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Tail Wheel Yoke Improvements

J

Jason Krause

Active Member
We were curious about the possible benefits of a Ball Bearing Tail Yoke as compared to the standard bushing type that come stock with tail the dragger RV’s. After building a few samples and doing some initial testing, the results are quite impressive.

We have determined the ball/needle bearings have made the tail wheel much easier to steer and completely eliminated the hysteresis or “stickiness” caused by the normal bushing friction. There also doesn’t seem to be any indication of “shimmy."

Currently we are testing the yoke to see how it performs in harsh conditions. Primarily, making certain the bearings can handle the loads and conditions. i.e. large cracks commonly found in taxi and runways, moisture and fine dirt/silt from unimproved surfaces. Additionally, some less than ideal landings are being performed to further abuse the complete assembly.

Edit: Check out this video http://www.youtube.com/watch?v=vOjhB2AX1YY

We would love to get some feedback from all you tail dragger drivers about this possible upgrade. If all goes well, we will have the yoke available for sale soon, in our online store. Be sure to visit JD Air Parts at JDair.com for more information and check out our other products.


CNC machined and welded from 4130 steel and powder coated gloss black.


Notice the reduced "squat" angle. As long as shimmy remains at bay this looks much better.


This yoke will work other tailwheel products that are compatible with the 7/8" Van's setup.
However when combined with our Steering Link, Fork, New Control Arm* (*not pictured) and a light weight tail wheel the result is very impressive.


Just a quick exploded CAD rendering for a look inside. The aluminum sleeve is needed so the locking pin slides between the bearings for assembly.


Some of the prototype parts separately here.
 
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Looks nice. Do you have any preliminary weight projections compared to the standard issue unit. Resolving the constant maint. requirements of the standard unit would be nice, but this is the least desirable location on most RV's for adding weight.
One comment though, at first glance (not having done any calculations) it looks like the bending moment where the fork attaches to the pivot shaft will be quite high. Has static load tests been done on it?

Any option to use standard links and springs (for those that don't like the single link)?
 
Thanks! Great questions.

Currently the weight increase is 4 oz's when comparing just the yokes. This is not much, and can be offset with a light weight tail wheel and/or our fork.

YES! All the standard parts and most others (springs, fork and arms) can be used with the this yoke.

The fork:
The bending moment I believe you are referring to is not a concern due to the thickness of the horizontal plate and the way the lower axle flanges are positioned under the pivot shaft. Calculations and more importantly load tests were performed and the result was a distorted stock tail yoke (not likely in reality because of the tail spring) The tail spring like the main gear legs permanently distorts before any damage will happen to the airframe or components bolted to the other end....we hope:)
 
locking pin area

Is the locking pin area that much larger than the pin itself to give a free-swivel area prior to actuating for full freedom of rotation? If I recall correctly, the 'old' style is positively captured in a much smaller range of motion prior to breaking loose. I assume that is for a more positive feel than if it were free to move through what appears to be a much larger range prior to release.
 
The loads are surprisingly large, especially in off-nominal conditions such as pulling the plane into the hangar, over a lip. By surprisingly large, look up "Hertzian contact stress" and see for yourself.

FYI....

Dave
 
Now that is something I am interested in! I am tired of having to disassemble and lubricate that tailwheel every 20-25 hours. I'm in. As long as Van's standard parts such as the wheel, arm, and chains will fit. Another desire is that it be offered in white or light gray powder coating. My tailwheel parts are all red and the paint would cover white or light gray much nicer.

P.S. Does the height of the tail change?

Jerry
 
A few responses

RV8Squaz said:
Now that is something I am interested in! I am tired of having to disassemble and lubricate that tailwheel every 20-25 hours. I'm in. As long as Van's standard parts such as the wheel, arm, and chains will fit. Another desire is that it be offered in white or light gray powder coating. My tailwheel parts are all red and the paint would cover white or light gray much nicer.
P.S. Does the height of the tail change?
Jerry
Click to expand...
Jerry, Glad you are interested. :)
  • The reduction in maintenance is very exciting, we are also looking forward to that.
  • The stock Vans parts should work fine, however we can't control their tolerances so I couldn't 100% guarantee that....The plan is for all the parts to be interchangeable.
  • There wont be much change in tail height with just the yoke. The aftermarket forks will of course raise the tail.
  • We will offer the yoke just like our fork either in Black Powder Coat or Plain without any coating.

David Paule said:
look up "Hertzian contact stress" and see for yourself.
Dave
Click to expand...
  • The possible brinelling of the bearings is certainly one of our concerns and will be inspected thoroughly during our testing process.

GusRV8 said:
Is the locking pin area that much larger than the pin itself to give a free-swivel area prior to actuating for full freedom of rotation?
Click to expand...
  • Not exactly sure what your asking but the locking/swivel mechanism remains mostly unchanged from the stock setup.
 
Ready to purchase.

I am about to pull the trigger on a Tailwheel upgrade and was planning to purchase one of yours. I was thinking the other day...this thing would not stick so bad with a bearing. If you have them available now I am ready to purchase. Please contact me at [email protected] or 281-455-6784 and let me know. Thanks.
 
Great idea!

Sign me up! I've got one of your originals and it definitely sticks (especially with a passenger in the back seat of my RV-4. This sounds like a needed upgrade.
 
When can I buy one?

I am very interested in this. Will you sell the entire thing as a unit? I have an early 4 with the non swivel tailwheel. It will me modified to accept the full swivel but if your unit comes with all the parts I am very interested.

Mark Burns
404-433-2787
 
Bearing info

rocketbob said:
Jason what kind of bearing are you using on the bottom? Angular contact ball bearing?
Click to expand...

The lower one is a deep groove, sealed, ball bearing. The specs of this bearing indicate it can easily handle the load. It's the impact loads and contamination I'm curious about.

Angular contact might be a better choice but a few problems prevented us from using those:
  1. Not available in the sizes needed.
  2. Very expensive!
  3. Not usually sealed.
Those are usually used for machine spindle bearings and are mostly ABEC-7/9 series. Probably a bit too precise for this application.

So far the Bearing is doing well, needs more testing to tell for sure.
 
Pre-order list

Thanks for the calls and posts from all of you that want the yoke. I do have a customer list started for the first batch. No payment or obligation required. Feel free to contact us, PM, email or call to get on it. Please keep in mind it's still in testing and is not officially going to be available at this time ;)

Skysailor said:
I am very interested in this. Will you sell the entire thing as a unit? I have an early 4 with the non swivel tailwheel. It will me modified to accept the full swivel but if your unit comes with all the parts I am very interested.
Mark Burns
Click to expand...
Yes, the plan is to offer the complete package as well as all the parts individually.
 
Jason Krause said:
The lower one is a deep groove, sealed, ball bearing. The specs of this bearing indicate it can easily handle the load. It's the impact loads and contamination I'm curious about.
Click to expand...

I have had thoughts in the past about doing a similar mod to an existing tailwheel. My idea was to take the components of the bottom half of a mountain bike headset and turn an adapter on the lathe to make it work. They're sealed thrust bearings with seals.
 
The "Wright" yoke bearings

Bob,
Certainly not a bad idea. Wouldn't be the first time bicycle parts were incorporated on a airplane.
 
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I think this is a great mod and well worth doing. It eliminates having to stab at the pedals to get the tailwheel to break loose. I've flown one airplane with this sort of bearing incorporated which really improved ground handling.
 
steering arm

Why don't you guys rework your steering arm? It needs more play. Not enough slack in it. The spring is way to tight causing the tailwheel to be to responsive for crosswind landings,
 
Ummm, Steering link.....?

The Wizzard said:
Why don't you guys rework your steering arm? It needs more play. Not enough slack in it. The spring is way to tight causing the tailwheel to be to responsive for crosswind landings,
Click to expand...

Steering arm? I'm assuming you are referring to the Steering link? It's not intended to have "slack" in it, in fact the opposite is the point. If slack is what you are after then maybe the stock springs and chains hanging loose would be better. It's really a matter of preference.
 
Lower drag, better integration

Your yoke design has significantly less aerodynamic drag than the Bell and Aviation Products yokes. Also, it would not be difficult to design a nice tail wheel pant that fits onto it. Perhaps you could provide the yoke with a couple of #8-32 tapped holes in it that would facilitate mounting of a fairing?

I do like the added tail height of the Bell style, helps see over the nose, but that is by no means a deciding criterion.

Nicely done!

An additional thought on the links, in response to some folks' desire for a bit of "play". If you could maintain the basic design, but increase the amount of travel in the springs by making the outer tube longer, and using somewhat softer springs, then you might get the best of all worlds. No actual play, instant response, but somewhat softer, more gradual 'transition' that would help in cross winds.
 
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scsmith said:
No actual play, instant response, but somewhat softer, more gradual 'transition' that would help in cross winds.
Click to expand...

I've made a couple tailwheel links for guys and my design is a little bit simpler and more robust than some of the commercially available ones. Its hard to find variable springs to do what you are talking about but its entirely possible to use a couple of different stacked short springs of varying spring rate to do this. I've also thought about using elastomers but the spring rate changes with temperature.
 
Hey guys,

Guess I should not have opened that can of worms. I would really prefer to keep this thread on track with the yoke, not about steering spring design.

Thanks for understanding.
 
Today I modified the tailwheel assembly to use a sealed angular contact mountain bike headset bearing. Machined some spacers and cut 0.400" off the bottom of the weldment with my mill. The cup is not pressed on or part of the weldment, the three pieces just drop onto the shaft and are sandwiched between the weldment and the fork. Just pushing the airplane around the hangar it makes a huge difference and the side effect could be that the airplane could easily weathervane if its not chocked or have the parking brake on. I like it.

Bearing, available on Amazon:
http://www.amazon.com/AheadSet-Ahea...UTF8&qid=1359847979&sr=8-2&keywords=HSS20133K

photo.JPG


image.jpg
 
Steering linkage

I would love to see somebody come up with a steering linkage that is less sensitive than the JD airparts! There has to be an affordable way to do it. The JD airparts is to sensitive for crosswind landings but looks great.

One other thing, does a tailwheel pant really make a difference in speed?

I know this is not the original intent for this forum but since we are on the "tailwheel subject" why not!

Dave
 
The Wizzard said:
I would love to see somebody come up with a steering linkage that is less sensitive than the JD airparts! There has to be an affordable way to do it. The JD airparts is to sensitive for crosswind landings but looks great.

One other thing, does a tailwheel pant really make a difference in speed?

I know this is not the original intent for this forum but since we are on the "tailwheel subject" why not!

Dave
Click to expand...

Dave, you could take it apart and put softer springs in it. In my picture you can see part of the link I made and its a bit larger, the size dictated by my choice of springs which are a bit softer (what I had laying around.) The springs really don't have to be heavy at all, as long as they don't "bump" if they bottom out.
 
The Wizzard said:
I would love to see somebody come up with a steering linkage that is less sensitive than the JD airparts! There has to be an affordable way to do it. The JD airparts is to sensitive for crosswind landings but looks great.
Click to expand...

The sensitivity thing isn't a matter of spring rate. It is lever ratio.

In a stock setup we usually connect the chains, cables, or single link to the rudder arm at the outermost end of the arm, just so the chains/cables/link does not rub against the fiberglass bottom fairing when the rudder is fully deflected. The result is roughly a 1-to-1 ratio (rudder deflection angle is matched by tailwheel angle), since the rudder arm and the tailwheel arm are about the same length.

You make a tailwheel less twitchy by reducing the ratio, i.e. less tailwheel deflection than rudder deflection for any given displacement of the pedal. You do it by reducing the length of the arm at the rudder connection (move the connection point inboard) or extending the length of the tailwheel arm.

If you are using dual chains or cables, drill a hole in the rudder arm inboard of the usual hole and install a AN42B-10A upside down with a stack of washers to space the eye a low as possible. Connecting to the eye will probably allow your chain/cable to clear the rudder fairing.

Many of the lovely links out there come with a single sided replacement arm for the tailwheel. Reducing the ratio is merely a matter of making that arm longer.
 
Not a good idea Dan, have fixed a couple of broken links for myself and others where the the 1/4" tubes failed. I fixed them by changing over to stainless rod. Changing the ratio would increase the stress on these parts.
 
bearing grease

Almost didn't dare write that title, for fear of starting yet another "grease war"...

But. I have several bikes (another weakness of mine) with that type of bearing. In my experience, the grease installed by the manufacturers isn't the greatest. Even on my road bikes the stuff seems to find its way out quickly despite the seal, particularly the bottom bearing. I've taken to popping the seal out with a dental pick before first use, and forcing in (fingers work great) what ever red synthetic grease I have lying around. The bearings last noticeably longer for a couple minutes work.
 
Testing video

The Wizzard said:
I would love to see somebody come up with a steering linkage that is less sensitive than the JD airparts! There has to be an affordable way to do it. The JD airparts is to sensitive for crosswind landings but looks great.

One other thing, does a tailwheel pant really make a difference in speed?

I know this is not the original intent for this forum but since we are on the "tailwheel subject" why not!

Dave
Click to expand...

I do have some slightly larger link bodies (about .035") that are required for more spring options. I'll be be happy to build one up for you with softer springs to see if this helps "your" crosswind landings. Please contact me directly.

rocketbob said:
Today I modified the tailwheel assembly to use a sealed angular contact mountain bike headset bearing. Machined some spacers and cut 0.400" off the bottom of the weldment with my mill. The cup is not pressed on or part of the weldment, the three pieces just drop onto the shaft and are sandwiched between the weldment and the fork. Just pushing the airplane around the hangar it makes a huge difference and the side effect could be that the airplane could easily weathervane if its not chocked or have the parking brake on. I like it.
Click to expand...

It looks pretty good! Wonder if it can handle this?

http://www.youtube.com/watch?v=vOjhB2AX1YY
 
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Some of that is an artifact of the rolling shutter on the camera. Another part of it is where the whole thing is rotating on the bearing giving the appearance of bending.
 
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