Why 4130 tube?

Leon McAtee wrote:

Why do we homebuilders use 4130 tube? My old Aeronca does just fine
being made of mild steel. A bit of napkin calcs says that going up
just one tube diameter for the size tube we normally use, the area,
and the strength/weight goes up between 15% and 20%. This pretty
much offsets the difference in tensile strength between 4130 N and
1026, and more than offsets it for something like 1040. 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.

For a typical rag and tube plane, properly choosing the tube sizes
should result in a weight gain of less than 15% for the same strength
which is, what, around 20 pounds for something like a Tailwind or
Aeronca. This to me seems like a good trade off to eliminate the
possibility of cracked welds due to poor technique. Not to mention
maybe saving a few bucks and being able to get the steel locally.

Could the availability of cheap WWII surplus steel have created a
tradition that has persisted in spite of other possibly superior
options?

I would think the 20 pound weight savings would be incentive enough.
But that's just me.

You know how hard it is to pull 20 pounds off of a bare airframe?

Or a girlfriend?

Richard

You know how hard it is to pull 20 pounds off of a bare airframe?

Or a girlfriend?



Lessee...20 pounds heavier, but not as brittle or corrosive...cheaper to
acquire, and easier to work with...

Sounds like my kind of girlfriend too.

A wise man, I think!

In Ron Webb wrote:

Lessee...20 pounds heavier, but not as brittle or corrosive...cheaper
to acquire, and easier to work with...

There is no difference between mild steel and 4130 as far as corrosion
resistance is concerned, and in a traditional welded tube aircraft
structure any increase in brittleness is going to be a non-issue. If
you hit something hard enough to break (not just bend) it, you probably
wouldn't have survived anyway. I've flown in an aircraft with a 4130
tube fuselage that was rebuilt following a stall/incipient spin incident
from (very) low altitude. Some tubes were bent but as I recall nothing
actually separated. Pilot and passenger both walked away.

----------------------------------------------------
Del Rawlins-
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There is no difference between mild steel and 4130 as far as corrosion
resistance is concerned,

Now you have got my curiosity in gear. As I said, my personal experience is
that I have seen a significant differance.

I went looking for some quantized data on the subject. I have not found what
I was looking for on the net, and may run up to the University library later
on. For now I found
http://www.armycorrosion.com/summit2...PM/schario.pdf

It does not have much in the way of quantized data, comparing 1010 to 4130
corrosion properties, but there is enough to refute the claim that there is
no differance.

Anybody got a link that does a better job with this?

Ron Webb wrote:
There is no difference between mild steel and 4130 as far as
corrosion resistance is concerned,

Now you have got my curiosity in gear. As I said, my personal
experience is that I have seen a significant differance.

I went looking for some quantized data on the subject. I have not
found what I was looking for on the net, and may run up to the
University library later on. For now I found http://www.armycorrosion.
com/summit2001/DAY_1_PM/schario.pdf

It does not have much in the way of quantized data, comparing 1010 to
4130 corrosion properties, but there is enough to refute the claim
that there is no differance.

The stuff in my garage doesn't seem to notice any difference. It is
more than happy to rust if I don't do anything to protect it. It could
be that it happens slower; I haven't done any sort of scientific testing
to see. But the bottom line is that rusty is rusty.

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

Richard Lamb wrote in message ...
You know how hard it is to pull 20 pounds off of a bare airframe?

Or a girlfriend?

Richard

Depends on the girl............. one simple comment can do the job -
if your willing to be the recipient of the other reactions as wellG

20 pounds may seem like a lot on a bare airframe but in the grand
scheme it's not really significant. My Aeronca for example lost a LOT
more than that with the change from Linen to Dacron. With the other
modern materials available to us now, that 20 lbs (if that) can be
made up for elsewhere. I know guys that have more than 20 lbs of junk
stashed in their planes that they haven't even looked at for years.

Other than weight - IS - there a reason not to use 1026 DOM? This
assumes of course that the design is based on the slightly lesser
strength and/or has adequate design margins to begins with.

==================
Leon McAtee

"Leon McAtee" wrote in message
m...

Other than weight - IS - there a reason not to use 1026 DOM? This
assumes of course that the design is based on the slightly lesser
strength and/or has adequate design margins to begins with.

I'll never forget the time I machined a new axle stub for a friend's boat
trailer. I bought a blank from the trailer parts company that was made from,
"1020 *Plow* steel". We installed it, lowered the jack and the axle
proceeded to slowly bend under the weight of the boat until the tire hit the
fender.

I bought a chunk of normalized 4130 and turned a new axle stub. He used it
for five years and never had a problem.

'Course this would never happen with that 1000 series steel from XYZ
company.

Rich "Mebbe you could save a buck on the leather jacket and silk scarf" S.

"Rich S." wrote in message ...

'Course this would never happen with that 1000 series steel from XYZ
company.

Rich "Mebbe you could save a buck on the leather jacket and silk scarf" S.

Money saving is not my main motivation. In fact the local rusty stuff
purveyor wants - more - for local 10XX tube than AS+S 4130 W/shipping
would cost. From what I have been able to gleen from the Internet
1026 DOM looses a good bit of strength when welded (normalized state)
but something like 1040 DOM ends up with 92% of the yeild strength of
4130 N after application of fusing heat.

The down side of the 1040 seems to be that post heating is recomended
- the same as 4130 (says one Internet source). Does this mean that
1040 has similar problems with embrittlement in the HAZ as 4130? This
seems kind of odd considering the stuff is originally resistance
welded during fabrication. The same source says nothing about post
heating of 1020.

===================
Leon McAtee

Leon McAtee wrote:

Richard Lamb wrote in message ...
You know how hard it is to pull 20 pounds off of a bare airframe?

Or a girlfriend?

Richard

Depends on the girl............. one simple comment can do the job -
if your willing to be the recipient of the other reactions as wellG

20 pounds may seem like a lot on a bare airframe but in the grand
scheme it's not really significant. My Aeronca for example lost a LOT
more than that with the change from Linen to Dacron. With the other
modern materials available to us now, that 20 lbs (if that) can be
made up for elsewhere. I know guys that have more than 20 lbs of junk
stashed in their planes that they haven't even looked at for years.

Other than weight - IS - there a reason not to use 1026 DOM? This
assumes of course that the design is based on the slightly lesser
strength and/or has adequate design margins to begins with.

==================
Leon McAtee

I think it's the last assumption that won't let me let go here, Leon.
WAS that structure originally designed for mild steel of 4130.


Also, there is a subtlety here that only applies to airplanes.

Building a truss structure with heavier tube probably doesn't ring
bells and wave red flags for you, but it really should.

It's not the actual increase in weight that's the issue, but the
distribution of that weight.

(everybody look blank for a moment and say "huh?")

But wouldn't the increased weight would be evenly distributed?
Very true.

The extra weight in the cockpit section is hardly noticeable
BECAUSE
it's all close to the center of lift.

But.

The longerons, verticals, diags, tail feathers, etc. in the aft section
all weigh more too.

And THAT increased weight can be a real serious BALANCE issue.

(Sorry for the caps, but I get loud when I preach
the Gospel according to Weight and Balance)

Can I get an Amen?


Richard