Experimenter

JAN 2013

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/101874

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E- M a il Other Airspeed Calibration Methods I am quite disappointed in your airspeed calibration article(s)…. By Ed Kolano's own admission, "This is a risky flight environment." …But in fact, there are much better ways with much less risk. The picture that accompanies the article on page 44 shows a GPS on the glare shield…. The problem breaks down into three phases: 1) Obtain ground speed(s); 2) correct for wind; and 3) correct for density altitude to calibrated airspeed. We must assume level flight in smooth air in all cases. Phases 1 and 2 get you to true airspeed, which is best obtained with a GPS. You can set it to kilometers for greater accuracy, but the instrument is extremely accurate in any unit of distance. The National Test Pilot School provides some excellent resources. If you don't want to bother with a three-way run, then use this: At your predetermined test altitude, slowly turn until the corrected compass reads the same as the (magnetic) GPS track. You are now flying either directly upwind or directly downwind. Observe your groundspeed. Turn either 180 degrees or until the compass and GPS agree again, but in the reverse direction. Observe your groundspeed. Average them. That is the wind-corrected groundspeed, which is the true airspeed. This can be done safely and with less chance of atmospheric disturbances at higher altitudes where thermals are zero or minimal and where ground proximity risk is absent. An error of 2 or 3 degrees has almost no effect unless the wind is very strong. Assuming your OAT is correct, your altimeter is correct, and it's set for 29.92 inches HG, then use your E6B to get your density altitude and then the same instrument to convert true airspeed to calibrated airspeed. TAS to CAS. The more precise math can be obtained from the spreadsheets on my website. Howard Handelman EAA 111399 Ed Kolano responds: Mr. Handelman is correct in that there are several methods for performing airspeed calibration. Indeed, the "three-way run" he mentions is an excellent alternative. Incidentally, the source for that procedure is a paper written in 1998 by David Gray entitled "Using GPS to Accurately Establish True Airspeed." Using GPS for a variety of flight-testing techniques may be addressed in future columns. I chose the ground course at this early stage of Experimenter because it offers a better opportunity to address attendant flight-testing considerations such as test planning, hazard analysis, risk mitigation, error sensitivity, and engineering judgment with a healthy safety emphasis while keeping the technical aspects manageable. 4 Vol.2 No.1 / January 2013 PUBLICATIONS STAFF Founder: Paul H. Poberezny Publisher: Jack J. Pelton, EAA Chairman of the Board Vice President of Publications: J. Mac McClellan Homebuilding Community Manager: Chad Jensen Editor: Mary Jones/EditEtc. LLC Graphic Designer: Chris Livieri News Editor: Ric Reynolds Copy Editor: Colleen Walsh Multimedia Journalist: Brady Lane Visual Properties Administrator: Jason Toney Contributing Writers: Marino Boric, Hal Bryan, Budd Davisson, Cy Galley, Joe Gauthier, Dan Grunloh, Tim Kern, Ed Kolano, Stephen L. Richey, Jeffrey Weisel European Correspondent: Marino Boric ADVERTISING Display Sue Anderson Jonathan Berger Jeff Kaufman Mailing Address: P.O. Box 3086, Oshkosh, WI 54903-3086 Phone: 920-426-4800 Fax: 920-426-4828 E-mail: experimenter@eaa.org Website: www.EAA.org Need to change your address or have other membership questions, call 800-564-6322 (800-JOIN EAA). EAA® and SPORT AVIATION®, the EAA Logo® and AERONAUTICATM are registered trademarks, trademarks, and service marks of the Experimental Aircraft Association, Inc. The use of these trademarks and service marks without the permission of the Experimental Aircraft Association, Inc. is strictly prohibited.

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