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martinlest2

How to increase drag when descending?

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I would like to make a change so that one or two a/c I have do not accelerate so much as I descend - it is almost impossible to get down to the altitude and speed required for landing without using spoilers all the way down: if I try to descend without spoilers at much more than 1000ft/min, the a/c eventually reach overspeed.

 

I tried increasing the parasite_drag_scalar and induced_drag_scalar values in the aircraft.cfg, but that seems to have had little effect and I am not sure what other parameters there to try tweaking.

 

Can anyone help with this? Thanks.

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Increase your angle of attack to increase drag! :)

 

Don't look at your vertical speed indicator during a descent, let's say that V/S is sort of out of your control. Say you're flying level at 300kt and want to start a descend at constant airspeed, what do you do? Smoothly close the throttles all the way to flight idle, the aircraft will descend. Make small corrections with the elevators to maintain your target airspeed of 300kt, then trim. The objective is to establish yourself in an idle-power descent at the same airspeed and same angle of attack as in the cruise condition. Your throttles are the "up&down" control of the aircraft. Accept the resulting vertical-speed.

 

If you want to slow down, pitch up a bit and let the speed come down naturally, then once you reach the new speed pitch down to maintain it, re-trim. If you want to accelerate, pitch down and let the speed increase. Pitch for airspeed.

 

What aircraft are you using? If it's a modern airliner, use FLCH or the equivalent AP vertical mode. That will do the same I described.

 

EDIT: If you're gonna play with the aircraft .cfg, parasitic drag increases with airspeed and induced drag increases with angle of attack (or lift, at zero-lift there's no induced drag), they work in an inverse relation like this:

 

 

Drag_Curve_2.jpg

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Are you reducing engine power before descending?

 

In the 737:

 

If I need to descend from cruise at 335kts @ FL310 to 250kts @ 8000', the first thing I do is reduce power to start decelerating before I start actually descending. I'll cut power and wait until airspeed hits 325 or so and then start my descent. If I need to descend rapidly, I apply a little spoiler (speed brakes) by dragging the handle. If you use the / key, you get 100%, so drag the lever with the mouse slowly just until you see the airplane start to slow down. As soon as I hit 250kts, I deploy flaps 1, and turn the speed brakes off.

 

Note: as mentioned before, if you reduce power, and pull back on the stick, you may gain a couple of feet before you descend, but the airplane will have no choice but to slow down, which will cause it to descend.

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Hi, thanks for the replies.

 

Most of my a/c (I am talking about Boeings/Airbuses etc. here, I should have said, not Cessnas) will descend just fine at say 2000ft/min (or more) and still lose speed until they get to the A/Thr setting; or if I use VNAV (Level Change), the a/c will maintain both a satisfactory rate of descent and the selected air speed.

 

A few others though, as I say, although they will slow down and maintain the air speed I select for a short period by doing the things suggested here, will only lose speed if my descent rate is less than about 800ft/min, which is never enough to get to the required altitude for approach and landing (I use PF3 for ATC and follow their instructions, so I cannot 'realistically' start a descent before the TOD, to compensate).

 

Yes, throttles are at idle of course, I also cut the speed well short of the TOD: I do add a touch of speed brake if necessary, and I extend some flaps as soon as I can (which usually does the trick), but my preference would be to tweak things a little so that speed brakes and flaps are not necessary at that stage. I have never seen in real world aviation (and I fly pretty regularly, usually nose glued to the window!) spoilers employed apart from during approach. For me to have to use spoilers at 30,000' to avoid accelerating even during a relatively gentle descent in FS9 doesn't seem 'right'.

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I can't recall the few previous examples (I'll note them down next time I encounter them!), but currently it is (actually an FS9 aircraft) - the CamSim a350.

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1)The flight dynamics are way off for the a/c you have selected

2) The flight dynamics are spot on for the a/c you have selected and its just naturally 'slippery' hence will require better speed management and or an earlier descent meaning that 3) comes into play.

3) The ATC instructions are not reasonable given item 1) or 2)

 

Modifying the FDE is not recommended unless you know for sure that 1) is the reason

 

To quote an old saying.......'you can either slow down or go down, not both at the same time'

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I don't know the flight characteristics of an A350 and I do not think CamSim accurately modelled it either since it was released before the A350 started flying. You are probably flying with a slightly tweaked default 737 fde.

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Modifying the FDE is not recommended unless you know for sure that 1) is the reason

 

+1

 

I wouldn't go tinkering with it unless I knew for sure what I was doing. And mind the user agreement, maybe you're not even supposed to do that.

 

Get in touch with the developers and ask them about this issue.

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Modern airliners are slippery beasts. They won't go down and slow down. Some tips to help.

 

- Use spoilers (they must be stowed by the time you are in the landing config however, but on the 777 you can use them with flaps and gear)

- Speed up to get down. If you're high you can dial up the speed and the aircraft will nose down to speed up, helping you to bleed off altitude.

- In the Q400 put the props to max as the drag from the props helps your rate of descent.

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Some a/c do need the spoilers cracked open during descent. Aside from the location of where you are descending (landing at any of the airports in Northern Italy coming from the Alps requires full speed brakes to get down in time, for all aircraft.)

The a/c to the left for example requires 25% speed brakes and M0.85 for the initial descent. Gradually reducing the throttle to maintain 300kts until it is necessary to fly more slowly at lower altitudes.

 

So what do the flight manuels of the a/c you fly say?

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Some a/c do need the spoilers cracked open during descent.

"cracked" is a good description. In a real plane, this might be 1/4" or less of spoiler deflection. It doesn't take much to create drag, You might not notice it looking out the window even if you were looking right at them. 

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I think that with this a/c I shall have to employ spoilers to descend. They are not very subtle on this plane, but I can experiment a bit. I suppose real-world pilots do use them at higher altitudes (just because I have never witnessed it doesn't mean it never happens, I agree - maybe a touch of spoilers is, as you say, hardly visible anyway), though trying to mimic everything that happens in real-world aviation is really not my holy grail in FS9 or FSX!

I am reasonably OK with much of the data in the aircraft.cfg file (and use the AircraftContainerSDKFS2004.doc to help out as needed), but many values in the aircraft.cfg file are inter-dependent and although you may 'cure' one thing, changing settings can have unwanted side effects.

 

That said, I can easily edit the air file to tame the a350 spoilers a bit if necessary - and I always make a backup before I make any changes of course...

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I think that with this a/c I shall have to employ spoilers to descend. They are not very subtle on this plane, but I can experiment a bit. I suppose real-world pilots do use them at higher altitudes (just because I have never witnessed it doesn't mean it never happens, I agree - maybe a touch of spoilers is, as you say, hardly visible anyway), though trying to mimic everything that happens in real-world aviation is really not my holy grail in FS9 or FSX!

 

I am reasonably OK with much of the data in the aircraft.cfg file (and use the AircraftContainerSDKFS2004.doc to help out as needed), but many values in the aircraft.cfg file are inter-dependent and although you may 'cure' one thing, changing settings can have unwanted side effects.

 

That said, I can easily edit the air file to tame the a350 spoilers a bit if necessary - and I always make a backup before I make any changes of course...

The a/c flight manuels should tell you if you need to apply a touch of spoilers during initial descent and by how much.

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I think that with this a/c I shall have to employ spoilers to descend. They are not very subtle on this plane,
You have to use your mouse to grab the handle and pull it back to get partial speed brakes. If you hit the / key to activate them, you get 100% "not subtle". They can be subtle, but you have to use the mouse to do that. 

 

I'm not sure which a/c you are using, but if you hit <Shift> / before you land it will arm the speed brakes so that they will auto deploy when your wheels touch the runway. Do that while at cruise altitude and take note of where the handle stops in the armed position (you can press <Shift> / to activate and deactivate them while flying and nothing will change).

 

Now, when you need to deploy just a little bit of speed brake, use the mouse to drag the handle just a little bit past where the armed for auto deployment position is. You can kinda tell that the a/c is slowing by the "head bob" or viewpoint shift that FSX uses to simulate deceleration.  

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You have to use your mouse to grab the handle and pull it back to get partial speed brakes. If you hit the / key to activate them, you get 100% "not subtle". They can be subtle, but you have to use the mouse to do that.

Yes, that's what I do at the moment. Even with the mouse, a number of a/c have very 'jumpy' spoilers though, which seem to like to go to 100% with the slightest excuse: you have to be ultra-gentle. Other a/c work just fine...

 

I'm not sure which a/c you are using, but if you hit <Shift> / before you land it will arm the speed brakes so that they will auto deploy when your wheels touch the runway. Do that while at cruise altitude and take note of where the handle stops in the armed position (you can press <Shift> / to activate and deactivate them while flying and nothing will change).

I already have 'Arm Spoilers' set to my Saitek X52. What I am trying to do though is to programme spoilers to extend and retract incrementally, via FSUIPC (as 'advertised' as possible in the FSUIPC manual) and a key press (and hence to my X52). It's not working all that well at the moment, so I posted on the FSUIPC forum...

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I usually override the VNAV/DESCEND speed if it is above 250 and use  250 down to 10000 ft.

 

nebojsa

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Yes, I usually set my rate of descent manually too, so as to hit 250 comfortably at 10000'.

 

The FSUIPC works just fine in the end - I was testing on the ground (where incremental flaps won't work) rather than in the air (where it is pretty cool!). I mapped the key presses to one of my X52 buttons and so now I can increase and decrease spoilers in the same way as flaps.

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Regarding the use of speedbrakes, I find it hard to believe that there are airplanes in which you HAVE to use speedbrakes per manual to commence a descent, but hey, I'm not all-knowing and this could be, I just find it surprising. Having to use the speedbrakes is not ideal. Ideally you want to descend from cruize FL to the IAF without having to use the brakes because that increases fuel consumption, increases vibrations and is less efficient overall.

 

It all comes down to a lack of descent planning. If the aircraft you use is very slippery, start descending 20nm before the T/D, or even further out if that's not enough.. If you're using ASN or a weather program, put the winds into the FMC to get a more accurate descent profile.

 

I'm not saying here that using speedbrakes is bad, don't get me wrong. What I'm saying is that you want to avoid having to use them, but if for whatever reason you find yourself to close to the airport, to high and too fast, by all means use the spoilers. If you think that given the present profile you will have to use them, anticipate and use them BEFORE you get too high. It's even worse having to do a 360º, enter a hold, lose the entry slot or something like that because you didn't want to use them. In fact, if the situation is somewhat extreme, you could also drop the landing gear. Anything to get the job done (within reasonable of course)

 

 


I already have 'Arm Spoilers' set to my Saitek X52

 

I have the speedbrake lever mapped to the "slider" on the throttle of my Saitek X52. Works like a charm, even for arming the spoilers.


 

 


I usually override the VNAV/DESCEND speed if it is above 250 and use  250 down to 10000 ft.

Yes, I usually set my rate of descent manually too, so as to hit 250 comfortably at 10000'.

 

Or you can use FLCH (or the equivalent mode, in Airbus I think it's called OPEN DESCENT) and once you reach 11000ft roll the speed dial down from your ECON DES SPEED to 250. The aircraft will almost level out to slow down. It works very well.

 

Usually you don't want to slow down from cruise speed to 250 when reaching the top of descent.

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I find it hard to believe that there are airplanes in which you HAVE to use speedbrakes per manual to commence a descent

Me too. Surely in any case not the A350!! The 'manual' for this a/c is just the usual ReadMe.txt, so no information there.

It all comes down to a lack of descent planning

Well, not necessarily. I use PF3 for ATC and the descent planning is fairly sophisticated. What it really comes down to is an aircraft that will not descend, even at TOD, at more than about 7-800ft/min without accelerating, throttles at idle of course.

I have the speedbrake lever mapped to the "slider" on the throttle of my Saitek X52. Works like a charm, even for arming the spoilers.

I haven't in the past been able to map anything to the slider - how did you do it exactly, including arming, on the slider? I'd like to do the same. I have tried today using FSUIPC to create incremental speed brake extension/retraction, and it works up to a point in some aircraft - early days though, I only just started testing. My ideal would be to have the slider increase spoilers as you move it forward and decrease as you pull it back. I could use a different button for arming. Presumably yours is still an all-or-nothing affair, or do you also use FSUIPC to get incremental movement of the speed brakes??

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I haven't in the past been able to map anything to the slider - how did you do it exactly, including arming, on the slider? I'd like to do the same. I have tried today using FSUIPC to create incremental speed brake extension/retraction, and it works up to a point in some aircraft - early days though, I only just started testing. My ideal would be to have the slider increase spoilers as you move it forward and decrease as you pull it back. I could use a different button for arming. Presumably yours is still an all-or-nothing affair, or do you also use FSUIPC to get incremental movement of the speed brakes??

 

I do use FSUIPC, yes. Also make sure you have installed the Saitek DRIVERS, otherwise your PC won't let you configure every button (for example, I couldn't map the "i" button on the throttle until I installed those drivers).

 

I don't want to tinker with FSUIPC right now in case that I mess up and lose my configuration. I'm just telling you it's possible.

 

BTW: I have the slider in the opposite sense as you say. In the full "up" position of the slider, spoilers are stowed. In the full "down" of the slider, the spoilers are full up. This is to simulate the same movement of the lever in the real plane.

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It's OK, it is working just fine now, but only so far in my default a/c -  I've been using the 747 to set up and test. I have one of the switches on the X52 ("T4") set to spoilers up/down and one ("T3") to Arm Spoilers. It was also easy to programme the slider (why did I have trouble before? i can't remember, but no matter) and now it works brilliantly (though I got a BSOD at one stage during the testing!) - the spoilers move gradually from fully down to fully extended as you move the slider upwards to its full extent. Great!

 

'All' (?!) I have to do now (as I rarely fly default FS9 planes) is to see how to get it all to work like that in my add-on a/c like PMDG Boeings and PSS Airbuses. (In the PMDG I get no spoiler movement at all; in the PSS a/c, things work up to 1/4 spoilers, then they suddenly 'snap' to Armed mode. Did you get your slider to work with all your a/c OK (assuming you also use PMDG etc.)?

 

(Yes, the Saitek drivers and programming software are installed!)  :-)

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Regarding the use of speedbrakes, I find it hard to believe that there are airplanes in which you HAVE to use speedbrakes per manual to commence a descent, but hey, I'm not all-knowing and this could be, I just find it surprising.

Believe it! I think you are immagining full deployment. Cracking the speed brakes keeps the speed under control and does not increase vibration. And in any case it does depend on the a/c manual.

That siad you would certainly need full speed brake deployment in an emergency descent!

 

Next tiem you fly from the UK to Torino you will need full deployment once over the Alps to get down in time. Otherwise you will have to go an agrande tour on Northern Italy.

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Yes, when flying in the Alps or Himalayas to get down between mountain peaks, but we are talking about a 'normal' scenerio descending from say 38000' when flying, for instance, Amsterdam to Moscow, no sudden drops necessary. Aircraft do not normally require any spoilers at all right from the TOD, assuming throttles are on idle and a standard -3 degrees AoA.

(though I got a BSOD at one stage during the testing!)

Got another one as I move the sliders (x07E - Saik075C.sys). A bit worrying.

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