Fligt Testing: Saw-tooth Climbs and Descents

Today was a maintenance day, so I changed the oil on the plane and generally poked and prodded to make sure everything was ok.  Tomorrow I'll be doing longitudinal, lateral, and spiral stability.

Meanwhile I started crunching the data from the previous two flights, which were saw-tooth climbs and descents.  Again following the protocol the climbs and descents are paired in airspeed so that it can be flown as a climb, then push over the top, pull the power to idle, and descend at the same airspeed.  The test order is randomized to minimize error caused by up or down drafts changing throughout the test, or weight loss or gain from burning fuel or refueling from creating a systematic error in the data.  The flight was broken into two, where I refueled in between.  Total flight time for these tests was something close to 3 hours.  

Again I am somewhere between mediocre and awful at holding my airspeed constant, but the data seems to have saved me, mostly.  I parsed most of it manually, but I think I can build in some automation into my spreadsheets to do it automatically.  Generally I chose 7500 ft DA as the crossing altitude for collecting data.  I picked up points from 7000 to 8000 and averaged the airspeed in that window as well as the vertical speed. I have data for most of them starting much lower and going much higher, so I could generate similar curves for different altitudes.

For the climb data, I got this:

Basically it is a very flat response curve, with some noise in the data.  Generally you couldn't go wrong climbing anywhere from 85 KIAS to something like 115 KIAS.  It looks like I have Vy climb at 90 KIAS, but I should probably repeat the data set between 75 and 95 to make certain that curve is correct. I have not corrected my pitot error, so these numbers are slightly high, but they generally agree with the published climb performance.  

If anything my climb rate is a little low.  I attribute that to the lack of wheel pants as well as the fact that I appear to be over-propped a bit.  WOT and best-power mixture generally were giving me about 2500 RPM at 7500 ft DA.  I'm going to leave the prop for now, and see how it does once the wheel pants are on.  My engine should be putting out a bit  more power than a stock 180HP parallel-valve O-360, but my Lightspeed prop is purported to be a 65.5" x 89".  The published data was done with a 3-blade Performance Prop that was 64"x76".  

The descent data looked very similar, although I think maybe I was better at holding a fixed airspeed on the descents.  Maybe because I wasn't worried about looking at CHT and oil temperatures on the way down.  It looked like this:

Here it is, again, pretty much by the published numbers.  It looks like I need to do some descents all the way down at stall speed to see if I can actually see the inflection point.  I'll be interested to see if these curves move up a bit once I have the wheel pants on it.  I suppose first I'd have to make a set of them...