|Mar 25, 2011, 02:05 AM|
100% scale, Electric Lazair
Over 30 years ago I designed the Lazair ultralight. My company 'Ultraflight' produced about 1200 of these aircraft kits between 1979 and 1985. I believe that, over the years, there have been Lazairs in 5 museums, including one in the Smithsonian right now.
Back then, there was a revolution of sorts when we married modern lightweight 2 cycle engines with lightweight airframes and ultralights were born.
Today, another revolution is possible. The RC model aircraft industry is propelling this revolution with the batteries, chargers and power systems we see today.
The twin engine Lazair is an ideal vehicle for electric conversion and over that last 10 years I have dabbled in trying to electrify one several times. Each time I was thwarted by many issues but this time I will do it. There has been an electric Lazair flying in England for a couple years using Predator motors.
Experience has shown me that the Lazair can fly around at about 30 mph using only about 3 kw of power.
The RCgroups forums have been invaluable to me in obtaining knowledge that I need to build this unique version of the Lazair.
Rather than hijack other threads I have been following, I have started my own Build Log here, in 'Batteries and Chargers', the heart of the enabling hardware that will make his happen. I am sure that 'Power Systems' will get their fair share of crossover reader interest.
I don't want to consume too much of my time posting and monitoring this thread but in a way I owe it to you guys to give some hard earned knowledge back to the ether.
Here is what I have chosen so far:
Two 10 kw Turnigy CA120-70 motors with 32-12 props reconfigured to WYE terminations.
Two JetiSpin OPTO 300 controllers.
96 pieces of Zippy 5000 mah cells arranged in 6 packs of 16s4p each.
Six of FMAdirect PL8 v2 chargers, each one running off two 12v 900 watt Dell Poweredge 6650 power supplies wired in series to get 1800w at 24v.
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) with this 'legal' ultralight setup and then be able to recharge the batteries in about 1 hr (turned out to be 1 hr 15 min, not too bad a guess).
I have attached a few pictures to this post and will add pictures as new posts as I can. Although I do expect to fly the Electric Lazair on this float setup, the first flights will be on wheels.
And by the way, my current plans are to fly this airplane from my home in Hammondsport, NY to the Atlantic ocean, to the Pacific ocean, to Oshkosh and then back home this summer.
|Mar 25, 2011, 08:05 AM|
Wow, what a great project!
To optimize efficiency, you should talk to these guys:
They build very advanced controllers, which are already in use on some electric paragliders.
What is the advantage of having two motors? Would one motor with a bigger propeller not be more efficient?
|Mar 25, 2011, 09:50 AM|
Nice project Dale.
Two smaller motors = hobby motors, available off the shelf, including the ESC and less expensive.
One bigger motor = non-hobby motor + non-hobby ESC, both more expensive.
In the air with two motors - one motor go dead-stick, other motor can take you a long way.
In the air with one motor - motor go dead-stick, you look for place to land.
|Mar 25, 2011, 02:17 PM|
Joined Dec 2006
|Mar 25, 2011, 03:44 PM|
Why are you using a turnigy motor? They are typically very heavy and have low output compared to other options.
For example, if you look at the hacker A100-10 you see it's the same KV, quite a bit lighter, and way more efficient.
The hacker A150-10 is still lighter and has a lower kv which is good for running large props.
The A200-8 is only 2oz heavier, a bit lower KV, and rated for much more power.
Remember, that the ratings don't mean much because some companies are very conservative (like hacker) and others tend to lie right through their teeth (hobby king.)
One last thing. Make sure you go through the bearings, confirm that the shaft is sufficiently hard, and the magnets are well glued in place. Loosing a motor would not be a good thing on a twin that light.
|Mar 26, 2011, 12:17 AM|
Joined Dec 2006
Its all a balancing act like anything else.Cost-benefit ratio has to be a big consideration in a project like this.Id probably tend to lean towards the more cost friendly approach to prove the concept.Theres always time to get the maximun efficiency later.Although 2-stroke power has gained alot of reliabilty in the last 20 years the angry monsters do like to quit from time to time for various reasons.One motor in a twin wouldnt be as bad as a complete deadstick.Thats just one of the things you keep handy in your thought process flying an Ultralight.Unless your flying low over a congested area its likely you can fairly easily find a safe place to land with an engine failure.At least now that cell phones are so common its not as important to land by a road or house so you can call a buddy to bring the trailer to get it home.
|Mar 26, 2011, 05:55 AM|
Sorry, haven't had time to post. Thanks for the positive and thoughtful comments everyone.
Excellent two engine answer rebell!
Hacker motors would have cost me about another $1,400 and I just mad a value decision. Yes I would like a lower kv but I would like to try the WYE configuration since the DELTA test showed acceptable efficiency lugging the motor at lower rpms. I will upgrade if I have to. I plan to limit rpm to around 5,000. I installed temperature sensors on the motor windings and I will limit my high power usage by motor temps. It should be very quiet cruising at about 3000 rpm. Attached is the DELTA test we did before I made the decision to go with the CA120-70 motor.
I went with the JetiSpin controllers for their apparent ability to handle 16s packs and their demonstrated ability to drive this motor at 16s. So far so good. Other options will be investigated if there are problems. Charging setup was a major decision factor in controller selection. I will have an 8kw generator on my chase vehicle that will let me recharge the 16s4p packs with PL8 chargers. They will charge as 8s8p (by removing a series jumper) and at about 30 amps each. This should charge all the packs at about twice the rate of power consumption at cruise, say 90 minute flight and 45 minute charge. I can do this 3 to 4 times a day for up to 6 flight hrs per day.
I hate to say it but I am not expecting 100% reliability, this will be an adventure and as aerocal has pointed out, I can land safely most anywhere (I have a lot of sailplane experience.) I was too busy running my company all those years ago to do something like this, I am glad I have the chance to do it now.
I should have my throttle quadrant mostly finished today. As you can see it is like Christmas everyday here with packages piling up faster than I can organize things, but as a lot of you know I have always lived in a bit of a mad inventor environment.
|Mar 26, 2011, 07:19 AM|
Joined Oct 2010
I have put this engine and 15sin the scorpion calculator and I think you are going to put to much current through the fet's of jeti.
This is 15S and 327A
on 16s it will be around 350A
limiting the RPM will not help you here. At half throttle the fet's need to switch much more and will need to dissipate a lot of power.
|Mar 26, 2011, 07:58 AM|
I have been in communication with the person who ran this test and saw that this setup did indeed work.
I know his voltage sagged more than mine will but it shows that the FETs seem to be able to handle this voltage and motor combo under full load, maybe for how long is the question.
I have only run my motor with no prop on it so far in WYE only with 16s4p pack. At 30deg timing the motor draws 12 amps at WOT. and I can run it very slowly at 0.6amps. About 8100 rpm no load WOT. JetiSpin was cold but only ran it for a minute at a time. Motor was slightly warm which surprised me a little. Sorry no other numbers yet I was just testing out some controller parameters.
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