RV-6A tail tie down and frame cracking

I used to fly from a rather bumpy grass strip that would occasionally throw my 6A onto the tail tie down ring, and I have also landed tail first a couple of times. Both of these types of arrival tend to bend the tie down, Wd-627, back into the rudder bottom fairing. To stop the tie down bending so much (and nearly jamming the rudder) I added another bolt lower down the bracket, with a spacer to match the fin spar thickness and another large (~1" dia) washer on the fwd side of the frame. That was great for a while, but a couple of reasonably good whacks put the tie down back into the rudder .

Yesterday I took the rudder off to fix the bottom fairing, and discovered my "fix" for the tie down was not such a great idea as the new bolt has tried to rip itself out of the frame - so looks like I will be replacing the frame as well. In fact most of the damage has probably been done when straightening out the bracket as the frame has bent rather than the bracket. I think the RV-7 type set up, with a screw in tie down ring is much better - although I will probably add some kind of abrasion strip on to the bottom of fuselage.

So I would suggest 6A builders use the 7A method for a tail tie down and 6A pilots leave the tie down bracket bolted to the fin spar and accept that it bends occasionally.

Pete

penguin said:

I used to fly from a rather bumpy grass strip that would occasionally throw my 6A onto the tail tie down ring, and I have also landed tail first a couple of times. <snip>...So I would suggest 6A builders use the 7A method for a tail tie down and 6A pilots leave the tie down bracket bolted to the fin spar and accept that it bends occasionally.

Pete

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I try to stay out of 'how to land nose-draggers' but I can't leave this one alone. I would suggest you not accept that the tie down ring bends occasionally and that you also not use the tail (tie down ring) of your plane as a skid plate. I recall a previous post of yours where I bit my tongue when I read it but will speak up now.

There is another way to arrest your sink rate: Add power. Short bursts of power work very well in arresting sink rate. 25-40 knots of 45-90deg crosswind is the norm at my airpark here in the desert so I speak from experience. Long bursts of power are used to go-around and try again.

Proper training with the right instructor will correct the tail-bashing problems you are having with your landing technique. Rosie

Double Yikes!

I have seen a "mod" on training aircraft (Cessna 150/152) that addresses this problem. Mounted between the tie-down ring and the tailcone is a steel strap bent into a comma shape. It starts out forward, then bends down and under the tie down ring, and extends aft of the ring for a few inches.

It becomes a bit of a spring, and protects the eye, and prevents it from being "ripped out of" the mounting hole. Also softens the blow on the sub-structure.

I have no idea how to draw a sketch and add it to this post.

I installed an aftermarket threaded bracket from George Orndorff that allows me to remove the ring when it is not being used to hold the plane on the ground. The bracket mounts on the bulkhead forward of the stock one.

question?

Since I'm not a builder (yet), my dumb question would be, if you have hit the tail hard enough to bent the tie down, has there been any damage to the bulkheads forward---maybe bending them? Just seems to me that an impact hard enough to cause the damage that you are talking about would also transfer those stresses to the bulkheads, or other critical structures. Maybe someone with more experience than I could chime in----
Tom

Another possible solution

I have thought long and hard about this problem. On an RV6A like I fly now - put a tailwheel on it to cushion the blows. On the RV8 I am in the process of buying, I plan to add a nosewheel to protect the prop.

A6PILOT said:

I have thought long and hard about this problem. On an RV6A like I fly now - put a tailwheel on it to cushion the blows. On the RV8 I am in the process of buying, I plan to add a nosewheel to protect the prop.

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I flew this thing with a tail wheel and decided I liked the wheel up front better. The structure is all there for the tail wheel and at one time had both which some friends thought was really cool.

The tie down ring has never made contact on landing and this airplane has a relative aft CG. The photo of the 6A aft end damage would indicate the airplane is out of rig or landing technique caused it. Either way it should not be happening.

David-aviator said:

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The tie down ring has never made contact on landing and this airplane has a relative aft CG. The photo of the 6A aft end damage would indicate the airplane is out of rig or landing technique caused it. Either way it should not be happening.

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Also, the RV geometry seems to show that the aft lower tip of the rudder would contact the runway/ground slightly before the tie down ring.

I would also look closely for rudder damage.

Guys,

Thanks for your input, indeed the rudder bottom fairing is damaged - removing the rudder to fix that damage was when I found the bulkhead crack. No damage further up the fuselage or in the rudder structure. My tie down ring bracket is quite bendy, so the ring will bend backward into the front face of the rudder fairing without too much provocation.

Paul, I realise that you have more time on a 6A than probably anyone else, but things do move on in 6 years. I found getting repeatably good landings in the 6A the most difficult part of learning to fly the aeroplane, especially in crosswinds. Its not particularly difficult, just different to what I had flown before (mostly tail draggers), and I probably should have gone off and practiced more before departing on cross countries that meant landing on unfamiliar runways with unpredictable crosswinds (small fields surrounded by trees, but with cheap fuel). But that was all many years in the past now. I have not had a tail strike on a smooth runway in a long time. Yes, I probably would have figured out the technique faster with good instruction. Now I can land repeatedly in 900' of grass with a light headwind and little braking.

However the basic problem now is probably more the airfield I was flying from, rather than my technique. I used to operate from an 1800' up and down and bumpy strip that was liable to flooding in the winter. Rolling out into the bumps often meant uncontrollable pitching as the speed reduced and the elevator became in-effective, mostly that was just a little annoying. Of course it is difficult to predict that might happen until it does, and aft cgs (heavy passengers) made it much worse. Once I realised which parts of the surface were bad it was possible to avoid the worst of the bumps. The tail strike that probably did most of the damage was when the wind favoured the end that meant I couldn't avoid the bumps and had changed direction since I took off. I has a heavy passenger and didn't realise just how easy it was going to be for the bumps to throw the aeroplane on to the tail. The grass was soft and the tie down ring bent back readily. Clearly my own fault and probably a limiting condition for a 6A on that runway (and there were several other factors that day which meant I should have had another go, but was under pressure to land at the first attempt).

I don't think there is a fundamental problem here with the aircraft and agree that tail-strikes should not be regarded as normal and should be avoided in most cases with good technique. My point is really to point out the pitfalls of arbitrary modifications. If I were building a 6A I would be tempted to use the 7A tail tie down method. If my aeroplane were not damaged I would not modify it and would concentrate on flying it better.

Pete

penguin said:

Rolling out into the bumps often meant uncontrollable pitching

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This sounds like a tip-over is long overdue! At some point, that "uncontrollable pitching" is going to put you on your back!