Air Speed Indicators
One of the primary instruments required for gliders is the Air Speed Indicator. Winter have been making ASI’s since the 1930’s and whilst the technology had not changed in 80 years, the materials have, leading to better accuracy and calibration. A range of 57mm and 80mm indicators are available with a choice of sing turn or 1.5 turns for all glider types.
The science bit, how does it work?
The measurement and indication of airspeed is accomplished
on board a glider by the airspeed indicator ("ASI") connected
to a pitot-static system. The pitot-static system comprises a pitot probe facing the on-coming air flow to measure pitot pressure (also called stagnation, total or ram pressure) and one or more static ports to measure the static pressure in the air flow. These two pressures are compared by the ASI to give an Indicated Air Speed reading. The measuring element is an open diaphragm unit with excellent elastic properties; hysteresis (differences between advance and return movement) and secondary elastic effects are negligible. The effect total pressure an static pressure acts on the diaphragm, causing a deformation that is transferred to the pointer by a linkage and gear mechanism.
How to choose the right ASI
Depending on how much panel space or the whole you have available you need to choose between a 57mm or an 80 mm form factor.
Next bit is what is the maximum range you need to display. Typically this is at least 20% more than your aircraft Vne (The velocity never to be exceeded). So if you glider has a Vne of 100 kts then you need an ASI that displays at least 120 Kts.
Some ASI ranges are available in single turn or 1.5 turn. i.e. a single turn ASI will turn 360 degrees from Zero to max indicated speed. 1.5 turn ASI's turn through 540 degrees to indicate from Zero to max indicated speed.
There is also a choice of units of speed, Kts, Km/h and Mph. If you need anything other than Kts, give us a call!
Finally, your choice is when you would like the zero to start, either at the bottom or at the top? Why the difference? well if you have the Zero at the bottom, typically the operating speed of the glider will be at the top and some people think this is easier to see.
Each ASI is provided with a Form one and should be fitted and signed off by a qualified inspector with the appropirate documentation updates in your glider log book.
Großkinsky flap ring,
The simple way to find out which flap setting you should be in for your speed and weight. Working on a similar principle to the MacCready ring, this ring fits on the ASI rather than the Vario. You set it for the glider ballast and then read of the flap to be used at the speed you are traveling at. Really useful tool which is simple to use and makes flap decision making easy when the pressure is on. This can be ordered at the same time as an ASI or retro fitted to an existing Winter ASI.