Suggested battery capacity for 30 min flight?

[Dui ni shuo de dui]

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

 

[DogDipstick]

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).

 

[Solarsail]

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.

 

[Solarsail]

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.

 

[Solarsail]

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.

 

[everythingisawave]

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]

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.

 

[Solarsail]

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

 

[SkyersJet]

Depends how its loaded. Max load at optimum operating point then yes 90% but if not it will be lower. Finding that point is tricky.