Can we leave the motor car experiments, for a while, and get back to the original question....
Could you explain me why more power is required to fly 150 KIAS at FL300 than at 5000 feet ?
The real solution is that, to generate Lift equal to the Weight of the aircraft, at a higher altitude. The wing needs a higher Angle of Attack, as the air is thinner. This higher AoA creates a higher Drag... Simple as that.
Scifi your explanation is wonderfully simple, but just plain wrong.
The term “150 KIAS” means 150 knots Indicated Airspeed. The ASI produces its indication (The Indicated Airspeed) by measuring the dynamic pressure. The ASI has no means of knowing what the altitude is, so every time it senses a particular value of dynamic pressure it will give out the same Indicated Airspeed. This means that if we fly at the same IAS at any number of different altitudes, we will always be flying at a constant dynamic pressure.
Both lift and drag are proportional to dynamic pressure so the constant dynamic pressure at constant IAS produces constant values of lift and drag, without any requirement to change the angle of attack. But as our altitude increases, the TAS at which we must fly to achieve our constant IAS must increase. It is this increasing TAS which causes the increase in power required.
All of this is explained in my initial post in this thread. The only error in that post is the final number 3.375