The graphs of Power V Speed in post #20 aren't very useful. They've plotted Power (Thrust * Speed) v Speed.
The gradient of the graph merely gives Thrust (which is more useful.)
Yes, the slope of the line = thrust. What's your point? The reason the slope equals thrust is because of the equation: Power = thrust x speed. The slope of any line is rise over run. And that equals thrust in this case. But I don't think you understand where that's coming from. The graph might make more sense to you if you look at the thrust graph.
http://i.imgur.com/FLRfH.png
Power is a function of thrust and airspeed (Power = thrust x airspeed). So, when you plug in the thrust at a certain airspeed, the resultant is THP. So, when the aircraft is not moving, the airspeed is zero and the THP is zero.
As a note, I'll use BHP or SHP in this post but for all intents and purposes, they are the same thing.
And you'll ask where does that thrust come from? It comes from the power of the engine (BHP). And that power is equal to the torque multiplied by the RPM. And that torque enables the RPM. And the burning of fuel inside the cylinder creates a force which acts at a certain distance from the rotational axis of the crankshaft, at a certain range of angles, which creates the torque. The thrust is directly related to the BHP of the engine. If you increase the BHP generated by the engine, you will increase the thrust.
As I have said before, THP has to do with
aircraft performance. Yes, you are creating lots of thrust and that requires power to do that and that power comes from the engine which is the BHP. No physics laws have been violated!
Aircraft performance is with regard to climbing, descending, gliding, turning, accelerating, decelerating, etc. I have a question for you - if your airspeed is zero, what is your climbing performance? What is your turning performance? It's quite obvious that it is zero! When you increase your speed to the point where Power available and Power required are equal, you will be able to maintain level, non-accelerated flight. If you increase your speed to a point where PA is less than
PR, you will have negative performance. If you increase to a speed where PA is greater than
PR, you will either accelerate or you will climb - or do both, until you reach a point where they will equal each other. When PA and
PR are equal, TA and TR will be equal as well. You've probably heard that angle of climb is dependent on excess thrust and rate of climb is dependent on excess power. That is correct! The airspeed for maximum excess thrust will be different than the airspeed for maximum excess power. That difference is not only related to the difference between PA and TA, but the difference between TR and
PR. TR is equal to drag and
PR is equal to TR x velocity, which is equal to drag x velocity and so on. Just like TR is equal to the addition of parasite drag and induced drag, the
PR curve is equal to the addition of two velocity curves: V cubed and 1/V - which are parasite power required and induced power required, respectively. It is a somewhat hard concept to understand because the difference isn't entirely obvious. But these graphs and equations will explain and prove that to be the case, as long as you understand where all the data comes from and what the data means. If you understand the purpose of these graphs and material I think you'll be able to understand better what THP really means.
I uploaded a section from the US Navy document about Thrust and Power:
US Navy - Thrust and Power.pdf - File Shared from Box - Free Online File Storage
Rolls Royce "the Jet Engine" has used the same graph but labelled the Y axis as "Propulsive Efficiency" % (work done on aircraft / Energy imparted to engine airflow).
If you could provide a picture of the graph that would be great. I should point out that it is
not the same graph. It might have a similar shape but it is not the same. Also, with jet engines the efficiency and amount of energy imparted for propulsive work is related to thrust, whereas with propeller aircraft it's generally related to power (BHP). A jet engine makes thrust a propeller engine makes power. Fuel flow is generally directly related to thrust in a jet engine and in a propeller aircraft is directly related to power. There are some variances but that's what they're based on. An example of variances are: a jet engine at 50 knots is creating a heck of a lot less power than at 500 knots assuming that in both cases the engines are producing 75% thrust. The fuel flow at 75% thrust in the case of the slower speed will be higher than in the case of the faster speed due to differences in efficiency, which is backwards to what most people think.
The document above will illustrate propeller (propulsive) efficiency as THP = SHP x pe (propeller efficiency). And working with the equation you get:
pe = THP/SHP = Thrust x velocity/SHP = Thrust x (distance/time) / Torque x RPM x 2pi
As the document says, gearbox inefficiencies and propeller drag will decrease pe from being 100%.
Note the document below (Aerodynamics for Naval Aviators) which also explains propeller efficiency.
Aerodynamics for Naval Aviators.pdf - File Shared from Box - Free Online File Storage
We agree that we are not creating any useful THP - but we are most certainly accelerating a mass of air and have given it a relative velocity - thus we are developing THP. Otherwise where is the energy of the fuel we are using going to?
I understand what you're trying to say but calling it THP isn't correct in this case. To really get a good understanding of how this THP actually works with regard to aircraft performance you have to start at the very basics and work up. The material to cover is at least the amount in a full university course and depending on how much detail you want to go into, it could cover multiple courses.
This is a good wiki article on Thrust:
Thrust - Wikipedia, the free encyclopedia -- It also explains what I have been in this thread. Read the "Thrust to propulsive power" section.
A C-130 with a failed #4 starter lines up behind another C-130 for a "buddy start". The "mother ship" runs up a couple engines while standing on the brakes. 100% RPM, rated torque, zero airspeed: No thrust horsepower relative to this stationary ship.
But the recipient ship feels the propwash, and its #4 prop begins to windmill, finally permitting it to reach self-sustaining speed.
Obviously there is useful horsepower available in the propwash, even though it's not being used by the mother ship.
So my conclusion is: Horsepower is in the frame of reference of the beholder!
Yes, that's definitely a relativity scenario! There is no difference - from the frame of reference of the #4 engine - between an airstart and your scenario.