Sunday, June 17, 2007

Electric not yet there -- Neil Allen

A month or so ago Burt Botha sent an email saying that all F4c Pattern fliers should go electric at once. I want to give my views, and maybe open a flame war or serious debate,

Burt said that pattern fuel needs 30% nitro methane and costs R25 a litre, then wonders why no fliers use four strokes. He just gave the answer, as two strokes run 10% nitro and cost only R8 per flight. S A Modellers tried four stroke motors, and I saw Chris Harris struggling with inadequate power at a Bloem Nats. The 0S 140 is the nicest motor ever built, with a lovely carb pickup, easy start, and reliable idle of 2,000 rpm These are universal in SA because they use cheap 10% fuel, and have plenty of surplus power at 5,000 feet. Hell, at 2,000 feet I restrict the throttle opening to 75 opening to keep the speed down, which I have never done to any engine before

We wont go four-stroke as the power is less, and the only advantage is an idle of 300 rpm slower, which really doesn't count. Tough luck if the judges overseas prefer them

As for electric, you glossed over the costs.
Already in my club I am considered the fat, rich, capitalist, as I can afford R7000 for the airframe, R3500 for motor, R800 for pipe, and a few digital servos, totaling R12 000. I get an OS140 plane, and I adore its flying characteristics (much nicer than those large scale Extra jobbies with petrol engines that cost R20,000)

Now Burt wants me to go to electric power. To get an afternoons practice of four flights I need 3 batteries at R4,000 each, for R12,000. I need two high rate fan cooled chargers for the field for a few thousand more rands. I need 2 of 12 volt deep discharge batteries to run these chargers (say R900). I am told that if you use the car, it will be too flat to drive home. If I use the car running with alternator it will burn that out for R5000 rands. So I go flying with three batteries, which I charge at home with, the 2 or 3 lead acid re-chargers.

I fly on one pack. The performance is inferior to a tank of glo fuel, as I usually do a pattern and three more minutes of practicing man oeuvres, even including hovering. But batteries get weaker throughout the flight, and cannot do this.

The total cost to go electric is maybe
Plane R9000 (covered)
Motor and controller R5000
Batteries R12000
12V Chargers? R3000
Field Chargers R4000
TOTAL (approx) R34000

R34000 is a LOT different from R12000. Maybe some factors are fudged, but that is more than I like spending on modelling. For that price I could get a scale turbine plane (not that I actually like turbines - 5 second motors lag is a total disaster!)

Then you take on a full time job of babying those cells. According to the Bob Violett site on electric ducted fans, they run pattern plane size cells and motors. They say that if it rains one weekend you must discharge all your cells to part charged to save their life. How many hours would it take to do this: -
Carry 12v lead acid batteries back from the car to the garage (don't forget they are strapped in to avoid smashing your car when you hit brakes)
Charge lead acid charger batteries (we haven't even included this cost yet)
On your explosion proof place you run down each pack in turn to 75% charge
Note that the instructions say that you may not leave them unattended, or do any charging while traveling in your car.
Next weekend you use your special balance charger to fill up all cells again (3 hours work). Top up the 12v batteries again
Load 2 X 12 v chargers into boot, using special straps

Come on, be serious, how many S A modellers will rush out saying "yeah sure "R34,000 is fine - give me one, and I am happy to take over babying those batteries"

Burt's electric F3A does fly very well, but not that much better. I can see that he is an "early adopter" who loves new technology, and in a few years we may follow him, but not yet, no thanks
Neil Allen

1 comment:

Piet Le Roux said...

A while back I spoke to a Springbuck pattern pilot, from a few years back, about his new plane that he is putting together. I asked him why he is not going the 4-stroke or battery way. His answer was that we must put the successes that have been obtained overseas in perspective. Those pattern pilots that do well with a YS engine is not using a off the shelf engine but a special factory engine and if he is not happy with his engine it is replaced. The same with electric planes, if you are sponsored and do not have to worry about batteries you can achieve a lot. The other reality is that these products cost more in South Africa due to shipping cost, exchange rates and import duties and spares are hard to obtain. The average income of the middleclass in SA is much lower than in the developed countries which make these items even more unaffordable. So the reality, for now, is that there is only one reliable and affordable power source for pattern flying in SA:
The OS140 or an OS91FX for sportsman.

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