# Experimental sailplane self-launch electric conversion

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#### henryk

##### Well-Known Member
35 kW for self launch should be OK.
=in THRUST we have thrust !
f.e. 35 kW engine with optimal propeller generate 105 kG
thrust force... (3 kG/kW)

=iff the same engine work in DIFFERENTIAL CR mode,
we can get circa 160 kG thrust (4.6 kG/kW)=the same diametr !

BTW=(1.3 +0.7) m diameter modell generate >10 kG/ kW .

#### proppastie

##### Well-Known Member
Log Member
OK, reality....
During flying with my D-14 project I have been using 33 kW motor from Rotex (custom made). Controller MGM 280 A / 120 V. Battery Li-Po from 135 GeBattery cells, 11 000 mAh. Nom. voltage 99,9 V. 27S/5P. 5,5 kWh capacity.
Than I bought MGM 400 A / 400 V and I increased nom. voltage to 144 V. 39S/5P. Capacity 7,9 kWh. The same motor.
Just give me know what exact data from fying do you need
I think that is exactly the data one might need to build a reliable system......Were there temperature problems? I assume the reason for the bigger controller was to get more KW out of the motor?...How does one know how much voltage or amps is too much and will damage the motor, controller, or batteries? Do you know the output of the motor with the two different systems. I am ignorant of these systems so if the questions are wrong please forgive me.

#### BoKu

##### Pundit
...Since I am going for a FES type installation...
What are you doing for a prop hub and blades?

#### John.Roo

##### Well-Known Member
Every controller has some basic parameters.
For example - controller with max. 120 V / 280 Amps.
120 V is max. voltage - not nominal. So if you have 27 cells serial you know that nom. voltage is 27x 3,7 V = 99,9 V. But when fully charged you have to calculate with 27x 4,2 V = 113,4 V.
280 Amps is max. current. So for T/O when fully charged you have available 31 kW (Volts x Amps) of power going into motor. With decreasing voltage you have lower max. power because controller not give more than 280 A.

In this case I was discharging with very high "C" rate - not very good for lifetime and safety. But Li-Po cells are in this parameter better than Li-Ion cells. 31 kW / 5,5 kWh capacity = "C" rate of 5,6. With new electric Phoenix we have 35 kwh capacity and 60 kW for T/O = "C" rate only 1,7. And for cruise only 0,3 - that is MUCH more safe.

Cooling...
Why you think I recommended you to go to direct drive?
Reason one - don´t waste power in belt drive (+ is more technically complicated)
Reason two - easy to get air for motor cooling.

Controller has very high efficiency - I had no problem with controller temp. Plus - controller has small "PC like" fans for active cooling.

Real reason for bigger controller was higher voltage possibility (from 99,9 V I raised voltage to 144 V) and increased battery capacity. In fact I had already battery from past when we planned to use Kelly Controller. It was pitty to use only part of already made battery

You go right way. Unless you are really experienced electro-engineer + test pilot (with experience with dead stick emergency landings) try buy whole system. It means motor, controller, battery with BMS and charger.
Budget 10-15K USD (probably more approaching to 15K USD) is achievable.

#### John.Roo

##### Well-Known Member
And when all works perfectly you can e-fly wherever you want

#### Exian

##### Well-Known Member
What are you doing for a prop hub and blades?
Ideal solution would be to still get the the original LZ design parts, for example by buying spare parts through someone that owns a FES glider...

LZ design may sell theses parts directly since they are not what they want to install at factory. I will ask them directly at AERO Friedrishshafen 2020, maybe...

But I am ready to get it done the hard way :
- having the prop hub milled by a professionnal metal workshop
- Making the prop myself : CAD modeling => plug (3D printed) => composite mold => composite blade (currently trying this for a new prop to improve my previous project cruise speed).

But I may also have the opportunity to rent existing prop molds from someone that built a FES himself.

#### blane.c

##### Well-Known Member
Having control of the pitch in some manner?

#### Brendan Wynn

##### Member
Hi sdupre et al

This thread is of special interest to me as I've had some fun with electric flight: https://www.homebuiltairplanes.com/forums/threads/hi-from-new-zealand.33110/

I have the Dongguan Freerchobby (company has been linked in this thread) MP12090 motor. I used it stock @ KV=80 in my project, with a Flier 22S/300A ESC and Falcon prop. The combo gave the following results:

Prop: Wood Falcon 36 x 12
Static Thrust: 33kg (wot)
Amps: 152 (wot)
Volts: 52
kWatts: 7.9 (wot).

The Flier ESC was problematic as its firmware is 'interesting'. Whatever you do don't update the firmware, even though you can easily.

The MP12090 motor is of ok quality. Bearings are good, thread tapping of screws average and windings a typical 'plate of spaghetti'. I'm currently looking to rewind the beastie with thicker gauge wire, better stator-slot fill (more copper, more efficiency) and much lower KV. Plan is to redesign with a larger prop (better prop efficiency) and higher Voltage (less current and more 'elegant').

I have also designed/built an Arduino-based parameter logger. This writes RPM, current, Volts, temps to a SDcard for post-flight analysis.

Hope this helps in some small way

Brendan.

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#### henryk

##### Well-Known Member
Prop: Wood Falcon 36 x 12
Static Thrust: 33kg (wot) Specific Thrust= 33/7.9=
4.2 kG/kW

Amps: 152 (wot)
Volts: 52
kWatts: 7.9 (wot).
Kf=circa 22...

=auer CR Differential=

D=1.3 m Ft=12 kG N=1 kW (1.36 HP)

Kf=27
Specific Thrust=12/1= 12 kG/kW .

#### Brendan Wynn

##### Member
12kg/kW....mein gott!
My setup is currently 4.2.

#### henryk

##### Well-Known Member
12kg/kW....mein gott!
My setup is currently 4.2.

Kf=Fthrust[kG]/N (power,[HP]) * sqr [ F (thrust) / S (propeller surface [m^2])]

Kf= kG/HP * sqr ( kG/m^2)

=practical formula for different propeller thrusters comparation...

Kf=12 kG/1.3 HP * sqr (12 kG/0.785 *1.3*1.3)=27.7

PS=in auer device we have <3 kW BLDC motor+1.3 m +0.7 m
coaxial propellers...

I=40 A, U=24 V N=960 W=1.3 HP...

#### sdupre

##### Member
I hadn't looked at this thread for some days since the 17 Feb. posts and am encouraged to see that others are also interested and are actually working on electric propulsion projects. I appreciate the inputs and will read the technical ones more closely. Actual experiences with specific vendors, brands, and models (MGM Compro, Rotex, freerchobby, Kelly, etc.,) are very helpful.

After starting conversations with all the vendors I’ve personally mentioned in this thread, it looks like a DIY system is my most likely way forward, given my inexpensive (single seat Schreder HP-14 glider, similarly-budgeted $10K-$15K USD upgrade limit, and, not least, the anticipated satisfaction of a challenging but hopefully achievable task.

I now do agree with a couple of people who advised using motor-propeller direct drive, even with a fixed mast. So the search is on for a relatively small-diameter outrunner BLDC motor that produces at least 35kW peak (for ~ 2min.) and at least 25kW continuous. Some deep-can motors in the 150mm diameter range look interesting. I'm checking with T-Motor on a customized version of their U15XXL motor. Also looking at Alien Power System’s 150100/S 35000W motor and their ESCs. Does anyone have experience with those brands and their products?

Henryk briefly mentioned “coaxial propellers…”, which paralells my recent thought of mountings two small-diameter (~120mm) motors coaxially on the same mast, each independently turning a propeller. The rear prop blades fold rearward, Graal style; the front ones fold forward, Carat style. Of course the two props contra-rotate. This means using two motor controllers, two traction batteries, two throttles, two sets of system monitoring sensors, displays, etc. Fun to contemplate. But a single motor system is likely the way to go.

#### henryk

##### Well-Known Member
But a single motor system is likely the way to go.
-see "CRFLIGHT"=moore thrust, better cooling (rotated stator !)
BTW=in this mode ( NO gear !!!) You can install different propellers,

PS=two individual motors +2 propellers are not so efficiant !

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#### Brendan Wynn

##### Member
Hey sdupre

Re: your: "This means using two motor controllers, two traction batteries, two throttles,"

Not necessarily. I have seen two identical motors connected in parallel in a synchronous mode....
found it @8:21

Re: Alien, Bruno rebrands Freerchobby motors, Flier ESC's and others. From what I read on the web, he adds value to the OEM products with tweaks, support and warranty.

#### John.Roo

##### Well-Known Member
If I understand well, you are planning to make simple propulsion system - something like on the photo.

https://www.espritmodel.com/sailplane-power-pod-launching-system.aspx
(this is RC model - not a real glider)

Not retractable propulsion system = no need to make major structural modifications on the fuselage. However still some modifications are necessary so few safety recommendations...

Simple installation - re-wiring, more motors... nice ideas but again - keep it simple. One motor, one controller, one battery, approved connectors and as good as possible wiring.

Don´t forget enough air flow for e-motor cooling. I don´t expect you wil use liquid cooled electric motor so bigger diameter = more air flow = better efficiency etc. Example from real UL glider:
http://www.mgm-compro.cz/novinky/partnerstvi-s-gp-gliders

Don´t use too small battery - too high discharge rate ("C") is not a good way. Again example on small GP glider - they have 8,1 kWh battery from Sony VTC6 cells. During T/O with 20 kW motor they have "C" rate of 2,5 - that is OK.

Check certification requirements for installations behind pilot seat. I don´t expect you will pass thru process of certified installation, but nobody wants to be killed by battery during emergency/hard landing. By the way - electric motor on top of the mast is also making some moment. Just imagine - energency landing, mast is broken... what will be trajectory of motor?

During my study our professor told us - each certification requirement was written by blood. He didn´t wanted to frighten us - it was just reminder that every requirement has good reason to exist.

Best regards!
Martin

#### henryk

##### Well-Known Member
Don´t forget enough air flow for e-motor cooling.
=this problem is good solved in CRFLIGHT construction=

=2-)1/ (+)1 reduction with NO Reductor !,
=rotated Stator (better air cooling),
=circa 50% moore thrust.

Conter Rotating propellers (can be different diameter and AoA), easy to retract into nose sides (closeable flaps,
we have seen on Martins pictures !)

=FES like,but propeller blades inside nose...

#### John.Roo

##### Well-Known Member
Of course I have no "patent for the best and the only technical solution"
I just use my experience so take my post as suggestion.

CR Flight looks interesting - especialy for drones and VTOLS. I have no personal experience with this system installed on airplanes, but parameters are good.

Reason why I bore you with "keep it simple" is because I am starting to be old and my "museum of burnt controllers and motors" is already large enough And (by the way) it also costed a lot on money...

I agree that aerodynamically far best is "FES like" system in the nose. Also relatively easy and safe for installation. However due to prop clearance is sometimes not possible to use prop big enough for safe T/O power. Higher undercarriage is also not easy solution - especialy on existing gliders.

So... thats it

#### blane.c

##### Well-Known Member
Of course I have no "patent for the best and the only technical solution"
I just use my experience so take my post as suggestion.

CR Flight looks interesting - especialy for drones and VTOLS. I have no personal experience with this system installed on airplanes, but parameters are good.

Reason why I bore you with "keep it simple" is because I am starting to be old and my "museum of burnt controllers and motors" is already large enough And (by the way) it also costed a lot on money...

I agree that aerodynamically far best is "FES like" system in the nose. Also relatively easy and safe for installation. However due to prop clearance is sometimes not possible to use prop big enough for safe T/O power. Higher undercarriage is also not easy solution - especialy on existing gliders.

So... thats it
So what is your plan in advent of a thermal runaway event?

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