DC-3 Development Update 5: Systems simulation part II – Automatic Pilot: The simplified version

ilias.tselios · September 6, 2020

Hey all you! Been about 1 month and a half since the last update. Due summer, family vacation, and a couple other obligations, the development speed was at minimum, but now I am cranking the speed up towards the final stretch. Also the rhythm of development updates, will return to normal, around 1 per 2 weeks. Enough of that, let’s move on, and let’s talk about Auto(matic) Pilots!

HISTORY
The original DC-3 was equipped with the Sperry Type A-3A Automatic Pilot (see the difference in the wording?), a 1930’s system. I will not analyze the operation here, but in a next update, dedicated to the original version that will be simulated as well. In short, The automatic pilot, based on pneumatic operation, was developed to correct the angular deviations from straight and level flight, so WWII era bombers (like the B-17 Flying Fortress) become somewhat stable platforms for weapons (bombs) delivery.

RATIONALE
You can might imagine, that the operation was not very accurate, which led to development of the A-5 version later, during the WWII. During the development of our simulation, and after a long hunting for gathering good information since the use of the automatic pilot was mostly avoided(!), was obvious that in a flight simulation environment, will be extremely difficult to perform a controlled flight with ease. Overcompensation due to slow roll rates was a thing in the real aircraft, imagine in the sim! This led us to the decision to have a simplified version of the automatic pilot as well, as an option. Again, this does not means that the simplified version will allow to perform complex navigation tasks, but an “easier” method to controlled aircraft’s attitude, by the same means with the original version.

SELECTION
You will be able to select the mode you want to through the menu, where you will find a short description. Make sure that you select the version of the automatic pilot you want to fly with, either before flight, or with automatic pilot disengaged, to avoid any unintended flight path changes, or loss of aircraft control.

OPERATION
By selecting the Simplified mode, we can now fly! Here are the steps:

Fly straight and lever and trim the aircraft to hold this attitude.
Engage the automatic pilot (knob on the left lower part of the pedestal). The aircraft will enter into pitch and roll hold modes.
Use the AIL (aileron) knob to roll the aircraft left or right. A small tick mark will move accordingly (not shown in the picture) to indicated the commanded roll.
Use the ELE (elevator) knob to pitch the aircraft up or down. Small tick mark on the right side of automatic pilot’s attitude indicator (not shown in the picture) will show the commanded pitch.
The RUD (rudder) knob, controls the aircraft heading, once you are in heading mode. On the left side of the automatic pilot panel there are 2 heading scales or cards. The lower card should be set to the aircraft heading as in magnetic compass, with the cage button/knob below. The top card is the automatic pilot heading command.
To enter the heading mode, before engage the automatic pilot, you should trim the aircraft in straight and level flight, and use the RUD knob to match both scales. Don’t have to a perfect match, a couple degrees off still will work. But more than that, the automatic pilot will enter the roll/pitch mode. Then turn the automatic pilot on to enter heading mode. From this point on, you can use the RUD knob to fly to the desired heading.