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

[Thermos]

Originally Posted by jeffw@sc47

I have been considering, with some apprehension, getting some instruction/introduction to some gentlemanly aerobatics in my recently completed 14A.

Although the RV-10 and -14 rudders still have riveted trailing edges, the internal structure is different from that in the-7/9. Stiffeners are tied to the rudder spar with shear clips, and the stiffeners themselves are much more robust - the horizontal flanges are joined to their mates on the opposite side with a rivet about halfway down the rudder chord. Also, the counterweight skin is integral to the rudder skin and not riveted on as with the -7/9.

My professional flight test work has only dealt with structures and flutter at a conversational level, but my sense is that these changes make the rudder quite a bit stiffer. Only Van's can say whether those changes were remedies for a weakness in the -7/9 rudder design, or if they were done for another reason.

ds

[Snowflake]

Are builders actually balancing the counterbalanced rudders?
Thought Vans said installed the kit provided lead and that was enough on the rudder.

Posts like this worry me. The point of the counterbalance is to balance the rudder, just like the elevators.

My original -6 rudder wasn't balanced at all.

Nor is mine. But it's a different design, with different size and shape and different speed limitations on the airframe. Van did switch to a counterbalanced rudder on the -6 before they stopped selling the kit, as part of the development of the -7. A number of -6's have been upgraded to that tail, or the -8 tail, to get increased rudder authority.

[rsr3]

Originally Posted by Snowflake

Posts like this worry me. The point of the counterbalance is to balance the rudder, just like the elevators.

You’ve got my attention, now. To balance the rudder as per the elevators would require significantly more lead. Is the rudder’s lead there simply to bring its cg forwards “enough” for safe flight or to balance it as per the elevators? The instructions so far have not suggested that it requires to be balanced like those. Please expand, if you’re confident you know what you’re talking about - I’m keen to learn!

[bjdecker]

Originally Posted by BillL

I hit a burble at 130kts (straight and level) and the tail seemed to shake like a wet dog. Nothing like this has happened in 250 hrs since. It would make me happy if there was a full ground vibration test performed, but that is out of my control.

Bill,

I encountered a similar issue in my first -7 with the big rudder (R-901), and 3" x 1/2" wedge attached to T.E. We were heavy, aft CG but within limits, in a descent from 9500 passing 8500 at 175KTAS. Hit a slight bit of turbulence and then I could feel/hear a vibration similar to a wooden ruler held flat on a desk - being thumped and then slid over the desk --- "brrrrrrraaaaaap" (not quite the A-10 brrrrrrrp...but close ). Put my feet on the rudder pedals (I usually fly feet off until maneuvering) , chopped power, and the vibration ceased.

Switched to the RV-8 rudder (R-801PP), flew another 300 hours in that airplane without issue.

YMMV FWIW

B

[PilotjohnS]

So how much heavier is a 8 rudder as compared to a 7/9 rudder?

[bjdecker]

Originally Posted by PilotjohnS

So how much heavier is a 8 rudder as compared to a 7/9 rudder?

I believe the -8 is lighter, but not by much. While the -8 rudder is smaller in area compared to the -9 rudder, it uses thicker skins (.020" vs .016"). The -8 rudder has fewer parts as well (no R-916 and associated rivets, smaller Rudder bottom, shorter counterbalance skin, smaller rudder tip).

[BillL]

Originally Posted by PilotjohnS

So how much heavier is a 8 rudder as compared to a 7/9 rudder?

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



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?

[MED]

Originally Posted by jeffw@sc47

EDIT > One question I have about aerobatics, and instruction in aerobatics is "Are parachutes required?". You can't or it isn't a recommended procedure to eject the canopy in-flight in an RV-14A, so what does a parachute do for you if they are required?

As I understand it, you are not required to have a parachute to perform aerobatics alone. You are free to kill yourself. However, if you have a passenger, you are both required to have parachutes. You aren’t supposed to kill innocent victims or, presumably, let them watch you go down with the ship, so to speak.

[plehrke]

Originally Posted by bjdecker

Put my feet on the rudder pedals (I usually fly feet off until maneuvering) , chopped power, and the vibration ceased.

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.

[bjdecker]

Originally Posted by BillL

...
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?

None whatsoever; crosswind (demonstrated) to 20kts (Airport T82) at heavy weights. I tend to land a bit on the faster side however -- usually over the fence at 75kts, rounding out / flare at 65kts...