Tailwheel Spring Tension: A video of how to do it

[Bruce Fenstermacher]

Bob,

I believe it was substantiated from Scott/Tyco just before they sold out some years ago, that arms were made with material that was to soft. This might not have been the problem in your case.

I don't understand how one spring could ever fight against the other because at the same time one spring is pulled on the other is given that much slack. Tension or having both chains tight from the start does load the steering arm and could effect the way the tailwheel releases. Neither the video or Scott instructions call for tension on both springs at the same time.

Remember the video is from and for a Maule not a 170. Maule of course has their own design tailwheels and designed the compression springs to work with them. The compression springs were designed with different rates to assist with shimmy with the Maule setup meaning a Maule tail wheel. I don't know if Maule is now using the Scott 3200 as shown on this video but I'd be surprised. I don't know it the Maule tailwheel will shimmy without the designed for them compression springs but the Scott 3200 should not shimmy without them and correcting a shimmy with the Scott wheel does not involve the steering springs at all.

I think the differential rate compression springs were a later development of Maule to help correct an issue their tailwheel had that Scott did not. That is why most people say Scott is better. Somewhere along the line Maule thinking if their differential rate compressions springs helped their tail wheels then it could help others. At least that is how they've become to be marketed.

Bottom line here is if you have a Maule use the stuff Maule designed and used and the Maule adjustment procedure as a baseline, it should work. If you have a 170 use the stuff Cessna designated and it manufacturers adjustment, it should work.

Of course to muddy the waters since the video Maule has a Scott 3200 it should probably be using tension springs. And I'll bet when the optional Maule tailwheel was installed on our 170s with the tension springs it didn't work very well and that is why you never see a Maule on a 170.

I want to note that when I mention a Maule tailwheel above I'm talking about their larger model the equivalent of the Scott 3200 not their smaller wheel the equivalent of the Scott 2000. The smaller one intended for smaller aircraft such as a Cub and works just fine with the smaller tension springs designed for smaller aircraft.

Bob after all of this it appears that you have found a slight compromise of the correct adjustment that works best for you just as I have for my aircraft and that is pretty much what I suggested way back in my first post here.

[GAHorn]

Whew!
Well, Bob...I didn't realize I was not "settled". (I think my strong opinions sometimes are interpreted somewhat differently than intended due to the internet/written-word thing.)

There are a few fine-points that are being mis-stated or misunderstood, even after all the discussion which has transpired.

The chains for a Cessna 170....should have NO SLACK.
The steering springs should be..... tension springs.
The tailwheel steering chain-lengths should be rigged with the tailwheel supported (on the ground) at typical aircraft operating weight.
PRIOR to rigging, the tailwheel should be in proper condition with no defects. (Proper parts, properly assembled, lubricated, and the release-pawl/detent should operate properly.) Note: A failed pawl/detent may "jam" and prevent the unlocking of a Scott tailwheel, resulting in a bent steering arm. Pre-flight inspections should include the pilot checking the proper operation/action of the tailwheel detent...BOTH directions.

Tailwheel shimmy is not caused by the steering chain tension in any way whatsoever. It is caused PRIMARILY by improper tailwheel caster and/or improperly maintained tube/tire and leafspring/bracket assemblies..

As for the steering arms and rudder-deflection relationship which still seems to be misunderstood regarding Cessnas versus other aircraft:

The Cessna aircraft rudder-cable circuit has NO INTERCONNECT. (The rudder pedal/cables may BOTH be pushed forward simultaneously. Pushing ONE rudder pedal forward...does not pull the other aft at all except via the cables running down thru the fuselage. The pedals are only held in their forward positions via tension springs which are below/fwd of the pedals.) Therefore a pilot who is standing on BOTH rudder pedals simultaneously...(such as when adjusting his seat, or when applying heavy-braking-effort to both wheels, etc.).... can inadvertently apply excessive PULL on both sides of the rudder-circuit. This can stress the rudder bellcrank and rudder itself, but If proper tailwheel tension steering-springs are used....they will absorb that conflicted-input. If compression springs are used they may "bottom out" and bend the steering arms. (And may also damage the internal tailwheel steering-cable brackets/bulkheads of post-SN-26505 aircraft.) The rudder-deflection may exceed the limits of an unlocked tailwheel, however once again, the tension springs will accomodate that. (In certain OTHER aircraft such as Maules, Stinsons, and some Pipers... the rudder-cable-circuits and/or rudder-pedals themselves, have an inter-connect which prevents the stresses imposed by simultaneious rudder-application from being transmitted to the tailwheel steering system. In those OTHER aircraft, compression springs are not a problem. Compression steering-springs are only suitable for aircraft with inter-connected rudder-circuits and/or tailwheel installations which have rudder-deflection-limits matched to the tailwheel deflection angles....NOT CESSNAS.

[N2865C]

The tailwheel should have only 3 internal compression springs for a Cessna 120/140/170 (not the 5 depicted in some parts books, which applies to C-180/185/L-19 and Pawnee aircraft.)

I don't disagree with you on this and it makes sense based on what little I know about 3200's.. Is there any documentation you can point me to that would back this up?

[GAHorn]

The tailwheel should have only 3 internal compression springs for a Cessna 120/140/170 (not the 5 depicted in some parts books, which applies to C-180/185/L-19 and Pawnee aircraft.)

I don't disagree with you on this and it makes sense based on what little I know about 3200's.. Is there any documentation you can point me to that would back this up?

Sure! Try page 154 of the 170-B IPC.


(Now tell the truth....you actually DID expect a smart-A__ answer from me on this didn't you?)

Scott 3200 Pg 154 B-IPC.JPG

[N2865C]

I don't disagree with you on this and it makes sense based on what little I know about 3200's.. Is there any documentation you can point me to that would back this up?

Sure! Try page 154 of the 170-B IPC.

(Now tell the truth....you actually DID expect a smart-A__ answer from me on this didn't you?)

Ummm... no, it was a serious question. It's interesting that in the aircraft spruce catalog the picture of the 3200 shows 3 springs but the parts list shows 5. http://www.aircraftspruce.com/catalog/l ... 3200tw.php
Does the 180-185 and Pawnee parts manual show 5 springs? "Back in the day did all 3200's come with 3 springs and later models come with 5 springs? Are there any Scott or Cessna instructions for modifying the 5 spring 3200 for 120/140/170's. Inquiring minds want to know.....

[Bruce Fenstermacher]

George I hadn't thought about the pilot pushing on both pedals and tensioning both steering cables at the same time. Hmmm do I do that? Only when I want to go straight.

[GAHorn]

Well...to be accurate and to make certain I did not give the wrong impression.....Application of pressure to both pedals does not tension both of the steering chains any more than usual ...the pre-SN26505 aircraft...unless one uses compression springs and have the chains adjusted improperly or some other failure occurs. But it does apply additional stress to the rudder belcrank and rudder hinges, etc,., and that can lead to tailwheel steering arm failure. On the later post-SN26505 aircraft (with external tailwheel steering cables) then simultaneous pressure of both rudder pedals CAN cause failure of the tailwheel steering assy. and if compression steering springs are used, can also bend the steering arm.

In correctly rigged and properly equipped systems the steering arm will likely bend only in the event of a malfunctioning tailwheel pawl/detent failure.

[lowNslow]

If you are pushing both rudder pedals there should be no effect on the springs at all. If you are pushing on both pedals the rudder does not move therefore there can be no change in the tension on steering cables regardless of the type of springs. There would be additional stress on the rudder bellcrank.

[GAHorn]

If you are pushing both rudder pedals there should be no effect on the springs at all. If you are pushing on both pedals the rudder does not move therefore there can be no change in the tension on steering cables regardless of the type of springs. There would be additional stress on the rudder bellcrank.

That's what I said. Or at least thought I said. Except that post SN26505 aircraft may place additional stress on the tailwheel steering if everyting is not rigged according to Cessna. (and, of course, all commentary applies only to aircraft that have no other failures in that system.)

[Bruce Fenstermacher]

Karl, I didn't understand what George thought he said.

But you and George are right I see that now.

[robert.p.bowen]

I don't understand how one spring could ever fight against the other because at the same time one spring is pulled on the other is given that much slack.

It seems intuitive that this would be correct. Perhaps the next time you have occasion to jack your tailwheel up for some other purpose, turn the tailwheel to its stop (just before break-out) and, holding the tailwheel in that position, lower the tail to the ground. I think you'll find that with the rudder full over, the off-side tension spring is--slightly--stretched, thus loading both arms at the same time.

But having said this, I don't think it matters. The off-side steering arm loading is slight, slight enough that if the tailwheel is is good mechanical shape, no binding should occur.

I am fortunate to own and fly three tailwheel aircraft: a C-170B with Scott 3200A, a Maule M7-260C with ABI 3224A tailwheel and a Stearman with its stock 10:00SC tailwheel. The ground handing habits of the 170B and Maule are quite similar, with the 170B being slightly more responsive. The Stearman is a different animal. What I've learned from this thread is I likely should replace the Maule's compression springs with tension ones. The compression springs may have been needed for the shimmy-prone Maule tailwheel assemble, but aren't needed, and may well be mechanically dangerous, with the Bushwheel set-up.

I now believe most steering arm bending results from excessive rudder input before the tailwheen has had time to respond. When that condition exists, the spring on that side really exerts lots of load on that steering arm. If the chain is too tight, it exacerbates that effect.

Thanks particularly to Bruce for his well-stated summary.

[sfarringer]

The scenario where the tailwheel steering arm experiences unusually high force is when the tailwheel steering arm has been pulled to one side by the rudder, and then the rudder position is reversed. When stationary or at low speeds, the tailwheel cannot respond. This requires the steering spring to stretch approximately twice as far as the scenario where the tailwheel is in trail and the rudder is moved to the stop.

Steve
N2568V Ragwing

[GAHorn]

I don't understand how one spring could ever fight against the other because at the same time one spring is pulled on the other is given that much slack.

It seems intuitive that this would be correct. Perhaps the next time you have occasion to jack your tailwheel up for some other purpose, turn the tailwheel to its stop (just before break-out) and, holding the tailwheel in that position, lower the tail to the ground. I think you'll find that with the rudder full over, the off-side tension spring is--slightly--stretched, thus loading both arms at the same time.

....

Another way this situation may occur (without gerrymandering the tailwheel while it's off the ground) is to imagine taxying in a left turn, under-way with left rudder applied (such as turning left off a runway with no high-speed exit) and then full-rudder application to stop the turning-moment because you did it while travelling too fast or the left cross-wind gusted and gave unexpected assistance to the turn.
But, as you say,... it doesn't matter. The (tension) springs are designed for that very purpose. And besides, before any damage occurs to a healthy set-up....the tailwheel unlocks. (And then you'd better be ready with that right brake!)

...for that very purpose.... Steering springs are designed for the specific purpose of allowing conflicting inputs of a steerable-tailwheel and full opposite rudder application. That's why it's inappropriate to consider them inadequate for positive steering, thereby replacing them with stronger/compression types.

[GAHorn]

A related topic regarding tailwheel steering are "which" exact tension springs to use?

Aircraft Spruce sells a "kit' which is NOT correct for the 3200 tailwheel. Their "lightweight" steering spring kit is for the solid-rubber-tire model 2000 tailwheel, NOT the 3200. That spring is only 3/4" in diameter, 4-1/2" long, and made of a lighter-gauge wire (about .12").

These are NOT to be used with the 3200 tailwheel.

The 3200 tailwheel uses the larger diameter (1-1/4"), but shorter (4-1/4") stiffer spring, and is made of .16" wire. it is SPECIFICALLY: SCOTT PN 3239 (This is a national secret and I cannot divulge how I found it without ...as Ol'Gar's friends in Kansas City say.... "whacking"you.)

The difference is not well illustrated in the IPC, but can be discerned by noticing the different part-numbers Cessna uses: PN 0442008 for the Scott 2000 (old Scott 3-24B) tailwheel, ... and Cessna PN 0442011-4 for the Scott 3200. (Neither of which would one likely wish to purchase from Cessna since they cost well over $100 each.)