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Frequently Asked Questions

With Answers

Q. What is Aerodynamics ?
Q What is Aerodynamic Drag ?
Q. What is an Airspeed Profile ?
Q. What is the difference between a Closed Circuit wind tunnel, and an Open                    Circuit wind Tunnel ?
Q. What is Efficiency ?
Q. What is the Exit ?
Q. What is a Jet ?
Q. What is Laminar Flow ?
Q. What is a Propeller Type Vertical Wind Tunnel ?
Q. How does Temperature effect flying ?
Q. What is Terminal Velocity ?
Q. What is a Test Section.?
Q. What is Turbulence ?
Q. What is a Vertical Wind Tunnel ?
Q. Why do skydivers use Vertical Wind Tunnels for practice ?
Q. Why are skydivers often dissatisfied with Vertical Wind Tunnels ?
Q. Can the air in an L-1 Vertical Wind Tunnel be heated and/or cooled ?
Q  How do windy/gusty conditions effect the quality of the jet ?
Q. Can the L-1 design be an indoor VWT ?
Q  What are the advantages and disadvantages of an indoor VWT ?
Q  Can the L-1 flight area be enclosed in a tube ?
 

Q. What is Aerodynamics ?
A. Aerodynamics is the study of air as a moving fluid. An aerodynamist studies or works with moving air, or objects moving through air. Wind tunnels are designed by aerodynamists.

Q What is Aerodynamic Drag ?
A. Aerodynamic Drag is the resistance an object encounters moving through air. In a VWT it is equivalent to LIFT because the drag is in an upward direction. Aerodynamic Drag is related to an objects size, shape, and surface texture.

Q. What is an Airspeed Profile ?
A. This is a line on a graph produced by plotting measurements of the airspeed in a jet taken at many points in a horizontal line passing through the center of the jet from one outer edge of the jet to the opposite edge. A very uniform jet will produce a flat line airspeed profile. The profile is an important measurement of the jet quality in a wind tunnel, and a strong indicator of the flight quality of a Vertical Wind Tunnel. In a Vertical Wind tunnel, these measurements are taken at different heights to show how much the jet quality decays with height.

Q. What is the difference between a Closed Circuit wind tunnel, and an Open Circuit wind Tunnel ?

Q. What is Efficiency ?
A. Efficiency is the measure of how much energy goes in compared to the work that is done. To a VWT operator it is how much fuel is used to produce the jet. A wider or faster jet has more energy and so requires more power to produce. Basically, if the jet has 1000 kW of energy, and the VWT is 70 % efficient, a 1300 kW motor is required. A less efficient VWT will require a larger motor and so costs more to operate per hour.

Q. What is the EXIT ?
A. This is where the jet enters the test section, or where it leaves the machine.

Q. What is a Jet ?
A. A Jet is the smooth uniform flow of air a wind tunnel produces. In a VWT it is often called a wind column. The Jet is the Flight Area of a Vertical Wind Tunnel.

Q. What is Laminar Flow ?
A. When all particles in a flow are traveling in the same direction at the same speed there is laminar flow. A goal of wind tunnel design is to produce as smooth a flow in the jet as possible so that movement through still air can be accurately simulated. In a VWT, a smooth jet is much easier and more fun to fly in.

Q. What is a propeller type Vertical Wind Tunnel ?

Q. What is Terminal Velocity ?
A  Terminal Velocity is the fastest speed an object will fall due to the limiting effect of aerodynamic drag. In a Vertical Wind Tunnel, this is the airspeed necessary to allow a person to fly. A heavier person and/or a smaller jumpsuit requires a higher airspeed due to the persons' higher terminal velocity.

Q. What is a Test Section.?
A. This is the area of the Jet designed for use. In a Vertical Wind Tunnel this is called the Flight Area.

Q. What is Turbulence ?
A. Turbulent Flow is the opposite of Laminar Flow. Turbulence can be in the form of ripples, eddies and vortices. Turbulence in a Jet causes the airspeed and direction at any point to change from moment to moment. In a VWT, turbulence makes flying more difficult.

Q. What is a Vertical Wind Tunnel ?
A. It is a machine that produces a vertical jet, or column of air. If this jet is fast and large enough, a person can float. Experienced fliers can perform an unlimited sequence of motions which can be acrobatic, or dance like. Skydivers practice in Vertical Wind tunnels, which are also known as Skydiving or Free Fall Simulators.

Q. Why do skydivers use Vertical Wind Tunnels for practice ?
A. Skydivers are typically limited to about 7 minutes of flight time per day. In a VWT a skydiver can get hours of flight time per day. Flight time is the competitive edge. For a four way team, skydiving costs about 10 times as much per minute as using a VWT.

Q. Why are skydivers often dissatisfied with Vertical Wind Tunnels ?
A. Many Vertical Wind Tunnel designs currently in use do not provide airspeeds high enough to satisfy skydivers. Also, poor jet uniformity makes some Vertical Wind Tunnels more difficult to fly in, and jet diameters are usually not wide enough for a four-way team. Even 2-way is difficult for experienced skydivers in most designs.

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