I've been thinking of ways to reduce the weight of my RV-4. The ideas so far range from the simple (install Odyssey battery) to medium (replace aluminum prop with composite version) to radical (build custom parts out of exotic materials). One idea in the radical column is installing a titanium exhaust system. If I go to the trouble, I'll replace the current 4-pipe system with a 4-1 collector.
It seems that titanium might be an ideal material for exhaust systems. Scratching about on the web, I found these numbers for the two materials. I chose 321 stainless and 6a1-4v titanium since they seem to be common exhaust system materials.
321 stainless 6A1-4V titanium Units Titanium/Stainless
density 8000 4429 Kg/m^3 0.55
tensile strength 515 896 MPa 1.74
modulus 193 114 GPa 0.59
Specific strength .064 .202 MPa/Kg/m^3 3.15
Specific modulus .024 .026 Gpa/Kg/m^3 1.08
Sorry for the formatting. I haven't been able to figure out how to create a decent table with this forum system.
References:
http://www.assda.asn.au/asp/index.asp?pgid=17971
http://www.rembar.com/Titanium.htm
So it seems that a titanium exhaust system would be 45% lighter than a stainless exhaust with the same dimensions. However, since the strength is so much greater, one might be able to use thinner-walled tubing and achieve even greater weight savings: maybe as much as 60%. Moreover, these numbers seem to be at "ambient" temperature. I'm thinking titanium's advantage at the high temps of an exhaust system might be even greater. Unfortunately, I haven't yet been able to find good numbers these metals at high temps.
From what I've gathered, many titanium alloys have excellent corrosion resistance; even in harsh environments. But, still, perhaps the longevity isn't as good as stainless? I've seen that some aftermarket performance companies are producing titanium exhaust systems for cars and motorcycles so it can't be completely inappropriate. Obviously, the cost would be higher (probably by a lot).
Does anyone here know of other reasons why titanium shouldn't be used in an aircraft exhaust? I'd like to gather some of the excellent knowledge generally available on this list before contacting exhaust vendors about it.
Thanks.
It seems that titanium might be an ideal material for exhaust systems. Scratching about on the web, I found these numbers for the two materials. I chose 321 stainless and 6a1-4v titanium since they seem to be common exhaust system materials.
321 stainless 6A1-4V titanium Units Titanium/Stainless
density 8000 4429 Kg/m^3 0.55
tensile strength 515 896 MPa 1.74
modulus 193 114 GPa 0.59
Specific strength .064 .202 MPa/Kg/m^3 3.15
Specific modulus .024 .026 Gpa/Kg/m^3 1.08
Sorry for the formatting. I haven't been able to figure out how to create a decent table with this forum system.
References:
http://www.assda.asn.au/asp/index.asp?pgid=17971
http://www.rembar.com/Titanium.htm
So it seems that a titanium exhaust system would be 45% lighter than a stainless exhaust with the same dimensions. However, since the strength is so much greater, one might be able to use thinner-walled tubing and achieve even greater weight savings: maybe as much as 60%. Moreover, these numbers seem to be at "ambient" temperature. I'm thinking titanium's advantage at the high temps of an exhaust system might be even greater. Unfortunately, I haven't yet been able to find good numbers these metals at high temps.
From what I've gathered, many titanium alloys have excellent corrosion resistance; even in harsh environments. But, still, perhaps the longevity isn't as good as stainless? I've seen that some aftermarket performance companies are producing titanium exhaust systems for cars and motorcycles so it can't be completely inappropriate. Obviously, the cost would be higher (probably by a lot).
Does anyone here know of other reasons why titanium shouldn't be used in an aircraft exhaust? I'd like to gather some of the excellent knowledge generally available on this list before contacting exhaust vendors about it.
Thanks.