Effect of no no cowl on flight?
 

I just got a Spacewalker II ARF from Seagull and to tell the truth, I like the looks of it better without the cowl (but with the spinner). Plus of course having easier access to everything. But I've been wondering just what effect the lack of a cowl has. Obviously, there will be additional drag but how much and will it really matter on a plane like this. Most trainers have a more or less exposed engine as do planes of the Ugly Stik design.

On a related question what is the diminishing effect a wide cowl has on prop efficiency. For example, I'd be using a 10/6 prop on my Magnum 40 and with the cowl in place only about the outer 2" of each blade are beyond the cowl.


--Don

RE: Effect of no no cowl on flight?
 

just watch you CG. For the rest it doesn't matter much.

RE: Effect of no no cowl on flight?
 

It may be only 2 inches beyond the cowls extreme edges but there's still lots of prop working for you as the cowl is tapered. The only time this would be an issue would be if the cowl was a end on bucket like a large radial cowl and there was no way to let the air out the back. Then the pressure would build behind the prop disc and you'd have a problem.

You see props work through two mechanisms. At rest they accelerate the air back and move forward. But at flying speeds they actually screw their way through the fixed air and generate a less energetic slip stream than at rest.

RE: Effect of no no cowl on flight?
 

The extra turbulence generated by lack of cowling will have an adverse effect on the efficiency of the tail feathers, noticeably degading overall handling qualities.

RE: Effect of no no cowl on flight?
 

Um, this is a Spacewalker ARF... detecting a degradation in its performance without the cowl.would require a lot of flying with the cowled airplane for a measurement base.
The net effect on this airplane will be minimal.

RE: Effect of no no cowl on flight?
 

Bruce, actually the cowl isn't very tapered. Seen from above it's basically a box. However, on the side it does have a bit of a slope along the bottom. What would looks really cool would be a more tapered Spitfire-style cowl which as far as I can see would suit this ARF every bit as well as the boxy one.

Paul, I think I'll just go ahead and fly it without the cowl for a while. Maybe down the road I'll "trick out" the cowl with some piano hinged sections. BTW, thanks for all your advise on my EIII project. It turned out fine but flying it is just a bit beyond my current newbie abilities, although we did get in several successful flights and I even got my own hands of the sticks via a buddy box. Also since I've had to relocated to Japan, I picked up the Spacewalker ARF here to work on my flying skills.

With my interests in WWI A/C, I figure I might as well get used to flying underpowered models with lots of drag!

RE: Effect of no no cowl on flight?
 

Different airplane, but I believe Adrian Page says the Gee Bee R2 is unflyable without its cowl....the turbulence makes the rudder inefective. We always think of cowlings affecting the thrust but seldom consider their effect on the rest of the airplane.