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[Edited title. Please see bottom post.]
Hello All,
(If you want to skip background fluff please fast-forward to my question at the 3rd paragraph)
I have been plagued by high oil temperatures ever since I got my plane. Mechanics I trust, including Ray Williams from whom I bought the plane, tell me that oil and CH temps that I am experiencing are within limits and shouldn't be a major concern so long as they don't get worse. Cruising at 2600 and 143 MPH I generally see OAT plus 110 F (90 degrees = 200F OT). CHT with that same setting will be somewhere between 350 and 390. 10 minutes of hard acro yields an OT of 235F but never more than that, plus a CHT well north of 400. The oil temp probe was tested to be accurate in boiling water. The baffles are good and the oil cooler is facing up at the base of the left air intake just in front of the cylinder. Most people seem to agree that its a good arrangement. There also seems to be agreement that my cowl arrangement might be back pressuring airflow at the bottom of the engine.
A picture is worth a thousand words but I don't have one better than this at the moment. I have S1-T cowl doors mounted flush--no side "cheaks". The bottom cowl curves to fit more snug than stock creating less room for air to exit. To compensate there is a nice niche, almost like a NACA duct formed at the base of the fuselage. If you are looking forward from under the cockpit you will see a squared off opening about a foot wide and maybe 4 inches deep creating a hole for the 2 exhaust pipes and air to exit. Forward of that is a small grill cut into the bottom cowl (pictured).
I want to install a lip to hopefully eliminate any back pressure and increase airflow--a bit like a small, fixed cowl flap. I have been told that this lip really only needs to be about an inch wide and needs enough of an angle to create suction for the airflow. First, can this help? Second, how do I build it? It was first suggested that I use lexan. I guess because its cheap and can be formed with heat into any shape I wish. It would be immediately forward of the exhaust so I'm not sure if that's the best choice. The cowl is aluminum so why not use aluminum? I've done a bunch of cutting, drilling and riveting but so far I haven't tried to bend metal. This might be an easy first stab at doing so. If I do, what would be the best way to secure it? Rivets or screws? And would I need any material between the cowl and the "lip" to use as a seal to keep noise and vibration down or am I just overthinking what should be an easy 2 hour job? Will any of this possibly work? Thanks for the help as always.
Hello All,
(If you want to skip background fluff please fast-forward to my question at the 3rd paragraph)
I have been plagued by high oil temperatures ever since I got my plane. Mechanics I trust, including Ray Williams from whom I bought the plane, tell me that oil and CH temps that I am experiencing are within limits and shouldn't be a major concern so long as they don't get worse. Cruising at 2600 and 143 MPH I generally see OAT plus 110 F (90 degrees = 200F OT). CHT with that same setting will be somewhere between 350 and 390. 10 minutes of hard acro yields an OT of 235F but never more than that, plus a CHT well north of 400. The oil temp probe was tested to be accurate in boiling water. The baffles are good and the oil cooler is facing up at the base of the left air intake just in front of the cylinder. Most people seem to agree that its a good arrangement. There also seems to be agreement that my cowl arrangement might be back pressuring airflow at the bottom of the engine.
A picture is worth a thousand words but I don't have one better than this at the moment. I have S1-T cowl doors mounted flush--no side "cheaks". The bottom cowl curves to fit more snug than stock creating less room for air to exit. To compensate there is a nice niche, almost like a NACA duct formed at the base of the fuselage. If you are looking forward from under the cockpit you will see a squared off opening about a foot wide and maybe 4 inches deep creating a hole for the 2 exhaust pipes and air to exit. Forward of that is a small grill cut into the bottom cowl (pictured).
I want to install a lip to hopefully eliminate any back pressure and increase airflow--a bit like a small, fixed cowl flap. I have been told that this lip really only needs to be about an inch wide and needs enough of an angle to create suction for the airflow. First, can this help? Second, how do I build it? It was first suggested that I use lexan. I guess because its cheap and can be formed with heat into any shape I wish. It would be immediately forward of the exhaust so I'm not sure if that's the best choice. The cowl is aluminum so why not use aluminum? I've done a bunch of cutting, drilling and riveting but so far I haven't tried to bend metal. This might be an easy first stab at doing so. If I do, what would be the best way to secure it? Rivets or screws? And would I need any material between the cowl and the "lip" to use as a seal to keep noise and vibration down or am I just overthinking what should be an easy 2 hour job? Will any of this possibly work? Thanks for the help as always.
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