RCU Forums - View Single Post - Problems getting an electric conversion to fly
Old 05-13-2019, 06:07 PM
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otrcman
 
Join Date: Oct 2004
Location: Arroyo Grande, CA
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Hello Dale,

I feel your pain. Having a model that doesn't want to fly is really frustrating. The key item is that you need a fairly well matched set of motor, speed control, battery, and propellor to give the power you need. If even one of the 4 components is undersize, you won't have enough power to fly the model.

OK, let's start at step 1. I can't tell the power of your electric motors from the information provided. The "1100 KV" number just tells us how fast the motor wants to spin with no prop installed. The analogy with glow motors would be to say that you have a 10,000 RPM motor, but don't know if it's an 049 or a 60. What we need to know is the "watts" rating of the motor. That's like "horsepower" in a glow motor. Many manufacturers don't list their watts, so that might not help us much. Do you have an amp meter or know someone you can impose upon to measure the full throttle current draw of your motor with the prop installed ? Even knowing the motor RPM under prop load might give us some idea of the power of the motor.

If you do have some information of the watt rating of the motor, I'd say you need around 180 to 200 watts per motor to make the model fly.

Next step is the battery. The 3S number of the battery just tells us how many cells you have. There should be a number like, "1000 MAH" on the outside of the battery. Again, I'd say that you need batteries of about 1800 MAH each to fly your model. Checking the model weight that you quoted, I see that the weight with batteries is only 5 oz. greater than the weight without. At 2.5 oz. each, those are mighty small batteries; probably around 900 MAH. To fly your model well, you will probably need batteries that weigh around 5 oz. EACH.

The last item is prop location. I apologize for being so critical, but I learned to my own dismay that seaplane props in that location will pick up a lot of water from the bow wave as you get going. The props bog down and make very little thrust with water pouring through them. You will probably find that the thrust line of the motors will have to just as high with your twin as with the original glow motor installation. That's one of the reasons that most seaplanes are single engine. The single prop is centered between the twin bow waves and don't pick up any water. The twin version props are perfectly positioned to pick up the bow waves.

Best wishes,

Dick