I don't complain about flying. Just a good excuse to fly. Its sort of a let down when all the test flying is over. Now what? sharpen up my lazy eights, Chandelles, pylon eights, spins, etc.Not at all. I had done numerous climbs (and descents) in my RV-4 testing trying to determine Vx and Vy over many, many flights. Terrible results.
In less than an hour during one flight I had numbers for 1,200', 2000', 3000', 4000', 5000' and 6000'.
Not terribly accurate because I had a hard time keeping the altitude as the plane accelerated from near stall to max speed.
But that's a pilot issue.
I had a conversation with Nigel (I wondered about the need to start at 500' below desired test altitude). Turns out the method was developed for jets (taking a long time to spool up to full power). In my RV-4 it worked much better for me to slow down to near stall at desired test altitude and then advance to full throttle keeping my eyes glued to VSI. Discounting any prop stall, it's up to full power in a second or two. A factor is that RPM increases as airspeed increases, but apparently that's not an issue. Someone here may be able to explain that?
This method does require data logging. Having an Dynon 100 EFIS (10A is fine to), that is taken care of.
After a flight I download the data log, copy and paste airspeed, altitude and OAT columns into a spreadsheet (I use Excel 97). Identify the rows containing the acceleration, chart the airspeed column for those rows. Right-click on the curve and Add trend line. Select option to show equation for trend line. Right-click on the equation, Format Data Labels..., Number, Number, increase to 10 or more digits. Click on displayed equation, starting with the "+". copy equation into Notepad. Replace All "x" with "*B2^" (remove last "^"). Copy and paste the result into cell B2 in a new sheet for that test altitude. Click on cell B2 and drag down 30 or so rows. (When you click or select a cell or cells you'll see a solid black square in the lower right hand corner. Simply grab that square with your mouse pointer and drag that down.) Enter 0 in A2, 1 in A3. Select A2 and A3 and drag down 30 or so rows. (Column A is your time column in one-second increments.)
When you have a sheet for one altitude, you can copy that sheet. In the copy you just need to paste the equation for the next test altitude in cell B2 and drag down.
The attached needs do be redone with data from flights where acceleration is flown more accurately.
By displaying the climb vs airspeed columns as a XY (scatter) chart, you can hold up a ruler to the screen from 0,0 to where the ruler touches the curve and see Vx. Vy is of course the top of the curve.
Perhaps I should make a video on how to do this in Excel if anyone are serious about using the method.