electricfan

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in a recent fly rc magazine i found a plan for a parkflyer seaplane called a splash E. i want to build it, but this will be my first scratch build. i really don't care how nice it looks. does anyone have any tips i should know about scratch building? this might be a stupid question, but whats the best way to trace the pattern onto the balsa so i can cut it out? how do i waterproof the floats besides monocoat, or is that it? it has a 43 inch span, 29 inch length, 324 sq in wing area, and weighs 15 ounces RTF. how does a direct drive speed 400 6 volt on 7 cells with a 6x4 prop sound? will the motor be too big, because he says he used a MGK motor with 4.8:1 gearing and a 7 1/8x4 1/2 prop? the motor in the picture looks way smaller than a speed 400. if the SP400 motor won't work, can i use a speed 280 or 300 geared? how much thrust does a model like this need? sorry about all the questions but my motocalc demo ran out.
thanks

Matt Kirsch

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If I am not mistaken, RCUniverse has at least one forum dedicated to scratch building. FWIW, the last time I attempted a scratch build, at the tender age of 10, I did it the old fashioned way. I used tracing paper to trace out the parts, then transferred the marks to the other side of the paper, and rubbed them off on the balsa. Nowadays, you can take your plans down to Kinko's and get two sets of full side copies made. One is for building on (never build on the original plans), and the other is for cutting up and making patterns. Stack up enough balsa blanks for the parts you need, spray adhesive the cutout on top, then bandsaw or sand to the line.

Surprisingly enough, your motor questions are the most difficult to answer. The 15oz AUW was probably achieved by using the presumably lighter motor/gearbox and lighter battery required. Unfortunately, I've never heard of an MGK myself, so I don't really know what would be suitable in its place. Sounds like there's only room for an 8" prop at best, so a geared 300 would need to have a fairly low ratio. The 400 would seem to be a pretty good choice, provides there's room for it or willingness to modify the design a bit, AND provided a smaller battery is used to keep the weight down. A 7-cell pack of CPB650 or KAN 650 NiMH, or a 2-cell pack of Kokam 1500 LiPolys won't contribute much to the final weight of the plane.

electricfan

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i researched on the MGK and found that it is used for free flight??? maybe there are different versions. it just doesn't seem like a free flight motor will pull a 15 ounce model. i know a 20 ounce model will fly with a geared 400, so im guessing this one will fly with a DD 400 or geared 300. ill see when i build it.

Thayer

There are FF models that span 10 feet or more. Just because a model doesn't carry a radio doesn't mean it has a little motor. There have been full scale planes flown free flight, though not intentionally. FWIW, a lot of RC models are lighter than this motor alone. (47.6 grams on my scale.)

The Splash-E prototype power numbers show 42 watts into the MGK, roughly a geared S-280, so base your substitutions on that.

Though recommended for 3-10 ounce models, I think the new little AXI 2204/54 would work nicely. It is about half the weight of the MGK, and has a max current rating of 6.5 amps. With a 2S Li-Poly, you will have about 48 watts in, 15% more than the MGK. The real performance gain would come from the increased effieciency of the ungeared brushless motor. I would guess it to be at least 50% more efficent than the MGK, thus providing at least 75% more power to the prop. Based on these numbers, you could run it well below its limits. It should provide a nice kick for a lightly built Splash-E. Unfortunately they are out of stock for another month, at least.

The AXI 2208/20 or 26 would offer much stronger performance, while adding more weight.

Thayer