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/149316
altitudes when the outside air temperature (OAT) matched the OAT during the test. We used the midpoint pressure altitude and the OAT (measured at the midpoint of the test block during each run) and an intimidating equation to calculate the 3,794-foot density altitude for the example test run in our worksheet. You can use a similar equation, a flight computer, or a density altitude chart to determine the density altitude for each of your test runs. The last column in our worksheet is the "Remarks" column. Some of this information came from the notes made in flight after each test run. We added other remarks during our analysis. Notice there are several runs with vertical speed indicator (VSI) readings. We did this as a "sanity check," and you can see that the VSI readings were close to the calculated ROCs but not close enough to use instead of the calculated values. Now, the Plots Figure 2 is a plot of climb rate versus observed airspeed. The numbers came from the "Avg ROC" and "Observed Airspeed" columns of the worksheet in Figure 1. Notice that because the OAT varied by one degree Fahrenheit during the testing, there are two different density altitudes, 3,794 and 3,859 feet. Because they're only 65 feet apart, we averaged them to get 3,822 feet. We labeled the plot in Figure 2 as 3,800 feet, but it's really 3,822 feet. We did the same thing for the 6,500-foot (6,700 feet density altitude) and 9,500-foot (9,600 feet density altitude) test blocks. Test Run Number 2 was annotated immediately after the climb as a low-confidence data point. That's why we repeated the test at the same 70 mph on Test Run Number 8. We plotted this data point (blue square in Figure 2) anyway, but we didn't use it when fairing a curve through the other points. We also labeled the 95-mph test at a 3/5 confidence level. We decided to keep this point because the elapsed times recorded for speeds slower and faster than this one indicated our timing for this point was probably reasonable. We performed the same data reduction for the other two sawtooth climb altitude blocks, which averaged 6,700 feet and 9,600 feet density altitude. After plotting the data for each altitude, we faired a curve through each set of data and removed the individual data points for clarity. Figure 3 shows our composite plot of climb performance curves. The peaks of the curves show the maximum climb rate and the maximum climb rate airspeed (VY) for each tested density altitude. Having the unique VY speed for just three altitudes isn't very useful, so we created a plot that filled in the gaps between the tested altitudes to show what V Y is for any altitude. Plotting the density altitude versus each density altitude's VY (the airspeed corresponding to the peak of each density altitude curve in Figure 3) gave us Figure 4. Drawing a line through the three points in Figure 4 gave us a curve that shows VY for any altitude between 3,800 feet and 9,600 feet density altitude. We extrapolated the line to zero density altitude for illustration, but this is a bit of an assumption stretch. Another sawtooth climb series that centered around 1,500 feet density altitude would have provided an additional data point through which we could have drawn the line, making the extrapolation more reasonable. The same argument applies above 9,600 feet. If you like, you can add a climb rate scale to the right side of Figure 4 to give you a single plot that will show both VY and the associated climb rate for any density altitude. Figure 1 EAA Experimenter 39