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Electric options?

1 year 8 months ago - 1 year 8 months ago #1715 by haiqu
Electric options? was created by haiqu
Seems like the big buzz in aviation these days is electric. This is a pity because batteries are still far too heavy and inefficient, and nobody has charging facilities. In fact it's a call-in and a two hour wait to get Avgas at most Australian airfields, if it's available at all, so I don't expect anyone to fit charging stations any time soon either. GA is dead, and has been since kit planes started coming out in the 80's. But I digress.

My life has changed (in oh! so many ways) since I was last here 11 1/2 years ago, and I'm finally in the position to actually build an airplane. And the engine options haven't improved much at all. I did email Jabiru to see if they'd consider making a 2-cylinder version of their engine but I don't expect to hear an affirmative reply.

Then I remember something. An old guy in a boatyard gave me the dead motor and controller out of his electric-powered yacht and I still have them. The motor is an LMC LEM-200-D127 of 12.5 kW rating (25 kW peak) which is ideal for the Quickie, especially since it only weighs 11 kg. The controller is a Navitas TPM 400-48 which will deliver 19 kW (25 hp) in short bursts, ideal for takeoff.

LiFePO4 battery options run at around AU$9500 for a 48V 200AH battery capable of delivering 400A in short bursts. That looks really expensive until you add up the fuel savings, although someone as old as I am probably won't get the full value out of them.

A Quickie will fly four hours on a tank of fuel (8 US gallons / 30 litres) with an Onan engine. How far can I fly with a full 10kW.H battery? Well, let's look at this in phases. First phase is takeoff. Expect full power for 5 minutes, which will use 1kW.H right off the top. From there you're probably using less than 8hp with such an efficient airframe, so that's 6kW for every hour aloft. Ignoring regeneration while descending, we're looking at a safe flight time of 1 1/4 hrs with a little margin for error. At cruise speed that will get you 115 miles (185 km) in an hour times 1.25 for the amount of battery available, or 143 miles (231 km) which is a pretty good run ... until you realize that there's nowhere to charge up when you get to wherever you're going.

But for me, a low hours pilot with a need for lots of local flying and without a nav rating, that might not be a problem. In fact it just might be a very cheap way to get some hours up.

I envy anyone living in the USA, you have so many more options. The cheapest viable aircraft for sale here is in the $15k ballpark, and two seaters start at $30k in dollaridoos. Yes, there are some decrepit converted hang gliders for cheaper money but they have no maintenance records and have never been registered, which means they've either never worked or, worse, have been flown illegally by idiots until somone scared themselves sufficiently to stop doing that. Then they sat in a shed for 20 years collecting dust and rust. Big nope right there.

According to a spreadsheet I did Lo! those many years ago, a parts kit for the Q1 will cost AU$7k in 2011 dollars, or probably double that amount nowadays after shipping and taxes. Then there's that $9500 battery to consider. Finally I need to repair the motor, fit it, and fly off the test period before I can have some fun.

That $40k 1979 Piper Tomahawk with 200 hours left on the engine is starting to look better by the minute. Just about any instructor will be rated in it, it can be used for dual training, and it will have an actual resale value should I choose to either upgrade or cease flying altogether. But the big one is, I can get a nav rating and leave the local area eventually. Burt, I luv ya like a brother, but the figures just don't add up any more, at least not unless a good, cheap and lightweight engine comes up.

Good, cheap, lightweight. Pick any two.
Last edit: 1 year 8 months ago by haiqu.

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1 year 8 months ago - 1 year 8 months ago #1716 by haiqu
Replied by haiqu on topic Electric options?
After such a long time away from aviation it occurred to me that Burt might have done something new in this area recently, so I went searching and was rewarded for my curiosity. In 2011 his last design before retiring was the BiPod, design #367, done in conjunction with a large number of employees who worked overtime to get it running in a few months. He evidently followed the same thought pattern as I have in the above message because instead of using large, expensive batteries he solved the issue with several small electric motors, a small battery (1.2kW) for the take-off phase and two onboard petrol generators. Nice lateral thinking there.

It might work at the scale of the BiPod but doing the sums for the Quickie I discovered that the required 6kW generator weighs 65kg and when you add the 11kg electric motor, 1.2kW battery, controller, charging circuit and all that extra electrical wiring you might just as well use any old 50hp aviation engine because there's no weight or fuel saved at all.

Well, it was worth considering anyhow. But I can see why the BiPod project stalled (pun intended), it just isn't viable with today's technologies, adding complexity and cost for no real advantage.
Last edit: 1 year 8 months ago by haiqu.

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