Originally Posted by
flyingchicken
Thank you for the link to the NACA paper. It is nice to see some actual data. I would be interested to see the other paper you mentioned if you manage to locate it.
Will do in the next few days, will also post some of the graphs from the NACA report with annotations, for discussion...
Originally Posted by
flyingchicken
My thinking is that the "cutover" pitch you mentioned will vary dependent on prop dimension, relative wind velocity, drag/torque from internal engine friction, and resulting prop RPM. Not sure if there is a way to solve this analytically.
Same of those factors are there
I'll take a quick stab, the graph in figure 4, is were all the data is combined into a working graph.
The graph gives negative thrust coefficients (i.e. Drag coefficient) for stationary blades of differing pitch. Not surprisingly the drag coefficient remains constant with variation in speed.
You can work out the drag coefficient from a free wheeling propeller i.e. zero torque at differing pitch, this too is constant. You do this 'by projecting down from the point of zero torque to the appropriate thrust curve' then moving across for the drag coefficient.
To work out the correct solution for a windmilling prop with friction, a friction/torque curve is needed, however the actual result should lie on the respective curves so many quantitative comparisons can still be made.
I will try an illustrate this later... Don't forget to consider how a CSU effects this.
Originally Posted by
flyingchicken
Keep in mind this is an airline pilot forum. The way you are going about analyzing the problem is beyond the variables a pilot can control from the cockpit. Either a prop can be feathered or it is stuck. Either the engine will windmill or it is seized.
That's true but the problem can be evaluated beyond the pilot/control limitations to further understand what's going on, is this not how this thread started?
This is the data relevant to the OP question:
fixed pitch 17degrees @100mph drag in pounds
stationary at 88° (i.e. feathered) 5.8lbs
free-wheeling at 17° 60.1lbs
stationary at 17° 94.4lbs
dead engine wind-milling at 17° 101.1lbs
Consider the scenario with C172P with an 18degree prop I believe I said there would not be much difference...
Anyway don't take my word for it read the data yourself, I could be a dog, this is after all the internet.
