T

tikicarver

Well Known Member
I'm interested in talking with anyone who has already put an -8 tail on a -4.
I know there are several out there.
 
complete tail.....

I have a complete tail set for an 8 if you are wanting to convert.

$1500 at ADS. Complete, needs a little prep to be ready for primer.
 
I am planning to put a -8 vertical and rudder on my -4 when the time comes. which is a ways off.
 
osxuser said:
I am planning to put a -8 vertical and rudder on my -4 when the time comes. which is a ways off.
Click to expand...

I have a question that Van's would not answer: Can you fit the -8 vertical tail on an RV-4 with the stock horizontal tail? Key measurement is the distance between the VS Spars.

I could run off and measure it, but if you know the answer, that's faster.

Thanks, Vern
 
I know of a Harmon Rocket that used a -8 tail. No issues. As an interesting
note, on a recent thread VNE was the topic, with a link to Van's articles
on this and one by Smokey Ray. The -8 tail (attached to an -8) has a 240 mph VNE and the -4 has a 210 mph VNE. The Rocket has the same rear fuse as a 4.
 
Yup, it's actually for a Rocket, not an RV-4. My question was whether a heterogenous tail (mix of -4 horizontal and -8 vertical) will fit, hence my question about the VS spars.

The Rockets can use more tail weight, although an unmodified RV-8 tail is not recommended. There are some structural improvements recommended and the elevator is a bit smaller than the RV-4.

Vern
 
Interesting. What mods to the -8 tail are you refering? The Rocket I know of
has both the vertical and horizontal (complete -8 tail). The skins are .020 on the 8, .016 on the 4.
 
Chino Tom said:
Interesting. What mods to the -8 tail are you refering? The Rocket I know of
has both the vertical and horizontal (complete -8 tail). The skins are .020 on the 8, .016 on the 4.
Click to expand...

Hi Tom.

Mark Frederick walked me through this, and it involves reinforcing the HS spar for the -8 tail, along with beefing up the fuselage attachments for the VS and HS. In addition, he recommends adding stiffeners throughout.

I don't have any pics, but I have a friend doing this right now for his Rocket, so I hope to have a look at some point.
 
Question?

Why would you want an -8 tail on a -4?

I have not heard anyone complain the about the -4's tail. Just curious.
 
I bought a completely assembled -8 tail and I will be putting it on my -4.
I know there are several -4s out there that have -8 tails on them. I am interested to hear if they made any mods or had any other issues.

For the weight issue, I started another thread where I put the weight of the individual -8 parts. If some people put the weight of their -4 parts we can see the actual weight difference in the parts.

I have looked over the plans of the -8 tail and if necessary for weight issues, the rudder counter balance can be removed and the rudder and V-stab can be made just like the -4 and the -6.

The interesting thing is the -4 and the -6 do not have a counter balance. the -7 and higher do. But if you look at the top speeds of each they are very close. So why did Van change the rudder design. If the stock -4 and -6 don't need one, it could be removed from the --8 tail when attached to a -4 fuselage.
 
"I have not heard anyone complain the about the -4's tail. Just curious."

well I guess we talk with different people :)

I went to lunch with a bunch of local RV guys. We were talking about the fact that i needed to buy a new tail for the -4 I bought that was ground looped. They suggested to buy an -8 tail because it was match drilled and would be easier and faster to build. Also they talked about several RVs including some of their own that had cracking issues in the elevators and rudder. they all rebuilt the parts using .020 skins and never had a problem since. Since the -8 has .020 skins that was another reason. Then one guy with a -4 said when he flys at and aft CG, the plane is "very squirrely" in yaw. he thought a little larger rudder would help.
then when i was thinking it over, I got a line on an -8 tail kit that was beautifully built.
 
-8 horizontal on a -4

I too was thinking of putting a complete -8 tail on my -4, but it looked to me like the -8 horizontal would require moving the rearmost top fuse bulkhead forward a bit. The distance between the spars on the -8 horizontal was greater than the -4 parts. I didn't want to got to that much trouble since the fuse is completed, so stayed with the stock parts.
I did weigh the parts for comparison and best I remember there wasn't too much of a difference.
 
There's a -4 in Nashua, NH with a -8 tail

A builder in Nashua NH put a -8 tail (horizontal and vertical) on his -4. It has been flying that way since new (around 2002). I have never flown it, but it looks good and seem to fly fine. The builder visits this site, so perhaps he will provide first hand info.
As I recall (we both built -4's in parallel), he had purchased his kit from a previous builder and decided to replace the already completed tail. He selected the -8 tail to save time as it was prepunched. The -4, of course, had no pre-punched parts. I assume this is still the case?
 
Yes, -4 tails are not pre-punched. Plus the -8 tail is all .020 skins. on the -4 you can now get an option for the rudder and elevator for .020 skins.
 
8 Empennage

If anyone is interested in pursuing this avenue, I have acquired an 8 empennage kit that has had some assembly done to it.

The horizontal and vertical stabs are assembled so it would be best for someone who is willing to pick it up.

PM me if you have any interest.

Ted
 
tikicarver said:
Then one guy with a -4 said when he flys at and aft CG, the plane is "very squirrely" in yaw. he thought a little larger rudder would help.
Click to expand...
The heavier -8 tail may only make things worse! It will put the cg further aft for the same load. A larger fin (vertical stab) might make things better, but the rudder might not. A better solution would be to move the cg forward. Making these kind of modifications is not something to be undertaken lightly - just coz some guy at a fly in said it was better doesn't really mean much. The stability and handling of most of Van's airplanes are pretty much spot on. I would check out very carefully that the mod will actually bring the benefits you seek.

Pete
 
The -8 tail would strictly be for ease of building. I have a -4 tail kit that the VS was messed up on pretty bad, so instead of building a new -4 VS, I was planning a -8 VS/rudder combo. I don't think there would be that big a difference in weight. I'll have to figure out about fitting with the -4 HS when the time comes. May just go to a straight -8 tail too, since my kit has the .016 skins, and lets face it, I can build the fuse to accommodate the -8 bits.

Obviously the Rocket beef-up wouldn't be necessary for a -4.
 
I now have a copy of the -8 plans. I looked at the H-stab. The difference in distance between the spars is 1/32 inch. So that should not be a problem.
Didn't have time to look at the V-stab.

True that you have to look carefully at this mod, but there are several planes out there with it that are flying. It would help the discussion if we can get direct information from someone that has already done it.

Also if someone that hasn't mounted their -4 tail could weigh the parts, that would give an answer about the difference in weight.
 
I am on my way to the airport right now Ron. Will weigh all my parts and report later.
 
Concerning the .016" skins.

There is absolutely nothing wrong with the .016" skins if built properly. My airplane has been flying for 16 years with no cracks. What causes the cracks is insufficient forming of the trailing edge. Look at your trailing from the rear. If you see any "bulging" between the stiffeners or between the stiffeners and the trailing edge, it is not formed properly. You can correct this by lightly crimping the trailing edge with seaming pliers. Put duct tape on the seaming pliers before hand to avoid scratches.
 
Last edited:
I looked at the V-stab dimensions on both. It looks like they are very close but I can't read the numbers on my copy of drawing #26 on the -4 plans.
(I'm missing the large drawing and only have the preview drawing)

If someone can look at their -4 plans on drawing #26 and give me the dimensions for the aft bulkhead distances, I'll do the math and post the results.
I need the dimensions starting with F410 and going aft.

One interesting thing I noticed.
The -8 fuselage is approx 12 inches longer than a -4.
 
Bigger vertical stab and rudder does not necessarily equal more stability. Have you ever flown a Stinson?! Ginormous stabilizer, and it wanders all the time. Wittman Tailwind W8 - small stab (and smaller rudder), quite stable. I agree that the aft CG was probably the root of the problem in that case.

The slow build emp doesn't take that long to build anyway, and it's lighter. That's always a good thing. Note: Don't forget to add in the weight for the lead if you're measuring the weight of 'unfinished' parts in the comparison.
 
You must log in or register to reply here.