Test Pilot: Grading Glide

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Test Pilot

Grading Glide

Block column (3750 - 3250 = IN JUNE WE STARTED DISCUSSING 500). We entered the altitude engine-out glide performance block as a negative number to by explaining the forces that show it was a descent. act on an airplane during a Descent performance data reduction Determine the average deglide and illustrating how scent rate through the altitude these forces are identical to block by dividing the altitude ED KOLANO those that affect an airplane in block height by the time it a steady climb (with the obvitook to descend through it. ous exception of the power deDuring the flight I recorded the Our block height is in feet, and our livered by the engine/propeller). We explained the flight test technique flight test data on kneeboard cards elapsed time is in seconds, so we'll that provides the data to determine and transcribed them to a worksheet have to multiply by 60 to have the your airplane's maximum range for the data reduction. The work- answer in feet per minute. glide speed and showed how this op- sheet has a single matrix of flight -500 ———— x 60 = -833 timum condition occurs when the test data that's easier to work with 36 plane is flown at its maximum lift- than a bunch of test cards and sepaConverting the average rate of rate worksheets. Figure 1 is the workto-drag ratio (L/D). descent to feet per minute can also This month we'll use data gath- sheet with the raw test data (yellow provide a data check. Had we noted ered during the descent performance columns) and the numbers we calcuthe descent rate on the vertical flight test in the EAA Young Eagles' lated in the data reduction (blue speed indicator (VSI) during the RV-6A to show how to turn the flight columns). We'll use the 100-mph test data into a couple of the most data in the first row of our work- test, we could compare it to our calimportant airspeeds you'll ever need sheet as an example during our data culated value. A significant difference could help identify a wayward reduction explanation. to know about your airplane. data point caused by a timing error We performed our test by timing or even a faulty VSI. Enter the calcudescents through a 500-foot altitude Numbers block from 3,750 to 3,250 feet pres- Here's the basic idea for data reduc- lated descent rate in the Avg ROD sure altitude. The mid-block pressure tion. If we know the descent rate (average rate of descent) column of altitude was 3,500 feet, which is and airspeed during the test, we can the worksheet. We now know how fast we came where we recorded the outside air determine the flight path angle, and temperature during each run. Aver- the shallower the flight path angle, down and how fast we flew along the flight path while we were timing age airplane weight during the test the farther the airplane can glide. was 1,435 pounds, or 215 pounds Let's start with some easy math. the descent. We'll have to take a litbelow maximum. Our center of grav- Subtract the End Pressure Altitude tle detour here because our average ity was right in the middle of the al- from the Start Pressure Altitude and descent rate is a true airspeed, and record the difference in the Altitude our forward speed along the flight lowable range. Observec Test Airspeed Order





80 110 70 120

3 4 5 6 7 8

65 130 140

Start Press Alt (ffi

End MidAlt Press Block Time Block Alt Art (sec) (ft) (ft) (ft)


3750 3750 3750 3750 3750 3500 3750 3750

3250 3250 3250 3250 3250 3200 3250 3250

-833 -682 -1000 -625 -1071 -643 -1500 -1667

-500 -500 -500 -500 -500 -300 -500 -500

3500 3500 3500 3500 3500 3350 3500 3500

36 44 30 48 28 28 20 18




(de9C) 9 11 11 11 10 11 11 11

Flight Density True Path Alt Airspeed Angle (ft) (mph) (deo.) -5.15 106 3663 -5.25 3794 85 -5.60 3794 116 -5.50 74 3859 127 -5.51 3728 -6.12 3609 69 -7.12 3794 138 -7.35 3794 148


Low confidence Short run - good data

Figure 1 Sport Aviation


Test Pilot jA.in.Ci3FtjaL.3F~r"

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