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 other light aircraft.
Issue link: http://experimenter.epubxp.com/i/81495
Fl ight Testing Techniques perform an airspeed calibration test after replacing your airspeed indicator, you can lump instrument and installation errors together and won't have to worry about the VO to separate VO from VI /VI relationship. for the compressible effects of air being shoved down the pitot tube at high speed. Generally speaking, if you fl y less than 200 knots and below 10,000 feet, this error is less than a couple of knots. VE – Equivalent airspeed is VC VT – True airspeed is VE due to insignifi cant compressibility errors) after it's been corrected for density altitude. (or VC VG – Ground speed is VT for wind. after it's been corrected So, to which airspeed did that advertised 110 knots refer? Or the cruise speed cited in either magazine article? Unless the ad or the author said, you can't know. If the author stated indicated airspeed and was kind enough to include density altitude or at least test-condition pressure altitude and temperature, you could perform the true airspeed conversion yourself. Of course you'd need that information for each source to have three VT values to compare. Being a diligent, precise, inquisitive pilot, you did the math, and the three sources still disagree. The answer might be as simple as different reviewers used different power settings or fl ew at different density altitudes for their cruise speed and climb performance checks. Okay, you should probably check this before doing all that conversion fun. Now what? Well, you might be out of luck in your comparison quest, but you still might be able to garner cruise performance information equally important to you, you savvy pilot. What if one reviewer used a power setting that resulted in twice the fuel fl ow as the other? Would an extra 10 knots be worth another $20 per hour to you? That burger will be just as tasty 15 minutes later. Wait a minute. If you pound down a few burgers, guzzle a quart of iced tea, top off your fuel, and pick Ed Kolano, EAA 336809, is a former Marine who's been fl ying since 1975 and testing airplanes since 1985. He considers himself extremely fortunate to have performed fl ight tests in a variety of airplanes ranging from ultralights to 787s. for most small airplanes after it's been corrected . If you (and you should) already have. Oh yeah, center of gravity location also affects performance. up a passenger (who also pounded and guzzled), your airplane will be heavier during the return trip. That's going to mean either a slower cruise speed or a higher power setting. Great! More cruise speed data that might not agree with all those other VT numbers you Sold on the importance of fl ight testing and criticality of having accurate performance charts yet? Plucking solitary performance numbers from company literature or magazine reviews won't help you plan your pre- or post-burger fl ights. And it won't satisfy the FAA either. A well-planned and executed fl ight-test program will get you those numbers, and we'll start next time with a detailed discussion of airspeed. Finally, questions about fl ight testing? Send 'em in. Chances are if you're asking a question, many others are wondering the same thing. So ask away and we'll share common questions here in this monthly column. E-mail experimenter@eaa.org; please put "Flight Testing" in the subject line. 42 NO. 1 / SEPTEMBER 2012