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tail skins

clam

clam

Well Known Member
-4 Drivers,
What's the deal with the tail skin thickness on the -4? I thought I recently read a post recommending upgrade (?) to .020 skins? Does the kit currently come with .016 skins or .020? And what is the consideration in changing it? I'm assuming to resist skin buckling/wrinkling tendencies under manuevering loads? What sort of loads have been known to wrinkle the skins if that's the issue? Thanks.... (I'm ordering the emp kit in about 2 weeks)
-Clam
 
The 020 skins are a little less prone to crack at the last rivet of the stiffener. Personally I believe a little proseal on the ends of the stiffeners and at the trailing edge would go further than the thicker skins. If you happen to be building one of those 4's with the clipped wings and larger engines, they generally go with 020 skins. I do know of one Rocket at Reno with 016 skins and no cracks, so it can be done.
 
clam said:
I'm assuming to resist skin buckling/wrinkling tendencies under manuevering loads? What sort of loads have been known to wrinkle the skins if that's the issue?
Click to expand...

Not a load thing at all, it's vibrational. The skins regularly crack out at the last rivet or on the seam after multiple years of service. When folks re-do them they do it in .020 and it seems to fix the problem. Pro-seal idea would fix it too. You just need to keep it from vibrating. It's plenty strong.

-Bruce
 
dangers of the internet

I re-did the perfectly good .016 skins in my 4 kit with .020. I did this because everybody had me convinced that the .016 skins will crack and I will fall out of the sky.

Last year I bought an RV4 that has 900 hrs on it and .016 skins. The skins are fine.

If you are building, you can hedge your bet and go with .020. If the .016 are done, leave them. You are supposed to lay a straight edge across the skins when done. There should be no humps or dips. If there are, you may have issues down the line. If not, fuggedaboutit and move on.

Good luck

John
 
clam said:
-4 Drivers,
What's the deal with the tail skin thickness on the -4? I thought I recently read a post recommending upgrade (?) to .020 skins? Does the kit currently come with .016 skins or .020? And what is the consideration in changing it? I'm assuming to resist skin buckling/wrinkling tendencies under manuevering loads? What sort of loads have been known to wrinkle the skins if that's the issue? Thanks.... (I'm ordering the emp kit in about 2 weeks)
-Clam
Click to expand...

I was faced this decision when I ordered my kit late last summer. I went with the .020. My logic was that it is only a few dollars extra, the weight is very little extra, and since I will put a 2 blade (as against 3) prop on, the pressure pulses are larger rather than smaller. It is mainly a peace of mind thing. Lots of -4 are fine with .016, but some are not.

One other thing. Sometime after my kit shipped Smokey mentioned he would get .040 forward skins if he were building again. I never did find out why. Smokey? Are you reading this?

I would be interested to know your build number Clam? I am #4478

Good luck, Steve.
 
skinny on skins

Steve, et al-
Thanks for the gouge. I'll monitor to see if Smokey jumps in with any .040 inputs...

Haven't ordered the kit yet. We are moving to Atlanta (Acworth) 27 April and I'm waiting until we actually close on the house JUST in case. Want to be sure it is really MY address the kit gets shipped to. I'll order the kit that evening. Although, Nomad with TeamRV says a friend of his is selling a very well built -4. Kinda makes ya think for a minute?? But, that route would not allow for all the fun (err, education and recreation) of building would it? What to do, what to do...

Regardless of the skin thickness, I'll go with the proseal technique.
-Clam
 
The skin cracking problem is almost always caused by imsuficient "squeezing" of the trailing edge radius. I built 2 RV-6s 13 years ago with .016 skins, no proseal, sub-ribs, or anything else and to this day there are no cracks.
.020 skins are more tolerant, but .016 works fine if done right.
Mel...DAR
 
Mel said:
The skin cracking problem is almost always caused by imsuficient "squeezing" of the trailing edge radius.
Mel...DAR
Click to expand...

My flying -6 has some bulges where the stiffners end. No cracking yet, after 300 hours.

Should I try to bend the trailing edge more?
 
I did the kit-supplied .016 skins on my -4 (#2179). I re-did them with .020 last year after about 200 hrs. I had under-bent the trailing edge of the rudder just a bit. Enough for the cracks around the last trailing rivet of the stiffeners. However, there were also cracks around the first rivet of the stiffener in some places. As there is no lateral connection between the spar and trailing edge, between the left and right sides of the rudder, if there is any oil-canning at all, there will be cracks. When the leading edge of the rudder is pulled around and riveted, it can cause the area just aft of the spar to be pre-loaded a bit, and all the load will be borne by the area around the first rivet of the stiffener. Combine that with my error on the trailing edge, and cracks were inevitable.

If I hadn't yet built the rudder, I would use the .020 skin. Not because it's impossible to do the job right the first time with .016, but because just in case, it's a LOT easier to do the rudder the first time, than to rebuild it. I had to have new Toucan stickers made for the rudder, too.

Jeff
 
I haven't heard anyone say the .016 skins are easier to dent or damage than the .020 during construction, but once assembled they are as good as the "thick" skinned surfaces.
Anyhow that's what I heard (somewhere) is the main issue, and possible cracks years from now...
 
Steve Sampson said:
Smokey mentioned he would get .040 forward skins if he were building again. I never did find out why.
Click to expand...

I know of one RV4 that has a crack in the forward fuselage skin, under the cowl cheek. The Rockets use 040 front fuselage skins.
 
My RV-4 has about 250 hours on it and develped cracking on the trailing edge of the LH elevator. I think it was caused by something or someone bumping into the trailing edge. Just something else to watch out for with standard tail control surface skins. I ordered the .020 skins to rebuild both elevators. And an Electric trim kit. :)
 
.016 / .020 skins

FYI
I purchased my -4 and was told at over 200MPH indicated it had a shake. It sure did & felt like it was coming apart. In talking to Vans I rebalanced the controls (no help) and then was told it could be control surface oil canning at speed. I added some foam to the inside and the shake stopped. I didn't do the rudder & it now has some cracks. I have a .020 rudder kit waiting to be built.

Gary
 
Tail skins

I think most of this skin cracking can be attributed to the higher engine horsepower. I finished my RV-4 three years ago (180 hp with C/S prop). It was built with .016 skins and I initially flew it unpainted. Cracks began to form on both the elevators and rudder at about 40 hours. I kind of thought this might happen. I bit the bullet and built new elevators and rudder with .020 skins and I also added another stiffner (and decreased the stiffner spacing). It now has 280 hours with no cracking and the control surfaces are much stiffer and robust which I truly think if necessary for a 180 hp RV-4.
 
emp kit ordered

Steve Sampson said:
I was faced this decision when I ordered my kit late last summer. I went with the .020. My logic was that it is only a few dollars extra, the weight is very little extra, and since I will put a 2 blade (as against 3) prop on, the pressure pulses are larger rather than smaller. It is mainly a peace of mind thing. Lots of -4 are fine with .016, but some are not.

One other thing. Sometime after my kit shipped Smokey mentioned he would get .040 forward skins if he were building again. I never did find out why. Smokey? Are you reading this?

I would be interested to know your build number Clam? I am #4478

Good luck, Steve.
Click to expand...


Steve,
I've finally moved into the new house. Ordered the emp kit. Builder #4502. Received part of the emp kit today. Expecting remainder of it tomorrow. I went with the .020 skins as you did. Planning to use the proseal as well.

What do you think of the "Fastback" mod for the -4? Looks pretty slick. I've always thought the pure bubble canopy was the way to go, but I may consider the fastback.

-Clam
 
Mel said:
The skin cracking problem is almost always caused by imsuficient "squeezing" of the trailing edge radius. I built 2 RV-6s 13 years ago with .016 skins, no proseal, sub-ribs, or anything else and to this day there are no cracks.
.020 skins are more tolerant, but .016 works fine if done right.
Mel...DAR
Click to expand...

Mel, I'm looking at a flying -4 that has had cracks repaired on the tail. The diamond shape patches were epoxied to the skin on the first rivet to the front of the stiffener.

Does the tail need to be re-skinned? Seems like a shaky repair to me. Thoughts?
 
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dougweil said:
I think most of this skin cracking can be attributed to the higher engine horsepower. I finished my RV-4 three years ago (180 hp with C/S prop). It was built with .016 skins and I initially flew it unpainted. Cracks began to form on both the elevators and rudder at about 40 hours. I kind of thought this might happen. I bit the bullet and built new elevators and rudder with .020 skins and I also added another stiffner (and decreased the stiffner spacing). It now has 280 hours with no cracking and the control surfaces are much stiffer and robust which I truly think if necessary for a 180 hp RV-4.
Click to expand...

Doug, any update on your -4 tail skins?
 
Sorry, I didn't understand your PM at first.

Geico266 said:
Mel, I'm looking at a flying -4 that has had cracks repaired on the tail. The diamond shape patches were epoxied to the skin on the first rivet to the front of the stiffener.

Does the tail need to be re-skinned? Seems like a shaky repair to me. Thoughts?
Click to expand...
Without actually seeing the repair my take would be that the repair may be OK for normal flight if inspected regularly, but I wouldn't recommend acro without re skinning the elevators.
 
Tail skins

I have found that the skin cracking on the -4 elevators is due to flexing at the attachment point of the horn ribs and the spar.
To test this hold the elevator full down on the stops at the trailing edge and load the counter balance up and down if the skin wrinkes badly about 4-6" in from the tip this is where it will crack.
This happened to a friends RV-4 prior to its first flight during an engine run with the elevators against the stops.
This was corrected by inserting a gusset at the spar to tip rib under the new skin.
My RV-4 has a doubler on the rib to spar junction and so far has not experienced this problem.
Both aircraft have .016" skins

Hope this helps

Gordon Pettigrew.
 
I apologoze for resurrecting an ancient thread, but I have heard a lot about the concept of .020" skins, yet I see no way to get them. Where do they come from? I just got my tail kit last week and did the inventory today and was somewhat surprised to see that the elevator and rudder skins were all .016".

There is no option on the order form for .020" skins and I can't find anything in the accessories catalog about them, although one can get a .020" trim tab skin for the -4.

Thanks
 
-4 tail skins

As far as I know, all -4s have the .016" elevator and rudder skins. There was an "optional" diagonal stiffener that goes in the outboard bay which stiffens the counterbalance arm,and was referenced as a recomendation for builders that planned to do acro as I remember. I put them in mine, and they may be shown on current plans. I am only aware of cracking at the trailing edge where the stiffeners end, something that can be somewhat prevended by applying a small dab of proseal when assembling. The -4 needs to be built with no excess weight in the tail, as that will ultimately limit your backseat/baggage capabilities. Keep the tail light !
 
.016 elevators and rudder

Just to add to this thread, my -6 is now coming up on 20 years of age and still no cracks. And again I have no foam, no proseal, no sub-ribs, etc. Just built according to the plans.
 
Mel said:
Just to add to this thread, my -6 is now coming up on 20 years of age and still no cracks. And again I have no foam, no proseal, no sub-ribs, etc. Just built according to the plans.
Click to expand...

RV6, 180/CS, .016, 500+ hours. Built per plans. No cracks. The crack issue was pretty well known when I started to build in '98. The likely cause was incorrectly bent training edge and/or the "vibration from large engines". I used a "blob" of RTV, recommended in the day, at the end of the each stiffener. When squished it ties the stiffener ends together. This is what was widely recommended at the time along with insuring the trailing edge lay flat or nearly flat on the spar prior to drilling. .020 skins where never even discussed or talked about to me anyway. So far so good.
FWIW
 
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