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Author Topic: shroud around props:  (Read 2378 times)

rathikrishna

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shroud around props:
« on: October 15, 2010, 07:49:49 am »
Good after noon friends.i am going to make a new TUG, which is intented for long time operation.i was looking for a good motor for that. and now i got it, a wiper motor from an old car. it drains only around 800 ma even while trying to hold its shaft at speed.its much tourquey also.so my doubt is this. i could find a ring covering around the props, in every tugs, just we see in a duct fan used in aircrafts.i have furnished a full unit of propultion, the props goes in to 3 inch dia.an apropriate sized pvc pipe is added as a duct.but i am in a confused state that, when i checks the motor prop unit under water it drops around 600 ma.at 12 volts. but when i adds the duct to the prop the current drops around 500 ma.means motor is less strained after fixing the duct..means less peformance...?..will any one guide me once...so simply my doubt is this. will a prop shroud increase performance ?. please..
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Pirate

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Re: shroud around props:
« Reply #1 on: October 15, 2010, 08:30:28 am »
A brief history of shrouds around props:
during the industrial revolution in England, much of the goods traveled by horse drawn barges, but when the internal combustion engine came into being it was quickly adapted to barge propulsion. Great fear was aroused to the new propeller driven craft eroding the canal bank sides with its wash, So it was found that a shroud around the prop reduced the side thrust and thus reduced the erosion. As a side issue it was also discovered that the engine was using less fuel for the same speed. (This is what you have discovered) the wasted side thrust is sent as drive thrust, thus the engine revs can be reduced to obtain the same level of propulsive work as before. This shroud has undergone vast research and development and is now the modern Kort nozzle. These Kort's have an airfoil section and act like a continuous circular wing and jet drive at the same time. For tugs this adds significant propulsive drive as compared to an open propeller. I feel that you with your aeronautical background will do great service to your Kort/shroud propeller driven craft.

Kind regards
Pirate
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woody_294

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Re: shroud around props:
« Reply #2 on: October 15, 2010, 10:44:06 am »
Great reply Pirate! I'm glad I now know that, I love the fact that they came across it completely by accident!
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Tug-Kenny RIP

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Re: shroud around props:
« Reply #3 on: October 15, 2010, 12:28:11 pm »

Thank you for that explanation Pirate.  I have often wondered about their design.

You mention aeronautical shape. Does the 'tube shape' of the 'Kort nozzle'  taper in it's internal and external diameter from front to back ? and does the thickness of the skin vary as well as being curved on the outside ?

The information would help Rathi and many others (including me!)

Cheers

Ken


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Colin Bishop

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Re: shroud around props:
« Reply #4 on: October 15, 2010, 12:43:52 pm »
Kort Nozzles were described in Terry Gosling's article on Propulsion published in Model Boats in 1999 and recently reprinted in this year's Commemorative Special issue. Well worth reading for anyone thinking of installing Korts in their model boat. An extract from Terry's article below would seem to answer your query Ken.

Colin

Mr Kort, who was an aerodynamicist, rather than a naval architect, proposed that a shroud be fitted around the propeller. With his aerodynamics experience he naturally made this shroud of a streamline shape similar to an aeroplane wing cross section to reduce the resistance as much as possible. It proved to be very successful as a preventer of erosion and still is so, but somewhat to Kort's surprise, a marked increase in efficiency and performance was noted whenever the shroud was fitted.
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rathikrishna

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Re: shroud around props:
« Reply #5 on: October 15, 2010, 02:51:27 pm »
GREATTTTTTTTTTT....oh my friends...sure ..i will finish my new tug with a shroud...and can save ample of battery power...OYE...OYE...thanks once again...
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Circlip

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Re: shroud around props:
« Reply #6 on: October 15, 2010, 03:57:25 pm »
The Aerofoil section is inside the ring which gives a Venturi effect, like a carburetter (Age thing) bore.

  Regards Ian.
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tt1

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Re: shroud around props:
« Reply #7 on: October 15, 2010, 04:33:10 pm »
Well done everyone, have learned a lot from this thread - thanks and regards to all.  :-))

                           Tony.
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Tug-Kenny RIP

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Re: shroud around props:
« Reply #8 on: October 15, 2010, 08:18:24 pm »

Thank you for the information gentlemen. I figured it wasn't quite a straight drainpipe.   ;)

Ken

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rathikrishna

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Re: shroud around props:
« Reply #9 on: October 20, 2010, 06:36:06 am »
Good morning Friends..sorry for the delay in reply...was bussy with my official things..have to compleate all resposibilitiies before my resignation.and will be a full time model maker.my elder brother Krishna is also back here. so i am too happy..but within my bussy i managed to fix a shroud around my prop, with PVC pipe, reworked with automobile body building metal paste,in to aerofoil,specification of NACA. my craft weighs around 2700 grams, with battery, still it flies over water by draining only 800 mah at full throttle, at 12 volts.so happy...i wonder about the thing that i dont know why i was not thinking about this device before..ommm..(sad).so i wll be back..thank you all..thanks once again..i dream to work with people like you all..all with a knowhow to things..and yes shows their mettle on time..god may bless you all..VETERANS...have a nice day..
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Pirate

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Re: shroud around props:
« Reply #10 on: October 20, 2010, 07:52:04 am »
Good morning Rathi,
so glad about your news, may all be well with you and your new career change. When you have time, I am sure we would all love to see your new vessel, especially the Kort nozzle. I am very happy that we are of service to you and that we all continue to be of mutual support not just to you but to us all. Modelling can be a career, therapy and great enjoyment. May it be so to you.
As you say
God Bless you and us all in this innocent passtime of model boating.

Regards
Pirate
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rathikrishna

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Re: shroud around props:
« Reply #11 on: October 24, 2010, 03:28:00 pm »
Pirate..a million thanks for the love and care. i am on half way to my resignation.but i have to wait untill the airshow of coming year, means untill march.because i have to submit some projects there all related to avionics.within that time i have to buy four or six two channel R/C systems for me..so i am too bussy to conclude my work...so will be back again..thank you all once again..good night.
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