RV-8 Rudder on 7

[dreed]

Hi all-

I installed the (now) standard RV- 9 rudder on my 7A, but I am going to install an 8 rudder and test which I prefer.

Question- and maybe I am just missing something. The 9 VS/Rudder has a taller glass tip (on VS) and the counter balance/horn of the rudder is taller too vs. the 8 rudder.

On my VS, the glass tip is not removable so I somehow need to add some height to the top rudder tip, unless I am just missing something. I need to measure, but I think I need to add 1-1.5" of height to the rudder tip on the 8 rudder.

I know others have made this move, so rather than reinvent the wheel I am looking for advice- or someone to point that I am a dope.

Attached a pic of my plane/rudder and a beautiful RV-8 to show what I am talking about

Thanks- Dan

 

[rvbuilder2002]

Just so you are aware….
The counter balance arm adds aerodynamic balance as well.
If you do what you are proposing, you will have an RV-8 sized rudder with the amount of aerodynamic balance of the larger RV-7 rudder.
This might cause undesirably light rudder forces. Can’t say for sure because I think you will be the first to have done it.
If your not interested in being that “experimental”, I would recommend changing the vert stab top fairing as well.

 

[mfleming]

On my VS, the glass tip is not removable so I somehow need to add some height to the top rudder tip, unless I am just missing something.

Yes, you are missing that the VS fiberglass is blind riveted on. The builder/painter filled in the transition so that those rivets are not visible.

 

[DSmith]

Just a little history; the original RV-7 rudder was the same as the RV-8 but Vans found out during testing that the RV-7 did not come out of a spin as quickly as they wanted so they put the RV-9 rudder on the 7. I had already built the RV-8 rudder and had put the VS fairing on the top. Van gave us the RV-9 rudder kit if we wanted it. I did installed it on my RV-7A.

The RV-8 rudder kit should have the proper balance weights but you will have to drill out your current VS fairing rivets and install the RV-8 VS fairing. All the parts should be available from Vans.

 

[scrollF4]

Dreed,
I drilled out the pop rivets that held on the taller RV-7 glass tip. I installed #6 plate nuts on the new 8-style tip, making the stab-mounted tip removable (I did the same to the original 7-style tip).

Now my original RV-7 rudder serves as the spare for my new 8 rudder. If I have to remount the old 7 rudder, I swap out the top tips as well.

 

[dreed]

Thanks All-

Sorry, I left out some info.

RVbuilder2002- I had wondered about that so thank you- definitely not my desire to be the first. I have a spare VS too that I could swap out along with the RV-8 rudder. It will add more work for sure, but is doable.

Mfleming, Thank yo- yup, I know that my painter covered up the rivets - I did it on all my tips. Looks better but adds complexity to this project. I guess that adds to the fun too?

DSmith- thank you. I was aware of this (actually when I purchased my Emp way back in 2000/01, I got the 8 rudder too (kit #581). Then I built the 9 rudder and gave an 8 builder the rudder parts as they messed theirs up and I never thought I'd need them again. I've got all the standard parts (tips, etc.) for both the rudder and VS, but was hoping I could just swap rudders, but it doesn't look that way. Guess it's a VS swap too, or some changes to tip on my original VS.

 

[dreed]

Thank you Scroll! I may consider that, the painter did such a great job I'd hate to hate to mess up the work with all my other tips/rivets/screws hidden, but maybe the better option vs mounting the new VS too. Would definitely make the swap easier after the initial work/repaint. As high up as those screws are, I don't think it would be that noticeable once it was done.

 

[mfleming]

Just a little history; the original RV-7 rudder was the same as the RV-8 but Vans found out during testing that the RV-7 did not come out of a spin as quickly as they wanted so they put the RV-9 rudder on the 7. I had already built the RV-8 rudder and had put the VS fairing on the top. Van gave us the RV-9 rudder kit if we wanted it. I did installed it on my RV-7A.

The RV-8 rudder kit should have the proper balance weights but you will have to drill out your current VS fairing rivets and install the RV-8 VS fairing. All the parts should be available from Vans.

Just to put a fine point on spins in a RV-7 with the smaller rudder.

Here's some verbiage from the SB 2-6-1

From the narrative:

"We did find that the RV-7 spin recovery characteristics easily met
FAA requirements* for normal category* aircraft, but not those of aerobatic category aircraft*. (The AEROBATIC
category requires that the aircraft be able to recover from a 6-turn spin within 1¼ rotations. A NORMAL category
aircraft is required to recover from a 1-turn spin within 1 additional rotation.)"

From the conclusion:

"CONCLUSION:
Flown within the recommended limitations of Section 15 of the Construction Manual, either the original or the enlarged RV-7 rudder will provide adequate authority for spin recovery.

The substitution of an RV-9 rudder on an RV-7 improved spin recovery. With the larger rudder, the RV-7 will have
better spin recovery from whatever flight condition the pilot may encounter."

 

[BillL]

Don't forget to install new rudder stops too. They are different and the short rudder stops will allow a little more rotation. I made both and have a
"8" set in standby.

 

[dreed]

Michael- thank you

Bill- good point and thank you. I have internal stops now, but I'll definitely make sure they will work and modify/replace as necessary.

 

[alcladrv]

I just finished my original 7/RV-8 rudder to install on my RV-7A after I get the rudder painted. Apparently Vans hasn't lost confidence in the original 7 rudder since it appears that they continue to fly it on their RV-7A demonstrator as seen at Oshkosh last month.

 

[bjdecker]

RV-8 Rudder -vs- Powerline

I was searching the NTSB database trying to find any updates on N787NV, when I ran across another incident involving an RV-8.

The accident narrative and pilot's description of what he felt during the accident sequence belies the actual damage -- [photo]

Now, I know all things aren't equal, flutter <> shearing force, etc., but I have to wonder how a -7/9 rudder would have held up under the conditions of this accident.

Hmmm...

 

[rvbuilder2002]

I was searching the NTSB database trying to find any updates on N787NV, when I ran across another incident involving an RV-8.

The accident narrative and pilot's description of what he felt during the accident sequence belies the actual damage -- [photo]

Now, I know all things aren't equal, flutter <> shearing force, etc., but I have to wonder how a -7/9 rudder would have held up under the conditions of this accident.

Hmmm...

Since it was sliced off be impact with a power line it is entirely possible the result would have been the same since a similar accident (power line encounter) happened quite a few years ago in Brazil with an RV-9A, and the vertical stab and rudder looked identical to this.