Chris,

Here is what I do...yes it is kind of lengthy but pretty simple..might help. Thru a large part of the flight envelop(from the stall point to about 2 times the speed at stall) you can figure that the glide slope of a plane is going to be roughly the same as the Aspect ratio(AR) or a little better. So a plane with a AR of 1 might have a glide slope of around 2. A plane with a AR=8 might have a glide slope of about 10. So, if you want to find the power need for a plane to maintain level flight.... first find the flight envelop then you divide this speed by the glide slope (which gives you the sink rate) and mutiplied the sink rate by the weight which will give you the basic power nessasary for level flight. But you want to be able to climb so from the min power with climb ... double the min power this will give you a plane that will fly but not be a real performer, from double to triple it if want a moderate performer to sport, from triple to quadrupale if you want something in the sport fly to 3d range.

EX: Find the rough flight envelop

Plane area .25 m^2
AR=1 so lets assume glide slope of 2 to 1
Weight=.6*9.8=5.88 N
wingload=5.88/.25=23.5 N/m^2
Max Cl assumed to be 1
q=1.225

Velocity=sqrt((2*wingload/(q*cl))
Velocity=sqrt((47/1.225)
Velocity=6.2 m/sec
So our flight envelope is 6.2 to 12.4 m/sec

6.2/2=3.1 or 12.4/2=6.2 (speed/glideslope=sinkrate) glideslope=about 2
18 to 37 watts for level flight (3.1*5.88= or 6.2*5.88) (sinkrate*weight=power for level)
so and average of 55/2=27.5 just to maintain level flight but at the very lest we double this so 55 watts of deleverd power is what we need, but lets say we get about 60% from input power, so we would need a minimum of 92 watts (55/.6) of input power just to have a poor performer.

You said that you are getting 450 g of thrust
.45*9.8=4.41 N thrust
and Thrust*speed=power
assume that the dynamic thrust stays the same as static(it usually drops with foward speed)
so at 6.2 m/sec * 4.41=27.3 watts delivered
and at 12.4=54.6 watts delivered. (Just barely what we need 55)

or another way to look at it we would need static thrust minimum of:

18/3.1=5.8 N or 600g thrust will provide min power.....I would not build this plane but it would fly.... I would want something with 900 to 1200 g of thrust static.

If you know the Diameter, Pitch and RPM of the prop you can get a better idea about what the dynamic thrust will be...maybe this help a little.

Happy Flying

Steve