100% scale, Electric Lazair - Page 14 - RC Groups
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Jul 11, 2011, 09:40 PM
Dale Kramer
KiloOne's Avatar

JM1 phase resistance

Originally Posted by munyard
very interesting project to follow KiloOne, and a well balanced approach to all the tech stuff, whilst getting into the air without long delays.

a question though, ive been testing the turnigy 120 motors and have a good measure now of their capabilities and in wye they also have a kv of around 84rpm/volt, so for comparison im very curious what the unloaded rpm/amps were from your kv test of the joby, and what resistance of the windings are? (prolly needs a good 5a+ dc to test volt drop)
-we can then work out their efficiency also.
Thanks Munyard,

What I can provide right now is this graph of my JM1 no prop test.

I have calibrated the voltage and current with a 4 1/2 digit DVM and a clamp on DC ammeter. I would place a margin of +- a half an amp or so on the current since the clamp on ammeter has a slight zero drift that was hard to keep at zero.

At some point I will try to get a phase resistance for you, I've been thinking of trying to use my PL8 charger to use as a current source (put the winding in series while I am charging a battery at 5 amps and read the voltage drop on the winding phase). Not sure when I can get to this though.

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Jul 12, 2011, 11:56 AM
Registered User

electric Lazair

Thank you for the Lazair, I have owned one and have a WTII that would look good electrified.
Have you posted any video or photos of the installation?
Keep up the good work!
Jul 12, 2011, 12:56 PM
Dale Kramer
KiloOne's Avatar
Thanks, to see all the pictures that have been posted to this thread, scroll to top of this page, click on 'Thread Tools' and then click on 'Show attachments in this thread' in the drop down menu that appears. Click on any picture to make it larger.

Jul 12, 2011, 01:29 PM
Originally Posted by KiloOne
Just to be clear as to what I refer to in my Hp and Watt numbers.

When I talk of gasoline motor Hp I mean mechanical shaft Hp.

The KW I refer to for my electric motors is input power to the speed controller and to actually covert to mechanical shaft Hp we would need to know the controller and motor efficiency at each and every temperature/voltage/current/rpm/etc to be tested. That is beyond my measuring capabilities.

One thing I have in the past done is to measure motor torque and rpm. I wish I had this setup now so I could get a true power conversion efficiency (at least in static thrust conditions).

One thing to be sure is that two strokes have a VERY narrow power band. You have a few hundred RPM where you are actually making rated horsepower but as soon as you go slightly above or below that RPM the hp drops of rather dramatically. If you over prop the 2-stroke it will never be able to get into the RPM range to actually deliver max output, if you under prop it the 2-stroke will spin too fast and also fail to deliver max output. Of course simply weather or altitude changes can under/over prop the motor. Also because you have no electronic engine management you have to basically re-tune the engine for any change in air density or the motor will not be running optimally for that air density.

Then you have to remember that the engine is rated to that power not only over a very narrow RPM range but also most likely at SAE air density (Sea level, 77F, 0% humidity). You take off on a hot and humid summer day in the south, add some altitude, and you are making no where near SAE rated horsepower.

The point of all this? Unless these engines are under-rated by the manufacturer it is unlikely that uncorrected shaft HP output in most real world conditions is very close to its paper output rating. However, I highly doubt most well thought out electric power systems will perform under 85% efficiency. Realistically the numbers are probably somewhere between 85-95% of input power depending on throttle setting. When you start getting under 80% you are generating so much heat that the system would likely not be capable of surviving sustained use. I would expect that in the real world 11kw of electric input power (~14.75hp) would outperform a 15 shaft HP rated 2-stroke in most conditions where you would actually fly an ultralight.
Jul 12, 2011, 09:43 PM
Dale Kramer
KiloOne's Avatar

Glenn Curtiss aside

Those who know me also know that Carmen and I are big Curtiss fans.

We live in Hammondsport where he grew his business 100 years ago.

In fact we live in the only building that still exists here which he and his wife Lena owned. You can see the house we live in that Glenn Curtiss had built in 1909 in the first picture of this thread, just behind the left wing tip float.

We have lived here for 9 years and only found out recently that the house was built by him. We did know they once owned the property when we bought it 9 years ago.

In some modifications I did to the house I had some of the original siding wood left over.

Any way, I used some of this siding to make my instrument panel for the electric Lazair. A poor picture of it is attached below. The two displays are Eagletree power panels, 1 for each motor.

This now allows me to use normal bifocal glasses to fly with. On my first flights I ended up wearing my bifocals up side down so I could glance my eyes up to see the wing mounted power panels in focus. It was either make some glasses with another reading lens mounted on the top of the eyepieces or move the power panels down to a normal instrument position. That latter option won out.

I just think that it is fitting that I fly with something on the Lazair that Curtiss owned (and possibly fitted personally to his house in 1909). I will treasure this piece always.

Last edited by KiloOne; Jul 13, 2011 at 04:42 AM.
Jul 12, 2011, 11:12 PM
Frankenstein recycled packs
rampman's Avatar
WOW, that is some history; how .
I was watching American Pickers when they found a rare Curtiss motor circa 1906. I would love to just have that on my fireplace mantle.

Jul 13, 2011, 12:58 AM
Registered User
Yes, very nice bit of history there Dale.

What props are you using on the JM1?

Jul 13, 2011, 05:15 AM
Dale Kramer
KiloOne's Avatar
When we selected the prop that we used on the 425 cc JPX engine for the Lazair Elite we had ordered a range of diameter and pitches from Culver Props.

So, I've had in storage for 25 years two sets of Culver props, 34x20's which we ended up using on the JPX's and 36x20's. I have some Ritz's but they don't hold up as well as the Culvers. I have chosen the Culver 36x20's for the JM1 as I really want optimum efficiency at cruise power settings.

Jul 14, 2011, 09:54 PM
Dale Kramer
KiloOne's Avatar

Joby JM1 powerd Lazair - Maiden flight!


Tonight, at 6:31 PM EST I added full power to the JM1 engines and started my timer. The takeoff was quick and the climb impressive with the motors at 4000 rpm. My Lazair and its 245 pound pilot (me) were at 1400 feet above takeoff 3 minutes after pushing the throttles full. The engine temp after those three minutes was 225 degF (in static conditions on the ground it would have been 250 degF ).

The ambient air temp was 85 degF and the takeoff elevation was 1300 feet MSL.

I spent the next hour and 18 minutes flying at cruise power setting of between 2300 and 2600 rpm. Generally that was between 30 and 40 amps if I can believe my instruments. My right Eagletree powerpanel was not displaying any voltage/watts/whr information since the voltage reading could not be trusted. My left engine display did seem to display the correct voltage so that was used to judge when I needed to land. The voltage was 53 volts when I reduced power on short final.

In between takeoff and landing I experienced sheer joy and was amazed at how well the aircraft performed. I have wanted to experience this care free electric flight since I was a small boy.

Tomorrow I fly some more, I will keep you posted.

Last edited by KiloOne; Jul 14, 2011 at 10:02 PM.
Jul 14, 2011, 10:02 PM
More Motors, More Fun... :-)
nioa's Avatar
Incredible! Congratulations Dale!
Jul 14, 2011, 11:21 PM
Registered User
That is so awesome!! Congratulations!! Have fun and be safe.
Jul 15, 2011, 01:35 AM
X-Era Motors
DavidB.'s Avatar
Fantastic job!!! Now if the rest of us could find a lazair that is for sale
Jul 15, 2011, 03:30 AM
My cat moderates better
BillzillaAus's Avatar
Outstanding! Well done.
Jul 15, 2011, 06:01 AM
Excellent - well done Dale. It looks a very neat job you've done there, and the Joby motors seem to be ideal. You're getting significantly more power than we did from the Predators (the JM1 motors are somewhat larger).

Great to see that the motors and cells are actually doing what they say on the box.

Enjoy the flying.
Jul 15, 2011, 08:41 AM
Registered User
Congrats !!! Sounds like the jobys are the one's for now.

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