Tailwheel Chain breaking While Taxiing

[Jim Herd]

I finally finished repairing damage on my BHP from landing with one tailwheel chain dangling due to a stretched connector link. Doing taxi trials yesterday (very experienced tailwheel pilot in the front seat) and ...... BOTH chain links stretched and disconnected! The chains were installed slightly loose when centered, and the springs did not fully compress at full deflection. We have installed new links with chains even more slack - see photo. But is something else going on here? Maybe the detent on the castor is too stiff and not letting the breakaway happen correctly?

I have searched for answers, and the way we had the chains seems loose enough. Now we have them 2 links looser but have not taxied yet. How much force should be required to break away the castor detent?

[whee]

I’d bet money the issue is those compression steering springs. They are a good way to break chains and steering horns. Ditch them for extensions springs and your problems will go away.

When you apply rudder the springs compress. Once fully compressed something else has to give. That’s why your links are stretching. I broke chains and a steering horn with those springs on a BH. A friend did the same thing in a Maule. We both replaced them with extension springs and no problems since.

[Battson]

I will double down on that. Compression springs seem a bad idea to me.

[Nev]

Jim, just to clarify, is the chain itself breaking, or is the stretch in the chain allowing the end links to fall off ? Mine "fell off" several times, probably due to it stretching under load. I would say that it is normal to stretch during the first few uses and probably no way to avoid this as it goes under load. I now lock wire mine in place at each end of the chain and it appears to have solved the issue. Incidentally, after discovering one chain hanging loose after flying circuits, I removed them both flew it for about a month with no chains. I really liked how it handled with the exception of taxying in a strong cross-wind.

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[AKKen07]

I ditched my compression springs for an Aeronca spring from Spruce. Much better. I also safety wire the spring ends.

[AKKen07]

I forgot to mention I also ditched the chain links and just made a couple steel cable links from the springs to steering arms.

[joehmason]

This problem is not unique to compression style springs. The wire links that come with the chain kits are not strong enough and tend to bend open and disconnect. They don't bend when you turn, it happens when you are in a turn and try to straighten the tailwheel up. It is in the geometry of the tailwheel plus the small amount of twisting flex in the tail spring.

The tail of the Patrol is heavy. I'd venture a guess that it is around twice as heavy as a cub. When you get a person in the back seat and some baggage and fuel, it makes it even worse. On our first engine run and taxi test I felt a pop in the rudder pedal and found that the link opened up and completely disconnected from the tailwheel horn. This was with 10 gallons of fuel on board and just me in the front seat.

I ended up safety wiring the links to make sure they don't bend open, and I had to change my taxi technique. Use a little brake to help straighten up the tailwheel, and then once straight, taxi as usual. When conditions permit, use neutral or slightly down elevator to help bring some weight off of the tailwheel. It all helps with controllability and keeping unnecessary tensions on the rudder horn, chains, and tailwheel horn.

Also, don't loosen the chains up too loose. I flew about 50 hours with the chains too loose. After tightening them the directional control was significantly better. There is a good YouTube video (https://www.youtube.com/watch?v=AmD6iiQic84) of setting up tailwheel chains for a Stinson. I think it has been shared here before. Skip to the 45 minute mark and watch the last couple minutes. The information is relevant for most tailwheel setups.

[Battson]

Good advice there.

I would add, those clips should not be bending like those pictures, under normal conditions. I have bent them slightly, and only occasionally, but only when something was wrong (i.e. I did something I shouldn't have). I have no idea how that could have happened. Cheaply made clips maybe...? The ones I bought (assume made in the USA) have lasted very well.

[alaskabearhawk]

FWIW, this is my tailwheel chain/spring setup.

IMG_2704.jpg IMG_2703.jpg

[Bearhawk Aircraft]

Hey Guys do not install the compression springs on any of the bear hawks, the springs do not have enough travel and will cause several issues. The proper chains are detailed in the picture below and the manual that was included with your tailwheel.
Tailwheel springs and chains.jpg

[Bcone1381]

I thought someone might want a link. I used this install but not yet tested, I'm still putzing with mine so exercise due diligence.

https://www.aircraftspruce.com/catalog/lgpages/tensiontype05-11457.php

[Nev]

I use the same chains, with springs from the hardware store that look very similar.

[svyolo]

I bought the kit from Spruce, but the chains were 1 link too short. Luckily I live very close to one of the US's last remaining awesome local hardware stores. I got identical chain from them, and could have also gotten springs all for 1/10 the price I paid at ACS, I will take one of the springs with me today and get the correct spec at that store and post it here, along with the brand of the chain.

[alaskabearhawk]

I don’t know why my photos didn’t post, so I reloaded them

[Jim Herd]

I made the mistake of ASSuming I would get emails if there were any responses posted to this forum. So I only just refreshed my browser to see all the help. DUH! In parallel with all the posts above, I have been working from first principles with a few tailwheel experts at my home field (KMEV). It is uncanny that – after a bunch of analysis & testing various solutions - we came up with the exact same conclusions that were posted above. It is also comforting that I am not the only Bearhawk owner that has had the tailwheel chains disconnect. In my case, as a relative rookie, it led to a runway excursion and damage. In the moment of landing, I had no idea why I could not correct to the left, so it kept turning right. So this is a non-trivial issue. I have a few additional comments …..

First, the Bearhawk community is awesome, and I am very happy to be a member! During the long & slow repair work, we did a lot of upgrades to the basic aircraft that I bought from the builder a year ago. So I suppose there is a silver lining because it is a totally different aircraft now – new instrument panel, mufflers added, new professional paint job, sump heater, and many more.

I think there is a problem with safety wiring the chain clips to prevent them from opening up and releasing under excessive tension. Those clips act as a “weak link” to prevent more serious damage such as a broken rudder horn. If the clips are failing, the ROOT CAUSE should be fixed, rather than masking the problem.

Undoubtedly, from all the posts and from my own deep analysis & testing, COMPRESSION SPRINGS SHOULD BE FORBIDDEN on these tailwheels! The design of the tailwheel is such that much more spring length is needed to absorb excessive tension. The compression springs allow only about one inch. Stretch springs allow something like three inches. This is necessary because the kingpin detent paul will not release due to rudder pressure. It releases only when the tailwheel is 30 degrees to either side – due to the cam action on the paul. So strong rudder pressure with less than 30 degrees of wheel deflection will be absorbed by the chain system (weak link) if the compression spring is fully compressed. So the weak link clips will not be over-stressed if the springs always have extra motion available.

My Patrol had compression springs when I got it, and after the initial failure I replaced the entire system - with exactly the same set-up. I did not have the benefit of the Bearhawk Tailwheel LLC documents, and maybe the builder didn’t either. He gave me extensive build files, but I found nothing on the tailwheel. Eric at Bearhawk Tailwheel responded very well and sent me the documents. What put me off the track was the statement in the manual (and apparently from Bob Barrows also) that compression springs are not recommended but are okay if the chains are slack. So I loosened the chains and went out taxiing with normal and extreme maneuvers that do happen in the real world. BOTH chain clips broke open! So that was the famous AHA MOMENT!

My buddy had a set of new Cub stretch springs. We installed them with chains just slightly loose. Repeated the taxi testing with no failures! BINGO! Those chains seemed a bit “soft” and normal taxiing was a bit “mushy”. So I installed slightly stiffer stretch springs. If compression springs are used, the amount of chain slack necessary to avoid chain clips opening up would be huge – so it would be just like having no chains at all.

And yes, I will be more “kind” with my taxi technique, such as unloading the tail with the elevator & a little power for tight turns. And I think we all need to be aware that we can not break the tailwheel to achieve castor mode unless the wheel is deflected at least 30 degrees. Inside that angle, extra rudder pedal force will do nothing but stress the system. And of course, it is actually impossible to know the tailwheel angle from the pilot seat.

As I understand it, the ubiquitous Scott tailwheel works perfectly with compression springs – because the breakaway force is less and does not require a certain tailwheel position to break away.

Attached are a few photos. Also, my wife rigged up a video camera on the stinger, with the latest set of springs & chains. You might be interested to skim through the video. It seems like the system is working well now, but I have not flown with it yet. Here is the video: https://tinyurl.com/3uk4s9hc


THANKS for all the help. I am at peace, and regaining confidence in my set-up. And I remain humble and eager to absorb other knowledge.


From Jim Herd

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[jaredyates]

Thank you for the follow up Jim. If you would like to subscribe to a thread for email notifications, there is a link to do that on the upper right. If you would like to do this for every thread by default, you can click on your username in the upper right, then select "User Settings". Once there, select the "Notifications" tab. On that page, there is a check box to automatically subscribe to new posts. Let me know if this doesn't make sense and we can work on it, it may be slightly different depending on the browser.

[Nev]

You can also tick "be notified of private messages" which I find helpful.

[Nev]

Jim great work and glad you've solved the issue and back on track.

I think there is a problem with safety wiring the chain clips to prevent them from opening up and releasing under excessive tension. Those clips act as a “weak link” to prevent more serious damage such as a broken rudder horn. If the clips are failing, the ROOT CAUSE should be fixed, rather than masking the problem.

I think we might be seeing two different failure modes here. One like you've experienced where the compression spring is exerting too much force on the whole system and the chain clip is acting as the weak link and opening up.

The second is where the chain wriggles its way between the chain clip and simply falls off. I've had it happen several times. Probably tightening the chains (removing a link) might help to prevent this, but I then run the risk that in the event that it does happen, or a breakage occurs, there's now tension on one side of the tail wheel and a runway excursion is more likely to occur. This is why I'm lock-wiring the chain clip closed - not to strengthen the clip, but just to keep it closed.

[jaredyates]

Well said Nev, and we should also be sure the reply above from Ken doesn't get lost about using the same material we use for control cables, with Nicopress ends. Russ Erb did a quick write up in the Beartracks about it and after I lost a spring on the runway during transition training on our first plane, I installed them also. It is on my to-do list to make a set for 303AP but I no longer have a pile of scrap cable buts to draw from.

Here is the link. If anyone doesn't have access let me know and I'll send a pdf.

https://bearhawk.tips/1639

[Jim Herd]

Good point about the weak link clips being able to wriggle loose! I would have thought they could be configured (bent) to remain closed with a bit of tension, sorta like a paper clip, to stay in place. And still be able to act like a weak link. But I am the rookie here, so I am all ears. And maybe that idea has been tried and failed. There is obviously a lot of room here for personal preference. That's why these aircraft are so attractive - not rigidly controlled by government dictators.

And I will certainly reconfigure my forum account settings to get emails as they are posted.

THANKS. This thread has been priceless for me!

[Jim Herd]

Regarding the tailwheel chain clips "wriggling loose". They come from Aircraft Spruce with a considerable gap, so I can see how they can self-release without any heavy tensile load to bend them open. But is it reasonable to bend them on assembly to close the gap and even introduce a little preload to keep them closed? Just like a paper clip. This should allow them to work as a weak link, and eliminate the possibility of wriggling free.

Also, note that these clips are labelled by spruce: "CLIP FOR COMPRESSION SPRINGS". Do they have a different clip for stretch springs? I could not find one.

I don't mean to be too anal, but I think this is one area where extreme attention to all details is critical. I bent my plane to teach me that!

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[Battson]

I think the gap is designed to "spring open" against the wide end of the chain link, hence keeping it from wiggling loose. Still, I always safety wire mine, for good measure. Only once have I had one jump off. That said, for about a year I flew without tailwheel steering chains, that was also perfectly acceptable.