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difficulty in getting 737 to descend! (Read 416 times)
Apr 20th, 2004 at 8:43pm

satz   Offline
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Hi all
I've run into this problem on odd occasions.   I'll be flying along in the default 737-400 when I find that it won't descend easily.

I really have to push the stick all the way forward to get it to descend.  As soon as I let go of the stick (ie in neutral position), the aircraft starts climbing at a high rate.  AT other times (different flights), the aircraft does the opposite (ie it's a battle trying to get it to ascend!)

I don't think it's the AP setting as it occurs even when AP is switched off.   Flaps are at 0.   engine anywhere between 50% and 100%

Speed somewhere between Stall and Overspeed!

Any ideas anyone

kind regards

Satz
 

P4 2.6C, 1.5 gB ddr400, NVidia 6600GT 128mB AGP card, Logitech Wingman Force joystick and pedals
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Reply #1 - Apr 21st, 2004 at 2:09am

Saitek   Offline
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Have u tweaked the trim?

Ben
 

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Reply #2 - Apr 21st, 2004 at 2:12am

satz   Offline
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Hi Ben,

I tried adjusting the trim but it didn't seem to make much difference.  Anyway, I thought the trim would do  just subtle trimming...

What I was getting was a major problem which I don't think that trim would fix (though I'm happy to be corrected)

cheers
 

P4 2.6C, 1.5 gB ddr400, NVidia 6600GT 128mB AGP card, Logitech Wingman Force joystick and pedals
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Reply #3 - Apr 21st, 2004 at 8:48am

Scottler   Offline
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If you're pushing the stick forward to descend, you're not trimmed properly.

Set your power to idle.  Trim the aircraft for level flight.  Then use your throttle to climb/descend.

 

Great edit, Bob.&&&&&&Google it. &&&&www.google.com
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Reply #4 - Apr 21st, 2004 at 10:54am

Poseidon   Offline
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Hi,

Like any kind of objects in the nature airplanes "want" to maintain their current kinetic condition (I hope I am using the correct term english is not my native language). Remember what happens to you when you are in a car and the driver pushes the brakes.

When you push the stick in your virtual 737 all the way forward you descend with an extreme nose down angle. This increases your airplane's airspeed dramatically and as a consequence it (the airplane) wants to climb up again in order to reduce speed and this eventually happens when you release the pressure.

In order to descend with a 737 you must maintain a slight nose down pitch (about 2-3 degrees) and ideally maintain clear configuration (no flaps no spoilers). Also keep in mind a 737 is not a Cessna which means do not expect to descend immediately. You should plan about 3 miles for each thousand of feet you want to descend. For example if you want to descend from 20000ft to 12000ft that is a descend of 8000ft and you should plan 8*3 = 24 miles.
Alternatively if you want to work with Flight Levels remove the zero at the end of the FL and multiply by 3. That is if you want to descend for landing from FL120 you have 12*3=36 miles.

Another rule of thumb to find the best rate of descend is to divide your Ground Speed (GS) by 2 and add a zero at the end. That is if your GS is 210 KIAS your rate of descend should be 280/2=140 making 1400 FPMs

The above numbers are not precise under all conditions (in fact it all differs regarding your altitude, the amount of your fuel thus your weight, the temperature and the wind) but it will work in FS in general.
 
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Reply #5 - Apr 21st, 2004 at 3:26pm

garymbuska   Offline
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I have just one question ??? is your autopilot altitude hold off Tongue
Try pressing F1 which is ground idle if you find that the airplane is still trying to climb either your auto pilot altitude hold is set or you have a major trim problem Tongue
 
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Reply #6 - Apr 22nd, 2004 at 2:35pm

francsal   Offline
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Hey there!

I would say that the problem you face is a combination of all the factors already expressed here. You should watch, IMHO, the airspeed, your flap settings and your trim. And don´t regard the trim as a "slight" adjust. It can have a huge impact on the plane´s behavior.

 

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Reply #7 - Apr 22nd, 2004 at 6:39pm

satz   Offline
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many thanks all.   Will try to apply this knowledge when next I fly on FS2002.

Another question....  when using Autopilot, what's the difference between using HDG and NAV?

And must NAV be used with the GPS/NAV toggle in the NAV position?

thanks again

cheers

Satz
 

P4 2.6C, 1.5 gB ddr400, NVidia 6600GT 128mB AGP card, Logitech Wingman Force joystick and pedals
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Reply #8 - Apr 22nd, 2004 at 11:11pm

Lux13   Offline
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HI!
If you use heading,your autopilot follow the heading that you have selected on heading panel.
For Nav mode you shoul know something about instrumental navigation.....The NAV mode just let your airplane intercept and follow or just follow the RADIAL (course) that you've selected on COURSE panel.But the course works with the frequency you've selected on radio NAV1 !!
I try to explain better......The course means your relative position respect to the radio aid (VOR) you have selected on your NAV 1.
If you are flying on radial 180° (course 180),it means that you are flying 180° south of your radio aid (nav 1).
But if there's a lot ot of wind you could fly on 180 course with an heading of (extreme example) 150!!!
And your autopilot moves your aircraft only if you are in NAV mode (not GPS).Otherwise yiour instrument panel is useful just to check if you are in route!!
About to descend with your 737......just use the trim!!!
Remember,737 is not a cessna 172!!!!It needs a lot of trim!I'm sure that if you use all trim down you will easily be in the opposite situation.......you r aircraft will not climb!!!!!
I hope that i was clear.......
CHEERS!!
 

Thank God for let me fly!
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Reply #9 - Apr 22nd, 2004 at 11:36pm

Nexus   Offline
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yeah apply as much nose down trim as possible.  Grin
Hey what happened to the good old idle thrust command when you want the aircraft to descend?  Roll Eyes

HDG means aircraft will maintain the selected heading (wind drifting not corrected)
NAV can either mean VOR/LOC course tracking or GPS tracking (depending on NAV/GPS switch position). Wind corrections are applied here since the aircraft "knows" where you want to go.
 
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Reply #10 - May 27th, 2004 at 4:43pm

Jamie   Offline
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Hi Satz ,

I was flying in multiplayer the other day and my friend and I were both in ultralights ( supposedly no autopilots ) .  His would go into dives , etc. and he only got the problem corrected by going back to his usual 172 and then back to the ultralight  .  I am not  sure what changes he made , but my thought was that it had to be the autopilot in memory from his previous flight ?? 

Your problem sounds more like an autopilot setting rather than trim to me .  Z on the keyboard is supposed to disengage the AP .  I always try that if my plane is acting crazy .  I would be curious to know how you solved the problem .

As to getting a large jet down , other than starting a descent far enough out , I have found that the spoilers do a fantastic job.  I never flew jets in the real world so I am not sure if one is supposed to use those in that manner or not and at what speed .  I am one of those who likes to fly rather than read !!  You can also slow to gear speed and lower the gear which adds drag and aids in losing altitude .   In my experience in small aircraft , there was a max. speed at which you should lower the gear and a higher allowed speed after the gear was down  .  The reason for the difference in speed  was due to the fact that the actuation of the gear doors into the slipstream could damage them at too high a speed .

Jamie
 
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