Trying to understand the drag and power required/available graphs for a piston + propeller airplane. Both graphs are from current book/website and while they are showing mostly the same thing, I noticed the shape of the power available curves are different.
If I have to guess I think the second graph make more sense, since power available from a piston engine should be almost the same throughout the entire speed range.
*If the above is true, can you please also explain why it's not a perfect horizontal line across? Ie: if the engine is rated for 150 BHP, then the line should be at 150 BHP, other things equal (density altitude)
I feel like I'm missing something fundamental here but can't seem to work this out. Thanks