I believe the RV-7/7A is safe if it is operated strictly within Vanís operating envelope (airspeed, weight, and load factor limits), the rudder is properly balanced, and the jam nuts on the control surface hinges are always tight.
The problem appears to be that there are small rudder strength margins and small fin/rudder flutter margins outside that envelope when equipped with the -9/-7 rudder. Note that RV-8s are not coming apart in-flight with the same regularity and for the same reason that RV-7s are. And I don't think RV-8 pilots are any better or more careful than RV-7 pilots.
Based on the in-depth investigations of two RV-7s coming apart in-flight (by the Canadian
and New Zealand
safety authorities) and evidence of the others that have come apart in-flight, if I had an RV-7/7A it would have an RV-8 rudder on it instead of the RV-9 rudder that came with the kits since mid-2002
. Note that the -9 rudder was designed for an airplane that has a Vne of 210 MPH, whereas the -7 has a Vne of 230 MPH. Now, of course, those speeds are designated as TAS values.
For the reasons given below, the -8 rudder would provide larger strength and flutter margins in case of an inadvertent excursion outside the published flight envelope:
- The -8 rudder has thicker skins (0.020") than the -9/-7 rudder (0.016"), making the -8 rudder stronger and stiffer.
- The -8 rudder has a folded trailing edge, which makes the -8 rudder stiffer and stronger than the riveted trailing edge of the -9/-7 rudder.
- The -8 rudder has less area than the -9/-7 rudder, creating smaller unsteady (oscillatory) aerodynamic forces (which are an important item in the flutter equation) than the larger -9/-7 rudder.
Part of the problem (but I don't believe it's the whole problem) may be that Van's has never issued a Service Bulletin or Service Letter for the older RV models (including the -7s) stating that Van's changed the definition of Vne from IAS to TAS. They did put out an SL for the RV-14, and they put out a POH revision for the RV-12s, but nothing for the older RVs. It's disappointing that Van's has not issued an SB or SL addressing their change of that critical safety-of-flight information. Many RV pilots are unaware that Vne is now in terms of TAS, instead of IAS. At higher altitudes RV pilots may operate above Vne without realizing it.
Van's did publish this article, "Flying High and Fast"
, on high horsepower and the concern about IAS vs TAS, flutter, and operating at higher altitudes. But it is not an acceptable substitute for an SB or SL for each model stating the new definition of Vne is in terms of TAS, since an SB or SL would reach a much wider audience of pilots and builders.
It does seem that more and more folks are putting -8 rudders on their -7s, and thatís a good thing, IMO.