Today's PPEL practice
Pierre, gents:
Went up today and had some fun practicing some PPELs to determine where a safe pattern would be and where hi key, low key altitudes would be. I also wanted to test the glide difference with the prop control full fwd (fine pitch) and the prop pulled full aft (coarse pitch).
Quick story (sorry, is it OK if I hangar fly with ya'll a bit
). As a new college-boy CFI, c1979 (yikes), I had an engine failure with a student in a C-150 during a final phase check for her PPL. Piston pin shattered, rod banging around the engine, and the racket was so loud I shut it down faster than you could say, !@#$%A^! We happened to be directly above a private glider field (appropriately enough), so I circled twice on the way down, and though my Navy days were still 2 years in the future, I flew what we would call a "double high key", or 720 degrees of turn to land. On the second downwind (low key), the prop stopped, and the plane became quite a glider. Stayed close to the field, slipped on base and final, landed, rolled out, and stepped out onto the ground...that's when the adrenalin kicked in the leg that hit the ground first started shakin'. The salty dog glider instructor came up, and I apologized for landing on his private strip, but said I'd had an engine failure. He just winked and said, "guess ya had no choice, now did ya son." He was cool! Then he said, "I looked up and saw ya, and turned to my student here, and said, 'that boy's prop's not turnin!'" Then he slapped me on the back and said good job. Like I said, he was cool, and my leg had stopped shakin'!
Interestingly, during the flight test today, I tested the pattern with the prop control forward, then pulled out, and it was almost as dramatic as the difference I saw with that 150 motor stopped (which is quite a sight to see, by the way!). I'll describe that more in the sequence below. First, here's an APRS grab of today's flight:
As I taxied out, there was a Waco biplane and a Citabria in the pattern on RWY 14, so my first takeoff was to the southeast and as I started up, both of them full-stopped and an L-39 came into the pattern on 8, so I did all the work in left traffic to RWY 8, with the wind about 130 @ 8-15. That made the wind direction sort of worst case, in that it blew me away from the field in the hi to low key portion, and then made it harder to make the field during the last 180 degrees of turn. But they weren't howling, so it was actually a good set up for testing.
The longer ovals are the climbs to hi key altitude, and the small circles are the PPEL patterns. Field elevation is 5,000', so I ran tests at 7,000 (2,000 AGL), 6,500 (1,500 AGL) with the prop fwd, and at 7K, 6.5K and 6,200 (1,200 AGL) with the prop pulled back. The 2K patterns were done at about 25 degrees angle of bank, the 1.5K patterns were between 25 and 30 degrees aob, and the one 1.2K pattern I did was about 35 deg aob, +/-. You can see the radius of turn differential in the APRS shot, with the larger circles being the higher patterns, and the tight circles being the lower patterns.
Since the runway is long, I used the fixed distance markers as my target, and used the old closed N-S runway/road as a marker to turn. Turns were flown at (well, at or near) 87 KIAS (my best glide) with flaps up until I had the field made. Rate of descent in the turns were as follows (and for reference, this is an RV-6 with an IO-540, and clipped wings...performance similar to a Rocket...depending on your model, your mileage will likely vary)
Prop fwd (fine): 1000-1500 fpm, tending to the 1500 side
Prop aft (coarse): 800-1100 fpm, tending to the 1000 range
From 2K, with the prop fwd, I hit a 1,000' low key, and the turn to final was comfortable. With the prop pulled out, I hit a 1,200' low key, the speed crept up on me and I had to slip on base and final to hit my mark, which was not that easy, because as I rolled wings level on final, she just floated and floated. I didn't test it, but if I was aiming for a short field, I would likely slip a bit more aggressively, and perhaps push the prop back fwd when I had the field made. I'll probably play with that a bit next time I practice this, and would like to hear other's thoughts on this.
With a 1500' hi key, I hit a 600-700' low key, albeit a bit closer abeam, and it was still pretty comfortable. With the prop pulled out at 1500', low key was a bit higher, about 800', and the turn to final required a little slipping...but I floated on final again.
When I did the pattern with a 1200' hi key, I had to stay pretty tight, and had to let the airspeed bleed a bit to make the runway, but held flaps till over the runway and I made it. There was not much room for error on that one.
So from this first test, I feel that if I can hit a high key between 1500' to 2,000' AGL, or a close-in low key between 1000' to 1200', I will be in the groove for the PPEL pattern. If I'm higher, I can extend the pattern a little or slip as needed. If the wind is really blowing, I'll want to be at the higher end of those ranges. If I haven't lost oil pressure and the prop will go coarse, then I may be able to hit the low end of the ranges and be confident of making the field. However, Murphy being who he is, I'm not going to count on the prop going coarse, and will aim for the higher end of the ranges if faced with the real McCoy.
It's a good exercise though, and was both fun and enlightening. I didn't play with the red knob at all...just don't have the cojones for that one. So I ran the tests at idle, and accepted a bit of after-firing (FWIW, in the normal pattern I normally use just enough throttle to keep it from popping). One interesting thing I saw, on the prop-back tests, when I pulled the throttle to idle, the popping started, and when I pulled the prop back, it stopped. Not sure why, but it did...maybe less back pressure from the windmilling prop?
Anyway, thanks for hanging in with the long post. Lemme know what you think, and what you see in your testing.
Cheers,
Bob