Tailwheel Steering Connections

[Nev]

Awesome Ed. Thanks. Mine appears to be steel hardened to Rc 47-52.

[Battson]

I assume that's your spring which is steel. Titanium spring should bend less, which may also improve your results. It would also be lighter which is good.

[marcusofcotton]

Tail wheel shimmy is one of those enduring topics. It has occurred to me that no matter the geometry of a given tail wheel, one universal trait and contributor or at least, inefficacious anti-shimmy aspects of most tailwheels designs is that they are free wheeling. Some designs have a dampener or friction device built into the pivot point, but with no rigid pivot connection between the airplane and the wheel, that tail wheel wants to swivel.

Not to say that felt shimmy can’t be reduced or eliminated with proper geometry, tire pressure, and rigging, but the inherent underlying issue should be recognized.

My daughter's Cassutt was an exception to the rule - had a rigid link from rudder horn to tail wheel, nice and clean. Of course not much spring deflecting going on in operations either...

[marcusofcotton]

I'm wondering if having a 10° bend downwards in the stinger would help. Any thoughts ? The idea would be to recline the kingpin angle (by another 10°). My idea is to make a second stinger to try it with a bend at the aft end near the tailwheel.

I assume that reducing tire pressure would have a similar but smaller effect.

This is why API Tailwheels offers the option of 10° or 20° mounts on their round spring models. https://apitailwheels.com/
Eric, this might be something for you to consider???

[Nev]

I assume that's your spring which is steel. Titanium spring should bend less, which may also improve your results. It would also be lighter which is good.

I think mine is probably steel Jon. It's reasonably heavy and had the appearance of steel. My plans mention steel too. Maybe Mark might weigh in to confirm what is being supplied with the kits. Are titanium stingers available ?The idea of changing the tailwheel end is a good one. Or perhaps even making an adapter. However one point is that with the tundra tire there is very limited space to clear the stinger when the wheel is facing forwards.

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[AKKen07]

A titanium spring would make you more nose-heavy…

[Utah-Jay]

Nev

Could be the lighting in your photo, could be it is discolored due to backcountry use, but my round spring is a very different color.
I do think mine is titanium
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[Nev]

It's the black paint on mine Jay
But yours does look different to mine for sure - before I painted it, it had a light coat of rust, hence the paint. There must be more than one type.

[whee]

The factory round springs are stainless steel. The ones for the 4 place are pretty beefy so I hate to imagine that it would take to bend one. Mine has been great.

The first attempts at putting a T3 on a BH used some kind of gas struts instead of springs. Kind of a cool idea. Idk why they didn’t continue with it.

I sure wish Mark or someone would come up with a titanium or composite tail spring. I’d order one immediately. I tried to get a bit for a carbon fiber tail spring and all the salesman/owner/engineer would tell me is that it would be “very pricey.”

[Utah-Jay]

The factory round springs are stainless steel.

Makes sense, Ti would be very expensive as well.

I would worry about a CF spring’s durability in an area that is prone to getting rocks and debris flying around

[Bcone1381]

Google says
AISI 6150 steel is chromium vanadium type spring steel. SAE 6150 spring steel combines spring characteristics with excellent resistance to both abrasion and shock. Hardened 6150 steel offers excellent toughness and shock resistance which make it a suitable alloy spring steel for parts exposed to stress, vibration and shock.

To me the tailwheel is the most abused airframe item and needs constant attention. Failure of this item is not an option. Experimentation is what we are about and this demands decision making using factual material engineering data. I am a pilot, not an engineer and would need an engineer like Bob to specify the material.

I'd also want Bob or an expert to consult me on adjusting the angle of the spring. For example.....Can I bend the spring cold or will I damage it that way? Maybe it needs to be heated, or heat treated after its bent?

NEV, Thanks for the reference of the steel specification on your Plans. The Patrol Plans do not give this material spec. it is merely a heat treated value. Additionally the Patrol Book Specs are not the same as the Patrol Plans Specs and neither of them match the specs stated in NEV's photo above.

I wonder if the Patrol Spring is identical to the Model B and the Five? Is it Beefier or use a Different Material?

A couple less invasive things to try. Tightening the wheel bearing in your tailwheel so its got a bit of rolling resistance may help reduce tailwheel shimmy. High Tire Pressure making the tire "rounder" induces shimmy.

[Nev]

I'll try reducing the tire pressure somewhat. That might also improve clearance in the yoke. Theoretically it would recline the king pin in the correct direction too, but probably by a very small amount.

[Battson]

Edit - will make it a separate post.

[Mark Goldberg]

The tailsprings on the 4 place & Model 5 are 6150 steel hardened to a Rc of 47-50. The tailsprings on the Patrol, Companion, & LSA are 17-4 stainless hardened to a Rc of around 45-46.

We have not researched a titanium spring. It might be a good idea. Bob told me a composite round spring would have one very undesirable feature - when it has a problem it would snap/break. Unlike a metal round tailspring which would bend but should not break.

It is possible to bend one of these round tailsprings. But they are pretty strong and it is not just real easy. But if you have a bearing press and are careful to keep the bend on the correct plane - several builders have done this. Just putting in a 2-3 degree bend can make a difference if your tailwheel kingpin is leaning the wrong way.

I would never think a 10 degree bend is needed. Just a few degrees would accomplish getting the kingpin laying properly. If it isn't already. Mark

[Nev]

Thanks Mark, all good to know.

[rodsmith]

I appreciate the information on compression vs tension springs for tailwheel steering. I have sent the Maule anti-shimmy kit back to Spruce and ordered the tension spring kit. I built my fuselage before there were plans using a round spring. I took my best guess at the angle for the spring but looks like with any weight on the tail the tailwheel will angle the wrong way. My sprring is hardened stainless, bought it from the company that makes them for the Pitts model 12. Debating whether to try to bend it, or butcher Eric's beautiful tailwheel and adjust the attachment angle. Way past being able to adjust the spring mount angle.

[Battson]

To me the tailwheel is the most abused airframe item and needs constant attention. Failure of this item is not an option.

Failure is not an option?? Nobody told my tailwheel that, it has failed about a half a dozen times! This isn't a Bearhawk issue, it just comes with the territory off airport.

But, if you can name a part on the entire tailwheel assembly and tailwheel structure, it has failed in some way in the last 1000 hours. I would like to shout out to Bearhawk Tailwheels, as this part is surely the most reliable. Aside from one strange crack which made no sense to any engineer, including Bob, it's been flawless.

Things that have failed due to heavy off airport use and abuse (these are all unique instances, it didn't all happen at once):
- Hat bracket bolts, snapped
- Hat bracket, bent
- King bolt at fuselage, bent
- King bolt at tailwheel, snapped
- Leaf spring, snapped one leaf
- Tailwheel bearings (all 3), spalling
- Tailwheel body, cracked in unexplainable way apparently unrelated to off airport use - certain strong enough for off airport use!!! Gets my full vote of confidence
- Steering chains, broken

I am still waiting for a flat tailwheel tire, so far so good

I guess my point is, while failure isn't a good option, it's seldom a major issue for the aircraft in terms of safe operations etc.

[Bcone1381]

I agree with your point.

[kestrel]

Last night I was going to post the same objection, but decided not to. Now that Battson has opened the gate, I'll follow. I once had the rod type tailwheel spring of my RV-4 snap off at the tail end. The builder had drilled the holes the wrong way and 1600 hrs later it failed. What did I do? I disconnected the chains, put the tailwheel in the baggage and flew home. No drama.

I have had a flat tailwheel. I had flown to FL from NH during the winter. I pulled the main skis but left the tail ski on. That drew some looks in FL! At one of the stops on my way home I noticed that it felt funny while taxiing in for fuel. There were no people or services available so I flew home with minor scuffs to the base of the tail ski.

[Brett795]

I had a composite tail spring fail on a Quickie Q-2 that I was flying back for a new owner. Before I left, we had re-routed the rudder cables & made a bracket where the cables exited the tail and went to the rudder instead of the plans/ kit idea of going directly to the tailwheel horn and then rigged to the rudder. On this particular plane w/ a composite tail spring, it’s not if it will break but when it will break. I told the buyer I thought it may be damaged before we got there and had it on the list to change out once we got it home. I guess that’s another reason why I’m not a fan of a composite tail spring.
In the end I still has rudder authority, just no tail wheel. Only damage on the next landing was the bottom of the tail that we grounded the rest of the way to make the repairs. Another great reason to be proficient in wheel landings on that plane.