>Keep in mind that the conversation was regarding landing speeds on a >windless runway, and why indicated airspeeds mean nothing from one >guy's plane to another. The context was advice for the appropriate >minimum airspeed one should shooting for. >Mark Langford ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Indicated airspeed is simply a "reference" number to fly by. It is a factor of how dense the air is that's rammed in to the tube and the accuracy of your individual system. An airplane will fly faster (indicated) at low altitude and cold dense air, and slower (indicated) at altitude and with warmer less dense air. As that is the same air the airplane sees and needs to fly, you fly the same indicated airspeeds regardless of the air mass you're flying in. If you approach at 80mph at see level or on a cool day, you approach at 80 mph (indicated) at Jeff's 7000 foot airport or on a warm day. Your actual speed over the ground will be different in each situation. That's why the ground speed at Jeff's airport gives you a blazing ground speed and the ground speeds Jeff's sees when landing say, at Mt.Vernon, seems so slow. The ground speed in each scenario is actually different. On your first flight do a power off stall and see what the ASI reads. Multiply that by 1.3 and use that for your approach speed. If your airspeed seems to be totally in error, disregard it entirely and fly the airplane by feel. The best approach is to check the accuracy of the system before the first flight using the water tube method. I once did a poor preflight and took off with the pitot / static tubes bent off line by 30 degrees or so. My first glance at the ASI on takeoff was when I was 20 or 30 feet in the air. I sensed something was wrong and climbed to altitude. Level flight and cruise power only produced 110 mph. I knew I had a system failure so I totally disregarded the instrument on landing. Don't let a single bad instrument indiction cause you to do something your gut says isn't right. Take a flight with an instructor and cover the ASI and see if you can fly the airplane without it's reference. I use my GPS to tell me time and distance to my destination, give me an indicated ground track, and get airport and airspace information. It tells me nothing on what indicated speeds to fly the airplane. It is useful, as Mark indicated, to check / compare actual liftoff and touchdown speeds on a zero wind day with what the ASI reads. With all of todays navigation aids it's still more important to remember your wife's birthday and your anniversary than to know what your true air speed is while flying. :-) Larry Flesner
