Which "Power Available" graph is more correct? 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
Power is work getting done over a period of time.
Work is force multiplied by distance.
So when you are sitting at the beginning of the runway, at full throttle and brakes on, while thrust available is very high, power available is 0, because no “work” is getting done.
Edit- basically you are applying a lot of force, or using a lot of thrust, but since distance traveled is 0, no work was actually done.
Which is why the power available is indeed 0 at a velocity of 0, and increasing rapidly.
Note- the second graph is exactly the same as the first, only it is showing the curve beginning at some point after the stall speed.