[oceanbird]

Hi,

There is an idea in my mind, and I need to ask.

Could I use an RV-8 Empennage on an RV-4 Fuselage?

My -8 tail kit had several parts numbered -4, so I guess
they are the same as the ones used on the RV-4, but
would like to know for sure if it could be done. Would the
change require estructural mods or would it be a more or
less "easy" swap? Anyone knows?

Thanks

 

[john02]

Bird,

Funny story. I figure I don't have the ability to build a million different planes, so I want to build something unique. I won't fit in an RV-3, but I like the idea of a single seater. My idea was to build an HRIII 'lite' (like the conversation above in this forum.) I read in an article, written by some kind of reporter that also comes with the plans, that the HRIII uses an RV-8 tail, so I got an old -8 tail and started building. I read somewhere else that a raised turtle-deck requires a change in dimensions on the VS. I checked the plans and sure enough, it requires shaving 3/4 inch off the bottom. Then I began comparing dimensions of the -8 tail and the HRIII tail plans....didn't match. Sent off for -4 plans, got them on x-mas Eve, ckecked dimensions...sure enough, the HRIII plans showed a -4 tail. OOps. (Rocket plans are notoriously bad like this...)

Have spoken to an HRII builder (crazyhorse) who told me that -8 tails work fine on -4's and that they have been used for some time because of the prepunched kits for the -8, the thicker rudder skin, and balancing. The actual dimensions of the two tails are VERY different, but the fuselage attach points are EXACTLY the same. I think that the original F-1 used a -8 tail? Can't remember. I would be interested to hear from someone who has a traditional -4 with a -8 tail to get a PIREP.

I have read/been told that the -4 flies best with the tail that is meant for it...so why change what works? If you have the -8 emp kit already, then maybe a trade on Barnstormers or the VAF classifieds would work. As for me...I think I'm gonna shoot from the hip on this one and try the -8 tail, see how it works.

John

 

[Tom Martin]

The eight tail works on a rocket ok. The only problem is that the elevators are adequate but there are times when more surface area would help. Another consideration is that the 8 tail will be heavier and this may affect your center of gravity, however if you are building a single seat version it may not matter. The current F1 tail is considerably beefed up vs a RV4 or a RV8 tail. My vote would be for the RV4 tail for your mission as light weight is your goal. Carefully do your weight and balance consideration before proceeding with either tail, or the project itself, as the light engine out front may limit where the single pilot seat will go. With the four cylinder engine weight will have a real factor on performance. I would reccomend going with the larger fuel tanks as it really does not add much weight but does extend the range of the airplane considerably.

 

[john02]

Tom thanks for the reply -

I found the W&B calculators on RVproject.com, went through various -4 combos with my weight plus 30 pounds in the back seat, no weight in the front seat, and 20 pounds in the baggage area (just a wag for an increase in weight for a turtle-deck/tail.) I assumed that moving the panel back would even out the decrease in weight and moment of taking out the front seat and associated weight and clipping the wings. The limits (with 32 gallon tanks...) come out at or around the aft limits for aerobatics in most of those calculators with full tanks. With shuffling all components and battery forward on the plane...I think it is reasonable - and an excellent excuse to use a metal CS prop with a 360 FI - angle valve even? I agree, -4 tail would be a better option [explitives deleted]...starting over is hard to do.

John

 

[RVjim]

Long Nose RV-4

I installed the RV-8 HS, which uses RV-7 elevators. (I really love the prepunched parts.)
I used a stock RV-4 VS and rudder.
(The rudder and elevators all have 0.020 thick skins.)

Just offering another possible combination. This would eliminate the additional weight increase from the counterweight in the rudder.

John Harmon said he picked up 2 knots on his HR3 by changing to the RV-8 style HS from the RV-4 HS. Of course, I probably wouldn't be in the same speed range as the HR3, so I may only pick up about 1 knot.

Regards,
Jim Ayers