born2fly

born2fly

Active Member
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.
 
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.
 
N941WR said:
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.
Click to expand...


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

G.
 
Greg,

I just found this picture:

partofvan%27sairforce_jpg.jpg


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

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
 
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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 said:
Greg,

I just found this picture:

partofvan%27sairforce_jpg.jpg


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.
Click to expand...
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.
 
Learning from the -7?

I am only guessing here. My -7A does not do that. Some 6's don't do it. It's at least reasonable to try some friction on the pedals. Or, instead of friction, I used a bungee on the PX side from one pedal to the other with some mild tension (the middle of the bungee is anchored to the firewall). I did not do it for tail wagging; I did it to keep the rudder from slamming around in a mild breeze before I could get the gust lock on. It works very well for that and is not detectable in flight. That or snugging the support blocks would be a very cheap fix if it worked and you could still build a fairing if you still needed it.
 
might be easier to make fin taller

It would be pretty easy to extend the top of the fin and rudder with taller fiberglass tips, or just add to the tip cap you have. Even an inch of added height would be a noticeable improvement.
Be careful not to add too much weight on the rudder - for the non-counterbalanced rudders, this could be an issue. If I were going to make an older rudder taller, I would go ahead and make it counterbalanced at the same time ( at least partial balance).

No question the taller, counterweighted rudder on the later models helps a bunch. If one can be retrofitted, that is an obvious solution too.

When you add to the tail height, you gain two ways: first, you are adding some area, which is good of course, but you are also increasing the aspect ratio of the tail, which increases the lift-curve-slope; in other words, the lift vs. angle of attack curve is steeper, so you get more lift (side-force actually) for the same yaw angle.

If you are only adding an inch or two of height, the increase in structural load would be small compared to the design safety factors ( I can help with calculation if you like)

Both feet firmly on the pedals helps a great deal, but you said you were already doing that.

Bob Axsom's point is good to remember - you can't put a dorsal on the sliders.
 
The P-51 look......

....is what the original builder of Brian's RV-4 wanted. I can attest to its reduced waggle in turbulence.

Brian1.jpg


Regards,
 
Best news yet

Well, I really like what I'm hearing and seeing: good looks and reduced "waggle".

BTW everyone - - there's plenty of room for about a 35" long dorsal fin on a slider. I think people may have been confused while looking at 4's or 8's which have a very long canopy. I've definitely made this measurement and confirmed that the canopy on a 6 does not slide back too far for a decent dorsal fin to coexist.

I also really like the idea of incorporating it as a fairing extension. That way, I could keep the original fairing and trade back if necessary.

So now, I'm thinking about amount of work, and amount of weight. Seems that 2" of VS height would be less of each, but would it give comparable results to (for example) a 35" x 7" fin? Hard for me to calculate.

Does anybody have an idea as to the weight difference between a 7 tail and a 6 tail?

Thx

G.
 
see other thread on VS size

There is another thread ongoing that discusses differences in vertical tails on early RV-6's vs late, and RV-7/8/9 tails.

If you have an early -6 tail, switching to a -7 tail should help with tail wag in turbulence quite a bit. ( even though a few posters said they couldn't tell the difference. the bigger tail won't help much if you also don't plant your feet on both pedals)

BTW, the technical term for the tail wag in turbulence is "dutch roll mode"
 
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