Landing the LM: P65, P66 and the Keyboard Commands

Wedge313

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Hello, trying to get comfortable landing the LM. The good news is, if do nothing after P64 and let it go to P65 the LM does a great job landing (perfect, obviously designed with me in mind). P66 can get interesting for me as I am still getting used to using the attitude to control horizontal/lateral velocity. A few questions: The only keyboard commands I've seen were posted here in the forum by Indy91 a while back, are those still current? Second, I'm not clear how I can increase/decrease my descent rate (the "-" and "=" keys don't seem to have any effect). I'd love to be able to hover briefly and experiment with the attitude/velocity control. Finally, Indy91 had posted a video landing a LM using Zerlina 56. In the video it seems that cycling the PNGS Mode from ATT HOLD to AUTO lets the computer null out any horizontal or lateral velocities. Is that a feature unique to the Zerlina programming? Any advice or trade secrets are appreciated, thanks.
 

indy91

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What is unique in Zerlina is that you can command horizontal and lateral velocities in P66 by deflecting the ACA and the LGC automatically holds those velocities. The nulling of horizontal/lateral velocities by switching back to Auto in P66 is not unique to Zerlina. It's a feature called "Auto P66" and got added for Apollo 13, at the same time as P65 and P67 got deleted. We only have a version of the Apollo 13 LGC software from before that feature got added so the first mission in NASSP where you get no P65 or P67 and some of their features integrated in P66 is Apollo 14. And Zerlina is essentially a branch of the Apollo 14 software, so it already had that feature (and expanded on it in ways that never made it into Luminary).

For Apollo 11 P66 is manual attitude control only, with attitude holding if you do no joystick inputs. Did you get into P66 at all from P64? It switches once you are in Att Hold and you command your first rate of descent change with those keyboard commands, which are still the current commands. One button press is a change of 1 ft/s in the descent rate. So if you got into P66 you already have commanded a change in the descent rate. You probably need to do a few button presses to notice a difference. And Apollo 11 also has an oscillating throttle command from the LGC, so it's sometimes difficult to see your current descent rate and any change in it. Just takes a bunch of practice.
 

Wedge313

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I've been getting the switch to P66 when I've switched PGNS MODE to ATT HOLD. But then I've sometimes gotten a little over-aggressive with my attitude control and developed higher velocities than I wanted, tried to arrest the descent rate, but haven't been successful. Just so I understand, these rate adjustments should work with the Throttle Control in Auto, correct? And the Numpad zero and decimal keys only come into play if I switch Throttle Control to MAN?
 

indy91

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Yes P66 uses auto throttle commands. So it should be flown with throttle in auto. Numpad zero and decimal can be used for P67, full manual control. Pretty sure it switches to P67 anyway when go to manual throttle.

You get P66 immediately when switching to Att Hold, without doing anything else? That doesn't sound right. Did you try some ROD switch commands before switching to Att Hold? When you use the keys for that switch you should also hear a clicking noise, like for any other switch. Do you get that?
 

Wedge313

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After my earlier post I was playing around with it and you're correct (as usual), it isn't the switch to ATT HOLD the causes the change to P66, I'm also mashing the ROD keys about that same time. To scan the instruments I'm finding most useful I have to set up my screen so I can monitor the FDAI, thrust, alt/alt rate, T/W, horizontal/lateral velocities and contact light. This way I can now see the thrust change when I make inputs to the ROD keys (so those are working, I wasn't really scanning the thrust before, just watching the descent rate and not giving it enough time to react to my inputs). But this setup forces me to displace the DSKY off-screen, so I'm not exactly clear on when the switch to P66 occurs. I've conditioned myself to make small corrections and be patient with them taking effect, and I'm able to land pretty much where I intend, avoiding craters etc. Thanks for the help, I feel like every time I post some stupid question I drag the Forum's average I.Q. down about 90 points, but I really appreciate the help.
 

indy91

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Ah there really are no dumb questions, especially not about complicated spacecraft like the LM. I'm sure someone will have the same question at some point and can now find this thread as reference.
 

Wedge313

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One issue I keep running into is: when searching for information I'll try finding it in the documentation (which tends to be scattered around, but I've piled up a bunch of links over the last year). If that fails I'll search here on the forum for posts that relate to my question. If that search fails I'll try a google search. When I feel I've run out of ideas I'll ask the question. But a few times here on the forum I've been reading a past thread that interests me, and buried in the thread is the answer to a question I just asked a few days earlier! So I know you (and others) end up answering the same questions over and over. I know I'm not the only one who appreciates you taking the time to answer them.
 
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