Exhaust Stack Length

[Jerry Cochran]

Anyone here have opinion on effect of exhaust stack length on power and/or aerodynamics of stacks hanging out in the airstream? I have standard Vetterman stacks and stock they extend from the bottom of cowling about 9". Anyone shorten them up with positive results?

Seems to me I saw some research someplace re this, but searches come up no joy. Just seems like they would be draggy. Ideas? Advice? Theory?

Jerry Cochran
RV-6a Phase One

[robertahegy]

I left mine stock length. I heard that cutting them might lead to more pulsing on the bottom of the fuselage. Mine don't seem to be more than a few inches below the cowl anyway.

Roberta

[gmcjetpilot]

Originally Posted by Jerry Cochran

Anyone here have opinion on effect of exhaust stack length on power and/or aerodynamics of stacks hanging out in the airstream? I have standard Vetterman stacks and stock they extend from the bottom of cowling about 9". Anyone shorten them up with positive results?

Seems to me I saw some research someplace re this, but searches come up no joy. Just seems like they would be draggy. Ideas? Advice? Theory?

Jerry Cochran
RV-6a Phase One

Leave them. Fly with them. You can always shorten them. The pros of longer (may be): less cockpit noise, less belly stain, more hp. Cons: drag (sure a little). Now how much are the pros true, I don't know. I am sure it would be hard to tell. On the other hand the drag reduction might be 1 mph? I have custom 4-into-1 and one big 2.25" dia pipe sticking out 18". I am going to leave it. Again I can always cut it off.