Cowl - With or W/O Does it Change Flight Characteristics?
 

I'm getting ready to test fly a new model.
I plan to fly without the Cowl to make sure the engine is solid.
Will flying without the cowl affect the trims?

Cowl - With or W/O Does it Change Flight Characteristics?
 

Flying without the cowl will make a negligible effect on the trims.

I do this quite a bit, and I think it is a good idea. You won't have a problem.

Cowl - With or W/O Does it Change Flight Characteristics?
 

Depending on the type of cowl you could make your plane tail heavy if you initially balanced with the cowl on. I had a H9 CAP 232 that was extremely tail heavy when the fiberglass cowl was removed.

Cowl - With or W/O Does it Change Flight Characteristics?
 

Simple solution: Weigh the cowl, make a weight the same and attach in the center area of the cowls location. My GP Space Walker cowl, after reinforcement, weighed 4 oz, so I felt I needed to have a counter weight when the cowl was remover.

Cowl - With or W/O Does it Change Flight Characteristics?
 

It definitely depends on the plane. Balance for any weight differences and it should fly though.

Better yet, get your engine sorted out BEFORE you fly it. This is so easy to do, yet most guys wait until they're at the flying field to try and get their engine running correctly. It's just a matter of finding the time at home I quess.

Why would you want to fly your new plane on a questionable engine?

Aerodynamics & heat
 

something you may notice is a difference in speed. If you have a plane with a sleek cowling. Running w/o cowl will cause more drag. It will slow down quicker, and maintain a constant speed on the down-line easier.

The first time I really noticed this was with an Extra. I would bring it in on throttle then chop the throttle and it would stop in half the length of the runway. As soon as the cowl went on I was using the whole runway to get it to stop.

I've also noticed that on my planes the engine will run a little hotter with the cowl on. So I compensate by running a "click" or two richer. I don't like big holes in my cowls. If you don't mind a bigger hole, or are willing to build in air deflectors to get better air flow over the head, you may not notice any difference.

I like to dial in my engines on a test stand and then do the fine adjustments in the air. After that I put the cowl on and forget it (unless I have to readjust for bad fuel).

Happy flying!

Scott