Why 4130 tube?

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?

On 17 Mar 2004 18:19:11 -0800, (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 built a set of wheel skis for my plane last fall. They are welded
mild steel tube with 1/2" thick plastic bottoms. I couldn't see any
advantage to uing 4130. My cost for everything including rigging was
under $200
Drew

I regularly use square ASTM A500 tube for all sorts of stuff. I like it a
lot, because MIG welding is much easier, it is very cheap.

It seems to resist corrosion much better. I left a rack on my pickup
unpainted all winter and there was very little rust when I painted it last
week. 4130 would have been badly corroded by now.

Square tubing also means that when I cut an angle with my cutoff saw, it
fits perfectly...no filing or joint jigger gadget needed.

My Adventurer Amphibian kit uses square tubing of some sort. I expect it's
just this same cheap structural stuff, even the engine mount and landing
gear are made of it. The Adventurer has a bad reputation (for such a cool
airplane), but not for THAT.
http://beta.communities.fr.msn.ca/Ad...entalAmphibian

I think the reason airplane types use 4130 is mostly tradition, and an
insistence that we need to have the best. But "the best" hasn't been
redefined since the 1950s.



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.

On 17 Mar 2004 18:19:11 -0800, (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?

There's really nothing wrong with using mild steel tubing to construct
a fuselage with the following caveat's: 1. That you properly size the
tubing and wall thickness to give you the proper strength. 2. That
you can find it.

I've read several times over the last few years that mild steel tubing
is almost as expensive as 4130, but I don't know that from personal
experience.

The last thing I'd mention is that because 4130 is stronger and
stiffer, you can probably use tubing that is lighter than mild steel
to construct your fuselage and still have a strong fuselage. In
airplanes, saving weight is almost a formal religion. The more weight
you save, the more weight you can carry, or the better the performance
or both.

Corky Scott

On Thu, 18 Mar 2004 13:07:22 +0000, Corky Scott wrote:

The last thing I'd mention is that because 4130 is stronger and stiffer,
you can probably use tubing that is lighter than mild steel to construct
your fuselage and still have a strong fuselage. In airplanes, saving
weight is almost a formal religion. The more weight you save, the more
weight you can carry, or the better the performance or both.

Corky Scott

4130 is certainly stronger than mild steel, but the modulus of elasticity
of all steel is about 29-30 ksi, with very, very small variations
depending on alloy. So for a given tube diameter and wall thickness, the
mild steel tube and the 4130 tube will have the same stiffness. If you
increase the diameter of the mild steel tube to make up for it having a
lower strength than the 4130, then the mild steel tube will be stiffer
than the 4130 tube.

The following links show modulus of elasticity of 29 ksi for mild steel,
and 29.7 ksi for 4130 steel, or a 2.5% difference. Not really significant.

http://www.matweb.com/search/Specifi...bassnum=M1030F

http://www.matweb.com/search/Specifi...bassnum=M4130A
--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

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/

Del Rawlins wrote in message ...

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,

Seems to be a contradiction here. If TIG works so well why bother
with the "stress relief of critical clusters and attach points"? This
either implies that the welding process is not completely acceptable,
or the rest of the structure has been over built and less than ideal
welds are acceptable. If the later is the case why not use something
like 1026 DOM and forget the post heat alltogether?

I'm not from Missouri but I still need to be shown that TIG is truly
acceptable for welding 4130. (I have a TIG and could use it, but
don't) I know some certified plane builders do it this way, and have
heard that at least one uses MIG, but to me it seems that heat is
heat, no matter how it is introduced to the metal. From my limited
understanding of metallurgy it's not the quantity of the energy put
into the metal it's the energy density, or peak heat, that is the
determining factor, coupled with the rate of cooling. The HAZ may be
smaller and closer to the weld with TIG but it - is - still there.
Isn't it? Maybe because the TIG HAZ is closer to the weld, and
therefore has a larger area than than the HAZ would have after being
chased out into the tube, one can get a stronger overall stucture by
not post heating a TIG weld?

Just to clear up a possible misconception from another poster - I am
NOT suggesting to, or wishing to, substitute ERW DOM mild steel for
4130 in an existing design. I'm well aware of the cascade effect of
changing something on an existing design.

If TIG, or MIG (I'm real good at MIG of thin metal, done lots of it)
welding of 4130 results in an overall better airframe then I'll stick
to 4130. But if there is a substitute, like 1040 DOM, that has a
strength only slightly less than 4130 N, that can be welded with out
any worry of developing a critical HAZ (not 100% sure about this),
then to me that would seem to be a better option for the average
homebuilder.

I'm not trying to be argumentative and have no desire to ignite any
flame here. I do like to occasionally challenge the accepted
traditions to see if there might be a "better" way of doing things.
Even if there isn't a better way I, and maybe some others, will get a
better understanding of just why "we do it that way".

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

"Leon McAtee" wrote in message
om...

I'm not trying to be argumentative and have no desire to ignite any
flame here. I do like to occasionally challenge the accepted
traditions to see if there might be a "better" way of doing things.
Even if there isn't a better way I, and maybe some others, will get a
better understanding of just why "we do it that way".

Understand where you are coming from, Leon. It seems that you are walking
awfully close to the line between "builder" and "designer" - one which I
avoid like STD's. )

The pitfalls of changing a design are many and legendary. One thing seems to
lead to another and it is my opinion that it takes an aeronautical design
engineer who is specifically trained in the field of homebuilt light
aircraft to fully comprehend and integrate changes to proven designs. You
say, "it's only 20 pounds"; but that may have far-reaching effects which are
not evident to a builder.

That being said, I would think that a change from 4130 steel to 2024
Aluminum would have many more advantages than from 4130 --- 1026. I was
given the option on the plans for my airplane to use either 1/4" 4130 or
3/8" 2024 Al for the wing joining plates. The 2024 was stronger and lighter,
so I chose to use aluminum. The difference here was that it was written
right there in the plans. I would not have elected to do this myself.

From what I've heard, the builder of John Denver's Long Eze had a better
idea for the location of the fuel selector valve. . .

Regards,
Rich S.

In Leon McAtee wrote:
Del Rawlins wrote in message
...

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,

Seems to be a contradiction here. If TIG works so well why bother
with the "stress relief of critical clusters and attach points"? This
either implies that the welding process is not completely acceptable,
or the rest of the structure has been over built and less than ideal
welds are acceptable. If the later is the case why not use something
like 1026 DOM and forget the post heat alltogether?

No contradiction. I haven't been convinced that stress relief is
necessary, but neither have I been convinced that it hurts anything, and
it only takes all of a few minutes to accomplish. From what I can tell,
even experienced welders can't agree on whether or not it is desirable.

I'm not from Missouri but I still need to be shown that TIG is truly
acceptable for welding 4130.

Over and above 50 odd years of experience in the aerospace industry?
I'm going to say Arkansas, but that's only a guess.

(I have a TIG and could use it, but
don't) I know some certified plane builders do it this way, and have
heard that at least one uses MIG, but to me it seems that heat is
heat, no matter how it is introduced to the metal. From my limited
understanding of metallurgy it's not the quantity of the energy put
into the metal it's the energy density, or peak heat, that is the
determining factor, coupled with the rate of cooling.

Speaking of contradictions, if heat is heat, why do you still need to be
shown that TIG is acceptable for welding 4130?

The HAZ may be
smaller and closer to the weld with TIG but it - is - still there.
Isn't it? Maybe because the TIG HAZ is closer to the weld, and
therefore has a larger area than than the HAZ would have after being
chased out into the tube, one can get a stronger overall stucture by
not post heating a TIG weld?

That's possible, I don't know.

Just to clear up a possible misconception from another poster - I am
NOT suggesting to, or wishing to, substitute ERW DOM mild steel for
4130 in an existing design. I'm well aware of the cascade effect of
changing something on an existing design.

If TIG, or MIG (I'm real good at MIG of thin metal, done lots of it)
welding of 4130 results in an overall better airframe then I'll stick
to 4130. But if there is a substitute, like 1040 DOM, that has a
strength only slightly less than 4130 N, that can be welded with out
any worry of developing a critical HAZ (not 100% sure about this),
then to me that would seem to be a better option for the average
homebuilder.

To play devil's advocate, I would like to be shown instances where
amateur TIG welding of 4130N resulted in homebuilt aircraft falling out
of the sky. Also, before deciding to switch from 4130 to something else
based on price, check out the prices at Dillsburg Aero in Pennsylvania.
Members of the Bearhawk list who live nearby to ACS in California, have
reported that it is still significantly cheaper to have 4130 shipped
from Charlie Vogelsong at Dillsburg than to buy it locally at ACS.

I'm not trying to be argumentative and have no desire to ignite any
flame here. I do like to occasionally challenge the accepted
traditions to see if there might be a "better" way of doing things.
Even if there isn't a better way I, and maybe some others, will get a
better understanding of just why "we do it that way".

Understood. As a relative newcomer to aviation, I get sick and tired of
the deeply held beliefs of many of the mechanics and pilots I encounter,
which often have no basis in reality, or are based on obsolete
information.

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

Del Rawlins wrote:
In Leon McAtee wrote:

Del Rawlins wrote in message
...


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,

Seems to be a contradiction here. If TIG works so well why bother
with the "stress relief of critical clusters and attach points"? This
either implies that the welding process is not completely acceptable,
or the rest of the structure has been over built and less than ideal
welds are acceptable. If the later is the case why not use something
like 1026 DOM and forget the post heat alltogether?


No contradiction. I haven't been convinced that stress relief is
necessary, but neither have I been convinced that it hurts anything, and
it only takes all of a few minutes to accomplish. From what I can tell,
even experienced welders can't agree on whether or not it is desirable.


I'm not from Missouri but I still need to be shown that TIG is truly
acceptable for welding 4130.


Over and above 50 odd years of experience in the aerospace industry?
I'm going to say Arkansas, but that's only a guess.



It was my understanding that the problem with TIG is that it doesn't put
in ENOUGH heat. That is, it melts the steel at only a very limited
section, as soon as you move on all the surround steel sucks the heat
out, basically quenching the weld and making 4130 brittle.

Don't know if it was my lack of skill, the cheap TIG contraption I was
using, or misaligned stars, but the few test pieces I TIGed together
came apart with my bare hands. I'm strong, but not like that. I
decided to stick with OcyAcet.

Luckily, I'm almost done with it.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber