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

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stanislavz

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Put battery into wingtip with % area of total mass. And jettison it woth wing tip.
 

Speedboat100

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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.

No. See the whole video.
 

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?????
 

12notes

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No. See the whole video.
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.
 

stanislavz

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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?????
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.
 

pictsidhe

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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?????
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.
 

Aerowerx

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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.
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?
 

Speedboat100

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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.

No there is proof of the 2+ hr endurance with 3 x the battery pack they have on Part 103 solution.
 

Speedboat100

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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?
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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stanislavz

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

14kW is 18.5hp
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..
 

Speedboat100

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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?

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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