# Electric SSDR Motor Glider

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#### hole in the ground

##### Active Member
The following is the rather delayed action of my inspiration derived from Topaz' Conceptual Design of an "Inexpenseive" Single-Seat Motorglider. Like that thread this is probably only a conceptual design but is more of a feasibility study than anything else: Is it possible using today's commercial technology to build a viable light aircraft powered by battery electric propulsion?

I think that the answer is yes and to me it seems that electric propulsion will require a very efficient aircraft in order to achieve a decent endurance. Endurance not range because pilots measure their experience in hours not miles and frankly you wont be able to go very quickly under electric steam (so to speak). It think that electric propulsion and motor gliders seem like a natural combination. Electric propulsion provides a very reliable restart system so that glider pilots can get lower looking for lift, confident that the donkey will restart when requested. Gliders with their long wings and clean fuselages are aerodynamically efficient requiring little power to keep them airborne. Additionally, turning the motor off is a very good way of conserving battery power and increasing flight duration.

So far I've just got to the point where I have done an initial sizing so the following will just be a quick skim over what I've done and found, with some eye-candy at the end. I've mainly followed Raymer's simplified but with some deviation for an electric build and SSDR requirements.

My reference aircraft for this are the Fournier RF4, Schleicher ASK14, and the AMF Chevvron 2-32. The first two because they are beautiful single seat motor gliders and the Chevvron because it fits the (now earlier) UK microlight regulations and has the lowest empty weight despite being a two seater (to be fair it is 20 years younger than the other 2 though).

Mission requirements are pretty modest:
Max mass = 300kg (SSDR limit - I will design up to it, using aspect ratio and/or battery mass to get maximum performance)
Stall speed = 35kts (SSDR limit - I expect that with glider sized wings that I can achieve this without flaps)
Cruise speed (power) = 60kts (I did a quick trade between 60 and 90 kts and it required nearly 1/2 of the aircraft to be battery for 90kts)
Endurance (power) = 1 hour (I havent yet fully worked out what the mission profile of my 1 hour power will look like - so this may change, at the moment I have estimated just 1 hour at cruise conditions. This will be one of the next things I need to spend some time firming up)
Climb rate = 500 fpm (this isnt a hard limit, more something to hang some figures on at the moment. I will play around with this along with the mission profile to see if I can find a knee in the curve somewhere)
Payload = 95kg (me plus some baggage, threshold would be 85kg - me plus some water and a light sandwich (maybe some cucumber in a pita))
Empty mass = 205kg (not so much a requirement as a fall out of the maximum mass limit)

For reference the RF4 is 270kg empty, the ASK14 is 245kg and the Chevvron is 175kg.

Take-off length - conspicuous by its absence (something I need to work out but I'm not planning on visiting any postage stamps).

In order to get to a reasonable CLmax the wing area popped out as 10.7m (I may just round this to 11m). I havent settled on a wing planform yet, I've got two parallel sets of calculations going on at the moment with a planform similar to the ASK14 and one similar to the RF4. This leads to one design with a 13.2m wingspan and one with a mere 11m, the trade-off I expect will be mass (though whether or not they are sufficiently different in AR to have much effect I will wait and see).

Using the other aircraft as references for power loading suggests a motor of ~ 22kW would be suitable. Coincidentally such a motor for gliders already exists. Front Electric Sustainer/Selflauncher - Future of gliding now. However this swings a 1m diameter prop at 4500rpm which is probably not too great for cruise but is clearly good enough for take-off and climb. I've used their battery mass/power to estimate how much weight of battery I would be lugging around too.

Initial L/D estimation and cruise duration of an hour spat out a battery mass of 51kg for the 11m span and 42kg for the 13.2m

One thing that I am hoping to achieve is having the wingtips further aft with respect to the pilots eyeline than on the RF4 and ASK14. Hopefully without an ICE at the front, and with the batteries mounted somewhere amidships, I'll be able to shift the pilot forward a bit.

I've done an initial layout in fusion 360 of the 13.2m wing using the data I've calculated/guessed, in order to get better numbers for Swet etc. (Tail is way too high an aspect ratio)

#### stanislavz

##### Well-Known Member
HBA Supporter
Totally doably to me, easy to build using composite molds from cnc cutted foam and foil covered.

Some thought - i would move wing more to the front, it looks too much nose heavy, or you are putting batteries behind the pilot ? They have to be put in stainless, fireproff, insulated container to say the least..

And you may add may raise turdley a little bit - it shall reduce drad a little bit. Like this :

And extend straight portion of fuselage till and of the wing.

#### BJC

##### Well-Known Member
HBA Supporter
Interesting project; I’m looking forward to future updates.

Wrt the RoC specification. For an airplane mission that you are describing, takeoff roll and climb gradient are more important to me than simply RoC. Designing for a takeoff distance to clear 50’ may be more relevant.

BJC

#### hole in the ground

##### Active Member
Totally doably to me, easy to build using composite molds from cnc cutted foam and foil covered.

Some thought - i would move wing more to the front, it looks too much nose heavy, or you are putting batteries behind the pilot ? They have to be put in stainless, fireproff, insulated container to say the least..

And you may add may raise turdley a little bit - it shall reduce drad a little bit. Like this :

And extend straight portion of fuselage till and of the wing.
Stanislav, I am deliberately trying to push the pilot forward of the wings. I will be looking to have the batteries behind the wing spar somewhere. I take your point on the turtle deck from an aerodynamic perspective, but I really like the aesthetic of a bubble canopy. I guess the additional argument for a raised turtle deck is that it provides a position in which to fit a role bar (though one could be fit within the cockpit under the canopy). I agree with your observation to extend the fuselage constant cross section to aft the wing trailing edge. There is a fair amount of just throwing that picture together at this point. Think of it as a posh napkin sketch.

Interesting project; I’m looking forward to future updates.

Wrt the RoC specification. For an airplane mission that you are describing, takeoff roll and climb gradient are more important to me than simply RoC. Designing for a takeoff distance to clear 50’ may be more relevant.

BJC
BJC thanks for the comment. I will throw together a sizing plot to try and identify the driving requirement. I guess worst case the answer will be that I need a more powerful electric motor.

#### jedi

##### Well-Known Member
.............
My reference aircraft for this are the Fournier RF4, Schleicher ASK14, and the AMF Chevvron 2-32.
,,,,,,,,

Your reference aircraft include two mono wheels and one tri gear. One of the early steps in the design process is the landing gear. It is time to discuss that before tweaking the profile.

It is assumed you are committed to a single nose mounted motor. I will accept that but would entertain comments and justification.

With respect to the landing gear I would suggest a dual mono wheel or fuselage mounted narrow stance conventional gear with a tail wheel. The single mono wheel requires outriggers and is difficult to taxi and steer as there is no differential breaking. The fuselage mounted gear will allow wing removal for storage or transport. You will still want a wing tip skid plate. The dual mono wheel will allow a wings level taxi on paved surfaces and provide the possibility of differential breaking for steering and to assist a steerable tail wheel. The nose high tail wheel stance is required for propeller clearance with the nose mounted engine. Wheel motors for taxi to save battery power are worth their weight for shortening the take off roll and allowing a smaller diameter propeller. Retracting gear? Probably.

Your "posh napkin sketch" has retained too much IC airplane design. Once you move the batteries aft and the pilot forward you can go more sailplane design. Consider more of an L-13 mid wing design (wing spar can go behind the pilot) to give additional wing clearance over runway lights ( nearly one meter high in the snow covered north).

Please replace the IC airplane nose with a nice clean glider nose. The folding prop is good with electric power. No need for the feathering prop.

Nice project!

#### BJC

##### Well-Known Member
HBA Supporter
If the objective is to have an airplane that is operable at most USA airports (the OP is in the UK), then I would lean toward a very wide main gear mounted far enough out the wing to allow folding the wings quickly and easily by the pilot. I would look at folding then in sort of an “X” across the aft fuselage so as not to impede access to the cockpit with the wings folded. Easy to do; just requires a stroke of genius.

BJC

#### Hot Wings

##### Grumpy Cynic
HBA Supporter
Log Member
Easy to do; just requires a stroke of genius.
I'd like to buy a stroke or 2. Can you give me the contact information for a reliable supplier?
Shelf life is important. My past supply has tended to go bad once opened and examined.

@OP
Agree with Jedi about moving things around to be more glider like rather than based on power plane.

I know it's more systems and development but I think you could loose some battery (and overall) weight and gain some operational flexibility by using a hybrid system rather than pure electric. The fuel quantity would be minimal for the stated endurance goal and the ICE/Gen unit can be mounted almost anywhere needed for W+B.

BJC

#### rdj

##### Well-Known Member
The following is the rather delayed action of my inspiration derived from Topaz' Conceptual Design of an "Inexpenseive" Single-Seat Motorglider. Like that thread this is probably only a conceptual design but is more of a feasibility study than anything else: Is it possible using today's commercial technology to build a viable light aircraft powered by battery electric propulsion?
There are already a few such planes in production, so it's certainly feasible. For example:
Pipistrel Taurus Electro

Totally electric, has it's own solar-charging trailer. Available now ready-to-fly. Kitplanes also lists it as an E-AB kit, but I've never come across any information on that aspect of it.

Unfortunately, it's about $100K, so it's nowhere near the price point Topaz was aiming for in his thread. Hopefully as more planes like this come on the market the availability of affordable components (motors, batteries, et al) will improve. #### John.Roo ##### Well-Known Member Totally doably to me, easy to build using composite molds from cnc cutted foam and foil covered. Some thought - i would move wing more to the front, it looks too much nose heavy, or you are putting batteries behind the pilot ? They have to be put in stainless, fireproff, insulated container to say the least.. And you may add may raise turdley a little bit - it shall reduce drad a little bit. Like this : View attachment 98423 And extend straight portion of fuselage till and of the wing. Hello! I like the idea of simple motorglider and I agree with Stanislavz and with Jedi. Try to make it more "glider like". Even if is not goal to have high performance L/D motorglider. Reason? With electric propulsion you have never enough energy I also agree to don´t use monowheel landing gear. Taxiing and crosswind landings are more difficult. Batteries behind pilot.... well this will definitelly increase the empty weight. Everything behind pilots must be tested for 12G load (if I remember well). It is safety requirement. In case of crash you have belts holding pilots body (normally are belts tested for min. 11G load) and all behind pilot must not move forward. Better position is tunel inside the wings. Or in the front - replacing mass of combustion engine. If you want to save money - start with small combustion engine anyway. Beleive me - I know what I am talking about You will focus yourself to make "tuning and testing" of flight characteristics. When airframe is tested, you can start to play with electric propulsion. Small and reliable seems to be for example this engine 36 hp / 18 kg (real installation weight will be for sure higher) together with reduction should be OK for oneseater. Good luck Martin #### stanislavz ##### Well-Known Member HBA Supporter 36 hp / 18 kg (real installation weight will be for sure higher) together with reduction should be OK for oneseater. Twice as much as needed for sky pup or similar.. This one is much better Single seat glider will launch itself on 12-16 kw. According to design - buble canopy do really steal some speed. Mine napkin designs are even worse #### stanislavz ##### Well-Known Member HBA Supporter And some more examples, which was fit to me, for same aircraft class : And #### hole in the ground ##### Active Member #### stanislavz ##### Well-Known Member HBA Supporter UK single seat de-regulated regulations Mtow of 300 kg for electric is much better start point compared to 115 kg empty with batteries in other part of world. For 300 kg - you may want to make an spredsheet with wing span/ airframe weight efficiency and possible battery capacity.. I could beat what 100 kg (airframe with motor) + 100 kg (battery) + 100 kg (load) is doauble for it. #### Mad MAC ##### Well-Known Member So really what is the differance between a self launching glider and motor glider. I only ask as far as I can tell the only differance is if you are willing to make the engine fold away. As a comparison airframe the PW-5 glider might be another good option. #### hole in the ground ##### Active Member Hi all, I've had a bit of time to read and digest your comments and so here are my thoughts and explanations. Configuration comments: Your reference aircraft include two mono wheels and one tri gear. One of the early steps in the design process is the landing gear. It is time to discuss that before tweaking the profile. It is assumed you are committed to a single nose mounted motor. I will accept that but would entertain comments and justification. With respect to the landing gear I would suggest a dual mono wheel or fuselage mounted narrow stance conventional gear with a tail wheel. The single mono wheel requires outriggers and is difficult to taxi and steer as there is no differential breaking. The fuselage mounted gear will allow wing removal for storage or transport. You will still want a wing tip skid plate. The dual mono wheel will allow a wings level taxi on paved surfaces and provide the possibility of differential breaking for steering and to assist a steerable tail wheel. The nose high tail wheel stance is required for propeller clearance with the nose mounted engine. Wheel motors for taxi to save battery power are worth their weight for shortening the take off roll and allowing a smaller diameter propeller. Retracting gear? Probably. Your "posh napkin sketch" has retained too much IC airplane design. Once you move the batteries aft and the pilot forward you can go more sailplane design. Consider more of an L-13 mid wing design (wing spar can go behind the pilot) to give additional wing clearance over runway lights ( nearly one meter high in the snow covered north). Please replace the IC airplane nose with a nice clean glider nose. The folding prop is good with electric power. No need for the feathering prop. Nice project! Jedi, I am not against pushers, the Janowski J5 I think is particularly good looking. However, for simplicity I have gone with a tractor arrangement here. Once I've got sufficiently far through this I may look at a second configuration. I've seen a lot of back and forth about the pros and cons of single main wheels. Having flown gliders I dont agree with many of the arguments about them with respect to landing. However, I've never had to taxi a glider on a single main wheel. I have however seen several aircraft achieve this on grass and paved strips without much fuss. I think that the design is still sufficiently fluid at the moment not to nail down the landing gear. It will be a tail dragger. If two mains it wont have retracts, if single I will try to retract it. Regarding the nose profile, I see what you mean about the "too ICE nose". However that is driven by a combination of factors. 1, I want to have a bigger prop than those seen on the noses of gliders fitted with a FES and this drives the thrust line up to keep landing gear short and light (which ever configuration). 2, Canopies are heavy, so I want to have as small a canopy as possible without restricting pilot visibility, hence the bubble - I may reduce it further to the rear to fair it in a bit better. 3, The pilot (me) has legs and heels and feet and with the prop raised up, there is still a need to accommodate those annoying limbs. Please see diagram below: At the moment, I am content with the nose profile and configuration. If the objective is to have an airplane that is operable at most USA airports (the OP is in the UK), then I would lean toward a very wide main gear mounted far enough out the wing to allow folding the wings quickly and easily by the pilot. I would look at folding then in sort of an “X” across the aft fuselage so as not to impede access to the cockpit with the wings folded. Easy to do; just requires a stroke of genius. BJC As you note, I live in the UK and as it is a speculative project, operating outside these Sceptred Isles is not a consideration. Neither at the moment is wing fold or storage. I'd like to buy a stroke or 2. Can you give me the contact information for a reliable supplier? Shelf life is important. My past supply has tended to go bad once opened and examined. @OP Agree with Jedi about moving things around to be more glider like rather than based on power plane. I know it's more systems and development but I think you could loose some battery (and overall) weight and gain some operational flexibility by using a hybrid system rather than pure electric. The fuel quantity would be minimal for the stated endurance goal and the ICE/Gen unit can be mounted almost anywhere needed for W+B. Not really interested in hybrid systems. They add system complexity that isn't really in keeping with the intended simplicity of SSDR aircraft. There are already a few such planes in production, so it's certainly feasible. For example: Pipistrel Taurus Electro Totally electric, has it's own solar-charging trailer. Available now ready-to-fly. Kitplanes also lists it as an E-AB kit, but I've never come across any information on that aspect of it. Unfortunately, it's about$100K, so it's nowhere near the price point Topaz was aiming for in his thread. Hopefully as more planes like this come on the market the availability of affordable components (motors, batteries, et al) will improve.
Thanks, I know that there are electric aircraft in this ball park already in existence. I wouldn't suggest that the Taurus really fits this bill though it is a two seater and definitely weighted towards the gliding end of the motor glider.

Hello!

I like the idea of simple motorglider and I agree with Stanislavz and with Jedi.
Try to make it more "glider like". Even if is not goal to have high performance L/D motorglider.
Reason? With electric propulsion you have never enough energy

I also agree to don´t use monowheel landing gear. Taxiing and crosswind landings are more difficult.

Batteries behind pilot.... well this will definitelly increase the empty weight.
Everything behind pilots must be tested for 12G load (if I remember well).
It is safety requirement.
In case of crash you have belts holding pilots body (normally are belts tested for min. 11G load) and all behind pilot must not move forward. Better position is tunel inside the wings. Or in the front - replacing mass of combustion engine.

If you want to save money - start with small combustion engine anyway. Beleive me - I know what I am talking about You will focus yourself to make "tuning and testing" of flight characteristics. When airframe is tested, you can start to play with electric propulsion.

Small and reliable seems to be for example this engine
36 hp / 18 kg (real installation weight will be for sure higher) together with reduction should be OK for oneseater.

Good luck
Martin
Martin, thanks Im glad you like the concept. As above re landing gear, I've seen a lot of discussion, very little quantitative information and my limited personal experience disagrees. But as before, this is so early in my investigating this concept that landing gear is still a moot point.

Im not sure what regulations you are quoting that states that everything behind the pilot must be tested for 12G. 12G in which direction? I dont think that is applicable to SSDR aircraft.

Im not really interested in ICE propulsion for this, under any guise. Designing for a different propulsion system will take additional effort. And its almost certainly not going to be built so I dont need a short cut to flight.

And some more examples, which was fit to me, for same aircraft class :

And

Stanislavz, I am quite partial to interwar De Havilland designs. Im not sure that it is necessarily a good fit for this purpose though. It is small and light, but draggy. Another project I would like to do would be an interwar racer stylised aircraft akin to a Chilton DW1, but that is not this project.

Mtow of 300 kg for electric is much better start point compared to 115 kg empty with batteries in other part of world. For 300 kg - you may want to make an spredsheet with wing span/ airframe weight efficiency and possible battery capacity..

I could beat what 100 kg (airframe with motor) + 100 kg (battery) + 100 kg (load) is doauble for it.
I have spreadsheets coming out of my ears

So really what is the differance between a self launching glider and motor glider. I only ask as far as I can tell the only differance is if you are willing to make the engine fold away. As a comparison airframe the PW-5 glider might be another good option.
This seems like quite a philosophical question! From my perspective and for this project I am trying to design an electric aircraft and am merely leaning on gliding as a practical means of extending flight duration. So I wont be exploring retracting motors.

#### John.Roo

##### Well-Known Member
Hello!
First about the landing gear - the best is always personal experience
I had opportunity to fly in few monowheel motorgliders and.... well my subjective opinion is that I don´t like it. Taxiing on airfields with taxiways or RWY lights is difficult - sometimes requires assistance. Is also not that easy to land with crosswind - but this is about the pilot experience. As I wrote - try it. At the end you will fly your airplane and you must like it - we can just write comments with our own experience

12G load test for attachement for mass behind pilot is about your safety. Imagine emergency landing or crash landing when 50 kg (or heavier) box with batteries goes stright forward.

"I dont think that is applicable to SSDR aircraft."
You opened interesting topic - I have to read carefully the description of the SSDR aircraft...
By quick review I found this text:

We would recommend you design the airframe to cope with all the main load cases of BCAR Section S even though this is not mandatory in this deregulated class. Appendix A and B of CS-VLA also provide a very helpful simplified approach to working out aircraft loads, which is especially useful for the deregulated microlight designer without too much previous aircraft design experience.

You are right - LAA can only recommend you to do at least basic strength calculations and tests. That is really interesting approach of the authorities

Best regards!
Martin

#### John.Roo

##### Well-Known Member
Propulsion system....
I support your idea to use electric propulsion system
Hybrid is not only more complicated, but is also necessary to do a lot of development. Plug and play hybrid system doesn´t exist.
ICE is simple, but where is a challenge and spirit of new construction?
Electric propulsion installation is not that easy as it looks like, but at least you can choose from different suppliers offering tested systems.

To choose the best solution is good to start from your calculations about performance.
For example - do you need 8-10 kW of power to stay in horizontal flight?
Try to do not overload the battery. Best is to stay under 1C discharge rate so you need battery size -+10 kWh. With low discharge rate you achieve lower battery temp. for horizontal flight.
2C discharge rate will give you 20 kW for takeoff + energy for up to 1 hour cruise.
Can you carry a bit more batteries? Perfect - if you can have 12-15kWh battery, Than you will achieve lower "C load" and also lifetime of battery will increase because you don´t need to go to "0%" capacity during flying.

It is a lot of small details you will need to solve... but thanks to Internet you can use place like this forum to ask for different opinions and other pilots point of view

Good luck!
Martin

#### Grelly

##### Well-Known Member
Just a couple of thoughts...

Another airframe you might want to look at for inspiration is the Europa aircraft. In its monowheel form, the outriggers are fixed to the flaps. So flaps up there is a measure of stream lining. Flaps (and outriggers) down for landing. The limitations of a monowheel are as said above. Turning circle is dreadful, no differential braking, a handful in a strong cross wind. You will want a big powerful rudder.

You wanted to slide the wings back for improved visibility. IIRC, the Schleicher K13 (a tandem two seater) gave the rear seat instructor better visibility by sliding the wings back, but giving them a 6 degree forward sweep. Maybe something to consider there.

Grelly

#### hole in the ground

##### Active Member
Just a couple of thoughts...

Another airframe you might want to look at for inspiration is the Europa aircraft. In its monowheel form, the outriggers are fixed to the flaps. So flaps up there is a measure of stream lining. Flaps (and outriggers) down for landing. The limitations of a monowheel are as said above. Turning circle is dreadful, no differential braking, a handful in a strong cross wind. You will want a big powerful rudder.

You wanted to slide the wings back for improved visibility. IIRC, the Schleicher K13 (a tandem two seater) gave the rear seat instructor better visibility by sliding the wings back, but giving them a 6 degree forward sweep. Maybe something to consider there.

Grelly
Grelly, thanks, I am aware of the Europa. I think for outriggers I'd either just leave them dangling or retract them with the main. I learnt to glide in the K13, its a lovely old girl. It may be that sweep is required in order to get the cg and structural requirements to match too. We'll have to wait and see.

Thanks for the interest.

#### User27

##### Well-Known Member
Hello Hole, interesting project! I would consider a whole airframe parachute as it allows another 15kg and only weighs 7 or 8kg. FES gliders have a full power endurance of around 15 minutes and a cruise endurance of around 40 minutes. To achieve an hour endurance will need a larger battery, you could consider building a battery from 18650 type cells - there is a fair amount of flexibility in weight, power, capacity and packaging. If this is a design exercise only then don't spend too much time on aerodynamics. If you have any thoughts of building then selecting a motor up front and concentrating on motor integration will pay dividends. Forward swept wings (the Arcus is a recent example) are now more straight forward to build than they were as the foam mould sections can be glued together with the required sweep.

While there are no strength/stress requirements for an SSDR the CS-VLA simplified approach does enable a design to be schemed that is unlikely to fall apart as soon as it hits its first strong thermal. It is worth reading the rules to understand what that code is asking for, even if you subsequently don't completely follow it.