Hi folks, I was wondering if canopies have a good or bad effect on the aerodynamic performance of a model ? If it is bad, then why is it needed on high performance models e.g. pattern planes, other than for the scale look ? Thanks for any inputs...........

Pattern models actually WANT the canopy.... or at least the side area that a canopy represents.... to aid knife edge flight. So while I know what you mean you picked a bad example in this case.

But you're right in that canopies add drag. Racing models only have canopies where mandated by the rules (Formula 1). If they didn't need them they wouldn't be there.

Depending on the shape a canopy can be a bad thing.... there was a model in this area that went from person to person... it required strakes on its upper edges to smooth the aiflow over the vertical.. the canopy was square in cross-section and must have had a serious burble behind it.
I recall watching two airplanes crash while carrying small video cameras on the top of the fuselage. Power on, no problem. Power off, they both nosed down into the ground. Mounting the camera under the wing next to the fuselage solved that problem.

Often competion planes are required to have a canopy of specific dimensions (such as in some forms of pylon racing). Careful faring of the canopy into the fuz can reduce the drag though. In early WW2 fighters for example, the canopy was faired into the rear fuselage (eg a P-51B) for maximum efficiency. This was found to give poor visability behind in combat however so later designs sported 'bubble' canopies (eg P-51D) even though there was a drag penalty.

Besides planes without canopies look plain rubbish!!