What should we say? Fun cub. It looks very, very similar to the multiplex fun cub it’s, a little bit smaller it’s, a 1.1 meter to get it in the air. As always, we’re going to need motors and servos and speed controls, and all that good stuff, and when i was looking around, i managed to find this bundle in the bundle we have. This 2217 1250 kv motor comes with the prop adapter and the mount and nice bullet connectors on there also the speed controller. We can see here a 40 amp up to 4s lipo with a 3 amp back. It has two 8060 size: props, a battery strap two el cheapo servos, and here is just the mounting hardware for the propeller. A very good selection then, provided that everything works okay and a complete bargain at under 20 euros. But can it be any good let’s check? The main components, the speed controller and the motor and see how they perform here, you can see my super sophisticated test rig botched out of an old set of digital scales and i’ll link to the video where i made this creation. It may not give us accurate numbers, but the important thing as far as i’m concerned is that it gives us a way to compare different configurations quickly. Just to remind you, then, our motor, the 1250 kv there as the motor spins up it will be exerting a force that we can measure on the little readout there.
I have in line my watt meter to be able to record the current and the wattage. The battery i intend to use, then is this 1800 milliampere hour 30 to 60c battery and that’s been fully charged. I’Ll make a note of the values and let’s crack on and, of course, safety squints on, i saw there i think 880 grams force. The watt meter shows 20.55 amps 238 watts. As a comparison, then let’s change the props. For one of these two, the first one will be going down from eight six to eight four, so just changing the pitch there and then we’ll try a seven by four and see what numbers we get next then the 8×4 750. I think again on the watt meter here: 1606 amps 188 watts. Finally, then our 7×4 620 11.19 amps, which then should be the propeller of choice for our little mini fun. Cub let’s, take a look at the numbers. What can we conclude, then, from our tests, which is the best propeller for our new project? Let’S then, look at the numbers that we recorded i’d be interested to know and please leave comments below whether you go through this type of process or whether you think i’m overly anally retentive. I do remember a story from eric brown, so called winkle brown. The famous test pilot who flew more aircraft types than anybody else in history – he was always one for reading all of the pilots notes and doing things properly and and by the book he was rather scornful of pilots, whose attitude was light.
The fires kicked the tires and the last man homes at anyway, moving on the estimated flying weight of of the plane is going to be 750 grams. Obviously, we can modify that after the build, if there’s any great change, assuming that that’s correct a typical trainer needs between 0.5 and 0.8 times the flying weight of thrust to fly well, that gives us figures between 375 grams and 600 grams of thrust. Clearly then, the supplied prop is uh somewhat of overkill at 880 grams and would also consume some 20 amps. Eight by four is one to one that would be uh overkill as well. I feel the decision that you make here is really based upon your intended flying style. I guess for me as a novice i’m more interested in flight time, so that i can practice and boy do i need it. My choice, then, is going to be going for this 7×4 prop providing 620 grams, which is still more than adequate for the typical trainer, and that will only consume some in 11. Amps should give us a reasonable flying time.