CYHeli:
Got it. From a helicopter point of view we use the expression (vector) of Total Rotor Thrust. We can map out the various forces on a vector diagram, and vertical component of TRT will equal the mass/weight in a stable hover. But the TRT will never be equal to zero unless you sitting on the ground with no pitch applied. But I see where you are coming from.
Yes, thrust is what is opposing the force of gravity. But THP is different!
The other reason that the helicopter example fails is, what is your point of reference? If you are using the ground then the aircraft has not moved, so you are correct. But the ground is irrelevant.
Use a random parcel of air adjacent to the aircraft in hover as your reference point. This parcel of air is being induced to flow down past the rotor blades by the pitch applied. The parcel of air is travelling at somewhere near 300 feet per second (we call it downwash). The force applied to the air is what keeps the helicopter in a stable hover, so the THP is huge.
Now apply that same reference point to an aircraft sitting on the ground at idle. The aircraft has not moved reference the ground (irrelevant) but measure the THP against the speed (dist/time) of the parcel of air being driven across the prop.
Yes, the ground is the reference and it is not irrelevant! You could hover in one position over the ground all day and you would have done no work on the aircraft. What's your performance, when it takes an infinite amount of time and fuel to get from point A to B? Zero! If something isn't moving, there is no work being done on that something. THP would be zero. Everyone needs to realize that THP is with regard to:
the work the thrust does on the aircraft! That's it! Nothing more than that.
Pardon my frustration but I feel like a broken record here. I've explained countless times in this thread what THP is. I've provided numerous resources which all explain it and relate it to performance. I don't know what else to say.
When you're talking about Total Rotor Thrust, that's just thrust. It's a nice way to compare forces. It's similar to talking about what happens to the Total Lift Force in a turn with an airplane. That force (Total Rotor Thrust) comes from the power of the engine (BHP or SHP).
Regarding your parcel of air explanation: as discussed, yes, it requires power to move air. That power comes from the engine. That power is called BHP or SHP. It is not called THP.
Or is thrust only measured against the distance that the aircraft moves ref the earth?
Thrust is related to how much air is displaced. You can see the variables described here:
General Thrust Equation
THP is related to the distance that the aircraft moves with reference to the earth. Distance/time = velocity which is what is in the THP equation.
I'd be happy to answer any questions you have but please read through this thread because most of them have already been answered.
Cheers!
blackhand:
Mmmm I'm concerned, that you, as a Physics Guru, missed the implications of "relatively" speaking.
Maybe if you moved on from Newtonian Physics and onto modern physics and explored exchange of energy you wouldn't have to be so rude.
I'm not a 'physics guru' as you say but I do know a few things about physics. I'm pretty familiar with relativity and what I do realize is that you're being sciolistic. There is no need to complicate this with special or general relativity. None of my references I've used so far have needed to and they've gone into more detail than I've written out on this thread.