Dorsal fin?

born2fly · #1 03-11-2009, 06:00 PM

I used to have a Cherokee, and it wanted to wallow a lot (fishtail) in turbulence. I kind of got used to it. After a year or two, I installed a STOL kit, which had a long dorsal fin as a part of the kit. WOW, what a difference! It reduced the wallowing by at least 2/3 or more. Seems that the extra stabilization area really made a difference on the stubby little airplane.

Has anyone tried this on an RV? I have an RV6 that makes me airsick in extended turbulence, and that dang tail-wagging is a major component of the upsetting behavior.

It would be pretty easy to add on (not counting paint and fairings) - - but I've never even seen a picture of one on an RV.

YES - I do the feet-on-the-rudder trick, and it helps a little but it is not a cure for more than 20% improvement.

thx
G.

N941WR · #2 03-11-2009, 07:16 PM

Greg,

A friend's RV-6 has a dorsal fin but since he has never flown another RV, so he has no idea if it helps or hurt. i.e.: Helps with the tail-wagging or hurts with cross wind landings.

born2fly · #3 03-11-2009, 08:00 PM

Quote:

Originally Posted by N941WR

Greg,

A friend's RV-6 has a dorsal fin but since he has never flown another RV, so he has no idea if it helps or hurt. i.e.: Helps with the tail-wagging or hurts with cross wind landings.

Any pictures? Attachment methods? I'd love to see some details...

G.

N941WR · #4 03-11-2009, 08:20 PM

Greg,

I just found this picture:

It was added during the build and the current owner is not the builder. I believe it was riveted in place, flangs out on the fuselage with pull rivets on the VS. This would be a good use for riv-nuts on the VS and plate nuts on the fuselage so you can make it removable if you need to make it larger or smaller.

Note that it is on a tip-up and not a slider.

Andy_RR · #5 03-12-2009, 12:16 AM

I don't know for sure, but I'm willing to bet that a lot of tail wagging on the -6 is due to the lack of a counterbalanced rudder.

sprucemoose · #6 03-12-2009, 01:31 AM

Does your six have the original, smaller VS and rudder? I noticed that the pic Bill posted with the fin does have the smaller rudder and VS. The later 6s had the larger tail from the 8 (and later the 7 as well, before they went to the 9 tail. Confused?) and it is reported that the larger tail cuts down on the tail wag. I've never noticed an objectionable tail wag in my 6, but I've always had the bigger tail. A new VS and rudder is a fairly simple retrofit and might be worth considering instead.

gasman · #7 03-12-2009, 03:47 AM

Just snug up the rudder pedal blocks so the rudder doesn't flop around. Your feet won't notice the added resistance.

Bob Axsom · #8 03-12-2009, 08:05 AM

I have the small tail RV-6A and I don't notice any fishtailing in any kind of weather - maybe the rudder pedal support pivot blocks are tight (as I recall, they are) or maybe I'm not sensitive to it. I have a slider and originally had the ELT antenna back there but there is not a lot of room. That needs to be considered if you have a slider.

Bob Axsom

vlittle · #9 03-12-2009, 08:15 AM

Try applying pressure to both rudder pedals during turbulence. This should dramatically affect the yaw stability of the aircraft. In effect, it locks the rudder and provides a greater effective fin area.

Vern

N941WR · #10 05-02-2009, 04:05 PM

Quote:

Originally Posted by N941WR

Greg,

I just found this picture:

It was added during the build and the current owner is not the builder. I believe it was riveted in place, flangs out on the fuselage with pull rivets on the VS. This would be a good use for riv-nuts on the VS and plate nuts on the fuselage so you can make it removable if you need to make it larger or smaller.

Note that it is on a tip-up and not a slider.

FYI - I ran into my friend and his plane today and gave it a close look over. The fin was made out of fiberglass and is just an extension of the empennage fairing. Where it runs up the back there is a flange with screws that go into platenuts on the top skin.