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Old 02-26-2021, 08:22 PM   #31 (permalink)
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Let us know what you find out. Thread-jack is OP approved. I've seen a racer-modded Porsche [picture needed].

I thought the original reference was suggesting thrust from the rearward-facing bells.

But I'm reminded of the Moller Supertrapp. It was invented to muffle a snowmobile engine (actually eight snowmobile engines. ) that drove a ducted fan.


http://8903e7f0897f2982f439-51d6683c...ite640x480.jpg

It would lose any additional thrust. Another possibility I saw but can't document was a muffler that was two back-to-back cones in a bellmouth.

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Old 02-26-2021, 10:48 PM   #32 (permalink)
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Some aircraft home builders have done this to help offset cooling drag by entraining with the exhaust. I’m thinking about doing it too. It looks like the exhaust pipe terminating in a Venturi. I like the shape they came up with at Tatra.
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Old 02-26-2021, 11:03 PM   #33 (permalink)
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I posted this for aerohead in another thread:

enginehistory.org: Waste Heat Utilization in High Output Aircraft Piston Engines by Robert J. Raymond
Quote:
3b. Added Thrust

A significant increase in thrust can be realized by the simple expedient of pointing the exhaust stacks toward the rear of the aircraft....
A rule of thumb given by Hoerner [3] is that between 0.11 to 0.13 pounds of thrust per horsepower can be expected from properly directed exhaust stacks with the appropriate exhaust exit area.
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Old 02-28-2021, 05:04 PM   #34 (permalink)
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Quote:
A rule of thumb given by Hoerner
There goes Hoerner, making rules of thumb great again!

That would be like +25 lbs of thrust at full chooch. I’ll take it.

Did I mention: Love that Tatra!!! The best colour. The best sound!
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Old 03-22-2021, 05:53 AM   #35 (permalink)
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back to Jetoptera

Finally got to post answer from VZLÚ (czech aviation research agency and proving lab), where Jetoptera (according to globenewswire.com did some tests.)

I therefore asked at VZLÚ, if Jetoptera really did approach them and did some tests to find out, if people at Jetoptera mean the bussiness or if it is a complete scam as Nikola Motors was and they simply abused a name of some-small-far-east-country-research-lab.

There is an answer I got from their PR dept. (rough translation from czech language done by me), will provide original on demand :-) :

"Project Jetoptera exists, or, rather existed, because investor experiences financial troubles corresponding to covid-19 pandemy and all development is on a halt for now. Jetopteras choice for our research institute was a logical step, because their demonstrator should use H80 series engine from GE Aviation, and that is offspring of our Walter M601. Moreover, GM facility lies just few blocks around.
To the proposed effecincy of the Jetoptera propulsion system we cannot provide any information, because it is not our know-how and we didn´t participate on its development. Our institute was involved only in testing."


.. so, at least we know they really did some tests (though unable to discern, if they bought the testbed and did tests in-house, or paid for certified testing :-( )
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Old 03-24-2021, 11:22 AM   #36 (permalink)
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Hoerner

Quote:
Originally Posted by freebeard View Post
He'd know. He was with Messerschmitt during WW-II, and brought over by the O.S.S. under 'Operation Paper Clip.' Like Kamm and Werner von Braun.

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