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Mar 01, 2008, 01:44 PM
the answer 42 is
Discussion

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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Mar 01, 2008, 06:42 PM
Registered User
vintage1's Avatar
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.
Mar 01, 2008, 09:11 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
@Edwin
Meet the natives:
www.modelbouwforum.nl

Hey, another 'uomo'

Vriendelijke groeten Ron van Sommeren
int. electric fly-in, Nijmegen, the Netherlands
Mar 02, 2008, 06:28 AM
the answer 42 is
thanks Ron But my dutch is not so good,

good fligths

EZ
Mar 02, 2008, 11:33 AM
ProBro Wulf
Wulf_Flieger's Avatar
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.
Mar 02, 2008, 12:03 PM
Registered User
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.
Last edited by Hasina75; Mar 02, 2008 at 12:21 PM.
Apr 01, 2008, 06:34 PM
Suspended Account
EDF30's Avatar
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
Last edited by EDF30; Apr 01, 2008 at 09:03 PM.
Nov 08, 2009, 12:07 PM
Registered User
rimshotcopter's Avatar
Quote:
Originally Posted by Hasina75
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.
Nov 15, 2009, 01:41 AM
Registered User
I am interested, too! :-)
Nov 15, 2009, 05:34 PM
I will be an angry old man!
marc1's Avatar
Quote:
Originally Posted by Edwinzea
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.
Nov 16, 2009, 07:32 PM
Registered User
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.

-
Nov 17, 2009, 05:21 PM
Suspended Account
***


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


Nov 18, 2009, 08:53 AM
Registered User
vintage1's Avatar
Quote:
Originally Posted by asm_
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.
Nov 20, 2009, 08:11 PM
Registered User
rimshotcopter's Avatar
Quote:
Originally Posted by vintage1
= any EDF!


And EDFs are at best 30% efficient at model flying speeds.
Would this change for the better as the KV goes higher?
Nov 20, 2009, 08:57 PM
Registered User
Dr Kiwi's Avatar
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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