Originally Posted by
wiedehopf
That question is exactly what is discussed in the reddit link i posted. So it was perfectly on topic.
Regarding the thrust load i get the impression we need to clarify what the rotor is, i would assume it's the complete rotating spool of the engine yes?
Now we are discussing the direction/magnitude of the load on the thrust bearing of the spool of a turbojet.
That's equal to the combined aerodynamic axial load of compressor and turbine.
Turbine will be pulled backwards and the compressor will be pulled forwards.
Now why would you expect a large axial drag component?
Check the picture on this page:
http://aeromodelbasic.********.com/2...bution-of.html
Edit: why would this forum censor ********? anyway via link shortener
model aircraft: Thrust distribution DISTRIBUTION OF THE THRUST FORCES
Now if you shove air down the compressor as in the SR71 the forward thrust load on the compressor reduces so that the forces on the spool eventually sum up in the other direction.
The overall forces as described in the picture still need to sum up as a force thats forward for thrust to be produced. But there are forward components on other parts of the engine that take care of that.
If any turbojet is at idle or while the aircraft is at high speed i would also expect the thrust load on the rotor to become negative.
This could still happen while the engine as a whole is producing thrust as the combustion chamber for example is being pushed forwards while the rotor is being pushed backwards a bit.
Anyhow clarify what exactly it is you are asking or what you are not clear about and i'm sure there will be some more answers.
So. At high speed, the engine thrust causes the engine to want to move forward in its mounts, the rotor has (net) forward thrust.
At a certain Airspeed, the Pressure on the Compressor end of the rotor is rearward, and of equal value to the thrust moment forward.
It is at this condition that the rotor “floats” in its thrust bearings, net thrust (on the rotor) is neutral?
Increase the Airspeed more, and the inlet pressure becomes dominant. The net thrust on the rotor is rearward (aftward).
Is that it?
Question. At the face of the compressor, is there a point where the inlet air is at such pressure that the compressor is
driven by the inlet, and morphs into a turbine? If so, do we expect there to be a neutral point where the compressor blades can accurately be described as
stators? That would be a complicated answer due to increasing angle of attack of the blades in sequence?
Where is the inlet drag, (pressure) expressed as thrust? It is dominant, per megan’s OP, fifty four percent of total. At high cruise, most of it is dumped into the Ejector, to be heated, expanded and ejected as thrust?
Here to learn.
concours
apropos not much: “took my girl for a ride in the Skylane. She pointed to.an instrument on the dash. “What’s that? Everything looks so complicated.” The pilot in me wanted to Say ‘Chronometer’. I had to say instead, ‘’honey, that’s a clock...’
“If this description of "thrust" is mostly true for structural calculations, I find it strange it was
(or the general public for that matter) that have little interest in this. This issue actually seems to fool pilots, and some engineers alike, if you'd take a look at this quote from
Design and Development of the Blackbird: Challenges and Lessons Learned (page 25)”
The inlet produces no thrust until the gas contents escape.