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Author Topic: Interesting proof of exhaust thrust from a piston engine.  (Read 23000 times)

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Offline WhizzbangK.C.

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Interesting proof of exhaust thrust from a piston engine.
« on: June 06, 2010, 01:54:59 AM »
Watching NHRA qualifying on ESPN2 tonight. One of the funny cars had the left side header break off during the run. The downward thrust from the open exhaust ports was enough to lift the car off the ground! They showed the high speed-high definition footage and you could see that the frame of the car was bowing upward as the engine pushed it up.

It's been discussed on more than one occasion how much benefit one can get from proper exhaust placement, and I thought that this was pretty interesting. I know that no one is going to be running a top fuel spec engine in LSR to make the kind of thrust that they make, but a lot of folks run pretty healthy stuff and to me this seems like proof that there are gains to be had from exhaust flow.

I thought it was interesting anyway. Not that my little 250 Triumph could ever show anything from it, LOL.
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Offline maguromic

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #1 on: June 06, 2010, 02:44:04 AM »
This is an old NASA paper on using a piston engine exhaust ejector to improve air mass flow through a radiator cooling duct. Tony
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091895_1993091895.pdf
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Offline RichFox

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #2 on: June 06, 2010, 05:01:09 AM »
Anyone who remembers Convair aircraft with P&W 2800 and "Exhaust Augmentation" is a believer.
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Offline Dr Goggles

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #3 on: June 06, 2010, 07:07:20 AM »
Not pointing your exhaust through the air that you are trying to keep stuck to the sides of your vehicle is  a good start so zoomies and cowl flush exhaust ports although cool looking are slowing you down.. Exhaust gas is hot , and cooling rapidly...that means it is shrinking ...........pointing that into your wake is a good move as it will fill AND tame the low pressure area that many cars and bikes have following them that is responsible for a large part of the total drag.

Any thrust you get is a bonus on top of the above...


EDIT:of course if there is any thrust you want it pointing STRAIGHT backwards, that's a no-brainer.
« Last Edit: June 06, 2010, 09:54:34 AM by Dr Goggles »
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Offline Seldom Seen Slim

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #4 on: June 06, 2010, 09:28:35 AM »
Ask Joe Amo about using exhaust to fill the vacuum behind the bike.
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Offline Dr Goggles

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #5 on: June 06, 2010, 09:46:35 AM »
Quote from: Seldom Seen Slim on June 06, 2010, 09:28:35 AM
Ask Joe Amo about using exhaust to fill the vacuum behind the bike.

Amen, Amo. .....and de Stoop our daily bread........ :wink:
« Last Edit: June 06, 2010, 09:49:48 AM by Dr Goggles »
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Offline Milwaukee Midget

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #6 on: June 06, 2010, 10:16:39 AM »
Raises a thought -

While the thrust factor would be minimal on a low output engine, might the flow be utilized to evacuate high pressure underneath a car to minimize lift? :roll:

Thinking out loud again.
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Offline SPARKY

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #7 on: June 06, 2010, 10:45:28 AM »
Amen, Amo. .....and de Stoop our daily bread........ now thats funny
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Offline joea

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #8 on: June 06, 2010, 11:16:29 AM »
jon amo did, i did not....:)

Joe :)
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Offline Seldom Seen Slim

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #9 on: June 06, 2010, 11:17:25 AM »
Sorry for the cornfusion, Joe -- I thought it was your bike.  Ah, isn't old age great?  I can remember things that never happened.
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Offline hotrod

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #10 on: June 06, 2010, 11:29:31 AM »
You might note this report done in "1935" regarding exhaust augmented thrust for aircraft.

http://contrails.free.fr/refroid_meredith_en.php

It would also be useful for landspeed builders to read up on the radiator extractor system on the P-51 fighter, that derived significant thrust in flight from properly expanded radiator heated airflow.

Larry
« Last Edit: June 06, 2010, 11:31:08 AM by hotrod »
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Offline streamliner

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #11 on: June 06, 2010, 11:49:29 AM »
Great discussion.  Alex Tremulis also looked into this during the development of the 1948 Tucker.  Here's his description from a 1987 paper he wrote for SAE:

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Offline jl222

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #12 on: June 06, 2010, 01:05:23 PM »

  That funny car also lost the downforce from the upturned zoomies which helps hold the the front end down during acceleration. The car also made a left turn from the right side zoomies still working.
  I have read that some aircraft fighters got up to 160 thrust hp from their headers and some engine designers didn't use turbos because of losing that thrust.
  We believe that we get downforce and thrust from the zoomies on our 222 camaro.

            JL222

  It always amazes me when those funny cars get so far out of shape and still go down the track right side up.
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Offline Dr Goggles

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #13 on: June 06, 2010, 05:29:36 PM »
Quote from: joea on June 06, 2010, 11:16:29 AM
jon amo did, i did not....:)

Joe :)

er, apologies Joe , I too thought it came out of your rear end...

so to speak.

no doubt you've been blamed for lots of things he did over the years,

probably balanced out in the long run.... :wink:
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Offline POPS

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Re: Interesting proof of exhaust thrust from a piston engine.
« Reply #14 on: June 06, 2010, 11:20:55 PM »
Hi ya'll,
I've seen flops go up even when the headers stay on.  I saw a the picture yesterday of the explosion but I couldn't tell if the headers were still attached to the head.  The height is usually due to the explosion under the body, just like a can with a cherry bomb under it.
POPS
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