The trouble with large dia props on airplanes is that tip speeds approach
Mach = 1.0 with tha associated drag rise and shock wave inefficiencies.
Tip speed is the vector sum of rotational + forward velocity: big props
going fast = high tip speed. More, shorter blades at lower speed can still
absorb the power without Mach effects. M = 0.95 is really the limit;
anything higher and the drag increase absorbs the power. All this has
nothing to do with Tiger fans since we are not running them at supersonic
tip speeds. The world record for prop planes (low alt, 3 Km) is 528.33
m/h, Lyle Shelton, Bearcat, 4 blades, 1989. Ref NAA Records Book 1996.
For Tigers, 6 works well
Bill Rogers
----------
> From: STUART_BRENNAN@HP-Andover-om3.om.hp.com
> To:
> Cc: tigers@autox.team.net
> Subject: Re: Canadian Fans
> Date: Wednesday, October 15, 1997 12:28 PM
>
> >The fastest prop plane ever was the 5 bladed scimitar propeller
P-47N
> >which did 504 mph.
>
> >Typhoons, Tempests, Spitfires, and a lot of Russian turboprops use
in
> >high performance versions used 5 bladed or more props.
>
> >mBrad
>
> Reply:
>
> I think the problem here was power. As the built more powerful
> engines, they could turn larger and larger props. At some point
they
> had to decide to either make the landing gear taller, or add more
> blades. Didn't I see an experimental DC-9 with a 6 or 7 blade
> turboprop engine stuck on the back? Again they were trying to
deliver
> a lot of power in a small diameter. Just like we're trying to move
a
> lot of air in a small diameter. For the same blade shape, the more
> the better until the start to interfere with each other.
>
> Maybe we would have seen more 5 or 6 blade machines if jets hadn't
> taken over just after this era.
>
> Stu
>
>
>
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