Thrust to weight ratio

I am building a 10kg electric VTOL UAV; I know the ideal t/w for VTOL motors is 2:1 or 3:1 but I don’t know the ideal ratio for propulsion motor.
can anyone help me?

I’d say about 1:3 to 1:2 for normal fixed-wing. Since a VTOL can handle the takeoff with the vertical rotors, I’d even go closer to 1:3.

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That seems really high to me. I think .5 - .6 is reasonable and more than adequate in plane.

As long as you use high quality Motors like T-Motors Anti gravity etc. Over engineering the VTOL will not hurt and they are not heavy and you are not going overboard. 1:3 is good number.

I am using these for my VTOL

My logic is that I want the ability to do such things down the road:

  1. Add a LiDAR
  2. Payload increase.
  3. Precision landing gear.
  4. Mapping cameras.
  5. Dual battery for longer flights.
  6. Have extra power to land in windy situations.

My Push Thrust motor is this

What is your plane type? Post a pic I am curious.

For the push motor, for a 10kg VTOL, assuming 2.2-3m wingspan pick a Tmotor 4120 long shaft,
250kv for 12s, 500kv for 6sLiPo, 7s LiIon.
15x8 to 15*12 propeller.

You can thank me after maiden.


Dimitris - What type of plane you built? can you show some pics. I am working on VTOL myself. First try so just going with basics at this point.

All shorts of composite Airplanes and VTOLs from 1m to 5m.
You can check

In our latest builds, based on mini shark vtol, which weight’s from 9 to 12kg based on battery and payload, we found that the 4120 offers one of the best efficiencies, response, quality and a very good price, thus I can suggest it.

The tricky part is to choose the correct kv, according to your battery set-up, whether you want the same battery or separate for the VTOL motors.

Thrust ratios given by the rest Friends above are correct, but you need to know the exact flight envelope. For example if you need ULtra efficiency for Cruise speed between 18-20m/s (reasonable for 10kg airplane 2-3m wingspan). Then you could go for the 250kv @ 6s and high pitch propeller.
But then you only have a flight envelope from 17-28m/s. At the other end if you Overkill the Voltage or Kv or Pitch you will loose specific thrust and efficiency.

Long story short, the previously proposed setups are tested and proven, providing a good envelope and efficiency.


Thank you and others for replies.
My VTOL is 10kg and has a 2.9m span.
and cruise speed is 20m/s. so it seems I should go for 250kv @ 6s and high pitch propeller.
thanks a lot!

Hi again,

Becarefull, as i mentioned, going for the 250KV and 6S with a 15x10-11 prop, you will cruise at 70-75% Throttle!
You will be very efficient, but it will leave you a very little room for wind gusts, climbs etc and at the end of your battery you will have significant thrust loss.

If i were you, for a new aircraft i would choose the 500Kv to start with and check how my 3m wing performs first.

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Hi Dimitris,

how much amps draw is with 70% throttle ?
it is very high throttle, i thought it will be efficient if we can get around 30% throttle.
But with that weight it will be hard to find the motors, i think.

Its all about margin…
with the 250kv motor your current draw @ 6S for cruise @20m/s would be arround 7Amps, but with minimal margin to play with.
with the 500kv motor your current draw @ 6S for cruise @20m/s would be arround 9-11Amps at 32% Throttle.

These numbers can change dramatically with aerodynamic factors like the airfoil, the wing area aand aspect ratio, draggy equipement wxtruding from the aircraft etc.

In an optimal scenario you could try a 9S Li Ion and the 250kv. But there is not such thing as optimal scenario for VTOLs, because:
A. 9S battery is a b%$64 to find/make/charge,
B. you will have to optimize your lift motors to accept the same battery if you go for single bat setup.

Summarizing, go for the 500kv motor that is safe and with a legit efficiency and try to gain back the small ~15% loss, by optimizing your aerodynamics, (Ie as slippery as possible), weight and airfoil choise for your wing loading.

As a side note, if you dont already know it.
When you calculate the thrust margin you have to take into consideration the max airspeed speed you want to achieve.
In most cases, i choose my max airspeed according to max windspeed i want my aircraft to fly into.

This means(as a rule of thumb), Max airspeed= Max windspeed x 1.5

i.e. If my aircraft has a max airspeed of 30m/s it can withstand Max windspeeds up to 20m/s.

Make your calcs and choose wisely

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Thank You Dimitris. I’ll post performance parameters’ values after it is built.

may be we all should put together a simple excel calculator.

Plug in the numbers and it outputs recommendations.

I have seen some really complex calculators, too many variables to plug in. We need something simple.

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You mean like

Hi Dimitris
What is your idea about Tmotor 4130 long shaft 450kv?
17*10 propeller

or Tmotor 4125 long shaft 540kv with 16*8 propeller?

With the longer case, it has a lot more power, but at a considerable more weight! 405gr its a beast!
Also at same ammount of thrust, is has different g/w curve, thus its more efficient in the 3-5kg Thrust region.

I think that more or less, all known ventors have similar models thrusts etc. As i noted above, it depends on your application. For example a big 17-18inch prop maybe cant fit within the VTOL clearance, more prone ground prop strike etc.

I strongly believe we live in a superb era!! with forums you can narrow down 5-10 best case motors, then use super tools like the ecalc mentioned above to close it even more to 2-3 models, then use lack, instict whatever to give it a try. I remember the not so far days, that we had to by motors from a few EU or US ventors 3 times the price. just google at rcgroups how much we paid for a good axi or scorpion or kde motor just a few years ago. nowdays are all at the same price tag (almost). and the ones poping out really have something extra to give.

Hello Dimitris,
I also build Vtol about 8-10kg and interested to use 7S Lion as your suggestion. Normally I use 6S Lion, but maybe 7S will be better as we have bigger margin. However the problem is that Hobbywing Esc (Xrotor pro 40 or 50A) can only stand upto 6S…Lipo or about 25.2 V max.While 7S Lion is about 28.7V whis is more than the Esc limit 25.2…So do think these Esc’s can handle this high voltage???
Thank you…

I had the same thoughts as you, so I picked an alpha hv 80amp ESC which can withstand every possible setup.
Till now, it behaves excellent! Even with the non airplane specific firmware. Stays very cool and it’s as efficient as advertised, also provides crisp and linear control.

But for VTOL this is become high cost as we need 5 Esc…By the way your website does not work… Did you build 10kg Vtol?? You said that your plane drew 9-10A during cruise, is it a 10kg Vtol??? If it is a Vtol, I think it is very efficient…