Search found 19 matches

by kubark42
Feb 23 2021 10:31pm
Forum: Electric Aircraft
Topic: Battery pack selection for self-launching glider
Replies: 7
Views: 218

Re: Battery pack selection for self-launching glider

A very marginal battery could end up not working at all after losing just 20% capacity. So cutting it really close could result in a very short usable life span. Then again from what I understand once you've taken off a sail plane can climb very efficiently. Throttling down once you've reached a sa...
by kubark42
Feb 22 2021 1:43pm
Forum: Electric Aircraft
Topic: Battery pack selection for self-launching glider
Replies: 7
Views: 218

Re: Battery pack selection for self-launching glider

Finding a way to eject the pack in event of a fire is much easier with the smaller pack. Keep in mind that using Lipo at high drain will reduce pack life way down. But then again how many flights per year are you going to get? As much as I would love to eject a burning pack, that's probably not in ...
by kubark42
Feb 22 2021 11:13am
Forum: Electric Aircraft
Topic: Battery pack selection for self-launching glider
Replies: 7
Views: 218

Battery pack selection for self-launching glider

I'm converting an AC-5M to electric, and I've been struggling for a while now to figure out how I want to do my battery pack. I keep coming back to LiPo as the right solution. When I look at the existing eGlider solutions, I've come to realize that they have unnecessarily large packs because they ne...
by kubark42
Feb 22 2021 10:31am
Forum: Electric Aircraft
Topic: Need advice about BLDC
Replies: 1
Views: 84

Re: Need advice about BLDC

I have a bunch of U-8 motors, so maybe can help. Want to tell us more about your project, and why the U-8 is not the right fit for it?
by kubark42
Feb 17 2021 6:27pm
Forum: E-Scooter and Motorcycle General Discussion
Topic: Looking for featherweight geared hubmotors, >10kW
Replies: 15
Views: 557

Re: Looking for featherweight geared hubmotors, >10kW

That's so very slow for a prop. What gigantic diameter are you working with? 1.92m @amberwolf, the slowest props are the most efficient. Prop dia. is largely limited by ground clearance, so usually you have to compromise on dia so you don't have obnoxiously large landing gear. You get the power by ...
by kubark42
Feb 14 2021 1:39pm
Forum: E-Scooter and Motorcycle General Discussion
Topic: Looking for featherweight geared hubmotors, >10kW
Replies: 15
Views: 557

Re: Looking for featherweight geared hubmotors, >10kW

I wouldn't rule out using multiple motors on the same shaft to get the desired power output. It's the torque that's the limiting factor. For reasons which I don't fully understand-- could be physical, could be economic-- there are no lightweight, high-efficiency, high-torque, low-power motors on th...
by kubark42
Feb 14 2021 12:52pm
Forum: E-Scooter and Motorcycle General Discussion
Topic: Looking for featherweight geared hubmotors, >10kW
Replies: 15
Views: 557

Re: Looking for featherweight geared hubmotors, >10kW

Thanks for the responses, everyone. I feel bad about discussing too much aviation in the motorcycle subforum, but I'm really, really happy to discuss the airplane more over at https://endless-sphere.com/forums/viewtopic.php?f=38&t=108791! So to keep myself from drifting, I'll just say that I've ...
by kubark42
Feb 12 2021 8:56pm
Forum: E-Scooter and Motorcycle General Discussion
Topic: Looking for featherweight geared hubmotors, >10kW
Replies: 15
Views: 557

Re: Looking for featherweight hubmotors, >10kW

Good questions. I try to avoid too much initial detail so responses don't get bogged down in trying to address readers' perception of my problem. My application is to swing a propeller, and I'm asking in this subforum because the torque and RPM requirements are similar to motorcycles. At the time I ...
by kubark42
Feb 12 2021 10:02am
Forum: E-Scooter and Motorcycle General Discussion
Topic: Looking for featherweight geared hubmotors, >10kW
Replies: 15
Views: 557

Looking for featherweight geared hubmotors, >10kW

I'm looking for the lightest of lightweight geared hubmotor options in the 10-15kW range. My particular application is one where I need high torque (~100Nm) at low RPM (~1300) in a COTS package, and hubmotors really fit the bill. However, the motors I've found so far seem to be trending around the 1...
by kubark42
Jan 06 2021 4:45pm
Forum: Motor Technology
Topic: Extracting maximum power from a BLDC
Replies: 2
Views: 505

Extracting maximum power from a BLDC

In theory, and somewhat in practice, a motor's power limit is determined only by its ability to (1) keep cool and (2) not fly apart under centrifugal loads. I want to know how to apply theory in order to determine on a case-by-case basis how to push a motor past its published specs. Assuming I have ...
by kubark42
Jan 06 2021 3:17pm
Forum: Electric Aircraft
Topic: Self-launching sailplane conversion
Replies: 23
Views: 995

Re: Self-launching sailplane conversion

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 h...
by kubark42
Oct 07 2020 9:03am
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

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. ...
by kubark42
Sep 28 2020 8:40am
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

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 high...
by kubark42
Sep 25 2020 10:32am
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

@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 cl...
by kubark42
May 16 2020 7:48pm
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

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 ...
by kubark42
May 16 2020 11:33am
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

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 req...
by kubark42
May 15 2020 7:08pm
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

.....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 reliabi...
by kubark42
May 15 2020 6:50pm
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

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 % o...
by kubark42
May 15 2020 7:27am
Forum: Electric Aircraft
Topic: motor glider project
Replies: 44
Views: 2641

Re: motor glider project

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 ti...