Tailwheel Spring Tension: A video of how to do it

[robert.p.bowen]

On the Maule forum, there's a video of how to rig the tailwheel chains correctly so that the arms don't bend. It's at:

http://www.youtube.com/watch?v=QtokU8mIDQk

The video shows the rigging procedure with weight off the tailwheel. It seems to me they got it right in the video, except one should confirm that rigging by turning the tailwheel to the breakout point, left and right, lower the fuselage to the ground and swing the rudder to the stop to confirm that the slightly different geometry with weight on the tailwheel doesn't mean a link needs removing. In my view, with this slight enhancement, the video is spot on.

[Bruce Fenstermacher]

Interesting. Here is another: http://www.youtube.com/watch?v=u3qFwzPNBgE

Of course it is worth noting that while this is a Scott 3200 tailwheel it is a Maule which has different steering arms and geometry and of course those compression springs. The Scott instructions for installation on a Cessna 170 say to adjust the chains so there is neither slack or tension on the chains. Scott does not specify whether this should be done with the wheel in the air or on the ground. I think that Cessna says the chains should be adjusted on the ground, or maybe that was George.

I personally have found the geometry of my tailwheel and leaf spring set up changes the tension on the springs making them tighter when in the air than when they are on the ground. George has reported that this is not the case. I adjust mine to be a tad loose on the ground similar to the video, knowing mine get tight in the air. Your setup and experience may vary.

I've never tested to see if moving the rudder on my 170 to the stop will actually move the tailwheel far enough for it to be in the unlocked position like the video. I just assumed it did. And if it doesn't there isn't much we could do about it.

[robert.p.bowen]

What I've never understood is why all tailwheel chains aren't installed about the same. I believe the compression springs are intended as a means to control shimmy in lousy tailwheels such as the Maule, but for those using a Scott 3200/A or the Alaskan Bushwheel 3200/3224A units that aren't shimmy-prone, I don't follow why tension springs and chains installed about as shown in the video, wouldn't work for all T/W aircraft.

Just because Scott says install the 3200 on Cesna's with taut chains isn't persuasive, particularly if that results in a rigging that can bend the steering arms. Lots of manufacturers publish bad info--like Lycoming and its advise against LOP operations and best economy is at peak EGT.

So my question remains...why not rig our airplanes as shown in the video (and as slightly revised as I suggest in the above original post)?

[Bruce Fenstermacher]

Bob,

I'm not trying to start an argument. I never said the video had no value. In fact I said the video was interesting. For example I never checked to see my rigging or the Scott recommended rigging unlocked the tailwheel on a 170.

I offered in contrast what the printed instructions for our aircraft are. The fact I offered how I adjust my chains on my 170 which is not exactly how the Scott instructions state I hope shows that I think every aircraft needs to be evaluated and adjusted on its own. But the manufacturer's instructions should be the baseline and I know someone will point out that from a legal point what we should be following to a T.

Using your argument that a manufacturer at one time or another, put out information we now find in contrast to an operating practice that can work, one could argue we shouldn't follow any manufacturer's instructions. Is that your argument? No I don't blindly follow manufacturer's instructions though I probably won't go wrong in doing so. Sometimes I exceed them like changing my car oil every 3000 instead of 10,000 miles or what ever the magic number is these days.

Why aren't all tailwheels on all aircraft adjusted the same? Because all aircraft tailwheel geometry is not the same. As I noted our collective has even seen slight variances between individual 170s. I have time taxiing 3 different 170s and the tailwheel response of all three is different yet the rigging visually appears the same.

As for the compression springs the reason we are against them on a 170 is that we have seen first hand the damage caused by them on our aircraft when they bottom out and cause damage to the airframe.

I've never operated a larger Maule tailwheel the equivalent of the Scott 3200 which is what we are talking about here but I have operated the smaller Maule the equivalent of the Scott 2000 and they work just fine.

[GAHorn]

Oh, dear! I am soooo sorrrryyyy when misinformed people make video clap-trap such as the first one being discussed. Why? Because "a picture worth a thousand words".... means an INCORRECT picture is a thousand-times more convincingly INCORRECT. Their intentions (to help others) are good...but their own understanding is wrong.

At the risk of the appearance of "flaming" ....(not my intention).... the first video shows a complete lack of understanding with regard to the purpose of the "detent" and the actual purpose of the chain and spring.
(BOTH videos use the compression springs, which are INCORRECT for Cessna 170 aircraft. TENSION SPRINGS ONLY on a Cessna. Cessnas have different rudder-throw than Maule's and certain other aircraft. Additionally, the wheelbase is different on different aircraft, which affects the turning radius of the aircraft versus the tailwheel.)

It's NOT the purpose of the steering chain springs to provide input for steering. (A common misconception and one reason that compression springs are sometimes mis-used in Cessnas.) The purpose of steering springs is to allow additional rudder-movement, beyond that normally used for steering on the ground (and to allow for tailwheel movement due to hard landings, etc..) That first video incorrectly demonstrates the detent-release (as if it) occurs in-flight to avoid steering-arm damage. NOT true. That is mostly the purpose of the springs.

The purpose of the detent is to allow braking to "pivot" the aircraft more tightly during ground operations than rudder-movement alone will provide, as well as to avoid damage to the steering mechanism (such as the rudder bellcrank, chains, etc.) should the aircraft momentum (sideways or turning-moment) exceed that anticipated by the pilot.

The reason that steering arms (on the tailwheel) bend is because mechanical failure of the detent to unlock, usually due to rough/incorrect/failed pawl/detent. (Although the first video does get one thing right.... if you use compression springs and your detent fails ... you WILL damage something! You'll also damage things in a Cessna if you use compression springs and apply pressure equally to both rudder pedals at the same time.) A contributing factor to bent steering arms was INCORRECT ALLOY utilized for a short time by Scott/Tyco. (A short production-run of the 3200A steering arms were made of a too-soft aluminum alloy which eventually bent regardless of how careful or correctly-installed they were. Those defective parts should be replaced.)

Regarding the second video: It's primary intent is to illustrate the correct angle of the king-pin or table which provides the correct caster of the tailwheel. It does a good job of showing that relationship.

It may be relevant.... (in light of Bruce's comments regarding how his steering chains behave differently (tighten when the tailwheel is off the ground) than the rest of the fleet.... to note that he does not have the standard leaf-spring installation shown in the IPC. His installation does not conform to the IPC.

[robert.p.bowen]

Very interesting dialog. Thanks to both Bruce and George. I posted not to be argumentative but rather to learn. Both of you helped with that.

A final question (I'm sure you must hope): With a tailwheel that doesn't have a tendency to shimmy, why would compression springs ever be appropriate? Bushwheel, for example, recommends compression springs for its assemblies, no matter the make and model on which installed. I'd have thought they would prefer tension springs.

Edited to add: I don't see anything wrong with how the mech. in the video rigged the tailwheel. It DOES prevent tensioning both steering arms simultaneously. So rather than rail on the video, how about a discussion about what's wrong with the way he rigged the chains? ...and as an aside, I didn't just fall off the pumpkin wagon; I've been flying and maintaining tailwheel airplanes for 48 years.

[Bruce Fenstermacher]

A final question (I'm sure you must hope): With a tailwheel that doesn't have a tendency to shimmy, why would compression springs ever be appropriate? Bushwheel, for example, recommends compression springs for its assemblies, no matter the make and model on which installed. I'd have thought they would prefer tension springs.

Perhaps Bushwheel is a manufacturer who doesn't know what they are talking about i.e. your reference to Lycoming earlier.

The problem with the compression spring with regard to our 170s is that the relief of the spring is limited to the amount the spring compress and become solid. Past that can cause damage to the 170 airframe. If the compression spring could compress as far as the tension spring could stretch and at the same rate there probably wouldn't be any difference.

If you were building a plane and you designed the control tubes or cables heavy enough and the geometry of the steering arms right I don't see any reason you would have to have a spring of any type.

As far as my tailwheel set up the modification George spoke of is that I have two main springs in the leaf spring pack, a modification I don't endorse but haven't got around to changing in 10 years either. Adding the second main spring doesn't change the geometry which would cause the the chain tension to act any different than a stock set up.

Someday I may have to make a more in depth study of whether the chain tension should change when the wheel is on the ground verses in the air on our 170s. Maybe tomorrow I'll get to it. No can't tomorrow, I've got a new porch rocking chair to stress test but some day I'll get to it.

[Bruce Fenstermacher]

I just looked at Alaskian Bushwheels web site to see if I could find where they might recommend compression springs for all installations. I didn't find it but I did find the following instructions which say twice, once in the lead paragraph and again in item D, to install their tailwheel following the original equipment installation instructions. In our case that would be with tension springs. See item D for the chain adjusting proceedure which is exactly what Scott put out.

The following was copy and pasted directly from Alaskian Bushwheels:

Installation Instructions for ABI-3200/3224A Tailwheel Assembly

This ABI 3200/ABI 3224A Assembly is an FAA-PMA direct replacement for Scott 3200/3200A Assembly. The installer is responsible for ensuring that the assembly is installed in accordance with the original equipment installation instructions.

Removal & Installation Instructions of 3200/3224A assembly:
A) Following airframe manufacturers instructions, properly raise and support the tail of the aircraft off of the ground.
B) Disconnect & inspect the steering springs & chains from the tailwheel assembly.
C) Remove the old assembly from the tailspring, inspect the attach bolt and tail spring for correct arch. The center pivot spindle should angle back away from the airplane 5 to 7 degrees when un-loaded and be perpendicular to the ground at maximum gross weight. (Note: ABI recommends replacement of all attachment hardware.)
D) Re-install and adjust in reverse procedure, following the original airframe manufacturers installation instructions. (NOTE: Tension on connector spring is not required or advisable. Over tension will create binding of the steering arm causing it to bend and damage internal parts. Connector springs and connector chain should be just slack. ABI recommends connecting the connector springs to an eye-bolt, not to the rudder arm.
E) All ABI 3200 series assemblies are pre-lubed at the factory with Exxon-Mobile SCH-100 grease. Over greasing of the axle will force the wheel seals (PN: ABI-1863) out against the bearing pre-load spacer (PN: ABI-3227-00) causing premature wear on the seals.

[GAHorn]

.... I posted not to be argumentative but rather to learn. ... I don't see anything wrong with how the mech. in the video rigged the tailwheel. It DOES prevent tensioning both steering arms simultaneously. So rather than rail on the video, how about a discussion about what's wrong with the way he rigged the chains? ...and as an aside, I didn't just fall off the pumpkin wagon; I've been flying and maintaining tailwheel airplanes for 48 years.

Robt, I certainly was not criticizing your posting the discussion or your posting the video. I applaud your starting this thread. My criticism is directed to the producer of that video.

What's wrong with the video?
Well, I thought I'd pretty well directly-stated what's wrong in that video. The primary error is the assumption that the steering chains/springs should not be rigged to the same length as the disengagement-position of the detent. Besides the error in understanding the design of the system (which of itself is revealing of the expertise of the producer)...that rigging procedure leaves slack in the chains. Slack does not provide steering input. Sloppy steering input is the primary complaint of most tailwheel pilots and the slack chains will exacerbate the problem.
The video stipulates that it's important that the tailwheel unlock prior to tensioning the opposite-side chain....in order to avoid bending the steering arms. While that may avoid such bending, that is not the correct rigging procedure and is not why the steering arms bend. (At least not when our correctly-installed tension steerng springs are used. Perhaps so when using compression springs, but that's a different installation. The video still misunderstands the detent function.) The purpose and function of the detent is misunderstood by the "mech" in the video. No amount of a "short" steering chain on the opposite side will have any effect whatsoever as to when/where that tailwheel will unlock. Doh! (All it will do is provide increased-resistance to the pull of the chain on the pulling side, and perhaps some stiffness may be felt by the pilot in his rudder-pedal input, but it will have absolutely no effect on unlocking the tailwheel.)
While the video does not state that the rigging should be accomplished with the tailwheel in the air, it errs in that it is suggestive of that. (There is never any reason or need for a tailwheel to unlock in the air.)
Our Cessnas should have their steering chains adjusted just-taut...no slack... with the tailwheel on the ground and the airplane at average weight. Cessna suggests 2000 lbs. They should have tension steering- springs only. 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.) And the caster should be positive, with the king-pin lower end forward, as depicted here, and in the second video.
A healthy tailwheel does not "unlock" because of pilot input thru steering chains. It unlocks ONLY due to sideloads experienced ONLY on the ground due to aircraft momentum in a direction other than that normally requested by the pilot. And example would be while taxying and sudden application of braking on one side. If the tailwheel did not have an unlocking feature, it could damage the rudder bellcrank and the rudder-circuit-cables and associated pulleys within the fuselage....or it would damage the tailwheel tire/wheel.

[N2865C]

I for one have learned a lot from watching youtube... Here is a great lesson on hand propping appropriately titled -How to hand prop. http://www.youtube.com/watch?v=Oxfjx61t ... r_embedded

[jrenwick]

I for one have learned a lot from watching youtube... Here is a great lesson on hand propping appropriately titled -How to hand prop. http://www.youtube.com/watch?v=Oxfjx61t ... r_embedded

Seriously? I'm not impressed with this guy's technique. It looks to me like he's standing too far away from the prop and leaning forward to reach it, then jumping away from it after pulling it through. It looks clumsy and dangerous to me.

OK, now I see the "shocked" emoticon at the end of your message. You were being sarcastic!!!

Instead of what this guy is doing, I'd like to see him stand closer to the prop, so that he's well-balanced as he reaches for it. Standing with his hands on the prop, he should start by swinging one leg forward, then back, pulling the prop through on the backswing. The momentum of the leg carries the body away from the prop as it comes through, and he's stepping naturally away from the prop as the engine fires. He's balanced and in control of his motions throughout, and he can step away gracefully as the engine starts. I don't have a video of that, though.

There are other problems with this video -- he generally doesn't show much respect for the prop as he handles it. If the engine had fired when he wasn't expecting it, he'd have been hurt. He needs to handle the prop as if he expected it to fire at any moment.

[jrenwick]

Back on the tailwheel spring topic. There are at least two problems with the compression springs, that I have seen. One is that if a spring becomes fully compressed, there is no more slack in the system and something will bend or break (like the tailwheel steering arm).

The other problem I've seen, that doesn't get mentioned much, is that if there's no slack in the chains and the springs aren't long enough, sideways force on the tail can pull a spring into full compression before the tailwheel unlocks. In one direction or the other, you might not be able to get it to swivel properly. You could get around this by lengthening the chains, but then your steering gets sloppier. Much better to replace the compression springs with tension springs, as everyone is saying here.

[N2865C]

There are other problems with this video

Sorry, sometimes my sarcasm just gets away from me The first problem is that this video should have been called "How NOT to hand prop an airplane" I can't see one thing he is doing right... It's one of the scariest things I have ever seen. And the frighting thing is that I have seen similar "operations" at local airports. Sorry for hijacking this treead.... I'll go away now.

[N2255D]

I can't see one thing he is doing right... It's one of the scariest things I have ever seen. And the frighting thing is that I have seen similar "operations" at local airports. Sorry for hijacking this treead.... I'll go away now.

Saw a guy up At Sussex NJ, after their air show, hand prop a commanche. First he had what looked lihe his father, late 60's early 70'S, doing the proping until he tired out. The pilot then got out of the airplane and put older gentleman in the right seat and he began proping. After several minutes the engine started. The engine was turning @1500 RPM. The pilot then goes over behind the wing and has the right seat passenger climb out and then he climbed into the pilot seat. The thottle was never pulled back! All the while there are 2 ladies in the back seat and the commanche is facing lots of airplanes in tight quarters trying to leave the parking area.

[robert.p.bowen]

The portion of this thread discussing tailwheel rigging was informative. Once George settled down he raised cogent points. So after watching the video several times, and rereading all the posts, here's where I come out: I believe the video makes a good point about chain rigging so as to not put tension on both arms simultaneously, but the rigging should have been done with the tailwheel on the ground. That is, disconnect the chains, turn the wheel to just before breakout, lower the airplane, turn the rudder to its stop and attach the off-chain with no slack. Repeat for the other side. With the tailwheel in the neutral position, this will likely produce chains with some slack in them. Do a taxi test to see if steering is acceptable. If not, take out a link from each side so that the chains are now snug but not tight. Recognize that by doing so, in a full castered turn but not after breakout, the off chain will be partially extended and thus loading the steering arm in both directions.

Second, I see no benefit for compression springs so long as the T/W isn't prone to shimmy. The compression springs seem designed to help control shimmy, but their downside offsets this modest benefit. In no case are they to be used on the 170's, so this discussion about their benefit refers to other tailwheel airplanes.

Finally, my experience doesn't support George's assertion that too soft metal produced the bending of steering arms. After rigging mine exactly as Scott recommended (i.e., chains snug but not tight) the arms on my Scott 3200 bent upward. Then after rebuilding the assembly with new parts and converting it to a 3200A, those arms bent upward. I believe the bending more likely results from full throw of the rudder before the tailwheen has had time to respond/turn. But slightly loose chains a' la the modified video precedure stopped my bending experiences and steering seemed to me to be about the same. I recognize that each airplane behaves differently, so my result should be viewed as anecdotal; YMMV.

I do now understand both points of view and can make my choice better informed, so thanks to all.