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Why does my tailwheel hate me

P

plagergren

Member
Two incidents where my RV-8 did a pirouette on the runway/taxiway when I made a) a rudder pulse when hit by a 90 deg crosswind 18 knot gust; b) when I was making a sharp turn on a really narrow taxiway and the tailwheel locking pin disengaged and I went into the lets-do-a-spin-turn mode. So I talked to Van's tech support and they told me "don't use that much rudder" which sounds like a really stupid thing to say because what if you have to use that much? The issue is that the rudder goes +-30-35 degrees and the tailwheel pin unlocks at +- 20 degrees. So how are you supposed to know when you are reaching the rudder travel limits without some kind of rudder travel restrictor while in ground operations? I asked tech support why it was designed that way and they said you have to talk to Van, it's been that way forever and and Van isn't available. Great.
So I have asked multiple experts why the tail wheel locking pin is built this way and no one knows, apparently. Obviously you want to tailwheel to unlock when you are dragging it into the hangar but why do you want the tailwheel to be able to unlock when you are taxiing or taking off? Does anyone have a real answer to that question, in engineering terms and not pilot technique terms?
 
I know someone who machined the grove in the tailwheel so that it has more steerable range before it unlocks. That being said, I’ve never had the tailwheel on my -4, or any tailwheel plane I’ve flown, act like you are experiencing or give me any problems.
 
If the tailwheel did not unlock with less than full rudder application, then you COULDN'T unlock it without getting out of the airplane.

The tailwheel unlocks in order to be able to make a tight turn in place. When there are air loads on the rudder and the tailwheel is rolling on the ground, the springs limit the amount of travel that the tailwheel actually deflects vs your rudder application. This is so that you don't drag the tailwheel sideways on the pavement and it continues to provide positive directional control when responding to yaw correction demands during takeoff and landing.

You might try adjusting the spring force and see if you can find something more compatible with the way you think it should work. You could retrofit a fully locking tailwheel (cockpit control for locked and unlocked). Or, just use less rudder/more brake in the stated situation.

plagergren said:
So I have asked multiple experts why the tail wheel locking pin is built this way and no one knows, apparently. Obviously you want to tailwheel to unlock when you are dragging it into the hangar but why do you want the tailwheel to be able to unlock when you are taxiing or taking off? Does anyone have a real answer to that question, in engineering terms and not pilot technique terms?
Click to expand...
 
Hmmm

Hi flyride,

The important part if your post is having to get out of the airplane to unlock the tailwheel. that's what I want to have happen. In my use of the airplane there is no reason I want toi to unlock while I am in t he airplane
 
Hi Taltruda, machining the locking pin pocket is what I am wanting to do but I would like someone able to tell me why I can't do that. I know I can, but what will that change that I am not considering?
 
pin

If you are serious, then machining a solid pin to replace the spring pin should do the trick.
 
Change the hole location on the rudder horn or the tailwheel arm so the tailwheel does not unlock until the rudder hits the stop.
Ideally I like it to unlock when the rudder hits the stop AND some brake is required to increase the tailwheel travel. For a pivot going slow.
Also, is 35 degrees of rudder travel correct ?
Sounds like a lot
In any event, lots of tailwheel troubles on mismatched arm lengths and travels relative to the break out point on the wheel.
Mike
 
I changed the stock tailwheel assembly to a JDAir setup which is much better. I had a locking tailwheel on my Staggerwing but why would I need that on an RV? It's only a tiny airplane. Referring to sliding the tailwheel sideways, seems to me that if that is a major issue why not use a "gear reduction" between the rudder input and the tailwheel response? Too complex - but what is the angle reached by the tailwheel that causes it to start sliding?
 
Taltruda said:
I know someone who machined the grove in the tailwheel so that it has more steerable range before it unlocks. That being said, I’ve never had the tailwheel on my -4, or any tailwheel plane I’ve flown, act like you are experiencing or give me any problems.
Click to expand...
Hi Tom,

I would like to contact the person who did the tailwheel lock groove change. Do you have a contact for them/
Peter
 
Tailwheel geometry and the mechanics of a proper tailwheel set-up are IMO, one of the most complex and least understood things on our airplanes. Like you, I’ve been in a situation where I needed to do something counterintuitive such as “take out right rudder to go right” and it doesn’t work in the heat of the moment. I have a Matco TW assbly on my biplane and they offer different steering arm “wings” to change the release angle. It took several phone and e-mail conversations with George at Matco and trail and error to get my set up to where it is now. He was fantastic in helping to educate me. As was mentioned, the release point should be very near full rudder deflection and spring tension is a critical part of the equation. Good luck, not sure a forum discussion is going to get you to where you want to be.
 
rmarshall234 said:
Tailwheel geometry and the mechanics of a proper tailwheel set-up are IMO, one of the most complex and least understood things on our airplanes. Like you, I’ve been in a situation where I needed to do something counterintuitive such as “take out right rudder to go right” and it doesn’t work in the heat of the moment. I have a Matco TW assbly on my biplane and they offer different steering arm “wings” to change the release angle. It took several phone and e-mail conversations with George at Matco and trail and error to get my set up to where it is now. He was fantastic in helping to educate me. As was mentioned, the release point should be very near full rudder deflection and spring tension is a critical part of the equation. Good luck, not sure a forum discussion is going to get you to where you want to be.
Click to expand...

The forum is my last shot. All the other sources could come up with was don't use that much rudder and recenter the locking pin by hitting the brakes, yadi yadi yadi. So this forum has actually provided more info than I have gotten anywhere else. Go figure.
 
It sounds like your tailwheel is working as expected. I am not quite sure what you mean by a rudder pulse. Is that pushing the rudder quickly to the stop? If so you might want to consider using a bit of brake.
 
You could try just removing your steering arm, or your two chains/door springs - whichever you have. You would then have a free castering tailwheel that is almost locked in that narrow range before the spring loaded pin slides to disengage mode. I’ve had my steering arm break (twice), and while waiting for a new one to be delivered, my landings got better. Taxiing required a little more differential braking, but not much. That centering pin will release when you get a little side load on the tailwheel in a turn, but I didn’t find taxiing difficult. Taxiing with a strong 90 degree crosswind would require considerable diffential braking, but I didn’t notice that being much of an issue either.

In another life I flew Beech 18’s and DC-3’s, and both of those had locking tailwheels. You engaged the lock manually from the cockpit with a lever cabled to the locking mechanism on the tailwheel swivel assembly when aligned on the runway for takeoff, and left it on until after you landed and wanted to turn off the runway. Someone here could probably engineer such a system for an RV. I haven’t experienced anything like you have, but I’m sure something could be done to help with your issue.
 
Sounds to me like the OP could use some remedial training on how to be quicker and more forceful with his differential braking technique.

We have 1000's of taildragger RV's out there, all built the same way as OP's. If the tailwheel design were really that lacking, we'd have many more ground-loops occurring.
 
hgerhardt said:
We have 1000's of taildragger RV's out there, all built the same way as OP's. If the tailwheel design were really that lacking, we'd have many more ground-loops occurring.
Click to expand...

They are not all built the same way, many have the tail wheel that does not have an unlock feature, like my RV-3.
 
Hi Peter,

Looks like you already have some good input. I'm keenly aware that perspectives and variables are all over the map so hard and fast rules are hard to come by. That said, as I read your post, it seems that low speed control in gusty conditions is the issue. In that case/scenario, I would agree that the use of brakes will be much more effective than the rudder. I suspect that may have been what Van's support was trying to communicate. In other words, in those conditions, a leg full of rudder (only) will only serve to unlock the tailwheel and allow the plane to go wherever the wind sends it. You need to use differential braking. I don't have a specific number/speed but clearly the rudder becomes useless (mostly?) at low speed and low power.

I encourage all RV taildraggers to go with a swiveling tailwheel as it massively increases your ability to maneuver to say nothing of simply pushing your aircraft backwards into the hangar. I spend most of my time in rather tight places and backcountry airstrips and love the full swiveling tailwheel - obviously not everyone operates as I do so perhaps it is less valuable to others. My point, however; is that full swiveling does work in 'harsh' conditions so before removing yours, it might be worth first ensuring that it is functioning as designed.
 
Raven Aircraft

Not difficult to make it locking or install a locking from Rob @ Raven.
Quality work and multiple ways to make it unlock.
Attach to stick so that full forward stick will unlock like many warbirds or add a lever.
A good fabricator could mod your current unit I'm sure, maybe with out taking it off the airframe.
 

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plagergren said:
Two incidents where my RV-8 did a pirouette on the runway/taxiway when I made a) a rudder pulse when hit by a 90 deg crosswind 18 knot gust; b) when I was making a sharp turn on a really narrow taxiway and the tailwheel locking pin disengaged and I went into the lets-do-a-spin-turn mode. So I talked to Van's tech support and they told me "don't use that much rudder" which sounds like a really stupid thing to say because what if you have to use that much? The issue is that the rudder goes +-30-35 degrees and the tailwheel pin unlocks at +- 20 degrees. So how are you supposed to know when you are reaching the rudder travel limits without some kind of rudder travel restrictor while in ground operations? I asked tech support why it was designed that way and they said you have to talk to Van, it's been that way forever and and Van isn't available. Great.
So I have asked multiple experts why the tail wheel locking pin is built this way and no one knows, apparently. Obviously you want to tailwheel to unlock when you are dragging it into the hangar but why do you want the tailwheel to be able to unlock when you are taxiing or taking off? Does anyone have a real answer to that question, in engineering terms and not pilot technique terms?
Click to expand...

You did not mention geometry and hardware. Do you have chains or single spring rod? The lever length on the tailwheel changes the angle relationship with the rudder. You might want to discuss with JDAir and be sure you have all the available adjustments where you want them. I find sharper turns when rolling is best started with braking and managing with the rudder. YMMV.
 
Last edited:
Been discussed

BillL said:
You did not mention geometry and hardware. Do you have chains or single spring rod? The lever length on the tailwheel changes the angle relationship with the rudder. You might want to discuss with JSAir and be sure you have all the available adjustments where you want them. I find sharper turns when rolling is best started with braking and managing with the rudder. YMMV.
Click to expand...

Bill,

Darwin from JD Air Parts. I've exchanged several emails with Peter. To me, it sounds as if the tailwheel is working exactly as intended. Maybe he is carrying too much speed when he kicks it around and doesn't give opposite rudder for the pin to re engage to stop the rotation.

We've got hundreds of these in the field and haven't had anyone express a concern like this. My suggestion is to get more time in the seat to get used to it. Machining for more travel I don't believe is the answer. Many are surprised at how sensitive the system is with especially with our steering link but quickly get used to it. More time with it will help.
 
plagergren said:
Hi Tom,

I would like to contact the person who did the tailwheel lock groove change. Do you have a contact for them/
Peter
Click to expand...

Peter, Pm me and I’ll put you in touch with my friend. Personally I don’t see the need to machine it. My JD air Tailwheel works great. I don’t think it’ll unlock unless I get to full deflection plus a little bit of chain stretching before it goes. I wonder if it’s either pilot experience or a weird setup where the steering arm is shorted and making the steering at the Tailwheel faster than normal? Post some pictures of your setup.
 
IMHO I think this comes down to technique and the geometry of the chains or steering links.
Chain tension or slack has a large bearing on the mechanisms behavior. Super tight chains or a link will guarantee the wheel unlocks as the rudder hits whatever deflection the tail wheel unlocks at. Loosen them up a bit and you get some more rudder before it does. But this is still a feel thing. It’s quite a personal preference. Do a search here. Lots of opinions.
In reality though if you’re using a boot full of rudder for any reason then you should be fully expecting it to be unlocked or you’re going to be surprised.
FWIW it took me at least 50h and maybe 6m to become comfortable in my RV7.
I went from the vans chains to a rocket link and then to the (sadly now unavailable) Tail Lynx. They are awesome.
 
RV7Guy said:
Bill,

Darwin from JD Air Parts. I've exchanged several emails with Peter. To me, it sounds as if the tailwheel is working exactly as intended. Maybe he is carrying too much speed when he kicks it around and doesn't give opposite rudder for the pin to re engage to stop the rotation.

We've got hundreds of these in the field and haven't had anyone express a concern like this. My suggestion is to get more time in the seat to get used to it. Machining for more travel I don't believe is the answer. Many are surprised at how sensitive the system is with especially with our steering link but quickly get used to it. More time with it will help.
Click to expand...

Thanks for that clarification, Darwin, makes good sense. I have a -7 with "rocket" link and never had this issue but absolutely get your point - it is precise.
 
+1 for what Darwin said. If you're tailwheel unit is properly maintained, it should work just fine. However, they DO REQUIRE periodic maintenance... all of them regardless of the manufacturer.

Blake has some good tech tips on his site. They can be found here:
maintenance tips

BTW, there is some questionable advice in this thread. I hope you'll disregard that advice and do this:

1) inspect and maintain the tailwheel parts regularly. There are no maintenance free tailwheels.
2) use proper tailwheel techniques. Get additional instruction if needed.
 
Xwind

I had an RV4 with the chains and springs with a little slack in the chains. Full rudder deflection such as doing a strong cross wind landing will unlock the tail wheel as its designed to do. When it became a problem for me is when the tail comes down and you lose rudder effectiveness and the tail wheel is unlocked and in a free castering mode. This could become a real problem especially if the cross wind had not subsided.

Put your tail wheel up on a stand, kick in full rudder to simulate what you would do in a strong crosswind. You could probably adjust it out with the chains, then it probably wont unlock on the ground when you want it.

I agree a lockable tail wheel controlled by the pilot would be an excellent idea for some of us that only have one runway that is always in a crosswind mode.

Tim
 
plagergren said:
...The issue is that the rudder goes +-30-35 degrees and the tailwheel pin unlocks at +- 20 degrees...
Click to expand...

RV7Guy said:
Darwin from JD Air Parts; I've exchanged several emails with Peter. To me, it sounds as if the tailwheel is working exactly as intended...
Click to expand...

I'm not a builder and I'm learning to maintain my RV-7. I have the post below from Scott McDaniels bookmarked. I'm probably not fully understanding how things are supposed to function but it sounds like Scott is saying that full rudder input shouldn't unlock the tailwheel. But the above comments are saying that it should.

Am I misinterpreting these comments?

rvbuilder2002 said:
...I have been cautioning builders for many years (ever since there was a rocket link on the RV-7 prototype) that they need to confirm that when the rudder is hard over at the left and right stop, that it isn't rotating the arm on the tail wheel beyond the disengage point.

I believe a lot of the ground loops that have occurred over the years were caused by this. Chains and springs have enough slack that this isn't a problem.

This is one of the reasons I don't like the rocket style links, and why the RV-7 prototype was switched back to springs.
Click to expand...
 
My understanding is that rudder input alone should not unlock the tailwheel - otherwise you lose steering force exactly when you are asking for more.

The tailwheel steering should be unlocked by the wheel, when the angle exceeds a certain value - either by ground handling, or sideways movement from brake input or aerodynamic forces on the rudder. At that point the wheel itself isn't providing steering force.
 
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