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%Increase In Drag With Spoilers?  
User currently online9V-SPJ From United States of America, joined Dec 2000, 752 posts, RR: 0
Posted (7 years 5 months 3 weeks 3 days 12 hours ago) and read 2098 times:

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

Thanks

9V-SPJ

5 replies: All unread, jump to last
 
User currently offlineSailorOrion From Germany, joined Feb 2001, 2058 posts, RR: 6
Reply 1, posted (7 years 5 months 3 weeks 2 days 2 hours ago) and read 2033 times:

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

SailorOrion


User currently offlineZeke From Hong Kong, joined Dec 2006, 9101 posts, RR: 75
Reply 2, posted (7 years 5 months 3 weeks 1 day 8 hours ago) and read 1967 times:

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.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 3, posted (7 years 5 months 3 weeks 1 day ago) and read 1942 times:

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.



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineSailorOrion From Germany, joined Feb 2001, 2058 posts, RR: 6
Reply 4, posted (7 years 5 months 3 weeks 16 hours ago) and read 1915 times:

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".

SailorOrion


User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6451 posts, RR: 54
Reply 5, posted (7 years 5 months 2 weeks 5 days 18 hours ago) and read 1859 times:

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.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
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