acam37

acam37

Well Known Member
I have a -4 that needed a new tail due to a mishap involving a hangar collapse. I bought a complete tail from a guy and now its ready to be drilled and bolted back on. Does anyone have some good pics of the tail installation? What I need is how the shims go back in place or an exploded view of the tail. I've got the plans but the previous owner didn't have the builder manual. When we took off the broke tail I neglected to take photos of the dis-assembly. Any help will be greatly appreciated.
 
Will do. I'll ask them about getting a new builder manual as well. I may need it in the future. I already mailed them the waiver form and had the owner name changed in their data base. So far I've had good dealings with Vans. They went ahead and shipped all the parts I needed to repair the damage before they got the paperwork back. That means I should be able to start the rebuild by the end of the week.
 
Yes, they are. I'm doing exactly the same thing right now.

I just bought the parts and am slowly building a new tail.
 
The RV-4 is an airplane that many builders had to shim the horizontal stabilizer during flight testing, so there is no "standard" shim set-up.
If you didn't record the shim set-up during disassembly, you might try fitting to the original fairing to get an idea of the proper incidence.
 
Good idea. I still have everything I took off the damaged tail. One problem I ran into taking it off is that it was tore up so bad I wound up cutting the horizontal stab spars in order to get some bolts out and the trim cable was stuck in the bent spar.
 
Mel
I set mine to zero (Level) with the fuselage level using the wood blocks at the rear as indicated in the manual and shimmed it. I had no problems. What Kind of problems were discussed:
 
No problems yet. The old tail had some shims on the vertical stab at the bottom. The horizontal stab did not.
 
acam37 said:
No problems yet. The old tail had some shims on the vertical stab at the bottom. The horizontal stab did not.
Click to expand...

Since they were not pre-drilled it sounds like the shims were there just to make up for some minor drilling/layout errors.

They probably were not very thick.
 
I finished the turtle deck on my fastback mod, so we decided to set the new tail on to see if it would fit. First off we noticed that the original tail installation was not done in accordance with the plans I have. The plans show that the F-410 top skin former is moved forward of the bottom former. Mine is lined up. Where the vertical stab attaches to the horizontal stab spar at F-410 my old tail section was attached to only one piece of angle that was bolted to the top longeron. The plans call for two (one on top and one on bottom) with the longeron sandwiched between and secured with 4 bolts. The horizontal stab was bolted to the angle instead of riveted.

(Edit) apparently I have two different sets of plans. I went back and looked at the original builder plans (931) and the tail attachment is correct. The new plans I have show a different installation. I think I'll give Vans a call and ask if I should go with the newer version. There must be a reason they were changed.
 
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Tail Pictures

This is what I have

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original (931) plans

These are what the original plans show (i think the kit was purchased in the late 80's)

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EEEk!

Eeek! :eek::eek::eek:

My plans must be the newer set. The attachment is similar to that on the RV-8 and look MUCH more secure - angle under the longerons, spacer, top deck then some another spacer, 4 bolts the outer ones through the top spacers, longerons and angle, the inner ones through the top spacer, deck, bottom spacer and then angle. That what you have?

Worth also looking at the area just in front to the attach bars at bulkhead 411. You have a piece of angle and a spacer there too, under the deck?



Chris
 
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I sent Vans an email regarding the change in the plans. They replied that it was not a safety issue and the tail can be installed either way. Since I have access to the attachment point, I think I'll go ahead with the newer version. It looks to be a lot stronger and will only add a few ounces.
 
Horizontal Stab Incidence

I'm ready to install the tail section and before I started drilling holes I wanted to get a little more information on the subject.
That's when I ran across Smokyray's post "get horizontal". It had some really good info on setting the horizontal stab incidence in order to reduce the extra down trim needed during higher speeds. After looking at my plane and wondering why the builder shimmed the forward stab. attach point as you can see in the picture in my previous post, that's one mystery solved. When I do my dry fit I'll stick my trusty R/C Robart incidence meter on the tail and it will give me exactly how much he added to make it fly right.
(Note) I put a tape measure to the forward angle bracket and it is raised 1/4"
 
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just checking the datum point.....

Arlie, that's 1/4" above the top surface of the longeron, right? When you get the incidence during your dry run, please post it. In the meantime I'm off to look at "getting horizontal"

Thanks

Chris
 
Tiki,
You have an RV-8 tail section. That will change the amount of lift on the aft end because if the larger surface area. I dont think the shim width will work the same on your set up. I zeroized the HS incidence angle with respect to the cabine longeron (flight attitude). I belive that is what dave anders (spelling?) did on his -4.
 
Incidence

Since this is a re-build and was flying prior to the mishap, I'm going to keep the 1/4" shim in place. However, i'm going to make it possible to return the HS to zero incidence if necessary. In the meantime I'll try to contact the original builder and ask if he remembers the reason he raised it.
 
Raising the angle mount

I was able to contact the original builder and yes, he had to raise the leading edge after the initial test flights so it would fly level with minimum down trim.
As stated in my previous post, when it gets bolted down ill stick an incidence meter on it just to satisfy my curiosity on exactly how many degrees it ends up being with the shim installed.
 
Arlie, if you are makng changes in weight (ie prop/new starter/etc) to the firewall foward (or tail), the spacer may have to be adjusted from it previous configuration.
 
(Noted) the only change we are making is the fastback conversion. Nothing else is changing. I even went with the same prop. I've got to change out the wing rear spar mount carry through because it was mis drilled by the original builder. So that means we have to re-set the wing incidence as well.
 
We finally got the new empennage mounted, with a lot of head scratching I might add. The plans do not call for spacers behind the middle (F-411) vertical stab attach point, but that's what had to be done to make it fit. This is how the old one came off. I'm not sure why this is how it fit? All the tail measurements on the new empennage are correct and the formers seem to be in the right place as well.
We also built the electric trim servo tray. As the tail was already built we had to cut open the skin. I moved over on the other side of the stiffener because I couldn't figure out how to make the doubler fit if it was where it goes in the plans. I wouldn't be able to get a doubler inside in one piece and get to the rivets to buck them.

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Neat work Arlie, tho if all measurements are correct I don't understand why you need a spacer behind the HS attach bars - should bolt up directly. Makes me think your front attach points are too far back? But is the VS goes on OK.....????

Even my wreck didn't need that spacer. Curious to understand.

Cheers

C
 
Spacer

Chris/Arlie

My 4 was built to plans with no spacer and flies well with the elevators in perfect alignment at cruise. There is plenty of trim for all stages of flight.

I would go with plans, test fly and only modify if there was a problem in flight. Having now test flown my 4 the one thing I would consider is a slight offset in the fin. Mine required a trim tab and most of the 4s I have seen have a trim tab to put in right rudder.

Again you might be happy just going with a trim tab its your decision.
 
I contacted Vans regarding the spacer behind the F-411 upright bars and the engineer told me that shouldn't be a problem. After doing some measurements it seems the F-411 former was installed 1/2" too far forward.
In order to correct this I would have to completely re-do the entire tail assy. With new formers, skins, ect. But since Vans told me it was OK, I'm leaving it the way it is.
Now the only reason I could figure out as to "why" the former was in the wrong place is because the tail wheel weldment is too long. There is no way for the former to go back any further in its current configuration. The plane was built from a 1985 kit so who knows how the weldment was built too long?
 
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Its so much more exciting, working on an old non-prepunched airframe. You never know what's going to turn up!

I'm sure your really don't want to redo that former and weldment. It gets too painful doing things a second or third time and who knows what else you might uncover.

C
 
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