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Old Jul 25, 2009, 08:52 PM
Mango the Parrot
arichards1969's Avatar
South Wales U.K.
Joined Jan 2009
197 Posts
Question
Watts per Pound

Hi,

Beginners question, but how many watts per pound for edf ?

This is my first foray into jets so I don`t want super-sonic

Thanks,
ants.
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Old Jul 25, 2009, 09:18 PM
Registered User
DForbes's Avatar
Michigan
Joined Jun 2005
620 Posts
Quote:
Originally Posted by arichards1969
Hi,

Beginners question, but how many watts per pound for edf ?

This is my first foray into jets so I don`t want super-sonic

Thanks,
ants.
Hey Ants,

IMHO it seems to vary but generally I have seen "approx" 350w per pound of plane.

Dennis
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Old Jul 25, 2009, 10:41 PM
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Joshua Wesley's Avatar
United States, NV, Sparks
Joined Oct 2004
1,139 Posts
I have seen EDF fly with as little as 120watts/lb, or as high as 500watts/lb. For good "sport" performance I'd somewhere around 250 watts/lb.
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Old Jul 25, 2009, 10:45 PM
Xtreme Power Systems
Lake Havasu, AZ
Joined Jun 2005
15,720 Posts
350w per pound would be an incredible amount of power. Most high speed jets are in the 250w per pound range. Tam's Spark with 4000w is 363 watts per pound, and almost 200mph.

We have flow big jets (27 pounds) at 125mph with only 185w per pound.
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Old Jul 25, 2009, 11:11 PM
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DForbes's Avatar
Michigan
Joined Jun 2005
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Quote:
Originally Posted by JimDrew
350w per pound would be an incredible amount of power. Most high speed jets are in the 250w per pound range. Tam's Spark with 4000w is 363 watts per pound, and almost 200mph.

We have flow big jets (27 pounds) at 125mph with only 185w per pound.

I believe that's why I stated that it varies and it was meant to be an approximate number. It is also dependent on airframe type. For a floaty type airframe like the F-22 you would be better served to have a little more watts to play with.

Another example would be the SAPAC T-45 comp. Using your number of 185w per pound, I have a hard time believing that a 1000w setup in this plane = 5.4 lbs of thrust.

Dennis
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Old Jul 25, 2009, 11:18 PM
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Aero Ace Ace's Avatar
Whitney, NV
Joined Dec 2008
263 Posts
I think we're talking about the airplane's weight, not thrust per watt, which will vary greatly. I think 250 watts/pound in an efficient setup will produce a well flying model; better than scale in many cases.
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Old Jul 25, 2009, 11:46 PM
Danger! Danger!
FrankW's Avatar
Portland Intl, Oregon, United States
Joined Dec 2002
1,913 Posts
100 W/lbs = flyable
200 W/lb = now we're flying like a jet
300 W/lb = fast and fun
350+ W/lb = hold on to your hat!

Just my 2 cents.

-Frank
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Old Jul 26, 2009, 01:35 PM
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
Joined Dec 2003
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To fly a plane you only need at least 30% of thrust/weight ratio. for gliders 20%. The efflux speed of a fan is always high or higher and this is not an issue for edf unlike prop planes. If you fly bathtub dynamic patterns you can achieve a nice top end speed too. Because of this I have build several edf jets with smaller fan units as they are designed for because I have enough thrust to scoot around at a very nice pace which suits the model. One will be able to power a lot of planes with a 70mm fan because the thrust ratio is approx 1.2-2kg which could make a 2.5-3kg edf jet fly very nice. Most 90mm edf jets are in the 1700-2500gr range so you have lots of playroom! This is why I do prefer a 70mm edf unit. I have the thrust I need and I have high top end speed where a 90mm fan needs gobs of power(=weight) to get even. My Uriah-BU was dopplered at 262kmh with only 550W where a 90mm unit needs 3.5kW to get the same top end speed (have to note the 90mm airframe tends to be bigger BUT the Jepe 90mm F16 needs 1200W+ for 300km/h in a dive and I need a lot less )

the thrust/weight ratio highly depends what you like yourself.

600W/1700gr:
http://airtoimedia.nl/web/upload/Emi...k_8-7-2007.wmv
400W/1400gr:
http://airtoimedia.nl/web/upload/Emi...nifan_Erik.wmv

300W/1200gr:
http://airtoimedia.nl/web/upload/emi...6april2008.wmv
300W/450gr:
http://www.rcgroups.com/forums/showp...&postcount=288
350W/750gr (unlimmited vertical)
http://www.rcgroups.com/forums/showp...&postcount=320


3.5-4kW/6kg
http://airtoimedia.nl/web/upload/Emi...28sept2008.wmv

290W microfan (an other plane!)/1200gr:
Jetmeeting ME 163 video (4 min 11 sec)
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Old Jul 26, 2009, 02:19 PM
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monkamarm2000's Avatar
NorCal Silicon Valley
Joined Aug 2002
11,778 Posts
That's exactly why I'd been trying to come up with an average system. For example if I'm looking at a 90mm fan to a 70mm fan first thing I do is take the weight of the heavier fan off the perforamance figures, then I see what I really have. If a larger fan makes 1 more thrust but weight is 1 pound more, I just got nothing for my swap except less velocity I also have to factor in, since it makes more power, it absolutely has to take more power to run so I have to factor in less runtime. I don't know what it will take, but I need to come up with some average figure to calculate standard useable figures. Someone penned the perfect term for it recently too, they referred to it as "Propulsive Efficiency" .

And don't say it, I know! I over think everything!

Howz the baby btw?

Barry
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Old Jul 26, 2009, 02:40 PM
James L
TANGOSIERRAROM's Avatar
Beck Row Mildenhall
Joined Mar 2009
789 Posts
I have found that less than 120 W/lb is going to be short on power, but there seems to be more to it than just watts and pounds.

Your ducting needs to be good to get the performance otherwise your fan wastes its power working to overcome turbulence in the duct and the efflux is not as fast as it could be. Work can be expressed in Watts

A ducted fan plane has to be considered as a whole entitiy so at play we have weight, lift, and drag. Wing loading is a handy if not scientific way of looking at the lift to weight ratio, low wing loading need fewer W/lb as they can fly slower so 120 W/lb will fly it but go above 15oz/foot^2 and you will need 200 W/lb to get it to be comfortable. Then again if you look at Pontious's threads on this website and the Vulcan thread http://www.rcgroups.com/forums/showthread.php?t=532258 in particular he has these specifications:-
All 5mm Depron.
72" Span.
4Lb All up weight. 2Lb airframe 1Lb 4brushless microfans. 1lb 3s1p 3200 Kokam
Wing Loading 7Ozs/Sq Ft
Total thrust 32 Ozs installed, 12oz per fan out of the plane
Total Current 40 Amps
Total Power 440 Watts
One Kontronic Jaz 80 E.S.C. (with B.E.C.) controls all four fans perfectly.

Drag this is difficult but basically you need a certain amount of thrust to overcome drag and thrust is connected to Watts so a flying brick is going to need a lot of power just to move it through the air. Thrust at maximum speed is pretty much equal to drag, if there is no drag, then v max would be when there was no thrust left to accelerate it. So a draggy airframe needs more power to get it to fly.

So what do you need, ballpark figures here,
150 W/lb to 200w/lb would be a good setup to aim for spritely performance from a sport type flyer.

200w/lb to 250w/lb for a typical high detail scale jet.

More if you want serious speed.
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Old Jul 26, 2009, 02:57 PM
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
Joined Dec 2003
4,974 Posts
Madelyne is 16 days now and loves coma drinking She falls asleep for 4hrs before the bottle runs dry . Building pace is slower

My rule of thumb is like prop choice: if one needs thrust, one needs a larger diameter. If one need speed one needs to increase pitch. It is pretty useless for a prop sport/speed plane to have 2:1 thrust/weight ratio, .5-.8 :1 will do great. The lower power increases flight time. If the airframe has a lot of drag it is useless to use a 9x10 prop because a lower pitch saves power as well.

same with edf, If one can build light you need less thrust thus a smaller fan/lighter setup. If you build heavy you need more thrust/larger fan to fly well. If you want all out performance it still seems useless to me to chose a large fan if one does not need the thrust. A 70mm fan will do in many jets.

I often wonder how an Eliminator or El Bandito would perform with a 70mm edf. Right now, I dig this Me262 with micros:
http://www.hobby-land.de/product_inf...597487d67a127a
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Old Jul 26, 2009, 03:00 PM
2014 EDF JET JAM We be Jamming
Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
6,757 Posts
Watts per pound is simply a starting point.

You will need to examine your planned flight profile and type of model.

An A-10 doesn't need +200 w/lb to fly scale-like but a F-104 might. This again depends on your flying style (flight profile).

I would shoot for 150 W/lb as a minimum for today's equipment.
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Old Jul 26, 2009, 03:01 PM
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
Joined Dec 2003
4,974 Posts
I am even reconsidering a 120mm He-162 salamander with 70mm edf in future. Very low wingload and great gliding ratio makes is very nice for bathtub pattern flight style. Performance and sound would be awesome and very scale!
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Old Jul 26, 2009, 03:07 PM
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
Joined Dec 2003
4,974 Posts
Quote:
Originally Posted by Kevin Cox
Watts per pound is simply a starting point.

You will need to examine your planned flight profile and type of model.

An A-10 doesn't need +200 w/lb to fly scale-like but a F-104 might. This again depends on your flying style (flight profile).

I would shoot for 150 W/lb as a minimum for today's equipment.

Jep, That is why I did not want to use 90mm spiderfans in my Jepe A10 but minifans. The spiderfans are way too powerfull and heavy for this model. 5 Years later an sizewise identical A10 went in production. Read the specs and see the vids!
http://www.jetarrows.com/thunderbolt/page.phtml?lg=en
http://www.jetarrows.com/thunderbolt...?go=down&lg=en
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Old Jul 26, 2009, 08:06 PM
Mango the Parrot
arichards1969's Avatar
South Wales U.K.
Joined Jan 2009
197 Posts
Thanks Guys,

Quite confusing!

I think 200w to 250w will do for now.

ants.
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