[wherewaldo]

Hi guys ...does anyone have experience in making baffles for the cowl of a pilot edge 540 37%... Engine installed is a dle 120
Want to do something simple yet effective ..any ideas on material to be used,
diagrams or pics would be appreciated...thanks

[Cougar429]

If you are near an airport look for a flying club or AMO to have a boo at how they do this with full-size. The theory and practice will be the same.

In short, you want to take the inlet air and direct it over the cylinder and head fins in a way that prevents it from finding another, easier path. If also like the full-size aircraft the cowl outlet will be on the aft bottom. This exit generally needs to be larger to accommodate the larger volume of heated air. Also, by having an adequate exit path you avoid pressure backup that can prevent positive flow even with the energized inlet action. This can stagnate air within the cowl and not carry the heat away.

If full size the inlet air is directed over the top of the engine and cylinders by use of a dam that starts as close to the cowl nose as possible, (to prevent bypass leaks in that area). The dam forms a box over the top and has vertical walls on the sides and back of the engine case to catch any inlet air. With the high pressure that box creates only one way for the air to flow, down over the cylinders to the low pressure area formed by the rest of the inside of the cowl.

I included some pics of my Skybolt setup. Although single cylinder you can see how the entire inlet flow was directed over the jug, held tightly by the dams added to the back of the former.

You will also see the lip on the bottom that mimics what you would get with a cowl flap open, a low pressure area at the exit.

The reason for all that was the first dozen flights with cowl off were trouble free. First flight with cowl mounted had it overheat. Traced the problem to cooling air finding a less obstructed path on the left and therefore not enough to adequately carry the heat away. Once installed there followed over 300 flights before selling the craft in favor of the 'Super.

I used the same method for other installations, more specifically Rare Bear and the Harvard.

NOTE: That last pic of the cowl from Rare Bear was an early fitting. The exit cutout was significantly enlarged before the maiden.

[wherewaldo]

That's great info..thanks
The engine I am trying to baffle 120cc gas twin cylinder , I'm going to try and cut out balsa ply and make a rectangular shape to the opening .. So the air coming in is deflected straight on the cylinders ,
I have the exit hole cut out twice that of the entry, hopefully it works well

[itizme]

https://youtu.be/5jD5OGa6mHY

[Mike Sebastien]

Don't use dams use baffles, you want to direct the airflow not stop it. Carden sells a fiberglass insert for there cowls and it keeps the airflow going over the heads and also the crankcase. I made one out 1/8 in balsa then fiberglassed it for another aircraft which used a DA100. it worked fine. The engine in the picture is a ZDZ 160 and never had any issues with overheating. Hope the Pics help

[Cougar429]

Here is some more info:

https://www.google.ca/search?q=aircr...w=1280&bih=599