/tech/ - Technology★

This is just a guess but it sounds like you answered your own question. Weight. It makes sense that they'd be used in tiny planes like racing planes but anything bigger the weight is the biggest factor. The stresses they encounter just aren't that high compared to the benefit from weight savings.

>>1038099 (OP)

>about the same strength/weight ratio.

Maybe so, but steel is about 2.5x the density of aluminum. Airliner skin is already constructed out of sheets just 1mm thick. Equivalent mass steel sheets would be just 0.4mm thick. I would think this makes aluminum the easier option to work with. What would be the benefit of using steel?

lrn2 statics

Bear in mind that this isn't just pure aluminum vs pure steel. You're referring to alloys in both cases, so the numbers are going to be different.

>>1038242

Obviously, i'm talking about chromoly 4130 steel vs 6000 seriers aluminum which is the most used in aviation.

The characteristics of the material remains, you can add some tensile strength to aluminum but it still has a fatigue limit, it will break after a finite number of use.

Going with a lighter material like aluminum, you get a thicker skin and/or larger diameter tube.

This in turn gives you higher area moments of inertia.

>steel tubes

>tubes

How exactly are you connecting those?

Since you are in aviation, they have to be flexible, so welding isn't a possibility, as that might alter the steels hardness.

AFAIK, bolting stuff together is the go-to solution in aviation, but bolting together tubes seems to be rather sub-optimal.

Also, I think steel might be to rigid for the needs of aviation, though I'm no expert on that matter.

>>1038099 (OP)

>>1038217

You can't just use a steel tube to replace an aluminum fuselage because there are two causes for failure in aerospace engineering: rupture and deformation. A steel tube does not have sufficient shape stability to warrant how much it weighs, you would still need bulkheads and probably stringers to make sure that skin is shape stable. If you mean we should move to a welded steel structure, I'd like to ask what the point of that is. That is still going to weigh more than the traditional method of building aircraft structure and definitely more than using modern composites. Speaking of modern composites, most of the cost associated with aircraft is in R&D, meaning you might as well not cut corners and just use the best materials that you can (in most cases). Carbon and fiberglass composites have a much higher strength to weight ratio than steel and can be implemented in a way which save considerable weight.

>will last indefinitely if properly protected against corrosion

That's the other thing, it's very difficult to completely protect a steel structure from corrosion and it may not always be visible.

There is a reason we don't built planes like we build bridges.

>>1038099 (OP)

>the weight penalty is limited

>why don't large aircraft use them?

If you're too retarded to understand why you answered your own question stop posting.

A small 10% weight penalty on a 747 (large) aircraft would be an extra 20 tons (1ton=1000kg)

>>1038311

>Welding isn't a possibility

Yes it is

>boliting is the go-to solution in aviation

>steel might be too rigid

Carbon fiber is currently replacing Aluminum, its way more rigid then steel and the pieces are held together with fucking glue !

There are aircrafts out there made out of 100% carbon fibers

>>1038217

So here's a question for you: In your pic it shows the diagonal trusses go one way instead of crossing both ways. From playing bridge simulators and also geometry it seems like this would make the structure have differing response to stress based on which direction is coming from. What's the logic of this kind of design? Is it just assumed that tensile and compression strength are identical for the tubes?