Stick & Rudder

LANCAIR IVP—JIM KOEPNICK

Test Pilot

Climb Performance Data Reduction

I N LAST MONTH ’ S “T EST P ILOT ” ginally faster at the bottom you learned how to fly a and marginally slower at the climb performance flight test top of the block. Your postusing a modified check-climb flight data check for reasonprocedure. The technique of ableness should have assured flying a series of climb flights no significant ROC change at different airspeeds and within the altitude blocks, recording climb data through and this assurance lets us use several altitude blocks was Turning flight-test data into something usable the midpoint of the blocks. straightforward, but we cauThe midpoint of each altiED KOLANO tioned you about the sensitivtude block is simply the altiity of the data to the way you tude halfway between PA1 fly the tests. We stressed precise air- have a set of data like these for every and PA2. Calculate the midpoints for speed control, repeatability, test- airspeed tested. Let’s see how to get each block and enter them in the planning judgment, and the impor- the Calculated numbers. Mid column on the grid. Determine the height of each altitance of your qualitative remarks, all The Mid column contains pressure of which have a say in the accuracy tude block by subtracting the bot- altitudes for the middle of the altiof your data and the usefulness of tom of the block altitude (PA1) from tude block, and the OAT column conthe top of the block altitude (PA2). tains the outside air temperature (in your test results. Now that you have all your data Calculate the rate of climb (ROC) degrees Celsius for our example) for cards brimming with numbers, it’s through each block by dividing the the middle of the altitude blocks. Ustime to transform them into some- block height (Diff on the grid) by ing a density altitude chart or flight thing useful. The data reduction the time it took to climb through it computer, determine the density altiprocess is a little time-consuming (see formula below). If the block is tude (DA) for each altitude block but not difficult. This month our in feet and the time is in seconds, midpoint and enter these on the grid. goal is to determine which airspeed multiply the result by 60 to have the Put this data grid aside and reyields the best climb rate, what that answer in feet per minute. peat the number crunching for climb rate is, and how VY and climb every tested airspeed. When you’re PA2 - PA1 ROC = x 60 rate vary with density altitude. finished, you should have several Time grids, each pertaining to a specific Crunching Numbers Altitude blocks were necessary for test airspeed. Last month we provided a data grid timing, but they’re cumbersome to for your flight-test and postflight data use for flight planning. It’s easier to Drawing Plots reduction numbers. Figure 1 repeats use the block’s midpoint altitude. It’s time to draw, and you’ll need that grid with test data numbers that This is consistent with using the av- some graph paper. Starting with one came from a single test flight, i.e., a erage ROC through the block, but we grid, i.e., one airspeed, plot ROC vs. single climb airspeed. You should know that the airplane climbs mar- DA as shown in Figure 2a and fair a Sport Aviation

117

Test Pilot

100 kt Test Airspeed _______

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Test Data

line through the data points. This line shows your climb rate for any density altitude between the midpoint of the lowest altitude block and the midpoint of the highest altitude block for one airspeed. Repeat this plotting exercise for every airspeed you tested. When you’re done, you should have a plot that resembles Figure 2b. (To minimize clutter, the example has only four tested airspeeds.) The more airspeeds you test, the better your climb performance accuracy will be. We labeled our example tested airspeeds from fastest to slowest as V1 through V4, respectively. Figure 2b indicates airspeed V3 yields the fastest climb rates of the airspeeds tested, but we don’t know if there’s some other speed that is slightly faster than V3 (between V2 and V3) or slightly slower than V3

PA1 PA2 Diff Mid OAT DA 1250 3250 5250 7250 9250

1750 3750 5750 7750 9750

500 1500 3500 5500 7500 9500

10 6 2 -2 -6

VT

1250 3250 5250 7250 9250

PA1 PA2 Diff Mid OAT

Bottom of pressure altitude block Top of pressure altitude block Altitude block height Midpoint of altitude block Outside air temp

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118

MAY 2003

Remarks

1500 1200 750 550 400

DA VT Time ROC FPA

Density altitude True airspeed Elapsed time through block Rate of climb Flight path angle

Figure 1

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Density Altitude Figure 2b existing ROC vs. DA plot. In Figure 2b draw a vertical line up from the DA axis through the lines of different airspeeds. Draw horizontal lines from the ROC axis to the intersections of the vertical line you just drew and each airspeed line the vertical line passes through (Figure 3a). Now you can read the ROC for each corresponding airspeed at this density altitude. Create a new plot (Figure 3b) of ROC vs. Airspeed, by plotting the corresponding values from Figure 3a, and fairing a curve through these points. You can now see the maximum ROC occurs at the top of the curve at a speed between V2 and V3. Because the vertical line in Figure 3a represents a single DA, the curve in Figure 3b applies only to that single DA. Repeat this cross-plot procedure for several density altitudes, i.e., several vertical lines on the ROC vs. DA plot (our example uses three). It doesn’t matter which DAs you choose, but it’s a good idea to space them evenly. Your plot of ROC vs. Airspeed should now look like Figure 4a. The peaks of each curve represent the maximum ROC and VY for each density altitude. To find the maximum climb rate for any of the plotted DAs, draw a horizontal line from the peak of the DA curve to the ROC axis. To find VY, draw a vertical line from the peak of the DA curve to the horizontal axis. Although Figure 4a provides a lot of very useful inFor more information, visit SPORT AVIATION on the Web at www.eaa.org

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119

DA3 ROC 3 ROC 4 ROC 2 ROC 1 V3 V4 V2 V1

Rate of Climb

Rate of Climb

Test Pilot

DA2 Lower DA

DA1

Vy

Higher DA

Density Altitude

Density Altitude

Airspeed

ROC 3 ROC 4 ROC 2

Figure 4a

Figure 5a

V4 V3

V2

V1

Airspeed

Figure 3b

DA1

Max Rate of Climb

ROC 1

Rate of Climb

Rate of Climb

Figure 3a

Vy

DA2 DA3

formation, it’s still a bit cumbersome. If you draw a line connecting the peaks of the DA curves, you can now find VY and its associated ROC between the plotted DAs. The problem is that you must interpolate between the plotted DAs. Another cross-plot will solve this. To create a plot of VY for all density altitudes, draw vertical lines from the peaks of the DA curves down to the Airspeed axis as shown in Figure 4b. Where the vertical lines cross the Airspeed axis is the VY for that DA. Use these VY/DA data pairs to create a new plot of V Y vs. DA (Figure 5a). Fair a line through the data points. The final step is just labeling another vertical axis on Figure 5a. The dashed line connecting the peaks of the curves in Figure 4a shows the relationship between V Y and ROC. Draw a series of vertical lines from the Airspeed axis up to this dashed line. Then draw horizontal lines from the ROC axis to the intersections of the dashed line and vertical lines you just drew. Notice that for every V Y there is only one ROC associated with it, regardless of density altitude. Draw another vertical axis on the right side of Figure 5a so it looks like 120

MAY 2003

Airspeed

Density Altitude

Figure 4b

Figure 5b

Figure 5b and annotate the ROCs associated with the VYs directly across. Now you have a handy, singlesource plot that shows your airplane’s V Y and ROC for a range of

for example, shows the ROC penalty you’ll pay if you choose to perform a cruise-climb at a speed faster than VY for better engine cooling or outside view over the nose. You can create a plot similar to Figure 5b by using your cruise-climb airspeeds instead of the peaks of the DA curves on Figure 4a. Sounds like a winter project, doesn’t it? Yes, we went through a lot of number crunching, plotting, and cross-plotting this month, but we transformed all your raw climb performance data into a single plot for your operator’s manual. Next time we’ll fill in the VT and FPA columns on the data grid. We’ll do a little more math and a lot less plotting as we complete our data reduction by explaining how to take that same raw data and determine your airplane’s maximum climb angle and the airspeed at which it occurs (Vx). Editor’s Note: While test pilot Ed Kolano is on sabbatical, we’ll be reprinting some of his most popular columns from the past three years.

This month our goal is to determine which airspeed yields the best climb rate, what that climb rate is, and how VY and climb rate vary with density altitude. density altitudes. No more looking up tables or percentage calculations for nonstandard temperatures or wondering about the applicability of the airplane manufacturer’s claimed climb performance. These data are useful for variations in climb schedules. Figure 4a,