hypothetical queston about drive shafts

I wonder how Titanium would hold up? I doubt there is a DS out there made of Titanium, but I know that Titanium is very light weight and fairly strong. I would guess the cost would be astronomical, and Titanium is a hard metal to weld so you would have to worry about any welds breaking.
Plus Titanium is a pretty malluble metal so it might not be ideal.
 
It's not that simple and you really shouldn't be asking an open forum this type of question because none of us have the engineering qualifications to answer that question. Call several specialists who make driveshafts for high HP applications and let them guide you. Get more than one opinion.


There are many things to consider when thinking about a driveshaft - shaft length, material and design harmonics, intended shaft rpm, and of course torque (HP is irrelevant to the driveshaft) and other consideration. But again, talk to an expert, don't rely on internet opinions.

I am a structural engineer and have considered the driveshaft question and was Aluminum something I would consider?

First, assuming both the steel and the aluminum shafts are designed correctly, both are just fine in terms of strength. Corrosion stress, fatigue, all that shouldn't be an issue. Now, the real question: Is the lighter aluminum shaft worth the extra expense? If you are looking to reduce static or rolling weight by a few pounds, then that is up to how bad do you want it. But for rotational inertia reduction, the mass moment of inertia of the 3 or 4 inch shafts is so close to that of steel, the difference is marginal at best. Those who drag at the most competitive levels may derive a measurable benefit, but it has to be small. A clutch fly wheel plate would have a MUCH larger difference in rotational inertia compared to the skinny shaft.

My $.02
 
I am a structural engineer and have considered the driveshaft question and was Aluminum something I would consider?

First, assuming both the steel and the aluminum shafts are designed correctly, both are just fine in terms of strength. Corrosion stress, fatigue, all that shouldn't be an issue. Now, the real question: Is the lighter aluminum shaft worth the extra expense? If you are looking to reduce static or rolling weight by a few pounds, then that is up to how bad do you want it. But for rotational inertia reduction, the mass moment of inertia of the 3 or 4 inch shafts is so close to that of steel, the difference is marginal at best. Those who drag at the most competitive levels may derive a measurable benefit, but it has to be small. A clutch fly wheel plate would have a MUCH larger difference in rotational inertia compared to the skinny shaft.

My $.02

I agree that power savings from using an aluminum drive shaft are going to be minimal, because of the shaft diameter and the fact that the drive shaft only accelerates 1 time on a typical drag strip pass, where the flywheel would be accelerated at least 3 times. Most people use aluminum drives shafts when upgrading from the two piece stamped steel factory drive shaft, not because it is better than steel, but because aluminum is pretty much all the aftermarket offers.

David
 
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I'm not an engineer or anything, but my understanding on the aluminum driveshaft was not that it was about accelerating it quicker, but rather that the lighter weight would help raise the critical speed of the shaft to prevent vibrations and transmission damage at higher vehicle speeds or with steeper rear end gears.
 
I'm not an engineer or anything, but my understanding on the aluminum driveshaft was not that it was about accelerating it quicker, but rather that the lighter weight would help raise the critical speed of the shaft to prevent vibrations and transmission damage at higher vehicle speeds or with steeper rear end gears.

In my 'Stang with 4.10's in the back, it feels like it has some harsher vibrations around and past the 65-70 mph mark. Mind you, I'd also put some J&M lower control arms in there as well, and there are times where the NVH is rough enough that I feel like going back to the stock LCA's. It would be nice if an aluminum DS would reduce some of the NVH.
 
I spoke with three different custom drive shift manufacturers and this is how all three started there explanation in so many words.

First, assuming both the steel and the aluminum shafts are designed correctly, both are just fine in terms of strength. Corrosion stress, fatigue, all that shouldn't be an issue.



One builder I spoke with in particular said "I can make you an aluminum drive shaft for 1 million FTLBS of torque if resources were unlimited but it does not mean it will fit in your car or I can build you a steel shaft 1/3 the size but 2-3x the weight that may fit in your car but could possibly not work in your car".

What he meant by that was if he was to engineer an aluminum shaft for a particular application the steel shaft for the same application would be smaller but heavier but depending on the critical speed may not work for the application. So application is a key factor in determining material.

He also stated it is very unwise to put your drive shaft on a diet.

Reason being weight reduction using an aluminum shaft won't free up enough power to make a noticeable difference to the average person as stated above. The lighter material is used to raise the critical speed. And there are many other places to trim weight that won't make the car fail on the track.

Basically if you don't engineer the shaft for your application it will fail at some point.

I guess this is what DD meant by it is not that simple. You have to know the application before engineering a shaft to best fit your needs. My hypothetical situation is impossible to engineer a shaft from because I did not give enough information.

That being said it is conclusive to me steel is stronger than aluminum but at what point is it necessary? If Mr. Neibert is not at that point yet I don't think we need to worry about it.
 
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