substitute aluminum for 4130?

[Robert Loer]

Plans call for wing spar to fuselage carry through attach fiitings to be
7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as I
have it on hand.

Your thoughts please. I have plans for another ship which uses the 6061-T6.

Thanks

[Ron Wanttaja]

On Sun, 21 Jan 2007 23:01:03 -0800, "Robert Loer" > wrote:

>Plans call for wing spar to fuselage carry through attach fiitings to be
>7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as I
>have it on hand.
>
>Your thoughts please. I have plans for another ship which uses the 6061-T6.

You're going to bet your life on advice from an anonymous USENET source?
Brrrr......

Ron Wanttaja

[[email protected]]

Robert Loer wrote:
> Plans call for wing spar to fuselage carry through attach fiitings to be
> 7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as I
> have it on hand.
> ----------------------------------------------------------

Hahahahaha! Good one.

This IS a joke, right? Trolling for the sim's? Because it isn't the
material but the load it has to carry, which I couldn't help but notice
was not mentioned.

-R.S.Hoover

[[email protected]]

Robert Loer wrote:
> Plans call for wing spar to fuselage carry through attach fiitings to be
> 7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as I
> have it on hand.
>
> Your thoughts please. I have plans for another ship which uses the 6061-T6.
>

At the maximum design load, how much deflection do you have with each?

What is your factor of safety with each?

If you don't know, don't substitute.

--

FF

[J.Kahn]

wrote:
> Robert Loer wrote:
>> Plans call for wing spar to fuselage carry through attach fiitings to be
>> 7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as I
>> have it on hand.
>>
>> Your thoughts please. I have plans for another ship which uses the 6061-T6.
>>
>
> At the maximum design load, how much deflection do you have with each?
>
> What is your factor of safety with each?
>
> If you don't know, don't substitute.
>

Just for fun, lets work it out.

The 4130 fitting will have a yield strength of around 7600 lbs @70 ksi
yield. The aluminum piece will have about a yield of a little over
4000lbs at 40 ksi yield.

You would have to stack two of of the alum pieces together to get the
same tensile strength. Which would probably open up a whole new can of
worms so it's better just to go with the steel.

John

[jls]

> wrote in message
ps.com...
>
> Robert Loer wrote:
> > Plans call for wing spar to fuselage carry through attach fiitings
to be
> > 7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6
aluminum as I
> > have it on hand.
> >
> > Your thoughts please. I have plans for another ship which uses the
6061-T6.
> >
>
> At the maximum design load, how much deflection do you have with
each?
>
> What is your factor of safety with each?
>
> If you don't know, don't substitute.
>
> --
>
> FF
>

Wing attach fittings on a 1953 Super Cub wing presently undergoing
rebuild in our hangar are 6061-T6 aluminum but quite beefy. Two
quarter-inch plates are bolted to each side of each of the spar webs
at the wing root. Interference fit steel bushings are then pressed
through the plates for the 5/16" diameter wing-attach bolts. The new
PA-18's built in Yakima are probably built with the same alloys, just
my guts feeling.

Wing attach fittings on the fuselage are steel. I don't know if
they're 4130 or not but suspect they are 1025 steel. Some of the
fuselage tubes are 4130, but most of them are 1025. One lift strut is
1025, the other 4130.

[Bob Kuykendall]

Earlier, Robert Loer wrote:
> Plans call for wing spar to fuselage carry through attach fiitings to be
> 7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as I
> have it on hand.
>
> Your thoughts please. I have plans for another ship which uses the 6061-T6.
>
> Thanks

**** Disclaimer: I'm not an engineer. This is not engineering advice.
This is stuff anyone with high-school physics oughta grasp. /disclaimer
****

Executive summary: normalized 4130 steel is good for 90000 psi in
tension. 6061-T6 aluminum is good for 42000 psi in tension. Do the
math.

Just for grins, let's take a swag at the proposed substitution.

For the sake of this swag, let's start by guessing that the fitting is
a simple tang loaded longitudinally through a 1/4" bolt in a hold
drilled through the middle of the metal strap.

The cross-sectional area of the steel strap is (7/8)/8=0.109in^2. The
hole subtracts (1/4)/8=0.031in^2, so the area at the hole station is
0.078in^2. If we say that the ultimate tensile strength of the steel is
90000 psi (90 ksi), that drilled strap might be good for a longitudinal
tension of 90000*.078=7030 pounds force (lbf).

For the proposed aluminum substitution, the cross-section area of the
strap is 9*3/(16^2)=0.105". The hole subtracts (3/16)/4=0.047in^2,
leaving a cross-sectional area at the hole of 0.058in^2.

If we wanted to, we could stop right there. Since the aluminum strap
has less cross-sectional area at the hole than the steel strap, and
since aluminum is generally softer, weaker, and more elastic than
steel, and has less forgiving fatigue properties, we know that the
proposed substitution cannot be as strong in simple tension as the
steel original. That doesn't mean that it isn't strong enough, but we
have way too little information to figure out exactly what "strong
enough" is. All we have to go on is "as strong as the original design,"
so that has to be our guide in this.

However, just for grins let's look at how much weaker:

The proposed substitution has a cross-section at the hole of 0.058in^2.
If we say that the ultimate tensile strength of 6061-T6 is 42 ksi, that
means that our drilled strap might support 42000*.058=2440 lbf. That's
only about a third of what the original will do in simple tension.

Oh, and it gets worse, much worse. Since we're talking about a major
structural attach fitting, there is no guarantee it is only loaded in
simple tension or compression. In fact, it is almost certain that it is
loaded in bending as well. Bending strength and stiffness are related
to the cube of the depth times the width.

I could go on and on about this, but I think we've already made as many
guesses and suppositions as we ought. Without specific details of the
design and how it is loaded we can do no more meaningful analysis. In
fact, the analysis I suggest above is highly suspect without knowing
how the strap is installed and secured.

To wrap this up, I'll not say that you should never consider such
substitutions. After all, homebuilt aircraft are all about making what
you need out of what you can get.

However, it oughta stand to reason that when you substitute weak stuff
for strong stuff, you're going to need a lot more of the weak stuff.
Trying to trade straight across isn't ususally a good idea, and trying
to get away with even less of the weak stuff than that is probably a
bad idea.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24
http://www.hpaircraft.com/glidair

[Capt. Geoffrey Thorpe]

"Bob Kuykendall" > wrote in message
ps.com...
> Earlier, Robert Loer wrote:
>> Plans call for wing spar to fuselage carry through attach fiitings to be
>> 7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as
>> I
>> have it on hand.
<...>
> However, it oughta stand to reason that when you substitute weak stuff
> for strong stuff, you're going to need a lot more of the weak stuff.
> Trying to trade straight across isn't ususally a good idea, and trying
> to get away with even less of the weak stuff than that is probably a
> bad idea.
>
> Thanks, and best regards to all
>
> Bob K.
> http://www.hpaircraft.com/hp-24
> http://www.hpaircraft.com/glidair
>

So, like, you are suggesting that he should go with the Handyman's secret
weapon? Would he have to use the whole roll to make it strong enough?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Bob Kuykendall]

Earlier, Capt. Geoffrey Thorpe wrote:

> So, like, you are suggesting that he should go with the Handyman's secret
> weapon? Would he have to use the whole roll to make it strong enough?

Heh, I hadn't thought of it that way. Some interesting material for
thought there!

One of the things I've been doing for fun lately is proof-loading bits
of rock climbing gear to see what they do under load. My latest test
was this series on a Ukrainian (sp?) camming anchor:

http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=1515428;#1515428

However, I have seen no such test results for good ol' duct tape. What
are its ultimate and yield strengths in ksi and kn? It's Young's
Modulus at 0- 45- and 90-degrees? Peel strength? Which brands are
strongest? Weakest? Inquiring minds want to know!

Once we have that data in hand, we can build a substitution table that
shows how many plies it takes to substitute for various thicknesses of
4130, 2024-T3, 6061-T6, and 7075-T6. An Akaflieg student (a real one, I
mean) can write a thesis on computational methods for analyzing duct
tape laminations, specifically addressing the previously
hard-to-quantify factors of tooth marks, thumbprints, and those places
where it folds over and sticks to itself. AC43.13 change 2e will
address the repair of duct tape laminates, with specific reference to
brand-name materials that went off the market in 1974.

Or something like that... ;)

Thanks, Bob K.

[ChuckSlusarczyk]

In article m>, Bob Kuykendall
says...
>
>Earlier, Capt. Geoffrey Thorpe wrote:
>
>> So, like, you are suggesting that he should go with the Handyman's secret
>> weapon? Would he have to use the whole roll to make it strong enough?
>
>Heh, I hadn't thought of it that way. Some interesting material for
>thought there!
>
>One of the things I've been doing for fun lately is proof-loading bits
>of rock climbing gear to see what they do under load. My latest test
>was this series on a Ukrainian (sp?) camming anchor:
>
>http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=1515428;#1515428
>
>However, I have seen no such test results for good ol' duct tape. What
>are its ultimate and yield strengths in ksi and kn? It's Young's
>Modulus at 0- 45- and 90-degrees? Peel strength? Which brands are
>strongest? Weakest? Inquiring minds want to know!
>
>Once we have that data in hand, we can build a substitution table that
>shows how many plies it takes to substitute for various thicknesses of
>4130, 2024-T3, 6061-T6, and 7075-T6. An Akaflieg student (a real one, I
>mean) can write a thesis on computational methods for analyzing duct
>tape laminations, specifically addressing the previously
>hard-to-quantify factors of tooth marks, thumbprints, and those places
>where it folds over and sticks to itself. AC43.13 change 2e will
>address the repair of duct tape laminates, with specific reference to
>brand-name materials that went off the market in 1974.

Hmmm I guess we would need to know the section modulus as well and the moment of
enertia of th section .Maybe a composite of duct tape and cardboard would give
better stifness .Ahhhh the possibilities are endless :-)

Chuck (tape 'er down boys tape 'er down ) S

[Capt. Geoffrey Thorpe]

"ChuckSlusarczyk" > wrote in message
...
> In article m>, Bob
> Kuykendall
> says...
>>
<...>
>>where it folds over and sticks to itself. AC43.13 change 2e will
>>address the repair of duct tape laminates, with specific reference to
>>brand-name materials that went off the market in 1974.
>
> Hmmm I guess we would need to know the section modulus as well and the
> moment of
> enertia of th section .Maybe a composite of duct tape and cardboard would
> give
> better stifness .Ahhhh the possibilities are endless :-)
>
> Chuck (tape 'er down boys tape 'er down ) S
>

Actually, it should be the optimal substitue for Stitts fabric / Polly blah
blah blah - Duct tape is both self stick and pre-finished...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Phil]

As I remember , it was the substitution of alum. instead of AN Steel bolts
that caused a Thorp T-18 to lose a wing panel at the EAA International
fly-in many years ago , would really want to do the numbers before I would
substitute any material on an aircraft , just the opinion of an old A/C
welder.
Phil Lohiser
Middlefield , Ohio
"Robert Loer" > wrote in message
...
> Plans call for wing spar to fuselage carry through attach fiitings to be
> 7/8x1/8 4130 steel. Advisability of using 9/16x 3/16 6061-T6 aluminum as I
> have it on hand.
>
> Your thoughts please. I have plans for another ship which uses the
> 6061-T6.
>
> Thanks
>

[[email protected]]

Phil wrote:
> As I remember , it was the substitution of alum. instead of AN Steel bolts
> that caused a Thorp T-18 to lose a wing panel at the EAA International
> fly-in many years ago , would really want to do the numbers before I would
> substitute any material on an aircraft , just the opinion of an old A/C
> welder.
> Phil Lohiser
>

I remember another that crashed because the builder used pop
rivets in the spar fittings instead of the AD rivets the plans called
for. Too many homebuilders have died because they made substitutions or
other changes without the knowledge necessary to do it. The designer
often has obscure but important reasons for the materials he specifies,
and the naive builder doesn't realize the peril he creates for himself
and others when he decides that he knows it already.

Dan