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Contra Rotating Propeller Drive System for use in F3A Pattern Competition

ContraRotating
Contra-Rotating Propellers eliminate the gyroscopic effects that exist when flying with a single propeller. Gyroscopic effects cause an airplane to yaw whenever the elevator is applied. The more elevator that is applied, the greater this yawing effect. Co
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Contra Rotating Propeller Drive System for use in F3A Pattern Competition
 
The Feature, the Advantage: 
  1. Contra-Rotating Propellers eliminate the gyroscopic effects that exist when flying with a single propeller. Gyroscopic effects cause an airplane to yaw whenever the elevator is applied. The more elevator that is applied, the greater this yawing effect. Contra-Rotating systems eliminate this, so there is no yawing of the airplane whenever the elevator is applied, and consequently, no radio mixing is required to remove it.
  2. Contra-Rotating Propellers significantly reduce the maximum torque that goes into the fuselage of the airplane. With a single propeller system the torque that goes into turning the propeller also reacts out against the motor mounts and the fuselage of the airplane, so if the motor is generating 7 N.m of torque to turn the propeller, the motor is also trying to rotate the fuselage with this same 7 N.m of torque. Whereas, with a Contra Rotating System the torque is divided by the gear ratio of the gearbox, so if the Drive is using a gearbox with a 10:1 gear ratio, then the torque into the fuselage is only 0.7 N.m. This means that an airplane with a Contra-Rotating Propeller System won’t change aileron trim on the downlines, or when entering a spin, or when coming in for a landing. With a single propeller system all of these situations will require different amounts of trim, which all need to be mixed in. However, with a Contra-Rotating Propeller System the trim never changes, so no mixing is needed.
  3. Contra-Rotating Propeller Systems eliminate the P-Factor effects that tend to yaw an airplane when the thrust line doesn’t coincide with the flight path of the airplane. This effect reverses when the airplane is flying inverted, so while right thrust in the motor can compensate somewhat when the airplane is flying right side up, rudder to throttle mixing is needed to compensate when the airplane is flying inverted. With a Contra-Rotating System no right thrust in the motor is required, and consequently no mixing is needed.
  4. Contra-Rotating Propeller Drive Systems have two propellers that provide more than twice the braking power that a single propeller system provides so ESC motor braking isn’t needed. Also, since ContraRotating Drive Systems have propellers that spin in opposite directions, each propeller generates an equal, but opposite braking torque, which eliminates the aileron trim effect that is seen on downlines when ESC motor braking is used with single propeller setups.
  5. Contra-Rotating Propeller systems are 15% to 20% more energy efficient than equivalent single propeller systems. This is because the air passing through the blades of the propellers is accelerated twice in order to generate thrust, instead of a single time as it is with single propeller systems. This means that each of the two propellers in a Contra-Rotating System is doing half the work that the propeller in a single propeller system needs to do so they can do their work with fewer viscous losses, and fewer losses due to radial air flow along the length of the propeller blades.
  6. The air that goes through the first propeller in a Contra Rotating System acquires a rotational twist, which is then cancelled out by the reverse rotation of the second prop. This has two functions. The rotational energy in the air is recovered as useful thrust, which increases propeller efficiency, and the air exiting the rear propeller flows straight back over the fuselage without rolling and yawing the airplane as it blows against the wings, the stab, and the rudder. This effect is most pronounced when the plane is flying slowly, such as during takeoff, or at the end of long verticals. A Contra Rotating system compensates for these effects so takeoffs are straight and true, and the airplane tracks straight when flying slowly after long vertical up lines.
Average rating: 5.0
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