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Why 4130 tube?



 
 
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  #1  
Old March 18th 04, 03:19 AM
Leon McAtee
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Default 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?
  #2  
Old March 18th 04, 04:27 AM
Drew Dalgleish
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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
  #3  
Old March 18th 04, 07:55 AM
Ron Webb
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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.



  #4  
Old March 18th 04, 02:07 PM
Corky Scott
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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
  #5  
Old March 18th 04, 04:50 PM
Kevin Horton
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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

  #6  
Old March 18th 04, 05:02 PM
Richard Lamb
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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
  #7  
Old March 18th 04, 07:32 PM
Ron Webb
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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.


  #8  
Old March 18th 04, 11:42 PM
VideoFlyer
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A wise man, I think!

  #9  
Old March 18th 04, 11:55 PM
Leon McAtee
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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
  #10  
Old March 19th 04, 12:05 AM
Rich S.
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"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.


 




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