A while back I mentioned trimming and balancing for keeping the airplane from rolling out of, or diving during a turn. Before you get to that point it is important to have a properly balanced airplane with the throws set right.
As I said last time, get the kit manufacturer’s recommendations for initial set-up. This will at least keep you out of trouble. Secondly, take a little extra time to set the dual rates of your transmitter. I use 20% more for high rate and fly on low rate. Any more than about 30% extra will get you in trouble if you accidentally leave the rates in the wrong place. 20% extra is just right for landing, if you care to flip them up.
Note: 20% is not a gross number, i.e., if your low rate is set at 43% (example), then set the high rate at 1.2 times that, or 43% x 1.2 = 52%, not 43 + 20 = 63%!!
Here is a simple method for balancing your airplane without any fancy equipment:
The beauty of this technique is that you never really have to balance the airplane. Just move it back and forth until it changes direction. It works like a beam balance and it’s fast and very accurate. Almost everyone who has seen this for the first time has laughed—then they start doing it.
- Either on the top, or bottom of the wing, near the fuse, take a scale and measure from a convenient point on the leading edge to the preferred C.G., e.g., 3”. Then mark, in 1/8” increments on both sides of the mark, i.e., 2 ¾, 2 7/8, 3.0, 3 1/8, 3 ¼, ….. These will be just dots on the wing. Mark both sides of the wing in exactly the same way.
- Get two wide blade screwdrivers, or bladed pencil erasers, etc. I just use two large , long bladed screwdrivers.
- Lay the wing across the arms of two armchairs, garbage cans, etc. that are high enough to crawl under. I use two lawn chairs.
- Lying between the chairs, and under the airplane, place the blades of the screwdrivers on your mark. (the blades run along the span, not from front to back) Gently lift up. If the airplane rotates tailheavy, move to the next mark back and pick up again. Do this until the airplane rotates tailheavy on one mark and noseheavy on the next one. You now know that the balance is between these two points.
- Generally this is close enough. If you want it closer, then move the blades between the two marks until the airplane balances.
- If you are out at the field, someone can hold the airplane for you while you move the blades back and forth. (out of the wind!!) If they gently turn the airplane loose and it rotates so quickly that the spinner stabs you in the chest, then the airplane is too nose heavy. File a claim with the AMA and move your battery back.
One last thing: Make sure you balance the same way every time. Use a propeller, empty the tank and make sure you have everything installed in the airplane. Keep notes so that you can make your next airplane the same. Next time: How do you decide where the correct balance point is.
Food for thought:Answers on page 31.
- Ever wonder why you bother to balance your propeller, then use an out-of-balance spinner?
- Why do people scream, “I got a light”, when they know they anticipated the light on purpose? Are they blaming the flagman for bad flying and calling?
- Why do we show cuts at all? Why don’t we just arm the judges and mine the area around the cages?
- Why do people still own F-1’s? Is it some kind of a regularity problem?
For those who bothered to read this far: Notice that your QM engine screams when you first crank it up, unless you open the needle a bunch. Try enlarging the hole coming out of the muffler to the tank. They sometimes plug anyway, so a little bit bigger (.046) helps a lot. It won’t affect your needle range or settings. Open your needle about ½ to 1 turn and bump the end of the muffler with your finger just after the engine fires up. This will pressurize your tank and your engine will be running nicely rich from the beginning.
Dub
