motor glider project

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carbon dragon   1 mW

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motor glider project

Post by carbon dragon » May 09 2020 2:24pm

I built an ultralight glider several years ago. It has great performance and I considered adding an electric motor for self launch but with all the mods required I decided building another would be the way to go. I have a background in electronics but after researching for the last couple months, I didn't realize how much I didn't know about brushless motors and their controllers. I bought a motor/ESC combo from China to experiment with (I'm making expensive mistakes early) My experiments lasted about a minute before I turned the ESC into plasma. I bought this motor:

https://www.alibaba.com/product-detail/ ... 90c4NCfow2

I searched for the Flier 500a ESC which is how I found Endless Sphere. Apparently the power specs are a joke...

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?
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Re: motor glider project

Post by amberwolf » May 11 2020 2:31am

My first recommendation is to look at other flight projects here on ES and elsewhere, to see what they did. There arent' any directly-comparable projects here, but Farfle has an ultralight homebuilt plane he started as electric (can't remember the conclusion).

There's also some paraglider projects.

Unfortunately many controllers (and even motors) are rated well-outside their actual continuous usability, though they may be able to handle peaks of whatever they rated them at. How long those peaks can be...well, taht depends. :/

I don't know the actual power levels you need; if you already have calculated that out, you should post that (and any other details you have) to help us help you find what you need.

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Re: motor glider project

Post by carbon dragon » May 11 2020 11:24am

Thanks for the reply.. I've looked at several other electric aircraft. It would be nice to buy an off the shelf solution but the closest plug and play systems I've found are in the $10k range. Paraglider systems are close but many are using multiple motors, wouldn't work for my application and are a little low in thrust. Weak climb rates can get you in trouble.. I would like the equivalent of about 25hp. The motor I bought is rated 30kw which I think should be about 40hp, my thinking was running it at half power should give it plenty of headroom for heat. It's rated 120v 120A continuous. And now that I've actually written that down and done the math, that's like 14.4kw. Those guys must totally just pull these numbers out of their...

I bought a cycle analyst but didn't have the shunt when I ran my test so I have no idea what kind of current I was pulling when it flamed out. Most of the components I'm finding seem to be targeted for the RC market. I was hoping to tap some of the experience here for something a step up. I was thinking my immediate need was for a motor control that could handle 100 amps continuous, now I'm starting to think I'm back to square one

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Re: motor glider project

Post by amberwolf » May 11 2020 11:57am

If you can keep them cool enough, many motors can handle a lot more power than their size might indicate, at least for short runs. That's one way the sellers "justify" their ratings in the RC world, where battery size limits runtime severely.

But cooling the motor means forcing air over it, whcih means diverting air from smooth flow around the plane. :( If the motor is completely exposed directly to the airflow in the propwash, and the prop is high speed, it can work well enough. But that makes for worse gliding aero.

Ducting air into the motor housing (keeping aero more intact when not running it) using high speed fans or just fanblades on the motor shaft itself, and well-designed intakes and outlets in the housing, is probably a better option for a glider. Might even be possible to make cable-operated covers for the intakes/outlets to reduce their aero impact during gliding (though the prop itself is going to make more drag by far than they would, even if you can feather it flat).


Another issue with motor ratings is that power output is RPM-dependent. So you'd probably want to see the dyno plot for the motor you want to use, to see if it can produce the power you need at the RPM you need, or if that is going to overload it.


There are places like Joby that make good motors with realistic ratings, according to those that use them; I *think* that was the kind Farfle used.
EDIT: no, looks like he was using a Zero motorcycle 75-series.
viewtopic.php?f=38&t=89043
but that gives you another option branch--used EV motors....



There are good controllers for the high current range...but you might also need a high ERPM range, depending on the specific motor you use, and whether you use a gearbox to gear down the motor speed for the prop, or directly drive the prop with it, and what kind of prop speeds you end up needing.

If the ERPM isn't too high, you may be able to use things like used EV controllers, with their brain replaced with something like a Lebowski brainboard, or something off the openinverter project, etc., depending on how far into the DIY realm you're willing to go. This projec helps show how that can be done, once it's finished:
viewtopic.php?f=30&t=105711




Another option is brushed motors. Not as efficient as brushless, so larger for the same power application, but there are some high-power motors and controllers out there relatively cheap in the used market. However, most of the big brushed motors are for ground-based applications in which size or weight is not a limitation.

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Re: motor glider project

Post by amberwolf » May 11 2020 12:20pm

Some things to think about regarding power, efficiency, waste heat, and specifications:
carbon dragon wrote:
May 11 2020 11:24am
The motor I bought is rated 30kw which I think should be about 40hp, my thinking was running it at half power should give it plenty of headroom for heat. It's rated 120v 120A continuous. And now that I've actually written that down and done the math, that's like 14.4kw. Those guys must totally just pull these numbers out of their...
FWIW, these are the specs listed on that linked page, edited to just electrical :

Voltage(V):
120V
Output Power:
30KW
Continuous Current(A):
150A

Efficiency:
88%
MAX AMP::
400A


ESC:
120V 500A
MAX VOLT:
120V
So if it was running at 120v, 150A, that's 18kw. The efficiency listed is 88%, which is probably the peak efficiency, since that changes depending on load and conditions (you need a dyno chart to really know for sure what it is in your specific usage). Being generous and using that as the actual efficiency, that means 88% * 18000 = about 15.8kw to the prop, and the rest is wasted as heat.

That's about 2.2kw as heat, right there (18 - 15.8). If there's not enough airflow, it stays in the windings, heating them up. (some flows into the stator and casing thru conduction, but this takes time...more than a minute).



If the current was even higher at the time, say, near the max that the ESC could produce, let's be generous and say it's at it's rating ;) , that's 120 * 500, or 60kw. At least 12% of that is going to be heating the motor (probably a lot more, because you're well beyond the continuous rating of the motor), so that'd be at least 0.12 * 60000 = 7.2kw of just heat. I would guess it is up to twice that.

Stuff that glows red hot, *in airflow*, in a hair dryer or heatgun, is only using a few hundred to a thousand and a half watts....


Realistically, during startup, it's going to be very low efficiency, so if that takes any appreciable time, the heat generated is MUCH greater. It shouldnt' take long to spin up...but if it does....


If the loading of the prop on the shaft decreases the speed enough from the unloaded speed of the motor at the same input, it also decreases the efficiency, while increasing the current draw, which increases the wasted power as heat.


So cooling the motor, even at "low" power usage, is essential. That will be true for any motor, but the lower it's efficiency at the speed and loading you're using it at, the more important it is.


Some motors are instrumented with temperature sensors in the windings themselves, so you can either have the controller monitor that and shutdown or throttle back if it's too hot, or you can manually monitor and decide what to do (probably better in a plane). You can add sensors to any motor relatively easily if there is space in it's wiring pass-thru for some very thin (30g-26g) wire pair(s).

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Re: motor glider project

Post by carbon dragon » May 11 2020 2:44pm

Lots of info there to chew on. I already had some ideas on vents to open and close so I think I could get quite a bit of airflow through the motor. I'm limited to a 36 inch prop so I can run it direct drive on this motor at 5000 RPM without it going supersonic. I still need to educate myself on matching motors and controllers and you have given me a couple of other rabbit holes to dive into. Thanks, I appreciate you taking the time to give me such a through answer.

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Re: motor glider project

Post by Hillhater » May 11 2020 7:10pm

Keep in mind as you work through th motor / controller requirements, that you will need a compatable battery pack that can supply the power,.. volts and Amps, ..for as long as you expect to need it.
And , more power or longer run time means a larger, heavier pack.’’(as well as many more $$$’s)
And ..i suspect weight is not something you want an excess of..
So , be aware if you overspec the power or runtime, you will have more pack weight to carry .
As a very rough guide, ..a pack able to supply 20kW for 15 mins (??) would be at least 45-50kg
Apply your own power, time, and safety factors to get a idea of what weight you are looking at carrying.
......the pack will also likely be the most expensive item in the electric drive system ! :bigthumb:
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Re: motor glider project

Post by JackFlorey » May 11 2020 9:51pm

carbon dragon wrote:
May 11 2020 2:44pm
Lots of info there to chew on. I already had some ideas on vents to open and close so I think I could get quite a bit of airflow through the motor. I'm limited to a 36 inch prop so I can run it direct drive on this motor at 5000 RPM without it going supersonic. I still need to educate myself on matching motors and controllers . . .
Keep in mind that that's only half the battle. Matching the battery to the load will also be important. Depending on your C rate discharge you're going to want different types of cells. For 5C (i.e discharging a 3kWhr battery at 15kW) you'll want a very different battery than if you are discharging at 1C. The good news is that due to the proliferation of EV's and ebikes there are cells optimized for several different C rates.

BTW is this Jim Maupin?

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Re: motor glider project

Post by carbon dragon » May 12 2020 9:14am

...and the more weight in batteries the bigger motor you need to get it all into the air air. When it comes to flying, weight is your enemy. The first page in the builder manual says if you are considering adding something to the glider not in the plans, first grab it and hold it at arms length, let it go, and if it falls don't add it to the glider.

this is a Jim Maupin designed glider, yes

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Re: motor glider project

Post by helno » May 12 2020 3:42pm

I'm still working on an EV conversion of a single seat motorglider.

viewtopic.php?f=38&t=89000

Got a motor and ESC but am still working on a battery. A Zero motorcycle battery would probably be perfect but there are not many in Canada so not many available on the scrap pile.

Something else you could look into if the single large motor doesn't work out is do two smaller motors mounted on the wings like a Lazair ultralight. Lets you run smaller props and you have more options as far as motors and speed controllers go.

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Re: motor glider project

Post by carbon dragon » May 13 2020 7:11pm

The deeper I dig into this, the more I'm tempted to bite the bullet and go with the off the shelf package, I already have a significant investment in what is appearing to be a dead end. There is an outfit in Germany that builds electric power systems for small aircraft and has everything from motors and controllers to folding propellers. And they are very proud of them...

https://www.geigerengineering.de/en/avionics/products

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Re: motor glider project

Post by Hillhater » May 13 2020 8:59pm

Have you managed to estimate your required power and run time for the system.
That will be a key starting point to which ever way you decide to proceed,.DIY or kit purchace. !
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Re: motor glider project

Post by carbon dragon » May 14 2020 7:44am

I would need the equivalent of a 20-25 hp motor which would give me about a 500 feet per minute climb rate, enough to be safe. With that I could get high enough to shut off the power and soar with thermals after a 5 - 10 minute climb. Having enough reserve to be able to repeat that a couple more times would be nice but not a requirement. Gieger proposed a 64 ah battery ($3600...ouch) and a 16kw motor which would give me the ability to fly for over an hour under power.

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Re: motor glider project

Post by Hillhater » May 14 2020 8:24am

You may want to get a second opinion on that.?
Their system seems to be a 50v (approx) nominal , so that 64Ah battery would give 3.2 kWh max capaxity.
Your 10 min climb out at max power would require nearly 3 kWh alone,..leaving nothing for further cruising or repeat climbs.!
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Re: motor glider project

Post by carbon dragon » May 14 2020 7:43pm

I had to educate myself on how to calculate runtime. I probably missed something but I came up with a little less than 10 minutes of full power. I'm sure to advertise the best numbers they are calculating full power only until you gain a few hundred feet and then throttling back, but it seems even the Germans are pretty optimistic when it comes to publishing numbers. (looking for the "your mileage may vary" fine print...)

I was thinking I may buy everything but the battery from them anyway. It looks like you can build battery packs and buy BMS systems to keep it all balanced. LIPO cells would not be quite as energy dense but would be lighter. If you buy quality components, can you do that safely? Seems like it would be much cheaper

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Re: motor glider project

Post by Hillhater » May 14 2020 9:06pm

Without asking them, but im pretty sure they are using LiPo/LiCo cells...most likely Tesla style 18650 or 21700 cylindricals ) assembled to give a 52/54v, 64 Ah , 3.2kWh, pack. (15kg is typical for such a pack)
Of course you could DIY build a similar pack using approx 300 cells (at approc $1500-$2000 worth). Interconnectors, BMS, fuses, etc etc.....its a lot of skilled, careful, work. Not to be undertaken lightly for an aircraft pack.
..and , as i mentioned previously, i suspect you will need at least double...possibly 3x, that battery capacity ! :shock: ... depending on your run time requirements, reserve , etc.
There are many pack build threads here on ES, you may want to review some of those before you decide what to do, also several members do offer pack building services, and component kits to use for pack builds
EG..check the last few pages of this..viewtopic.php?f=31&t=38252
There are also options of using modules from EVs (Volt is a good candidate) which may be more practical.
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Re: motor glider project

Post by kubark42 » May 15 2020 7:27am

carbon dragon wrote:
May 14 2020 7:44am
I would need the equivalent of a 20-25 hp motor which would give me about a 500 feet per minute climb rate, enough to be safe. With that I could get high enough to shut off the power and soar with thermals after a 5 - 10 minute climb. Having enough reserve to be able to repeat that a couple more times would be nice but not a requirement. Gieger proposed a 64 ah battery ($3600...ouch) and a 16kw motor which would give me the ability to fly for over an hour under power.
How did you determine this power rating? Check my math, but my first-order analysis shows a smaller motor might be reasonable.

I don't remember the Carbon Dragon's MTOW, but I guess it's around 155kg if it's an ultralight. Allowing for a 26:1 glide ratio at 155kg, this gives 155*9.81/26 = 60N of thrust required for forward flight. At 22kts (11m/s), that's 11*60 = 660W for steady cruise drag.

Adding climb into the equation, at 2.5m/s (~500fpm), that's an extra 2.5*155*9.81 = 3.8kW. So the amount of net energy to impart onto the airframe is 4.46kW. Allowing for prop inefficiency at 65%, that means 4460/0.65 = 6.86kW shaft power. Allowing for a motor/ESC at 90% efficiency (which should be very easy), 6860/0.90 = 7.62kW total power.

You know your numbers better than I do, but it does seem like a 15-20kW motor is massively overpowered. Is the over-speccing just for cooling purposes?

Also, a 500fpm climb at 22kts seems like an enviable climb slope of 10 degrees. I wonder if you wouldn't be perfectly happy at 300fpm? Within 30s of takeoff you're at a very safe 150', which gives you 90 seconds of flight time in case of motor failure. This reduced climb rate would only require 3kW airframe power, or ~5kW electric power. At 48V, that's a paltry 100A controller.

You also only require half the weight in batteries and motor. That's a nice virtuous spiral if you can get into it!

At these low power levels, you're in a sweet spot for non-manned aviation scale flight hardware. IMO R/C hardware is a better fit than full-scale stuff, the guys at rcgroups.com are using bigger motors with higher power and being much harder on them.

For props, check out MagCAD and order some of their COTS 36x15 folding props. The price is awesome, the service is impeccable, and the quality can't be beat. MacCAD props are flying on some of the world's cutting edge manned e-planes. If 15" pitch doesn't work for you, you can machine a yoke adapter to advance the pitch a few degrees without issue. They do wind-tunnel testing and advanced simu, which shows a good fit for the RPM you are looking at.

BTW, I have heard that Geiger's motors are great, but that their speed controllers are not. Since, as I understand, the two come matched you want to be careful and make sure you do your homework if you ultimately settle on them.

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Re: motor glider project

Post by carbon dragon » May 15 2020 3:46pm

I am working to get a better understanding of the theoretical numbers for all of this, calculated thrust, runtime, etc, but I'm afraid at this point I[m still seriously lacking. I was basing my power requirement on experience with similar gliders to mine. I've flown an Aerola Alatus. It's empty weight is almost identical to my glider (80kg unpowered, 115kg powered), but the it's performance is slightly less. With a 20hp 2 cycle motor (15kw) I got about 2 m/s (400 fpm) climb. I saw an electric Archaeopteryx fly. It's performance specs are almost identical to mine but it is about 25kg lighter. I'm not sure if it had the 15 or 18kw motor but they claim 2.5 m/s at 75 kph.

I agree that at this weight and performance, it seems that there should be large RC power setups that would work. I've flown gliders for a long time so I'm used to always having landing options and I could tolerate a less than perfectly reliable system. A battery fire is something different. It's hard to imagine a more horrible situation to be in, hundreds or thousands of feet in the air and on fire. I had a friend that made an electric power system for his hang glider (less than half the performance of my glider) using RC components and it did surprisingly well. Seeing his results and doing some research is what gave me the confidence to make the investment.

I just recently found the MagCAD folding props. I didn't see the 36x15 but they have a 3 bladed 34.2x22.5 that looked interesting.

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Re: motor glider project

Post by kubark42 » May 15 2020 6:50pm

magcad.de has the 36x15 prop a little down the page. And in a few weeks, I'll have four of them. ;) Each blade is 75-78g, so it's all quite impressive.

My theoretical numbers don't take into account prop/airframe interaction, and this is a big source of mystery for me. I don't know if it's a few % or if it's quite significant. This detail might be the devil for why the Archaeopteryx claims 2.5m/s, although at 40kts they're clearly going for a speed significantly above stall. That's probably worthwhile for you to consider as well, since you don't want to be slow and nose-high on climb-out.

I would severely discount any ICE claim of power. Those are best case numbers for STP at sea-level, for a perfect-shape engine.

I could not agree more about a battery fire. Of course, we're all wearing parachutes, but who really wants to have to step out of a plane to jump? And anyway, there are battery chemistries which are far, far safer. Personally, I would not skimp on battery price and I would not go for energy density. I'd rather carry a few hundred grams extra and pay a few hundred dollars more than take a risk of fire.

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Re: motor glider project

Post by Hillhater » May 15 2020 6:58pm

.....at this weight and performance, it seems that there should be large RC power setups that would work. I....
I am sure there are.....
But at those power levels, it is at the extremes of RC systems and may not be as low cost as you hope.
Also, RC components are not designed with safety or reliability as a primary concern.
Search some of the threads where ES members have attempted to use high power RC motors and controllers for alternate drive systems....many end in smoke and disapointment with only a few well developed components surviving regular use...notice even Geiger use duplicate components (controllers ?) where practical.
Chose very carefully.!
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Re: motor glider project

Post by kubark42 » May 15 2020 7:08pm

Hillhater wrote:
May 15 2020 6:58pm
.....at this weight and performance, it seems that there should be large RC power setups that would work. I....
I am sure there are.....
But at those power levels, it is at the extremes of RC systems and may not be as low cost as you hope.
Also, RC components are not designed with safety or reliability as a primary concern.
Search some of the threads where ES members have attempted to use high power RC motors and controllers for alternate drive systems....many end in smoke and disapointment with only a few well developed components surviving regular use...notice even Geiger use duplicate components (controllers ?) where practical.
Chose very carefully.!
You make good points. Consider, though, that If it's under $5000 in aviation, it's a positive steal!

If you can use one of Neu Motors standard 80xx motors then you're looking at <$500 for the motor. If you can use one of MGM Compro or APD's pro motor controllers (no skimping on the ESC!), then you can hope for ~$1000 for the power train. Another $2.5k for batteries (again, no skimping on quality!) and then $300 for the prop and hub. So it's reasonable to electrify a glider for <$5000 (not including dev efforts, broken prototypes, etc...).

Or, you could get a standard APD controller for $200, and get some recovery batteries from crashed cars ($100/kWhr). Use a rando $100 prop and a MAD Components motor and you could try to get away with <$1k.

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Re: motor glider project

Post by Hillhater » May 15 2020 8:04pm

There are many options, but As i said,...chose carefully, get independent verification of performance and reliability.
Most RC gear is just poor quality compared to other aviation equipment.
And again , you are not going to get much battery capacity for $2.5k.
But until the power and duration requirements are better defined, its not really possible to estimate costs or weight. However, it pretty certain the battery will be the most critical, expensive, and heavy, component in the drive package
I am no expert on flight power requirements, but i suspect an 80 kg airframe, with an adult pilot, and a suitable Edrive power flight package, ....is likely to be more than 155kg ?
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Re: motor glider project

Post by carbon dragon » May 16 2020 8:44am

Some of the reasons I think an ultralight glider is the perfect platform for something like this: Light weight and very efficient so power requirements are much less than a conventional airplane. It's a glider so you are always flying as if you are not going to find that next source of lift and may have to land, so a power failure is not a big deal unless you put yourself in a situation where you needed power to escape a bad situation (dumb) or if the failure resulted in a fire. Minimally you need enough power to launch and get high enough to thermal, 2000 feet will do it on a good day, so in my case 16kw motor and a 3.1kwh battery would probably work. I still haven't decided whether to pursue another ESC for my motor, or if that would be throwing good money after bad. I've written to the manufacturer to see if there are charts available that plot power, rpm, current, etc something in retrospect I should have done before buying. The folding propeller looks excellent but there is a whole 'nuther rat hole. What size prop, what pitch, how many blades to get the most from the motor? $5k for a relatively solid DYI system is pretty good, but that would only be if you selected everything properly the first time around. I've spent hours on Endless Sphere and have already greatly increased my knowledge but also made me more aware of how much I don't yet know and whether I can cost effectively build my own system.

Hillhater, do you do consulting work? :-)

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Re: motor glider project

Post by kubark42 » May 16 2020 11:33am

Hillhater wrote:
May 15 2020 8:04pm
There are many options, but As i said,...chose carefully, get independent verification of performance and reliability.
 Most RC gear is just poor quality compared to other aviation equipment.
 And again , you are not going to get much battery capacity for $2.5k.
But until the power and duration requirements are better defined, its not really possible to estimate costs or weight. However, it pretty certain the battery will be the most critical, expensive, and heavy, component in the drive package
I agree much of R/C equipment is not of the highest quality, but it's also easy to find extremely high quality components from companies with decades of experience. Scale R/C pilots aren't quite as sensitive to crashes as human pilots are, but they don't want to see $10k models destroyed because of failing hardware so they're pretty careful about quality. And because of the volumes at which they buy, there's a lot more edge-testing going on than for certified-aviation hardware.

Relatedly, and surprisingly, longevity is actually not as important here as it looks at first glance. The lifecycle of the propulsion system is likely 25 hours of operation. That sounds low, but it actually works out to several thousand flight hours, possibly more flight hours than the airframes service life (frequently ~6k hrs). The beautiful part about a 25hrs MTBF is that you can do full life-cycle testing in a single day!

You still need quality parts, but you can push them a lot harder without worrying as much about bearing life or fatigue limits. The bigger long-term threats are corrosion, UV aging, embrittling, etc...

Regarding the mission profile, here's the strategy used by most pilots of electric self-launch gliders, especially production craft using the FES system:
  1. Full power to safe altitude (typically 500', but likely half that in the Carbon Dragon performance class)
  2. Continuous climb power to 1000'
  3. Reduced climb power while hunting for a thermal
  4. Nominal power while in first thermal till 3000'
  5. Power off
The full power phase lasts ~30 seconds, and total motor operation lasts 3-10 minutes.

Pilots flying the miniLAK FES report typically using 20% of their 4.2kWhr pack per flight. Their MTOW is 350kg with a 22kW motor and they report around 400fpm climbs. (There's a recent rec.soaring discussion with a strong consensus that no one is complaining about self-launch climb rates.)

Translating to the Carbon Dragon-class weight, and allowing for a heavy pilot and propulsion system, it's reasonable to think that a similar climb profile would require 400-500Whr.

@carbon dragon, you're spot on for your motivations of using an ultralight. Barring fire, the sharp edge of failure is very, very dull. Costs at this power and energy level are not high, and the powered ePPG community has a very similar power and operation scope so you don't have to stray too far from a known-good path. You're not alone!

BTW, if you haven't already started looking at thermal issues, esp. with regards to the motor operating temperature, I strongly encourage you to do a dive into this before going too far. Severe thermal issues are almost intractable without a full redesign. With anything other than exceptional cooling, thermal issues, not battery power, are the bottleneck.

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carbon dragon   1 mW

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Re: motor glider project

Post by carbon dragon » May 16 2020 7:35pm

I knew this project was getting too easy, throw me another wrench... :-)

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