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I'm trying to replace the 20hp gasoline engine in my ultralight aircraft (trike) to 10kw BLDC motor, asking to know if the 10kw BLDC motor will work

Motor+battery weight, is less than the actual engine weight.

Ben Fabulous
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    How is this different from the very similar 4 or 5 questions you previously asked? On at least two of which you've received answers. –  Mar 19 '22 at 17:19
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    two observations: 1.) 10kw, are only 14hp, so you might end up with an underpowered aircraft. 2.) https://www.youtube.com/watch?v=hp7JcmwKQcU – U_flow Mar 19 '22 at 17:24
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    10kw is 13 HP. If you were flying on 20HP, 13HP is going to be pretty doggy. You need a 15kw motor. Hobby King sells a 15kw outrunner that would work, but if you want to use it direct drive with a decent sized prop you'd have to rewire the windings to optimize it for low RPM. As a general rule, HP for HP and pound for pound, you will have 1/3rd the endurance of gasoline with electric power. LioN batteries are really not adequate except for short flights or motorgliding. They aren't any good for electric cars either, really, when you only get a 3rd of the range of a gas tank. – John K Mar 19 '22 at 17:45
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    But, but, electricity has no emissions, so it has to be better, right??? – Ralph J Mar 20 '22 at 00:04
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    Well, I suppose, if most electricity didn't come from nat gas and coal. And nobody has even thought about the nightmare of disposing of millions upon millions of LioN batteries that wear out. I think we're better off with gasoline until fully recyclable batteries with 3 times the current power density come along. Then I'm all in. That being said, I'd love to have an electric ultralight motorglider right now. That's its niche, at this point. – John K Mar 20 '22 at 00:14
  • @JohnK "nobody has even thought about the nightmare of disposing of millions upon millions of LioN batteries that wear out" Absolutely nobody. Apart from tens of companies (just one example https://www.fortum.com/products-and-services/fortum-battery-solutions/recycling/lithium-ion-battery-recycling-technology ) plus: do you really think that refining produces no waste? the slop oil residual from refinery is a waste, that is then reprocessed to extract whatever is valuable from it ... exactly like from the exhausted lithium battery. – EarlGrey Mar 23 '22 at 10:47

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What you need to do converting from gas to electric is to look at peak rpm for a given prop, and endurance.

HP comparisons may be meaningless because gas motors have much lower max rpm, and most aircraft need much more thrust taking off and climbing than cruising in level flight.

Also, extremely important to include glide ratio as a measure of thrust requirement for your airframe. Generally, peak thrust requirement will be around 2x Vbg drag. An electric motor should give you more, but endurance will be another major concern.

Recently a personal electric aircraft came to market that could hover, but with endurance of less than 1 hour!

So, please be aware there is no direct conversion and both gas and electric have their virtues. It may be possible to keep the gas with an electric booster. This would enable a much smaller gas motor. Another approach would be the "diesel-electric", using a gas motor simply as a generator, greatly reducing battery size.

But for the personal ultralight, peak rpm (thrust) for your prop may be adequate with a lighter electric motor.

Robert DiGiovanni
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It might. This answer shows two graphs from a now dead link, from am article that concluded that a 20 hp electric motor does a better job at powering a hydraulic pump than a 50 hp combustion motor.

Range and endurance will be pretty poor though, unless you use that extension cord.

FreeMan
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Koyovis
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