Why 4130 tube?

Richard Lamb wrote:

Leon McAtee wrote:

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

Or a girlfriend?

Richard

Off of a dressed girlfriend is easy off a bare one is tought!

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.


you are probably correct there.

I'm slowly restoring an Auster built from T45. that is an alloy which
preceeded 4130 and has a tensile strength of 45 tons to the square
inch.
you get to appreciate lots of things beadblasting a 50 year old
fuselage. the thing I appreciate most is that the alloying components
have protected the steel from corrosion so much that a simple bead
blast and a repaint is all that 99% of the entire fuselage requires.

you get the same corrosion resistance with 4130.
moisture that only sees light surface corrosion in 4130 will probably
deeply pit a mild steel component.

my tailwind fuselage is 4130 and has no discernable rust in 18 years.

for corrosion resistance alone I'd go the extra mile for the
recognised alloy.
Stealth Pilot
Australia

Gentlemen,
I have no real experience and very little formal training. The
absolute reliance on 4130 is a wives tale. Very serviceable aircraft
were and are built regularly with mild steel tube. For amateur
construction mild steel makes more sense than 4130. On the Yahoo
Piper Cub site in the files section is a factory drawing of a Super
Cub fuselage. It is predominently mild steel in the sizes of 3/8-7/8
..035 wall. These planes did not rust away or disappear from tubing
failure. The US military materials book from WW2 notes that after
welding 4130 is reduced substantially in tension, 74 thousand #/ as
compared to mild steels 54 thousand #/, and the compression of tubes
is a minor difference in the lengths we deal with. Please reference
Bob Whittier's book on tubing for this discussion.

The problem of weight moving backward is real but not a reason for not
using mild steel. The Circa Nieuports with thier aluminum tubes work
fine, it is a matter of design. A second coat of paint, a big swivel
tail wheel, or balancing the elevator will be as much of a change and
many homebuilts have these changes made over the plans regularly. If
a guy can't keep control of his C of G then he needs help. I have
done a design study using .049 mild steel to replace .035 4130 in a
standard low wing Warren truss fuselage. The effect on the C of G was
neglidgeable due to the increased weight in the forward fuselage were
the largest and more cocentrated collections of tubing existed. The
added weight in the tail feathers was compensated for with a movement
of the speced A65 forward 2-3 inches. I've decided to use wooden tail
feathers and actually save a lot of weight.

Many homebuilts do not come close to the designers empty weight and
operate over stated design grosses all the time, even those built from
4130. Or the guy who puts an extra hundred #'s of Lyc. and electrics
in an A65 design is never questioned so severly as a guy who wants to
use mild steel tube accepted and certified for aircraft construction
by civil and military specs for 70 years.

Many fine planes were built and designed using common sense, alternate
materials and the engineering from established designs. Pete Bowers
discussed this in his book on Homebuilts he wrote in the seventies
prior to the litigation era we now live in. In fact I have a
collection of fuselage plans from the past and they would appear to be
designed in 1930 out of light gauge mild steel and copied since.

Recently I saw some sitka from an established aircraft supplier. I
wouldn't have used it for ladder rails. I have hand picked perfect
quarter sawn Western Hemlock for a fraction of the cost at a local
building store that was far superior to the aircraft grade stuff that
cost more in brokerage fees than my wood. Get educated about
inspection and alternatives using established experts and build around
the limitation. A can of line oil or linseed oil used according to
Tony Bingelis in a properly ventilated fuselage will take care of
rust. Probably good idea with 4130 as well.

To All:

Bob Babcock's conclusions closely match my own.

I believe anyone wishing to become airborne safely and at least cost should
devote a bit of time to the areas Bob has mentioned, then draw your own
conclusions.

On close examination a great deal of the aviation information available on the
internet turns out to be one novice parroting another. Tracked back to its
source, many of the Conventional Wisdoms espoused by the novice as fact turn
out to be tainted with commercialism, fallacious data meant to promote a
particular product or dealer.

Due to the anonymous nature of the internet I think the wiser course is to
assume EVERYTHING you read here is bull**** (yes, even this :-) and to not
accept any opinion as valid simply because it is popular.

Think for YOURSELF.

-R.S.Hoover

On 27 Mar 2004 23:12:41 GMT, (Veeduber) wrote:

To All:

Bob Babcock's conclusions closely match my own.

I believe anyone wishing to become airborne safely and at least cost should
devote a bit of time to the areas Bob has mentioned, then draw your own
conclusions.

On close examination a great deal of the aviation information available on the
internet turns out to be one novice parroting another. Tracked back to its
source, many of the Conventional Wisdoms espoused by the novice as fact turn
out to be tainted with commercialism, fallacious data meant to promote a
particular product or dealer.

Due to the anonymous nature of the internet I think the wiser course is to
assume EVERYTHING you read here is bull**** (yes, even this :-) and to not
accept any opinion as valid simply because it is popular.

precisely.


.....but I have this 1951 Auster fuselage out in the workshop that I
have beadblasted all myself and it did have one or two areas of
corrosion.
take the rudder for instance.
someone forgot to put in the bottom two drain holes.
that rudder had something like 50 tide lines formed in rust on the
inside of the cotton covering. the entire bottom steel bow of the
rudder was corroded almost totally away.
a quarter of an inch above the rust I hacksawed it through. there was
not one hint of rust inside the sound tube.
the combinations of alloy and surface passivation advocated over the
years actually do work.
the bow is repaired in 4130 and the bottom rib is stainless steel tig
welded.

4 reasons to use 4130.
the design was stressed for it.
it offers better strength to weight ratio
bare surfaces of it have better corrosion characterstics.
it is available in tube sizes which are neat fits inside each other.

if your design was intended for mild steel then go for it.
typically all the homebuilts by Roger Druine were designed for mild
steel fittings. make sure they are adequately corrosion proofed.

if your design was competently stressed for mild steel then go for it.

in either steel dont be stupid and use square tube. it is needlessly
heavier. (calc the amount of steel in an inch square with 1/8" wall
thickness and do the same for inch round with 1/8" wall thickness. the
reason isnt rocket science)

btw every time my tailwind does a heavy arrival I'm thankful that the
fuselage is 20% stronger than mild steel.
ymmv.
Stealth Pilot