RV-7/7A In-Flight Breakup Accident Information

[bjdecker]

Originally Posted by plehrke

More likely to have bad things happen with "stick free" (in this case rudder pedals free) than with "stick fixed". Control cables/tubes provide another constraint when held with control pressure.

No argument -- I now rest the balls of my feet on the outside of the rudder pedals, takes up any slack in the cables.

[Walt]

Originally Posted by BillL

The 7 Short (aka 8) rudder is smaller, lighter, and CG closer to the pivot than the 7Tall/9 rudder.


Attachment 29671
Area and weights not including fiberglass. Area is from spar rivet line aft.

Thanks Brian, I have just been lazy and not installed my 8 (aka 7 Short) rudder, and will have to invest in painting it too. I did all the glass fitting but not the final ready-to-paint details. Di you find any significant changes to landings?

Interesting that the 8 rudder CB weight is 1.85lbs vs the 7 rudder is 1.43lbs

[bjdecker]

Originally Posted by Walt

Interesting that the 8 rudder CB weight is 1.85lbs vs the 7 rudder is 1.43lbs

Plans for the -7 big rudder (RV-9) call for the E-612-020 weight. Which according to Van's weighs in at 1.85lbs.

[rockwoodrv9]

Originally Posted by BillL

I bet some would if it was lighter (like the 8), carbon fiber, stronger/stiffer in torsion and bending. Then counterweight factor could be better. Reno/racers might want it.

Can this be done in carbon?

Would it be as simple as producing a skin that folds at the edge rather than being riveted? How about a piece of .062 or even thinner bent to scab on over the trailing edge?

[Walt]

Originally Posted by bjdecker

Plans for the -7 big rudder (RV-9) call for the E-612-020 weight. Which according to Van's weighs in at 1.85lbs.

Ok now I'm confused.
According to the Van's website for the -20 weight:
"Counterweights for optional 0.020 Skins, RV-6/6A, Early RV-7/7A"

[PhatRV]

Originally Posted by rockwoodrv9

Would it be as simple as producing a skin that folds at the edge rather than being riveted? How about a piece of .062 or even thinner bent to scab on over the trailing edge?

From the manufacturing perspective, a folded rudder will cost more material since less number of rudder skin can be cut from a larger sheet of raw stock because of the odd shape. For a zip leading edge, more smaller rudder skins, left and right skins are identical, can be stamped from a larger sheet, thus, more economical use of the raw stock. We all love the low prices of Vans aluminum parts.

[Walt]

Originally Posted by BillL

edit: confirmed the 7 tall-9 has the E-614-020 (1.85#) called out.

Yes but "I think" that was for the early 7 rudder (which was the 8).
The RV8 plans call for the -20....

Update: Van's tech support (Stirling) just confirmed both rudders (7/8/9) use the same -20 weight.

[rockwoodrv9]

Originally Posted by PhatRV

From the manufacturing perspective, a folded rudder will cost more material since less number of rudder skin can be cut from a larger sheet of raw stock because of the odd shape. For a zip leading edge, more smaller rudder skins, left and right skins are identical, can be stamped from a larger sheet, thus, more economical use of the raw stock. We all love the low prices of Vans aluminum parts.

I understand the reason. Shipping for all the tail kits that go out is big too. Im looking for a way to strengthen the zipper. If I took a 4" piece of .062, bent it to about 160 degrees (not sure if that is the correct bend) and then epoxy or rivet to the trailing edge? That would strengthen it considerably and maybe help with AV type wind damage too.

I flew today and on my walk around, I tried flexing the rudder like it would in the wind. It feels pretty solid, but I can see how a wind gust could weaken it and after several smacks, I could see it weakening. I imagine flutter do the same thing in seconds.

[jrs14855]

Things I haven't seen mentioned;
Utah airplane was in an area of possible moderate to severe turbulence.
Utah airplane was "estimated" by NTSB to be 128# over aerobatic gross weight.
The Washington airplane was never recovered from the water except for a few small pieces. Therefore the probable cause is loss of control for undetermined reasons. Although this was an experienced pilot the NTSB does not address aerobatic experience. I believe in this case it is POSSIBLE that the airplane was in a fully developed accelerated spin with full power that exceeded Va and failed the rudder which was fully deflected in excess of Va.
Apples to oranges but Jurgis Kairys in the SU26 and SU31 did accelerated spins that transitioned into snap rolls. Approximately 14 turns, at the halfway point the rotation was considerably faster than one can count. Now consider a RV pilot, relatively inexperienced in spins, inadvertently enters a spin with full power and elevator neutral. Panics and maintains the full power and full redder deflection.

[jrs14855]

The Polen Special is derived form the Midget Mustang I which was designed by a Pier Engineer in the 40's. The Polen flew successfully for many years and then developed rudder flutter. The fix was a carbon fiber rudder.
Years ago I met a Harmon Rocket builder/pilot who bragged about flying at 300 indicated. It would seem that if the -7 does have a rudder problem the first thing to consider would be the construction and balance of the rocket rudder.
Again apples to oranges but since the starting point for the Harmon Rocket is RV4 parts, maybe John Harmon and other HR builders know things that would be applicable to the RV7.