DC-7 autopilot

[connieguy]

Tom,

   I have been flying the DC-7B and find that when I engage the autopilot and altitude hold it holds the correct altitude but over a period slowly wanders away from the heading I started off with. Am I right in thinking that it should not be doing this?

Ken

[Tom/CalClassic]

First, make sure the green light is on on the AP.

If there is a significant crosswind and it changes so that the AP has to make significant corrections then it is possible for it to be off by a few degrees. This simulates the real life need to occasionally adjust the rudder trim of the plane and the AP as I understand the real one does?

It's part of my coding to re-adjust the AP if the bank angle becomes too great during adjustments. The "realism" comes as a side effect. I do not use the FS Heading Hold because that causes rocking when it is engaged. If you want a modern AP with perfect behavior just replace the AP gauges with other ones.

[connieguy]

Many thanks for your reply, as always. Our experiences with the DC-7 autopilot seem to differ. It is my belief, rightly or wrongly, that classic autopilots would hold a course and an altitude, and that is all I want. In the 049 Constellation I use the classic Sperry, where the autopilot is switched off before one turns to a new course and then switched back on again to hold it. Maintaining the correct height also needs some adjustment at times, but it all works perfectly satisfactorily. I have used more than one autopilot in the Connie Team's L1049, the one I have settled on being the NEW CC autopilot you issued a little while ago. That can be used to turn without being switched off, of course, and then holds the new heading selected even in quite a strong crosswind. I have sometimes gone to frontal external view and noticed how the wings are banked to hold the heading against the wind. It also holds the height very well. On my system the DC-7 is holding the height but wandering off the heading even in very light winds. As such it is simply not suitable for long flights because I would need to sit before the monitor all the time correcting what it is doing. I have enjoyed short flights with the DC-7 but it is the longer ones where it really becomes noticeable, and as matters stand not useable.

[Tom/CalClassic]

The L1049 AP uses the FS Heading Hold, which does hold heading perfectly. My DC AP’s do not use FS Heading Hold, and will not keep a perfect heading. If you want that behavior I suggest you swap AP’s.

If you want I can supply the old AP to replace the new one.

[connieguy]

I have put the Super Connie autopilot in the DC-7, with an interesting result. It certainly holds the heading, but the turn knob doesn't work. However, switching to the yellow light allows you to adjust the heading and then when you have it going back to green will hold it, like the Sperry. I can settle for this. With the turn knob there can be a certain amount of hunting, and I have just used this system on a flight perfectly successfully. You might possibly consider a pinned post explaining the different autopilots and what they do in different aircraft. Thank you

[Tom/CalClassic]

Glad you worked out a solution.

[connieguy]

On the matter of whether autopilots could hold an accurate heading there is some interesting evidence in 'Air Navigation', published by the RAF in 1944. I think probably all the Allied four-engined bombers had autopilots. Certainly the B-17 did and the British trio of Stirling, Halifax and Lancaster. The British aircraft only had a single pilot and there was no dual control. When discussing the sextant this manual stresses how important the holding of an accurate and steady course is for the use of the bubble sextant, and that good cooperation between navigator and pilot is therefore essential:
'This naturally calls for a high proficiency in instrument flying on the part of the Pilot... Whenever provided, the Automatic Pilot should be used during Astro-observations'. p. 141.
And on page 145:
'It must be thoroughly understood that careful flying is essential for good astro observations... If available, an Automatic Pilot should be used by night. By day a D.R. Compass provides the best steering datum as it is free from precession; but unless the pilot is skilful it may be preferable to use the Automatic Pilot at all times'.