The International Cessna 170 Association

ive been trying to improve my tail wheel the past couple of weeks.. It wore off almost all the tread when it castered the last cross country trip i took so i felt it was time to solve the problem. after searching the world wide web and reading countless articles talking about the issue i decided to buy a new spring. I have a 1948 170 and found that the mounting is like that of a 140/120, and a local 140 pilot printed me off a article he had found on the 140 club page. I installed the spring made new rubber cushions torqued it down and put it back on its feet. Now that i had the right caster angle i attached the steering springs and chains and figured all was fixed, wrong.. i could not release the scott 3200 without putting tons of side pressure on the tail of the 170.. so i went back to the internet and decided to buy some parts for the 3200 and a steering spring kit from univair. Took it apart replaced the parts installed the new springs and chains sat it back on the ground and found that it broke over better but i have zero steering and the spring twists with side pressure... is this normal? i have thought about buying a second main spring thinking the twisting might go away, but i cant figure out why i cant put enough tension on my chains to get steering without binding it.. hope it all makes sense here are a couple pictures of the tail wheel with side pressure and the spring twisting..

It's normal for 170s to have poor tailwheel steering, but yours seems like an extreme case. With the tail jacked up, can you move the wheel freely by hand? How many springs do you have on the thrust plate? How tight is the pivot bearing nut?

FWIW, Mine has all 5 springs inside and I torque the king pin bolt to where I can just barely unlock it with my bare hands while holding it in a vice.
really technical but it seems to work.

It's a huge mistake to think of these things as "steering" tailwheels. They are not.

They are "steerable" tailwheels. If you use brakes.... they can be made to steer along with the airplane's movement. They are a huge improvement over tailskids because they don't tear up the grass so much and they don't make as many sparks on pavement.

The pics of this tailwheel look fairly normal. Also, take a look at where the axle is on the tailwheel while it's turned to the side. The weight of the tail...about 130 lbs or so... is what is twisting the mainsprings. Think of levers and fulcrums..... it's normal action.

The steering chains should be "just taut"...not overly tightened. They only "encourage" the tailwheel to follow rudder imputs....that's all. With added braking...the airplane may be given more guidance to change direction...

Well I don't think it looks right. There is way to much caster. Looking at the thin red lines I drew on the picture at the base of the bracket assembly of the tailwheel should be flatter. Only slightly raised in the front over the rear. When the aircraft is loaded to 2200lbs it should actually be flat.

I think it looks like the spring pack is not installed in the fuselage bracket right causing it to exit the bracket at to steep of an angle. There shouldn't be a gap at the red arrow head. This is where I'd look for miss installed parts and correct if found to allow the spring pack to exit at less of an angle thus changing the angle the bracket assembly is held

What is happening with this much caster is that to turn the wheel the aircraft has to be lifted and that just isn't going to happen and the control springs will just stretch.

bagarre wrote:FWIW, Mine has all 5 springs inside and I torque the king pin bolt to where I can just barely unlock it with my bare hands while holding it in a vice.
really technical but it seems to work.

My method is also pretty technical: I torque the king pin nut so the pivot is just starting to bind, then back it off just enough but not too much! FWIW, I use three springs on the torque plate.

That's a good observation, Bruce. I should have zoomed into the area you pointed to and I would have noticed that looseness where the spring-stack leaves the bracket, and have better seen the twisting.
NOW... I have zoomed in... I can see this is the earlier steel "box" bracket. They are famous for cracking and allowing all sorts of "play" in the tailwheel springset and wheel. The later aluminum "alligator" bracket holds the tailwheel assy much more securely and with less stress upon the tailcone.

Aryana wrote:Another problem that can cause issues with the locking action/mechanism is putting too much grease in the tailwheel. 3 or 5 springs installed on the torque plate may become moot when so much grease is pumped in that it's coming out of the seals. It will affect the amount of torque required on the kingpin to get the action desired.

IMO, the grease fitting should be used only if you don't have the time/facilities to take the tailwheel apart and clean and grease it properly. In addition, the engagement/alignment of the internal leaf spring to the notches in the tailwheel body is also crucial.

Just sharing what has worked for me and my family on a bunch of planes we've owned over many decades with the 3200 installed, so take this advice with a gallon of salt!

Interesting! Thanks, Arash!

Thanks for all the the responses! I lifted the tail and inspected the attachment points. i don't believe there is any gapping on the lower mount, there is a small spring with a little lip that is made to keep a rubber bushing from sliding back towards the tail wheel.. as i was inspecting the spring i grabbed ahold of it and noticed more that what i thought of movement in the top through bolt.. i re torqued the bolt and found it to have loosened. I think it was the rubber bushings settling out after a couple touch and go's. it has less twisting now but still a slight amount. i did tighten my chains, i think that will help my ground steerability. before these springs it had the compression style and any tension would cause the scott to bind and not break over at all but the correct style allows it to break over just fine with a bit of tension on the chains. the angle of the caster section is not level, but is it within tolerance? im not to sure how to change it. i guess i can add a spacer to the front mount?

The caster looks good to me.

Here is a good view of how the caster should be (pay no attention to the fact it's not installed on a 170.)

I took my Scott 3200 tail wheel off and cleaned the excessive amounts of grease from the exterior and interior of the unit. My question is how tight should the nut be on the bolt that holds the unit together? I tightened it until the unit could not be swiveled and backed the nut off so the unit would swivel. Was that correct.

Ron

I learned from the club that my tail wheel was excessively greased. It would wobble as I taxied. Will tighten the castleated nut to take 15 ft/lbs. thanks for the help.

Ron

Thanks for the correction. That is a substantial difference.

Ron

Bruce Fenstermacher wrote:Well I don't think it looks right. There is way to much caster. Looking at the thin red lines I drew on the picture at the base of the bracket assembly of the tailwheel should be flatter. Only slightly raised in the front over the rear. When the aircraft is loaded to 2200lbs it should actually be flat.

I think it looks like the spring pack is not installed in the fuselage bracket right causing it to exit the bracket at to steep of an angle. There shouldn't be a gap at the red arrow head. This is where I'd look for miss installed parts and correct if found to allow the spring pack to exit at less of an angle thus changing the angle the bracket assembly is held

IMG_5122.JPG

What is happening with this much caster is that to turn the wheel the aircraft has to be lifted and that just isn't going to happen and the control springs will just stretch.

Isn't the 5th spring in there where red arrow is? As for the thin red lines, it's hard to tell with that wheel position but I think the airplane shows a good positive castor. I doubt its at max gross.

Hard to tell about the spring tension in that left turn picture.....

Pretty new to the 170B but my chains , with the tailwheel centered, are pretty taught. Like twanging a guitar. I doubt that's right! Lots of power and brake tapping to turn.

The tailwheel steering chains should be “just taut” ….. IE, the springs should be tensioned but not stretched…. when the tailwheel is straight-ahead.