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The E-flite Sobre’ is an excellent all-around aerobatic flyer, and ideally suited to hovering. Article and photos by the author. Featured in the Fall 2008 issue of Park Pilot.
Is that airplane hovering like a helicopter? How can an airplane fly like that? Learning to hover is a challenge, but hovering is one of the more creative ways to fly airplanes. Most pilots consider hovering as the cornerstone of 3D flying, a style of aerobatic flying during which the airplane is in a state of stall for a high percentage of the time. Here are the hovering basics for model setup and flight techniques. When hovering, a model is essentially stalled, and the wing is not generating enough lift to overcome gravity; the airplane will lose altitude unless it gets some help. Gravity must be overcome by the thrust of the motor, while directional control is maintained by the elevator, rudder and ailerons to direct the propeller slipstream. Hovering essentials are an airplane with independent throttle, aileron, elevator and rudder controls, and enough power to climb vertically with authority. Hovering at 90 percent power leaves very little reserve for quick escapes if — no, when — needed, and relatively large control surfaces with lots of throw also help. Most pilots prefer a relatively aft center of gravity (CG) for 3D work in general, as having an aft CG makes the airplane more responsive.
The E-flite Sobre' is a very capable aerobatic airplane that is equally well suited to precision flying and 3D, indoors or out. The Sobre' has excellent control authority at all speeds, is light enough to fly slowly, and strong enough to handle high speeds and the occasional encounter with stationary objects. A hovering airplane is analogous to a soccer ball balanced on your head, or a basketball spinning on the tip of your finger. When done right, it looks easy, but anyone who has done these things knows that it is about continuously making minute adjustments, and the only time a major adjustment is made is when the ball is on the verge of plunging to terra firma. The big difference is that a model is far less likely to bounce on arrival. To prevent such encounters, try to learn new maneuvers, including the hover, at a relatively high altitude. When I hover my airplane at low altitude, I need to be able to accelerate quickly to regain airspeed and prevent a stalled condition. I need to be able to fly the airplane from inverted or either knife edge, and I need room to fly away safely in any direction. Before you attempt hovering, I recommend being comfortable with flying inverted and in knife-edge. Having a color scheme on your airplane that makes the top, bottom, left and right sides very distinctive may help keep you better oriented during recoveries.
So here ya’ go. Maximize all control throws on your airplane. Use long arms on the servos, and maximum travel percentages if your radio has that capability. Dual rate and exponential are helpful if your radio has these functions. Low rates are used for regular flying, and high rates with additional exponential are generally used for hovering and other 3D maneuvers. The use of rates and exponential help prevent the airplane from being too sensitive in regular flying, but still responsive for hovering and other 3D maneuvers. Practice in the early morning or late evening, when wind conditions are calm. A suitable indoor site is ideal. The common entry is to fly a straight-and-level, slow-speed, right-to-left line at 3 to 5 feet high. Pull the nose to vertical, then quickly complete a 90 degree roll to the left. You will now be looking at the top of the airplane. Add throttle to stop any descent, and reduce it to stop any climb. If the model is leaning forward (toward its wheels) or even walking (slowly advancing away from the entry position), a bit of up elevator will be needed to bring the model to a perfectly vertical attitude (in pitch), at which point the walking should stop. Similarly, down elevator must be used if the airplane is leaning toward its canopy. Rudder is used in the same way. If the model leans or walks to the right, left rudder is used to bring it to a perfectly vertical attitude (in yaw). Some airplanes consistently fall out of a hover in the same direction, and small adjustments to the elevator and rudder trims can often reduce or eliminate this condition. If the airplane consistently falls forward, add a couple clicks of up trim. If more than a couple of clicks is needed, it is an indication that the vertical CG and/or up/down thrust of the motor are not optimal for hovering. In the case of falling forward, shifting the battery, receiver or ESC toward the top of the model may help. Adding a small amount of up thrust to the motor may also help. Use small shims behind the motor to tilt the front of the motor upward. Similarly, left or right thrust adjustments can be made if the rudder needs more than a few clicks.
Ailerons are the least effective controls because most of their area is outside of the slipstream of the propeller so they cannot effectively deflect a lot of air. For the most part, if the airplane is walking in any direction, it will not rotate in the roll axis. If it does rotate in the roll axis, it will generally be to the left , becoming more pronounced as the airplane gets closer to perfectly vertical (in pitch and yaw), and even more so the longer the airplane stays vertical. Rotation to the left is a reaction to the motor torque. The torque of the motor is turning the propeller counter-clockwise, and the equal and opposite reaction is for the airplane to rotate to the left. Application of right aileron can be used to counter motor torque, but depending on the airplane, there may not be enough (right) aileron authority to completely stop the torque to the left. The fun begins when the model starts torque rolling. As the airplane rotates, its orientation changes but the control inputs required to maintain the hover do not. Once the airplane has rotated 180 degrees, 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 versus stage left). Many pilots learn to hover and slowly walk the airplane around fairly quickly, but take much longer to learn control of the model while it is torque rolling. Have your airplane checked out by a pilot with good hovering skills. Hovering is easier to learn with a model that has been set up correctly. Many a pilot has befriended the CA bottle after a failed hovering attempt, so RC flight simulators can be very helpful for learning the basics of hovering and torque rolls. Hitting reset is always easier than making repairs.
The E-flite Sobre’ is an excellent all-around aerobatic flyer, and ideally suited to hovering. Article and photos by the author. Featured in the Fall 2008 issue of Park Pilot.
Is that airplane hovering like a helicopter? How can an airplane fly like that? Learning to hover is a challenge, but hovering is one of the more creative ways to fly airplanes. Most pilots consider hovering as the cornerstone of 3D flying, a style of aerobatic flying during which the airplane is in a state of stall for a high percentage of the time. Here are the hovering basics for model setup and flight techniques. When hovering, a model is essentially stalled, and the wing is not generating enough lift to overcome gravity; the airplane will lose altitude unless it gets some help. Gravity must be overcome by the thrust of the motor, while directional control is maintained by the elevator, rudder and ailerons to direct the propeller slipstream. Hovering essentials are an airplane with independent throttle, aileron, elevator and rudder controls, and enough power to climb vertically with authority. Hovering at 90 percent power leaves very little reserve for quick escapes if — no, when — needed, and relatively large control surfaces with lots of throw also help. Most pilots prefer a relatively aft center of gravity (CG) for 3D work in general, as having an aft CG makes the airplane more responsive.
Dave Lockhart shows the preferred orientation of the model when learning to hover.
The E-flite Sobre' is a very capable aerobatic airplane that is equally well suited to precision flying and 3D, indoors or out. The Sobre' has excellent control authority at all speeds, is light enough to fly slowly, and strong enough to handle high speeds and the occasional encounter with stationary objects. A hovering airplane is analogous to a soccer ball balanced on your head, or a basketball spinning on the tip of your finger. When done right, it looks easy, but anyone who has done these things knows that it is about continuously making minute adjustments, and the only time a major adjustment is made is when the ball is on the verge of plunging to terra firma. The big difference is that a model is far less likely to bounce on arrival. To prevent such encounters, try to learn new maneuvers, including the hover, at a relatively high altitude. When I hover my airplane at low altitude, I need to be able to accelerate quickly to regain airspeed and prevent a stalled condition. I need to be able to fly the airplane from inverted or either knife edge, and I need room to fly away safely in any direction. Before you attempt hovering, I recommend being comfortable with flying inverted and in knife-edge. Having a color scheme on your airplane that makes the top, bottom, left and right sides very distinctive may help keep you better oriented during recoveries.
As Dave explains in the text, the airplane will likely rotate to the left when it is perfectly vertical. In this picture, the Sobre’ has rotated approximately 90 degrees to the left.
So here ya’ go. Maximize all control throws on your airplane. Use long arms on the servos, and maximum travel percentages if your radio has that capability. Dual rate and exponential are helpful if your radio has these functions. Low rates are used for regular flying, and high rates with additional exponential are generally used for hovering and other 3D maneuvers. The use of rates and exponential help prevent the airplane from being too sensitive in regular flying, but still responsive for hovering and other 3D maneuvers. Practice in the early morning or late evening, when wind conditions are calm. A suitable indoor site is ideal. The common entry is to fly a straight-and-level, slow-speed, right-to-left line at 3 to 5 feet high. Pull the nose to vertical, then quickly complete a 90 degree roll to the left. You will now be looking at the top of the airplane. Add throttle to stop any descent, and reduce it to stop any climb. If the model is leaning forward (toward its wheels) or even walking (slowly advancing away from the entry position), a bit of up elevator will be needed to bring the model to a perfectly vertical attitude (in pitch), at which point the walking should stop. Similarly, down elevator must be used if the airplane is leaning toward its canopy. Rudder is used in the same way. If the model leans or walks to the right, left rudder is used to bring it to a perfectly vertical attitude (in yaw). Some airplanes consistently fall out of a hover in the same direction, and small adjustments to the elevator and rudder trims can often reduce or eliminate this condition. If the airplane consistently falls forward, add a couple clicks of up trim. If more than a couple of clicks is needed, it is an indication that the vertical CG and/or up/down thrust of the motor are not optimal for hovering. In the case of falling forward, shifting the battery, receiver or ESC toward the top of the model may help. Adding a small amount of up thrust to the motor may also help. Use small shims behind the motor to tilt the front of the motor upward. Similarly, left or right thrust adjustments can be made if the rudder needs more than a few clicks.
Dave demonstrates how control orientation effectively becomes reversed as the airplane rotates through 180 degrees from the starting point.
Ailerons are the least effective controls because most of their area is outside of the slipstream of the propeller so they cannot effectively deflect a lot of air. For the most part, if the airplane is walking in any direction, it will not rotate in the roll axis. If it does rotate in the roll axis, it will generally be to the left , becoming more pronounced as the airplane gets closer to perfectly vertical (in pitch and yaw), and even more so the longer the airplane stays vertical. Rotation to the left is a reaction to the motor torque. The torque of the motor is turning the propeller counter-clockwise, and the equal and opposite reaction is for the airplane to rotate to the left. Application of right aileron can be used to counter motor torque, but depending on the airplane, there may not be enough (right) aileron authority to completely stop the torque to the left. The fun begins when the model starts torque rolling. As the airplane rotates, its orientation changes but the control inputs required to maintain the hover do not. Once the airplane has rotated 180 degrees, 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 versus stage left). Many pilots learn to hover and slowly walk the airplane around fairly quickly, but take much longer to learn control of the model while it is torque rolling. Have your airplane checked out by a pilot with good hovering skills. Hovering is easier to learn with a model that has been set up correctly. Many a pilot has befriended the CA bottle after a failed hovering attempt, so RC flight simulators can be very helpful for learning the basics of hovering and torque rolls. Hitting reset is always easier than making repairs.
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