prop design
 

hello guys

I am looking for some information about turbo props like the saab 2000.
At the moment I am designing a prop for a model airplane where the tips are reaching mach 1 (re 200000)so I suspect some serious problems with shock waves and reduced effiency at the outer 25 % of the blade
I do have some information about the arad sections develloped in the 70's but cannot find any more recent information about profiles used on props for e.g. the saab 2000.
I would also like to know the mach number on the commuter airplane props like the saab 2000 or other ones, If you can give me the RPM,prop diameter,cruise speed and level I can do the calculation myselve.
If you know any sites of interrest or other sourses I would be very happy.

A 737 pilot with to many spare time

Thanx Robbert


[This message has been edited by robbert (edited 10 January 2001).]

[This message has been edited by robbert (edited 10 January 2001).]

I'm not going to be much help on the Saab, since apart from a vague recollection that I've read somewhere that the thrustlines are about 2½° off parallel with the longitudinal axis to counteract torque, I've never been near a whole one.

I do however do quite a lot of work matching fixed pitch props to smaller engined GA aeroplanes. It's a bit of a black art, but in general I find that if at max RPM you design for a tip speed of about 0.65M and you set pitch on the ground so that firewalling the throttle you can generate about 90-95% max.rpm in still air, the prop matching is pretty damned close, and no more than a couple of degrees of adjustment is likely to be needed.

I certainly wouldn't even contemplate flight testing an aeroplane that had tip speeds in excess of 0.85M - my career is too precious to me.

There's quite a useful document that covers microlight engine : propeller matching at http://www.bmaa.org/011.pdf which might be useful to you (bear in mind that it's written around Rotax engines which have a max.rpm of aroun 6,500 to 7,000 rpm and usually a 2.58:1 gearbox.)

G

Hi robbert, here are some figures for the ATR42-300:

100% RPM = 1200
Cruise RPM = 86%
Prop diameter = 13ft
Cruise = 255 kt TAS
Max FL = 250
Vmo = 250 kt
Mmo = 0.55

What kind of model are you building?

THAI TUN

Robbert,
You might try going to an engineering library at a University. You can probably find all kinds of test results and research on supersonic props. You can probably find info on some of the old projects like the one with a jet engine in the back and the supersonic prop on the front, I can't remember what it was. You'll probably find info on more modern projects also. I have found quite a lot of design information on many different helicopters from older to more modern at the University af Washingtons engineering library.