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Guest NN_Avirex

difficulty with ALT using AP

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Guest NN_Avirex

Using the Auto pilot in the jet41, everything seems to be ok (IAS,HDG etc) but altitude.I set the altitude, press ALT, engage the AP but it doesn't reach the desired altitude.I think I'm missing something here.Most of the tme (but not always) the plane will only keep his current ALT.THe other point is: where can you set the VS before engaging it ?.Thank you.Loic Derrien

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Yeap, You have missed reading AOM wink.gif AP in J41 doesn't work as in modern airplanes. There are two ways to climb or descend: using IAS mode, or VS mode,IAS - set desired altitude with altitude knob, press ALT SEL, press IAS, and reduce power for descend or add power for climb. IAS can be adjusted with IAS knob on center console.VS - set desired altitude with altitude knob, press ALT SEL, press VS, and adjust VS with VS knob on center console.Note that VS knob and IAS knob is the same knob on center console, the one to the left from AP/YD buttons! VS and IAS can not be set before engaging proper AP mode. And here are some best "explanations" I found, but if You'll use search engine You'll find more, I also strongly recommend reading AOM and Flight Tutorial pages 79-81 wink.gif

Marc,No, the airspeed bugs on the EADI are for reference only, and do not control any aspect of the Autopilot or Flight Director.The proper procedure for initiating a climb or descent is to set the new altitude, press ALT SEL, then select a vertical mode and adjust the thumbwheel as necessary to achieve the desired rate of climb or descent.When you choose Vertical Speed mode, the mode will engage at the present VS value - that is, if you were in a 500fpm climb when you press the button, the FD will continue to command a 500fpm climb. You may adjust the selected VS using the thumbwheel. This mode is straightforward, but does not offer stall protection so you have to make sure you decrease the VS as you climb and airspeed bleeds off.IAS mode also engages at the airspeed present upon selection. In IAS mode, the FD attains and maintains the selected airspeed by commanding changes in pitch attitude. The pilot influences the the commanded pitch attitude by manipulating the power levers. For instance:If you are in level, unaccelerated flight at 200kt (with the AP on) and you engage IAS mode, the airplane will continue to fly straight and level. Without touching the power levers, if you roll the pitch wheel to an IAS of 210kt, the airplane will begin a shallow descent. Now, if you rapidly increase power, the nose will rise and you will begin a brisk ascent to maintain 210kt.You also need to be gentle when selecting a new target IAS. Any large changes in commanded airspeed will rapidly result in excessive vertical speeds. For instance, if you're descending at 250kt and ATC asks you to reduce speed to 200kt, spinning the thumbwheel to 200kt will result in a zoom climb with >6000fpm followed by a "pushover" at the top. Not good. Note that in the first example, the airplane vacated its original altitude, then performed both a shallow descent and a steep climb all without ever selecting a new altitude, or arming ALT SEL. Unlike most airplanes, the IAS mode does not care whether your selected altitude is above or below you...it will use whatever pitch attitude is necessary to achieve the commanded airspeed, even if it means going in the wrong direction.Thats why the proper procedure is to "Set it, Arm it, Do it" - SET the new altitude, ARM ALT SEL, DO the mode selection (VS/IAS).From your description it sounds like you did things correctly. Just verify you're setting an appropriate VS value, and if you're using IAS mode, be sure that you're using the power levers appropriately.EDIT: I walked away for a few minutes while replying and somebody beat me to it.
Neal,If you are looking at this autopilot as if it is a Boeing/MD/Airbus autopilot, you are setting yourself up for failure. Keep in mind that just as aircraft are made by different manufacturers, so are autopilots. The way each works is entirely dependant on who programmed it.Here are the main things to understand:On the pedestal:AP - turns the autopilot onYD - turns the yaw damper on (should be on from takeoff to short final in this type, if I recall correctly)On the glareshield:Lateral ModesHDG - holds a defined heading based on the heading knobNAV - follows a NAV course*APP - follows a LOC or LOC+GS (ILS)*NAV course is a set course defined by the selected source. If you have LNAV selected, the AP's NAV function follows the FMS computed course. If in V/L (VOR/LOC) mode, it follows a radial or inbound/outbound course, set by tuning a VOR or LOCalizer on the radio, and setting the inbound course with the CRS knob. In a sense, there is no dedicated LNAV mode in this aircraft, per se.Vertical ModesALT - holds the altitude of when the button was pressed (best selected when you have established level flight)ALT SEL - climbs/descends to the ALTitude that has been preSELected, using V/S or IASV/S** - climbs/descends at the preselected vertical speed (select V/S and adjust with the wheel on the pedestal)IAS** - climbs/descends at the preselected Indicated AirSpeed (select IAS and adjust on the pedestal as above)**V/S and IAS can be used alone, or with an "end goal" set by ALT SEL. When you use them in combination, V/S or IAS will show ON and ALT SEL with show an amber "CAP" (or similar - I know it's amber).Now to address your issues:While in the LNAV mode of the NAV function, you can still set up your VOR/LOC courses by clicking the V/L button once. When you do this, a magenta course needle appears. Set it using the course knob. This frees up time for later, while your A/P can still do nav work for you. Chances are, ATC will vector you off of your filed/flown route or arrival, which will require the use of HDG anyway, but planning ahead never hurt anyone.In order to APP to engage, the aircraft needs to be off of LNAV and on V/L. Once you are ready to switch off of LNAV and onto V/L, click V/L twice (remember, clicking once just allows you to align the course in the background, as we did earlier). On the second click, the aircraft will switch to V/L mode, allowing you to engage APP.Being vectored by ATC does not matter. Most likely, all that means is that you're on a set heading, and will be vectored to intercept the approach course. In this case, an intercept of no more than 30 degrees from the final course will be given, and when instructed to make the turn, dial that in using the HDG knob. At this point, engage APP mode by clicking on it. At first, it will show "CAP" in amber to show it is primed to take over as soon as it gets within tolerances of the localizer beam. Once it kicks in (and if ATC vectored properly) once you hit the glideslope, it should guide you down. For the purposes of realism, kick off the A/P at 1000' (or company policy) and kill the YD at 200' (to make sure you land the plane instead of leaving a crater, you can ignore the YD until taxi off, because the non-flying pilot would do this for you).Hope this helps. If you have further questions, PM or ask here.Kyle
Hope this helps.Regards,

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Guest NN_Avirex

Thank you very much for the answer.Don't worry I'm reading manuel and tutorial, but 583 pages are a lot !

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Hey guys, just wanted to test the climb method with v/s.I found the v/s instrument in front of the condition levers, but where can I adjust the rate? :(

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Use Shift+5 to bring up the AP controls. The black rocker switch is what you're looking for. Otherwise, in the regular VC without using the Shift+5 popup, the black rocker switch is on the pedestal, so you set the VS function on the glareshield, and then look down and set the VS using the rocker.What I normally do is preselect everything - initial altitude, initial heading, and VS (once you select a climb mode, you can then hit ALTSEL). I then take off, fly by hand until I like the picture (or until I'm on/near my assigned heading), and then set the AP. The AP will then adjust the heading to the one I entered and hold a climb of the selected value.Everyone expects that they'll be able to jump in whatever plane they want and have everything work exactly the same. Unless it's the same manufacturer, it's unlikely. Manuals are your friend in that case.[EDIT]I just realized that the big quote in Grzegorz' post was one of my old ones...nice. And thanks for the repost. Saved me some typing.


Kyle Rodgers

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Hey Kyle, thanks again! BUT I've never said that I expect myself to get into a plane and fly it like a senior captain... Shame%20On%20You.gifAnd I have read the AOM, but the problem for me is (regarding to the fact that I'm not yet familiar with this plane) that I understand the procedures described in it, but sometimes do not find the right switches and knobs. :Hypnotized:Greetings from a learning pilot :(

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Daniel,I don't think anyone here gets too annoyed when they point out something is in the manual, unless you're constantly coming here asking for that kind of stuff, so don't worry about our comments too much. It's more of a friendly reminder than anything, but this is a place where people come to share information and learn, so don't hesitate to ask for clarification. Adding "hey, I checked the manual, but it doesn't quite make sense (or I can't find the buttons)" goes a long way.Glad we could help.


Kyle Rodgers

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Hey Kyle, sorry for being stupid. Just opend the "Pilots Introduction" and I recognized that it is like a switch and knob guide. :( (I only read the tutorial and the AOM before)Found out a few things I was looking for. :rolleyes:It can be so easy... It is an advantage if someone can read! :(

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Daniel,Sometimes it helps. But sometimes it's just not in the places you've been looking, which is why you come here, catch a little crap for not reading in the other places, but in the end you get your answer. You're not stupid. Everyone blanks once in a while....like me, this morning when I went looking for my keys for 5 minutes, only to remember they were in my pocket the whole time.


Kyle Rodgers

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