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Old Mar 01, 2008, 02:44 PM
the answer 42 is
Switzerland, AG, Lenzburg
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Thrust Vs Weight??

Hey there

Im new in electrics, Im now plannig to build a EDF BD5 but I was wondering how to select and EDF what is a good relation Thrust Vs Weight??

thanks for your advices

Edwin
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Old Mar 01, 2008, 07:42 PM
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EDF? go for at least 150W/lb unless the model is quite slow. Probably at least 30% thrust to weight needed.

Probably more info in the forum devoted to EDF.
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Old Mar 01, 2008, 10:11 PM
homo ludens modellisticus
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@Edwin
Meet the natives:
www.modelbouwforum.nl

Hey, another 'uomo'

Vriendelijke groeten Ron van Sommeren
int. electric fly-in, Nijmegen, the Netherlands
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Old Mar 02, 2008, 07:28 AM
the answer 42 is
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thanks Ron But my dutch is not so good,

good fligths

EZ
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Old Mar 02, 2008, 12:33 PM
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Edwin, General rule of thumb for 3d is 150watts/Lb of plane for good 3d, 200 watts/pound for great 3d power. Depends on your flying style.
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Old Mar 02, 2008, 01:03 PM
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Edwinzea> As a rule of thumb, you need at least 1lb of thrust to fly a 3lb model. A model aircraft can not be flown or it just barely stays in the air if the thrust to weight ratio is less than 1/3= 0.33. Some cheap r/c flying toys you purchase at your local toy store have a ratio of 0.25. That's why many customers are not happy with them. They just bring them back to the store and ask for a refund!!!. These are the thrust to weight ratio guidelines:

1lb/3lbs = 0.33 basic flying

1.5lb/3lbs = 0.5 advanced flying


1.71lb/3lbs = 0.57 aggressive flying



There is also a relationship between watts/lb and thrust to weight ratio. If you are curious about it, just look for my thread in which I talk about it. I can not post it twice.
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Old Apr 01, 2008, 07:34 PM
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Quote:
Originally Posted by Hasina75
Edwinzea> As a rule of thumb, you need at least 1lb of thrust to fly a 3lb model. A model aircraft can not be flown or it just barely stays in the air if the thrust to weight ratio is less than 1/3= 0.33. Some cheap r/c flying toys you purchase at your local toy store have a ratio of 0.25. That's why many customers are not happy with them. They just bring them back to the store and ask for a refund!!!. These are the thrust to weight ratio guidelines:

1lb/3lbs = 0.33 basic flying

1.5lb/3lbs = 0.5 advanced flying


1.71lb/3lbs = 0.57 aggressive flying



There is also a relationship between watts/lb and thrust to weight ratio. If you are curious about it, just look for my thread in which I talk about it. I can not post it twice.
That's the bottom line. I've found the watts/pound guidlines assume a reasonably light wingloading of 15oz/sq-ft or less. I have EDFs that need 200W/lb to even fly decently.

I'm ready to fly my 4oz EDF30 Vampire now, and am hopefully just above the minimum specs for decent flight. Well see:
1. The Cox 109 wing platform seems to fly well at low power levels with their planes at 5.5oz. I'm at a good bit less, being 4oz AUW.
2. I have 30W total, or 120W/pound.
3. Thrust to weight ratio with 1.5oz thrust is about 37%.

I'm keeping my fingers crossed.

Bill
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Old Nov 08, 2009, 01:07 PM
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Originally Posted by Hasina75 View Post
Edwinzea>

There is also a relationship between watts/lb and thrust to weight ratio. If you are curious about it, just look for my thread in which I talk about it. I can not post it twice.
Please post it, I am interested.
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Old Nov 15, 2009, 02:41 AM
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I am interested, too! :-)
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Old Nov 15, 2009, 06:34 PM
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Quote:
Originally Posted by Edwinzea View Post
Hey there

Im new in electrics, Im now plannig to build a EDF BD5 but I was wondering how to select and EDF what is a good relation Thrust Vs Weight??

thanks for your advices

Edwin
Assuming you use quality components, 160-180W/lb is a good setup for an EDF. If you use an inexpensive motor and fan unit, then you may require more than that to get good performance (220-250W/lb).

The most expensive EDF units will be about 75-80% efficient, the cheapest about 50-60% efficient.
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Old Nov 16, 2009, 08:32 PM
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I'm glad marc pointed out. It's not as simple as x number of watt per x number of lb. A poorly designed power system could wast more then half of the electric energy by converting it into heat. It's all about efficiency.

-
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Old Nov 17, 2009, 06:21 PM
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***


for high performance EDF jets, 300+ watts/lb... Or
something like 1.5 T/W ratio is very normal.


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Old Nov 18, 2009, 09:53 AM
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Quote:
Originally Posted by asm_ View Post
I'm glad marc pointed out. It's not as simple as x number of watt per x number of lb. A poorly designed power system
= any EDF!
Quote:
could wast more then half of the electric energy by converting it into heat. It's all about efficiency.

-
And EDFs are at best 30% efficient at model flying speeds.
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Old Nov 20, 2009, 09:11 PM
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= any EDF!


And EDFs are at best 30% efficient at model flying speeds.
Would this change for the better as the KV goes higher?
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Old Nov 20, 2009, 09:57 PM
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I think the problem is that we have miniscule impellers spinning at ridiculously fast rpm (we must do that to get any decent thrust at all).... a tiny impeller generating 100-200mph "pitch speed" is not moving a lot of air (it is just making a hole in it) so, for our modest flight speeds, the system is simply wasting energy making noise and heat. A relatively far larger prop is always going to move air more efficiently than an EDF.

Higher Kv might be fractionally better.....31% efficient???
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