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 22, 2019 #61

    Hot Wings

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    Naw. Just suck them in closer to the CG to reduce the polar inertia.

    Now how fast can you spin!:D
     
  2. Aug 22, 2019 #62

    stanislavz

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    Put battery into wingtip with % area of total mass. And jettison it woth wing tip.
     
  3. Aug 22, 2019 #63

    Speedboat100

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    No. See the whole video.
     
  4. Aug 22, 2019 #64

    Aerowerx

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    So the answer to a situation that you may not be in if you did not have the batteries at the wing tips is to eject the batteries??? Then what next, after you recover from the spin?
     
  5. Aug 22, 2019 #65

    stanislavz

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  6. Aug 22, 2019 #66

    Aerowerx

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    Dumb question...

    Is this thread about REAL full size people-carrying airplanes powered with electric motors, about wind generators, or small-scale RC planes?????
     
  7. Aug 22, 2019 #67

    12notes

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    I've watched the whole video twice, there is ZERO mention of 3kW cruise. None. Not ever mentioned. The guy makes some projections on endurance for future modifications, but no actual flights or data. The only actual flight mentioned is "about 50 minutes". The company website states endurance of "about an hour". The batteries they use have worse energy density than lithium ion.

    There is no proof of your claims that the eLazair has an endurance over an hour, Lazair itself contradicts that. There is no evidence that it uses 3kW per hour in cruise.
     
  8. Aug 22, 2019 #68

    stanislavz

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    Nope, only about how to build perfect and safe home build electric airplane from obtainable elements now/today/in this galaxy.

    Not after batteries will get better. Just now.
     
  9. Aug 22, 2019 #69

    poormansairforce

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    I think I'm developing an electron allergy with all these pie in the sky electrics threads:confused:
     
  10. Aug 22, 2019 #70

    pictsidhe

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    I've tried giving real answers, but people don't like those.

    Yes, it would be great to have 2 hour duration e-plane. But it sure as hell isn't going to happen with any amount of wishful thinking and impossible numbers plucked out of someones backside.

    You want to know a easy way to determine the approximate minimum level flight power of aircraft X?

    It probably has a spec for max rate of climb. People like that number, Joe average can also tell if it is realistic, so the manufacturer probably isn't going to fudge that one too much. Max rate of climb is close to best glide speed. This is not deadly accurate, but should be within 20%. unlike the numbers plucked out of backsides...

    So, class. Stop talking at the back and pay attention.

    Climb power = climb speed * mass * gravity.

    I saw 900 ft/min specified for the 40hp 562lb gross Himax. The Himax is a sorta Ranger-ish aeroplane. the Ranger uses it's wing, so it will serve as an example.

    Now, any fudging on the climb rate is probably with the actual weight, lets take it as 520lb.

    520lb = 235kg
    900 ft/min = 4.6m/s
    climb power = 235 * 4.6 * 9.8

    = 10.5kW

    Now, take a guesstimate at prop efficiency of 65%. We're flying slow so it won't be stellar. It will should improve a bit if we back to level flight power. But I'm going to keep this simple and pessimistic ;)

    10.5/ 0.65 =16kW

    With a 40hp (30kW) engine, it takes 30kW-16kW = 14kW to not climb. AKA 'fly level'.

    14kW is 18.5hp

    For a 2 hour duration you will need 28kWhr of batteries. But you're a fool if you run them 100 to 0. Add 25% to get 35kWhr. Yes, that's really heavy, man!

    A ranger is likely draggier than a himax

    Ok, class, you can go back to La-la land now. For homework, run this analysis on an aircraft of your choosing.
     
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  11. Aug 23, 2019 #71

    Aerowerx

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    So it IS about "REAL full size people-carrying airplanes powered with electric motors"!

    So why all this chatter about RC"toys" and wind mills?
     
  12. Aug 23, 2019 #72

    Speedboat100

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    No there is proof of the 2+ hr endurance with 3 x the battery pack they have on Part 103 solution.
     
  13. Aug 23, 2019 #73

    Speedboat100

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    Cause you can charge you electric Atlantic crossing range electric aeroplane with a handy windmill...not inflight, but on the Azores for instance...to get to the cruising altitude again where the sun shines for the solar cells.

    I dunno know why the R/C stuff was brought here..maybe because they paved the way for Dale Kramer and others who believe in electric flight.
     

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  14. Aug 23, 2019 #74

    Speedboat100

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    Okay..lets give them a rest for a while...after all we cannot change the inefficiency of the batteries of today.
     
  15. Aug 23, 2019 #75

    stanislavz

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    As far as i know - hi-max have rather poor glide ratio ? 1 to 6 ? but with rotax 582 its rather far from far 103 category.. 14 kw is 35-45 kg of thrust ? So only motorglider way is ok now..
     
  16. Aug 23, 2019 #76

    Mad MAC

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    Cool so if we ever solve the energy density problem of batteries its contra-rotating ducted fans for all, complete with no fan tip clearance issues.
     
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  17. Aug 23, 2019 #77

    Speedboat100

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    You figured it out too.
     
  18. Aug 23, 2019 #78

    Speedboat100

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    Motorgliders are ok:
     
  19. Aug 23, 2019 #79

    Speedboat100

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    It uses total of 8,2 KW initially..also for take off.

    http://lazairinfo.com/

    Here:

    Experience has shown me that the Lazair can fly around at about 30 mph using only about 3 kw of power.

    https://www.rcgroups.com/forums/showthread.php?1412424-100-scale-Electric-Lazair

    So 2 hrs worth of batteries takes you 96 km ( 60 miles )...100 km tops.
     
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  20. Aug 23, 2019 #80

    Aerowerx

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    WARNING! CYNICAL COMMENTS AHEAD. PROCEED WITH CAUTION.

    I want to build my own hyperdrive interstellar craft, so I think I will start a thread titled transcendental existentialism. There's sure to be a valid answer pop up sometime.;)
     

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