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Marc,
In order:
1) It adds weight compared with no augmentor. Tracy's experience not withstanding, most rotary engine installations are coming out heavier than Lyc powered counterparts. Mine is 100 pounds over Vans number and at least 50 pounds heavier than typical RV-4s out there. Every pound counts. Yes, if it only takes a couple of pounds to solve a cooling problem then its worth it. But this has not been the real world case, only the theoretical case. In the real world there are plenty of examples of successful rotary installs with good cooling and without resorting to an augmentor. As far as I know there are no installations of an augmentor demonstrating an actual reduction in drag and consequent measureable increase in performance. Nor any examples of an augmentor solving a cooling problem. You want to solve a cooling problem before you have one? Copy somebody elses working system, don’t reinvent the wheel.
2) Unless you run plugs up exhaust routing on a rotary install is more difficult than a typical aircraft engine. Particularly true on a skinny airplane like mine or an Eze. Unless you have plenty of under cowl room its not easy to get the exit where you'd like it. Squeezing in an augmentor complicates the problem. This may or may not be an issue for your airframe.
3) No, they don’t and they arent. An augmentor makes a lousy muffler but a pretty good echo chamber. Take a listen to an augmentor equipped airplane sometime. C-310 and T-34 come to mind. Both have a pretty boomy exhaust note. Now I have seen a shrouded exhaust system that was designed to reduce noise, but it couldn’t be called an augmentor. In that case the interior was lined with sound absorbent and the exhaust was directed at the absorbent, not the exit. Definitely not an augmentor. And since you mentioned Charles Airesman, I met him in person and spoke to him at length about the augmentor. I made the same comment to him that you made. His response, "No, the augmentor is a noisemaker". After seeing/hearing his airplane fly I concur.
4) Refer to number 3. I read the Contact articles and spoke to the man. Based on his comments to me in person as well as input from others, I stand by what I said. And I did seek out those sources - if you have sources that contradict mine please share. When I spoke to Charles he was already a couple revisions into the augmentor to try to realize the expected advantages. He encouraged me to pass on the augmentor. I took his advice.
But hey, feel free. I'd love to see someone actually demonstrate it improving performance (cooling as well as speed) and reducing noise. If I thought it would work I'd do it. But I don’t. Its another one of those silver bullets with great theoretical promise but no actual evidence that it performs as claimed.
Mike Wills
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From: "Marc de Piolenc" <piolenc@archivale.com>
Sent: Saturday, May 01, 2010 4:24 AM
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] Ejector cooling
Mike Wills wrote the quoted passages:
"1) It adds measurable weight."
Compared with what? What if a small addition of weight solves your cooling problems and reduces cooling drag. Would you refuse to do it?
"2) It adds complexity."
How complex can a device with no moving parts be?
"3) It adds noise (that alone in hindsight makes me glad I didn’t do it - god knows I don’t need more noise)."
No. Mixer-ejectors are used for noise REDUCTION. Successfully.
"4) And finally, not a single person I spoke with noticed a measurable improvement in either cooling performance or drag reduction after adding an augmentor, or noticed a measurable reduction after eliminating the augmentor."
You seem to have consulted a very select group. In volume 2 of Alternative Engines, page 139 et seq, Charles Airesman Jr. documents his experiments with a very primitive ejector that generated 6 inches of water pressure drop under shop runup conditions. That equates to a considerable shaft power savings, more reliable ground cooling and a big step forward. And this was Airesman's first attempt.
There are other success stories if you choose to seek them out.
Best regards,
Marc de Piolenc
Those seem like good enough reasons to pass on an augmentor unless you are one of those guys that just has to prove it to yourself.
Mike Wills
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