I have installed a DA50 with a Slimline pitts muffler in my new 28% Extra Special. I have trimmed the cowl to fit without the muffler and I am now trying to decide how to trim it with the muffler installed. My question is, can the cowl be trimmed and installed without cutting it completely through the lower trailing edge ? If so, how much cowl remains between the cutout and the lower trailing edge ?

I am in the process of fitting my DA to my Edge at this very time and I can tell you ESPECIALLY if you are going to put it on its nose like hovering and torque rolling that you need to take a section of the trailing edge out for exit air. The general rule of thumb is 3 times the exit air as entrance air. If there is not enough exit air the engine is going to run hot. A little removal of the trailing edge in the center will alow for exit air and will not look bad either.

I take out as little as possible of my cowls always as I like a nice look as well.

Take it easy,

Norman Ross Jr.

You can cut around the exit tubes in a square and run the spark wire between the stacks without cutting all the way to the back edge. That is how I did it but I had to shorten the exhaust tubes a bit to allow the cowl to slide on and off. I'll try to take a picture and post it so you can see what I mean. Just a thought.

That looks nice and clean...How much did you have to cut off the exhaust tubes??

That is a nice clean setup, but I do not see where the air is going to exit. That makes for a hot running engine. I have been modeling for just over 20 years now and tried everything with cowls and you just simply have to have plenty of exit air or if you put it in its nose and 3D it I can guarantee it is goign to get hot and quit and that can cost you the plane. I've seen a 40% go in for that reason. Engine was hot as a firecracker.

Norman Ross

How much dou you need to remove..Can you post a pic???

I am working on mine right now and I will post a pic as soon as I get it done. I am going to start on it tonight I think.

Take it easy,

Norman Ross Jr.

Please do post a picture when you get it cut out. I agree with you about Jdeckers cut out in that it does not have enough air exit. Also, I really don't want to cut off the exhaust tubes if possible. I look forward to seeing what you come up with. Also, there is bound to be some folks out there that have solved this problem.....lets see some pics.

I don't remember how much I cut off but probably somewhere between a half an inch to an inch.

I don't know about the engine running hot but Friday was it's maiden and I flew it twice. Today I flew it eight times.

Never a burp or hiccup. The DA ran just fine. Took about 10 seconds to clean so I guess the stacks are long enough to exit the exhaust off the plane.

I guess I am just lucky.

Maybe this will help.
The hole is 7 1/2" x 5" and the strip at the back is 2 1/2" wide.
I can get the cowl off by moving it forward till it clears the prop hub then rotate it down
and lower it from around the muffler.
I don't know if its the 3 to 1 ratio or not, but no engine problems and I didn't cut the tubes.

I will hold the cowl spacing closer to the engine, but that is exactly what I am talking about. I am not going to cut the exhaust pipes any as I want all the length to keep the plane clean and also the shorter you get them the louder the engine is going to get. Noise is not an issue at my field, but I still do not like a loud engine. A guy at my field has a G62 with a Bennet exhaust on it and it is freight train loud. He has it on a Double Vision (looks like a piece of garbage on it. Waste of a good plane as far as I am concerned).

Hovering one is a world difference than just flying around as there is no where near the airflow and the cowl cheeks do virtually no good with a single as the head hangs down and recieves virtually no air from the cheeks.

I have yet to cut my cowl and I hope to tomorrow. I got tied up tonight.

Norman Ross

This is true of a twin cylinder engine where it depends on air coming in the cowl front to cool the cylinders and that air must exhaust somewhere.

It is less axiomatic on a single where the cylinder sticks out the bottom into the air stream. Much of the air that crosses the fins never goes into the cowl but just slides along the bottom outside the cowl.

A 2 stroke engine radiates most of the heat at the top of the cylinder. As long as the fins at the top half of the cylinder are exposed to cooling air it will probably get adequate cooling.

That being said it's always a good idea to test things before you start trying to hover and do tail touches.

TF

Great picture and information. That is the direction I have been heading in (grind and fit, grind and fit) but I'm not quite there yet. Just a little more grinding tonight and I think it will fit. I will post a pic when complete.

Also appreciate all the posts on this thread. I learned something about cooling as well as cowl cutting. This is a great forum for a great airplane.

Thanks to all.

Just to throw this in and I am sure Tom will agree, the first time you hover it get some air under you and do it high enough that if it is going to get hot give yourself some recovering room. Don't come by and yank the nose up 5 feet off the deck. I know it is not easy to hover a plane way up but that is not what matters. Keep the nose up and chase it around if you have too. Try to get it hot and if it never hesitates than you are fine. I hover around for about 30 seconds and then stick it wide open and see how it pulls out. If it sags then rich the needle a hair.

Take it easy,

Norman Ross