Scott T/W 3200 :Unlock

[Jetfever]

Hey guys, Is there a way to make my Scott 3200 "unlock" more easily? I have lubed it with the grease fitting on a regular basis. When Taxi on hard surface I really have to get on the brake. I did some "off roading" /dirt biking today. We landed on a dirt track, one way in. When I went to spin the plane around via the fuselage handle, I could not get the tail wheel to unlock, it just skidded in the dirt. The first photo shows the "one way" road in. Pacer and Skywagon are still on the "road".

[Steve Pierce]

Looks like some fun flying. Here are some pictures of a Scott 3200 tail wheel. http://picasaweb.google.com/Pierceaero/Tailwheel# If everything else is in good shape you might check to see if you have all five springs pushing on the thrust plate. If you do I would remove two of them and adjust the tension on the head to fork nut. This will allow the fork to swivel more freely, just make sure it is not sloppy lose.

[Gilbert Pierce]

adjust the tension on the head to fork nut. This will allow the fork to swivel more freely, just make sure it is not sloppy lose.

Remember, adjusting that nut adjusts the preload on the tapered bearing that the fork swivels on. You want to adjust it like a wheel bearing. Swivels easily with no play.

[Jetfever]

Thanks, Looks like I will be cleaning and adjusting the T/W soon. (400 hours TTon a new tailwheel).

Is there a downside to removing 2 of the 5 springs?

Gilbert, I would think the springs make it difficult to tell when the preload is adjusted correctly unlike a wheel bearing?

[Gilbert Pierce]

Gilbert, I would think the springs make it difficult to tell when the preload is adjusted correctly unlike a wheel bearing?

The springs on the clutch are not that tight. You can feel the bearing get tight if you get too much preload. Just loosen it unitl you feel a tiny bit of play in the bearing and then tighten just enough to get it out.

I have put about 1600 hours on the Scott 3200 on my Clipper and it was not new when I got the airplane. It has always had only 3 of the 5 clutch springs in it. I have no shimmy and tail wheel releases where I think it should.

[birdofprey]

Be sure to check the caster angle of the crown pin when the tailwheel is mounted to the aircraft. If the pin (the point where the tailwheel swivels) looks like it tilts forward rather than being plumb this can make it prohibitive to reach the steering angle nessecary to unlock the tailwheel from it's steerable range. This is also a common culprit for tailwheel shimmy. Anyone who has ever pushed a shopping cart with a damaged front caster has seen this. You can either order a new spring from univair (expensive) or bring your spring stack to a local spring shop and have it recurved (cheap).

If you do disassemble your tailwheel (and you should to clean and relube) be careful and note the order of the thrust washer/dust cover stack. Avoid the temptation to file the steering arm to make it unlock easier. This is a great way to ruin a expensive arm. I've also seen people change to leaf spring (the spring that engages the steering arm detents) shim stack to acheive the same thing. DON'T do this. The Scott 3200 is a great tailwheel if you take care of it.

I'll see if I can attach a photo of a tailwheel set up correctly.[attachment=1:2ussfpi9]Pacer tailwheel 001_trans.jpg[/attachment:2ussfpi9][attachment=0:2ussfpi9]Pacer tailwheel 002_trans.jpg[/attachment:2ussfpi9]

[Steve Pierce]

birdofprey, Good point. Here is a good article on the subject also.

http://www.pierceaero.net/tws.php

[birdofprey]

Ha Ha, I read that artical some time ago when my tailwheel was shimmying so bad it bent the rudder! Didn't associate the author with this forum. I'd like to take credit for the idea but clearly I can't!

[Jetfever]

Knock Wood, I have never had this tailwheel shimmy on me.

I am surprised to know quote: "If the pin (the point where the tailwheel swivels) looks like it tilts forward rather than being plumb this can make it prohibitive to reach the steering angle nessecary to unlock the tailwheel from it's steerable range".

Why this is will take some thought. I will take a photo and try and measure the trail today.

It sounds like you guys pull the T/W apart to clean/ re-grease on a regular basis? How often? I take it the grease nipple does not do the job?

Has anyone else removed 2 of the 5 springs for an easier "unlock"?

[birdofprey]

If you operate the tailwheel by hand you should be able to viualize this. Try to unlock the tailwheel out of it's steerable range with your hand. You'll note that it has to reach an angle beyond which you can apply with the rudder alone. Part of the reason for this is the maximum deflection available of the rudder is only 16 degrees if it's set up to spec. If the pivot axis is not striaght up and down forward motion of the airplane will make the tailwheel always want to "lag" behind the rotation desired by the application of an individual brake by the pilot. Because of the anglar relationship between the pivot point and the trail manufactured into the tailwheel fork to move the tailwheel beyond inline with the airplane requires the tailwheel to also lift the weight of the airplanes' tail--when the tailwheel pivot point has a forward angle. Read the Pierces' artical. This steering geometry is also why your car steering wheel "wants" to return to center.

Another problem I've seen is people bend the steering arms up to try and align the rudder fork and steering arm. This makes the arm bind on the crown before it can get the the angle necessary to unlock it using the mechanism designed into the tailwheel. (which works very good) You'll note in the picture I posted the arms on that particular wheel are bent up at a point well away from the crown. This is a bush-type arm designed to prevent damage to the springs and chains from rocks/stumps/etc. This type arm is NOT necessary; it just so happens to be on this airplane. My airplane has a standard arm and it works great.

Hope this helps.

[Steve Pierce]

I disassemble, clean, inspect, grease and reassemble the tail wheel at every annual. In my experience it is one of the most neglected part on a tail wheel airplane and also the most abused.

[Jetfever]

I disassemble, clean, inspect, grease and reassemble the tail wheel at every annual. In my experience it is one of the most neglected part on a tail wheel airplane and also the most abused.

Holy cow Steve! I would have to agree with you now that you say this. You mean abused because it is not disassembled at annual, correct?

I will do this service next week. Thanks

[Jetfever]

Well, 3 questions: Here is a photo, camera flat on the floor. From what you guys say, I need the spring "re-arched" correct? 1. How do I tell the spring shop exactly how much?
2. Should I leave all 5 springs in the Tailwheel when I disassemble/ lube it or wait and see if this is "angle" is my "very difficult to unlock" problem?
By the way, I have never had a shimmy! I do notice the T/W tire seems to wear quickly, not sure how many hours they last on paved runways. I might as well replace the tire on this service. 3. Your favorite tire sales shop?
Thanks, Steve

[Steve Pierce]

I would take the tailwheel apart and inspect it first. Desser is where I get my tailwheel tires and tubes. Re-arching a new spring has less propensity to break than an old during the rearching process.

[Jetfever]

Steve, Desser it is! I have used them for years.
I will service the T/W.
Do you think a 400 hour spring is "old"?
I do have the "bad geometry" or negative castor in your link, no? http://www.pierceaero.net/techdata/tws.jpg
Eaton thinks there is only one good way to re arch springs: http://www.eatonsprings.com/rearching.htm

[Steve Pierce]

Hard to say on the 400 hours. Definatly bad geometry. Worst thing is it will break when rearched. My Dad's was rearched cold and has retained it's arch for the past 6 years or so. I think the car guys are dealing with different problems.

[d.grimm]

I've re-arched tailwheel springs as many as five times. I always had a spare that was re-arched so I could change it quick.
The springs don't have the proper arch when new. I made a pattern by guessing and had the spring shop use that.
I changed mine every six months because I would carry three people on a regular basis, and I had VG's that would have the tailwheel touching slightly before the mains on most landings.
Dave

[Gilbert Pierce]

In my opinion Dave is absolutly correct. The springs you get from Univair are not properly arched. This has been brought to their attention but their answer is we just following the drawing. Well folks guess what. The drawing must be wrong because I have seen a new Univair spring put on a Clipper that sagged as bad as Jetfever's and the airplane was empty.
The spring on my Clipper was also new and was 4 leaf instead of the Clipper's usual 3 leaf. I fought tail wheel shimmy when loaded for too long before I figured out the "new spring" was the problem. I had it re-arched cold 7 years ago and have had no more problems.
I won't argue with Eaton over the spring bending routine they use however my $20.00 cold spring re-arch has lasted 7 years so far and is going strong vs their $220. re-arch. It does not take a math whiz to figure out the economics of this problem.

[birdofprey]

The spring angle is definatly your number one problem. Like these guys, I had mine arched cold at a local auto spring shop. The guys there knew exactly what it was and just asked how much I wanted. I guessed and it was a pretty good guess. Chances are if you don't do anything radical it won't be too much. They charged me 15 bucks for this service and I hope you have a similar experience. As for the 5 vs. 3 arrangement of friction springs I have five and no prob. I've seen three, I don't have any problem with it...However it was designed with five. Don't know if it really makes too much of a difference but your steering springs don't appear to be the correct ones from Scott. You'll likely have to adjust the length of that spring/chain arrangement due to the change brought about by the new spring angle.

Here's a couple photos of the latest profile I came up with. The last picture I attached of the tailwheel setup I recently installed has this exact profile on it. I liked it so much I traced it for future reference. Hopefully from the rulers you can get some sense of scale and degree of adjustment needed. Good luck.[attachment=1:1reotre6]Pacer tailwheel profile 001_trans.jpg[/attachment:1reotre6][attachment=1:1reotre6]Pacer tailwheel profile 001_trans.jpg[/attachment:1reotre6]

[d.grimm]

Birdofprey,
Nice pictures, good idea about how to measure it. I checked it against mine and it's really close. I have always used the Scott heavy duty springs with good success. I think once he gets his spring re-arched and some new tailwheel springs he will really notice a big difference on ground handling.
Dave

[Gilbert Pierce]

I made a cardboard template like the pictures above. Gave it to the guy operating the press. He made the first and longest spring to match the drawing and then individually bent the rest of the springs to lay in with the first. I added too much arch so I took it back and told him I wanted the tailend 1/2 higher. He rebent them to match each other with slightly less arch. Still only $20.00 in 2002.

[Jetfever]

Thanks, everyone. Remember, I do NOT have a shimmy problem. (Knock wood) even at gross wt. If I try to remember, I think the Pacer IS harder to steer/(move the T/W) at gross wt. but not enough to bother me. I assume this is caused by "worse geometry" as the spring compresses. Birdofprey, the "Steering springs" came with the Scott T/W, they "should" be correct. There is extra chain, (you can just see it hanging in my photo) so I should have extra chain for a re arched spring. I love full stall/ 3 point landings so I assume I give the T/W spring more than a good workout.

Does anyone have a good link to an "Exploded View" of the Scott T/W. This will be very helpful at rebuild time. (The one at A/Spruce is pretty small).

[Steve Pierce]

Here is a link to a tailwheel breakdown I am working on. http://picasaweb.google.com/Pierceaero/Tailwheel#

[birdofprey]

The springs in the photo look awful lot like those for a Scott 2000. It could just be the picture. The instructions for setting up the Scott springs call for just a slight tension of the coils (think matchbook cover slips in between individual coils) when rudder and tailwheel are straight. You should end up with an equal number of chain "links" on either side if all is correct. The one in my picture has five links each side, but I have the connector links on my rudder arm and the tension springs in the tailwheel arm. You'll have to experiment.

Looking in Spruce's catalog, I guess it's not critical what tension springs you use, they list a "Heavy" and a "Light". Funny enough they are not listed on the same page! I've been using the "Heavy" springs on the 3200 and above and have had good luck.

Not to blow your head up too much, but likely your lack of shimmy is due to setting the airplane on perfectly straight every time! Asphalt aggrevates a shimmy as well.

[rmalone]

Univair sells a complete kit for the Pacer with the correct springs, chain etc...

[Jetfever]

Did it myself! I made a template using "Birdofprey" measurements. I recurved (bent) the springs myself using a press on the field. The press was designed to bend Jeep leaf springs so it was easy.
As you can see, I needed to go a couple more degrees, she is approximately 1.7 degrees or so from level (using a digital level) with no load in the plane, but what a difference! Taxi is easy, I push so much less on the rudder pedal for a change in direction. Thanks to everyone here. I have not had a shimmy problem, and still don't after the test flight.

[Jetfever]

One other question:
How do you feel about steering spring tension on the tailwheel?
I have a Scott caution in a RED BOX: "Spring tension is neither desirable or necessary".
Why is this, and do you run with just a little spring tension? My plane came set up with springs tensioned a bit.
With no tension, I can feel the slack "take up" when I taxi.