Scott Tailwheel.... 3 springs or 5?

Gary · Post by **Gary** » Thu Nov 06, 2003 1:24 pm

I am rebuilding my Scott 3200 tailwheel. On the parts page, it shows 3 compression springs (part number 3233) under the thrust washer from the fork assembly. There are 5 holes where springs can be placed, but only 3 pins on the thrust washer to hold them in place during reassembly. One part diagram I saw, said "required 5" for the quanity of springs. In the drawing, it shows only 3. Mine had three compression springs on disassembly.???? I ordered 3 new ones but still have the 3 old ones (which are about 1/4 shorter due to wear?) Should I put in 2 old ones in the holes to even out the pressure on the thrust washer? I have had my 170 now for a month and have 17 hours. At that rate, I will have a 200 hour year. Wx here in VA has been great this Fall. Don't think I will fly as much during the dog days of summer. Thanks for all the help, support and advice from the members of the Association. Great site!!! GARY 1909C

Post by **GAHorn** » Thu Nov 06, 2003 5:49 pm

I'm not sure which "parts pages" you're referring to, but the Scott 3200 assembly drawing and the Cessna 170B Illustrated Parts Catalog only show three pn 0442010-17-compression springs in the assembly.

Gary · Post by **Gary** » Fri Nov 07, 2003 1:01 am

George, the parts page if found that listed the number of compresson springs at 5 came from Sacramento Skyranch's web page. I printed it up to look at parts. It has the list of parts needed for different models of tailwheels and it lists 5 springs (part number 3233) for all the 3200 tailwheels. Here is the link http://www.sacskyranch.com/acatalog/scott_tailwheel.pdf
I wonder why there are 5 holes in the fork assembley if they only want 3 springs in the wheel. Looking at my Cessna 170 parts catalog, it shows only 3 springs for the Scott 3200. But looking at the diagram, it only shows 3 holes for these springs in the fork assembly. Both the new fork I purchased from Spruce, and the old one that came with the aircraft, have 5 holes in the fork. I also see a descrepency in where the spacers go that hold the spring (part 19 3222). It the cessna book, it shows a spacer on each side of the spring. In the other diagram, it shows both spacers on the outboard side of the spring.??? I am also having difficulties removing part number 10 (the fiber washer in the bracket assembly. It looks ok, I have a new one but don't want to destroy it getting the old one out. Thanks again for all your input. GARY

Post by **GAHorn** » Fri Nov 07, 2003 4:20 am

Using the Cessna IPC, items 19 and 20 are not pn 3222. They are different parts, (Scott PNs 3258-1 and 3258 respectively) and in my tailwheel they were installed exactly as depicted in the Cessna IPC. Item 21 is Scott PN 3222 and is an angular spring which engages the pawl (item 15, Scott PN 3219), making up the locking "detent" action of the tailwheel. (When you lose the detent or ability to lock the tailwheel in one direction only, it is this spring, item 21 Scott PN 3222 which is likely broken.)

Gary · Post by **Gary** » Fri Nov 07, 2003 2:17 pm

The problem with my tailwheel is that it will not unlock in one direction. It locks fine in both directions, but unlocks to the right only when excessive force is applied to the wheel (when jacked off the ground). The spring part 3222 is worn but not borken. I am replacing the spring 3222, both spacers 3258, 3258-1 and the Pawl 3219. I also feel there is excessive wear and some damage in the stearing arm that holds the pawl, so I ordered a new heavy duty arm 3214T. I received the new fork, but the stearing arm and pin are coming from CA and won't be here until Tuesday. I still am questioning the number of compression springs (pn 3233) that should be installed in the tailwheel. There are 5 holes where they can be installed to make a complete circle of pressure around the thrust washer. The Cessna parts Catalog only shows 3 holes in the fork.?? My new one and the old one have 5. Meanwhile, the mechanic will start to install the wingtip strobes, with a rack behind the baggage compartment, that I asked you about in an earlier post. Thank you for your input. GARY 1909C

Post by **GAHorn** » Fri Nov 07, 2003 4:54 pm

How many ways can I suggest it? Use three springs in my opinion.

zero.one.victor · Post by **zero.one.victor** » Sat Nov 08, 2003 6:27 am

My 3200 has 3 springs,as did the exploded view drawing I looked at when I rebuilt it.
Trouble unlocking might be caused by a burr on the spring p/n 3222,or in the notches of the steering arm p/n 3214. Or maybe by improper (too tight) tension on the steering springs. Trouble locking can be caused by fatigued spring p/n 3222,and also by worn (rounded) notches in steering arm p/n 3214. Rounded or burred notches in the steering arm can sometimes be remedied by some careful file work. Go easy,a replacement part is close to a hundred bucks.

Eric

Gary · Post by **Gary** » Sat Nov 08, 2003 12:55 pm

Closer to $180 bucks for the stearing arm 3214T, which I ordered as the old one is kinda beat. The arms have been bent a few times and the surface where it touches the fork is not quite flat. I will replace both the fork and the stearing arm. $325 and change. Still better than a complete new tailwheel at over $1000. George, I think I will use three springs. Sorry if my request for clarification from a neofite caused any stress.
Gary N1909C 54' B

Post by **GAHorn** » Sat Nov 08, 2003 5:52 pm

Stress? What stress?

I just didn't know how else to say it.
(BTW, I can't help but notice that more than 3 springs should have the effect of making the thing unlock even more difficult due to excessive tension on the friction plates.)
The locking/unlocking feature in a healthy tailwheel is a function of the bent-spring against the pawl.

JDH · Post by **JDH** » Wed Nov 12, 2003 2:33 pm

When I ordered my brand spanking new 3200 (later converted to 3200-A), being that we had to open it 3 times because of faulty rigging and weak steering arms (they had an aluminum alloy part for a while; now back to steel steering arms), we were able to note that there was 5, yes boys and girls, 5 springs in the little holes, when new. I contacted Scott because I was going to be rebuilding my old 3200 and that one had 3 springs over the pins. I was told that over the years, probably because of only having 3 pins, and the schematics that only showed 3 springs, people had been only replacing 3 springs. I got the Scott tailwheel and accessories 10 page Fax sent to me by Bill Waterose and the breakdown shows 3 springs, but if you look at part number 3233-00 (item #5) it shows quantity required: 5.
Bill says its probably cause they could not fit 5 on the breakdown picture. To confirm, check out page 218 in Spruce's catalogue, they also show 5 riquired. JD

Post by **GAHorn** » Wed Nov 12, 2003 6:17 pm

Thanks for the contact, JDH!
I've just gotten off the phone with Mr. Waterose having discussed at length this issue. Here's the result of that conversation.
Yes, Scott (a div. of Tyco), mfrs the Scott 3200-00 tailwheel. (That number is their's assigned to the entire assembly, not the compression springs in question.)
Mr. Waterose states that he is not the in house expert on these tailwheels, but that he will have their engineer, Mr. Tim, contact me regarding this matter.
The reason this conversation is ongoing is due to the fact that the approval basis for installing a Scott 3200 on a Cessna 170 comes not from Scott, but from Cessna who certified the unit on the airplane and caused it to be added to the type certificate.
According to Mr. Waterose, Cessna's Illustrated Parts Catalog is the final word on the matter, due to that certification. The IPC illustrates and specifies 3 springs per unit. (See the far right-hand column of pg. 155 for item 12, Scott pn:3233, compression spring.) Mr. Waterose does not know why Cessna chose 3 springs, but surmises they found that number of springs to provide the desired damping effect for an airplane the Cessna 170's weight. He goes on to point out that the Scott 3200-00 is used on a great many airplanes/applications and that their production version (containing 5 springs) is only a "standard" assembly, not one specifically tailored for specific aircraft.
He and I are pursuing this matter through Cessna. I'll post any findings from that as soon as I learn them.

mrpibb · Post by **mrpibb** » Wed Nov 12, 2003 10:07 pm

Hey, here's a service letter refering to the scott tail wheel pull from the cessna service letters.

DATE: 10-24-1950 S.N.L.
SUBJECT: Scott 3200 Tailwheel Shimmy Adjustment

"We have had some reports on Scott pneumatic tailwheels shimmying. The Scott 8" pneumatic tailwheel Is designed with a friction type shimmy dampenenr. This friction is regulated by 3 small compression springs inside the upper casting. If the main king pin nut becomes too loose the shimmy dampener effect will be lo6t. When the shimmy occurs, it is recommended that the large nut be tightened in increments of 1/6 of a turn until the tailwheel starts to bind when rotated by hand. Then back off 1/6 o[ a turn for correct tension oil the shimmy dampener, The king pin nut is on the underneath aide of the lower housing directly above the tire. This procedure will definitely assure that compression springs in the dampener are acting against the friction dampener disc. We recommend a tire pressure of 30 pounds on both the 140 and 170 for the 8" pneumatic tailwheel. When connecting the springs and chains on this assembly, it is recommended that the stretch in the springs be from 1/8 to 1/4". The springs used with the 3200 assembly have a high tension rate and if stretched to any extent on a.s~embly the mechanism may not release easily. No slack should be left in the chain and spring hook-up when both sides are connected."

JDH · Post by **JDH** » Fri Nov 14, 2003 3:13 pm

George, When I first had to contact Scott, I found their coordinates on the Internet. When you go to their Homepage, you notice real quick that tail wheels is not their #1 thing. I got bounced around a little to end up with Mr. Waterose, who could not answer too many questions; you see, this is old technology and no one is too current on its applications and not much has changed in the design since?? I could sense that Mr. Waterose, as nice as he was, was using his dancing shoes on almost any of my questions; i/e: materials used on the steering arms, number of springs, etc. That one would not know that materials had been substitued, did not surprise me, that happens in using outsourced components in manufacturing all the time. He did have me speak with a woman, Jodi Sliwinski (technical administrator), who really knew what she was talking about, you could tell in a second. She knew the 3200, told me all I needed to order to convert from a 3200 to a 3200-A and where to buy the parts. She did not know why the materials had changed and as a matter of fact, Bill asked me to return the parts (2 steering arms) for him to inspect and replaced it with the 3214T.
But here is what is important: I think we are getting into a Mogas kind of discussion. I have 2 wheels, my original straight 3200, completely rebuilt which uses 3 new springs and a brand new 3200-A with 5 springs. Here is what I found: If they are tightened and mounted the same (with or without penetrating ski), on grass or hard top, neither shimmy, they both give me the same steering, lock and unlock the same (with or without steering extension for ski operation), I can't tell the difference. As was discussed before, rigging is the key; from the kingpin angle, to tightness of the kingpin nut, to tire inflation, to tail springs, etc. From an engineering perspective, you could argue that 5 springs would give a more balanced pressure between the friction plates vs 3. Where 3 springs do not necessarily mean less pressure, that is dependent on how tight the kingpin nut is. An object that weighs 1 Ton is still one Ton whether it is resting on 3 or 5 jacks. All that changes is the amount of force applied per jack changes if 3 or 5 are used...
I also spoke to some mechanics and bush pilots that have flown and worked on all sorts of tailwheeled airplanes and most have found that be it a Cessna, Piper, Taylorcraft or God knows what, most of the 3200 they see or happen to open up have 3 springs and 5 holes.
What is important is not how many springs, in my opinion, since my 2 wheels work just as well, but the combination of all the rigging and in the case of the springs specifically, the tightness of the kingpin nut and the kingpin angle.
By the way, one of the tailwheel plane repair, bush plane gadget and mods (approved) gurus up here does the following for winter operation: He kept an old wheel (wheel only) and an older tire which he fills with silicone. He puts that on his 3200 assembly in the winter; it prevents sheering off the valve stem and flat tire in the case that the wheel is seized-frozen from being buried in the snow or down in the slush, then flown in cold weather, followed by a landing on a harder surface. I haven't needed to do this, but thought I'd share it. So, just to be different this winter, maybe I'll clean it in Mogas, slap a coat of MMO, do Eric's little dance, land it after dark using nothing but torches, to scare off a few drunks... There's the 2 cents worth. JD

zero.one.victor · Post by **zero.one.victor** » Sat Nov 15, 2003 6:30 am

When you say that he fills his winter tire with silicone,I assume you're referring to solid silicone (as in sealer)? I wonder what that weighs compared to a tire full of air,and what that does to the CG being located back about (as I recall) 249" aft of the firewall? Probably doesn't have to pull very hard when he's flaring to land,eh?

Eric

JDH · Post by **JDH** » Sat Nov 15, 2003 1:39 pm

Yep! Caulking silicone. You split the wheel, remove the tube, fill the tire, in layers. Don't forget that this guy rebuilds (legally) floats, has jiggs for wings, does alot of tin work, etc. so, he has a few old wheels laying around. The last bit of silicone is inserted while the wheel ison a half wheel. But, like I said, I've seen it on his L19, but haven't done it on the 170B. BTY, his L19 has tandem bogg wheels on the mains. Now, that's something that'll make you go Huh? The first time you see it. JD