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  #1  
Old 08-03-2006, 07:45 PM
Joe Berki Joe Berki is offline
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Default Exhaust Augmented Cooling

I finally got the engine mounted along with the oil cooler and the scoop that feeds it. I planned on possibly using an ejector in the design of the cowl when it suddenly occured to me that I was going about it the wrong way. Every time i would come up with a system an element would just not fall into place. I started reading the NACA paper about rectangular ejectors. I had seen several rotary pusher aircraft at OSH over the years with round ejectors just below the engine. I tried to start to think out side the box. Heat rises so we put the exhaust on the bottom? During ground ops and shutdown we are baking the whole rear end of the airframe. I also was concerned about the airflow in the cowl. I needed lots of room for the air coming through the rads. If objects are too close to the rad behind it air will not flow through it. I decided that I wanted to use the whole cowl for this and dump it out the rear. The next problem was that ejectors need to be long to be effective. The air flow through the cowl was restricted by the engine and oil pan. There would not be enough length. There was alot of room at the top. I could put a 36" + long ejector along the top of the engine. Let the ejector be the outside wall of the upper cowl. What is not ejector could seal against it like the shaker hood scoops on old muscle cars. The lower cowl could be tighter and cleaned up. This change would require remote water pump, move the alternator to a flywhell pulley, intake tubes need to go straight out and down into the wing root area fed by an armpit or NACA inlet. Heat shielding for the header or stock exhaust manifold. The exhaust would have to be routed forward and up dumping into the throat of the ejector. Just another idea or what?
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  #2  
Old 08-03-2006, 09:31 PM
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John Slade John Slade is offline
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Quote:
The exhaust would have to be routed forward and up dumping into the throat of the ejector. Just another idea or what?
Hmmm. I'm not too sure about that, Joe. Routing the exhaust that way would get you a lot of radiant heat in the cowl. It would also put heat where you dont want it - near the intake, fuel supply lines and rail.

I prefer the idea of ejecting the exhaust as directly as possible. My augmenter (if you can call it that - its just a 6 inch stainless tube about 14 inches long with the 3 inch exhaust pipe in the middle) provides enough ground cooling for me to taxi (gently) all day long on a hot day. At Lawrence recently I taxied for more than 30 minutes. Temps stabalized at just over 200F. Obviously you won't get ideal augmentation with a short round tube and no venturi, but if you join it to the turbo heat shield the turbo itself acts as a constriction a la venturi. This, a big rad and a couple of oil coolers is enough to give you the edge you need. The alternatives I've seen may put more heat into the cowl than they extract.
After flight I simply open the coolant access door at the top of the cowl to let the heat flow out.

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Old 08-03-2006, 09:32 PM
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Dust Dust is offline
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why not go into your driveway and use your car exhaust to play with ejector diameters, shapes and lengths? you can use heating and cooling ductwork for cheep experimentation
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Old 08-03-2006, 09:36 PM
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John Slade John Slade is offline
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The problem I found was that all the good theory and experimentation doesn't overcome the physical space limitations. You end up having to make a lot of compromises to get everything to fit.

My theory - exhaust is the nastiest thing under the cowl. Get it outta there as quick as you can.
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  #5  
Old 08-04-2006, 12:05 AM
eracer113 eracer113 is offline
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Joe
Look at Lynn Erickson's lower cowl and exhaust system. In my opinon he has the best system as far as exhaust and perfect airflow goes and his tuffting backs that up. If I had to redesign my exhaust and lower cowling, thats how I would do it. I have tried round and rectangular ejecters/augmenters over the last 3 years and find they work great on taxie and up to 195 kts, above that airspeed, they are very restricting and limit cooling. The rectangular system worked about 25o better than the round system, the same size. These units worked extremely well during long taxie and delays on takeoff and on a NA Cozy or Long EZ would work well.

Jack
E Racer 113
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  #6  
Old 08-04-2006, 05:19 PM
Joe Berki Joe Berki is offline
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Thank for the input guys. I agree that we need to dump the heat and I am working on that. I would like to see some good shots of Lynn's plane. I am getting close to a good compromise.
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