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Takoff to cruising altitude under AP takes hundreds of miles

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Takoff to cruising altitude under AP takes hundreds of miles

Postby HFC3 » Sat Nov 03, 2018 4:19 pm

I've learned how to add altitude to the AP route (ABCD@24000), and the route is showing it; ""FL24". However, once in the takeoff pattern under AP control, the altitude increases at a snails pace taking 300 or 400 (estimate) to get above FL20. I haven't been able to locate a VVI to tell what it's using, but the artifical horizon is usually at the 7 or 8 degree position. To reach FL, I have to alternate between overspeeding and forcing a steep VS climb, back to WNAV when speed drops close to stall, and repeat.

When flying commercially (passenger), I don't remember waiting an hour until "we're at cruising alt of xx" mentioned and that the climbing alt was much steeper than apparent in FlighGear (although, that's difficult to tell as my tuccas is firmly set into my recliner :)).

I've tried various aircraft and they all behave the same way, and even tried putting a cruising altitude off FL25,FL30 or FL40 on the first waypoint hoping it would force the AP to do it's best to reach that. I saw somewhere in the documentation someone has added an "A" or "B"?? to the rout planner altitude to instruct the AP to reach that waypoint at or above, or at or below - the letter was ignored so either I misunderstood, that feature doesn't work on the aircraft I tried it on and/or it's in a different version.

Any ideas on what I'm missing?
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby Thorsten » Sat Nov 03, 2018 6:04 pm

Use an aircraft which actually supports this kind of route manager + AP control? I don't think the average aircraft does that (and you haven't told us what you've been using).
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby V12 » Sat Nov 03, 2018 8:09 pm

HFC3 :
What aircraft ? For example, with Concorde and maximum takeoff weight, I need approximately 250 nm for climb to FL600...
Fly high, fly fast - fly Concorde !
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby tdammers » Mon Nov 05, 2018 12:07 am

As others have said, the most likely explanations would be a) you're flying a type that doesn't fully support VNAV (either because the real type doesn't have it either, or because it's not implemented in the FG model), and b) you're flying the aircraft at or above its physical limits (i.e., at or above MTOW).
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby HFC3 » Mon Nov 19, 2018 4:15 pm

Sorry - my bad. I was using the 777-800 and the 747-8. I've tried other miscellaneous aircraft, even the SR-71 (weee!).
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby HFC3 » Mon Nov 19, 2018 4:29 pm

One other item; I noticed that what I set a cruise alt manually or in AP, the vertical speed indicator is blank. Watching some generic YouTube footage, the vertical speed is still active when changing alt simply by ALT, it just determines how quickly the change is implemented. Is this normal behavior, or am I doing something else which is bypassing VS?

I've seen this on all the aircraft with "normal" AP gauges. in 3D cockpits, but I'm usually flying the 747-8 or the 777-800. Aircraft without the gauge displayed behave the same way (slow alt change), but no visible gauge.
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby legoboyvdlp » Mon Nov 19, 2018 4:38 pm

If you press ALT, it should hold the altitude if I remember correctly, or climb very very slowly to the cruise altitude.

you can press FLCH (sets max power and climbs holding an indicated airspeed using pitch) or VS (holds vertical speed) in the 777 / 747-8.
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby dilbert » Sun Dec 23, 2018 3:03 pm

May not be as bad as you thought.
Depends on your climb airspeed.
Had it been a somewhat reasonable speed of 434 Knots
(500 MPH) it would have taken 30 minutes to make
250 miles. If you climbed 60000 in 30 minutes, your rate
of climb was 2000 FPM. I believe 747 and 777 type aircraft have climb rates in the 2000 to 3000 fpm range, so 2000 fpm isn't all that bad. If you were in the Concord
climbing at 646 Knots, the rate of climb would have been
3000 fpm, since you would have made the 250 miles quicker. In a J3 climbing at 60 MPH it would only have been 240 FPM.:)
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby SurferTim » Wed Dec 26, 2018 4:55 pm

I use the autopilot in the 777, and it climbs great if the vertical speed is set at an appropriate value.

Set the altitude, then select vertical speed (V/S in the autopilot panel) of about 2500 ft/min. It will climb great. Watch your N1 speed on climb. As you gain altitude, it requires more power to maintain a climb rate.

Edit: When you reach your selected altitude, it will disable the V/S and maintain the selected altitude.
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Re: Takoff to cruising altitude under AP takes hundreds of m

Postby legoboyvdlp » Wed Dec 26, 2018 5:31 pm

FLCH mode does this automatically actually if it helps - it maintains speed using the pitch. So if you set 0.78 it will pitch up or down to maintain 0.78 therefore meaning you don't have to adjust vertical speed as you climb :)
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