Crazy Fan/Prop Design Questions

[Kevinrmcd]

Disclaimer: I'm a computer programmer, not a aeronautical engineer. With that said, I've always been fascinated with flight and originally went to school to major in AE. Here a couple of ideas I have had for which I have not been able to find any info online.

1) Counter-spinning Fan/Prop - basically 2 fans, with one nested inside the other, that spin counter to each other. This is a crude representation of this design:

Diameter looking down (v and ^ are direction the blades move):

^=|v=O=^|=v

Cross-section view (v and ^ indicate air flow):

^ v v ^
=|=x=|=

The vertical lines represent the separation between the inner/outer vanes. The Would this design generate lift? What if the outer vanes forced the air down and towards the middle?

2) Counter Force Prop - basically a prop that forces air in both directions. It is similar to number one, except that a single blade has two sections pitched opposite of each other, rather than two separate blades pitched and rotating opposite of each other.

Is there any merit to these ideas?

thanks

 

[btrueblood]

#1 - counter-rotating props (typically two props staged axially relative to each other) have been done. Do they generate lift? Only if their thrust vector opposes gravity... If you mean "do they generate thrust" the answer is yes, and the configuration has been used in a number of production airframes, with various levels of success.

#2 - Well, as a propulsion device, it leaves something to be desired. A bit like having a 4-wd vehicle, with the front axles operating in reverse when the rear axles are in forward gear...somewhat counter-productive. But, as a mixing device, it's a great idea (think of a butter churn, or an ice cream mixing paddle). Of course, it too has been done before, and is in use in a number of production devices...

 

[Kevinrmcd]

Thanks for the quick feedback btrueblood. Do you have any examples of the counter-rotating props? Additionally, I actually meant lift - but more in the hovercraft line of thinking. I didn't know if the counter rotation would create any gravity-defying gyroscopic forces (precession?) that would help generate lift.

thanks

 

[IRstuff]

The simple answer is no.

TTFN

 

[btrueblood]

Examples? I'd suggest googling for it. IIRC, the Russian Bear bomber used counter-rotating props, as did an airliner (probably one based on the Bear).

 

[CESSNA1]

KEVINRMCD:

For examples beside the Russion BEAR. There was the Convair pogo in the early 50's that used counter rotating props and jet exhuast to lift it vertically, then transition to horizontal flight. Done as an experiment it required a tower to land vertically. No horizontal takeoff/landing could be performed because the small wheels were on the wing/tail tips.

Then there was the Bristol Brabazon from England in the early 50's also. It was a huge four engine passenger plane that was likewise unsuccessful.

There was also a post WWII single engine airplane that I think was the Grumman Guardian (not sure)

I also think the British Fairey Gannet had counter rotating props.

Hope this helps
Regards
Dave

 

[GregLocock]

Yes, the Gannet had contra rotating props.

Cheers

Greg Locock

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