Speed to fly
The speed to fly theory is used to maximize the cruising speed of non-powered aerospace equipment ( glider, hang glider, paraglider ).
Basic assumptions
The speed to fly theory refers to a model which is shown on the right. The aircraft slides of an updraft to the next, covers a distance and loses altitude. Arriving at the next thermal, circling back up to the starting height. The pilot is flying too fast, so he comes deep in the updraft and have to climb a very long time. If it flies too slowly, though he comes to high but is very slow. Between these two extremes lies the optimal airspeed in the travel speed becomes maximum.
The speed to fly theory is based on the following assumptions:
Especially the last two assumptions are not always the case in practice. Does the rise of the next updraft not the expectation, then it is also flown with non- optimal speed. Can not be safely reached the next thermal, it can be useful under certain circumstances, to fly with a different drive.
Mathematical derivation
The travel speed
Equation ( 9) applies to any speed flown and each aircraft sinking.
The optimum airspeed
The term can be applied as a spot on the Y axis. The Optimal speed is obtained by applying a tangent to the glider polar. This is expressed by the expression on the left side of equation ( 6). On the Y - axis the determined optimum ride can be read.
The practice runs about like this: The pilot initially underestimated the strength of the next updraft and makes this size at its speed command (usually in the variometer integrated) a. During the gliding vary the speed depending on the meteorological updrafts and downdrafts () according to the specifications of the speed command. If the air mass decreases, the pilot flies faster; if it rises more slowly. By doing this, it optimizes its speed and is faster overall goal. A glider pilot, Paul McCready, invented to a rotatable ring which is attached to the variometer. You can read the optimal speed so directly. Paul McCready won the World Gliding Championships in 1956.
Approximate calculation of optimum airspeed
The speed polar of the aircraft is the relationship between airspeed and Eigensinkgeschwindigkeit of the aircraft represents the polar curve can be approximated by a quadratic function. By inserting the approximate equation in the equation, the optimal travel speed command can be easily calculated.
Swell
- Reichmann, Helmut - Streckensegelflug, engine book publishing house, Stuttgart 2005, ISBN 3-613-02479-9
- John Cochrane - A bit faster, please, German translation, original ( English ) (MS Word, 144 kB)
- Vogt, Matthias paper for the McCready theory PowerPoint