In particular, why so even at higher altitude where the air is thinner.
The picture should be more complex as the ratio of induced drag to parasitic drag changes.
Power proportional to TAS - why?
Where, exactly? It wasn't for me last time I tried.
Peter,
Did you mean power is proportional to TAS at a given IAS (I.e. If you increase altitude and your TAS at a given IAS increase 10% then the power output has also increased by 10%)?
If so, it is in the definition of power = Force (I.e drag) * Velocity
Spot on! At a constant IAS drag is constant
OK, yes, thanks, I get that.
Holding a constant IAS as the level increases is not possible unless one has a turbo, however, because the engine power drops off.
Holding a constant IAS as the level increases is not possible unless one has a turbo, however, because the engine power drops off.
Surely that must depend on the IAS you begin with? If you fly at 150 KIAS in a jet you can maintain that IAS all the way up to FL400 in most cases. Similarily in your TB20 you can get 100 KIAS from sealevel up to FL100..
You mean to say that you can't maintain max IAS, correct?
Yes, of course.
Power proportional to TAS - why?
Only correct if you look at the theoretical definition of power, as said above [power = force x speed], so given constant force, power is proportional to speed. But as you say, force is not constant so this is BS in any real flying situation (in fact, only true at one point of the drag curve so far ahead of the bottom that it is never encountered in the cruise)
In any part of the (IAS) drag curve you would conceivably fly in the cruise, power required increases with anything between TAS (minimum drag IAS, where the total drag is briefly constant with speed) up to (almost) the cube of the TAS (at the right where parasitic drag is dominant).
