Does anyone here have a clue about propellers?
They were not covered at all in lectures and we have an extra 'project' that counts for 15% of the final grade in fluid mechanics, that does not seem like much but it's ~30% of the points we need to pass
I am unfortunately unable to find really suitable or helpful info online -.- I even read some chapters in the "Pilot's Handbook of Aeronautical Knowledge" ffs and could not find anything that might really help... just the basic drawing
just ignore the bad english, apparently no one bothered to spellcheck before uploading it (we also have a german version that only differs slightly)
i drew this..
Vr is the circumferential speed
Q sheer force? (googled that ... german 'Querkraft')
R resulting force
alpha is the aoa
beta is 'steigungswinkel' .... angle of climb according to dict.cc
a) already did that in the drawing... should be right, the german version also asks about the angle at which the flow hits the propeller (phi) should be tan(phi)= V/Vr
b) So what do i take here, do i take the maximum aoa of 16°
or 11° where the lift coefficient is at its maximum?
i first assumed that the aoa will be zero at the tip, took an aoa of 11° for 0,15m and 0° for 0,6m and calculated a straight between those two points since the graph is almost straight between those two points
might be right...might be wrong, dunno what exactly they are asking
The point is, as far as i understood propellers you really want the thrust to be the same across the whole propeller/radius, that's probably what they mean with the assumption of constant axial force, but i only have equations for drag and lift, that would give me the resulting force and from there i could get to the thrust with phi ... but i did not manage to get to any decent result because something seems to be missing
c) now comes the weird part: isn't the twist supposed to allow for a constant aoa? I mean then b) would be pointless or the aoa constant with the blade twist changing, dunno how to calculate the twist...
d) here i guess i'd just have to fiddle with matlab and the second graph to get some correlation
e) i believe i should see the propeller as a series of infinite small wings (airfoils)? find an equation for the thrust depending on the radius r and integrate across the raduis? or something...
f) same for the force Q ... momentum =r*Q?
It's really just annoying if you have no info whatsoever in your lecture notes ... maybe someone knows that stuff well and can help