Powered Parachute Flying Handbook

Chapter 2 - Aerodynamics of Flight

Turning Effect

Torque is a reaction to the mass of the turning propeller. If the propeller is turning to the right, the reaction is for the cart to want to turn to the left. Therefore, a right turn is sometimes designed into the PPC system to counteract the torque.

PPC manufacturers compensate for this with various designs:

1. Dual (counter-spinning) propellers. This is an ideal way to counter prop torque, but counterrotating gearboxes are complicated, more expensive, and weigh more.

2. Different riser lengths. On a clockwise-turning propeller, the left riser is longer than the right.

3. Swivel the wing attachment on a tilt bar above the cart.

4. Adjust the PPC frame (longer on the left, shorter on the right) to compensate for the engine torque (for a clockwise spinning prop).

Additionally, P-factor, as discussed in the Pilot’s Handbook of Aeronautical Knowledge can be a factor, producing a left turn if the nose of the cart is too high through improper CG balance of the PPC. Rotating propeller gyroscopic action can also produce turning tendencies if a force is applied which would deflect the propeller from its existing plane of rotation.

There is no corkscrew effect of the slipstream on a PPC because it does not have a tail in the propeller prop blast.

Weight, Load and Speed Changes

Greater load factor creates increases in speed. For unaccelerated and stabilized flight there are only slight variations in speed for different flight conditions. [Figure 2-29] For an 800-pound PPC in gliding flight, both the lift and drag components support the weight of the PPC (lift is 759 pounds, and drag is 252 pounds, with the resultant 800 pounds vertical force).

In level flight, the PPC does not have the vertical component of total drag to support the weight so additional lift must be generated through speed or angle of attack increases.

The numbers are small and difficult to measure or feel so the industry rule of thumb is to assume the PPC flies at a constant speed and angle of attack with changes in throttle. However, increased load (weight) and load factor has a significant effect on speed. [Figure 2-30]

As discussed in Chapter 2 of the Pilot’s Handbook of Aeronautical Knowledge the following points apply to powered parachute operations:

• During straight and level flight, the lift opposes the weight.

• In a banked turn, the lift is no longer directly opposite the weight; it is losing some of the vertical component of lift. More lift is needed so the vertical component of lift will equal the weight.

• In a banked turn, lift must be increased and load factor goes up. [Figure 2-30]

In a 45-degree turn, the 800 pounds weight would equal 800 times 1.4 or 1,120 pounds total load. This 45-degree turn, 1.4 G loading is the same as adding 320 pounds of weight to the 800 pounds. This new 1,120 pounds of lift must be produced by the wing by increased speed and/or angle of attack. If all the additional lift is produced from airspeed, airspeed would increase about 5 MPH, a noticeable difference. Reference your Pilot’s Operating Handbook to understand the specific design considerations for the aircraft you will be flying.

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