F14 Tomcat with sweep wing electric powered

I had two 6s 5000 to each of my 120mm fans to get the 7 kg thrust from each one ?

I'm way out of my depth here but, 5s=18.5Volts, 6s=22,2Volts an increase of 20% in rpm. It would be better to measure the static current at wot on 5s then again on 6s. The percentage increase in current should be equivalent to the increase in thrust you could expect.
Personally I wouldn't use 6s, too many people have found that their system became unreliable and prone to burn outs.

Following on from Klippy's post going to 6s from 5 is indeed a 20% voltage increase but the current that flows will go up by approximately the square of that increase ie 36/25 = 1.44. A 44% increase! You need to be sure the ESCs (and the motors and battery) can handle such an increase in amps before actually trying a 6s.
The only sure way of doing this is to measure the full power current on 5s so you know how close you are to all the components limits. The 5s would have to run at no more than 66% of the ESC's limit to be safe (and even then only just!) to go to a 6s.

If you are worried about the thrust level get somebody to support the F14 nose down on a set of bathroom scales. If the reading rises by 50% or more when full power is applied then you are good to go.

You also need to note the KV number of the motor.
That is how many revs per volt. Then ensure that total number does not exceed the safe max rpm's of the fan, otherwise it can explode from the centrifugal forces involved.
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Also - with these big cell counts and big fans, it is wise to use the 'soft-start' option on the speedo settings, or only open the throttle slowly. The stresses on the fan blade roots, from accelerating from stopped to max rpm's in half a second or so weakens them, and again you find you start shedding blades. (Remember BB's exploding fans?)
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I will agree to differ with Simon's comment on the stalled fan blades - but you will probably find that as the model air-speed increases, the available thrust will, too.
Draw your own conclusion!

Simon, I'm not sure I agree with your statement about the current increase. However I can't argue against it, I don't know enough, it just doesn't feel right!

Re- read Simon's statement about increasing volts increases current - and I think he's got that backwards. Increasing volts DECREASES current!
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www.rapidtables.com/calc/electric/Watt_to_Amp_Calculator.html

Eric
Surely applying an increased voltage to same set up will result in an increased current and thus the speed of the motor.

On the other hand if you want to maintain the same power level (Watts), but to do this you have to adjust a characteristic of the circuit, then the current required is reduced in proportion to the voltage increase.

Increasing volts will decrease the current for the same power. Increasing volts into a resistance will increase the current and thus the power. However, in this instance we have a 3 phase square wave driving a highly inductive load at a 20% increase in frequency. If I remember correctly, the inductance will increase with frequency thereby reducing the extra current, by how much is a piece of string. The increased rpm will attempt to cram more air into the same space to create the extra exit pipe speed. We also know that below the speed of sound, to double the airspeed we need to square the power required. I'm sure someone at NASA could work it out theoretically, it's beyond me now and would have been when I was young and knew everything!

Gentlemen please, it’s a hobby, it’s not life or death.
It either will fly on a 5s, or it won’t, if it doesn’t, i will have to alter it, simple

No problem James, just a free and frank exchange of views! We've all been here much too long to allow a discussion to get in the way!

It's just a good argument to liven up an otherwise dull day! [badass]