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Additional stress due to ? internal rudder stop? ??

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Pilottonny

Well Known Member
Hello,

I have purchased one of those plastic ?internal rudder stops? from one of our fellow builders. I have read some pro?s and con?s about this, but today while adjusting the rudder swing, I noticed that it is not the rudder that takes the extra blows, but the very rear fuselage bulkhead (the smallest one right at the end of the tail cone). There is a twisting force on the rudder attach bracket, that tries to twist the rear horizontal stabilizer spar, that on its turn puts these forces on the rear bulkhead.

If it is not the pilot who is hitting the stops hard, it might be the wind!
Has anybody, who is using the internal stop, noticed any problems in the long run?

Thanks in advance for your replies. Regards, Tonny.
 
Pictures included

Many have this setup, but, as requested, a picture of the internal rudder stop, installed with the rudder in place. It is plastic so it is softer than the aluminium stops on the outside of the fuselage, but because it is closer to the hinge the forces will be higher. I will put some sticky-back rubber strip on the rudder where the stop hits, so it is cushioned.


f_P7030238m_4d6d33d.jpg



THis is a picture without the rudder in place.

f_P7030243m_de9b221.jpg


It does work great, just curious about the forces on the rear spar.

Regards, Tonny.
 
an internal stop I guess would be ok. I like my outside one, because it allows me to put a brace between the stop and the horn that the cables for the peddles hook to. I don't have a pic, but this weekend I'll be using mine. So if I remember I'll take a pic. I used a desk handle, all I had to do is drill two 1/4 holes and inset the brace, than I hook a long red remove before flight to it.
 
Internal vs external rudder stop

I made my own internal stop and it has worked just fine.
Whenever I leave it outside I use a gust lock, made from PVC pipe, that goes between the rudder pedals and the spar (don't have a picture handy).

Even the external gust locks aren't bullet proof. A buddy's 7 was left outside at the radio shop (no gust lock installed) during some gusty winds and the rudder. with external stops, hit the elevator and poked a hole :mad:
 
I cautioned builders about casually changing to an internal stop when people first started talking about it.

When the RV-10 internal rudder stop was developed it was found that the force applied to the stop was quite high because of the short arm length between the stop and the hinge point (the law of leverage...the rudder stop is the fulcrum and the rudder is the long lever).
Very likely the movement you are seeing is a result of the vertical stab. spar being twisted. On the RV-10 it was found that another set of bolts was needed so that the top hing bracket was bolted through to the fuselage bulkhead just like the bottom one is.
 
I've had one on my -7 for 500 hours and no problems noted (yet). I usually don't hit the stops when flying, and the tail is always locked when parked, so I assume the stress is minimal.
 
MCA said:
I've had one on my -7 for 500 hours and no problems noted (yet). I usually don't hit the stops when flying, and the tail is always locked when parked, so I assume the stress is minimal.
Click to expand...

I can see that being more the case with a tail dragger (RV-7). Not so with a trigear though. The typical/correct operation of the rudder when steering an "A" model on the ground is to steer using rudder input only. If you use full rudder input and it is not enough turning force then you also add some brake (a lot of brake if you are needing to turn very tight). Adding the brake input with full rudder deflection does put a pretty good load against the rudder stop. This is the condition that has been found to be a problem with this type of rudder stop.
Reiterating my other post...if you are using this type of rudder stop and haven't added extra fasteners to the upper of the bottom hinge brackets, you are probably bending the vertical stab. spar when you hit the rudder stops while steering on the ground.
 
Well... I'll be a monkeys uncle. I guess that the tail wheel bracket must be tweaking the &*!% out of the same bulkhead... :eek: We're all going to loose our rudders soon. :D If you are steering the plane in this manner, for any reason you might want to consider selling. If I'm not mistaken, the large aluminum angle mounted on the rudder spar that hits the fuse mounted stops sticks out a couple of inches on boths sides which would provide much more leverage on the vertical and rudder spars which could tweak the same rear fuse bulkhead if abused. Oh, and please lock your controls.
 
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LifeofReiley said:
Well... I'll be a monkeys uncle. I guess that the tail wheel bracket must be tweaking the &*!% out of the same bulkhead... :eek: We're all going to loose our rudders soon. :D If you are steering the plane in this manner, for any reason you might want to consider selling. If I'm not mistaken, the large aluminum angle mounted on the rudder spar that hits the fuse mounted stops sticks out a couple of inches on boths sides which would provide much more leverage on the vertical and rudder spars which could tweak the same rear fuse bulkhead if abused. Oh, and please lock your controls.
Click to expand...

Steering in what manner? Please tell me what manner you have determined to be correct.
Before criticizing my comments, I suggest you analyze the load paths of the two types of stops. I have actually been involved in engineering both types and am well aware of the different issues related to them.
The standard plans built stop is mounted on the fuselage which is relatively solid. The internal stop is mounted on the rudder hinge bracket. This applies all of the load on the stop as a twisting load on the vertical stab. spar.
 
OK, additional bolts in top-bracket.

Hello, this is turning out to become a fun question.:)

OK, so I put two additional bolts in, through the top bracket, into the rear bulkhead. But,..... to avoid cracking the rear (double) bulkhead, I better put a backing plate on the inside of the bulkhead as well, right? Or at least some large washers. But then it is the rear bulkhead that will take the higher forces (well at least a part of them, because the rear spar is quite thick and the load will spread over a certain length of the spar, through the rear bulkhead into the skin and the stringers), I guess. What about a brace from the bracket to the #2 bulkhead?

One thing to considder is, that I have return springs on my rudder peddals, which will cushion the end-movement of the rudder when blown about by the wind. But of cource I will always put in the gust lock (on other side, not seen in the pictures), which is just a simple U-shape rod, with a "remove before flight tag" that goes into the rudder horn and a small tab (where the external stop used to be).

About the braking forces: Isn't there a foot on the other peddal, countering the forces of the foot that is pushing on the brake?
Well If there is people out there that have been flying for 500 hrs, without any problems, I am not that worried anymore.

Keep your suggestions coming, we can all learn.

Regards, Tonny.
 
LifeofReiley said:
Well... I'll be a monkeys uncle. I guess that the tail wheel bracket must be tweaking the &*!% out of the same bulkhead... :eek: We're all going to loose our rudders soon. :D If you are steering the plane in this manner, for any reason you might want to consider selling.
Click to expand...

When taxiing in a crosswind I frequently hold the rudder against the stop to minimize brake use ("A" model). I'm not considering selling.

LifeofReiley said:
If I'm not mistaken, the large aluminum angle mounted on the rudder spar that hits the fuse mounted stops sticks out a couple of inches on boths sides which would provide much more leverage on the vertical and rudder spars which could tweak the same rear fuse bulkhead if abused. Oh, and please lock your controls.
Click to expand...

None of the force is transmitted to the spars- the cables are connected to the rudder horn which contacts the stops directly.
 
Jim Percy said:
When taxiing in a crosswind I frequently hold the rudder against the stop to minimize brake use ("A" model). I'm not considering selling.



None of the force is transmitted to the spars- the cables are connected to the rudder horn which contacts the stops directly.
Click to expand...

Jim,
It does if you use the internal (not standard kit part) rudder stop that this thread is talking about. In that case teh stop is mounted to the top hinge bracket which transfers the rudder stop loads to the vertical stab spar.
 
rvbuilder2002 said:
Steering in what manner? Please tell me what manner you have determined to be correct.
Before criticizing my comments, I suggest you analyze the load paths of the two types of stops. I have actually been involved in engineering both types and am well aware of the different issues related to them.
The standard plans built stop is mounted on the fuselage which is relatively solid. The internal stop is mounted on the rudder hinge bracket. This applies all of the load on the stop as a twisting load on the vertical stab. spar.
Click to expand...

Sorry Scott... I went back and reviewed my post and did not see your name even mentioned, did'nt even quote you? I made a comment, you know my side of the story.

Oh, and I steer my (A) model with differential braking, not rudder to the stops. It works very well. :)
 
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rvbuilder2002 said:
Jim,
It does if you use the internal (not standard kit part) rudder stop that this thread is talking about. In that case teh stop is mounted to the top hinge bracket which transfers the rudder stop loads to the vertical stab spar.
Click to expand...

Why would you mount the rudder stop to the top bracket? Wouldn't it make more sense to mount it to the lower rudder bracket?
 
LifeofReiley said:
Sorry Scott... I went back and reviewed my post and did not see your name even mentioned, did'nt even quote you? I made a comment, you know my side of the story.

Oh, and I steer my (A) model with differential braking, not rudder to the stops. It works very well. :)
Click to expand...

That works but I see no sense in wearing out brakes faster than needed. In some instances this can also result in an over heated brake when rudder may have been enough. The logical procedure in my mind is to use all of the primary control first (Rudder). If or when that is not enough, then you add brake as needed.
 
That's exactly the technique I use...I use maximum rudder input first, only braking when necessary, then right off of them and back to rudder. I notice myself using rudder feet often when taxiing, more effective on the 7 rudder than the RV6. So far, brake pads look new.
 
No, no, no, not on the bottom bracket!

Oh boy,..... I am really enjoying this! :)

No, you can?t put the internal stop on the bottom bracket, because it will interfere with the spar attach bolts (you schould have seen this, if you would have looked at my pictures! :D). Yes, right, ...... those! The ones that transfer the loads to the rear bulkhead. Though! Sometimes life is easy, sometimes it just sucks!

Keep the suggestions coming! Still learning!

Regards, Tonny.
 
rvbuilder2002 said:
That works but I see no sense in wearing out brakes faster than needed. In some instances this can also result in an over heated brake when rudder may have been enough. The logical procedure in my mind is to use all of the primary control first (Rudder). If or when that is not enough, then you add brake as needed.
Click to expand...

For safety reasons, I do not make it a habit to taxi my plane fast enough to make the rudder very effective... also, don't ride the brakes at all just a tap here and there as needed. I didn't even elect to upgrade the Cleveland brakes to the Groves and the pads are still looking good... :)
 
When you said upper hinge bracket, I thought you meant you were installing it on the UPPER hinge, at the top of the rudder. :)

Pilottonny said:
Oh boy,..... I am really enjoying this!

No, you can?t put the internal stop on the bottom bracket, because it will interfere with the spar attach bolts (you schould have seen this, if you would have looked at my pictures! :D). Yes, right, ...... those! The ones that transfer the loads to the rear bulkhead. Though! Sometimes life is easy, sometimes it just sucks!

Keep the suggestions coming! Still learning!

Regards, Tonny.
Click to expand...
 
I mentioned earlier on why? do the internal, the only reason I can see is you don't want a couple little pieces coming out on a paint job, don't know, the ones on the rudder kind of look bulky as well. Anyway, I like mine for using a rudder lock, which in my opinion is more important.

As far as using the rudder and hitting the stops, when in a massive slip, very hard to hit the stops at 80kts, that's pretty much the speed for using a slip on a major. At least for me it's very hard to hit the stops.

Second, for taxi, I haven't hit the stops yet and I use rudder first for keeping straight than the brakes, which are a quick jab. Now, I do run about 20kts at my home airport, down under 15kts at a any other airport. Why? obvious, I don't know the other airports like my own. I have grove brakes, which have twice the kenetic stopping power, and yup thay work great, so if I need to slow, I do it fast. Now, some are wondering why I go so fast, simple, my 7A works great. No shimmy, taxi straight and smooth, except when I have a cross wind than it goes to the side a little. I have all wheels balanced and the Grove nose wheel.

Sometimes I think people reengineer things and get off track and spend way to much time on stuff like this.
 
allbee said:
I mentioned earlier on why? do the internal, the only reason I can see is you don't want a couple little pieces coming out on a paint job, don't know, the ones on the rudder kind of look bulky as well. Anyway, I like mine for using a rudder lock, which in my opinion is more important.
Click to expand...

I fail to see why also. It's not like this is a streamlined tail with no rudder cables hanging in the wind! If there were no cables and a exposed rudder horn, along with clevises and bolts; then I could see a need for something hidden.
BUT...............it just isn't the case!

Today, since it was on my mind, I took these two pics. With all the stuff down there; what's one more piece; especially when it's all around tougher. And BTW, in both setups, the cable completely misses the rudder stop.






Now seriously, if these rudder stops are removed, does it somehow look more streamlined? I d-o-n-'t think so!

L.Adamson --- RV6A (flying)
 
In my case, I built the 7 rudder and put in the
external stops. Everything fit fine.
Then, Vans sent me the 9 rudder to replace my original one.
I don't know if it was me or Vans, but the external stops
didn't give me enough clearance between the rudder and elevator.
I played with the rudder hinges, but no joy.
I extended the external stops and they looked awful.
I saw the drawing on the internet for the internal stop.

It seemed to have solved my problem on a painted A/C.
I hope my rudder doesn't fall off.
Tom
 
I hope my rudder doesn't fall off.


Hahahaha, that was my smile for the night, thanks Tom. Hope it doesnt fall off either, haha. :D
 
Compare with 10 internal stop

I read Tonny's posting on a thread on 10 internal stop. Before that I was not aware of the issue. After comparing my 9A and 10 here is my comments.

10 is designed to use internal stop. Without putting 9 and 10 side by side my impression is that their VS and rudder are about the same size (no major size difference). Of course I could be wrong on this one. However, 10 has much beefed up rudder and VS. When rudder horn hit the stop the force is transferred to the hinge then rudder spar then bulkhead. In additional to the spar doubler that 9 has 10 has two angles (caps) along side the spar that hinge brackets are mounted upon. So it can take the stress much better (given the stress induced by wind gust hitting the rudder are about the same). Of course the bulkhead where the VS is attached to is also much stronger. I would not worry about the stop when we operate the airplane. I would concern more when the wind gust hit (will not be as gentle as our foot) while the plane is parked. Without a thorough engineering analysis or experiment we would not know how much gust the stop can take (in some cases heavy foot). If the spar or the bulkhead is twisted, it is hard to fix. Make sure you have gust lock on while parked outside with either internal or external stop! It is not fun to build a new rudder (I did) even worst to build/repair VS and bulkhead.
 
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