Powered Parachute Flying Handbook

Chapter 7 — Takeoffs and Departure Climbs

Runway Surface and Gradient

Runway conditions affect takeoff performance. Typically, powered parachutes take off from level grassy surfaces. However, runway surfaces vary widely from one airport to another. The runway surface for a specific airport is noted in the Airport/Facility Directory (A/FD). Any surface that is not hard and smooth will increase the ground roll during takeoff. This is due to the inability of the tires to smoothly roll along the surface. Tires can sink into soft, grassy, or muddy runways. Holes or other ruts in the surface can be the cause of poor tire movement along the surface. Obstructions such as mud, snow, or standing water reduce the powered parachute’s acceleration down the runway. Many of these same hindrances are multiplied in effect by the use of soft or wide tires that increase resistance themselves.

The gradient or slope of the runway is the amount of change in runway height over the length of the runway. The gradient is expressed as a percentage such as a 3 percent gradient. This means that for every 100 feet of runway length, the runway height changes by 3 feet. A positive gradient indicates that the runway height increases, and a negative gradient indicates that the runway decreases in height. An upsloping runway impedes acceleration and results in a longer ground run during takeoff. A downsloping runway aids in acceleration on takeoff resulting in shorter takeoff distances. Runway slope information is contained in the Airport/Facility Directory.

Takeoff Performance

Takeoff performance is partly a condition of accelerated motion. For instance, during takeoff, the powered parachute starts at zero speed and accelerates to inflate the wing, then to takeoff speed and becomes airborne. The important factors of takeoff performance are as follows:

• The takeoff speed.
• The rate of acceleration during the takeoff roll.
• The takeoff roll distance is a function of both acceleration and speed.

The minimum takeoff distance is of primary interest in the operation of any powered parachute because it defines the runway requirements. The minimum takeoff distance is obtained by taking off on a length of runway that allows sufficient margin to inflate the wing, perform the LOC procedure, and then satisfactory room to initiate a lift-off and climb.

The powerplant thrust is the principal force providing the acceleration and — for minimum takeoff distance — the output thrust should be at the maximum after the wing is inflated and successful LOC procedure preformed. Use smooth, gradual throttle settings to avoid porpoising. Drag is produced as soon as the powered parachute moves forward. The drag of the wing decreases as it rotates into position over the cart.

In addition to the important factors of proper procedures, many other variables affect the takeoff performance of a powered parachute. Any item that alters the takeoff speed or acceleration rate during the takeoff roll will affect the takeoff distance.

The most important variable to affect the takeoff performance is how fast the pilot can get the wing overhead, centered, and ready to take the load of the cart. Often, most of the runway used will be for the inflation and wing LOC procedure. Unlike almost any other type of flight, a powered parachute pilot has to create the airfoil and clear it on the ground before liftoff. It is always best to practice this skill at a longer field where mistakes can be made and corrected in plenty of time before taking off.

Even a slight headwind will have a dramatic effect on takeoff distances for powered parachutes because a wind helps inflate a wing much faster than can be done on a calm day. Even light winds can be a large percentage of the flying speed of a powered parachute. A powered parachute that flies at 35 mph taking off into a headwind of only 3.5 mph is working with a 10 percent headwind. A headwind that is 10 percent of the takeoff airspeed will reduce the takeoff distance approximately 19 percent. In the case where the headwind is 50 percent of the takeoff speed (a brisk 17.5 mph), the takeoff distance would be approximately 25 percent of the zero wind takeoff distance (75 percent reduction).

Gross weight also has an effect on takeoff distance. Proper consideration of this item must be made in predicting the powered parachute’s takeoff distance. Increased gross weight can be considered to produce a threefold effect on takeoff performance:

1. Higher lift-off speed,
2. Greater mass to accelerate, and
3. Increased retarding force (drag and ground friction).

If the gross weight increases, a greater speed is required to produce the greater lift necessary to get the powered parachute airborne at the takeoff lift coefficient. As an example of the effect of a change in gross weight for a typical PPC, a 21 percent increase in takeoff weight will require a 10 percent increase in lift-off speed to support the greater weight.

A change in gross weight will change the net accelerating force and the mass that is being accelerated.

The takeoff distance will vary at least as the square of the gross weight. Adding a 200-pound passenger to a machine that already weighs 400 pounds, with a pilot weighing 200 pounds, will increase the gross weight by 33 percent. That increase of one passenger will degrade the performance of the powered parachute dramatically. The 33 percent increase in takeoff gross weight would cause:

• At least a 25 percent decrease in rate of acceleration, and
• At least a 76 percent increase in takeoff distance.

For the powered parachute with a high thrust-toweight ratio, the increase in takeoff distance might be approximately 76 percent, but for the powered parachute with a relatively low thrust-to-weight ratio, the increase in takeoff distance would be more. Such a powerful effect requires proper consideration of gross weight in predicting takeoff distance.

The effect of pressure altitude and ambient temperature is to define primarily the density altitude and its effect on takeoff performance. While subsequent corrections are appropriate for the effect of temperature on certain items of powerplant performance, density altitude defines specific effects on takeoff performance. An increase in density altitude can produce a fourfold effect on takeoff performance:

1. Greater takeoff speed.
2. Decreased thrust and reduced net accelerating force.
3. Reduced rate of climb.
4. Increased runway required.

If a powered parachute of given weight and configuration is operated at greater heights above standard sea level, it will still require the same dynamic pressure to become airborne. Thus, the powered parachute at altitude will take off at the same indicated airspeed as at sea level, but because of the reduced air density, the true airspeed will be greater.

Proper accounting of pressure altitude (field elevation is a poor substitute) and temperature is mandatory for accurate calculation of takeoff roll distance.

The most critical conditions of takeoff performance are the result of some combination of high gross weight, altitude, temperature, and unfavorable wind. In all cases, the pilot must make an accurate calculation of takeoff distance from the performance data of the AFM/POH, regardless of the runway available, and strive for a polished, professional takeoff procedure. In the calculation of takeoff distance from the AFM/POH data, the following primary considerations must be given:

• Pressure altitude and temperature — to define the effect of density altitude on distance.
• Gross weight — a large effect on distance.
• Wind — a large effect on wing inflation and overall distance.
• Runway slope and condition — the effect of an incline and the retarding effect of factors such as snow, ice, or uncut grass.

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