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 23, 2019 #81

    12notes

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    Not in that video, there isn't. The 3x battery pack is a untested projection, not evidence of any real world flight.
     
  2. Aug 23, 2019 #82

    RonL

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    I seem to be the main chef cooking pies in the sky, but in my opinion, batteries are just about good enough as they are.
    Applying power to overcome friction and then rejecting the thoughts of how to apply friction to make power, seems to be a mind twister that only a few seem able to entertain for even a short time.
    I think you might be peeking behind the curtain a little bit.

    I have stepped back a little because everyone wants to talk about only what is on the shelf right now.
     
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  3. Aug 23, 2019 #83

    Speedboat100

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    Don't forget the mexican theoretical physicist Miquel Alcubierre:
     
  4. Aug 23, 2019 #84

    stanislavz

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    A live example from another converted airplane (Just not 220 km/h with 55 minutes endurance.. ):

    Electric aircraft development of the basic design, first flown on 1 August 2011. Powered by 26 hp (19 kW) electric motor running from a 4.7-kWh Kokam battery. The aircraft weighs 113 kg (249 lb) empty and has a 55 minute endurance on a charge. The aircraft has achieved a top speed of 220 km/h (137 mph).

    source https://en.wikipedia.org/wiki/Colomban_MC-30_Luciole#cite_note-EAA10Aug11-10
     
  5. Aug 23, 2019 #85

    Speedboat100

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    Maybe able to travel 150 km tops ?
     
  6. Aug 23, 2019 #86

    Speedboat100

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    Only way to ever accomplish anything wortwhile in electric flying is to be able to load the craft more than 3 times its empty weigh...like the Voyager by Scaled Composites.

    Small/light pilot is an asset too.

    https://en.wikipedia.org/wiki/Rutan_Voyager
     
    Last edited: Aug 23, 2019
  7. Aug 23, 2019 #87

    stanislavz

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    Do not know. 4.7 kwh of battery, is just ~ 25 kg...

    Rutan bird is super, and is close to Zwilling b109z in sailplane shape as can be.. (why not giant sailplane just ?)

    I am from lucky country, where we are able to include battery into fuel weight, to totall 135 kg for unregulated class. Officially..
     
    Last edited: Aug 23, 2019
  8. Aug 23, 2019 #88

    Dan Thomas

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    Doubling the RPM of an electric motor doesn't double its HP. Inductive resistance goes up with RPM so that the max torque is generated as the motor stalls. The electron flow in windings is constantly stopping and reversing; any coil resists that, causing the inductive resistance. There will be some happy RPM where the HP is best so the motor needs to be designed for that RPM. If we want to avoid the weight, cost and failure possibilities of a PSRU, it needs to be designed for direct-drive at the optimum RPM for the best prop for that particular airplane.

    So therefore the airframe has to be designed for the motor, or the motor for the airframe. Just putting together off-the-shelf stuff into whatever airframe is cheap and available is a good way to accumulate so many compromises as to guarantee failure and disappointment and maybe an accident.
     
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  9. Aug 23, 2019 #89

    Speedboat100

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    I have estimated that the present technology with batteries is roughly 7 times less efficient...so a 41 000 km divided by 7 gives 5860 km roughly..that is what Voyager ought to do with batteries. Could it cross the pond to Japan from California ?

    I bet it could..LA-Honolulu-Midway-Tokyo.
     
    Last edited: Aug 23, 2019
  10. Aug 23, 2019 #90

    Speedboat100

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    Ok..let's say that you are right....happy now ?
     
  11. Aug 23, 2019 #91

    stanislavz

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    Not only. You may and have to think differently. ie - 100 hp IC motor is not same as 100 x 1hp Ic motors on reliability and weight. On electric - 100 x 1hp motors may be same or even better..
     
  12. Aug 23, 2019 #92

    12notes

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    From your rc group link. "Testing so far shows that I can expect to have close to 2 hours endurance (turned out to be 1 hr 20 min, so much for tests)"

    Actual flight time 80 minutes, his expectation was 120 minutes. His projections are 50% greater than reality. His "experience" of 3kW being able to sustain 30mph was also way too optimistic.

    And later in that thread, the same person (Dale Kramer) posted:
    "My duration estimate was based on my guess that 3 kw would keep the Lazair in the air. Unfortunately that was probably a low estimate based on Series I and II airplanes that were up to 100 lbs lighter than my Elite Electric Lazair"

    It still seems that batteries are heavy.
     
  13. Aug 23, 2019 #93

    Speedboat100

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    Batteries are heavy...and Lazair is a bit too heavy too to keep it electrified inside Part 103 rule.
     
  14. Aug 23, 2019 #94

    Aerowerx

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    The proper term here is inductive reactance.

    XL=2*pi*F*L

    As you go to higher RPM your drive frequency has to go up (for a fixed number of poles). Consequently the inductive XL reactance goes up. IIRC, the RPM of a brushless motor is related to the number of rotor and stator poles, by a relationship I don't recall at this time. So you, again IIRC, can optimize the number of poles and drive frequency for a specific RPM to reduce reactance.

    Actually, there is no power lost in a pure reactance. It is the resistance of the windings that causes the loss. To avoid the sharp voltage spike when the square wave drive current shuts off (V=L*dI/dT can get quite huge) you can use a step approximation to a sine wave to drive the motor.

    Exactly what I was getting at in an earlier post!
     
  15. Aug 23, 2019 #95

    Aerowerx

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    NO! NO! NO!

    He is talking Warp Drive. I said I wanted a hyperdrive, as in HyperSpace! Not the same thing at all!;)
     
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  16. Aug 23, 2019 #96

    Speedboat100

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    Is that where the spaceballs live ?
     
  17. Aug 23, 2019 #97

    henryk

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    =+8.3 kg level exender,,,
     
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  18. Aug 23, 2019 #98

    pictsidhe

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    At double the rpm, you double the back emf. The solution is to either double the voltage, or halve the number of turns. Copper losses stay the same.
     
  19. Aug 23, 2019 #99

    pictsidhe

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    Ok, I'm out.
     
  20. Aug 23, 2019 #100

    stanislavz

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    But not iron - whey sky rock after certain point. This is 1 point of losses in cheap china motor - to thick lamination.
     

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