Phil May Posted May 13, 2011 Share Posted May 13, 2011 I'm just about ready to fit the cowl on my Seagull Edge. The motor is a .61 two stroke which fits easily in the huge cowl, bar for the top end needle and obviously exhaust, do I need to cut any of the cowl to allow for cooling. Maybe the picture below will show what I mean ( this is a catolouge photo not my model ) but the fit on mine is the same. Any advice please guys Phil Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted May 13, 2011 Share Posted May 13, 2011 The inlets at the front look OK for starters, but to get an effective air flow you need an outlet for the air. The rule of thumb is that the outlet should be 2-3 times the area of the inlet. This is because as the air enters it heats up, as it heats up it expands. So you need a bigger outlet than inlet if the air is flow freely and not "back-up" as it were. BEB Quote Link to comment Share on other sites More sharing options...
Phil May Posted May 13, 2011 Author Share Posted May 13, 2011 Ok, so I need to check the opening at the rear bottom where it fits on the fuse' for size, if this is to small then, in your opinion, is it ok to open up this area or do I need to expose the cylinder head area. Phil Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted May 13, 2011 Share Posted May 13, 2011 You should be OK just opening up the bottom of the cowl to promote the air flow. Try that out first. If you do get any overheating then the next step would be to make up some simple in-cowl baffles (make them from a bit of cut tin can) these baffles would be to direct air from the intakes directly onto the cylinder head. But as I say you very probably wont have to do this - the air flow itself may very well be enough. BEB Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted May 13, 2011 Share Posted May 13, 2011 As well as considering what to cut, it would help to leave the opposite cheek hole closed - or blanked off if it's already opened up. Any air going in there will be competing for the exit without providing any cooling. As long as the air entering is compelled to travel closely past the cylinder and head then the size of the inlet hole is almost irrelevent. As an example, I used a hole no larger than 1/2" x 1/4" with the scale radial opening unopened and painted black on a 1/12 scale Hellcat directly in front of the cylinder of an Irvine 25 - the only exit for the air was directly behind the cylinder head with a small lip formed in front to encourage some suction. The head was more or less flush with the edge of the cowling and pretty much filled the hole which was extended to an egg shape behind. This meant the air was forced to flow through and around the cylinder and cooling was absolutely fine despite the tiny inlet and small exit holes. I've cured overheating on several clubmates Flair radials (Puppeteer, Magnatilla, Harvard for example) by getting them to install dummy engines to block off the open parts of the cowlings - sometimes they took a lot of convincing that it was too large an opening causing their problems! Quote Link to comment Share on other sites More sharing options...
Jump Jet Posted May 15, 2011 Share Posted May 15, 2011 Sometimes you can 'steer' the airflow to the head with help of deflectors made from balsa etc. Iften the air going in does very little to help with cooling as it misses the engine. Quote Link to comment Share on other sites More sharing options...
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