Self-launching sailplane conversion

[AC5ME]

Hello everyone. I came came across this forum recently while I was researching options for my project. I’m hoping some of you would share your thoughts with me on my conversion. I’ve got a Russian Aviastroitel AC-5M glider with a 25-ish HP 2-stroke. On a cool day at sea level it might do 500 FPM, I’m flying out of Boulder, CO so that’s just not going to be enough.

http://www.glidingsport.ru/ac/en/m05/mg05.htm

I’ve looked into some complete kits available like these:

https://www.mgm-compro.com/electric-propulsion-systems/
https://www.geigerengineering.de/avionik

Which may work, but I’d really like to do something DIY and closer-to-home without spending the $15-20K that these systems go for.

I’ve researched a bunch of different components and suppliers but I’m not a real engineer, so I’m not knowledgeable enough to integrate it all in a safe and efficient manner. Any input would be much appreciated, thanks!

 

[helno]

You should look at some of the electric paramotor drives people have worked out.

They have similar prop size constraints and power requirements.

https://openppg.com/shop/paramotors/openppg-sp140/

 

[AC5ME]

That's a good tip, it's very close to what I'm doing. Thanks helno. One area where I'm flailing is how to calculate the thrust required for my application. I'm guessing around 100-150 pounds to get at least 500fpm. This number will drive the rest of the design, so I'd like to get it right and I'm having trouble finding someone who really knows how to do that math.

 

[helno]

You could just measure the current thrust and that gives you a starting point.

One thing you will need to take into account is the thrust available at the speed you climb at. A paramotor is all about static thrust but a glider will be moving quite a bit faster while climbing.

 

[AC5ME]

I never ran the motor, and it's already removed. Long story... Are you aware of any online calculators to help determine this?

 

[helno]

There are plenty intended for R/C motor and prop selection that will do the trick.

 

[AC5ME]

Any opinions on Neumotor 120xx, APD UHV 28S controllers and the batteries that Neumotors supply? It looks like they may have most of what I need. I'm thinking 28S5P, for around 100V and 250A. 25Kw max output and around 150lb of thrust as a preliminary goal.

Thanks!

 

[topspeed]

This is a good find AC5ME !

I just tumbled across the US designer Jim Bede BD-5S.

It was a pure glider, but certaily can be motorized as we know.




Being small it also very light.

Winward is selling 69.75 kg ( 155 lbs ) sailplane too.

https://en.wikipedia.org/wiki/Windward_Performance_SparrowHawk

https://www.compositesworld.com/articles/sparrowhawk-all-carbon-composite-sailplane



My glider like design is now 9 m spanning....and has AR of 14.25.

One model has flown so far.

 

[AC5ME]

It's a shame Windward Performance quit making this line of gliders, very innovative and made right here in the US of A. They were pursuing a self-launcher years ago based on this airframe, but they're not even answering the phone these days. I considered buying one but it would have been a big job to mount an engine on it.

 

[topspeed]

How come they are not answering the phone...they build the Perlan record setter as well ?

What I know they are developing this: https://www.windward-performance.com/img/GosHawk%20Electric%20Soaring.pdf

 

[SlowCo]

Beautiful designed electric sailplane: https://www.windward-performance.com/gosHawk.html

 

[Stealth_Chopper]

Mount your engine.
Run the engine and measure thrust ( Fn ).
Because you don't know anything, best by test , thrust you can trust.
Sincerely
Mike

 

[AC5ME]

I've considered re-mounting the engine, there are a number of issues though. The main problem is that no matter the thrust number I come up with through testing, I don't have any real data to show what kind of performance this would produce because nothing's been published in the manuals. I've done a review of comparable gliders though, and spoken with some owners. I've gotten wide agreement that what I've got, if it's giving rated HP (25-ish) at sea-level will not give 500 FPM on a hot day here at 5300ft (I would expect at least a 7HP loss, or close to 30%)

The good news is that comparable gliders at sea-level are climbing at around 500fpm, which leads me to believe that 25HP or 20+ kW electric would do the trick. Plus I can spin the prop faster with a direct drive electric vs. the 2700 rpm it was doing with the ICE.

 

[Stealth_Chopper]

You have no data only stories,
Guessing the pounds of force (or Neutons) of thrust required to fly your machine where you live.

 

[topspeed]

Germans made a flight with Sunseeker II like pusher Birdy: https://www.youtube.com/watch?v=GRkL6ECl7QY&t=88s

 

[topspeed]

Trust needed for level flight with a good glider is about 15-20 kg...take off needs more: http://godolloairport.hu/calc/strc_eng/index.htm

 

[SlowCo]

Seems you'd need around 5kW (out of the battery) for cruise flight with the GosHawk. And they have a 40kW motor to be able to take off and climb. A wrecked Zero motorcycle to get the motor, controller, battery etc. from seems ideal then.

 

[topspeed]

GosHawk.jpg

Seems you'd need around 5kW (out of the battery) for cruise flight with the GosHawk. And they have a 40kW motor to be able to take off and climb. A wrecked Zero motorcycle to get the motor, controller, battery etc. from seems ideal then.

That is two seater...I recall Electra One boasted 3 kw for cruise..that is a single seater.

https://en.wikipedia.org/wiki/PC-Aero_Elektra_One

It has retractable main gear.

If someone made a plane using 2 kw for cruise that would be very affordable and lite weight.

 

[AC5ME]

I contacted Zero about that possibility and they said they'd like to help me except the lawyers won't let them...

I'd like to avoid using anything "wrecked", and since there are affordable new components available I have the luxury of selecting something that's just right.

It sounds like I'm in the ballpark with 20kW, now I need to figure out the details. Any opinions here on these guys?

https://mad-motor.com/product/mad-torq-m40-c30-pro-kv43/

Thanks!

 

[JackFlorey]

It sounds like I'm in the ballpark with 20kW, now I need to figure out the details.

You will tend to be power limited on takeoff.

Perhaps consider a battery you can drop after takeoff? That will give you more power for takeoff, and less weight to deal to increase range and/or deal with problems.

 

[John in CR]

...Any opinions here on these guys?
https://mad-motor.com/product/mad-torq-m40-c30-pro-kv43/

They may well be built tough, but their claims of high efficiency are drastically overstated. The no-load current is quite high even though they listed it at an rpm using only 30V. It would be over 3 times higher at max rated voltage. Also, the winding resistance is quite high for that Kv and power rating. I use hubmotors that are far more efficient. To make matters worse they lie on the motor test info, because it shows an efficiency of 100%. The 18+KW they show as max power is the same as input power (voltage X current), and output power (Nm of torque X rpm / 9.5488) comes to the same number. I could trim the smaller hubmotor I use down to about 7kg and rewind it to the same Kv as the motor you linked. It would then be capable of significantly higher power and thrust at much greater efficiency due to lower core losses as demonstrated by a lower no load current at the same rpm, and about half the winding resistance so half the copper losses at the same level of current.

That said, efficiency isn't all that critical in your planned use since the motor will be well cooled with forced air cooling, but at that price level I'd expect a motor of better design. It makes me question overall build quality.

 

[AC5ME]

Thanks John, that's exactly the kind of input that I'm looking for and I've heard rumors elsewhere along the same lines. I'm not an engineer so a lot of this stuff escapes me but I'm learning a lot as I go. I'd really like to find something US built but I know that's a long shot. Any suggestions?

I've also had trouble finding a good ESC this size, I'm leaning towards this:
https://powerdrives.net/products/hv_pro/

I'll need to park the prop vertically in order to retract the motor, this seems doable according to them with the right sensors.

Thanks again!

 

[Stealth_Chopper]

Nonsense

" The main problem is that no matter the thrust number I come up with through testing, I don't have any real data to show what kind of performance this would produce because nothing's been published in the manuals. "

You missed a baseline, bought a motorized sailplane, didn't run the engine and propeller to measure the OEM thrust.

 

[kubark42]

That's a good tip, it's very close to what I'm doing. Thanks helno. One area where I'm flailing is how to calculate the thrust required for my application. I'm guessing around 100-150 pounds to get at least 500fpm. This number will drive the rest of the design, so I'd like to get it right and I'm having trouble finding someone who really knows how to do that math.

You're in good company, there are several of us who are going down the path of making an AC-5M eRussia. Check out https://nbviewer.jupyter.org/gist/kubark42/53b0ccd7ec310fcf0136b47c166cbdbb, in specific the section "Airframe power requirements" and "Powerplant description" for some rough numbers I whipped up.

Note that one of the neat advantages of an eRussia is a much improved CG envelope. You no longer have to have a very far forward CG to account for the heavy engine moving backwards a half meter when deployed.

 

[AC5ME]

I though an update might be of interest. I've made the first taxi test recently, and all is well so far. I'm hoping for first flight next week, depending on how the ground testing moves along. I'd be grateful for any input from the members here, as I've yet to have my design vetted in-person. Except, by a couple of A&P's who seemed impressed but befuddled.

MGM-Compro HBC 280120-3
Rotex RET-60
E-Prop 115cm
Molicell P-26A 18650: 28S 16P
Thunderstruck motors BMS