# Boeing cargo Drone Prototype. Does this make sense?

This Boeing experience seems very interesting to me. This octocopter is the biggest I've seen. I estimate that the propellers should be about 2100mm.
Batteries and flight time: 7 or 15 minutes is enough?
This prototype could fly 7 minutes with 227kg and about 15 minutes with 100kg, according to my calculations.
Perhaps this short flight times have non sense but, if it could flight for 50 minutes with a lighter payload? it is possible and they say than they want scale it. 100 or 200kg for 50 minutes? this could replace helicopters in some missions.

But the question now is this:
Do multicopters have size limit?

Many times it has been said that large propellers do not achieve stability and multicopters can not be scaled up, but some recent examples deny this theory.
big propellers have more inertial but aircraft have also more inertia so it need less response time to get stability. So Are there propeller size limit?
Some time ago it was said that the limit was 26-28 inches, but now you can see multicopters with propellers of 1500mm with good stability, so Can we see fixed pitch propellers of 3 or 5 meters?

Known specifications:
MTOW - 747 lb  (340 kg)
Payload - 500 lb (227 kg)
Dimensions: (4.57 m) by 18 ft wide (5.49 m) by 4 ft tall (1.22 m)

Assumptions:
Propeller 84 "
Battery = 40S 40Ah 148V (li-ion)
Battery weight - 40kg total
Empty weight (no payload, no battery) - 70kg

Thanks, Josip Nunth

Views: 1059

Comment by Andrew Rabbitt on March 30, 2018 at 10:30pm

Boeing spent \$5.25 at BangGood and got millions of dollars-worth of publicity.  Sure, it made sense!

Comment by Peter Dobber on April 2, 2018 at 3:42am

Hi Josip, you raise a good question. Do multicopters have size limit?

I believe they have. I started some 5 years ago with the looking into if you could scale up a quadcopter to carry a person. The answer to question was Yes, as you can see in this video, but there are some limitations.

The most important limitation is caused by simple physics and it's the same reason you don't find animals of unlimited size. Volume and therefore weight scales faster then surface as in prop surface to lift the weight.

Having said that, E-volo and Ehang are the best examples that you can carry a weigh of several hundred kg in a controlled way. In fact the combined weight lifted in our Sky-Hopper video is already about 130kg. It performed quote good and was very easy to control.

Out next prototype will be considerable stronger though we'll maintain the small footprint. I expect numerous multicopters, lifting up to around 450kg in the coming years, but I would be surprised if it quickly rises above that.

Comment by Randy Sonnicksen on April 4, 2018 at 9:44am

I wondered the same thing.  Here are my thoughts..

Multicopter Scalability

Comment by Josip Nunth on April 8, 2018 at 4:02am

Hello Peter, What I am proposing is if a quadcopter with only 4 propellers can be scaled, using propeller arrays it seems easier to scale. Be careful testing this vehicle! an awesome work, Are you thinking to continue this project?

Hello Randy,

I did a small experiment, I have weighed with a scale 3 different propellers, 2 genfan small plastic propellers and a big carbon propellers, this carbon propeller is the lightest i have, the other models weight a bit more, not too much.

Genfan 5030 - 1,61gr

Genfan 9x4.7 - 9,86gr

30" carbon - 97gr

If you scale weight of small propellers to 30 inch the weight is 347gr and 365gr respectively, the carbon propeller is hollow, it have a foam core, so it is lighter than plastic propellers.

It is very interesting document, it could be interesting to analyze e-hang multicopter example, it seems stable enough and they use 1500mm propellers

Comment by Randy Sonnicksen on April 8, 2018 at 11:17am

Josip,

Yes, my assumptions were that if you just scaled the model up using same materials.

I think you are right that carbon, especially carbon with a light filler material changes the equation dramatically.

The variable pitch quad I am working on now has a rotor diameter of 2.4m.  With a flexible rotor and constant RPM, I actually want my rotor to have some mass to give it rotational inertia, and to generate relatively large centrifugal forces like a helicopter, to support the weight of the vehicle with the rotor dihedral angle.

In your testing, how large is the Genfan5030?  Is it 50mm diam with 30mm pitch?

Comment by Josip Nunth on April 9, 2018 at 2:42am

Genfan is a race quadcopter propellers , it is very small  - 5 inch x 3 inch

Comment by Peter Dobber on April 13, 2018 at 1:35pm

Hello Josip,

Thank you for the compliment. I most definitely are continuing, have a look: https://www.facebook.com/Sky-Hopper-1856511447908122/

Regarding the Ehang 184, I have some info on that:

 Take off weight 300 kg
 Power of 1 motor 13.25 KW
 Diameter 1 rotor 1.5 m

And now for the interesting stuff, what this means is:

 opp 1 rotor 1.77 m2 Totale rotor opp 7.07 m2 Disc load (hover) 42.44 kg/m2

What I find fascinating is the high disc load. Having a lowish disc load is key to gaining efficient control over any multicopter. I'm intrigued Ehang is able to have apparently little issues on the control front with a fairly high disc load.

If you want to know more on the importance of discload have a look at some of the discussion trains of Hugh in this forum.

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