How far are we from the perfect electric "homebuilt" ?

Discussion in 'Hangar Flying' started by Speedboat100, Aug 20, 2019.

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  1. Aug 21, 2019 #21

    Speedboat100

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  2. Aug 21, 2019 #22

    stanislavz

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    Sad and angry. Again you have to think different in e world.

    As in best ant safet airplane for me - pazmany pl2 - place batteries in wing tips. Not in wing spar, nor in bucket under you seat. Or in front of you.

    If it will burn - you want stop it or have any chance, except of full eject seat.
     
  3. Aug 21, 2019 #23

    Speedboat100

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    What if it is "just" a cooling problem ?
     
  4. Aug 21, 2019 #24

    Speedboat100

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    One thing is for sure...Lazair excels as it uses only 3 KW of electricity in level flight...in cruise. This concept could take you a long way..unless the pilot wasn't hanging underneath the wing and causing a tramendous drag.

    So a light weight plane with some sorta aerodynamic pod/hull for the pilot could possibly increase the speed by 100 %...and then 2 hrs flying time would yield 300-400 km distance.
     
  5. Aug 21, 2019 #25

    stanislavz

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    Not only cooling. Cells are not identical. Some is weaker, some is stronger. Most bms do limit upper charge - so all cells behave as weak one. And going into deep discharge - may over discharge some cells and gradually form metallic lithium crystal, which reaps its way through separator. And you have fire.
     
  6. Aug 21, 2019 #26

    Hephaestus

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    I still like the battery pod concept, off the wing or fuselage like a long-ez style baggage pod. Run fire protection style fusible links so there's an automatic x° mechanical release, and physical seperation from structure if release fails. Mount it on CG so when it sheds you drop the weight and are otherwise unaffected.only problem is the Anderson plugs likely would hold the pack, needs to be some kind of breakaway battery contact that I don't currently see in existence yet.

    Even with billions invested even Tesla still has issues. All the electric ev's have had battery fires for one reason or another.

    It's all about risk mitigation.
     
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  7. Aug 21, 2019 #27

    Aerowerx

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    What happens if you are on an electric bicycle and the PSRU fails?

    What happens if you are at 2000 feet above ground and the PSRU fails?
     
  8. Aug 21, 2019 #28

    Aerowerx

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    Why?

    You still need the same power delivered to the prop. The reason for a PSRU is to match the power curve of a gasoline engine to the power required at the prop. A brushless DC motor can be (theoretically, anyway) designed to provide just about any RPM at any HP desired. No need for a PSRU.

    If you have a non-optimum brushless dc motor and then add a PSRU, you are loosing power between the motor shaft and the prop. And how much will both of them together weigh?

    Disclaimer: I am not a motor expert. This is just from what I have read about brushless motors.
     
  9. Aug 21, 2019 #29

    Speedboat100

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    The benefit ought to be more than the loss for the PRSU gearing.
     
  10. Aug 21, 2019 #30

    12notes

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    This number is unsubstantiated, but you keep claiming it for some reason. It should be using a lot more than 3kW (4HP) , 11% of maximum power, while in cruise. Do you have any evidence to back this number up?
     
  11. Aug 21, 2019 #31

    stanislavz

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    Just my opinion :

    [​IMG]

    And for 1 to 12 glide ratio, it will give you maximum weight of airplane of 12 * 16 ~ 200 kg. This is just an example, it is only static thrust, and it will decrease with speed - so as required power. Just an fast example.
     
  12. Aug 21, 2019 #32

    Speedboat100

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    They claim it is 3 KW and also their batteries and their endurance vs weight confirms it. Might be a tad higher with more batteries.

    HPAs only use 250 watts continuous.
     
  13. Aug 21, 2019 #33

    Speedboat100

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    Better glideratio certainly helps alot. Heavy sailplanes can climb with just 20 kg of static thrust.
     
  14. Aug 21, 2019 #34

    Dan Thomas

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    Well, we've been waiting for 55 years now already...

    [​IMG]
     
  15. Aug 21, 2019 #35

    Speedboat100

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    Indeed we have..many things.
     

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  16. Aug 21, 2019 #36

    stanislavz

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    I do take 1 to 12 glide ratio from wiki for lazair. So far, for me it is just mathematical optimisation - for any wanted parameter, as maximum range or speed or endurance.

    Henryk posted some time ago, a german flying wing with enclosed pod for pilot with 1 to 25 glide ratio... So it should cruise with 1.5 kw of power..
     
  17. Aug 21, 2019 #37

    pictsidhe

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    The torque of a motor and resistive power loss is set by it's size. The speed is set by how fast it can spin before it comes apart. Running far slower than it can safely run will result in far less power than it is capable of. yes, higher speed means more iron losses. But low loss cores and a little derating takes care of that. Double the RPM, you get nearly double the power

    Long life gearboxes have been built for over a century. I suspect that RC gearbox builders aren't aiming for long life...

    25:1 glide ratio at how slow?
     
  18. Aug 21, 2019 #38

    RonL

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    Last edited: Aug 22, 2019
  19. Aug 21, 2019 #39

    12notes

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    Lazair has made no such claim, you have not substantiated this any time you've mentioned it. Their endurance for the e-Lazair on their website is about an hour, their endurance doesn't agree with your claim.
     
  20. Aug 21, 2019 #40

    henryk

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    40 (wing) + 30 (fuselage with motor) +100 (pilot+gas)=170 kg

    170/25=7 kG thrust...

    70 N x 30 m/s=2100 W= circa 2 kW !
     

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