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Old 03-05-2017, 06:10 PM
jrs14855 jrs14855 is offline
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,061
Default Rudder

Originally Posted by scsmith View Post
Wait! Don't confuse a dutch-roll yaw oscillation with a vague or bi-stable rudder issue. Two very different things. A poorly formed trailing edge will cause the latter, but not the former.
No confusion, This was described to me as uncommanded rudder movement. It went away after squeezing the trailing edge. I did not fly the airplane.
I have experienced a similar issue on Pitts ailerons. The Pitts aileron trailing edge is .020 x 2" wide strip folded into a V and then further formed to the proper angle. Underbent trailing edges on the Pitts remove any centering force. The ailerons will move at least half travel if you let go of the stick. Squeezing the trailing edges eliminated this and made it like most Pitts. I did fly that airplane both before and after and with a pervious set of wings.
All of this and much more is in Barnabys article in Kitplanes.
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Old 03-06-2017, 11:17 AM
RV Jerry RV Jerry is online now
Join Date: Jan 2009
Location: Chino, CA
Posts: 156

I have built several Rockets both with RV8 tails and with RVV 4 tails RV8 woks ok but my preference is the 4 tail ,it's lighter easier to taxi in x- wind and has a little more elevator area and suits my eye. The reason I originally used the 8 tail was a concern for flutter but it seems to be a non issue.
Jerry Scott
Rocket II
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Old 03-06-2017, 09:44 PM
RV-4 RV-4 is offline
Join Date: Oct 2007
Location: St-Jerome,Quebec,Canada
Posts: 993

Thank you guys for the good info.


2018 Due paid gladly
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Old 03-06-2017, 11:02 PM
131RB 131RB is offline
Join Date: May 2009
Location: Colorado
Posts: 293

I have no experience with the 8 tail. I have the 4 tail on mine and most likely would do it that way again. It flys great and I prefer the look.
One thing I didn't see anyone else mention to keep in mind. Last time I checked their were no service bulletins on a 4 horizontal stab.
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Old 03-07-2017, 12:54 PM
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vfrazier vfrazier is offline
Join Date: Jan 2007
Location: Mount Vernon, IN
Posts: 1,074

Just a data point: I had an RV-4 tail on my Rocket and am installing the same on my F4.

The RV-4 tail on the Rocket did not "wag" that I ever noticed.

Jim Winings has some interesting stories about flying RVs that have improperly formed trailing edges. It's an easily overlooked problem, but usually easily corrected too.
Vince Frazier
F1 Rocket and F4 Raider components
RV and Rocket Accessories, Tailwheels, Tools, & More
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F4 Raider - under construction
F1-H Rocket "Crazy Horse" - sold
RV-4 "Chief Pontiac" - sold
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Old 03-20-2017, 09:37 PM
F1 Rocket F1 Rocket is offline
Join Date: May 2008
Location: Melboring, FL
Posts: 34

N14ZM has the RV-8 tail. Flys great although it could use a bit more authority during the flare when I'm flying solo with a lot of fuel. Since I hate flying by myself it's not a serious issue with me. Never seem to have trouble finding someone to act as ballast in the rear seat
F1 Rocket #25
N14ZM "Dreamer"
Melboring, FL
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Old 03-22-2017, 03:02 AM
autoglide autoglide is offline
Join Date: Aug 2009
Location: Rockport,TX
Posts: 306
Default Tail wag

My 22 yr old Rocket (Production #1) has absolutely no bad habits at all....orig built w a 4 tail.....a great bird indeed!

Marv Bein
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Old 03-23-2017, 02:12 AM
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rvmills rvmills is offline
Join Date: Nov 2007
Location: Reno, NV
Posts: 2,060

My Super Six was originally built with a stock 4 tail. As I began to race, and started to do speed mods that increased the top speed, I found myself cornered...actually squeezed between, Dave Anders and John Huft (modifiers and racers of considerable note) during dinner at AirVenture Cup. They said in chorus, "when ya gonna put a counterbalanced rudder on that beast?" So I built a slightly modified and strengthened 8 V-Stab and Rudder, and it has flow well in this configuration. The mods included pinning the stiffeners together to make them more similar to ribs, adding a doubler to the aft V-stab spar (to absorb the inputs from the stiffer rudder and avoid just moving a potential point of failure), adding a small, calculated amount to counterbalance weight, and doubling the connection between the counterbalance cavity and the main structure of the rudder. All done with some consultation with an appropriately knowledgeable aircraft engineer. The added height did cost a bit of speed (2-3 knots).

I've flown HRIIs with a 4 rudder, and they all flew great...none seemed to exhibit any tail-wag. Elevator authority was always good too, but when 2 up, the bigger bloke has always been in the front (I was instructing the owner then).

An 8 tail works well, but as Mark said, flown conservatively in descents, the 4 tail may be just fine. If you want to go race-fast, or are concerned about overspeeding in descents, the ultimate win-win here may be a modified 4 tail, built with a counterbalance. Greg Nelson built and raced a beautiful F1 Rocket with such a tail, and the tail is a work of art...the plane even has 3-axis electric trim. The plane is very fast as well. I believe Dave Anders and Robby Attaway built similar tails for there 4 and 6, respectively. Were I to do it over again, I would go that route. You may look into those gents' accomplishments in this area.

Another mod that Steve Smith and I have talked about is using pressed-fit bearings instead of rod-end bearings for the elevator and rudder connections, where possible. Steve may be able to add some more data points on this as well.

Bob Mills
RV-6 "Rocket Six" N600SS
Reno-Stead, NV (KRTS)
Sport Class Air Racing "Race 49"
SARL "Race 49"
West Coast Ravens FFI RV Formation Squadron
APRS Track
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