I put 4 motors on the eLazair4 for a lot of reasons but mainly I did it because I simply wanted to.
I have always wished I had lived during the short era of the great 4 engine flying boats ;)
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Every successful electric powered aircraft takes a tremendous amount of effort to get things just right, I am not sure I am done yet but I am happy enough at this point to share what the hard work of the last 5 months has yielded.
The tail is a down V tail because when yaw moment is created by the ruddervators, there is also a rolling moment created. With this inverted V tail, that rolling moment turns the airplane in the same direction as the yaw moment and with a normal V tail the rolling moment generally fights the yaw moment. This is tried and true tail design with 45 years of use on 1200 Lazairs. It is cable braced forward and I don't know of any tails removed from handling on water or land .
Immediately after this 1st flight ever of the eLazair4, I moved the floats backwards 4" and now they are now not in water when stationary and I am not concerned if they get wet since I always fly from fresh water lakes.
Here are the main power system component costs for my eLazair4 (in US dollars as of Jan 1, 2023):
$427 delivered for one Dual 14s 1800w balance charger: www.alibaba.com/product-detai...
$920 (on sale) delivered cost for 256 Samsung 40T cells to make batteries for 4 motors (spot welded into 14s4p battery packs): www.18650batterystore.com/pro...
$1,520 delivered for four MAD M17 IPE V1.1 100kv motors: www.mad-motor.com/products/ma...
($200 delivered) for four Eolo props 36x12.8 carbon fiber polymer (trimmed to 32” diameter): sunnyskyusa.com/collections/p...
$300 delivered since the above Eolo props were replaced by four Fiala 32x20 wood props which gave this 230lb pilot 420 fpm climb at 3800 rpm at 33 mph airspeed. Level flight cruising is now at 2500 rpm and 33 mph airspeed. www.aeroscale.shop/collection...
$920 delivered for four 14s 200a controllers APD 200F3[X] : www.getfpv.com/apd-f-series-2...
$95 delivered for four 19000uf Low ESR high frequency controller capacitors: www.mouser.com/ProductDetail/...
TOTAL Power System: ~$4,200 PLUS miscellaneous connectors, wire, throttle components etc…
At takeoff about 8 electrical hp is output from of each of the 4 batteries.
There is one 9.25 lb battery inside each motor nacelle and my 2 port charger will charge all 4 in about 3 hours.
This eLazair4 (with floats and batteries) weighs ~290 lbs without pilot.
The floatplane version can stay aloft for about 30 minutes and the wheeled eLazair4 will likely stay up about 45 minutes.
If I carry a second set of batteries on board along with the charger I will have a great time barnstorming around the country.
One complete nacelle with prop, motor, motor controller, battery and a large capacitor weighs about 17 lbs.
Static thrust per motor is about 50 lbs.
Top speed is only about 45mph but I would almost never fly that fast since it discharges the batteries quickly and inefficiently.
Efficient cruise speed currently appears to be 30-35mph.
I designed and made a single lever throttle quadrant to control all 4 motors. I programmed its BLE Arduino board to send PWM signals to each motor controller using a closed PID loop which is based on the actual RPM of each motor. That way the forward RPM of each motor is based on the “frictioned” throttle lever position and the Arduino keeps all 4 motors synchronized using just a single throttle lever.
The throttle lever also moves left and right by a self-centering spring action so I can add/subtract a proportional yaw bias RPM to the left and right motor pairs for yaw control.
And, the throttle lever also has a spring loaded proportional reverse thrust action which allows me to have air brakes in the air and for braking on the water.
With this throttle quadrant the maneuvering on water is nothing short of amazing since I can back up and spin on a dime…
Dale Kramer