful flying, and also wonderful new people to meet.
The aircraft in question is not a flier, more of a restoration project. but the folding wing mechanism was out in the open for easy viewing. I'd say it's pretty straight forward, and similarly strong.
 
I wonder if that's true, or if it's "Common Knowledge"?...
I've got to go with what the builder told me and the Mustang web site.
M-II FAQs said:
Does the Folding Wing Make It Weaker?

The folding wing modifications for the Mustang II do not change the main wing spar. Ultimate G loading is therefore not changed. The only structural difference is the wing rear spar attachment. From a design standpoint the folding wing version is stronger than the standard fixed wing airplane. This is because a 4130 steel bracket is used on the center section rear spar to attach the outer wing rear spar. The wing has an extra rear spar attach fitting added to sandwich a rod end bearing threaded into the center section steel fitting.

The folding wing is a mechanical device and is therefore more vulnerable to user-induced damage. Because of this, the manual says no aerobatics with the folding wing. The problem is if the wing is damaged while being folded and not repaired before being put through the rigors of aerobatics. We cannot control a circumstance where someone drops the wing while folding it or trailers it improperly and then without completing a proper inspection subjects the aircraft to high inflight loads. The rear spar absorbs the wing's drag load, which is highest during high angles of attack and high airspeeds. There has, however, never been a problem with our folding wing design over the many years it has been used.
 
Sounds like more of a "CYA" than "it's not aerobatic". As with any aircraft used for aerobatics, you want to be sure you know it's history and inspect it carefully before every flight where spirited manoeuvers are to be performed.
 
Hmm...

I find it totally amazing that the first thread posted referencing to this plane here on VAF was deleted almost ASAP due to a relation/reference to a Barnstormers ad, and this thread is totally ignored by the moderators... go figure. :confused:

Nice plane!
 
Thought about buying

I looked at this plane about 4-5 years ago and what I remember is:

1. Was Subie - converted to o290.
2. Lots of engineering on the folding wings to fit in a garage at Widby? Island.
3. Tested to Utility class.
4. Handheld ICOM mounted as radio.

It was too experimental for me at the time.

If you are really interested, why not contact the seller?
 
The folding wing on the T-18 was designed by the same gentle man that designed the S-18. He also designed the wider fuse mod on the T-18 that you can still get with the plans and that is standard on the S-18. The T-18 plans are no longer sold with the folding wings options (although the wider body options is available) and the S-18 is only available in a kit.

Bob

I wonder if that's true, or if it's "Common Knowledge"?
The final Thorp T-18 model, the S-18, is folding wing, and the aerobatic gross weight is 1500 pounds. The 'older' T-18 aerobatic gross weight is 1250 lbs.
The folding mechanism is said to be the same for the S-18 and the Mustang II.
I just flew out with the wife to look at an S-18 folder, on a trailer in a garage.
It was a great day trip with wonderful flying, and also wonderful new people to meet.
The aircraft in question is not a flier, more of a restoration project. but the folding wing mechanism was out in the open for easy viewing. I'd say it's pretty straight forward, and similarly strong.
 
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