Suggested battery capacity for 30 min flight?

Things that fly
User avatar
Dui, ni shuo de dui   10 kW

10 kW
Posts: 565
Joined: Jan 29 2016 3:21am

Re: Suggested battery capacity for 30 min flight?

Post by Dui, ni shuo de dui » Jan 28 2021 10:36pm

I suppose you already saw this video from Peter Sripol, but in case you haven't:
https://www.youtube.com/watch?v=DPJaHkz2Ado

I'd suggest you to start with such "simple" project. Get a grasp of all the challenges involved in building such vehicule, first in a simple, relatively low power way, and then maybe go a step further later if you feel you can overcome all the difficulties. Doing a simple project will also give you real life figures on the kind of data you are looking for right now in this thread.
Other than just autonomy and power, an other big issue is control and stabilisation. It might sound trivial but I really don't think it is in this kind of application, with a heavy load that can move around (you).

Building an electric flying machine is also a project I wish I can try someday, and if I had the money and space to do it I would definitely start by doing a proof of concept like this one. Maybe try to give it a thought ;-)
:bolt: New Build in Progress: Electric Roadster, 30 000W Kelly KLS72701, 24S2P A123 cells :bolt:
viewtopic.php?f=12&t=109246

:bolt: My electric Ninja 250 clone: 16 000W Sabvoton 72200, 23S2P A123 cells : :bolt:
viewtopic.php?f=12&t=90032

:bolt: My electric Scooter: 11 000W Sabvoton 72150, 72V 50Ah LiFePO4 cells: :bolt:
viewtopic.php?f=12&t=75912

User avatar
DogDipstick   10 kW

10 kW
Posts: 936
Joined: Aug 19 2018 12:39pm
Location: Fleetwood Pa

Re: Suggested battery capacity for 30 min flight?

Post by DogDipstick » Jan 29 2021 12:53am

Bgt2u wrote:
Jan 08 2021 10:43pm
That is correct. I do realize that if l lost power, that unlike an airplane, l would drop like a rock, so yes, l will have battery percentage available to view, during flight.
Are you getting out of ground effect? Cause you need alot of power to get out of ground effect.

I love me my KED DIrect motors. Always treated me well.

Honestly dont think you will have the thrust necessary to break ground effect. Those motor choice are under powered. KDE makes motor that take 240A @ 16s.. ( 72v)... let alont 110A. contin.

I love my 6 foot collective pitch prop that I fly. I bet it hits 160mph with that KDE. The math is not that hard. Flight calculation.

My RC heli could lift a person. Well, a child. I could lift a 90 lb dog or kid I bet. Easy peasy.

I hover at around 60A @ 12s, and punch out climb at up to 12* pitch and 160A~... Drain a hundred Wh in like.. 3 min? KDE motors love to run hot hot hot.

A pair of 700 size rotors could lift a full grown adult. Easy peasy. There are vids of it on Yt.

I would never fly something that does not have a safe way down. ( autorotate).
83.1v of Ironhorse XC.. :) :bolt: by Chevy :bolt: :D Ok So that was what you call a "glitch:" :twisted: (...No Mom. The formula is Kaw > 1(Hr) = Impounded. The math checks out. I'll be fine. ).. :? Broke20Horsies! 17,830w !! :x 1 (pound / second) Horse Power = 338.24 M^2 Kg^2 / Sec^4 ( :twisted: prove me wrong :twisted: ) :| (gottenymoem4115thangs?Yall?) :confused: Fabricator @ BSECo. Inc.

User avatar
Solarsail   10 W

10 W
Posts: 89
Joined: Oct 05 2017 8:11pm
Location: British Columbia, Canada

Re: Suggested battery capacity for 30 min flight?

Post by Solarsail » Mar 22 2021 12:39am

Hillhater wrote:
Jan 07 2021 5:26am
Solarsail,... as i said, we have to be realistic, not idealistic.
True. I do agree with most you say. You need at the minimum 10 min of flight time in reserve when landed.

I believe AliBaba can give you $5 50E cells, if you do it the Chinese way -- i.e. haggle.

Naturally the builder will fly the thing pilot-less, and then at very low elevations (< 5 m) for a long period of testing before planning to go any higher. Maybe a bank of 2 kWh supercaps can kick in during an emergency? In fact, I would not recommend exceeding 5 m ever. This thing is not a helicopter.

User avatar
Solarsail   10 W

10 W
Posts: 89
Joined: Oct 05 2017 8:11pm
Location: British Columbia, Canada

Re: Suggested battery capacity for 30 min flight?

Post by Solarsail » Mar 22 2021 1:19am

Bgt2u wrote:
Jan 08 2021 10:43pm
That is correct. I do realize that if l lost power, that unlike an airplane, l would drop like a rock, so yes, l will have battery percentage available to view, during flight.
Flying above 5 m is prohibited! And you should do a lot of remote testing with bags of sand before you even put your foot into the thing. 10 min reserve is mandatory.

There is this formula called the "momentum theory" of propellers that you can find on the net. Plugging your numbers in, I get for -- 30.5" 2 blade props, 12 rotors, 550 lbs lift, you need

4.6 kW per rotor, and a total of 53.2 kW. You may have to run at 4000 RPM which is pretty high.

With 10 rotors, you have 6.5 kW per rotor.

Of course this assumes that your propellers are ideal, dragless, no turbulence, ideally pitched, etc. The efficiency will be anywhere from 70% to 85%. So increase the above numbers by dividing by the efficiency.

What you need is better props. You need larger props with exactly the right pitch, more blades, and more efficient props. RC props are generally rubbish. Even standard general aviation props are rubbish for electric use because their efficiency is low, and they don't care. Gasoline has lots of energy. With good props, you can reach 85% or more efficiency. So let's try

48" 3 blade props with optimal pitch to match motor torque. 10 rotors, 550 lbs lift: 3.7 kW per rotor at 100% efficiency. If you drop to 450 lbs, you get 2.7 kW. Note the total thrust is not linear to the weight. As the thing gets heavier, everything becomes disproportionally less effective. Neither is the total thrust linear to the number of rotors or the diameter of the rotor. The more the better.

48" 3 blade 8 rotors 450 lbs you get 3.8 kW or a total of 30.4 kW.

In short go for largest props, most blades, most rotors, and lightest weight.

The last case above will require for 30 minutes of flight time and 10 reserve: 30.4 * (30 + 10) / 60 = 20.3 kWh. This does not include cell, cables, controller, motor inefficiencies. The 2nd law of thermodynamics bites!

How good is the momentum theory formula? I don't know. In fact I have seen different formulas for the same theory! I have seen a formula that gives much better (lower W) results.
Last edited by Solarsail on Mar 22 2021 1:45am, edited 1 time in total.

User avatar
Solarsail   10 W

10 W
Posts: 89
Joined: Oct 05 2017 8:11pm
Location: British Columbia, Canada

Re: Suggested battery capacity for 30 min flight?

Post by Solarsail » Mar 22 2021 1:40am

Bgt2u wrote:
Jan 08 2021 10:43pm
That is correct. I do realize that if l lost power, that unlike an airplane, l would drop like a rock, so yes, l will have battery percentage available to view, during flight.
As for batteries, I would suggest getting Samsung 50E 21700 from a reliable source. I once bought Panasonic NCR18650B from Alibaba, and they all turned out to be good and true (tested under low C conditions).

This will give you both the lightest and cheapest DIY pack with new cells. A minimalist design pack will be about 10 lbs/kWh. Nobody can beat this.

Building packs takes some skills, but there are lots of YouTubes on that. For ease of wiring, keep the modules small. Such as 16 modules each 1.25 kWh or less. Build 4 modules and test the drone with these before increasing modules. With the 50E, these 4 modules (5 kWh) can supply about 2C x 5 = 10 kW. That should be sufficient to lift the thing without a pilot if the modules are on the ground. 16 modules will give you a max of 40 kW.

Go for the higher voltages such as 14S5P (60V max) or 17S4P (72V max), but do not exceed the controller's rating.

User avatar
everythingisawave   100 mW

100 mW
Posts: 49
Joined: Sep 13 2016 8:01pm

Re: Suggested battery capacity for 30 min flight?

Post by everythingisawave » Mar 31 2021 3:53pm

What is the licensing category under which you intend to test the aircraft? Probably a good idea to understand that as well, there may be restrictions on height etc..

SkyersJet   1 mW

1 mW
Posts: 10
Joined: May 11 2021 2:41pm

Re: Suggested battery capacity for 30 min flight?

Post by SkyersJet » May 28 2021 10:26pm

Solarsail wrote:
Mar 22 2021 1:19am
Bgt2u wrote:
Jan 08 2021 10:43pm
That is correct. I do realize that if l lost power, that unlike an airplane, l would drop like a rock, so yes, l will have battery percentage available to view, during flight.
Flying above 5 m is prohibited! And you should do a lot of remote testing with bags of sand before you even put your foot into the thing. 10 min reserve is mandatory.

There is this formula called the "momentum theory" of propellers that you can find on the net. Plugging your numbers in, I get for -- 30.5" 2 blade props, 12 rotors, 550 lbs lift, you need

4.6 kW per rotor, and a total of 53.2 kW. You may have to run at 4000 RPM which is pretty high.

With 10 rotors, you have 6.5 kW per rotor.

Of course this assumes that your propellers are ideal, dragless, no turbulence, ideally pitched, etc. The efficiency will be anywhere from 70% to 85%. So increase the above numbers by dividing by the efficiency.

What you need is better props. You need larger props with exactly the right pitch, more blades, and more efficient props. RC props are generally rubbish. Even standard general aviation props are rubbish for electric use because their efficiency is low, and they don't care. Gasoline has lots of energy. With good props, you can reach 85% or more efficiency. So let's try

48" 3 blade props with optimal pitch to match motor torque. 10 rotors, 550 lbs lift: 3.7 kW per rotor at 100% efficiency. If you drop to 450 lbs, you get 2.7 kW. Note the total thrust is not linear to the weight. As the thing gets heavier, everything becomes disproportionally less effective. Neither is the total thrust linear to the number of rotors or the diameter of the rotor. The more the better.

48" 3 blade 8 rotors 450 lbs you get 3.8 kW or a total of 30.4 kW.

In short go for largest props, most blades, most rotors, and lightest weight.

The last case above will require for 30 minutes of flight time and 10 reserve: 30.4 * (30 + 10) / 60 = 20.3 kWh. This does not include cell, cables, controller, motor inefficiencies. The 2nd law of thermodynamics bites!

How good is the momentum theory formula? I don't know. In fact I have seen different formulas for the same theory! I have seen a formula that gives much better (lower W) results.
The motors are like 70-80% efficient as well so drones usually have around 50-60% overall efficiency.

User avatar
Solarsail   10 W

10 W
Posts: 89
Joined: Oct 05 2017 8:11pm
Location: British Columbia, Canada

Re: Suggested battery capacity for 30 min flight?

Post by Solarsail » Jul 24 2021 7:57pm

Three phase AC motors seem to have efficiency above 90%. But the propeller efficiency is probably 50% to 65%.

Post Reply