motor glider project

Things that fly
kubark42   100 µW

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Re: motor glider project

Post by kubark42 » May 16 2020 7:48pm

carbon dragon wrote:
May 16 2020 7:35pm
I knew this project was getting too easy, throw me another wrench... :-)
LOL, don't worry, this just means that you don't want to glass in your bulkhead until you've done thermal performance testing. This can be as easy as putting the cowled motor/prop on the roof of your car and driving it down a long runway for a few minutes. :wink:

P.S. I PM'ed you, dunno if you saw.

Hillhater   100 GW

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Re: motor glider project

Post by Hillhater » May 16 2020 7:56pm

This type of feedback data is exactly what is required.
Some of these flyers must have data logging to record exactly their power, duration, speed, climb rates, etc etc ?

I realise these powered TO and flight assist glider systems will use much less power, but there are reports on this forum from several Epowered microlight craft and hang gliders , where they record much higher power consumptions !
This forum owes its existence to Justin of ebikes.ca

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Aug 29 2020 8:15pm

Any progress on this interesting project?

topspeed   10 mW

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Re: motor glider project

Post by topspeed » Sep 07 2020 12:55am

I wonder if 10 kw was feasible for an electric AC ? I know human powered planes can do with 230 watts continuous power. :wink:

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Sep 24 2020 7:10pm

topspeed wrote:
Sep 07 2020 12:55am
I wonder if 10 kw was feasible for an electric AC ? I know human powered planes can do with 230 watts continuous power. :wink:
It depends on the drag and lift efficiency of the AC. I think 10 kW is feasible, but would need a glide ratio of about 12:1 or better.

Gliders with glide ratio of 30:1 have reported below 10 kW power.

Do you have a project in mind?

kubark42   100 µW

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Re: motor glider project

Post by kubark42 » Sep 25 2020 10:32am

@Solarsail, the glide ratio of the plane is not sufficient to determine the power requirement to sustain altitude. Modern passenger jets have an L/D ratio of around 20:1, but they require orders of magnitude more than 10kW to stay in the sky.

Furthermore, the important part of power is more about climbing than sustaining. The sustaining power can be determined by the L/D ratio and the plane's weight. However, the climb rate is purely how quickly the plane can add potential energy. So for the same output power a plane which weighs twice as much as basically half the climb rate. That's a problem when you start getting into the 1-2m/s area, because it takes an excruciatingly long time to get to a safe altitude.

topspeed   10 mW

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Re: motor glider project

Post by topspeed » Sep 26 2020 3:12am

Solarsail wrote:
Sep 24 2020 7:10pm
topspeed wrote:
Sep 07 2020 12:55am
I wonder if 10 kw was feasible for an electric AC ? I know human powered planes can do with 230 watts continuous power. :wink:
It depends on the drag and lift efficiency of the AC. I think 10 kW is feasible, but would need a glide ratio of about 12:1 or better.

Gliders with glide ratio of 30:1 have reported below 10 kW power.

Do you have a project in mind?
Yes I am concentrating on being able to hang the plane in the ceiling and wings detached they can fit in a normal sedan car.

Wing loading is low 24-29 kg/m2. Glideratio in around 1/12.

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Sep 26 2020 9:05pm

kubark42 wrote:
Sep 25 2020 10:32am
@Solarsail, the glide ratio of the plane is not sufficient to determine the power requirement to sustain altitude. Modern passenger jets have an L/D ratio of around 20:1, but they require orders of magnitude more than 10kW to stay in the sky.
Yes, and I did not claim that the L/D ratio is sufficient to determine power.
In fact I did not even talk about L/D ratio. I talked about absolute drag (and lift efficiency). Larger planes have higher drag values, and thus need more power. And the more weight, the more lift is needed, and thus higher speeds, which results in more drag. That should be obvious.
kubark42 wrote:
Sep 25 2020 10:32am
Furthermore, the important part of power is more about climbing than sustaining. The sustaining power can be determined by the L/D ratio and the plane's weight.
The question was about sustainable cruising and continuous power. Clearly for climbing you need more power.

Power (kW) for climbing has never been a problem for electric flight. Just like acceleration has never been an issue for EVs. The important issue is range or energy with the unit kWh - and thus cruise power. A small 15 kWh battery pack can easily give you 45 kW of continuous power. And a small PMAC electric motor can easily give you 30 kW of power continuous. Given that "Flight hp" (i.e. the hp advertised by Rotax and others) is only about 0.5 kW (not to be confused with electrical or mechanical hp which is 0.74 kW), even a small battery pack and a small motor of 30 kW can give you 60 hp of sustainable flight, and 100 hp of peak climbing power. 100 hp for an LSA plane is far more than necessary for good climbing. Electrical aircraft will always have faster climb rates than general ICE powered aircraft.

Can you please provide the formula to arrive at the sustaining power from the L/D ratio and weight?

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Sep 26 2020 9:29pm

topspeed wrote:
Sep 26 2020 3:12am
Yes I am concentrating on being able to hang the plane in the ceiling and wings detached they can fit in a normal sedan car.

Wing loading is low 24-29 kg/m2. Glideratio in around 1/12.
Glide ratio is pretty decent. I don't get it. Is this a single occupant ultralight or an RC plane? How can you fit it inside a car? For an RC plane, you can easily get away with 200W. Or is it a paraglider?

For a powered paraglider, I believe the engines used are about 20 to 30 practical-hp. That would be 10 to 15 kW. (Each practical-hp is only about 0.5 kW). So for climbing, it would be 10 kW, and cruising about 5 kW.

What is the maximum take off weight? Are you building this from scratch? Or is it a kit? Do you have a link?

topspeed   10 mW

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Re: motor glider project

Post by topspeed » Sep 27 2020 3:11am

Solarsail wrote:
Sep 26 2020 9:29pm
topspeed wrote:
Sep 26 2020 3:12am
Yes I am concentrating on being able to hang the plane in the ceiling and wings detached they can fit in a normal sedan car.

Wing loading is low 24-29 kg/m2. Glideratio in around 1/12.
Glide ratio is pretty decent. I don't get it. Is this a single occupant ultralight or an RC plane? How can you fit it inside a car? For an RC plane, you can easily get away with 200W. Or is it a paraglider?

For a powered paraglider, I believe the engines used are about 20 to 30 practical-hp. That would be 10 to 15 kW. (Each practical-hp is only about 0.5 kW). So for climbing, it would be 10 kW, and cruising about 5 kW.

What is the maximum take off weight? Are you building this from scratch? Or is it a kit? Do you have a link?

Fuselage in on a ski rack on top of the car.

It is a bit secret still.

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Sep 27 2020 6:34pm

topspeed wrote:
Sep 27 2020 3:11am
Fuselage in on a ski rack on top of the car.
But why is it so important to fit it on top of a car? Just get a trailer and put it there. You will make the thing unusable if you insist it must fit in or top of a car.

Is this thing electric and does it carry a pilot?

Just curious.

kubark42   100 µW

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Re: motor glider project

Post by kubark42 » Sep 28 2020 8:40am

Solarsail wrote:
Sep 26 2020 9:05pm
Yes, and I did not claim that the L/D ratio is sufficient to determine power.
In fact I did not even talk about L/D ratio. I talked about absolute drag (and lift efficiency). Larger planes have higher drag values, and thus need more power. And the more weight, the more lift is needed, and thus higher speeds, which results in more drag. That should be obvious.
I don't mean to argue, but in fact you are talking about L/D. That's because L/D and glide ratio are identical, as in they are mathematically and theoretically one and the same. I'm happy to explain this if you'd like, but it's a little outside the scope of the original discussion.
Solarsail wrote:
Sep 26 2020 9:05pm
Can you please provide the formula to arrive at the sustaining power from the L/D ratio and weight?
Check out the second paragraph of viewtopic.php?f=38&t=106128#p1555722. It's a trigonometry calculation, where you know how much weight you need to support (plane weight) and then because of L/D ratio you know how much drag (force) which results from that much weight. So if your plane weighs 1500N, and has a 50:1 glide ratio at a certain speed, then you have 30N of drag. If you know the speed, then you can determine the work, which is speed * force.

In short, (mechanical) cruise power = weight(force) / glide_ratio * speed(@glide_ratio)

Please note that these calculations do not take into account any inefficiencies in the system.
Solarsail wrote:
Sep 26 2020 9:05pm
kubark42 wrote:
Sep 25 2020 10:32am
Furthermore, the important part of power is more about climbing than sustaining. The sustaining power can be determined by the L/D ratio and the plane's weight.
Power (kW) for climbing has never been a problem for electric flight. Just like acceleration has never been an issue for EVs. The important issue is range or energy with the unit kWh - and thus cruise power. A small 15 kWh battery pack can easily give you 45 kW of continuous power. And a small PMAC electric motor can easily give you 30 kW of power continuous. Given that "Flight hp" (i.e. the hp advertised by Rotax and others) is only about 0.5 kW (not to be confused with electrical or mechanical hp which is 0.74 kW), even a small battery pack and a small motor of 30 kW can give you 60 hp of sustainable flight, and 100 hp of peak climbing power. 100 hp for an LSA plane is far more than necessary for good climbing. Electrical aircraft will always have faster climb rates than general ICE powered aircraft.
I understand where you're coming from, but strongly disagree that the important value is range. As a glider and powered plane pilot, I have some small experience with watching the ground retreat on takeoff. More to the point, I have experience with watching the ground approach on takeoff, which is *very* scary. If you sufficiently powerful hit sink right after takeoff, and I did just about did yesterday, you can wind up in a situation where you have no options whatsoever other than to hope that the sink goes away before the tow plane hits the ground, with you about 2 seconds behind. Sometimes the sink is stronger than the tow plane and the result is tragedy.

The only protection is climb rate. The higher your climb rate the more you can combat sink and the sooner you can get to a safe altitude. Once I get to 1000' in a glider I can catch some lift and have a five hour flight without issue.

I also disagree that climbing is not a problem for electric flight. Climbing is *the* problem for electric flight, as the heat capacity of the components is very low. The motors I'm using to convert a glider to an eGlider will fail much beyond 100C. Since the motor only weighs 1.2kg, it doesn't take much internal heating before it reaches peak temperature and can no longer run at full power.

Batteries and speed controllers have similar problems. None of them like to go much beyond 80C. Some can handle as much as 100C, but that's really getting close to system failure and you're overstressing components, esp. electrolytic caps.

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Sep 28 2020 11:52pm

kubark42 wrote:
Sep 28 2020 8:40am
I also disagree that climbing is not a problem for electric flight. Climbing is *the* problem for electric flight, as the heat capacity of the components is very low. The motors I'm using to convert a glider to an eGlider will fail much beyond 100C. Since the motor only weighs 1.2kg, it doesn't take much internal heating before it reaches peak temperature and can no longer run at full power.

Batteries and speed controllers have similar problems. None of them like to go much beyond 80C. Some can handle as much as 100C, but that's really getting close to system failure and you're overstressing components, esp. electrolytic caps.
Thanks for the reference and I will check it out. Good to be speaking to an actual pilot, from this aspiring pilot.

The heat capacity of electrical component is not so low. For example the Emrax 188 PMAC sync motor is air cooled and can supply 23 kW continuous and the liquid cooled version can supply 29 kW continuous. Peak is 52 kW. This is far more than you need for a glider, even during climb. It weighs 7 kg. The motor you mention at 1.2 kg is probably a BLDC RC motor of 3 or 4 kW and is not suitable for what you are trying to do. May I ask what brand?

Batteries running at 100C are again the wrong thing. You need to go for high kWh and not for high C. A 10 kWh battery pack in the wings can be easily air cooled and will supply easily 30 kW, which is more than you need. Try using lighter 18650 cells (250Wh/kg) instead of heavy and dangerous LiPoly cells. 10 kWh will weigh 40 kg but will give you almost unlimited climbing and staying power. It should be built in two modules so that on some days you may just want to take 5 kWh up there. I am happy to show you how.

Modern 3-phase inverters can easily supply synchronous power at 30 kW with a bit of liquid cooling or even air cooling.

Could you please do a mathematical calculation of the power you need during climb (600 fpm?) and cruise? I am sure you will find 30 kW adequate for climbing, even after a loss of 15%.

SolarSail

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Sep 29 2020 12:06am

kubark42 wrote:
Sep 28 2020 8:40am
I understand where you're coming from, but strongly disagree that the important value is range. As a glider and powered plane pilot, I have some small experience with watching the ground retreat on takeoff. More to the point, I have experience with watching the ground approach on takeoff, which is *very* scary. If you sufficiently powerful hit sink right after takeoff, and I did just about did yesterday, you can wind up in a situation where you have no options whatsoever other than to hope that the sink goes away before the tow plane hits the ground, with you about 2 seconds behind. Sometimes the sink is stronger than the tow plane and the result is tragedy.

The only protection is climb rate. The higher your climb rate the more you can combat sink and the sooner you can get to a safe altitude. Once I get to 1000' in a glider I can catch some lift and have a five hour flight without issue.
Yes sink can be scary. But I don't think this is an issue with an Emrax 188, where you can produce 100 hp for a couple of minutes and 60 hp continuous. If this is inadequate, add a second motor with the same batteries. You will then get 200 hp for a while. That should give you 2000 or 3000 fpm? How much power would you need for 2000 fpm?

Finally, with one Emrax 188 and 10kWh pack, you don't need a towplane. You could probably get more airspeed than from a towplane.

SolarSail

Solarsail   10 mW

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Re: motor glider project

Post by Solarsail » Sep 29 2020 6:07am

carbon dragon wrote:
May 09 2020 2:24pm
I've already have an investment in this but not so much that I wouldn't abandon it for a better more reliable solution ( my ass will be riding in this after all) Are there higher power ESCs that will work with this motor, or would I be better off to start with a different motor/ESC combo?
I think you are better off with a PMAC synchronous motor. Take a look at the Emrax 188 specifically designed for electric aircraft. Will give you a true 23 kW, air cooled.

BLDC are not as efficient as PMAC and have other control problems. And the Emrax comes in a 400V version which will reduce the current and allow you to have a smaller and lighter inverter (ESC). For battery packs, it is easier to have higher voltage than higher current. And it is more efficient.

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carbon dragon   1 mW

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Re: motor glider project

Post by carbon dragon » Sep 29 2020 7:30am

After watching my first tests go up in flames, I decided that instead of spending time trying to design a power system, I would rather spend the time and money building a glider so I purchased a system from Geiger. More money but I have a system that is pretty well proven.

topspeed   10 mW

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Re: motor glider project

Post by topspeed » Sep 29 2020 10:25am

Solarsail wrote:
Sep 27 2020 6:34pm
topspeed wrote:
Sep 27 2020 3:11am
Fuselage in on a ski rack on top of the car.
But why is it so important to fit it on top of a car? Just get a trailer and put it there. You will make the thing unusable if you insist it must fit in or top of a car.

Is this thing electric and does it carry a pilot?

Just curious.
Yes..piloted electric aeroplane.

topspeed   10 mW

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Re: motor glider project

Post by topspeed » Oct 06 2020 4:45am

I checked I could get 23 kg of batteries at 3 000 euros...for an hour flight ( under 4 kwh ) ?

From a well known hobby shop.

Sounds a bit steep ?

kubark42   100 µW

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Re: motor glider project

Post by kubark42 » Oct 07 2020 9:03am

Solarsail wrote:
Sep 28 2020 11:52pm
The heat capacity of electrical component is not so low. For example the Emrax 188 PMAC sync motor is air cooled and can supply 23 kW continuous and the liquid cooled version can supply 29 kW continuous. Peak is 52 kW. This is far more than you need for a glider, even during climb. It weighs 7 kg.
I think your approach is the right one for powered flight, but for a self-launching sailplane there are other dimensions to the problem which become dominant. Since I only have 10 minutes of batteries, there's not much gain to designing for steady-state performance. And since I only need to get 300' off the ground before I'm safe, I can afford to have standard climb performance far below peak performance.

To put things in perspective for the 100C limit, the Neu motor 8057/75 can make 45kW before reaching magnetic saturation. However, at only 2.6kg it will basically self-immolate after just a few tens of seconds at that power level.

So much of the Emrax (I have one of their motor bells) is aimed at handling thermal issues. 100C peak (really, 80C preferable) is quite a low temperature when you're trying to exchange heat with 40C air. In contract, an ICE is running at 300C, so has a much easier time radiating heat to the environment. So the extra 5kg of metal adds greatly to the motor's ability to run at peak for long periods of time.

BTW, 5kg of extra weight is a huge amount in my application, equalling >2% of my glider's weight. Extra weight causes performance issues via weight and balance, landing gear overloading, max weight limitation, etc...

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