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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Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/

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/

But the bottom line is that rusty is rusty.



Agreed...but if it took 30 years to rust out the back of the longerons on
your new float equipped Bearhawk to the point of them being unsafe, since
they are .049" 4130 - but it would take 100 years to do the same thing to
..063 1010 --that might be enough to tip the scales if the weight differance
was 20 pounds or so...

OK, I'll admit it...I made the longerons on my MoHawk out of 1/2 x.032
4130 too, just like the plans say...but there are MANY things I'd do
differently if I was starting over...like start with a set of Bearhawk plans
for instance;^}

In Ron Webb wrote:

Agreed...but if it took 30 years to rust out the back of the longerons
on your new float equipped Bearhawk to the point of them being unsafe,
since they are .049" 4130 - but it would take 100 years to do the same
thing to ..063 1010 --that might be enough to tip the scales if the
weight differance was 20 pounds or so...

My position is that if the lower longerons are getting rusty, there are
other parts in there that I need to be just as concerned about. Beefing
up parts doesn't make the airframe any stronger necessarily, it only
shifts the weak point elsewhere. I would expect that to be true of
corrosion issues as well as overall strength. I would rather go the
extra mile with corrosion protection measures NOW while the plane is
under construction, than add a bunch of unneeded weight by making
everything thicker. In 20-30 years I will most likely want to tear the
fabric off and inspect everything closely no matter what anyway. I've
got a sandblaster and I'm not afraid to use it.

OK, I'll admit it...I made the longerons on my MoHawk out of 1/2 x.
032 4130 too, just like the plans say...but there are MANY things I'd
do differently if I was starting over...like start with a set of
Bearhawk plans for instance;^}

I hear that a lot. 8^)

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

A building material that is less expensive and more available may in
practice end up building a lighter airframe. The reason is that
you're more likely to be able to use the exact right stock instead of
just over building because you couldn't find or afford the expense to
buy a special piece of the lighter guage material.

Bend versus break. Old cars were build on rigid chassis, the safety
argument was that you want something really strong. But modern cars
are generally built uni-body designated crush zones to dissipate some
of the energy instead of transfering it to the passengers.

"In theory, practice and theory are the same. But in practice, they
are often very different."

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