I'd like to tell you about some RV-12 fun with VNAV. Although I am instrument rated, I’m not current and would certainly not try this for real. It’s just for fun. As a matter of fact, fun is the reason I built my RV-12. I had no plans to ever fly it in IMC, or to the NW Territories or even to Oshkosh. I like my comforts, and am a bit too old for that all day in the cockpit, or busy IFR stuff, I’ll be eligible for the UFO’s
two years from now.
But, I love the neat IFR pilot stuff and one of the main reasons I spent the time and money last winter to upgrade my D-180 panel to SVT was all that eye candy, and capability, on the screen. For fun only, of course
So, yesterday I launched out of my home aerodrome (KPWT) to try out the SV autopilot on a NAV to an extended runway centerline, and descend on a VNAV profile to the runway, on autopilot. This airport has an ILS and also a VNAV approach to RWY 20. The approach angle is 3.0°. In checking the default SV settings I found the VNAV glide slope angle set to 2.5°, so I had to change that. I also changed the height above the runway from 100’ default to 50’. I was not too sure what I was doing here.
Once airborne and about 15 miles out, I set the ALT target to 2500’ in order to fly to the IAF (WUMOX) and intercept the glide slope from below and instructed the autopilot to start down to 2500’ and fly a HDG of 152° to intercept the GPS extended centerline outside of WUOMOX. During the descent I armed VNAV. Then I noticed that the ALT HOLD was 2700 and the target altitude was now 491’. At the time I was not too sure what had happened.
Now I realize that arming VNAV activates ALT HOLD at the point where you pushed the button. OK, I armed VNAV while passing through 2700’; that explains that. I also could not figure out why my target altitude was 491’, a seemingly peculiar number. Back on the ground doing the debrief, I see now that the Touch Down Zone Elevation is 441’ and with my map options set to 50’ above the runway the total is exactly 491’. It’s nice when you see how everything adds up!
In this screenshot the AP has turned her onto the GPS track line and approaching WUMOX the blue “angle” tick mark and the magenta “VS’ tick mark are coming together as they should be. There is a rain squall approaching the airport at about 19 knots. There are a couple of traffic targets that could become factors.
Passing the IAF the VNAV activates in the top bar, she points the nose down and the VS and tick marks are right together and we’re headed down to the target altitude of 491’ (50’ AGL) over the TDZ....it can’t be legal to be having this much fun!
The pilot does need to control airspeed with the flaps and throttle…no auto-throttle — dang.
After this I goofed up trying to take a screenshot when the runway came into view on the synthetic vision and I touched the GO AROUND button and Chatty Patty told me to go around. I didn’t know what the autopilot was going to do and getting close to the ground so I pushed the auto pilot disconnect. I beat the rain squall in and got her back in the hangar.
It was a short flight but the SV dished out the fun in spades. I’m liking it.