BillC Posted June 9, 2014 Report Posted June 9, 2014 I just flew a 1400 mile trip and boy are my arms tired...........REALLY! I don 't have altitude hold so I hand flew the whole way at 8-9000'. After carefully trimming for level flight, I couldn't let the yoke go for more than a minute or two without having to grab it to stop the divergence of one to two hundred feet per minute both climbing and descending. My passenger and I sat very still to see if the pitch sensitivity was from leaning forward. It wasn't. The airplane is now open for the annual and I can not find any loose connections in the elevator system, trim system or empenage. I would expect some thermal activity in places but some of the flight was over the Atlantic ocean. Made no difference. Has anyone experienced this and found a problem or do I need to look harder? It's a '79 M20J. Thanks, Bill 1
jlunseth Posted June 9, 2014 Report Posted June 9, 2014 You can certainly look further for issues with the aircraft, but I don't find what you experienced to be unusual. You don't state your altitude, but I have found that thermals are at issue at pretty much all altitudes up through my service ceiling, which is 24,000. At higher altitudes they are not "the bumps" as they are at lower altitudes, they are simply upward and downward pushes and pulls that result in the aircraft changing altitudes often, and these currents are usually over a larger area than the one's at low altitudes. It depends on the day. This past weekend I flew KOLV to KFCM with a diversion to KDSM for fuel. I have an AP and it was holding altitude perfectly, but I noticed small changes in the MP and RPM, which are an indication that although the aircraft is level, it is alternating flying downhill and uphill depending on the currents. Some days they are not there at all, this past weekend I was over the backside of a large front and they were definitely there. On one trip out to KRAP a year ago we saw an airspeed drop of close to 15 knots for awhile, right after passing over the back side of a front. It was definitely not the plane, it was a prolonged downdraft or wave. It is also possible that you were loaded with a CG in a location that made the aircraft less stable than normal. In my aircraft, that is usually a CG close to the forward limit.
KSMooniac Posted June 9, 2014 Report Posted June 9, 2014 Sounds like some mild, long-period mountain wave activity to me.
John Pleisse Posted June 9, 2014 Report Posted June 9, 2014 Check push tubes, trim jack screw and all bell cranks for any play. I get this over rough terrain and at lower altitudes, but not at 9 over the water or in flat lands.
KSMooniac Posted June 9, 2014 Report Posted June 9, 2014 I get it out here in the flat lands, sometimes up into the teens. With altitude hold engaged, it shows as airspeed fluctuations and trim commands to maintain level flight. 1
Alan Fox Posted June 9, 2014 Report Posted June 9, 2014 It sounds like a Mooney......My E is very pitch sensitive in the summer months.... 1
BillC Posted June 9, 2014 Author Report Posted June 9, 2014 I'll check everything again real close and then look into an S-tec ALT added to my Century 21 autopilot. Thanks for the help. Bill
Marauder Posted June 9, 2014 Report Posted June 9, 2014 I'll check everything again real close and then look into an S-tec ALT added to my Century 21 autopilot. Thanks for the help. Bill Even with the STEC alt hold you will see what Scott describes above. My airspeed will fluctuate 5 KIAS as the AP rides the waves.
BillC Posted June 10, 2014 Author Report Posted June 10, 2014 Jim, I didn't calculate the CG for this flight but loaded it as follows: Pilot and Pax - 370 lbs Dog in rear seat - 50 lbs. Baggage comp. - 35 lbs. Full fuel - 64 gals. My Pilots Handbook is in the airplane otherwise I'd be able to tell you the CG. Thanks, Bill
jlunseth Posted June 10, 2014 Report Posted June 10, 2014 So a Crappy ride to Krap....hmmm... The ride was not bad, but I get your pun. My personal favorites, of the places I have landed, have been KCLT and KSUX. KRAP is pretty mild by comparison. Sioux City has been trying to get theirs changed with the FAA for years, without success. Even with the STEC alt hold you will see what Scott describes above. My airspeed will fluctuate 5 KIAS as the AP rides the waves. That is pretty typical in my experience also, for just about any long distance trip. Glad to have Alt Hold.
chrisk Posted June 10, 2014 Report Posted June 10, 2014 I've experienced this in a number of planes. I've always assumed that the oscillation was natural, where the plane would cycle between pitching down, gaining speed, then climbing again (because of the speed), then slowing because of the climb. Most of the time, I just set the altitude hold. But I seem to recall if you caught the oscilation at the right time (half way up or down) it would stay stable for a few minutes. I'll have to pay attention when I work on my hand flying again.
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