Basic Aerodynamics

Wingsuit Flying and Basic Aerodynamics 1

What every good wingsuit pilot should know about wingsuit flying…

Does wingsuit fly or it is just an aerodynamic drag that lowers its vertical speed? Well, wingsuit really flies, since available area is not enough to produce such a low vertical speeds and flat flight path. But, the only force available to propel the wingsuit through air is gravity. What wingsuit tries to do is to use the gravity induced vertical free fall and turn it into as horizontal flight as possible. The same principle applies as for gliders, hang gliders and even square parachutes everybody is familiar with. Wingsuit flies because it IS an AIRFOIL, just like aircraft wing, square canopy or Space Shuttle (actually, by its basic flying form and flying characteristics wingsuit is more comparable to space shuttle then to any other flying object).

Wingsuit, like any airfoil, creates LIFT and DRAG. The better the ratio between lift and drag, the better flying body is. For a particular aerodynamic shape, this ratio between lift and drag varies with speed. There is a speed at which this ratio is the best, and this speed is usually 30 – 40 % higher than the stall speed (ask any glider pilot about minimum and best gliding speed, 90% of times the answer will be 55-65 km/h minimum speed and 80-90 km/h best gliding speed). Flying at the best gliding speed, the flying body will cover most distance for available height. Flying below or above that speed, the flying object will cover less distance for particular height. Every flying body has its minimum airspeed at which it will still generate enough lift to fly. Below that speed it looses lift and will stall (remember, square parachutes will also stall and lose lift. Forward speed in that case is close to zero, while vertical speed will more then double). The same goes for wingsuit. It requires speed to fly. But there is a question what is the best speed for the best glide in wingsuit. This is very complex question since wingsuit is not rigid airfoil. Every flyer flies differently, using slightly different arms, legs or body position. This means that every flyer is different airfoil. Add different pilot weight and size and different length of arms and legs and the issue gets even more complicated.

This is why it also very difficult to measure minimum speed for the wingsuit. But there is general rule for any flying body. Ratio between effective wing area and weight of the flying body is known as wing loading. Most of skydivers are familiar with that term in relation with their canopies. The higher the wing loading is, the canopy will fly faster, but will also have higher stall speed. Today, square canopies are operated with wing loading between 0,5 and 3,0 lbs per square foot. Hang gliders have wing loading around 1,2 and 1,5 lbs/sqft, and their minimum airspeed is around 35 km/h (22 mph). Cessna aircrafts have in general wing loading of 20 lbs/sqft, and their minimum airspeed is 80 – 90 km/h (50 – 55 mph). Space Shuttle, with its short span wings and extremely high wing load, lands at more then 350 km/h (220 mph!!!).

For average person size, wingsuit has wing area of 15 – 16 lbs/sqft, and the weight is 170 – 190 lbs. This gives us wing loading of 10,5 – 12,5 lbs/sqft, ten times higher then square canopy. Some basic math will tell us that for ten times bigger wing loading, the minimum airspeed will be roughly 3 times higher. This is consistent with measurements of wingsuit flights, where the best glide ratio was achieved at airspeeds of 130 km/h (75 mph). At that airspeed the vertical speed was 40 – 50 km/h, resulting in glide ratio between 2 and 2,5. You can go for lower vertical speed, but that will also result in significantly lower horizontal speed and poor glide ratio.

Regarding attempts of landing the wingsuit, much bigger wing area will be needed to generate more lift and reduce minimum airspeed. But human body has definite shape, which is not suited for flight at all, and we'll need at least few million years of evolution effort to change it to more appropriate shape for wingsuit flying. That means that wingsuit potential for more lift is limited by human inadequate shape and available strength. The only option for more lift will be some kind of rigid wings, but we already have these. They are called airplanes.

Also, if you are still thinking of landing the wingsuit, do one normal parachute jump, but when you open the canopy, try to position your body horizontally (can be done by hooking your feet around rear risers) and try to land small elliptical canopy in that position. After that painful experience, multiply pain and injuries by 9 (three times the speed = nine times the forces of impact = 9 times the consequences), and decide if you are willing to give it a try.

Robert Pecnik
moc.ylf-xineohp|trebor#moc.ylf-xineohp|trebor
www.phoenix-fly.com

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