Tailwheel spring

[Conrad Nordquist]

Hi everyone.
A couple of years ago I was told my tailwheel spring was too flat and sure enough- when I lined it up next to other Eagles it was way flatter than any others. I replaced the spring but I have no record of where I got it or what it cost! Today I looked and it's gone flat again (the shaft of the tailwheel fork is pitched way forward at the top.
Has anyone had this problem?
Know where I can get a replacement other than Aviat?
Do any of the other springs in the Spruce catalog fit the Eagle?
Thanks for your input.

 

Conrad Nordquist
N22XS at Flabob (KRIR)

[daz.t...@gmail.com]

Hi Conrad

I had my tail wheel replaced about a year ago. When I contacted
Aviated they naturally said that only Aviat parts will do, so I
ordered the aviat part.... but when it came through it had a Piper Cub
sticker on the under side! Cheeky eh?

As to why the spring flattens out, I try to use an amount of back
stick that is proportional to air flow over the tail. No problems
since.

Cheers

Darren
G-EGLE

On Apr 4, 3:06 am, Conrad Nordquist <conradnordqu...@sbcglobal.net>
wrote:

[al]

Hi Conrad,

I've been looking at my own tailwheel and note that the top of the
pivot shaft faces forward. It was further brought to my attention
because I found some shims stacked above the spring pack at the rear
support point, and the front of the spring would not tighten up flat
to the front support point..... obviously an attempt by a previous
owner to change the angle of the pivot shaft without changing the
springs.

A few years ago I was flying a friends new-2-her Acrosport II across
the country to its new home. I noticed near the end of the trip that
I was occasionally getting a little shimmy. She started taking some
tailwheel training in it and was having difficulty with directional
control :-) and some shimmy..... her instructor was also an
experienced mechanic and immediately changed the tailwheel springs so
the pivot shaft was closer to vertical. End of problem.

I once watched a fellow doing circuits in a Pitts Ultimate and was
thanking my lucky stars that I wasn't the one in the front office.....
it was all over the place once the tailwheel touched the pavement. An
experienced aircraft mechanic on the field had a look at the tailwheel
assembly and said that the pivot shaft needs to be vertical, or within
about 10 degrees of vertical. Too much off in one direction can give
you the shopping cart shimmy and too much off in the other direction
makes the aircraft hard to handle when landing. The Ultimate pilot
got a new tailwheel 'stinger', installed it so the pivot shaft was
vertical, and the directional control problem went away.

If both of these were not just lucky guesses, perhaps the top of the
pivot shaft should be angled to the rear when the Eagle is empty so
that with the pilot, parachute and normal fuel load it would sit about
vertical, and with a passenger included it would angle a little
forward. I'm interested in what comments others on this newsgroup may
have about this subject.

A few years ago I found the leaf springs on my truck had gone flat,
and I found a shop in the nearby city that would anneal them, re-arc
back to standard dimensions, and heat treat. This was their full time
business and they did a good job -- my truck springs are still good.
I was thinking about getting the Eagle springs done but I don't know
how much they need to be changed in order to make the pivot shaft
vertical (if indeed it is supposed to be). I was thinking of heating
up the springs red hot, allowing them to cool very slowly, bending
them to the dimensions I wanted, and then having this shop heat treat
them. I also see a few 1.25" wide steel tailwheel leaf springs
available at Aircraft Spruce under landing gear/tailwheel accessories.

Cheers,

Al MacDonald


On Apr 3, 9:06 pm, Conrad Nordquist <conradnordqu...@sbcglobal.net>
wrote:

[David Wolf]

The parameter we are discussing is called "trail." It is the distance
between the wheel touchdown point and the point at which the pivot bearing
axis intersects the ground. It is really critical on motorcycle choppers to
get them to ride descent at all.

This is from memory so I may get some details wrong but you'll get the idea.
Let's call positive trail the case where the touchdown point is aft of the
axis intersection with the ground. This is the stable case. If it is too
positive it won't steer. The other case, negative trail, in which the
tailwheel touchdown point is forward of the axis intersection, is unstable.
Kind of like pushing a shopping cart backwards. It wants to veer off. I am
not exactly sure where a "shimmy" fits in this discussion but I think it is
affected by the amount of trail and spring tensions balance. My intuition
says that tight side springs would cause shimmy by causing an overshoot in
the restoring force with positive trail. I have positive trail and loose
springs and no problem. Note that trail would go unstable, more negative,
as the mounting spring bends up more. My thinking is that significant
negative trail can be grossly uncontrollable well beyond a shimmy problem.

Please feel free to fix this discussion as you might see error.

Dave

[FrancoisMarquis]

Aircraft Spruce P/N 06-14200: $106

It is also true that it is a Cub leaf spring!

Francois Marquis

On Apr 3, 11:06 pm, Conrad Nordquist <conradnordqu...@sbcglobal.net>
wrote: