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budyerly(at)msn.com
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 Posted: Tue Aug 07, 2012 8:20 pm Post subject: N120ej trails and tribulations |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> About that Jab cooling. Europa does not have a firewall forward so I have been bad and not commented on cooling this engine.
I have found that putting a dam above the cylinder tends to work for the cylinders forward of the dam, but consider you have reduced the size of the plenum effectively as the air behind the dam becomes quite stagnant, may starve the aft cylinders of air.
The object is to get high pressure air to pool above the cylinders and allow it to pass through the fins in an orderly manner to absorb the heat. If the air rushes through the slot, the air won't pick up enough heat to help cool the cylinders. Since the heads are square-ish you have the problem of having horizontal air flow over the heads as well as vertical. Also what about the bottom of the heads and cylinders?
Quite some time ago Graham noted that the engine almost needs a set of horns focusing air down over those square heads. From that idea and his work, I put simple metal air guides down through the cylinders as guides as suggested in the NACA cooling of air cooled engines work done pre and post WWII.
I sent Rick picks of some of my Jab solutions we perfected in the shop. We are quite pleased that at least we have made the Jabs flyable.
Prop pitch, carb tuning, intake manifold leaks, inlet size and more importantly, the mechanical or aerodynamic draw of the cowl exit is essential to get air through those poor overworked fins. The poor guys at Lightning Aircraft opened a huge hole in the bottom with a large flange, but it slows the plane because of the cooling drag. Much fine tuning was required. But it does cool. Sonex has also had modest success with their extensive mods.
Pay attention to your prop. The torque curve of the Jab falls off beyond 2750 and that is where the heat starts to build. Pete at Jabiru USA likes to run his engines at 2900 which needs a 62 inch prop and a bit of carb tuning, but it gives Pete descent cooling. In the Jabiru aircraft, with its large suction hole in the bottom, it does allow it to cool at steady cruise. I prefer the larger diameter 64 inch, but have a bit of an issue above 2750 RPM.
We need to get away from the two existing cowls and probably work a 5 inch diameter type inlet (just look at the new Zenith huge holes) and control the air carefully over the square heads. As Rick and others have found, the oil coolers need to be more like a certified type (I suggest the 8 bar) and of course sealed well with a guided exit. Guide the air over the fins and don't overcool those front cylinders in cruise or on descent.
I know I should do an article about some of the solutions that we have confirmed work, but there is just not enough hours in the day.
Keep plugging away guys, you're on the right track.
Just my two cents....
Regards,
Bud Yerly
Custom Flight Creations, Inc.
www.customflightcreations.com
(813) 653-4989
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carlmeek(at)gmail.com
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| Posted: Tue Aug 07, 2012 11:15 pm Post subject: N120ej trails and tribulations |
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I am enjoying reading this discussion.... We are going through the same ourselves. Here is my dynon screen of progress so far, this is in steady cruise. I am wondering if fuel burn is a bit too high still. We have just reduced damming on cylinder 6 so hopefully it will come down a bit. Egt still very uneven.
Sent from my iPhone
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