Written by Dave Lockhart
Sport & Aerobatics
As seen in the SUMMER 2020 issue of Park Pilot
>> Many current-day aerobatic airplanes possess an extremely wide flight envelope. A single airplane can be capable of precise, traditional loops and rolls, extreme aerobatic tumbling maneuvers, and post-stall 3D maneuvers. Harriers, rolling harriers, and hovering are examples of 3D maneuvers in which an airplane is partially or fully stalled. Arguably, the cornerstone of 3D is a basic hover that leads to the torque-roll maneuver.
A hovering airplane is analogous to balancing a soccer ball on one’s head or spinning a basketball on a finger. When well executed, both might look easy, but they can be challenging to learn. Solid hovering and torque rolls are the results of a continuous string of fine control inputs to precisely maintain a vertical attitude.
The classic 3D hover/torque roll can be challenging to learn, but it has long been considered the cornerstone of 3D flying.
The general recommendation for learning any new maneuver is to practice at least “one-mistake high.” If an attempt at a new maneuver is not successful, there should be enough altitude available to make a comfortable recovery. Hovering is possibly an exception. Precisely maintaining a vertical attitude is more difficult with increased distance. There is the paradox: Hovering is easier to learn low and close, but the risk of crashing is higher.
There are several options to make it easier to learn hovering without undue risk to an airplane. First, be prepared to recover from a failed hover attempt. The airplane might “fall out” of a hover into any direction and attitude and in a partially stalled condition. A pilot should be capable of flying the airplane back to normal flight from inverted or knife-edge flight.
Shown is the traditional starting orientation for learning to hover. The challenge of the maneuver starts with achieving a good entry that results in the airplane at a nearly vertical attitude with no airspeed low to the ground.
Flight simulators can be valuable for learning to hover. Crashes simply need a tap of the reset button—which is much preferred to a bottle of glue.
The traditional starting point to learn to hover is to look at the canopy of the airplane. The most common entry is from a slow, low-level straight line. Firmly pull the nose to vertical and quickly complete a quarter roll to present the top of the airplane and add throttle to the amount needed to maintain a hover. The goal is to have the airplane approximately 5 to 10 feet high and 10 to 20 feet in front of the pilot in a perfectly vertical attitude with zero airspeed. The entry itself requires practice!
To maintain a hover, throttle, elevator, and rudder are used as the primary controls. Throttle is used to maintain altitude, which is easy to discern. Yaw attitude is easy to see, and rudder is used to keep the airplane from drifting to the left or right.
Pitch attitude is hard to determine because it is difficult to see if the airplane is leaning slightly forward (toward the wheels) or backward (toward the canopy). If the airplane is drifting forward (toward the wheels), it is leaning forward and up-elevator is needed to achieve a truly vertical attitude and stop the forward movement.
The ailerons can also be used in a hover, but they are the least effective control surfaces because most of the ailerons are located outside of the slipstream of the propeller. If the airplane rotates in the roll axis, it will generally be to the left. Rotation to the left is a reaction to the torque of the motor and an indication that the airplane is truly vertical or very close to it. Some airplanes will have enough aileron authority to completely stop the torque to the left; others will not.
Simulators are particularly useful for learning the needed control responses for different orientations of the airplane. When it is truly vertical, the motor’s torque will cause the airplane to rotate to the left in the roll axis. After it has rotated 90°, it becomes easy to see the attitude in pitch but harder to see the attitude in yaw.
Maintaining correct control inputs is a challenge during torque rolls when the airplane is rotating through different orientations.
As the airplane continues to rotate through 180°, up-elevator will move the airplane away instead of closer. Right rudder is still the airplane’s right, but it becomes left relative to the pilot (same idea as audience left vs. stage left).
Hovering and “walking” the airplane around in a hover are skills that many pilots can achieve in relatively short order. Maintaining full control of the airplane while it is torque rolling is comparably more challenging for most pilots.
What’s the next step? If an indoor flying site is available, the absence of wind is of great assistance when learning to hover. Fancy Foam (fancyfoam-com.3dcartstores.com), Twisted Hobbies (twistedhobbys.com), and West Michigan Park Flyers (wmparkflyers.com) all make suitable 3D airplanes of EPP foam construction. EPP is, for the most part, “bounceable,” and can absorb many low-speed crashes from low altitude.
Failed hover attempts require an immediate decision from the pilot. Option 1: Reduce throttle and accept a low speed “flop” to the ground from low altitude (which rarely damages an EPP model). Option 2: Advance the throttle and fly away in whatever attitude is needed (and accept the higher risk of damage if unsuccessful).
On calm mornings and evenings, indoor EPP foam airplanes can also be flown outdoors. Practicing over tall grass greatly reduces the probability of damage from a flop. Larger EPP airplanes can handle a much wider range of wind conditions and retain most of the resilience of smaller EPP aircraft. Those equipped with three-axis or six-axis gyros can greatly improve stability in a hover, giving a pilot more time to react.
During a torque roll, discerning the relative attitude of the airplane in yaw is most difficult when looking directly at the side of the fuselage.
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