RADIO CONTROL AEROBATICS
Eric Henderson, 303 Shady Ln., Marlton NJ 08053; E-mail: eric.henderson@comcast.com
AS DO MOST of us, precision aerobatics models have a big problem with gaining weight! Unlike most of us, a precision Pattern airplane can't starve itself to get back into the game. There is a worldwide F3A competition weight limit of 11 pounds. There is also a two-meter dimension "box" size limit, but there is no size limit on the engine that your model can use.
The bigger engines tend to be heavier, so the airplane has to be lighter to beat the total 11-pound weight limit. This is why you see Pattern pilots taking such fanatical approaches and employing exotic and often expensive materials.
Many Pattern pilots worship at the temple of the "lighter is better" formula. "Lose Some Weight and Start Winning Rounds" is their bible. Meeting the weight limit is not the only reason for this goal; it does appear that lighter airplanes seem to fly better.
A word of caution: if you make an airplane too light, the wind can become a problem as it gets lighter. Very few current Pattern designs can be made too light! Nine to 10 pounds is a very good target for a two-meter airplane.
Following are some suggestions for how to lose weight. Some may seem trivial and even extreme, but the sum of all these actions may well be that elusive half-pound you were looking to shed.
- Spinners: You will find many differences among different brands of spinners. Aluminum spinners are strong but not necessarily lighter than plastic spinners. Don't sacrifice strength in this area. Go with the spinners that you know are suitable, then choose the lightest.
- Propellers: The popular APC propellers perform very well but are not particularly light. Mejzlik hollow-blade, carbon-fiber propellers save weight but are not always available in all the required Pattern sizes. Wooden propellers may be the right option for you.
- Propeller nuts and washers: These are often made from heavy metal. It may be that the washer and nut can be exchanged for slimmer or lighter materials.
- Engine mounts: Not only can you shop around and choose a lighter engine mount, but you can cut off any unwanted material that is forward of the front mounting bolt. The mounting bolts only need to be 1/16-inch longer than the nut it goes into. Only use washers if you are using a bolt that is too small for the hole in the engine lug. All engine bolts can be cut to exactly the right length.
- Mufflers: Muffler choices are broad, and you can do well by selecting the lightest. Carbon-fiber pipes are hard to beat when they can be as light as two ounces.
- Exhaust couplers and clamps: Use only as much coupler length as you need. Try UV (ultraviolet)-resistant tie-wraps instead of metal clamps or hose clips. With four-stroke engines, Teflon™ header tubing will not only last longer than metal flex pipe, but may well be lighter.
- Wheels: Wheels offer a good way to save weight. You will be surprised by how heavy they can be. Tires can often be substituted for a lighter type. For axles it may be a good option to choose titanium, especially if you have a smooth field. Axles and wheel retainers are available in aluminum with very light C-clips instead of the more common brass wheel collars.
- Undercarriage: Retract mechanisms should be weighed because they tend to vary in weight. Retract push/pull wires need only be 1/16 piano wire or carbon-fiber rod. Fixed gear can save weight, a servo and battery consumption, and may well be a retrofit option; weigh the pros and cons for yourself.
- Fuel systems: All fuel tanks are not created equal. You can get pretty creative in this area and maybe save an unexpected ounce. Those without big synthetic bungs, etc. can be lighter. Consider the tank size you are using. Many pilots carry far too much fuel. You only get to fly each maneuver once in a contest; why practice two rounds at a time with a big tank when you only need enough fuel to do one round? The second consecutive flight will be with a lighter airplane and might teach you the wrong thing! Fuel-line tubing is much heavier than aluminum tubing you could use for the two times, 15 inches or so inside the fuselage.
- Fuselage: Your building skills may have improved since you built your model. A wooden fuselage instead of a fiberglass fuselage is worth looking into. Even more tempting is a new Nomex® version of your current fuselage that may have reached the market. It is all up to you and how passionate you are about saving weight. At least be ready for your wallet to get significantly lighter!
- Paint: Don’t be afraid to get a bit radical and completely repaint a fuselage. Paint is much heavier than most of us realize. Use a white undercoat and avoid having to apply many layers of paint to get a deep color. Spray lightly with colors, and shine the complete surface with a clear gloss coat. There is no prize in Pattern for a car-showroom finish. Light—in both senses—and lovely will do! There is potentially big weight savings hiding in your paint scheme.
An accurate scale is a weight-saving fanatic’s friend. One tip is to put everything you take off the airplane in a box, and weigh the accumulation. Then weigh everything before you add it to the airplane. When you are finished, subtract the additions from the removed weight and celebrate the new weight.
Maneuver of the Month: The Humpty Bump
The Humpty Bump was the first aerobatic maneuver that I just had to rush out and try for myself after reading about it. There was something that reached inside of me and appealed to the growing Pattern pilot. That may not happen for you with this maneuver, but one will get to you sooner or later.
The Humpty Bump requires your model to climb vertically then pull or push a half loop at the top. Then the model dives straight back down to earth. Some Humpty Bumps require multiple roll components in the vertical lines. A snap roll can be thrown in now and again to make life really interesting—or difficult, depending on your flying ability. A good idea is to perfect the simple Humpty Bump, then add the “fun” at your leisure.
This maneuver is mainly used to turn the airplane around at the end of a line of flight to your left or right. The most used turnaround Humpty Bump includes a single half roll on the up-line. The half loop would be a pull or a push over the top.
The best place to try a Humpty Bump is directly in front of you, then gradually move it out to the corners of the aerobatic box. Fly straight and level at approximately half throttle. Pull a quarter loop, and add throttle as you go vertical. Halfway up the planned vertical line, perform a half roll. At the top of the line, pull a half loop. You can try pushing the half loop at a later date.
Reduce the throttle as you begin the down section of your half loop, coming back to idle for the actual down-line. At the bottom of the down-line add a small “purr” of throttle, gradually increasing to half throttle after you complete the quarter loop to level flight. Your goal is to try to keep the speed the same all the way through the maneuver. This may well mean that you do not go so high that the airplane slows too much as gravity begins to win.
You will often see Humpty Bumps with qualifying descriptions that specify the up or down direction of the quarter and half loops. Any roll components will also be specified. My favorite is the Humpty Bump with Options. This maneuver is popular with aerobatic-schedule designers because it allows wind-correction repositioning if needed by the pilot.
The options are one half roll on the up-line or one quarter roll on the up-line and the down-line. This allows you to stay on line or move the airplane out slightly or even move it back if required. It does require a little thought when you elect to do the quarter rolls, or your model will finish up going the same way as when it entered the maneuver or perhaps exiting the Humpty Bump inverted.
One key point about turnaround maneuvers is that the entry and exit heights do not have to be equal. If it is used as a center maneuver, the entry and exit heights need to be the same—unless otherwise specified.
There are and have been schedules in which the Humpty Bumps are entered and/or exited inverted. Up- and down-lines can contain quarter, half, and full rolls and many other combinations. Sometimes they specify with descriptions such as “Full, pull, and pull with half roll on the down-line.” Please figure out which way the airplane is going to be before you try it for yourself. Do not, under any circumstances, pull up-elevator if flying inverted!
This apparently simple maneuver has many possible permutations. These complexities have kept me captivated for more than 20 years. Hopefully you will give it a try and get just as hooked! MA
Transcribed from original scans by AI. Minor OCR errors may remain.
