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Old Oct 05, 2008, 05:30 AM
dongfang
Switzerland, ZH, Zurich
Joined May 2008
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Has anyone seen a Duct-O-Copter?

Hi,

I was (naively) thinking about this: Take the motor and (maybe 12") propeller from a 3D plane, and put a duct around it (Depron or the like). Flip it on the side, so the shaft is vertical, with the propeller up. Add 4 vanes under the propeller, that cancel out the twist in the airstream + torque. Add a control surface with servo to each vane. Add a custom computerized servo mixer to control the thing.

Has anyone seen anything like that?

I know it would probably be unstable, and hard to fly (there is not even a head or a tail on it). And useless for aerobatics, too. The only thing I am sure I could get to work is the control computer

What do you think about it? Feasible? Has anyone seen one?

Regards
Soren
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Old Oct 05, 2008, 09:29 AM
Our Daddy and Heli Junkie
Fred Bronk's Avatar
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Joined Aug 1999
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They tried that in the 50s fo real, and didn't like to go foward.

But they are not helicopters.

http://www.vectorsite.net/avplatfm.html

FB
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Old Oct 05, 2008, 02:39 PM
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Joined Jul 2004
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It might be 'easier' to have some pipes taking feed from the main airflow and terminating around the periphery of the device.... three or four would do the job. These could have flaps to control airflow and would provide more 'direct' thrust for manouvering. But that would be even more ccomplex and I suspect that flight time would be pretty limited.

It would be an interesting "science project"... gotta wonder whether you could make use of electronics from a v-bar (like the new low cost Gaui unit) to help with stability. Not sure if the Gaui unit is customizable enough though... it seems to be designed specifically for heli flight out of the box - and the other options out there (like Mikados offering) would make it an expensive experiment.
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Old Oct 05, 2008, 05:36 PM
dongfang
Switzerland, ZH, Zurich
Joined May 2008
109 Posts
Hi,

Thanks Fred for the link. Interesting page! So someone did it before, and got it to work so-so.

ukgroucho, I will probably use this project - if I launch it - as a reason to take up AVR (a single-chip computer) programming. Then, I will make my own universal servo mixer. I pretty much have the idea about how I will structure the hardware and software, and I will make it so that it can be used for other purposes too (quadricopter, elevon and V-tail mixer etc). Of course it will need gyro stab around the prop axis. I have a 401 lying around...

Regards
Soren
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Old Oct 05, 2008, 05:53 PM
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dgoslee's Avatar
Seaford, DE
Joined Jan 2002
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Yes

You mean like this:

http://www.honeywell.com/sites/porta...video&theme=T8

A couple of companies are doing this.




Quote:
Originally Posted by dongfang
Hi,

I was (naively) thinking about this: Take the motor and (maybe 12") propeller from a 3D plane, and put a duct around it (Depron or the like). Flip it on the side, so the shaft is vertical, with the propeller up. Add 4 vanes under the propeller, that cancel out the twist in the airstream + torque. Add a control surface with servo to each vane. Add a custom computerized servo mixer to control the thing.

Has anyone seen anything like that?

I know it would probably be unstable, and hard to fly (there is not even a head or a tail on it). And useless for aerobatics, too. The only thing I am sure I could get to work is the control computer

What do you think about it? Feasible? Has anyone seen one?

Regards
Soren
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Old Oct 05, 2008, 07:45 PM
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jasmine2501's Avatar
United States, AZ, Mesa
Joined Jul 2007
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It's just a coaxial helicopter with a bunch of stuff in the way to reduce the efficiency... there's a reason why there aren't hundreds of these in the air every day.
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Old Oct 05, 2008, 10:23 PM
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Denver, CO
Joined Dec 2005
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I used to have plans for an airplane with a ducted propeller. The duct was centered on the CG, had 4 vanes for thrust control, and the whole duct tilted for forward flight. It was in an early 90's RC airplane magazine. Had gyro's on the vanes for hovering stability.
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Old Oct 07, 2008, 08:23 PM
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Quote:
Originally Posted by jasmine2501
It's just a coaxial helicopter with a bunch of stuff in the way to reduce the efficiency... there's a reason why there aren't hundreds of these in the air every day.
Really? Do you have any basis to say ducting reduces efficiency?
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Old Oct 07, 2008, 08:33 PM
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Quote:
Originally Posted by krush
Really? Do you have any basis to say ducting reduces efficiency?
Nothing other than well-known aerodynamic principles


It is primarily because of this (from Wikipedia):
"At low speeds, the presence of the duct may create more drag than extra thrust, and therefore its comparative advantage to an open prop is canceled."

Since we are talking about a helicopter here, we are talking about super-low speeds, where the above becomes a problem. At higher speeds though, this comes into play (same article):
"By reducing propeller blade tip losses and directing its thrust towards the back only, the ducted fan is more efficient in producing thrust than a conventional propeller."

IMO, the primary reason for working on a project like this is because a ducted fan helicopter would be really quiet... really sneaky.
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Old Oct 07, 2008, 09:30 PM
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Actually, some ducting increases eff., but it depends on the aircraft and prop size.

For a heli now way (look at the Osprey) but for planes with smaller props the duct and some vanes are fine. But it is better to move the entire unit than use vanes to direct the thrust.

Wikipedia is OK, but there are many mistakes too.

FB
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Old Oct 08, 2008, 12:12 AM
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It's a good place to refer people to when it's correct. The quotations were the most succinct way I could find to explain something that would have taken me a long time to type. What I mean about efficiency is about fuel in/power out and I think most people familiar with jets know that they burn a crapload of fuel in order to do what they do. What they do is amazing for sure, but things like the Harrier burn way more fuel in a hovering maneuver than things like the Apache.

I think the happy medium is the "ductless fan" but the technology hasn't quite been figured out yet, and it is super-loud, which isn't a great thing on a stealth observation craft.

http://en.wikipedia.org/wiki/Propfan
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Old Oct 08, 2008, 08:58 AM
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Georgia, USA
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Has anyone successfully reproduced a Harrier in RC form? I watched many VTOL exercises at NAS Beaufort,South Carolina, back in 1979.

Thrust vectoring control would possibly require a seperate,cyclic like control of the nozzles.It would be a handful to operate a model, as it is to fly the full scale jump jet.

I got to see some very smooth operation and a few close calls. One landing attempt had the craft almost vertical on the roll axis before it was corrected. I held my breath for several minutes before I remebered to breathe.

Jimmy
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Old Oct 08, 2008, 12:01 PM
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I have seen that Harrier in person doing hovering and stuff, and it is the scariest plane I've ever seen up close. Also one of the loudest planes I've ever seen.

Some people are experimenting with vectoring and stuff... there's some threads about it.
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Old Oct 08, 2008, 01:45 PM
dongfang
Switzerland, ZH, Zurich
Joined May 2008
109 Posts
Hi,

No it's not a coaxial helicopter. There is only one single rotor. The other element is a 4-vane (or 8 maybe) stator.

The duct is really more a frame than anything else. If it will introduce too much drag, some other kind of frame could be used instead.

I got my AVR programmer today .. I can start playing with programming a universal receiver side mixer.... I guess I will try to build such a copter (which is no helicopter at all, I was told).

Regards
Soren
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Last edited by dongfang; Oct 08, 2008 at 04:12 PM.
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Old Oct 08, 2008, 01:54 PM
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Interesting... be sure to post back to this thread if it works!
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