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

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

Help Support HomeBuiltAirplanes Forum by donating:

  1. Aug 21, 2019 #41

    Aerowerx

    Aerowerx

    Aerowerx

    Well-Known Member

    Joined:
    Dec 1, 2011
    Messages:
    4,899
    Likes Received:
    1,315
    Location:
    Marion, Ohio
    Huh?

    Can you give an example explaining this, with equations?

    So, you are saying that a motor "optimized" to run at, for example, 3000 RPM, going through a PSRU to turn a prop at, for example, 2000 RPM is more efficient than a motor "optimized" to run directly at 2000 RPM???? And weighs less (motor and PSRU)? And is more reliable? (Remember Pops signature: If its not there, it cost nothing, weighs nothing, and is 100% reliable.)
     
    Last edited: Aug 22, 2019
    282ex likes this.
  2. Aug 22, 2019 #42

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,702
    Likes Received:
    1,765
    Location:
    North Carolina
    Electric motors produce torque in direct proportion to the active magnetic area. Take a square whatever of iron surface area, run 1 tesla of flux through it and a number of ampere-conductors. That gives you a force. It is the same if you have 1000 conductors and 1 amp, or 1 conductor and 1000 amps. Rewinding does not change torque potential. The flux density is limited by magnetic core properties and maybe your magnets. The ampere-conductors is limited by space in the core and resistive heating. Power is force times speed. The faster you spin at that force, the more power you produce. A motor that produce 1Nm will need a lot less iron, copper and magnets than one producing 10Nm. yes, it'll need a 10:1 gearbox, but the gearboxes tend be much lighter than DD motors.

    For an example with a low desired output speed and a given power, have a look at e-bike motors. Compare the weight of the direct drive and geared motors...
     
    Norman likes this.
  3. Aug 22, 2019 #43

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe

    Yes either way...but basically those allow a large hole in the middle.
     
  4. Aug 22, 2019 #44

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe
    No cannot give calculations...air resistance comes to play too.
     
  5. Aug 22, 2019 #45

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe
    On the video there is a claim for 2+ hrs endurance.
     
  6. Aug 22, 2019 #46

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member

    Joined:
    Aug 22, 2016
    Messages:
    176
    Likes Received:
    32
    Location:
    Lt
    Yes and no... Just to certain degree. Hub motor are way to slow.

    But on standart thick of silicon iron - you ho up to 100hz of frequency for ok losses. For 0.1mmlamination - this can go up to 300-400hz.

    And how much rpm you will get from 400hz - depends on your poles number. But you have maximum possible force per each coil in any case.

    But.... With e motor, you can make in place of one big prop, 4 smaller. Or 8.. And have much lover prop weight and inertia.
     
  7. Aug 22, 2019 #47

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member

    Joined:
    Aug 22, 2016
    Messages:
    176
    Likes Received:
    32
    Location:
    Lt
    Was thinking, while driving to work - I do like more and more option with 4 small motors and 4 small propeller in place of one big. Or you have one 1.5 m diameter of prop, or 4 with 0.75m - same area, but with 0.75m - you can turn it 2 times more rpm with same efficiency ?
     
    Last edited: Aug 22, 2019
  8. Aug 22, 2019 #48

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe
    Okay...lets keep them simple.
     
  9. Aug 22, 2019 #49

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member

    Joined:
    Aug 22, 2016
    Messages:
    176
    Likes Received:
    32
    Location:
    Lt
    Just an example.. https://en.wikipedia.org/wiki/MacCready_Solar_Challenger

    So, 2-3 kw for cruise should be the target for longer distance with clean air frame..

    Plus https://en.wikipedia.org/wiki/Distributed_propulsion

    Recent analytic and experimental distributed propulsion studies suggest several improvements in aircraft performance.[2] They include fuel consumption efficiency, noise abatement, steep climbing for short take off and landing (STOL), novel control approaches (in particular eliminating control surfaces for roll, pitch and yaw moments), and high bypass ratios. It has also been suggested that smaller propulsors will be cheaper to manufacture and easier to handle during assembly and maintenance.[3]
     
  10. Aug 22, 2019 #50

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe
    Yes..these are only 23:99 USD a piece..have 4 of these to fly at 7.2 KW.

    I bet the propeller are sold at 5-10 USD a piece.

    https://www.banggood.com/N5065-320K...Kit-p-1270024.html?rmmds=buy&cur_warehouse=CN


    Props are cheap too: https://www.amazon.com/Sail-Propeller-USA-Beechwood-Propellers/dp/B01HCBMPI4

    Sorry they use 17x10 props: https://www.amazon.com/Sail-Propeller-USA-Airplane-Beechwood/dp/B07RBZSGC6

    That would make almost 150 usd to engines and props.

    Simplicate and add lightness has to remebered in the designs.

    http://www.houseoffrog.co.uk/gliders.htm
     
    Last edited: Aug 22, 2019
    stanislavz likes this.
  11. Aug 22, 2019 #51

    Aerowerx

    Aerowerx

    Aerowerx

    Well-Known Member

    Joined:
    Dec 1, 2011
    Messages:
    4,899
    Likes Received:
    1,315
    Location:
    Marion, Ohio
    Masses away from the CG like this does bad things to the stability.

    It is better to have masses as close to the CG as possible.
     
  12. Aug 22, 2019 #52

    Aerowerx

    Aerowerx

    Aerowerx

    Well-Known Member

    Joined:
    Dec 1, 2011
    Messages:
    4,899
    Likes Received:
    1,315
    Location:
    Marion, Ohio
    Ok, then. Can you give an authoritative source for this?

    Or an actual working example?
     
  13. Aug 22, 2019 #53

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member

    Joined:
    Aug 22, 2016
    Messages:
    176
    Likes Received:
    32
    Location:
    Lt
    Why ? I do only found for addition flutter possibility if wrongly designed. From wing spar it is life much easier, especially on long wing with high aspect ratio.

    On normal situation with 100% mass at the center of wing of 200 kg and with 25% on sides and 50% at the center - you have half load at center section ? Or think as two airplanes joined by wing tips, with half of wing aspect ratio.
     
  14. Aug 22, 2019 #54

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member

    Joined:
    Aug 22, 2016
    Messages:
    176
    Likes Received:
    32
    Location:
    Lt
    Windage losess

    Windage losses refers to the losses sustained by a machine due to the resistance offered by air to the rotation of the shaft. Windage Losses occurs in electric rotating machines such as motors and generators.
     
  15. Aug 22, 2019 #55

    stanislavz

    stanislavz

    stanislavz

    Well-Known Member

    Joined:
    Aug 22, 2016
    Messages:
    176
    Likes Received:
    32
    Location:
    Lt
    I still do like more flatty motors. "Sqaured" brushless do have to use additional thin ball bearing for any higher load. Here an example with more data in this eppg :

    https://openppg.com/shop/paramotors/openppg-22/
     
  16. Aug 22, 2019 #56

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe

    I don't think I can. But I have one in my wind turbine..that works the opposite..it rews higher than the system rotates to increase the rpms of the generator.

    Planet gear in question looks like this:

    Another:
     
    Last edited: Aug 22, 2019
  17. Aug 22, 2019 #57

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe

    Most motors ever even considered in an aeroplane is 45.
     

    Attached Files:

  18. Aug 22, 2019 #58

    Speedboat100

    Speedboat100

    Speedboat100

    Well-Known Member

    Joined:
    Nov 8, 2018
    Messages:
    653
    Likes Received:
    49
    Location:
    Europe
    In german electric flight explained:

    IC engine produces only 30% of its energy to movement...whereas electric engine 95%.
     
  19. Aug 22, 2019 #59

    12notes

    12notes

    12notes

    Well-Known Member Lifetime Supporter

    Joined:
    Aug 27, 2014
    Messages:
    823
    Likes Received:
    506
    Location:
    Louisville, KY
    You mean at 3:40 or so of that video, where the interviewer says "you were up for over two hours" and the pilot responds "my timer said I was up for about 50 minutes"? The interviewer's mistaken opinion doesn't count as evidence.
     
    Red Jensen likes this.
  20. Aug 22, 2019 #60

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,702
    Likes Received:
    1,765
    Location:
    North Carolina
    Spin recovery;
    1: jetison batteries.
     

Share This Page

arrow_white