JUMP TAKEOFF
Gyroplanes with collective pitch change, and the ability to prerotate the rotor system to speeds approximately 50 percent higher than those required for normal flight, are capable of achieving extremely short takeoff rolls. Actual jump takeoffs can be performed under the proper conditions. A jump takeoff requires no ground roll, making it the most effective soft-field and crosswind takeoff procedure. [Figure 20-5] A jump takeoff is possible because the energy stored in the blades, as a result of the higher rotor r.p.m., is used to keep the gyroplane airborne as it accelerates through minimum level flight speed. Failure to have sufficient rotor r.p.m. for a jump takeoff results in the gyroplane settling back to the ground. Before attempting a jump takeoff, it is essential that you first determine if it is possible given the existing conditions by consulting the relevant performance chart. Should conditions of weight, altitude, temperature, or wind leave the successful outcome of the maneuver in doubt, it should not be attempted.
 
The prudent pilot may also use a “rule of thumb” for predicting performance before attempting a jump takeoff. As an example, suppose that a particular gyroplane is known to be able to make a jump takeoff and remain airborne to accelerate to VX at a weight of 1,800 pounds and a density altitude of 2,000 feet. Since few takeoffs are made under these exact conditions, compensation must be made for variations in weight, wind, and density altitude. The “rule of thumb” being used for this particular aircraft stipulates that 1,000 feet of density altitude equates with 10 m.p.h. wind or 100 pounds of gross weight. To use this equation, you must first determine the density altitude. This is accomplished by setting your altimeter to the standard sea level pressure setting of 29.92 inches of mercury and reading the pressure altitude. Next, you must correct for nonstandard temperature. Standard temperature at sea level is 59°F (15°C) and decreases 3.5°F (2°C) for every additional
Density Altitude—Pressure altitude corrected for nonstandard temperature. This is a theoretical value that is used in determining aircraft performance.
 

one thousand feet of pressure altitude. [Figure 20-6] Once you have determined the standard temperature for your pressure altitude, compare it with the actual existing conditions. For every 10°F (5.5°C) the actual temperature is above standard, add 750 feet to the pressure altitude to estimate the density altitude. If the density altitude is above 2,000 feet, a jump takeoff in this aircraft should not be attempted unless wind and/or a weight reduction would compensate for the decrease in performance. Using the equation, if the density altitude is 3,000 feet (1,000 feet above a satisfactory jump density altitude), a reduction of 100 pounds in gross weight or a 10 m.p.h. of wind would still allow a satisfactory jump takeoff. Additionally, a reduction of 50 pounds in weight combined with a 5 m.p.h. wind would also allow a satisfactory jump. If it is determined that a jump takeoff should not be conducted because the weight cannot be reduced or an appropriate wind is not blowing, then consideration should be given to a rolling takeoff. A takeoff roll of 10 m.p.h. is equivalent to a wind speed of 10 m.p.h. or a reduction of 100 pounds in gross weight. It is important to note that a jump takeoff is predicated on having achieved a specific rotor r.p.m. If this r.p.m. has not been attained, performance is unpredictable, and the maneuver should not be attempted.