Engine cooling on pushers

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wsimpso1

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If you have a certain frontal area no matter what you do, and the airflow through the cowl is controlled by exit sizing, if the opening is just right or too big has little effect on drag. The air going through is set, you can not put more in just because the inlet is bigger. The rest just flows around the outside of your nice low drag cowling.

What I do not like here is there is no splitter. The pressure you make at the front of the HX's is directly related to q of the air coming in. With a splitter, all of the air is at free stream velocity and thus as large a q value as you can get. If you are swallowing the boundary layer, that fraction of the air is at a tiny fraction of the q. It does not just make the system act like your inlet is smaller, it makes the system act like the HX face is smaller too.

So, use a good inlet with a boundary layer splitter, then a good expanding diffuser to convert as much of the free stream energy as you can to pressure to push air through the HX, then allow that air to only pass through the HX's, and then you can let it wash over the engine, exhaust system, etc, before being brought back up near free stream to exit into the prop disc. Oh, and do not believe me, listen to Ross. He knows his stuff.

Billski
 

Voidhawk9

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...all you have to do is make sure the rear opening is as close to the propellor as can be safe (around an inch clearance is all), this will ensure the prop will act as a fan and extract the cooling air as best as possible.
Not necessarily correct. There have been pushers that have seen significant cooling gains by increasing the distance from the outlet to the prop (ie trimming the cowl) several inches. Keep in mind that the root section of many props isn't particularly efficient at moving air (thick & rounded), and in fact may cause positive pressure pulses that block the flow.
 

Eugene

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Not necessarily correct. There have been pushers that have seen significant cooling gains by increasing the distance from the outlet to the prop (ie trimming the cowl) several inches. Keep in mind that the root section of many props isn't particularly efficient at moving air (thick & rounded), and in fact may cause positive pressure pulses that block the flow.
That also makes sense!!! Everything you guys talking about sounds correct to me. So, who should I listen to? Oh, I forgot I supposed to listen to Ross... All I need is to find him
 

pylon500

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Taree Airport Australia
Not necessarily correct. There have been pushers that have seen significant cooling gains by increasing the distance from the outlet to the prop (ie trimming the cowl) several inches. Keep in mind that the root section of many props isn't particularly efficient at moving air (thick & rounded), and in fact may cause positive pressure pulses that block the flow.
You're right, and a Warp Drive prop is probably the worst offender (still a good prop though...)
Need to look at props with 'cuffed' roots?
ARPLASTprop.jpg
 

Rik-

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It is common in many ballistic parachute applications to fire through a port with a cover that is supposed to be broken free. Look at the Cirrus install and the retrofits on a variety of certificated ships.

When the rocket first fires, there is no speed on the package, just the rocket motor pushing. Even a modest extra force could stop the parade. Put a panel a few inches above the ejecta and now the ejecta has momentum and kinetic energy that can pop a fragile line of adhesive or blow through a deliberately brittle panel. Arrange it so that only a narrow amount of that frangible line is being broken at one moment during the progression, and then the join unzips with pretty low forces. BRS must have some guidance on the topic for you.

Billski
Here's a actual test of the rocket parachute and the theories behind the installation methods.

 

ToddK

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The Real Texas
I like the Rotax 2 stroke radiator arraignment. They put the the radiators pretty close to the prop so that they are sitting right in the low pressure zone. That way the turning prop, even if the airplane is not moving, pulls enough air through the radiator to keep the engine cool.
 

dog

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Another approach to intakes is found on the
Anderson Greenwood AG-14
Anderson_Greenwood_AG-14.jpg
 
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