RADIO CONTROL SCALE AEROBATICS
Michael Hurley, 11542 Decatur Ct., Westminster CO 80234; E-mail: [email protected]
DURING A RECENT conversation with a pilot who is new to Giant Scale and gasoline engines, the starting procedure came up.
It occurred to me that many pilots are getting into the Giant Scale gas airplanes for the first time and are pioneering Giant Scale aerobatic models at a local level, and they may not have a point of reference for some of the most basic procedures.
Many procedures and mechanical setups are similar to those of the smaller glow airplanes, but there are differences that, when recognized and implemented, can make working with a big model easy and safe.
In glow engines, fuel is drawn into the carburetor mostly from vacuum created on the downstroke of the piston. Only after the engine is running does a slight amount of pressurization take place in the tank from a line off the muffler.
It's common to open the carburetor venturi, cover the carburetor opening, and flip through a couple of times to draw fuel to the engine. With the throttle wide open there is a direct signal from the piston to the tank, facilitating fuel draw.
I've recently run into a few people who are unwittingly taking this procedure over to their big gas burners, thinking they need to choke them at wide-open throttle (WOT)!
Please, never flip your gas engine over at WOT. The design of the Walbro and Tillotson carburetors used on these engines is much more sophisticated than those on our glow engines, and opening the throttle does nothing to increase fuel draw.
Fuel is pulled from the tank by a very effective diaphragm built into the carburetor, and throttle position does not affect its efficiency. When starting a gasoline engine, it's best to choke with the throttle position at idle and to start at idle or maybe one click above idle.
It can be extremely dangerous to start one of these very powerful engines at full throttle. If you stay in the habit of checking to see that your throttle stick is down before you flip, you will be much less likely to have an accident.
Thanks to those of you who have E-mailed and called me with comments and questions.
The following E-mail query from Les Sullivan might be of interest to many readers, including those who are not Scale Aerobatics (SA) enthusiasts but who share the airways with those of us who are.
"With respect to your column, which wasn't in the latest issue of Model Aviation, you would be doing us guys a favor if you devoted some space to telling us just what constitutes 3-D flying.
"I know it only as a bunch of guys hovering vertically while I fly a racetrack pattern, and this tends to distract me. Please give us some word on this."
Aha! You noticed; the Scale Aerobatics column is published every other month. If you would like to see it every month, please let the people at Model Aviation know. After all, it's your magazine.
"3-D" can be described as "high alpha" or sustained, controlled flight, where the aircraft is stalled or otherwise not relying on lift from its wing. Flight is maintained by thrust generated by the engine, and control is maintained by huge control surfaces and radical control throws vectoring that thrust.
This type of gravity-defying flight is catching on with some of the more daring full-scale stunt pilots, and full-scale airplanes are being modified to enable the execution of these maneuvers. Yes, the full-scale aircraft can do this stuff too!
The Elevator is the most basic 3-D maneuver. The airplane is slowed to a stall. Full elevator deflection coupled with a balanced power setting keeps the aircraft's attitude horizontal or slightly nose-high. The airplane descends on a steep line of 60° or more. Any wing rocking is controlled with the ailerons, and direction is maintained with the rudder.
The Harrier can be described as high-alpha flight or an extreme nose-high fuselage attitude while maintaining very slow forward movement well below stall speed.
The Harrier is an extension of the Elevator maneuver in that controlling the aircraft is much the same, but power is added to maintain altitude, and movement is horizontal rather than descending.
The Waterfall is a series of stalled loops so tight that it appears the airplane is revolving around its wing axis. Enter by bringing the aircraft to a stalled vertical attitude. When the model comes to a stop, full elevator deflection is applied along with full power.
Timing is critical. The Elevator deflects or vectors the engine thrust in a strong burst, causing the fuselage to rotate around the aircraft's center of gravity. Some pilots elongate the loops by reducing power after the top of the loop, rotating into a short, inverted Elevator, then powering back into the Waterfall with another quick burst of thrust.
Control the aircraft using the ailerons to keep the model from rolling out of the maneuver. Use the rudder to keep the direction straight. Try to keep the airplane on an even descent while maintaining smooth, tight rotations.
The High Alpha Knife Edge is similar to a standard knife edge but at a much slower forward speed and a very high fuselage angle of attack.
Flown in the 3-D mode, this maneuver does not rely on airspeed but is sustained by the aircraft's enormous amount of power and its ability to vector thrust.
The High Alpha Roll is the quintessential 3-D maneuver. The figure combines a slow, forward momentum while rolling in an extremely nose-high attitude.
Power is continuously vectored to keep the nose up and the airplane aloft. Continual power management and complete aileron, rudder, and elevator synchronization work together to make the maneuver possible.
The High Alpha Roll can also be described as a Rolling Harrier.
The 3D Flat Spin varies from a standard flat spin in that very little or no aileron cross-control is needed. Throttle is kept low and is used to control the rate of descent, and ailerons can effectively control rollout during this maneuver's execution.
Rather than a traditional stalled spin, it might help to visualize the 3D Flat Spin as a rotating Elevator.
Many consider the Torque Roll the most difficult maneuver to perform with a fixed-wing aircraft.
The airplane maintains a constant altitude while in a vertical attitude. However, once the aircraft's neutral position is reached, the model begins to rotate around its center axis because of the offsetting torque of the engine.
Maintaining position becomes exceedingly difficult because of the airplane's continually changing view for the pilot. Control must be adjusted as the model rotates, and stick inputs invert with each turn of the aircraft.
There are many more variations of each of these examples, such as point rolling elevators, harrier rolling circles, and so on. The possibilities are endless, but this should give you a basis for understanding 3-D.
Back to the E-mail. I question whether there's really a "bunch" of guys hovering at the field while you fly. I don't think all of the pilots in the US combined who are capable of hovering would constitute "a bunch."
There just aren't that many people who possess the skills you see at some of the high-profile events, such as the Joe Nall IMAA [International Miniature Aircraft Association] Fly-in or the Tournament of Champions.
Maybe that's why 3-D gets so much attention from the press. I suspect that you're echoing a perception rather than an actual experience, and if you're distracted, perhaps it's because you'd probably like to watch. That's just a guess.
Flying in a racetrack pattern is a must for large-scale events with crowds of fliers, such as IMAA fly-ins, or for fields that commonly have four or more pilots in the air together. But for the stunt-flying enthusiast, that mode of operation is like putting on a pair of handcuffs.
If I had to fly a racetrack pattern all the time, I'd give up the hobby. One of the great things about model aviation is the diversity of styles and aircraft. We all have to live with each other and give each other a little breathing room once in a while.
The 3-D pilot is no different from the helicopter pilot learning to hover, the Pattern pilot practicing, the warbirds doing full-throttle strafing passes, or the Quickie pilot executing pylon turns.
And if a pilot truly is executing 3-D maneuvers close in while others are on the flightline, he or she needs to learn some manners.
Please, don't Torque Roll your airplane over the runway while others are on the flightline. It's inconsiderate and annoying.
Most of the guys I fly with really enjoy watching me do the 3-D stuff, and most of them will stop what they're doing and watch.
But on days when there is a fair number of fliers at the field, I'll often only get a couple of flights in where I can fly alone, rather than practice hard-core 3-D stuff with other pilots on the flightline.
Please send photos, drawings, scribbles, anything!
I'm looking for material for the column, and I'd truly like to see some new SA stuff. Does anybody out there have a new aircraft design you'd like to share? I'd like to hear from you.
What's going on in your part of the world? MA
Transcribed from original scans by AI. Minor OCR errors may remain.
