On 17 Mar 2004 18:19:11 -0800, (Leon McAtee)
wrote:

The "mild
steels" can be welded using MIG or TIG with little worries about HAZ
and since we are not heat treating the 4130 to obtain its strength
advantage it seems to me to actually be a poorer choice for amateur
aircraft construction.

To add to Corky's comments, 4130 can be TIG welded with little worry
about the HAZ as well, which is how I am welding the steel components of
my Bearhawk together. I may do some stress relief of critical clusters
and attach points using a rosebud torch, not because I think it is
necessary, but only because it is easy and I haven't seen a convincing
argument that it hurts anything to do so. MIG welding of aircraft steel
components is generally not recommended, not because of the alloy so
much as it is difficult to control the heat applied throughout the weld.
What an amateur can end up with using MIG, is a weld that starts cold
and finishes burning through. It is also possible to lay down a nice
looking bead with MIG that doesn't have any real strength to it. This
is less likely with TIG, and darn near impossible with oxy/acetylene
welding.

While it is true that we don't typically heat treat 4130 to obtain the
ultimate stength that it is capable of, the normalized condition that it
is generally supplied in is a heat treat which is optimized to provide a
good compromise between strength and toughness. This is what makes a
steel tube fuselage hold together and protect its occupants during an
accident.

Finally, any cost difference to be had using mild steel instead of 4130
is totally insignificant compared to other costs incurred during a
homebuilt project. The 4130 for my fuselage should run a little over
$1000, while I may end up spending 20 to 30 grand on an engine package.
Even if it only saves me 20 pounds, that is 20 pounds that I won't have
to carry for the life of my airplane. That is also 20 pounds more of
gear, fuel, or whatever than I can carry for the life of the airframe.
I don't know about you, but I'm planning on keeping my plane for a long
time, considering the trouble I am going to in order to build it.
Figure that I am 29 now, hope to fly it before I turn 35, and plan to
fly it as long as I am medically able to do so. I'd have to truly be a
retard to want to skimp on materials in this fashion, even if the parts
were resized to maintain equal strength.

----------------------------------------------------
Del Rawlins-
Remove _kills_spammers_ to reply via email.
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/