Here is what I would do + an explanation of my reasoning:

39" long and a static load of 205 lb gives a bending moment of 39*205 = 7995
in lb.

Assume a ground reaction factor of say 3 which is not unreasonable based on
experience - this can only be a guesstimate because you didn't provide
enough info to calculate it properly. Thus the bending moment at limit load
is 7995 x 3 = 23985 in lb. In order to calculate the actual ground reaction
factor the deflection of the spring has to be calculated, the decent
velocity of the airplane during landing estimated (function of wing loading)
and an analysis performed based on energy of the impact cf strain energy
stored in the spring. Beyond this dicussion.

The max moment will occur where the spring enters the fuselage where the
diameter (D) =1.25" (note I am assuming that this is the critical location
but on some tapered rod springs the maximum may be at some other location on
the spring - it needs a lot more work to establish if that is the case).
The second moment of area (moment of inertia) of the spring at this location
is

I = (pi * D^4) / 64 = 0.1198 in^4

Thus the stress is

s = My/I = 23985 * 0.625 / 0.1198 = 125130 psi

where y = 1.25 / 2 = 0.625"

Applying a safety factor of 1.5 which corresponds to the reserve energy
requirements of FAR 23.723/726 the ultimate stress is 187695 psi.

Assuming that the spring is 4130 / 4140 etc then it is clearly going to need
heat treatment. This approximately equates to Rockwell C 41 (191 ksi). I
would probably heat treat the spring to more like Rockwell C 47-48 to
provide some additional margin (these are typical heat treatment levels for
a landing gear spring).

You will need to anneal the spring prior to straighening. Then re heat treat
following straightening. I would just take the spring to a shop who does
heat treatment work for aircraft - heat treatment is relatively cheap to
have done so their is no sense in trying to save money by taking it to an
auto spring shop etc.

See MIL-H-6875 for specific process specifications for the heat treatment.
Get that from http://stinet.dtic.mil/str/index.html

Only catch is that you are going to have to figure out what alloy the metal
is before you try to anneal and heat treat. Can the kit supplier or builder
help with this ?? Otherwise there are some ways to figure this out but I
won't elaborate on that yet.

Hope that helps .....



"David H. Uhrbrock" wrote in message
news:SWP1d.5756$Xc.546@lakeread01...
After a rough landing, I minimally bent my experimental's tailwheel spring
and need to have it straightened. It is a piece of round solid ferrous
steel, 39" long, 1.25" in greatest diameter as it enters the fuselage
midway along its length and tapers to about 0.75" at each end. Alloy
composition and type of heat treatment are unknown. At max gross, the
static load on the tailwheel is ~205 lb.

Is it possible to have it straightened? If so, what type of shop should I
look for to do this kind of work. Does it need to be heat treated after
straightening and if so, to what PSI. Any help is appreciated. I live in
Phoenix but am glad to ship it somewhere to have the work done right.
Thanks in advance.

Dave Uhrbrock