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Engine offset

Mark Burns

Mark Burns

Well Known Member
I'm fitting the cowling and I didn't realize until now how far the engine is offset to the left side. It's about 3/4" at the rear of the engine. The engine is angled to the right so the prop winds up in the center.

I know the vertical stablizer is offset, so I thought the engine would be centered and straight. I knew the carb and airbox favored the left side but I didn't put 2 & 2 together until now. Why isn't there more talk about this? I can't find anything in the archives. Do builders just not notice it?

The rocker box cover for #2 cylinder is about 5/8" from the cowl.
It's way closer than #1 that is more forward and getting into the inward curve of the cowl sides.

I sort of freaked out when I noticed it. I thought I had a bad engine mount.

Mark
 
It is what it is

Hi Mark,

Yes the engine does have a lot of angle to it and does result in some parts of the engine being closer to the cowling than others. I don't think anyone talks about it since they know the engine is offset and expect some differences. If it fits inside the cowl then you have no problem.
 
Common practise

Hi Mark,
Yep, it's a pretty common industry practise with clockwise rotating engines. BTW....it's clockwise from the pilot's view, as is "left"..meaning the side on which the pilot sits, not looking from the front:)

Bigger engines like the Pratt R-2800 also have a large downward angles (in the Bearcat) in order to minimize P-factor...how? the spiral flow of air goes over the fin/rudder, instead of impacting them and creating even more need for right rudder during power application.

Regards,
 
I guess I never gave it much thought because of flying radio controlled airplanes for years. The engines are always at an angle. Sometimes a lot.
 
Vertical Stab Offset

Vans does not offset the vertical stab. Only does the engine. At least it's that way on the 8 and I beleive all other models also.
 
Vans does not offset the vertical stab


I don't think so. I have an A&P that built an 8 and he was very concerned that I put in the 5/16 (I think) off set in my vertical. I showed him that my prepunched kit came with it automatically in the mounting bracket in the front.
 
7 Too

The -7 VS is slightly offset as well (I believe .25"), as is the VS on my Wolf Boredom Fighter.
 
Offset Vertical Stab

I double checked the plans for the 8. Vans does not offset the vertical stab.

Specifically states " before drilling for the vertical stabilizer forward spar, it must be shifted until the stab is perfectly parallel to the fuselage centerline."

Double checked my old 6 plans and same thing, no offset. Specifically states "zero incidence angle"

Don't know specifically what your plans say but thats what mine say! I remember having a conversation with one of the tech support guys at Vans about this and he stated the compensation was done in the engine mount only.

If your A & P who built an 8 and put an offset in it, he did it of his own accord. Not per the plans.

Come on other 6 & 8 builders out there, please chime in. Are my sets of plans the only ones that state this!!!!

Ted
 
Ted RV8 said:
Come on other 6 & 8 builders out there, please chime in. Are my sets of plans the only ones that state this!!!!
Click to expand...

The "6's" are definitely straight, as is mine. But I'm nearly positive that some newer models have the vertical stab offset built in.

edit: after some research, I'm seeing numerous mentions of the 9's having an offset, as well as a revision for the 7's. Nothing "concrete" though.

L.Adamson --- RV6A
 
Last edited:
st called vans on this the other day. There is no offset to the vs as there is so many different engine prop combinations. There is some offset in the engine. their words.
 
Vertical

The 7A is definitely offset by approx. 1/4" per the plans and pre-punched parts

Gary
N715AB
400 hours
 
Thanks for the replys

My RV-7A S/N 72183 has a 1/4" offset on the vertical stabilizer.
That's why I was thinking that it was all that was needed.

Years ago when I worked as an A&P I remember that Cessna's had the vertical stabilizers offset and Pipers had the engines offset. I'd just never heard of doing both on one airplane.

Mark
 
I gave my -6 about 1/8" offset and wish I had given it more. Still need a small trim tab at cruise. I have the original small vertical.

Heinrich Gerhardt
 
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