budyerly(at)msn.com
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 Posted: Wed Aug 19, 2009 3:26 pm Post subject: Congrats to Jeff,Cooling feedback for Bud |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Jeff,
Glad to hear the cooling issues are relieved. Well done and thanks for passing it on.
For consumption by others and for feedback, I'd like to hear other fliers comments also.
From my shop experience:
Evans replaced by 60-40 or 50-50 is a 10 degree drop minimum. (Sorry Mr. Evans)
I Jeff's case, by moving the duct two things probably happened:
For the tri-gear, (those with the wide open area around the nose gear trunion and with the firewall moved back behind the nose gear to the added bulkhead), moving the duct down, doesn't cause as much of a difference. But the bungees/springs/hoses etc. in the back portion of the nose wheel well can restrict flow, and moving the duct down will help as it opens the two triangles on either side of the duct adding significant air exit for the heat. It also moves the hot accelerated air of the radiators lower in the duct. This heated air streaming out can cause a potential suction which may help pull air out of the cowl. (Same affect as using the exhaust venturi.)
I once did this with a cowl flap which lowered a reshaped upper metal duct ramp and and the cowl ramp bottom together and went from 12 minutes to overheat on the ground to 30 minutes to 240 F. It was capable of max continuous climb with the flap open. I now just reshape the fixed ramp dimensions for simplicity.
Finally, I have found that moving the air intakes up to near the seam and putting a plenum over the engine or perhaps adding a duct like Jeff did, forces air over the cylinders. This helps on climb out in super hot conditions, but not much affect in cruise.
Tips for those who prefer a stock install:
Sealing the front and sides of the metal duct tight to the fiberglass cowl opening is really important. A leak in this area can cause a high pressure bubble of air in the cowl under the cylinders and literally trap heat under the engine and reduce the effectiveness of the inlet air intakes. It also reduces the pressure differential across the radiator/oil cooler which is essential to the heat transfer for cooling.
The hole for the nose gear leg adds turbulence and pressure to the back side of the radiator exit. Consider a piece of silicone cowl seal slit to make cowl installation easy and close this hole up.
Open up the inlets fully. Don't leave a lip as it just restricts the flow into the cowl.
Mostly, you can lower temps 20 degrees just doing the following:
Begin by closing off the area between the sides of the oil cooler and duct.
Always lower the oil cooler as far as you can if you have a 912S or 914 (2-2.5 inches is possible but change the elbow out for a straight fitting).
I just found this leak. The area between the oil cooler and radiator is nearly a 1/2 inch and you'd be surprised how much potential cooling air goes under the radiator, up and over the oil cooler then out through the space above the oil cooler. This high pressure air degrades the radiator effectiveness as the air passes up the back of the radiator and out. Assembling the oil cooler as close to the radiator as possible, or by adding sheet metal/sealing material to reduce this exit air gap is a help. (Don't let any seal rub the cooler though.)
Finally, the seal under the oil cooler must be tight between the oil cooler and the fiberglass ramp and continue up the sides of the oil cooler.
From NACA documentation, I found it interesting that 70% of the air hitting against a radiator will build pressure and force itself out around the radiator in either free air or in a loose duct rather than go through the core. So keep it tight.
Also somewhere I found the statement that in a tightly cowled inline engine, for efficient cooling drag ratios, the ratio of air outlet to inlet should be as close to 1-1 when in cruise as possible, and 4 to one with the cowl flaps open, in climb. I can't find that reference right now. However, in the Europa, with the cowl inlet air hole area of 14 or so square inches, we need a minimum of 56 inches of exit air, just for the cowl air. But in a mono wheel, ours is two triangles either side of the duct and fiberglass ramp of about 15 to 20 inches, and if you are lucky, 13 square inches between the firewall and upper metal duct for a total of 33 inches of cowl exit air max. As you can see, this makes the air exit of the cowl nearly 1 or 2 to 1. This is OK for cruise, but a disaster for cooling in high power climbs at low speed, especially if turbo equipped. This 4-1 ratio works in my experience. To cool well in summer I try to get 100 square inches of exit air (Tri-gear) out of the cowl (Mono with fixed duct 60 square inches, cowl flap added 90). That is just for the cowl air, and does not include the duct exit for the radiator. That is a lot of glass and metal work, and seems to be worth it.
I would like the time to reshape my duct in my demonstrator to see the affect of each of the above. My demonstrator just passed airworthiness, and will fly soon, (N12AY, Classic, tri-gear, 914, fixed pitch for data reasons (LSA experimenting) then Airmaster). I am obligated to do a stock installation with just sealing the duct as above and taking data. It's not rocket science, it just takes time.
Feedback?
Again, Good Job Jeff!
See you at Rough River.
Bud Yerly
Custom Flight Creations
Europa Dealer
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