I have been doing a lot of Garmin SmartGlide testing recently (yup - look for a possible future article in Kitplanes....), and today I took the RV-6 out in very smooth air to quantify the difference in descent rate in a glide with the prop full forward versus full aft.
Testing was solo, about half fuel, RV-6 with standard O-360 and a paddle-blade Hartzell (from the Jurassic, but recently overhauled...). Temperature on the ground about 40 degrees F, and ground elevation 4,400 msl (which is why I test so high).
Methodology was simple – I climbed to 10,200’, stabilized on autopilot with prop pitch full fine (forward, high RPM). Pulled the throttle to idle, engaged Smart glide to control speed at 93 knots, and let it descend, with the autopilot holding speed and heading. The EFIS captured steady state data between 9,800 and 9,200 msl. Then at 9,000, I pulled the prop all the way back to coarse (full aft, slow RPM), and let it stabilize. Descent rate immediately slowed. Got steady state data between 8,800 and 8,200. All data was recorded on the EFIS card, and I analyzed that at home, taking averages over the periods of interest, when airspeed was steady. Repeated the tests, and got good correlation between the two tests.
Prop Full Forward
RPM 1790
Descent 1400 fpm
Prop Full Aft
RPM 1030
Descent 910 fpm
It was amazing to see the see the difference - and the jump in size of the "glide zone" on the EFIS map.....
Testing was solo, about half fuel, RV-6 with standard O-360 and a paddle-blade Hartzell (from the Jurassic, but recently overhauled...). Temperature on the ground about 40 degrees F, and ground elevation 4,400 msl (which is why I test so high).
Methodology was simple – I climbed to 10,200’, stabilized on autopilot with prop pitch full fine (forward, high RPM). Pulled the throttle to idle, engaged Smart glide to control speed at 93 knots, and let it descend, with the autopilot holding speed and heading. The EFIS captured steady state data between 9,800 and 9,200 msl. Then at 9,000, I pulled the prop all the way back to coarse (full aft, slow RPM), and let it stabilize. Descent rate immediately slowed. Got steady state data between 8,800 and 8,200. All data was recorded on the EFIS card, and I analyzed that at home, taking averages over the periods of interest, when airspeed was steady. Repeated the tests, and got good correlation between the two tests.
Prop Full Forward
RPM 1790
Descent 1400 fpm
Prop Full Aft
RPM 1030
Descent 910 fpm
It was amazing to see the see the difference - and the jump in size of the "glide zone" on the EFIS map.....