Testing and Tuning

This section is dedicated to all things learned during flight testing.

One of the tasks pictured below was trying to get the right AHARS direction calibration. The alternator's field current dramatically affects both the compass and the AHARS (located at about the same distance from the alternator on the front dash). You can see by the plot that direction is significantly impaired at high charge rates. Luckily, the static draw for the Skyview system, transponder and radio is quite small and the error introduced by supplying that current once the battery is charged is repeatable. The calibration will be done after flying (to make sure the battery is fully charged) at with the engine at 1500 rpm after the battery has recovered.

Another fun task has been trimming the static system for airspeed. One of the plots below depicts different configurations I tried and the "Three DR30" plot shows the final solution. This configuration has allowed me to get ground speed to bracket true air speed when I fly a box (all four primary directions) which should happen when TAS is accurate.

Aug 8, 2012 Went out over the fields to do some climb performance work. The plots below were from runs from roughly 250 to 2000 AGL. Zoom in to get a clear picture. It was a hot day so density altitude is a bit high. I found it un-nerving to say the least trying to point the nose high enough to maintain airspeed at the lower numbers. I was using the forward air speed indicator and not Skyview's so my attempts to make 110, 100 and 90 knots did not pan out. No matter, I think you can get a good indication of performance. All CHTs stayed below 360 DegF with OAT at 80 Deg F. Fuel flow ranged from 29.6 to 28.4 gallons per hour as the plane gained altitude.

I've started to work with full fuel and cruise performance. I've included a plot below from a trip to La Belle. It was an economy setting 2321/21.3 rpm/map yielding 169 knots TAS at a density altitude of 8650 feet and 12.2 gallons per hour. These numbers were with full fuel (minus a few gallons) and pilot only. This should improve just a bit with wheel pants installed.

I did my first top speed run today (8/13) choosing about 700 AGL which equated to 2500 Density Altitude. True Air Speed was right at 202 knots with just under 30 gal/hr fuel flow and 31.5 inches of manifold pressure (about an inch over ambient). I need to verify this number against ground speed and then recheck all numbers with the wheel pants on.

Wheel Pants - If you told me wheel pants would be good for 13 knots I would tell you to check your instruments. Well, someone needs to tell me to check mine (and I will repeat the test tomorrow for that very reason). I finished mounting the wheel pants yesterday and did some high speed taxi work to confirm that nothing would rub with a little side yaw on the ground. All was well so I flew them this morning (8/15). I noticed IAS was a bit higher during my normal aerobatic session by about ten knots and the plane was not loosing as much energy as normal during maneuvers. I decided to drop down at the end of the session and try another speed run. This time I made a point of checking GPS ground speed in addition to TAS. The results are posted below and I confirmed that GPS ground speed was 217 knots while TAS was indicating 215 knots. It was early and the winds were calm. I typically see ground speed slightly higher than TAS. Manifold pressure before firing up (at ground level of course) was 30.0" so I was seeing better than a 2" rise in manifold pressure if you take into account the 650 AGL altitude. We calibrated the AHARS magnetic compass today so wind vectors should be much more accurate and useful in verifying the above data. I'll also do four passes on each of the primary compass headings to further verify these numbers.

Propellers - I had the chance to try an MTV9 -20 blade profile with a 203mm disk. The speed data is shown below. I will try to repeat this run on a calm morning as thermal turbulence made it hard to hold altitude (for us armatures).