History, and why pitch and trim rules were important and worked.
The pitch and trim rule was created before turbine engines appeared.
Instrument flight took place in an environment mostly without radar.
ATC kept track of where you were from position reports, and filed airspeed.
When I started doing cross countries in a Cessna 172, my flight planning used a very few airspeeds, and the goal was simplicity. Climbs were at 90, and I knew time to altitude for all the altitudes I regularly filled. That made the first segment easy to put into the time total for the plan.
Cruise was always at 120, 2 miles a minute, so divide any segment by 2, and you have the time for that segment. That made the calculation by ATC for where you SHOULD BE for crossing traffic at your altitude stone simple for the controller. Every reporting point on the chart, you gave the name of the present point, estimated time and name of the next reporting point, and just the name of the point after that. There were more than 30 reporting points between Washington DC and St. Louis. We did not have small digital calculators, and neither did controllers, they had not been invented.
Descents were at 120 for the same reason.
If you have read this far, the use of trim explanation starts here.
Climbing out, at full throttle, I pitched to 90, and trimmed to hands off. As the plane climbed, the rate of climb decreased as air density reduced power available, but the plane continued to fly at 90.
As the cruise altitude was approached, the wheel was pushed forward gently, reducing the rate of climb and increasing the true air speed to 120, hopefully just as the filed altitude was reached. Then power was reduced to maintain altitude. Once equilibrium was found, trim to zero pressure on the wheel, and power was adjusted occasionally to correct for any tendency to climb or descend, but the magic 120 remained constant for the simple reporting calculation. Pushing or pulling the wheel and then retrimming resulted in speed variations, which were undesirable. This was especially true if the altitude change was the result of up or down drafts, as using the elevator resulted in large changes in airspeed, wrecking the time to reporting point.
If head or tail wind components were large, the circular slide rule became necessary to calculate, and the workload went up, as the ground speed was what went into the calculations.
Going over the Appalachian Mountains, E or W, I have used full throttle to maintain altitude in downdrafts, and 1500 RPM to avoid going too high. Trim and elevator not used, the reporting points arrive right on time.
I have never gone from full throttle to idle without touching trim, to see if the airspeed is constant over that large a power change, but 1500 to 2700 was quite close.
Sudden changes in power, such as from idle, on the approach to landing at 70, followed by full throttle for a go around, will cause a violent pitch up to an unsafe angle of attack and stall, before the plane has time to oscillate and settle at a stable climb at 70. I have seen a pilot do that and crash.
On ILS’s, I customarily trimmed to 90, and then adjusted power to stay on the glide slope. The increased or decreased power from normal represented the head wind or tailwind component, and the power necessary to get the rate of descent to follow the glide slope, due to non standard ground speed.
When I received my PPL Adcock A/N ranges still existed, and Norfolk VA had an Adcock approach still in use.
