sport & aerobatics Park Pilot
Indoor flying season begins
Dave Lockhart
davel322@comcast.net
>>
For many fl iers in the northern US, wintertime is
workshop time. It’s time to complete preventive maintenance, repair broken airplanes, make performance upgrades to existing aircraft, and build new ones. It is also the time of year when many pilots partake in indoor fl ying— including aerobatics. Indoor fl ying can present
a variety of challenges, depending on the type of space. The most important parameter is the size of the space, but physical obstacles within the space, such as light fi xtures, basketball hoops,
utility pipes/conduits/rigging, etc., as well as lighting, moving air from ventilation systems, and temperature, can present challenges. Uneven lighting can
create bright spots and dark shadows—making it harder to maintain orientation with an airplane. Cold temperatures mean the motor and LiPo batteries will not produce as much power, and fl ight times will be shorter. One of the biggest misconceptions is that smaller airplanes are better suited for smaller spaces. It is assumed that they will fl y slower and be more maneuverable. In many cases, smaller aircraft might actually fl y faster. For aircraft of similar design (aerobatics for the purpose of this discussion), the fl ight speed is not infl uenced by size as much as it is by wing
Despite its size, the Arrow V.6 is easily flown in small gyms because of its light wing loading and high degree of maneuverability.
loading, which is a function of both size and weight. Airplanes with lighter wing loadings can fl y at slower speeds without stalling. The airfoil also affects the stall speed, but it is generally not a big factor for aerobatic aircraft suited for fl ying indoors because they all use similar symmetrical or fl at- plate airfoils. Maneuverability is also infl uenced by wing loading—lighter is more maneuverable—as well as control surface authority. Larger control surfaces and increased control defl ections generally increase maneuverability. Wing loading is typically expressed in ounces per square foot of wing area. For simple, constant-chord, rectangular-shaped wings, the wing area is calculated by multiplying the wing chord in inches (front to back) by the wingspan in inches (tip to tip), and then dividing that fi gure by 144 to convert it to square feet. An airplane with a wingspan of 36 inches and a chord of 12 inches, for example, would have 3 square feet of wing area: 36 inches x 12 inches = 432 square inches; 432 square inches ÷ 144 = 3 square feet. The wing loading is calculated by dividing the aircraft weight by the wing area. In this example, assume the airplane weighs 8 ounces. The wing loading would be 2.67 ounces per square foot: 8 ÷ 3 = 2.67.
20 PARK PILOT [Winter 2016]
Examples of aerobatic airplanes, to help illustrate the difference between size and wing loading, are as follows:
1. My Arrow V.6 weighs
5.5 ounces. The wing chord is 10 inches at the center and 4.25 inches at the tip. The average chord is 7.125 inches, so with a wingspan of 33 inches, the wing area is 235 square inches, or 1.63 square feet. The wing loading is 3.37 ounces per square foot: 5.5 ÷ 1.63 = 3.37. 2. My UMX Yak 54 weighs
2.5 ounces. The wing chord is 5.5 inches at the center and 3.25 inches at the tip, for an average chord of 4.375 inches. Its wingspan is 17.8 inches, so the wing area is 77.875 inches, or 0.54 square feet. The wing loading is 4.63 ounces per square foot: 2.5 ÷ 0.54 = 4.63.
These examples show that although the Arrow V.6 is more than twice the weight of the UMX Yak 54, the Arrow V.6’s wing loading is approximately 25% less. Both airplanes have large control surfaces and substantial control defl ections, but the Arrow V.6 will fl y at a slower speed and perform tighter loops than the UMX Yak 54. This is because of wing loading and because the Arrow V.6 is larger. With equal wing loading, a larger airplane (of the same design) will fl y slower
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