Help with Power Curves for Steady Level Flight

Massiveattack

Hello all, first time poster here so please go easy :)

I have to create a set of Power curves (Power Required and Power Available vs. Velocity) for a propeller-driven Ryan Navion A aircraft at intervals of 1000m.

My question to you is this, due to the fact that the aircraft is in steady level flight will the Power AVAILABLE curve simply be a flat line at:

P(av)=ηP
where η=propeller efficiency (0.8)
and P=engine power variation with altitude


... or is it more complicated than this? When I think about it i'd assume that the power available would vary slightly with velocity but I am just not so sure. Any corrections/help/advice would be appreciated!

Happy New Year.

Massiveattack

Thanks guys, really helpful