Safety Issues and Concerns
Macon Aero Modelers Safety News February 5th, 2011
From the Safety Coordinator
Spring Safety Thoughts--2011
I trust you are having a good winter and excited about spring coming in a few months. Hopefully you’ve been able to spend some time working on a new model or two. I put together a P-38 Profile kit and bought a used Ultrastick 25 electric that I purchased from club members. I’d like to share a few insights that came to me as I worked through these models.
Electric ain’t cheap! By the time you purchase a motor, electronic speed control (ESC), and battery you probably have spent $200. The equivalent power set up in a nitro-powered airplane would probably be $100. So it may pay you to review this article and see if what I discuss applies to you and your model. If you buy a model from someone else—beware!!
Let me talk about the used Ultrastick. It came with a motor, ESC, and battery. As I looked at the motor and compared it with others I have, I found it would not have the power to fly the airplane as I might like. I could put either a “25” or “32” sized motor according to the flight manual (instructions). So naturally I purchase a new “32” sized motor under the bigger is better principle (AKA Doubleday/Ramey conversion); also, I thought I might fly it with floats at some point. Well, hanging that big motor with a 14.8, 4-cell LIPO is going to affect the center of gravity (CG). If I had positioned the battery where it “looked good” on the battery tray it would have resulted in a severely forward CG. So the recommendation is to get out the CG stand and do the work of balancing your model! If you change motors, go from a 3-cell to a 4-cell battery, you’ve added weight and probably affected the CG.
How about props? Do you have the right one for your motor? Astro Flight, Inc makes a good WhattMeter that gives you the amps and watts for a prop that you hang on the motor. As you go from a 3-cell to 4-cell battery you will allow the motor to pull higher amps and watts; same for increasing prop diameter. Here you want to compare to the motor maker’s specifications for amps at continuous and burst draw. The goal here is get the watts you need for power without burning up your ESC! How about balancing your prop? While manufacturers do a pretty good job I find very few props that are balanced without some sanding.
You’ve completed your airplane build and it looks great, but what you’ve got at this point is a great static display model! Next you power up the radio and what do you find? Hopefully you took the steps to center the servos and the servo arms. Next you centered the control surfaces (rudder, aileron, etc) by adjusting the clevises. Did you take the safety precaution of installing some clevis keepers (fuel tubing) to keep the clevises from opening in flight? If using a “Y” servo lead to pair two servos do the servos move in the right direction? It’s best to have one aileron move up while the opposing side moves down. Remember that with a computer radio you can use the “sub trim” function to make a fine adjust and center a control surface. It’s also best to follow the manufacturer’s recommendations (dimensions) on Control Throws at least for the first few flights. What about “dual rates” and “expo” for your radio? Again, it’s best to address on the ground before the first flight.
In summary, the preparation you take on the ground before flight should lead to an “uneventful” first flight. In the real world it would be called “pre-flighting your airplane”. So take the time to balance the airplane; both a lateral balance (left and right) and center of gravity (fore and aft). Next, make sure flight controls perform correctly. Put retainers on clevises and servos. See you at the field!
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