Helicopter electric tail rotors

The Tesla and Prius electric motors seem to be the best motors for EV applications, but are still a bit off the power to weight ratios achievable with outrunner motors like the EMRAX motors. Outrunner motors are perfect to aircraft applications, but not practical for EV use.

My education continues ... I had never heard of EMRAX motors before .... thanks for the info.
 
Oskar, fantastic achievement! It is people like you who are pioneers that lift the bar higher, keep developing your innovations...

Looking forward to further updates.
Thanks Leo, if you hadn't left you would have been right in the middle of all the action! Now the electric heli has taken your Magni's spot in the hangar :)
 
Wow, Oskar !!!
What is your current flight duration?
Brian
 
Wow, Oskar !!!
What is your current flight duration?
Brian
I have flown more than 10 minutes on a charge, but can see from the measurements that flying carefully at the minimum power point a 20 minute flight would be achievable. That would be boring though, I defintely wouldn't want to do it.
 
How long between 'fill ups' ? Can it scale up to 550 lbs GW?
Batteries don't like getting charged quickly as it reduces their lifetime. I usually charge them in 3 to 4 hours.
It only takes a few minutes to install/remove the batteries, if I had a second pack I could be up and flying again in 5 minutes.
I'm looking at the numbers for a Mosquito XE with 80kg of batteries, that would have a GW of about 205kg (450 lbs) and should get 30 to 40 minutes of flight time. I suspect the EMRAX 228 motor will be over its continous power limit at 550 lbs GW.
 
EMRAX makes bigger ones... :)
 
EMRAX makes bigger ones... :)
The next size up (EMRAX 268) would be perfect for a two seat helicopter, the EMRAX 228 I'm using is perfect for a single seat. 550lbs GW is in that awkward in between spot, neither motor is well suited for that.
 
Real nice Oskar. Will be interesting to see the rate of descent on a longer auto, and if not driving that tail makes a noticeable effect.
 
Here is a recent article from Electric VTOL News on "Stielau's Electric Helicopter" which also includes a YouTube link on flight - Click Here
 
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Oskar,
congrats on your nice development.
Just to note about can bus...
From the experience of glass cockpit upgrades on Cessna using mostly Garmin,
like to suggest you to use shielded twisted pair and to be careful on possible short
circuit on buss - especially on connectors. Use shirms on each soldered wire.
Please keep good work...
Regards
Djani
 
The electric Mosquito now has about 1.5 hours of flying time. So far the main aim has been to find out what the limitations are, and I’m getting a very good idea of what they are. Some were expected, other totally unexpected.

Firstly a few of the expected ones.

Looking at the main rotor first, IGE hover power is around 21kW which was expected. OGE hover power is about 25kW, a bit less than expected. Moving through ETL power drops to about 17kW (expected) and then starts rising as speed increases. What was a surprise is how quickly the power goes up as airspeed gets to 30 mph and higher. At 30 mph the power is already more than hover power, and the maximum power limit is reached at a S&L speed of just over 40mph. Airframe drag absolutely kills high speed performance.

Tail rotor power measurements were very interesting. Hover power with no wind is about 1500W, but pedal turns influence power hugely. Even with moderate turns the power drops to 500W (right turns) and increases to 3000W (left turns). With 15 knots of wind tail rotor power is a strong function of orientation to the wind (expected), in some orientations the power will be below 500W and in other orientations more than 3000W. In forward flight tail rotor power drops quickly to somewhere between 500W and 700W and seems to stay there, a vertical stabiliser will need to be added to decrease tail rotor power further. The vertical stabiliser will also mean that height can be maintained with a total loss of tail rotor, at the moment S&L tail rotor power can be reduced to about 200W by flying sideways, but not to zero. For now complete loss of tail rotor requires an immediate descent and landing.

From a pilots perspective there was one aspect that was unexpected. At slow speeds up to about 20 mph the pilot can hear the rotor, and changes in rotor rpm can be detected immediately. As speed increases the wind noise increases as well, and above about 30mph the pilot can no longer hear the rotor. All the pilot can hear is wind noise, a loss of power has no effect in the noise level which is very disconcerting.

One of the tests done was thus to close the throttle at 40mph and see how the aircraft reacts (of course dropping the collective soon after closing the throttle). The video shows that there is enough of a yaw reaction to make the pilot aware of a loss of main rotor power.


On a side note have a look at the shadow of the tail props during the flare. Some are still turning slowly but most are stationary. Because the main rotor does not have to drive a tail rotor the aircraft flies just like a gyro during an autorotation, and a total loss of tail rotor power is not a problem during an auto.
 
When starting up the drive is in torque control mode using the throttle to control motor torque. Once speed gets to 60% it switches to speed control mode, all the pilot has to do is keep the throttle at 100% and the drive keeps the speed at 100%. It works amazingly well.
Oskar, on your autorotation to landing comment, you mentioned "closing the throttle" ( :LOL: ); my assumption is that means cutting ALL power to the EMRAX 228 motor from the drive. In such a state, I'm guessing it is neither 'torque control' or 'speed control', but does the drive still somehow know the rotor RPM (stator to armature relative position)?

For example, what happens if you close the throttle, but then decide to re-engage power SLOWLY to the rotor until back up to full power?
It would seem, in that scenario, that descent would be slowed as power was added.
I'm thinking the motor and drive must still be communicating (when throttle closed) so that the drive knows when/how to 'sync up' the motor if you were to re-engage.

Do you have a rotor tachometer?

Thanks again for sharing info on this cool experiment !

Brian
 
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Oskar, on your autorotation to landing comment, you mentioned "closing the throttle" ( :LOL: ); my assumption is that means cutting ALL power to the EMRAX 228 motor from the drive. In such a state, I'm guessing it is neither 'torque control' or 'speed control', but does the drive still somehow know the rotor RPM (stator to armature relative position)?

For example, what happens if you close the throttle, but then decide to re-engage power SLOWLY to the rotor until back up to full power?
It would seem, in that scenario, that descent would be slowed as power was added.
I'm thinking the motor and drive must still be communicating (when throttle closed) so that the drive knows when/how to 'sync up' the motor if you were to re-engage.

Do you have a rotor tachometer?

Thanks again for sharing info on this cool experiment !

Brian
Brian, the motor/drive is very much top end. There's a resolver on the motor which tells the drive what the position of the rotor is relative to the stator. One of the setup steps is to calibrate the resolver, once that is done the drive knows the motor position with an accuracy of 1 degree.

The "throttle" I uses is the opposite, it is very much bottom end. It's a cheap assembly from an electric scooter which has a very non linear output, good enough to run up the motor but not good enough for in-flight control. The options were to get better throttle or otherwise cheat, which is what I did. Once the main rotor is up to speed I basically use the throttle to switch between speed control and torque control, changeover happens at about half throttle. If throttle is above half the drive is in speed control mode, if the throttle is below half it is in torque control mode where in theory you could control torque with a better throttle. With a fully closed throttle I programmed in a very small torque, enough to keep the motor turning at about 20% speed.

For rotor tach I use the original rotor rpm gauge that came with the Mosquito helicopter, it's independent of the electric drive.

Will post some readouts of motor speed and power during the auto, they show very nicely what's happening.
 
Being fully electric I am guessing it's a perfect/easy situation for an electric governor, or is that what you mean by speed control mode after 50% throttle?

wolfy
 
Being fully electric I am guessing it's a perfect/easy situation for an electric governor, or is that what you mean by speed control mode after 50% throttle?

wolfy
Hi Wolfy,

Speed control is basically a governor, you tell the drive what speed the motor should run at and the drive does whatever is necessary to keep the motor running at that speed. During normal flight it will keep the speed within 1% of the set point.

Oskar
 
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