Training question

[Stinson driver]

I've tried many times to get my 170 to the runway without using brakes, but I don't recall ever being successful

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I had the same problem untill a old tail wheel pilot told me to sort out the angle of the scott tail wheel pivot- we made new tail wheel springs that put the pivot horizontal to the ground when the plane was loaded- the ground handling improved so much it was like a new plane

[rudymantel]

Stinson Driver, you may not need brakes when operating on a grass field with little wind, but taxiing a 170 on a taxiway in a crosswind, you DO need them. At least I do.
Rudy

[GAHorn]

I've tried many times to get my 170 to the runway without using brakes, but I don't recall ever being successful

.

I had the same problem untill a old tail wheel pilot told me to sort out the angle of the scott tail wheel pivot- we made new tail wheel springs that put the pivot horizontal to the ground when the plane was loaded- the ground handling improved so much it was like a new plane

A lot of words have been typed here, and a lot of money has been wasted attempting to do what you're suggesting Stinson driver...and the attempt to put that tailwheel as you suggested is incorrect. The correct angle of the Scott tailwheel "pivot" is illustrated below:

[CraigH]

Very good article on tailwheel shimmy written by Gilbert Pierce.

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

[GAHorn]

Very good article on tailwheel shimmy written by Gilbert Pierce.

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

That article is good (and probably the origin of the pic I posted) but there are two errors in it, as applied to 170's.. The tailwheel tire pressure for our 170s should be 34 psi...not 45. And the practice of re-arching a leaf spring is a dubious one at best. There is no approval basis for it, and it likely weakens the spring. This spring already has a reputation for failure and if it does, it will damage the rudder with a flailing tailwheel.
If your spring is incorrectly shaped (see the IPC, if original it correctly has two bends in it) then the better solution is to replace it with a correct spring, available from either Univair or Spruce.

[CraigH]

George,
The article was written pertaining to Short Wing Pipers. My reference to it was simply to emphasize the importance of the correct geometry of the gear. I'm aware that the tailwheel tire pressures are different for the 170s.

As far as re-arching the springs, there are some aircraft where the factory springs do not work very well to eliminate shimmy. The Bellanca / American Champion line is one of them. My Citabria had a very persistant shimmy and re-arching the springs was about the only cure. If I'm not mistaken, the factory has been trying differnt spring angles / combinations but has not completely eliminated the problem. The factory new replacement spring on my 7GCBC shimmied almost as bad as my old one. So far, I haven't had any shimmy problems with my 170, so I'd suspect that the Spruce / Univair springs already have the correct geometry and do not need any "tuning".

[cessna170bdriver]

Several years ago I had a discussion with Cleo Bickford concerning my frustration with trying to make the tailwheel steer more positively. Cleo is one of the most experienced maintainers and flyers of 170's in the Association, and because of that, I respect his opinion as much as anyone in the Association. If it has to do with flying or working on a 170, Cleo has been there, done that, and worn out the t-shirt. It's his opinion that tailwheel steering on a 170 is marginal at best and that's just the way it is. That was when I quit worring about it. Cleveland brake pucks are cheap.

Miles

[Stinson driver]

it will damage the rudder with a flailing tailwheel

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Been there done it I still have the dents in my rudder- thanx guys for the info- My plane has to go in for MPI next week- I think we will put the originlal spings back after reading all the above

[spiro]

I think we will put the originlal spings back after reading all the above

the stock spring is only the correct angle if you have stock gear legs and stock tires. It will not put the tailwheel at the right angle if you have (like most of us in AK) 180 gear and 8.50 tires. Cold-bending the spring to achieve the correct angle is very common - that's most likely how the spring was formed in the first place.

if it's working fine now, why mess with it?

[Curtis Brown]

Are there two different types of springs you can use on the steering chains? Which is the best to use. I think I have tension springs installed and that may be what is causing my steering arm to bend upward. Could this be correct with a different spring?

[Bruce Fenstermacher]

Well Curtis there are 2 types of springs you can use if your not worried about legality.

The tension spring is the approved spring. The compression spring is not approved but used and loved by some people.

I'm thinking if you are bending the steering arm upward with tension springs you will do it with compression springs.

I wonder if there is any relationship between MMO, mineral oil wheel landing, wheelpants, wing cuffs, 180 gear, big tire users and tension verses compression springs.

[GAHorn]

Bruce, MMO is not specified for our airplanes. Ordinarily, Maximum Operating Mach number is only aplicable to jets, etc., but perhaps Joe Harris's airplane has an MMO.

I can't help but believe that any change of "stance" with regard to the installation of 180 gearlegs and 850 tires would have no effect whatever on the tailwheel leaf spring angles. That would be a very small change of angle indeed. Bending the springs in the field might be "common"...but it's not legal without approved data and approved methods to support the modification. The correct springs are either OEM or PMA (which dictates their manufacturing method/material/bend/etc., for good reason.)

There were some Scott tailwheel steering arms which were made of soft aluminum and susceptible to bending no matter if they were installed with tight spring tension or rubber bands. Replacement with correct steering arms cures the problem.
The compression springs are more likely to compress to the point of rigidity and cause damage to the steering arm and/or the rudder bellcrank. The belief that the compression springs are more likely to improve tailwheel steering on a 170 is in error, because the tailwheel unlocks and casters with much less effort than either type spring offers. (In fact, it's this loss of steering caused by castering that misleads one into believing more rigid steering is desired.)
Get used to using brakes while taxying.