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Bye bye Rocket Steering Link

abuura

Well Known Member
Upon the last of 5 landings from my post-mx checkout, I felt a strong and prolonged vibration from the rear that continued until I slowed to a walking pace. Inspection revealed that the steering link had sheared off as shown in the picture.
The maintenance I performed before flight simply consisted of cleaning and lubing the tailwheel axle and bronze bushing, and tightening the assembly so the steering arm was tight but the wheel still able to swivel freely 360 degrees - same as I've always done.
Has anyone experienced this before? I plan to return to the original chains-and-door-springs that worked so well before but I'm just curious. Thanks for your input.
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I’ve had two of these steering link fractures over the years. I never noticed any vibration or shimmy. I use the door springs now too. I wish the tail lynx was still available.
 
I can't tell for sure from the posted pic but the shape of the fracture surface and apparent lack of necking, etc. would suggest fatigue. Possible overstress but I'm doubting based on the one pic. If you'd like, I can see if our guys in the metallurgical lab can take a quick look.
 
Rocket Steering

I also recently had the rod end bearing sheer off in the same location. No big deal, ordered and installed a new one. It performed fine for 710 hours. Looking forward to another 700!
 
Shimmy...

Upon the last of 5 landings from my post-mx checkout, I felt a strong and prolonged vibration from the rear that continued until I slowed to a walking pace. Inspection revealed that the steering link had sheared off as shown in the picture.

The pneumatic tailwheel and extended Bell fork seem to be more sensitive to the caster angle of the Van's yoke.

The vibration you felt was the tailwheel shimmy, which caused the rod end to fail.
 
Supports the observation and theory:

Shimmy => cycles => metal fatigue

Sounds like there's plenty of options to make this avoidable.
 
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TW Shimmy is most often a result of other than ideal castor angle.
Lesser contributors are pivot bushing slop and /or TW spring too soft or loose clamping of the leaf stack.

I have never experienced shimmy with a steering link.

On the other hand I have a Maule TW that is fine on grass, dirt or gravel but on pavement is a holy terror. I generally bring it to a stop with the tail in the air and then set it down to taxi back to the hangar on black top. The castor angle is wrong, and the leaf stack is very soft, but on grass and dirt roads it redeems itself, so I live with it.
 
One more for shimmy

I'll second those pointing the finger at a tailwheel shimmy event.

We collected data from a few pieces written by smarter people than me on the topic and put together this article on shimmy and what can be done to fix it: http://flyboyblog.com/2020/06/26/addressing-tailwheel-shimmy-in-rvs/

Earlier comments about the Condor2 fork presenting a shimmy issue a little more often are not wrong, though there are plenty of them flying with no issues (if it caused problems frequently, we wouldn't sell them!) As near as I can tell the main reason for the correlation is just that the tire is bigger and the fork sits higher, so it raises the tail enough to slightly change the angle into a more shimmy-prone condition.

I've kicked around the idea of making a mounting socket with a shallower angle to make an easy way to correct an assembly with a drooping caster angle, but for now, that project is on hold and the best way to handle a shimmying tailwheel may well be the rod-bending method outlined in the article above.

Cheers!
Blake
 
...
I've kicked around the idea of making a mounting socket with a shallower angle to make an easy way to correct an assembly with a drooping caster angle, but for now, that project is on hold and the best way to handle a shimmying tailwheel may well be the rod-bending method outlined in the article above.
Blake, at a fly-in this summer I spent some time looking at other tailwheel aircraft, and while I'm sure that the RV style is probably the lightest, some of the others look down right space-age in comparison. I think there is room for innovation here, for sure.
 
Blake, at a fly-in this summer I spent some time looking at other tailwheel aircraft, and while I'm sure that the RV style is probably the lightest, some of the others look down right space-age in comparison. I think there is room for innovation here, for sure.

What do you mean space age?
 
Add me to the list. My rocket steering link snapped just like the OP’s pic above after landing today in calm winds. Started with a shimmy as soon as I gently lowered the tail to the runway. This is second flight since I had the whole TW assembly apart for cleaning/lubricating.

Btw, I also have the condor and pneumatic wheel.
 
Is this primarily a condor pneumatic TW issue? I’m on the back order list for one and don’t want to add additional issues unnecessarily.

Anyone with the standard TW and rocket steering link having issues?

Thanks
 
I've had a Rocket tail wheel steering link for over 20 years with no shimmy with my solid tire.

I've had the link break twice and each time I replaced the rod end bearing. For most of these years the link functioned without issue.

My on-going issue is the tail wheel locking easily breaking lock. So much so that I no longer trust the steering and just use whatever rudder and brakes needed to keep us pointed down the runway.

I've disassembled, cleaned, and lubed the locking nubbin and verified its profile. I am not sure what steps to take to fix it. I have been considering replacing the link with the screen door springs.
 
I've had a Rocket tail wheel steering link for over 20 years with no shimmy with my solid tire.

I've had the link break twice and each time I replaced the rod end bearing. For most of these years the link functioned without issue.

My on-going issue is the tail wheel locking easily breaking lock. So much so that I no longer trust the steering and just use whatever rudder and brakes needed to keep us pointed down the runway.

I've disassembled, cleaned, and lubed the locking nubbin and verified its profile. I am not sure what steps to take to fix it. I have been considering replacing the link with the screen door springs.

Check the profile of the notch in your steering arm. If the corner has started to round off, the pin will retract very easily, and your wheel will go into castor mode more easily than it should. This is not going to be fixed by changing steering links or chains.
 
I flew the first steering link, made by Terry Jantzi, over 20 years ago. Since that time all my airplanes have used the link. It works well on my F1 rocket and I have broken one in all these years.
The key to longevity is maintenance. The tail fork needs to be disassembled, cleaned and lubricated twice a year or every 25 hours. Eventually you will likely have to replace the steering arm whether you use the link or chains. Proper lubrication will greatly extend the life of the arm. A little work with a chainsaw file can increase the life of the link but do not go too deep or the pin will not disengage. Carry a spare in your tool kit.
 
Thanks, Paul and Tom. After your pointing out replacing the link with chains won't fix the problem I understood why. I have two steering arms and both have the same issue. I'll try deepening the notch a little on one. I will also order a new one.
 
Keep a spare arm in your tool kit. In a pinch, I have put a drop of weld on the warn notch and used a chainsaw file to get it working.
 
Designed to release by cam only?

Check the profile of the notch in your steering arm. If the corner has started to round off, the pin will retract very easily, and your wheel will go into castor mode more easily than it should. This is not going to be fixed by changing steering links or chains.

Paul, it is my (limited) understanding that this should only release when the pin is actuated by the cam. In that case, I had the same release issue on my new Vans unit and surmised that it requires a flat contact area on each side for it to eliminate release due to force (torque), and only due to cam action. I then modified (with files) the pin and slot to ensure it landed home with some flat side exposed/engaged. Unexpected release disappeared for 200 hrs now.
 
I've had a Rocket tail wheel steering link for over 20 years with no shimmy with my solid tire.

I've had the link break twice and each time I replaced the rod end bearing. For most of these years the link functioned without issue.

My on-going issue is the tail wheel locking easily breaking lock. So much so that I no longer trust the steering and just use whatever rudder and brakes needed to keep us pointed down the runway.

I've disassembled, cleaned, and lubed the locking nubbin and verified its profile. I am not sure what steps to take to fix it. I have been considering replacing the link with the screen door springs.

How did you verify the profile? I had a this happen on an RV-3. The pin looked fine to me until I compared it to a new pin. The pin and spring run less than ten bucks from Flyboys. A new pin has a very squared off profile they refer to as bull-nosed.
 
BillL, "I then modified (with files) the pin and slot to ensure it landed home with some flat side exposed/engaged."

Hi Bill,

Any pictures, drawings? to further explain your modifications, please.

Thanks,

Merrill
 
So many questions and problems can be resolved forever just by reading the maintenance documents that Blake provides here:

tailwheel maintenance documents

Regarding one poster's comments on space age improvements, I respectfully disagree. While a product like he showed works great on a Super STOL, it's hardly the streamlined, lightweight simplicity that we need on 200mph machines. Ideally, we'd all be using tail skids (WWI technology), but those tail skids, while maintenance free and lightweight, make it so hard to spin the plane into a parking space. :rolleyes:

Cheers!
 
I verified the pin's profile using the docs at FlyBoys pointed to by vfrazier. I have two arms on order.
 
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