RV4/6 rudder lock

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…..

Lot of cringing here also. Sorry, but I sure hope you don't use that in any serious wind. You are applying an awefull lot of force against two pieces of .025 aluminum. Just don't see how that will hold.

Larry

My recommendation is to NEVER use any control lock outside of the cockpit,
so you will never forget it.

Glenn


P.S. Donation is up to date but can't figure out how to correct.

I agree with this being a bad idea in terms of forgetting it. Unless you plan on hanging your ignition key from it i would personally not recommend this method.

sinjin said:

I agree with this being a bad idea in terms of forgetting it. Unless you plan on hanging your ignition key from it i would personally not recommend this method.

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Well, I haven’t used this lock, and most likely won’t - I’m coming up with a more conventional external lock. Forgetting to remove this little yellow lock would be no more likely than any other external control lock, and I can’t imagine taxiing my RV6 taildragger with this lock installed. That being said, the external lock I will have will be a RVPlastics RV6 type (most likely that one if he still has them). That rudder lock also captures the two elevator control locks. Forgetting to remove it would involve taking off with two sets of controls locked - an obvious Darwin move…..

I tried to make the ASA UGL work, but couldn’t make it fit without the elevators being locked in a nose dive position. I DO have the hanging rudder pedals in my RV6, but the geometry of the weldment didn’t work for me.

Scott Hersha said:

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.

Click to expand...

I agree with Steve.

(less noteworthy, but I do have a degree in Mechanical Engineering with an Aeronautical specialization...)

Snowflake said:

I agree with Steve.

(less noteworthy, but I do have a degree in Mechanical Engineering with an Aeronautical specialization...)

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Anyone want a free RV6 rudder lock? Might be OK on a calm day….

Gust lock

I often have to leave my plane tied down outside for a week or so, in all kinds of weather, while traveling. After years of using separate gadgets for the ailerons, elevator, and rudder, I finally bit the bullet and bought the Anti Splat Aero Ultimate Gust Lock.

It's a very clever design. Extremely happy with it.

Dugaru said:

I often have to leave my plane tied down outside for a week or so, in all kinds of weather, while traveling. After years of using separate gadgets for the ailerons, elevator, and rudder, I finally bit the bullet and bought the Anti Splat Aero Ultimate Gust Lock.

It's a very clever design. Extremely happy with it.

Click to expand...

I bought that UGL also, but returned it. I could not get it to fit my airplane unless the control was locked in to a nose dive (elevator). The stick angle (straight up and down) v.s. the control lock weldment geometry didn’t fit my airplane with the elevators in the neutral positions, which ASA says should be done - on one of their videos.

Easier way

When I was at OSH this year, I just used a thin strap from the ground steak to the rudder hinge and back down the other side to the ground steak. Rutter is trapped. It spreads the load out, has to be removed so you can taxi, and is something that I carry to tie down anyway. I would show you a picture, but some ran into the back of my plane as I was departing, and cut the rudder off.

Lock

Ntsb in the final report cites failure to remove the flight control lock as the probable cause of the crash of a SIAI-Marchetti SM-1019B that killed respected airshow performer and retired naval aviator Dale “Snort” Snodgrass in July 2021.