this aeroplane can do.
Commercial gearboxes are available, ranging from the MFA Olympus belt drive with a 700 conversion kit at around £23, the Graupner belt drive at £38 and the in line Graupner unit which comes complete with motor at around £75. (don't forget the very versatile Modelair-Tech Belt drives, either. - Ed.) There's also the Flying Sparks

every time you fly, fast charging stops the dendrites forming.
The wiring in your plane will look like Fig. 1. Note the fuse and the way the male and female connectors are set up so that you can't plug things together the wrong way. This won't work with the common Tamiya connectors. Great! They're rubbish for electric flight - I'd rather use auto spade connectors than those things. Best of all are the 4mm gold connectors from Mike Donkin and others. Sermos Powerpoles are good as well but they are hermaphrodite (don't have a male and a female) so you can plug them in the wrong way round if you're not careful, and then you'll get a cloud of very expensive smoke.
What about motors? What you should use is a Speed 700 9.6V (£20) and a gearbox. Don't even think about running it direct drive, because ferrite motors (Astros have cobalt magnets, Speed series are nearly all ferrite) are very inefficient at low revs - a Speed 700 12V on direct drive with a 10x6 will turn at around 9000 rpm and have an efficiency of around 50%. That's right, you're chucking away half the power you're putting in! Not only that, but the piddly little propeller won't produce an awful lot of urge either. Put a gearbox on a Speed 700 9.6V and spin it at around 18000rpm and the efficiency rises to over 60% - plus - you can use a dirty great prop that really throws some air and you can use less current for the same thrust. Winner! Of course we all know that big props provide more thrust - how many helicopters would take off with a 10x6 as the rotor blades?
The Taube uses just such a set up. Speed 700 9.6V with a gearbox made out of the back end of an old electric racing car with a 16 tooth pinion on the motor and a 50 tooth gear on the propeller shaft (which was the rear axle). The only awkward bit is drilling out the pinion for the 5mm motor shaft. Or you can cheat like I did and run the motor against a grinding wheel until the shaft is down to 1/8in. You do need to make sure none of the grinding dust gets inside the motor by sealing it with tape. I use a 13x9 APC which turns at an apparently slow 6000rpm (hence the big pitch), but don't be fooled - the static thrust is over 3 lbs. More than enough for touch and go's and the kind of mild aerobatics

TG4O by Dave Chinery, a ready made combination of gearbox and two car racing can motors at about £85 - expensive, but mine works very well. I once worked out that these little motors are turning at over 28000 rpm. Makes you think, doesn't it? Or you could always go for an Astro 25G at around £150. Guess why I made my own gearbox?
The really important thing you absolutely must do is to measure the current you're putting through the motor. It took me a long time to realise that the voltage rating of a motor doesn't mean much, it's just a guide to what sort of motor it is, what's really important is not to exceed its current rating. Three things will happen if you ignore this - one, the motor will get very hot and melt the windings - two, you'll get a very short run and three, the batteries will cook. Nothing kills ni-cads quicker than heat. Buy an ammeter (£12 from Hillcott) and use it.

Never exceed currents for popular motors are -
Speed 400 10Amps
Speed 600 25Amps
Speed 700 30Amps

Here are a couple of simple rules you can use to estimate if your proposed conversion will fly
You're going to need a minimum of 50Watts per pound of all up weight. What you do is to measure the motor current, assume each cell is 1 Volt and multiply the two numbers to get the Watts. For a Speed 700 on 14 cells that's 14cells x 25Amps = 350Watts. At 50 Wattts per pound, the maximum flying weight should not exceed 7 lbs - obviously, less is better. The Novice is flying at 7 lb, the Taube at 6 lb. A 40 with tank and servo, but no fuel, weighs around 16 oz, about the same as a geared 700, a 14 cell battery will weigh around 28 oz. Assume a six ounce tankful of fuel and you're adding around 22 oz by going electric. You could save some weight by using lighter wheels and taking out pilot figures. Maybe recover the wings with film.
The wing loading (all up weight divided by wing area) should be less than 22 oz/square foot for this size of aeroplane. Quite apart from the fact that light aeroplanes fly continued