October 2012

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

Issue link: http://experimenter.epubxp.com/i/84816

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Page 42 of 47

Fl ight Testing Techniques Airspeed Basics By Ed Kolano I once had the privilege of flying an airplane that did everything at about 130 knots. Big deal, you say, because you've probably had that privilege yourself. The difference with this airplane was I did it somewhere on the other side of 60,000 feet. That put the true airspeed around 480 knots. Don't plan to fly that high? Doesn't matter. Understanding airspeed is essential if you want to know – and you do – your airplane's best climb speed, maximum range cruise speed, and just in case, its maximum range glide speed. To get there, you'll need to perform flight testing, and that involves a lot of work with air- speeds. Last month we identified the various kinds of airspeeds pilots should be familiar with. This month we'll get into the details. That'll put us in a good position to move on to calibrating your pitot- static system, which you'll have to do before you start collecting the data that will eventually become the performance charts in your airplane flight manual. There are five airspeeds to deal with. They are: 1. Observed 2. Indicated 3. Calibrated 4. Equivalent 5. True We're going to examine each of these airspeeds by themselves, then put the puzzle back together. Observed and Indicated Airspeed Observed airspeed is what you see on the airspeed indicator. I know, you thought this was indicated air- speed. Well, it is according to FAA publications and many pilot's oper- ating handbooks. There's no harm in doing this, because these manu- als just want you to be aware of the difference between what you see on the airspeed indicator and EAA EXPERIMENTER 43

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