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Old 26-09-2012, 08:24 PM   #1
Tony_L
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Default Electric Ducted Fan R/C Eagle - Feasibility Study.

I have this crazy idea to build a "stand-off scale" EDF powered Eagle, using a quadcopter controller to control four electric ducted fans for lift. Building it out of Depron should make it light enough and with 90mm fans I should be able to get around 3.5 to 4kg of static thrust.

So, to get an idea of how big the Eagle would need to be to accomodate 90mm fans where the VTOLs in the main body would be I went on the hunt for some drawings or pictures I could scale to the right size. I duly printed a side elevation across... er... "several" sheets of A3 and have made the somewhat disconcerting discovery that the resulting beast would be 64" inches from nose to tail !

I'm only looking to get her a few feet off the ground into a hover with some low-speed flying and I'm pretty sure that the fans can provide enough lift, even taking into account the batteries & associated electronics, but is 64" simply too big to even attempt ? I know Depron is rigid, but would something of this size simply require too much (heavy) reinforcement to be practical ? The passenger pod would be permanently fixed to provide structural integrity as well as carrying the electronics so I'm not worried about having a super strong spine, and the fore & aft cages as well as the spine would only be a painted representation on flat sheet anyway.

Am I mad ? Thoughts and opinions welcome.
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Old 27-09-2012, 10:01 PM   #2
Tony_L
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I think I am mad. At that size the VTOL's are only about 70mm in diameter and unless I fork out 60+ per EDF unit I can't get units with sufficient static thrust to give the necessary thrust to weight ratio for even a hover (1.15:1 I believe) 240+ just for the motors and then goodness knows what for a good 4S LiPo and four 45A speed controllers is just going to blow the budget even further out of orbit than Moonbase Alpha.

Back to the drawing board...

(Mind you, the side elevation looks bl**dy impressive draped across the whole of the kitchen worktop !)

Last edited by Tony_L; 27-09-2012 at 10:03 PM.
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Old 27-09-2012, 10:18 PM   #3
Darren Robertson
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I'm building a 50 inch eagle and I'm mad.

By comparison, you are stark raving bonkers....
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Old 28-09-2012, 05:04 AM   #4
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No, you're a modelling genius !

My eagle, whatever size it turns out to be, will simply be a collection of flat sheets with details drawn/printed on. No fiddly cage work to assemble, no greeblies to place, engine bells simply made out of a basic cone of neoprene foam or stiff card. The most difficult part to construct will be the CM, but even that will simply have the window sections painted on rather than inset as per the "real" thing. My main aim is to make it fly if at all possible, then make it look like an eagle.

I've seen quite a few failed attempts at this sort of thing, maybe I'll be another addition to the list, but I'm hoping I've done my sums right. Come pay-day there'll be some ducted fans, LiPo's and a quadcopter flight controller being ordered. Then I can play around with a test rig. Fingers crossed.
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Old 28-09-2012, 06:08 AM   #5
Darren Robertson
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Thank you for your kind words

In all seriousness, you have to do this.....it's a cool project. Loads of build pics and video of the flight, though, or it never happened!
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Old 28-09-2012, 08:09 AM   #6
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There is a thread about a flying R/C Eagle in this forum. http://www.eagletransporter.com/foru...ad.php?t=29910
Maybe this gives you some inspiration. Good luck!
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Old 28-09-2012, 09:10 AM   #7
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Darren - There will be plenty of pics once I've got the materials together.

Transporter - That's one of the threads that gave me the inspiration in the first place, but I want to see if it can be done without using rotors. No offence to the guy who built that model, it's a brilliant piece of work, but Eagles don't have rotors, they have rocket engines. Sadly I don't have somewhere in the region of 10 grand spare to put four miniature jet turbines in it, so I'm going with the next best thing :-)

There's a high chance of failure with this project, it seems lots of people have attempted similar things without success but who knows, maybe I'll be the lucky one.
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Old 28-09-2012, 06:54 PM   #8
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I now have a dorsal view printed out at the same size as the starboard elevation. I'll glue the sheets together later this evening when everyone's gone to bed and I can hijack the living room floor to lay them out on. I'll post some pics so you can get an idea of -
a) How big it is and,
b) How stark-raving mad I probably am !

I've found a 68mm fan unit that can push out 950g of static thrust on 4S, so four of those should hopefully give enough thrust. I'll have to be very careful with the overall weight though.

Proof that someone has built & flown an EDF powered quadcopter : http://vimeo.com/41811715

Last edited by Tony_L; 28-09-2012 at 08:18 PM. Reason: Added link to video
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Old 29-09-2012, 08:51 PM   #9
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Here's the starboard elevation. That's a two foot straight-edge at the lower right to give an idea of scale.



Big, innit ?
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Old 08-10-2012, 05:47 PM   #10
armadillozenith
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I ought to admit I have no experience with RC - except watching and being impressed.
I do love the Eagle design and the idea of a flying version with no visible rotors!
How about having the fans in a row along the main body (cages and pod), with panels only at the sides (immediately inboard of cage gridwork, and pod sides) - the spine being air intake slot and the rocket nozzles below being supported only on thin cross-struts?
Might this allow max airflow and max fan size without impinging on overall shape and look of the Eagle.
For stability, I realise at least a portion of the airflow would need to be ducted out and down off the centreline.. through landing pods perhaps?
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Old 08-10-2012, 07:06 PM   #11
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The general idea, subject to a test bed (when cash permits) is to fit four 68mm ducted fans in the same place as the VTOL's in the passenger pod. The roof of the pod will be open so that, as you suggest, the spine will be the intake slot. I don't want to duct any of the airflow as the losses would be too great. Weight is already a major inhibitor as to the size of fans I can use, introducing ducting and flow loss would mean more powerful fans and hence heavier batteries to supply the necessary current.
The fans would be controlled by a standard quadcopter controller to provide roll, pitch and yaw by altering the speed of the appropriate fan pair.
Still very much on the drawing board at the moment. (And at 64" in length, it's a BIG drawing board ! :-) )
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