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Rocket Steering Link Geometry

N96TJ

Member
I learned in this thread about a problem I didn't know I had, and I'm glad I did. My tailwheel was unlocking well before the stop to the left and right at the stop to the right. I never realized there was so much asymmetry to this system. I have also found that it is much worse when your rudder travel limit is the maximum (35 degrees) instead of the minimum (30 degrees).

After playing with this a while I believe the best fix is to move the forward link attach point both forward and inboard. The closer you can get to the rudder hinge point the better but there is a practical limit to this. I also tried a few different locations for the rear link attach point. Here is a look at the old and new geometry:

amz87c.png



b4uxqv.png


Here is the intallation:
2lw7jol.jpg


28s7bl1.jpg


5lp6o8.jpg


You can see I put a slight bend in the link to clear the rudder bottom. With this geometry and the standard rear arm (3.0") I no longer release before the stop but with +/- 35 degree rudder travel I think it still releases too soon. I can either reduce my rudder travel to +/- 30 or make a longer rear arm which I think is preferred. Once the rudder is at the stop I want it to take a hard push to get the wheel to unlock.
 
Thanks for this! clever solution for moving the forward attach point.

Your drawing is a little confusing to me. It looks to me like the rudder horn and steering arm angles are drawn symmetric left and right, but the length of the link changes. Is that what you wanted to show?

Your data tables make sense - it shows that for the stock link set up, you get 41 degrees of left wheel steer angle for a 30 degree left rudder angle, and 30 degrees of right wheel steer angle for a 30 degree right rudder angle.

But the drawing under the table doesn't show that.
 
Thanks for the info Tom. I made a pile of measurements on my steering link installation on Friday, and so I could analyze various mods to address the issue. I was thinking that the easiest fix would be to move the forward arm attachment forward and inboard, as you concluded. You drawings are a lot prettier than mine will be :)

Seeing the details of your mod is very helpful, as I was puzzling over how to move the arm hole forward of the rudder horn.
 
Excellent work!

Please let us know how the taxi/landing feel is with the slower geometry.
 
Final Version

JDAir sells a control arm with three link attach holes. None of those holes will work for me but this does make it easy to add an extension.

2e5s29e.jpg


With this addition I have the tailwheel travel limited to +/- 25 degrees while the rudder travel stops at +/- 35. It now takes a firm push to unlock the tailwheel with the rudder at the stops.

Please let us know how the taxi/landing feel is with the slower geometry.

I did not feel any difference during landing but for taxi the tailwheel response is noticeably slower and has a more deaden feel. In that sense I liked the original configuration better.
 
Very interesting thread. I had a look at my setup and moved my rudder horn steering link attachment point to an existing hole that I was using for a control lock. This hole was forward and inboard as discussed.

I can now get full rudder travel without unlocking the tail wheel. Just a little bit more push (on the brakes) and the wheel unlocks. I'll give it a try.

Remaking the control lock was easy.
 
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JDAir sells a control arm with three link attach holes. None of those holes will work for me but this does make it easy to add an extension.

2e5s29e.jpg

Very clever. Its ironic that JDair would be the ultimate solution here. I wrote them asking if there was any chance I could encourage them to make a steering arm that was longer and more back-swept. Less than zero interest on their part. "we've sold a bazillion of these, you are the first person to complain about this". Which makes me a know-nothing rather than someone who would like to help them improve their product.
 
Less than zero interest on their part. "we've sold a bazillion of these, you are the first person to complain about this". Which makes me a know-nothing rather than someone who would like to help them improve their product.

I have been cautioning people about this potential problem for years but it has always seemed to get drowned out by the "newer must be better" syndrome.

I am happy to see that people are evaluating the performance of there tail wheels which hopefully will help avoid some accidents in the future.
 
Great thread, which is spot on. The geometry is dramatically improved by moving the mounting hole forward and inboard.

I have an Aviation Products tailwheel which required the tailwheel rod to be shortened. It also has a smaller shaft which goes vertically through the tailwheel assembly (3/4" vs 7/8").

I purchased the RV Rocket Steering Link from Flyboy Accessories (great customer service, BTW). They did not have the control arm in stock for the smaller vertical shaft, but I noticed the tie down ring on their standard control arm was 3/4"! So, I filled in the notch on the larger side, machined the notch on the smaller size, flipped the control arm over, SHAZAMMM.....3/4" control arm with a 7/8" tie down ring. They should consider notching both holes so that the control arm is a universal fit.

I made my rudder mounting adapter (the part used to move the rudder mounting position) out of 1/4" aluminum plate. To avoid interference with the rudder cable clevis, I made an additional 1/4" spacer to position the adapter lower. By spacing the adapter lower, it gives me clearance on the rudder cable and more clearance for the link and the bottom of the rudder at full deflection.

Ground steering is very crisp. My first roll out after landing was a little bit wiggly as I adjusted to the better control on the tailwheel. Overall, I like the whole set up.

Either way, be sure to check your tailwheel breakout geometry.

Fly Fun,
J
 
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New Arm and Link

In conjunction with Steve Smith JD Air has developed a new arm with improved geometry. Steve is flight testing now and any tweaks will be made based on the flight testing.

I hope we will have this done and ready to go in early November. Thanks for your support!!
 
In conjunction with Steve Smith JD Air has developed a new arm with improved geometry. Steve is flight testing now and any tweaks will be made based on the flight testing.

I hope we will have this done and ready to go in early November. Thanks for your support!!

Since I last posted on this thread and others about the asymmetrical geometry of the "rocket" link, Darwin at JD Air Parts connected with me and we have been testing a new steering arm. I worked out an alternative geometry for the steering arm that makes the tail wheel deflection symmetrical and has the correct travel so that it releases the lock to allow the tail wheel to swivel at the right point. This was done by finding the right combination of sweep angle and length of the steering arm. Darwin graciously made the new arm and I have been flying with it now for several months. Here is a picture:

img_1054.jpg


Installation of the swept steering arm also requires a longer link. In my case, the center-to-center length is 14". Darwin was able to supply the longer link along with the arm.

It does indeed have very nearly the same deflection to the right and left, and the release point is right where I wanted it. If you go to full rudder travel, but have pressure on the tail wheel trying to make it straighten, as you would any time you are landing or taxiing, the swivel will not release. If you go to full rudder travel and then apply additional pressure in the direction of the deflection, as you would if you were moving the airplane on the ground and wanted the wheel to swivel, it does release. The additional travel allowed by the springs in the rocket link accomplish this. The result is a link that feels pretty much exactly like the original rocket link, with the added benefit that it will not release the wheel to swivel unexpectedly.

The one caveat that I would alert people to is that not everyone has their rudder stops in exactly the same location, so there is some variation of maximum rudder travel among all the thousands of RVs. While in my case the release is exactly what I think it should be, meaning full rudder travel plus some additional travel from the link springs is enough to release the swivel, others may find that rudder deflection alone might release the wheel, or might find that the combination of rudder deflection plus link spring deflection is not enough to make the wheel release. This variation in rudder travel is not something the vendor can control. You can be assured though that your tail wheel deflection will be nearly symmetrical right to left.
 
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All this engineering and pain for what net improvement to chains and springs? I'm very happy with my chain setup. What is the benefit of the rocket link, against the added trouble to get the setup satisfactory for safe operation?

Not trying to be a naysayer, just don't see the draw to the link despite all the crashed airplanes they've caused (or assisted in causing)...
 
I had a similar tailwheel unlock situation when I landed my newly acquired RV8 with a slight right crosswind. After touchdown, I got a fairly large gust which the rudder could not completely correct. I lowered the tail thinking I now had steering and found that I was pretty much a passenger since the tailwheel was unlocked.

I made a "controlled" departure between a couple runway lights at a turnoff.

No damage occurred and I was lucky...this time.

After evaluating my setup (Tail Lynx system), It appears that the engagement groove in the tailwheel itself is not routed far enough both directions to prevent unlock at full rudder deflection.

My neighbor is a machinist and he is going to mill out the engagement groove so that I have full rudder deflection with the tailwheel still engaged.

My two previous planes, RV4 and PL4, both had Aviation Products Inc systems and they worked perfectly, only disengaging with brake application.

Mitch Garner
N188R
 
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I like the better geometry. I'm waiting for the version with an integrated tie down ring, like the Flyboy Accessories' control arm has. It is very handy.

1200-1T-2T.jpg

You will have to ping Darwin so he knows that is a feature that his customers would want.
 
All this engineering and pain for what net improvement to chains and springs? I'm very happy with my chain setup. What is the benefit of the rocket link, against the added trouble to get the setup satisfactory for safe operation?

Not trying to be a naysayer, just don't see the draw to the link despite all the crashed airplanes they've caused (or assisted in causing)...

It is probably a stretch to accuse them of "crashed airplanes they've caused". A few partial ground-loops that fortunately seem to miss the lights and signs.

Seriously - It definitely is a preference thing. The rocket link is crisper in response, without the lag. If you set chains so there is no lag on the ground, they put a sizeable load into the bottom rudder hinge when the tail wheel spring relaxes in flight. It is also tidier, given that it is only on one side.

But it definitely is a personal preference thing.
 
All this engineering and pain for what net improvement to chains and springs? I'm very happy with my chain setup. What is the benefit of the rocket link, against the added trouble to get the setup satisfactory for safe operation?

Not trying to be a naysayer, just don't see the draw to the link despite all the crashed airplanes they've caused (or assisted in causing)...

I agree with Steve?s comments (above) - we use Silver Bullet links (no longer available, but the same concept) on all of our RV?s - thousands of hours, no issues, no problems, crisp handling, very clean installation, no ?crashed airplanes?.... It?s personal preference if you like their handling.

Paul
 
Available soon

I have the new geometry arms being fabricated now and will have steering links completed soon. I'll make an announcement here when they are ready to ship.

I have not flown this combination but Steve has put forth a great effort in making this happen. There is certainly nothing wrong with the current system but we are always looking for improvement.

Regarding the tie down ring on the arm, I'm not convinced this is a good place to tie down the plane. Any movement of the tail is going to cause the arm and locking pin to interact potentially causing nicks and burrs in the metal. The tail parts take a beating as is and there is no reason to add to that. However, if people like them, I'll see about having them made with a loop.

The one problem I see over and over again is a lack of MAINTENANCE on the tail wheel assembly. I'm going to start a separate thread on the proper care and maintenance of the tail wheel assembly.
 
Not trying to be a naysayer, just don't see the draw to the link despite all the crashed airplanes they've caused (or assisted in causing)...
Given the RV's fly and handle wonderfully on the ground with neither chains nor steering link, i'd have to say that any accident that happened with either installed was probably more related to complacency than the hardware.
 
Agree with Rob, I've flow a 9 without anything on the tailwheel for several landing after the lynx rod broke at the rod end and was removed for several weeks.
 
Given the RV's fly and handle wonderfully on the ground with neither chains nor steering link, i'd have to say that any accident that happened with either installed was probably more related to complacency than the hardware.

Rob, I think you are missing an important distinction. I have flown plenty of tailwheel airplanes with a fully castoring tail wheel without a problem. The problem that arises is that a locked tail wheel suddenly and unexpectedly releases. It is just not the same.
 
Resurrecting an old thread. Are any photos of the setup still available? All the photos from back in 2016 are no longer viewable.
Trying to set up the rocket link so the tail wheel doesn’t unlock prior to full rudder deflection.

Thanks, Tom
 
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