Rocket Steering Link Geometry

[N96TJ]

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:






Here is the intallation:






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.

[scsmith]

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.

[Kevin Horton]

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.

[BillL]

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

[N96TJ]

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.



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.

Originally Posted by BillL

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.

[vlittle]

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.

[scsmith]

Originally Posted by N96TJ

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.

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.

[rvbuilder2002]

Originally Posted by scsmith

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.

[pecanflyboy]

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

[RV7Guy]

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!!