Scott tailwheel

[Richard]

I think I got a handle on why we seemed to run out of rudder after landing. Seems the 'horns' where the control cables attach to the wheel (Scott 3200) were bent upward a bit. A bent horn will result in a slack cable. Evidently, this happens when someone stomps on the pedals too hard, too quickly (wasn't me!). Also, what I'm hearing (2 pilots) is this is a fairly common problem, or is it?

Another potential problem I'm going to research is how often can these horns be bent back into shape. My concern here is that a former owner now remembers having had this problem several years ago. His fix was to have a local A&P bend the horns back into shape.

It seems to me it would be a torsional force which would cause the horn to deflect. That makes me wonder if it is a design flaw or could be improperly tensioned or mis-rigged cables?

 

[Skip Miller]

Another possible cause is pushing down on both pedals simultaneously. Just a guess, I have no experience here. -Skip

 

[Tom-D]

I think I got a handle on why we seemed to run out of rudder after landing. Seems the 'horns' where the control cables attach to the wheel (Scott 3200) were bent upward a bit. A bent horn will result in a slack cable. Evidently, this happens when someone stomps on the pedals too hard, too quickly (wasn't me!). Also, what I'm hearing (2 pilots) is this is a fairly common problem, or is it?

Another potential problem I'm going to research is how often can these horns be bent back into shape. My concern here is that a former owner now remembers having had this problem several years ago. His fix was to have a local A&P bend the horns back into shape.

It seems to me it would be a torsional force which would cause the horn to deflect. That makes me wonder if it is a design flaw or could be improperly tensioned or mis-rigged cables?

There is a model of Scott that has the last inch of each arm bent up 90 degrees.

What springs do you have?
Does the rudder drive the tail wheel, or does the rudder pedal cables go to the steering arms?

You didn't say what aircraft you have?

Or I missed it.

 

[Richard]

There is a model of Scott that has the last inch of each arm bent up 90 degrees.

Nope, our's are straight.


What springs do you have?

(EDIT) Part number SCT 3219.


Does the rudder drive the tail wheel, or does the rudder pedal cables go to the steering arms?

The rudder does drive the wheel, we don't have a steering yoke like you might find on an Aeronca.


You didn't say what aircraft you have?

Stinson L-5 Sentinel. Derived from the -108 it's actually a OY-1.

Or I missed it.

I just got off the phone with the A&P. He says the ears get bent because the cables are not perpendicular to the attachment points, that the cables come in at some acute angle to the ears so the bending is bound to happen. He suggested a 337 repair featuring a wedge to get the cable to attach to the wheel assy at the correct angle.

Either the Scott is not original to this plane, or it is but the design flaw (angled cables) was acceptable for the time.

I'm going to school on this one.

 

[Richard]

I just hung up from talking with Univair. I was told to call them because they have lots of Stinson experience. They thought the cables might be too tight and more chain should be added to the cables.

They couldn't (wouldn't?) provide me with the information for proper tension. All they said was they shouldn't be hanging. So, somewhere between piano tight and dragging on the ramp, I guess. My next concern is, are the cables too tight because of improper tension adjustment by the A&P, the same A&P who currently works on the plane.

 

[Tom-D]

I just got off the phone with the A&P. He says the ears get bent because the cables are not perpendicular to the attachment points, that the cables come in at some acute angle to the ears so the bending is bound to happen. He suggested a 337 repair featuring a wedge to get the cable to attach to the wheel assy at the correct angle.

Either the Scott is not original to this plane, or it is but the design flaw (angled cables) was acceptable for the time.

I'm going to school on this one.

The L-4 had its own tailwheel assembly very much like the PT-26, scott is a replacement. and the oem tail wheel was not steerable, everything you have is a modification.

 

[Richard]

The L-4 had its own tailwheel assembly very much like the PT-26, scott is a replacement. and the oem tail wheel was not steerable, everything you have is a modification.

It's an L-5, don't know if that makes a difference WRT tailwheel from the L-4. After many e-mails and phone calls toady I found out the original was made by Lakes State Mfg, out of business since the '50s.

Also, I have beeen advised the springs should be compression type, not direct tesion springs. I'm not certain how that would be rigged and/or if it would require additional parts. Longer springs may help as would longer chain but no one seems to know what length springs or how longer the chain. I did find some data for correct cable tension. The previously mentioned springs part number, SCT3219, is a Scott number.

Thanks for your responses. I'll keep digging but if y'all have anything to add I would appreciate it.

 

[Tom-D]

It's an L-5, don't know if that makes a difference WRT tailwheel from the L-4. After many e-mails and phone calls toady I found out the original was made by Lakes State Mfg, out of business since the '50s.

Also, I have been advised the springs should be compression type, not direct tension springs. I'm not certain how that would be rigged and/or if it would require additional parts. Longer springs may help as would longer chain but no one seems to know what length springs or how longer the chain. I did find some data for correct cable tension. The previously mentioned springs part number, SCT3219, is a Scott number.

Thanks for your responses. I'll keep digging but if y'all have anything to add I would appreciate it.

Raise the tail off the ground, set the chain length to no slack, no tension, they will be loose while taxing, but not tight in flight.

 

[Richard]

Okay, we have the correct cable tension, the springs are correct and rigged in compression but now my concern is the arm assy on the wheel.

In the past few weeks I've found numerous folks who have had the same problem of the arms being bent upward because of the angle from where they exit the fuselage to where the attach to the arms.

One guy, an A&P, came up with several mods but thought they looked hokey and detracted from the a/c value. He eventually machined his own arm assy but that is on a Travelair and we'd have to get together to determine if it will work on the L-5.

My question now is if I can swap the beefier arm assy from a 3250 or 3400 series tailwheel onto my 3200 wheel.

Univair won't even touch that question and I'm still waiting for a call back from Avox, the folks who bought Scott.

And I still don't know if it's the rudder which controls the wheel or vice versa. I suspect it's the former since I don't think their is any advantage to having the wheel travel more than the rudder. Obviously, I'm guessing.


It's like solving a whodunit. I'm gonna' apply for the detective position after this is all done.

 

[gismo]

And I still don't know if it's the rudder which controls the wheel or vice versa. I suspect it's the former since I don't think their is any advantage to having the wheel travel more than the rudder. Obviously, I'm guessing.

What do you mean by that? In every airplane I've seen with a steerable TW the rudder pedals directly control the rudder and the tailwheel is connected via springs to either the rudder or a separate linkage to the pedals.

Has anyone ever seen an aircraft where the tailwheel was connected to the rudder pedals and the rudder was only connected to the tailwheel?

 

[Richard]

Lance, the delay in response is because I had to think about what I had said. Anyway, this is what I meant, I think...

The rudder cables attach to the arm assy which is part of the wheel. Does the wheel turn the rudder? My understanding is when in flight the wheel is unloaded and slips into a detent which means the wheel remains in a neutral position regardless of rudder position. How the heck this works I have no clue.

I'm gonna' have to get someone to 'splain to me the workings of the Scott 3200 tailwheel. Either that or I'm gonna stick an old leaf spring under there and call it a skid.

 

[gismo]

Lance, the delay in response is because I had to think about what I had said. Anyway, this is what I meant, I think...

The rudder cables attach to the arm assy which is part of the wheel. Does the wheel turn the rudder? My understanding is when in flight the wheel is unloaded and slips into a detent which means the wheel remains in a neutral position regardless of rudder position. How the heck this works I have no clue.

I'm gonna' have to get someone to 'splain to me the workings of the Scott 3200 tailwheel. Either that or I'm gonna stick an old leaf spring under there and call it a skid.

I'm certain that your Scott TW doesn't move the rudder. There just about has to be springs in the connection between the TW and rudder. With the TW on the ground try moving the rudder by hand from stop to stop. I think you'll find that you can do that even if the TW hardly moves. If you can get someone to work the pedals while you watch from the rear I expect you'll find that the rudder moves from stop to stop while the TW barely moves at all (on pavement). The springs should be compressing to allow that.

I'd also be surprised to find that it remains "neutral" when the tail is off the ground. The detent is to allow you to turn a tighter radius (on the ground) than you could if the TW was limited to the angles the rudder can make. You should be able to pop the TW out of the detent just by pushing the tail sideways by hand (on the ground). If you can get someone to lift the tail while you move the rudder by hand you would be able to see that the TW moves with the rudder in the air.

 

[Tom-D]

The detent is to allow you to turn a tighter radius (on the ground) [/QUOTE]

Scott 3200 & 3400 series are full castering tailwheels. All 3 of my 170s had tention springs and moving the rudder by hand on the ground would move the wheel to the extent of the rudder.

 

[gismo]

Scott 3200 & 3400 series are full castering tailwheels. All 3 of my 170s had tention springs and moving the rudder by hand on the ground would move the wheel to the extent of the rudder.

Tom, I'm not sure what your point(s?) is/are and I can't tell if you are agreeing or disagreeing. Full castering means the tailwheel can rotate 360 degrees, right? AFaIK these tailwheels must come out of the detent to do that.

WRT the tension springs, wouldn't you agree that because of them, you can still move the rudder when the tailweel movement is restricted? Granted if the springs are stiff enough, they can rotate the wheel even when the full weight of the tail on the wheel means the wheel must skid on the ground. From what I've seen, even with stiff springs, the rudder will rotate further than the rudder if the plane is sitting stationary on asphalt.

 

[Tom-D]

Tom, I'm not sure what your point(s?) is/are and I can't tell if you are agreeing or disagreeing.

The aircraft in question was not equipped with a scott from the factory, the tailwheel that is in place now was an after thought. WE don't know how much of a Rube Goldgerg we have here. From what I read in the thread the adaptation is not working as it should, or the arms would not bend. So using that installation as an example would be misleading.

"Full castering" does not necessarily mean detent, Maule tailwheels do not have a detent.

Having a "Scott" with a detent allows you to have steering with in a range of motion, beyond that range it is free to swivel as it must to allow the aircraft to turn by differental braking. This range of motion is normally more than rudder travel. so in normal taxing you have steering, until you tap a brake and force the wheel out of detent.

In the "Rube" adaptation in question we don't know if the detent is working or not.

That really is dependent upon what springs are installed. When you have the proper springs by Cessna part number installed on a 170 you can make inputs to the tailwheel by the rudder, in fact this is the normal method, because the rudder has horns (levers) at the bottom to work the tailwheel and it will swivel setting on the ground. BUT-- you won't get as much swivel from the tailwheel as you will get motion from the rudder, due to the springs

With the little 4" tires found on a Scott this should happen quite easy.

Normally we find that the rudder throws are less than the Scott 45 degrees of steerable range.

Scott Tailwheels must be forced beyond the steerable range to get the detent to disengage, you can't make that much of an input from the cockpit by the ruddr pedals, or the rudder, you must stomp a brake to get that to happen, because the detent is operated by a cam, not a spring, and the cam action won't happen with in the normal rudder throw.

 

[gismo]

Scott Tailwheels must be forced beyond the steerable range to get the detent to disengage, you can't make that much of an input from the cockpit by the ruddr pedals, or the rudder, you must stomp a brake to get that to happen, because the detent is operated by a cam, not a spring, and the cam action won't happen with in the normal rudder throw.

Is that true of all detented tailwheels or just Scotts? I wonder if the small solid TW on the Porterfield works that way.

 

[Tom-D]

Is that true of all detented tailwheels or just Scotts? I wonder if the small solid TW on the Porterfield works that way.

small solid TW on the Porterfield ??? prolly a Maule = no detent

 

[gismo]

small solid TW on the Porterfield ??? prolly a Maule = no detent

AFaIK it doesn't say Maule on it, and it definitely has a detent. If you push the tail sideways on the ground or lock up one brake it pops loose from the rudder. I'm just wondering if the detent has a cam release like you described for the Scott.

 

[Richard]

The consensus from the Sentinel Club is... no consensus. To begin with there aren't that many L-5s. Those who have Scott 3200 tailwheels have experienced the same problems of the arms on the arm assy being bent upward. The solutions are varied. One guy, an A&P and machinist, made his own arm assy. Another is in search of just the right spring, yet another has experimented with changing cable tension and adding or deleting chain links.

The following is part of a running dialog with the the last guy I mentioned:

Unfortunately, I have not yet solved this problem. I have the Scott 3200 with compression spring attachment to the control cable. I don’t have the specific spring type available right now. The problem is that the compression spring does not allow sufficient travel and it reaches full compression before the wheel hits the free caster release point. The attach horn is the weak part in the system, so it bends up as you describe. I do not think the control arm would bend if you never forced the tailwheel into free caster, unless the geometry of your control attachment is significantly different from mine. I know from experience that the control arm is pretty soft metal, so if yours has only been bent back into shape twice, that’s probably not a problem (I am not an engineer) but you obviously don’t want to bend them too many times. The control arm is a replaceable part and the job of taking that assembly apart (and putting it back together) is not at all complicated. New parts are available from at least a couple of suppliers.



If I loosen my system up by even a single chain link, I find there is so much slack that I lose positive steering control, but if you have not yet tried this, I’d say you should give it a try. You should also check your rudder travel limit adjustments. If they do not allow the rudder to move through the required range, that would clearly contribute to the horn bending problem. If the rudder travel is correct, then I think the best solution is to find a spring that is strong enough to give positive control, yet long enough to allow the wheel to reach the free caster point before bending the control arm. Seems like a simple solution, but I have not yet found that spring. If you find it, please let me know where.

_____________________________________________________________________

Today while taxing I noticed something much more profound than previously. While taxiing I noticed left rudder inputs resulted in an immediate response as typical while right rudder resulted in a delay of a couple seconds and then she started to slowly come around. Like turning the Queen Mary... Without opposite brake I'd likely have run off the taxiway.

Back at the hanger we again jacked the tailwheel off the ground. With someone at the rudder pedals I watched as full left rudder brought the rudder to the stops and the wheel to about 45*. Full right rudder brought the rudder to the stops but the wheel came back to center (nuetral) only; the wheel would not go to the right past the center position. We played with it doing different things to no avail.

The rudder itself travels to the specified degree deflection; the cables leading the wheel were slack with the wheel off the ground although the right cable felt to be just a bit less slack, we have compression springs.

The obvious question is what does my A&P think? Well, I think I need a new A&P and that's all I'm going to say about that.

Univair is little help, Avox Systems who bought Scott is in New York and I'm in CA; we keep missing each other.

Unless something happens this coming week I won't be flying into yet another airshow next wknd and I don't feel too good about it.

 

[Tom-D]

Unless something happens this coming week I won't be flying into yet another airshow next wknd and I don't feel too good about it.[/QUOTE]

Call me, 360-675-2117

Interesting problem..

Jack the tail off the ground, remove the input cables from the steering horns, and operate by hand tell me if it works free in the steerable range.

Hold one horn all the way forward, and hit the rear of the wheel in the direction of travel and see if it will brake free and swivel all the way around.

Still holding the horn in the full travel position, see if the wheel will lock in the detent when it comes into steerable range again.

Do the same procedure with the other horn.(in the oppsite direction)


If it does not work properly by hand with no weight on it some thing is wrong internally.

IF it is broken internally dump it and get a 10" tail wheel assembly from Tom Anderson.

http://www.xpmods.com/