Aerodynamics ~ Two electrically driven rotor concepts for future rotorcraft.

[Dave_Jackson]

The following links are to a couple of rotor concepts. For the purpose of development, the projects are directed at the Ultralight helicopter category.

ElectrotorPlus (http://www.UniCopter.com/ElectrotorPlus.html) consists of a 2-bladed rotor where the rotorhub has hub springs, or alternatively offset teetering hinges, plus a control moment gyroscope (http://en.wikipedia.org/wiki/Control_moment_gyroscope); for enhanced cyclic control, particularly during zero-gravity.

The intent of this posting is to place the above concept (invention) into the public domain.

Any critiques or thoughts will be appreciated.

_________________________

The above concept is an alternative to the Electrotor (http://www.UniCopter.com/Electrotor.html) concept, which was posted on the Web a year ago. This earlier concept consists of a 3-bladed rotor where the rotorhub contains a constant velocity joint c/w hub springs for enhanced cyclic control.


Dave

[Dave_Jackson]

A little more info on electric flight.

Ultralight Electraflyer web site. (http://www.electraflyer.com/)
Electraflyer video. (http://www.lightsportaircraft.ca/volume1-issue17/webcast-2/) More information on the trike. (http://www.electraflyer.com/ufmag_aug2007.pdf)

[slowrotor]

Dave,
This might be the newest in high discharge batteries: Lithium-Manganese.
Burst discharge at 40C claimed.
http://duralitebatteries.com/flight/batteries-mg.php#Powerbox

Thanks for the electric trike article. I wanted to see the total power system weight but unfortunately that was not provided.
The question is: can electric power systems beat internal combustion engine in pounds per horsepower?
slowrotor

[Dave_Jackson]

slowrotor,

Thanks for the information Lithium-Manganese.

The question is: can electric power systems beat internal combustion engine in pounds per horsepower?

The answer is ; Yes :eek:

for short duration flights. :O

Perhaps the important future questions will be; At what 'time-of-flight' does the gasoline system become more weight efficient then the electrical system, and, how fast will technology lengthen this 'time-of-flight'.


Dave

[quadrirotor]

What does limit the duration of the max power use of the electric motor? cooling system?

[slowrotor]

Dave,
The question is: can electric power systems beat internal combustion engine in pounds per horsepower?

Looking at the trike example I find:
19hp motor= 26 pounds listed
battery = 75 pounds listed
controller = 10 pounds (estimated, not listed)
cables etc. = 2 pounds (estimated)
----
113 pounds total power system for one hour (19hp)

113 divided by 19hp = 5.9 pounds per hp

This is not better than a gas engine with 1 pound per hp for 2-stroke or 2 -3 pounds per hp for a small 4-stroke.

I think electric is still too heavy. And the $ 17,000 price listed is about 10 times higher than gas.
slowrotor

[slowrotor]

Watching the electraflyer video, it looks like the video was carefully edited to conceal a rather poor climb rate. It shows a zoom after a long ground run. Rather noisy as well.
I am not impressed.

[Dave_Jackson]

quadrirotror,What does limit the duration of the max power use of the electric motor? cooling systemYes, the predominant limitation is that of excessive heat. Some electric motors are equipped with liquid cooling systems.
This may not be of interest. (http://www.unicopter.com/1478.html)

One advantage of the electric motor is its ability to provide very high power for a very short period of time.


slowrotor,

In the above you are not comparing apples with apples. You are not including the gasoline, plus the engine support equipment.

I'm surprised that Electraflyer use such a heavy motor [1.4 lb per hp]. The Predator (http://www.plettenberg-motoren.com/UK/Motoren/aussen/Predator37/Motor.htm), which is NOT recommended for human flight, is 15 KW and 1,900 g [0.21 lb per hp]

The crude argument that I was making on the previous posting is;
1/ The weight of electric storage is greater than the weight of gasoline storage.
2/ The weight of an electrical-mechanical converter (motor) is less than the weight of a gasoline-mechanical converter (reciprocating engine ).

Therefore, the GW weight of an electrical helicopter will be less than the GW of an internal combustion helicopter, IF the flight duration is only 5 minutes long. ;)

In the future the two competitor may well be the motor and the turbine. It will be interesting to see which field develops faster.

Dave

[slowrotor]

Dave,
Your logic makes sense. Electric for brief power, gasoline for endurance. That is why the hybrid car is somewhat successful.

What is the total weight of the Predator with a battery and flight system capable of 5 minutes?
I am still not convinced that electric is lighter even for a 1 minute burst of power because the battery must be large enough to handle the high current. A small battery would not work.


slowrotor

[Dave_Jackson]

slowrotor,

I believe that this Web page (http://www.unicopter.com/1584.html) and its linked pages have the answers.

Dave

[slowrotor]

Thanks Dave,
I calculated the flight system weight of the Predator 30-8 with the 14 cell pack to be about 12 pounds.
The output is 8912 watts to the prop=11.94hp (48volt x 211amps listed =10128 watts input x .88% efficiency = 11.94hp at prop)

That is a 1 pound per horsepower rating. Thats good.

But this two-stroke gas engine weighs 7.96 pounds and 16.5hp = .48 pounds per horsepower. The fuel weight is not significant.
http://www.desertaircraft.com/engines_detail.php?Page=DA-150

slowrotor

[Dave_Jackson]

slowrotor,

Not shabby. :ok:


Here is another engine, however it is not as light as yours. http://www.limflug.de/files/pdf/DS-L275E.pdf

Incidentally, all the Limbach engines are made for manned aircraft, but they are expensive.

Dave

[slowrotor]

Dave,
One advantage of electric is no starting system is needed.
If the gas engine has a starter and battery the weight may be similar to the electric system.

I am looking for the best way to get a brief burst of thrust. The electric might be best mainly because it is instant on and off without any starting hassle.

Also looking at flywheel energy storage and compressed air etc.

slowrotor

[Dave_Jackson]

slowrotor,

This was in today's newspaper;

"Toyota also said it was preparing to start mass producing lithium-ion batteries for low-emission vehicles. ....

The lithium-ion battery will be used in a plug-in hybrid, which would recharge from a regular home socket, and travel longer as an electric vehicle than the Prius."


Dave

[ShyTorque]

This link gives some idea of the raw torque / power available with modern electric systems; albeit in short bursts. I believe the batteries will do five runs before recharging.


http://uk.youtube.com/watch?v=fHtAkM3CYLA&feature=related

And no carb icing! :ok

Here's another, even more impressive clip.

http://uk.youtube.com/watch?v=-Ev72ppww7Q&NR=1

Note that the noise is from the adjacent, slower machine; you can hear it run out of gears and power! The times at the top of the tote board are for 1/4 of a mile, the speed below.

[slowrotor]

Thanks ShyTorque,

The battery supplier is claiming 60C burst discharge!
http://www.a123racing.com/

slowrotor

[Graviman]

I haven't kept up with battery technology from when i last looked at any of this stuff. Batteries have come on in leaps and bounds from the need for laptops and hybrids though! Fuel cells are still progressing slowly...

The trick with high performance motors is to run them at as high an RPM as practical, to push up power-to-weight. This is made easier with the latest generation of brushless DC motors, which use Insulated Gate Bipolar Transistors (http://en.wikipedia.org/wiki/IGBT) to replace the commutator for very high speed switching. Designs are stuck with about 1 Tesla magnetic field strength from NdFeB magnets (http://en.wikipedia.org/wiki/Neodymium_magnets), until liquid nitrogen cooled superconductors (http://en.wikipedia.org/wiki/YBCO) become more widespread, so the best designs pack in the most amount of copper for the least amount of iron magnetic return circuit. This all leads to high voltages (>1000V).

Dave, this is a good area to get into. If you stick to electric you will be ahead of the curve when the industry eventually swings this way. I've changed my view since i became aware of this emerging technology:

http://www.eurekamagazine.co.uk/article/8475/Power-chips-can-kill-all-engines.aspx
http://www.powerchips.gi/

PowerChip technology is working it's way down from the space industry, so is still cost prohibitive. The performance numbers add up though...

[Dave_Jackson]

Mart, you say;... be ahead of the curve when the industry eventually swings this way. Now we're talking the same language. :ok:

Let others develop the electrics and we'll develop the rotors. :D


Dave