Wing evolution

Can anyone explain the difference in the modifications of the wings. I have knowledge of a non pp set and don't know it's age but I am interested in buying if the price is right. What should I look for? Non phlogiston.i read that some kits had tank baffle one way and flipped around the other way on later models. I won't learn if I don't ask.

There is a thread on tank baffle change. I have the phlogiston spar and have no regrets, but would not be afraid of building the spar from kit form. The kits are well thought out, but do take some time to make sure you understand the process. The RV-4 is more of an old school kit than the other RVs in the sense that you "build"it vs "assemble"it. When I am closing the hangar door after a flight I stare in amazement at what I built and what it does.

I've got a 1990 model that needed a minor spar repair and slosh removal from the tanks. The rear baffle flange faced forward so the rivet holes were in the tank. I used lots of sealant and closed-end pop rivets. No leaks so far. If you have to build the spar, Vans still rents out the pneumatic rivet squeezer that's needed to buck those 3/16 rivets. I used it recently and it worked great. The "build it yourself" spar looked to me like it could handle way more than the advertised 6g+ and 3g-

If the kit is complete, make an offer and grab it. I bought my kit(tail, still in box) from someone who backed out on starting it. I got a great deal on it too. See if he has any tools. I bought 98%of my tools from Avery, and specialty tools (Dotco right angle drill, and some sioux drills, and a 3/8" pneumatic belt sander)from Browns.
Ps- belt sander and right angle drill are like my AR-15A1, pry it from my cold, dead hands.

Arlie,
I looked at an RV-7 spar and walked away shaking my head. The RV-4 spar looks three times as strong. When I was in phase one testing and did the 6G pull, I had no worries.

Billythekid

I will go and ask the holder of the wings a fear questions and maybe make a offer. My worry is should I go pre punch from vans and all the latest mods or go inexpensive and build the old kit. I had a idea of using the pp skins from vans and using the older kit I may get. Any thoughts on that idea. I will not learn if I don't ask

Michael Henning said:

Arlie,
I looked at an RV-7 spar and walked away shaking my head. The RV-4 spar looks three times as strong. When I was in phase one testing and did the 6G pull, I had no worries.

Click to expand...

The -4 and -6 spars are (apparently) pretty over-built. Once upon a time, the factory tested a -6 wing to failure and published a summary of the results in the RVator. As I recall, their synopsis was "We're not going to provide the actual figure, but the wing failed well beyond 9 G's"

In contrast, there is an RV-7 wing panel still on display in the Van's Aircraft hangar after many years of collection dust. It has portions of the skins cut away to allow customers to see what the inside of a wing looks like.

People that look closely might notice the small note attached to the upper left corner that identifies it as one of the original engineering static test wings which was static loaded to 9 G's in at least 2 different load conditions, at which time the testing was stopped (it had met the requirements).
Since the test was stopped, there is no way to know how far this wing (the one that everyone thinks isn't as strong) would have gone beyond 9 G's.

The most significant factor (to me anyway) is that with all of the cutaway areas on the skins, the interior can be closely inspected. I challenge anyone to find any deformation evidence that shows that it has been loaded to 9 G's

BTW, for those not aware, when testing, the wing only has to survive the 6 G limit load test with no evidence of permanent deformation. For the ultimate load test of 9 G's, permanent deformation is totally acceptable (and to some degree expected). It just has to survive with no catastrophic failure.

My first three builds were non prepunched. They are not that hard to do, and kind of satisfying.
If the price is good, no corrosion from poor storage, and No work done then go for it and enjoy the process.
Prepunched skins might not fit if any of the ribs have been mounted.

Spar Design

Kyle Boatright said:

The -4 and -6 spars are (apparently) pretty over-built. Once upon a time, the factory tested a -6 wing to failure and published a summary of the results in the RVator. As I recall, their synopsis was "We're not going to provide the actual figure, but the wing failed well beyond 9 G's"

Click to expand...

Looks can be deceiving. I presume the 9 G ultimate load test of the -4/-6 wing was done at the equivalent structural loading at the 1375 lb max aerobatic gross weight, while the -7 wing was likely loaded to simulate 9 G's at the designed 1600 lb aerobatic gross weight.

Skylor

I don't think any prepunched parts would work with a -4 kit. Too many variables.

Michael Henning said:

Arlie,
I looked at an RV-7 spar and walked away shaking my head. The RV-4 spar looks three times as strong. When I was in phase one testing and did the 6G pull, I had no worries.

Click to expand...

So you can tell how strong a spar is by looking at it? This was his 4th kit, so I would expect that he had learned something by then. He could have massively overbuilt the 4 because of the issues he had with the 3, but I don't know which came first. You can certainly fly the 7 with complete confidence.

The proof is in the pudding. There is a marked difference in design philosophy in the way the spars were engineered, I like the spar on the -4, but would have no reservations flying a -7. I prefer overbuilt, which is why I think the A-10 is probably the best built airplane for its role.

My recollection is that when I started building my -4 (in 1991) the advertised G-loading was +/-6. Today's values are, of course, +6 and -3. I went thru some old paperwork, but was unable to confirm (or refute) my memory. Does anyone else remember (or have documentation) from the 90's?

I have some of the old brochures from the late 80s when it was just the 3,4&6. I will check it out.

Old brochure

I still have my first brochure from Vans which isn't dated, but I think its from the late 1980's. The only models were 3/4/6/6a. Under the "aerobatics" section it says: "The RVs have a design stress limit of plus and minus 6 Gs at aerobatic gross weights: 1050 lbs for the RV-3, and 1375 lbs for the RV-4, RV-6 and RV-6a. This equates to an ultimate or failure limit of plus and minus 9 Gs." There are no other G load figures or text. The picture on the cover is a wood prop RV-4 with a young blond lady standing on the wing walk area next to the cockpit. All black and white. I have another old brochure around here somewhere that is in color.

Brian Vickers said:

I still have my first brochure from Vans which isn't dated, but I think its from the late 1980's. The only models were 3/4/6/6a. Under the "aerobatics" section it says: "The RVs have a design stress limit of plus and minus 6 Gs at aerobatic gross weights: 1050 lbs for the RV-3, and 1375 lbs for the RV-4, RV-6 and RV-6a. This equates to an ultimate or failure limit of plus and minus 9 Gs." There are no other G load figures or text. The picture on the cover is a wood prop RV-4 with a young blond lady standing on the wing walk area next to the cockpit. All black and white. I have another old brochure around here somewhere that is in color.

Click to expand...

Hi Brian,

Thanks for checking. My recollection seems to be consistent with your brochure. I wonder what inspired the changed from -6Gs...

Regards,

Nine G"s

Kyle Boatright said:

The -4 and -6 spars are (apparently) pretty over-built. Once upon a time, the factory tested a -6 wing to failure and published a summary of the results in the RVator. As I recall, their synopsis was "We're not going to provide the actual figure, but the wing failed well beyond 9 G's"

Click to expand...

RV History lesson 101.
The RV3 original design had a simple spar box and attach point method which was not stressed for aerobatics beyond basic sport category. After several inflight wing failures/fatalities the 3 spar mod was offered free of charge to owners. It was a band aid on a arterial wound IMHO. Discretion is the better part of valor in RV3 (or any RV) you don't need more than 3G's to enjoy it.

Enter the Dragon:
in 1978 Van introduced the RV4, a bigger, better RV3. Rumor has it the wing was designed by someone other than Van, and way overbuilt. Kylie's statement is correct,. In fact, when the FAA guys left the building, sandbags were piled on the RV6/4 wing until rivets popped and bending began. It never broke. The G force equivalent at failure is a well kept secret but a friend who was present that day told me it exceeded 11G. Having pulled 9 G'S for 20 years regularly and knowing the beating the airplane (and YOU) endure its a great testament to the design.
The latter day RV's have a completely different spar design, a single extrusion.(not laminated) Easier to produce and strong in it's own right yet all the stress eggs are in one basket, so to speak. As far as I know, there has never been an RV4 pr 6 wing failure in flight. The 8 wing however can't make that claim.

My advice, take photos, show them to some 4 builders on the site or take one with you to inspect (me included) and your decision is easier.
You can't go wrong with a 4.
V/R
Smokey

smokyray said:

Rumor has it the wing was designed by someone other than Van

Click to expand...

I submit exhibit A: www.youtube.com/watch?v=E9eEwyVrAps

At 1:10:48 John Roncz asks the audience "any of you guys flying my RV-4 wing?"

The video is and EAA presentation by John Roncz about his work with Rutan designs, very interesting.


edit...I know he is an airfoil designer, but who knows how much he really did, he called it "my rv-4 wing"!

Im building a 6 and want to trade for a 4 unbuilt but I'm stoked I started the discussion because I must raise questions or I will not learn. I'm a even rv guy 4 or 6.. All I need is a tasty rv4 a cool rv6 and I'm fine

smokyray said:

RV History lesson 101.

Rumor has it the wing was designed by someone other than Van, and way overbuilt. Kylie's statement is correct,. In fact, when the FAA guys left the building, sandbags were piled on the RV6/4 wing until rivets popped and bending began. It never broke. The G force equivalent at failure is a well kept secret but a friend who was present that day told me it exceeded 11G.

Click to expand...

CATPart said:

I submit exhibit A: www.youtube.com/watch?v=E9eEwyVrAps

At 1:10:48 John Roncz asks the audience "any of you guys flying my RV-4 wing?"

Click to expand...

I guess this is how rumors get started......

There was no FAA guys present for the tests on the RV-6 Wing, and I remember a different (lower) G value (but my memory isn't what it used to be).

And John obviously doesn't know much about the different RV models.... because the airfoil he designed under contract for Van's was used on the RV-9, not the RV-4.
I don't think Van even new John in the late 70's when the RV-4 was being designed (of which I am pretty sure he did the engineering on himself), and besides the RV-4 (and 3, 6 7 and 8) all use the NACA23000 series airfoil that had already been around for decades (I think it is what is on the Bonanza and DC-3).