IMAC aerobatics

Model Airplane News, Sep 2002 by Wolanski, Dan

FLIGHT TECHNIQUES

Fly the 2002 IMAC basic sequence

Every year, the International Miniature Aerobatic Club (IMAC) releases new maneuver sequences for each of its classes. This year, IMAC added a fourth Intermediate class between Sportsman and Advanced to provide a natural progression through the classes. This has simplified the Basic sequence of maneuvers to attract more newcomers. The sequence can be flown with any size or type of aircraft, and that means anyone who has a plane capable of performing simple aerobatic maneuvers can compete in an IMAC event. A scale-type aircraft is not required until competitors reach the Sportsman class.

HOW TO FLY THE 2002 BASIC SEQUENCE

Here are some insights and tips on how to fly the sequence. To start, fly your plane into the wind, its wings level, approximately 100 feet high and about 100 yards away from you. Call the box to the judges by saying, "In the box!" (See the February 2002 issue of Model Airplane News for a schematic of the aerobatic box.)

The maneuvers shown on the left of the diagram should be flown approximately 600 feet left of center; the maneuvers on the right should be flown 600 feet to the right of center. The center maneuvers must be centered, or they'll be downgraded. I recommend that you use a minimum 100-foot altitude for all maneuvers and a 500-foot ceiling. This will allow for recovery in the event of any errors.

1. Loop. Fly to the exact center of the box and advance the throttle to full; begin to execute a loop with a diameter of 150 to 200 feet. Keep in mind that once you make the initial pull, you must use the same radius throughout the maneuver to keep it symmetrical. Gently pull through the first part of the loop and throttle back at the top. Coast through the back of the loop at idle and advance to 1/2 throttle as you exit the loop. It should end at the same place as you started it. Now keep your throttle at about 1/2; this will allow you time to think and set up for the next maneuver.

2. Humpty Bump 1/2 roll down. Begin this maneuver 500 to 600 feet from the center of the box. Pull a gentle radius up, climb vertically about 500 feet correcting the vertical line with rudder as the plane travels upward. When you reach the top, execute a 1/2 loop, reducing throttle to idle at the top of the loop. The radius of the loop does not have to match the previous radius. Travel straight down 200 feet and perform a 1/2 roll. Travel another 200 feet down and exit the maneuver using the same radius as you entered. You do not have to enter and exit the maneuver at the same altitude. Now advance to ! throttle and fly to the other end of the box.

3. Hammerhead (also called a stall turn). Fly through the center of the box to the end. When the plane is 600 feet past center, with the wings level, pull vertical using a gentle radius. Climb 400 feet, then reduce the throttle while still pointing straight up; the plane will begin to rapidly slow down. Once it has stopped completely, apply full rudder and blip the throttle. This will provide airflow over the rudder to help the plane rotate. Once it starts to rotate, slowly remove the rudder input and coast down about 150 feet. Pull out of the maneuver using the radius at which you entered the maneuver, and advance the throttle to 1/2. This maneuver does not require you to enter and exit at the same altitude.

4. Roll. Just before you approach the center of the box, apply aileron to start rolling, and use 1/2 to 3/4 throttle. Feed in down-elevator during the inverted part of the roll to avoid losing altitude. The speed or duration of the roll is not important; centering the roll in the box is. The airplane should be inverted during the roll as it passes the centerline. Also, there should be no change in altitude or heading.

5. Shark's tooth 1/2 roll up. At the end of the box, advance to full throttle and pull vertical. Once you reach an altitude of 500 feet, pull up-elevator until you achieve an inverted 45-degree down line, and reduce the throttle to idle, or slightly above. Hold the inverted down line for a few hundred feet and then perform a 1/2 roll to upright. Hold the upright line for the same distance as the inverted section. Return to level flight using the same radius as when you entered the maneuver. This maneuver does not have to be exited at the same altitude as you entered.

6. Vertical up line. This maneuver starts fairly quickly after the shark's tooth, so be prepared. At the center of the box, go to full throttle and pull your plane vertical while you remain on the centerline. To track the plane straight up the centerline, use whichever correction is necessary to counter the wind. Once you have reached 500 feet of altitude, push to level flight using the same radius as when you entered. Reduce throttle to 1/2 or less.

7. Split-S. As you reach the end of the box, reduce the throttle to idle and immediately perform a 1/2 roll to inverted flight; the plane's nose will drop slightly. Apply up-elevator and perform a constant-radius k loop to upright flight.