Stainless Structures?

[dynacure]

I would like to know out of an engineering point of view how welded stainless
structures are rated in gyrocopter design. The Spanish ELA as well as the German MT-03 are build in 2 - 2 stainless, AISI 304 I do believe. Besides many
European UL-trikes are build that way. Please, shine your light on this subject.

BTW, thickness is like 1.5 mm.

[donshoebridge]

Willem,

This is news to me. I have never seen a welded stainless airframe. The first obvious fact is that it would be very heavy. But, as has been proven with the F-4 Phanton (jet fighter), anything will fly with enough power. :)

[Not Yet]

Stainless steel is about 75% iron; yes even the nonmagnetic verities…300 sires.
Stainless requires free oxygen to remain stainless. So it must be polished or it will rust. It usually just gets a tan color to it. It is also very sensitive to crevice corrosion. A tiny pin hole in a weld can allow the inside to rust away leaving a nice pretty outside with no strength left. I have seen a sailboat mast go over the side because of this.
So use it with care.

[dynacure]

Manufacturer of the MT-03, Autogyro Europe Gmbh, does electropolish their
frames. I am not very well informed on the ELA, but to me it is an older Magni
design they sold to Spain and now it has a SS structure.

[donshoebridge]

Stainless steel is about 75% iron; yes even the nonmagnetic verities…300 sires.
Stainless requires free oxygen to remain stainless. So it must be polished or it will rust. It usually just gets a tan color to it. It is also very sensitive to crevice corrosion. A tiny pin hole in a weld can allow the inside to rust away leaving a nice pretty outside with no strength left. I have seen a sailboat mast go over the side because of this.
So use it with care.

I now have another reason not to buy stainless firearms. Thanks David.

Hey! I just noticed that you are in Waterford. I grew up in White Lake. My mom still lives there.

[jos]

Stainless is a very dangerous material for welding.
Extreme care needs to be taken during welding. The welds always look good but without extreme care ther are a billion micro porosity's.
Stainless is a lot weaker to deformation than 4130.
It bends very easily,but has a strenght close to 4130.
The ELA people had a lot of problems with broken welds, hopefully it is past now.



JOS

[Sapientino]

Manufacturer of the MT-03, Autogyro Europe Gmbh, does electropolish their
frames. I am not very well informed on the ELA, but to me it is an older Magni
design they sold to Spain and now it has a SS structure.

For sure is not an old magni besides it is very similar.
material choiche in ELA is not so understandable to me:
they use stainless steel for the airframe (with the big problem in welding you mention and poor mechanich caracteristic), and they paint it (so they don't need it for anti rust purpose!)
and for the rotor head they use stainless steel and peralluman (very problematic in my opinion)
and not other more usefull material (like 2024 and high resistence steel)
for me is a mistery!
on the other hand I must say I flew it and it flies very well (it is very similar to magni but with less stick shake)

Sapientino

[Jim]

Very good aeroplanes have been built using stainless steel. About 15 years ago an excellent German aerobatic plane was build with stainless steel tubes in the fuselage. (I think that it was the Extra 300, but my memory may fail me.) This plain had to endure high g-loads.

I am suspicious of stainless steel though: As Jos said: welding it is not difficult, (I have done that with TIG for an exhaust manifold) but to do it without contamination takes a lot of skill and knowledge. — The filler and base material must be 100% compatible and the shielding inert gasses must really form a good shield during the welding process. Vibration and stresses also tend to harden stainless steel — to the point where it becomes brittle, cracks and break. A high safety factor therefore needs to be build in.

I therefore hope that the folks building the ELA and the MT-03 took all the factors into consideration. If they did these machines may be very good.

Jim

[jos]

Simple exercise, take two almost identical pieces of flat material one stainless, next 4130 and try to bend in a vise.
The stainless bends with half the force of the 4130.
The 4130 needs to have a far bigger deformation before it stay's bend. It is a lot more flexible
The stainless get very hard and brittle where it bends.
The weight of stainless and 4130 is similar.
The cost for 4130 is higher but it is a far better material to work with and to fly with.


JOS


JOS