ELECTRIC 73" YAK

We built an electric version of the 67" Yak and the photos above are of the 67", not the 73". The same components will be used on the 73" version as well since the two planes are similar in size and weight. The 73" will fly with a lower wing loading yet give up a little vertical. The 67" plane few beautifully at 1/2 power and had tons of vertical for hammerheads, loops and more. It flew very locked in even though we were at the most rearward CG. The plane without batteries but with motor and speed control was 9 lbs, about the same weight as the plane with a Saito 125 without fuel. The electric version can use a variety of motors and battery packs. For our tests we chose a very large set up capable of 20 lbs of thrust. The plane was ballistic. The batteries weigh 2 3/4 lbs bringing the weight of the plane up to 12 lbs which is 33 oz/ft2 which is higher than the 30 oz/ft2 we would like to see, though the plane still was very easy to fly. Of course a much lighter and less expensive set up is possible and all that will be given up is vertical acceleration, and there is too much now. We offer a video on the set up and the flight characteristics. This electric set up is great for the 73" Magic hand Yak since the wing loading is about 30 oz/ft2. Even so, we are evaluating lighter and less expensive batteries.

In the above photos you will see that we initially used 2.5" DA standoffs and the isolation mounts that came with the Himax motor. On the second flight the mounts broke and off flew the motor. See video. Fortunately the motor, spinner and even the prop came through unscathed. The cowl didn't fare so well, but we patched it up and tried again using 3" DA standoffs and no isolation mounts. There was little vibration whether we used the isolation mounts or not. Because our experience was not good with the isolation mounts and we didn't notice and benefit from the isolation mounts, we don't recommend them. If you have used isolation mounts before and like them then feel free to use them. For the 73" we need to determine the correct length of the stand offs required, but the DA 3" standoffs will be required plus an additional stand off.

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73" YAK PARTS REQUIREMENTS

1) Servos: 6@HD-2550A ailerons, elevators, rudder, throttle
2) Servo arms: 4@1" MPI JR, 1@3" MPI JR
3) Powerplant: MPI Combo 120 electric motor, speed control and prop or Saito 125 or RCS 140.
4) Extensions: 2@3"(ailerons to Rx), 2@12"(ailerons in wing), 2@24" (elevators)
5) Linkages: the rudder pull pull which comes with the kit is good. The horns for all surfaces are good. I suggest replacing the linkage with the following: 4@ball links, 4@dubro clevis, 2@12" of 4-40 threaded rod
6) Motor Mounts: Use included motor mount for gas. Use DA 3" stand offs for MPI electric. You will also need a few washers to extend the stand off properly.
7) RX, Rx battery and switches like the MPI miracle switch and TBM LiIon pack with JR Rx.
8) Misc: Velcro, J&R servo screws
9) Spinner: The MPI 3.5" spinner is the correct diameter and fits the MPI electric motor perfectly.
10) Batteries for electric motor: A 10S pack is required for the MPI Combo 120. Two 5s 5,000 mah packs and a Y-harness are way overkill for discharge rate, and provide long flight times. Other alternatives are being evaluated. Don't forget Dean's Ultra plugs for the batteries, and a few extra to make a Y-harness.