Propeller (air)flow ... [uni 'project']

[RZS10]

well i calculated the force Q for each airfoil and then multiplied it with the corresponding r and by this got the torque for each piece and then calculated (at least thats what i think i did ) the resulting torque

ofc those values are total rubbish ...

my plane has two bugatti veyron engines =D>

should probably be around 200kW

[Blanchimont]

The total thrust should be: constant@spinner * rho/2 * (r_max - r_min) * l * 2

How does this compare with your total axial force of 16534 N?

Edit: inserted the 2, forgot that there are two blades!

[RZS10]

54,39 vs 16534

[Blanchimont]

well i calculated the force Q for each airfoil and then multiplied it with the corresponding r and by this got the torque for each piece and then calculated (at least thats what i think i did ) the resulting torque

How does your formula for Q look like?

[RZS10]

A=(rho/2.*clr*Aref.*(Va.^2));
W=(rho/2.*cdr*Aref.*(Va.^2));
R=sqrt(A.^2+W.^2);
Q=sqrt((R.^2)-(Sr.^2));

all those give an array of results so
S is constant @ 54
A ranges from 64 to 161
W ranges from 2 to 6,6
R ranges from 65 to 162
Q ranges from 57 to 161

[Blanchimont]

The sum of Q*r for the array should give you the torque of one(?) blade.

But are these numbers correct? 54 N axial force seems pretty low...

[RZS10]

S=((rho/2.*clr* Aref.*(Va.^2)).*cosd(phi)-(rho/2.*cdr*Aref.*(Va.^2)).*sind(phi));
S=((1,2/2.*1,05*0,045.*(75.^2)).*cosd(68)-(1,2/2.*0,04*0,045.*(75.^2)).*sind(68));

thats 54 for one blade

so 108 for two

but the sum of the array can't be right, since i would end up with different results depending on the number of "steps" in the calculation.... i have 150 ... with less i would have a smaller torque

whatever, doing it like that gave torque of 4970 Nm and power of 93kW which is reasonable i'll leave it at that

maybe they'll just skim through the text and be like "ooh that looks nice, i like the colourful drawings" and ignore possible mistakes ...
_____________________


Well thanks a lot! I really appreciate your help =D>

[Blanchimont]

Did you have a chat today with some other students who had to solve the problem?
If so, how did their results regarding torque, power and thrust look like?

[RZS10]

Sorry i did not check back here ... those i talked to had completely different results, and not just different to mine but also to each others results ... no one was really eager to share results etc, not even in the facebook group where normally everything is discussed, but there was a huge stack of handed in projects, none of those i saw were as extensive as mine.

But i passed the exam with a decent grade so big thanks again! Will see how many points i got for that project maybe this or next week

[RZS10]

I finally got around to check the exam, unfortunately they did not even have the projects available, i was told i couldn't see it and that it would be pointless since they did not even write any remarks or comments in there, i only know i got 21/25 points for it, i guess it were the power and the torque questions i didn't get the points for, still a shame we don't get the info, especially sucks for those that did not pass and surely want to improve next time and won't know what was wrong after all ...
But yeah... 1/5 of the points i made were for the project, which is cool ...i feel like i owe you a beer ^^

[Richard]

Might be worth having a beer with your tutor so you can work out what they were looking for!

[RZS10]

Yeah... but they are very secretive with that stuff, probably because they don't want to come up with new ideas/questions for upcoming 'projects' ... what i found weird is that i apparently got the same amount of points as someone who made some veeery simplifying assumptions and i was pretty sure what she did was not 'covered' by the wording of the questions ( i might ask her to go check it, maybe they'll be more willing to give a lady some infos ) ... it wasn't a tutor (those are mostly very talkative about such things) but an overworked assistent at the fluid mechanics professorship btw