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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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