| 摘要 |
An audible speed indicator for hang gliders or the like comprises an air driven impeller 16 whose initial point of rotation start-up may be adjusted to correspond to the stall speed by rotating cowling section 14 relative to housing 13 to thereby vary the opening area of side exhaust windows 15. The impeller drives a slotted disc 18 which passes light pulses from a source 19 to a photocell 20, whose output triggers an oscillator 23. The oscillator output energizes a speaker 24, whose audible pulse frequency is thus proportional to air speed. The audio volume may also be reduced or blanked within a predetermined air speed range by a frequency detector 27, whose upper and lower triggering frequencies are adjustable.
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