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Author Topic: Ducted fans  (Read 3193 times)

raflaunches

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Ducted fans
« on: December 16, 2012, 05:59:50 PM »

I would like to know how powerful a brushless motor and the size/diameter of a ducted fan would have to be to move a hull, 31inches long and 13inches wide but only sits in the water in about an inch, at a pretty decent speed. The project is in the theory stage at the moment but the boat in question will built to 1/12 scale, the real vessel ended in disaster with the front planing shoe collapsing. Don't want to give too much away at the moment but I am sure there are members who have an inkling which silver and red boat I am talking about! ;)
Any ideas will be gratefully received.
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richald

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Re: Ducted fans
« Reply #1 on: December 16, 2012, 07:01:55 PM »

Quote
I would like to know how powerful a brushless motor and the size/diameter of a
ducted fan would have to be to move a hull, 31inches long and 13inches wide but only sits
in the water in about an inch, at a pretty decent speed.

Not sure as to how much thrust you would actually need to achieve the performance you are after
but a quick look on the HobbyKing website shows quite a wide range of EDF units w/r to size, thrust 
(and price!) some examples....

GWS EDF40 Power System      40mm dia., 87grams thrust, 5.40

EDF55 with 4300kv Motor Assembled     55mm dia., 400grams+ thrust, 10.79

9 Blade Alloy DPS 110mm EDF unit - 10s 4070watt 980KV     110mm dia., 7KG thrust (Yes! 7000grams), 159.77


Richard
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dreadnought72

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Re: Ducted fans
« Reply #2 on: December 16, 2012, 07:10:29 PM »

Quote from: richald
9 Blade Alloy DPS 110mm EDF unit - 10s 4070watt 980KV     110mm dia., 7KG thrust (Yes! 7000grams), 159.77

If the boat masses less than 7kg, that could be rather entertaining.  %%

Andy
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Circlip

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Re: Ducted fans
« Reply #3 on: December 16, 2012, 08:30:24 PM »

Gonna need a BIGrudder O0
 
 
   Regards  Ian.
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richald

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Re: Ducted fans
« Reply #4 on: December 16, 2012, 10:22:57 PM »

bit of an error on my part ....

the 110 mm unit is only 6kg of thrust but more expensive - 169.30

the big daddy is the 120mm unit ....

Alloy DPS-2 Series 120mm EDF unit with 4 Pole 980kv Motor - 5000watt (12s)    120mm dia., 7KG thrust, 159.77

Incidentally both units pull around 110 Amps at maximum power - the wiring would
have to be a bit beefy!

Richard
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raflaunches

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Re: Ducted fans
« Reply #5 on: December 17, 2012, 10:32:06 AM »

Thanks guys


This gives me something to think about, who knows there might be a red and silver streak at Wicksteed park in the next couple of years!
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Nick B

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andrewh

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Re: Ducted fans
« Reply #6 on: December 17, 2012, 02:45:27 PM »

Very INTERRRRRESTING
 
Don't forget, raflaunches that these quoted thrusts are STATIC thrust for ducted fans - it increases radically as the fan starts to move and I can't quirte remember then it peaks - I seem to remember its when the vehicle speed is 50% of the jet velocity.
 
There won't be much published data on boats use with d/f, but you could regard it as a staggeringly draggy plane and see what can be learned that way
Generally tiny diameter high-speed D/F s are used for high speed aircraft.  Trainers etc use relatively large fans running slower.
Many areomodellers use home-rolled fan ducts with cut-down aero props and achieve very good results
 
red and silver?
andrew
 
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raflaunches

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Re: Ducted fans
« Reply #7 on: December 17, 2012, 03:05:01 PM »

Thanks Andrew


more for everyone to ponder...
Red and silver with two outrigger/floats!!! And went like a flash when it worked!!! (unfortunately it went bang on its last run)


Regards


 Nick B



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Arrow5

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Re: Ducted fans
« Reply #8 on: December 17, 2012, 03:42:09 PM »

Daily Express , Scottish edition. %)
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bikerdude999

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Re: Ducted fans
« Reply #9 on: December 17, 2012, 06:17:12 PM »

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tobyker

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Re: Ducted fans
« Reply #10 on: December 17, 2012, 07:23:40 PM »

John Cobb.
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raflaunches

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Re: Ducted fans
« Reply #11 on: December 18, 2012, 03:24:20 PM »

Tobyker has it in one.  :-))





John Cobb's jet powered Water Speed Record challenger, 'Crusader'.


Let us hope when I build it works and doesn't end up like the original.




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Nick B

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Arrow5

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Re: Ducted fans
« Reply #12 on: December 18, 2012, 04:03:28 PM »

You missed post #8 then  %)   I think the air intakes will have to be enlarged and a cheater intake in the cockpit if possible.
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essex2visuvesi

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Re: Ducted fans
« Reply #13 on: December 18, 2012, 08:42:49 PM »

I have a 90mm ducted fan unit with 3.5Kg thrust from an aborted aircraft project, plan is to put it in a shovelnose Hydro at some point.  Looking at modifying the Notre Dame plans on Astec models
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tobyker

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Re: Ducted fans
« Reply #14 on: December 18, 2012, 11:49:42 PM »

we didn't miss post No 8 - it was obviously a bit too subtle. Indeed I didn't see the significance of it until I thought of his name, and the name of the boat naturally followed - Ah SO!!
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