by Chappy » Wed Mar 04, 2009 2:07 pm
It is good to see someone finally convert a Lazair. Helps that there is financial backing of some sort. For now, though, for the rest of us, I still think it comes down to batteries. Other than endurance and cost, this set-up could fair OK on a series one when you consider that due to prop loading, the direct drive Pioneers really only produced 4.5 HP! Also, in my experience, the HP to HP conversion is not perfect, and 4.5 HP electric will always come out a bit stronger than 4.5 HP ICE. Just from a "flyability" standpoint, wouldn't it be nice to be able to set a nominal power setting and have the motors hold that setting together in a stable manner. That's not something our 2 stroke engines are known for!
The series one only carried a very small fuel tank, and was more suitable for lighter pilots, certainly under 200 pounds. Larger pilots and especially heavy battery packs cry out for more HP and/or efficiency (prop speed reducers & longer props), and even more so for a series 3. But unlike slapping a little larger engine (like the Pioneer to 185's) and gas tank on the airframe, and carrying a couple more gallons of relatively cheap gas, putting larger but still inefficient motors means giving up endurance or spending big bucks for more heavy batteries.
Since designing a prop speed reducer unit for these motors is so much easier than for the Pioneer (I say that because I've done both-at least of paper-LOL), I'm really surprised they didn't consider going that route. But perhaps they are counting on the future availability of larger motors designed for lower speed torque (very low rpm/V ratings). I'm sure those motors are coming, but all the current ones trade off significant efficiency and peak horsepower for that low speed torque, and appear to have heating issues.
For those of us that don't have a benefactor or investor, there are much more affordable motors out there right now with higher rpm/v ratings suitable for use if you go with a re-drive. There are also much, much cheaper controllers on the market that might be usable. So, going with a re-drive opens up the choices of motors and controllers quite a bit.
One more thing to consider. Current, state of the art lithium-ion battery design calls out for properly designed battery management devices. Not cheap or easy right now. Battery mounting, location, BMS, wiring, charging/chargers, it's all rather challenging. Perhaps even more so, I think, than the motor/redrive/prop/controller issues.
This whole thing reminds me of a friend of mine that years ago bought the plans and aluminum to build a popular homebuilt, 2 place aircraft. After a few years, I asked him home the plane was coming. He said he had pretty much given up on it. He started having nightmares about it. In his dreams sat his finished airframe sitting in his garage - with a big hole in the front where the engine and prop were supposed to be. Every time he had the dream, he realized that even though he could afford to build the plane, the money for the engine/prop was something he had no way of coming up with - short of robbing a bank. That's kind of where I am right now. I believe I could build a reliable, re-drive based system for my Lazair for a reasonable price. But when it gets to the point where I start thinking about buying all those expensive batteries, BMS's and chargers that would be required to make the whole thing a PRACTICAL airplane, I chicken out. The numbers just don't make sense for me. Now, if I lived on an airstrip and could pull my LazairE out of the shed for an hour or so flight everyday, then it might be another matter. That wouldn't call for as much battery power and a less expensive charger, and that would be more affordable.
Chappy
Blue Skys and fully charged batteries!