Scott Hersha
Well Known Member
At the risk of looking like a graduate of the Rube Goldberg institute, I’ve come up with what to me seems like a simple rudder control lock for my former RV4, and my new RV6:
Pictures are a bit blurry, but you get the idea….
Noted KHAO aero engineer, Steve Melton, took one look at this and just cringed. “Way too much leverage at that point pressing on the aft bulkhead”, said Steve. I understand that is the point of greatest force when the rudder is loaded on a windy day, but it doesn’t seem like it could generate enough force to cause a problem. That aft bulkhead has the bottom end of the aft VS spar bolted to it and there are two rows of rivets holding that assembly to the aft tailcone skin. Plus, the front end of the lock is pressing on the bulkhead (when loaded by the wind) right next to the bulkhead flange. I haven’t used this contraption yet and don’t want to cause damage. It seems to me that grabbing the bent trailing edge of the .016 skinned rudder to secure it to the elevator counterweight locks with rope would not be all that robust either.
The first set of these I made had the loaded leg of the lock (the forward leg) as a straight piece with two 1/8” rivets. I decided that under enough load, the weak point would be the shear strength of just one 1/8” rivet, because if you shear one then that leg could move (pivot). So I made the next one with the triangular piece with three rivets. You would need to shear two rivets at once in order for it to pivot. Of course you need a lock on each side of the rudder control horn or it won’t work. When it’s is in place, the rudder doesn’t move at all.
Anytime I’ve shown this to my local pilots, they have all said the same thing right away - “don’t forget to take it out”. It’s not real visible, but that could be easily remedied with strategically placed flags.
Opinions please…..
Pictures are a bit blurry, but you get the idea….
Noted KHAO aero engineer, Steve Melton, took one look at this and just cringed. “Way too much leverage at that point pressing on the aft bulkhead”, said Steve. I understand that is the point of greatest force when the rudder is loaded on a windy day, but it doesn’t seem like it could generate enough force to cause a problem. That aft bulkhead has the bottom end of the aft VS spar bolted to it and there are two rows of rivets holding that assembly to the aft tailcone skin. Plus, the front end of the lock is pressing on the bulkhead (when loaded by the wind) right next to the bulkhead flange. I haven’t used this contraption yet and don’t want to cause damage. It seems to me that grabbing the bent trailing edge of the .016 skinned rudder to secure it to the elevator counterweight locks with rope would not be all that robust either.
The first set of these I made had the loaded leg of the lock (the forward leg) as a straight piece with two 1/8” rivets. I decided that under enough load, the weak point would be the shear strength of just one 1/8” rivet, because if you shear one then that leg could move (pivot). So I made the next one with the triangular piece with three rivets. You would need to shear two rivets at once in order for it to pivot. Of course you need a lock on each side of the rudder control horn or it won’t work. When it’s is in place, the rudder doesn’t move at all.
Anytime I’ve shown this to my local pilots, they have all said the same thing right away - “don’t forget to take it out”. It’s not real visible, but that could be easily remedied with strategically placed flags.
Opinions please…..