Got a extra 300 of a guy who messed it up got plane togheter now but the cowl is gonners. How wil it affect flying without the cowl, wil it be more unstable? Plane is 60 size will run it with 91 4 stroke

There will be a little more turbulence that'll affect some maneuvers but it won't be enough to notice and certainly not enough to affect normal flight. Later on if you're fussy enough to notice you will find that some things will be easier like knife edge thanks to the extra area up front.

Removing the cowl on an airplane with a rather wide fuselage will increase drag considerably, due all that additional flat plate area slamming into the slipstream, slowing the airplane and steepening the glide. Stability and controllability may also be hurt by the slower, more turbulent air flowing over the tail feathers. CG will come back a bit, causing a little higher pitch rate. I have noticed overall handling degradation in an airplane with a much smaller cowl in relation to its overall, size when only the top half of the cowl is removed. I would leave the cowl in place, except for experiments.

I agree that pulling the cowl on that airplane is going to increase parastitic drag but I think that claims of instability are somewhat exagerated. I have flown full size aerobatic aircraft without the cowling in place during engine testing and have found the airplane to be slower but otherwise unaffected by the missing cowl. With respect to balance, assuming the cowl was one of the simple thin fiberglass or APC plastic variety, the cowl likely has very little weight and shouldn't noticeably affect the CG location. I would say fly the airplane and have fun. Chances are you'll barely miss the cowl other than the looks you're gonna get on the flight line

you won't notice the difference!!!

Almost all my airplanes have been flown without cowl and without difficulty sometime during their lifespan. It won’t make much difference.

Bill

I to have a 60 size Extra 300... Flies fine without the cowl. In fact, its hard to tell a difference.

I had a 60 sized vector flight extra. I flew it with and without the cowl and noticed no difference it flight. It just looks better w the cowl.

According to the theory I have read, removing the cowl will make the plane slightly more stable (in pitch and yaw, harder to knife-edge), as cowls and fuselage area ahead of the CG are de-stabilizing. It will usually be a little slower too, but maybe not noticeable. I say a little slower because few models have efficient cooling baffling in their cowls. If they did, then the difference would be much greater. I once read that a very large percentage of total drag (I wanna say 80%) of the full-scale Swift at cruise was engine cooling drag. That's why Roy LoPresti had such a ball cleaning it up. I could be remembering the percentage wrong, but I remember thinking "wow".