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/134623
Rate of Climb Once you've determined the altitude change for each test event, calculate the average rate of climb (ROC) by dividing the altitude change by the elapsed time for that change. The numbers include standard atmospheric values and conversions that allow you to plug in OAT in degrees Centigrade and average pressure altitude in feet. However you determine density altitude, enter it in the worksheet under the "Avg DA" column. True Airspeed We multiplied by 60 to convert the ROC to feet per minute. Enter this value in the ROC column of the worksheet. Now you have density altitude and calibrated airspeed, so use whatever gizmo or equation you're comfortable with to determine the true airspeed for each test point. Enter the true airspeed for each test point in the TAS column of the worksheet. For our example, 85-knot point, the density altitude of 2,182 feet and calibrated airspeed of 85 knots translates to a true airspeed of 88 knots. Average Pressure Altitude Flight Path Angle You'll need a pressure altitude for further calculations, but your test spanned an altitude block. Because the altitude block was limited to 500 feet or less in the test procedure, we can use the average pressure altitude without suffering a significant error. This assumption is further supported by the fact that the largest altitude block measured during our example test was only 360 feet, and the OAT only changed one degree throughout the testing. Figure 2 shows how the relationship between an airplane's true airspeed and vertical speed determines its flight path angle, γ. Recalling basic trigonometry, Average pressure altitude is the halfway point between the start and end altitudes during each test. ROC, on our worksheet, is listed in feet per minute, while TAS is shown in knots; so a conversion to the same units is necessary. Perform this calculation for each test, and enter the average pressure altitude in the "Avg PA" column of the worksheet. Now, both ROC and TAS are in feet per minute. If your airspeed indicator is marked in statute miles per hour, just substitute 5280 for 6076 in the equation. Back to the flight path angle calculation: Average Density Altitude Not too long ago I'd tell you to get out your whizwheel for the density altitude determination. These days, get out whatever electronic thingie does it for you. You might have even recorded density altitude directly from some gizmo in your cockpit during testing. If not, you can use one of the density altitude charts readily available in a variety of aviation publications or the Internet. For you hardcore number crunchers: We now know what the sine of the flight path angle is, but we need to convert that to degrees. Using a trigonmetry table or inexpensive calculator, EAA Experimenter 39