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T-38 autopilot tricks & tips :: Archived
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JG300-Stoopy
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Location: Group W bench
PostPosted: Mon Feb 28, 2005 11:09 am
Post subject: T-38 autopilot tricks & tips

Had another great group flight in the T-38 last night (S!~ and thanks to Hoppa, EXOS and Lurps!) with a full-speed afterburner run all the way to the destination (WOOHOOOO!!), and thought it might be a good idea to share observations about that neat, but finicky, vacuum-tube-driven 60's-era autpilot.....since it's always a subject of pain & pleasure in these flights!

You'd think it's pretty basic stuff, but each of the 3 basic features has some kinda fun little quirk! After turning the A/P on - either by the "Z" key or the funky 50's kitchen-gadget dial switch at the bottom of the panel - ya got the following.....

Altitude Hold (middle button):
Wayyy different from the standard A/P. The only thing this gizmo controls is rate of climb, and that's it. It can go up, down, or keep you where you are - well, more or less. And this is all that a real jet pilot back in the day needed, right?

Now for the funky twist : When you turn it on using the "ACQUIRE" switch, it's tiny little brain looks at your current altitude, not vertical speed....and sees, for instance, the altitude of 8,500 ft...and it says, "Hey that looks like a good number for me to climb at, too!"....and correspondingly, sets your CLIMB RATE to that exact figure....and UUUUPPP goes the nose, trying to climb at 8,500 fpm (which it'll do)! Gets to be real fun when you hit the button at much higher flight levels.....it's a mad dash for the little knob at that point, cranking the climb rate down to something realistic!

Somewhere behind the panel, my guess is there's a blue wire from the A/P connected to a yellow wire on the altimeter. But the plane flies and as long as no electrical fires break out, crew chief says it's no problem!

So the trick here is......if the plan is to climb out from departure at 4,000fpm, get the A/P master switch turned on early and be sure to hit that ACQUIRE switch right as you are passing through FL040 (4,000 feet)....Bingo, you've beaten the thing at it's own game, becuase it now reads pretty close to what you wanted, and just a little fine-tuning on the knob is the only thing ya need to fuss about.

Ohhh...but......yeah, you could try to set it at 2,000 feet for a shallower climb.....might work, might not. I've had cases where it just wouldn't turn on at all below about 2,000 feet. Could be a safety feature, but...wasn't Ralph Nader too busy going after GM back then to get involved with Northrup?


Heading (bottom button):
Or, "Course Acquire" as the label by the button says, and that's the truth to it. Like the altitude hold, this part of the A/P grabs a reading from one instrument and locks it in. UNlike the Alt. Hold, it uses the right intrument, and not the G-meter or the fuel gauges! So, it's easy.....fly the plane and get on the desired heading you want, and hit the switch. At that point, you can use the heading bug on the HSI to drive the airplane around, but c'mon....that's not how the 6-million dollar man Steve Austin would fly the thing, is it? And besides, when this part of the A/P is turned on, guess what? The heading bug moves at 5 or 10-degree increments! Turn this off, and then the heading bug can be fine-tuned at 1-degree increments. Why, is anyones guess. Stop asking questions. So what I do for minor corrections is just turn the heading off, bank a little, get on adjusted course, hit the switch again, done.

Again, it's a strange quirk. Maybe the vacuum tubes are gettin' old. I got a matched pair of Groove Tube 6L6's for my old Fender amp that I'm not using, might try swapping 'em in to my personal T-38 and see if it improves things...

Hey what about GPS heading? So glad you asked....there's no NAV/GPS switch in the thing of course (that'd require the crew chief to drill a hole in his precious panel, which he refuses to do apparently) ......so, slaving the A/P course to the GPS plan doesn't seem to be in the cards for us.

But, lest we forget, this plane has more in common with 60's automotive technology than late-model aircraft tech, and as such, we can just hotwire the dang thing! All you need to do is find the wires under the dash, so......Hehe....load any other plane, like the Cessna or whatever, flip the GPS/NAV switch in that cockpit to "GPS", then get back in the T-38 (preferably, before takeoff!) and you're all set. Hit "Z" and she banks right over and tracks the GPS flight plan.....smart little bugger eh?


Speed Hold (Top button)
After the above, what can possibly be bizarre about this?!?! Ohhh...nothing.....other than it thinks it's the MOST IMPORTANT BUTTON ON THE DANG PLANE!

It's an auto-throttle that can't decide if it's part of the autopilot or not. You can't turn it on unless the autpilot master switch is on....that part makes sense. But what'll get ya....especially turning onto quick final...is that it stays on when you turn off the A/P.....and, just to make the last few moments of your flight even more interesting, it can't be switched from ON to OFF unless the A/P is ON (yes, read that part twice). This is because it wants to be more important than the lowly A/P switch.

I'm hoping I'm not the only one that's switched off the A/P, set up an approach to the active runway, and then deployed spoilers to start slowing down only to hear....the friggin' engines spooling up! D'oh, dang that speed hold....hurry!...hit 'view' key 3 times to get to the 2D cockpit, turn the AP on....oh dang there goes the frikkin' Altitude Acquire suddenly deciding I want to ascend at 8500fpm, stop it willya!....hit "Z" key by reflex, A/P is off, nose stops rising ...NOW try to turn off speed hold...can't, becuase A/P is off, dummy! Turn on A/P, turn off Speed Hold, turn off A/P, go back to VC, and then...arrrgghh go around because I missed the threshold......and, oh cripes the spoilers were still deployed that whole time, even with the plane climbing, numbnuts!!!, and now that the throttles are finally pulled all the way back, with full spoiler, and nose high, gonna stall OHHH GREEEATTTT....

Shoulda just left autothrottle on and set it down at 200, slammed the brakes and flat-spotted the tires all the way down the runway....

So......it's the most important button on the plane becuase if ya turn it ON LAST, and turn it OFF FIRST, it's happy. The world revolves around the mighty Speed Hold switch!


So, man, maybe this'll help someone besides me......I love this plane more and more every time I fly it. Turning it into a full-on bush plane these days even (hey there aren't gonna be noise statutes at Com-C Wilderness HQ are there?!?!). The A/P on this thing has got that psychedelic 60's flavor for sure, man! Maybe some Grateful Dead or Hendrix next time out to set up a copasetic frame o'mind......

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Last edited by JG300-Stoopy on Mon Feb 28, 2005 2:53 pm; edited 6 times in total
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Uhu_Fledermaus
Aircraft Demolition Expert

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Joined: Nov 28, 2004
Posts: 4369
Location: Blaricum, The Netherlands ~GMT+1
PostPosted: Mon Feb 28, 2005 12:05 pm
Post subject: Re: T-38 autopilot tricks & tips

Cool

Great tutorial Stoopy !!

mush appreciated !! Laughing


fled
Twisted Evil
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JG300-Lurps
Power User

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Joined: Jan 11, 2005
Posts: 167
Location: In back of the sty .... sighting in my Luger ....
PostPosted: Mon Feb 28, 2005 7:56 pm
Post subject: Re: T-38 autopilot tricks & tips


I'll be the first to admit that the T38 a/p is very basic .....
BUT ..... Man ain't she purdy and she flies like a well
oiled female college co-ed ..... Mr. Green


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JG300-Stoopy
Power User

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Joined: Jan 05, 2005
Posts: 5840
Location: Group W bench
PostPosted: Mon Feb 28, 2005 9:09 pm
Post subject: Re: T-38 autopilot tricks & tips

Oh, DEFINITELY!!!!!

The whole point of the above wasn't to diss her....not in the least! Just sharing the finer points & info in a (hopefully) humourous way!

Had fun flying her tonite with ya too, buddy, and Dep. Dale.....runnin' up the coast on full burner huggin' the deck...splittin' off to make our approaches from 2 merging directions.....landing within a few seconds of each other......HOT DANG TAMALE it don't get much better than that!!!


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berlopez
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Joined: Dec 28, 2006
Posts: 263
Location: Copenhagen.DK
PostPosted: Mon Apr 30, 2007 12:06 pm
Post subject: Re: T-38 autopilot tricks & tips

Smile Thanks for the tip for the T38, Very nice plane Laughing

I'd llike to ask if the afterburner effects are visible on the model?
At full throttle there are no flames???

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Began simming with Fs2002 have developed my sim and computer skills with these.Dell Vostro 220,Penduim Dual Core E6300 2.8; 2.79 Ghz;3.00GB, Nvidia GeForce 7600GS; High Definition Audio. Windows 7 Pro. My old computer fried.
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