9V-SPJ
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%Increase In Drag With Spoilers?

Fri Mar 30, 2007 10:19 am

Does anyone have any idea how much drag is increased with spoilers are increased? Even a delta Cd would be nice!

Thanks

9V-SPJ
 
SailorOrion
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RE: %Increase In Drag With Spoilers?

Sat Mar 31, 2007 8:37 pm

The main thing about spoilers (at least upon landing) is not the increase in Cd, but the decrease of Cl to get more weight on the wheels. I unfortunately have no numbers  Sad

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zeke
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RE: %Increase In Drag With Spoilers?

Sun Apr 01, 2007 2:38 pm

Quoting 9V-SPJ (Thread starter):
Does anyone have any idea how much drag is increased with spoilers are increased? Even a delta Cd would be nice!

That very much depends on the design, you can have a look at table 1 in NACA-TN-1939 "The effects of aerodynamic brakes upon the speed characteristics of airplanes" it gives a comparison for many designs.
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lehpron
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RE: %Increase In Drag With Spoilers?

Sun Apr 01, 2007 10:39 pm

Quoting 9V-SPJ (Thread starter):
Does anyone have any idea how much drag is increased with spoilers are increased? Even a delta Cd would be nice!

Not to nitpick, Cd is usually in reference to 2-dimensional aerodynamics, CD is for 3-dimensional.

Quoting SailorOrion (Reply 1):
The main thing about spoilers (at least upon landing) is not the increase in Cd, but the decrease of Cl to get more weight on the wheels.

Well, the L/D ratio goes to near zero from loosing the lift, if you knew the value prior to touchdown. Thrust required to maintain velocity is weight divided by that ratio; without engines on, that thrust IS (mathematically) the drag force due to air.

I suppose you can calculate the equivalent CD yourself knowing the force.
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SailorOrion
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RE: %Increase In Drag With Spoilers?

Mon Apr 02, 2007 6:14 am

Quoting Lehpron (Reply 3):
Thrust required to maintain velocity is weight divided by that ratio;

But that is no longer valid on the ground  Smile Depends on what we are talking about. "Spoilersb" are used for several purposes:
1) Temporarily increase drag to lose airspeed
2) Augmentation of aileron deflection (up aileron only)
3) Decrease of lift, hence spoilers are often referred to as "lift dumpers".

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prebennorholm
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RE: %Increase In Drag With Spoilers?

Wed Apr 04, 2007 4:09 am

When approaching the most busy airports, the spoilers are used very often to increase drag in order to shift fast to a lower FL to get traffic moving.

Most often wing spoilers are lifted only a couple of inches, which increases the drag and consequently descend rate dramatically.

Some planes, for instance BAe-146/ARJ has a tail brake instead. One poster on this forum once told how he had made a very hasty descend with those brakes on a 146, to the surprise of ATC.

Another poster said: "Guess that stunt was with no pax on board".

And the original poster answered: "76, but all on seat row 1".

Airliners are extremely smooth when clean. But going for instance 300 kts at FL 100 or 150 it doesn't take much to brake them dramatically.
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