Thrust to wight question

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Thrust to wight question

Postby seedo » Tue Nov 22, 2011 4:58 am

Dear Members :)

I have 1000g EDF jet, it have twin EDFs each one produce 700g of thrust, will this be enough to fly my jet?
also i want to ask if to EDFs each one produce 700g thats mean the thrust will be doubled? 2 EDFs each one produce 700g of thrust = 1400g of thrust?

Regards
Seedo
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Re: Thrust to wight question

Postby Aussie Joe » Tue Nov 22, 2011 10:43 am

seedo wrote:Dear Members :)

I have 1000g EDF jet, it have twin EDFs each one produce 700g of thrust, will this be enough to fly my jet?
also i want to ask if to EDFs each one produce 700g thats mean the thrust will be doubled? 2 EDFs each one produce 700g of thrust = 1400g of thrust?

Regards
Seedo

Hi seedo,

YES and NO, If thay have there own battery, then YES you will get 1400g of thrust BUT NO if thay share the same battery, thay would create a voltage sag reducing the thrust from both EDFs. You need a battery with the highest "C" raiting you can get to reduce the voltage sag if using only one battery.

Cheers
Joe
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Re: Thrust to wight question

Postby seedo » Tue Nov 22, 2011 11:23 am

Aussie Joe wrote:
seedo wrote:Dear Members :)

I have 1000g EDF jet, it have twin EDFs each one produce 700g of thrust, will this be enough to fly my jet?
also i want to ask if to EDFs each one produce 700g thats mean the thrust will be doubled? 2 EDFs each one produce 700g of thrust = 1400g of thrust?

Regards
Seedo

Hi seedo,

YES and NO, If thay have there own battery, then YES you will get 1400g of thrust BUT NO if thay share the same battery, thay would create a voltage sag reducing the thrust from both EDFs. You need a battery with the highest "C" raiting you can get to reduce the voltage sag if using only one battery.

Cheers
Joe


thanks for the reply man
ok my c rate is 35-75 turnigy tanotech, is this enough?

Regards
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Re: Thrust to wight question

Postby Aussie Joe » Tue Nov 22, 2011 11:59 am

seedo wrote: thanks for the reply man
ok my c rate is 35-75 turnigy tanotech, is this enough?


Maybe??? It will depend on how many amps the two motors draw and for that you need a watt meter. just don't go over the 75"C" rating, and that 75 "C" limit is only for 5-10 second bursts of power, 35"C" is continuous.
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Re: Thrust to wight question

Postby seedo » Tue Nov 22, 2011 12:03 pm

well each motor will draw at max 36A, so is it enough?

i think my battery can handle a draw of 77Amps at max
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Re: Thrust to wight question

Postby BillGriffiths100 » Tue Nov 22, 2011 2:49 pm

Hi Seedo,
The thrust to weight ratio to make an aircraft go vertical is 1 to 1 or better.
Modern jet fighters have better than 1 to 1 when they have used up some of their fuel and are not loaded with maximum armament.
To make an aircraft fly a thrust to weight ratio of far less is required a 747 has a thrust to weight ratio of 0.25 to 1 for example.
The Wright flyer had significantly less. http://www.google.co.uk/url?sa=t&rct=j& ... DA&cad=rja

The wing supplies the actual lift to keep the aircraft up.
Your thrust to weight ratio will be capable of vertical acceleration!
You could easily fly on one engine with 700g of thrust even climb quite steeply.
Hope your reflexes are good a couple of seconds of full thrust will be out of sight!
Be sure to have plenty of space for your first flights.
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Re: Thrust to wight question

Postby seedo » Tue Nov 22, 2011 2:54 pm

ok guys after a watt meter test these are the numbers,

using 1 battery 3s 2200mAh 35-70c & 30A ESC:

Amp draw is 48A at max with a power of 488 watt, the jet fly from ground vertical on 3/4 throttle.

using 2 batteries 3s 2200mAh 35-70c (identical) & 30A ESC:
Amp draw is 64 at max with a power of 565 watt, the jet fly from ground vertical on 1/2 throttle.

i was astonished!

the thrust was around 1200g-1500g.

the down part:
the 30A ESCs were fairly hot in a 10 seconds test and throughout the 10 seconds the battery lost 102mAh, so i think i need to use 45A ESC witch i have already .
oh and a bigger battery too.
so what you think guys?
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Re: Thrust to wight question

Postby seedo » Tue Nov 22, 2011 3:54 pm

ok guy i did another test but with the 45A ESCs and here is a brief for the results,

with 1 battery 2200mAh 3s 35-70c:

the 1 of the motors quickly dropped down once the bat reached 40% of capacity, so its bad with only 1 battery 2200mAh

with 2 batteries 2200mAh 3s 35-70c:

it was a blast, very loud sound and much power, i got 630watt of power with a draw of 70Amps at max, and produced 1500g of thrust, ESCs were not even warm.

so i think i will go with the 45A ESCs but with the 4000mAh 3s 30c battery that am waiting for they are in the delivery process.

Total weight of the jets with the new ESCs and the 4000mAh battery is 1250g, and the thrust is 1500g, though there is 1 question remains:
Wingspan: 793mm is this wingspan size enough to lift the jet?

thank you
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Re: Thrust to wight question

Postby quarry44 » Tue Nov 22, 2011 7:24 pm

If its drawing 70A at max,you're going to need an 80A esc.Your 45A will burn out fairly quickly.
It's total wing area that determines lift,not just wingspan.Jets have fairly flat aerofoil shapes,so need more thrust for a given size to carry a certain amount of weight.In your case it's more or less "suck it and see",unless some one smarter than me can calculate your total wing area.
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Re: Thrust to wight question

Postby seedo » Tue Nov 22, 2011 7:31 pm

this is the wing details
Wingspan: 793mm
Wing Loading: 55g/dm²
Wing Area: 15.6dm²
thrust 1500g
jet weight with all electronics is 1200g
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