[F1Boss]

Hey Fellas:

I'm gonna try an augmenter type system on my plane over the winter. Can any of you lead me to an paper where the parameters are put into an equation so I can get a SWAG on the initial sizing? Or, should I just ask Dan Horton how to do it...

I suspect there is some cooling system drag we can shed if this can be accomplished.

Carry on!
Mark

 

[rv7boy]

Maybe Dave Anders?

Mark, I can't help you other than to say I first saw an exhaust augmenter on an RV-4 at Oshkosh. I'm sure you've heard of Dave Anders. I'm not sure he is still running that exhaust system, but perhaps there are some links to some of his meticulous work to shatter the CAFE foundation records way back when. (P.S. I do remember Dave Anders telling me his cooling exhaust area was about 80% of the inlet area, which was counter to what all the literature was saying, which was "exit area should be equal to or slightly greater than cooling inlet area.") I wish I had made more photos.

Of course, you are on track to talk to our current RV guru. Dan's RV-8 is really nice.

Good luck,

 

[RV8RIVETER]

Mark

Here is a link to the report.

http://aerade.cranfield.ac.uk/ara/1945/naca-report-818.pdf

The report test was done with a single cyl engine and the recommended length for our applications would be quite long. I think it also shows there is sill good benefit without the "optimum" length. Paul Lipps used a more of mixture chamber or box that fed his outlet. He posted sketches of a "coanda augmentor" on this forum as well as sending me some by email.

I posted pic's of my set-up as fabricated so far.
http://www.vansairforce.com/community/showthread.php?t=1741&page=51 POST 501 AND 507

I also have some idea's on different nozzle configurations to test, just laid nozzle 2 in the mold last work day.

Feel free to drop by Kestrel some time if you want to take a look in person.

 

[rv7charlie]

Have you read through the documents on the CAFE web site?
http://cafefoundation.org/v2/tech_lib.php

IIRC, there are some comments about the technique making significant improvements at low speeds & high power but actually increasing drag at altitude & cruise speeds, apparently due to pumping excess air through the cooling system at speed.

At SNF about 10 years ago, Tracy Saylor (sp?) of RV-6 fame once told me about working on tuning his exhaust length, & said that each time he cut off a bit of exhaust pipe length, he got a bit more power. He said that he was fearful to make the 'next cut', which would put the ends of the pipes inside the cowl, in front of the plane of the firewall. He decided to go ahead & try it, and when he did, power again went up and coincidentally, his slightly high oil temps actually came down. He also mentioned having cooling guide vanes below his cylinders, so he probably created an augmenter when he made that next cut.

Charlie