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F-16 Flap Settings At Takeoff?  
User currently offlineMidEx216 From United States of America, joined Jun 2005, 651 posts, RR: 4
Posted (5 years 5 months 4 weeks 1 day 19 hours ago) and read 11450 times:

So I was recently (about a minute ago) looking around the 115th FW website for pictures of the plane who's tail I designed (shameless plug: http://www.airport-data.com/aircraft/photo/212149.html). I found a media gallery that had some videos, so I decided to check them out. While watching, there was an F-16 rolling onto a runway and doing a full-afterburner takeoff. I was watching how much the wings flex going down the runway when I realized that the plane seemed to have a much higher flap setting than I thought it might.

Is the flap setting on these planes variable depending on conditions, or is there a standard setting? About what setting is it, if I may ask? Are they retracted immediately after liftoff, or is this high setting kept during the ballistic climbout?

Feedback appreciated. Thanks
P. Valenstein

http://www.115fw.ang.af.mil/shared/media/document/AFD-080501-022.wmv


"Cue the Circus Music!"
4 replies: All unread, jump to last
 
User currently offlineStarglider From Netherlands, joined Sep 2006, 667 posts, RR: 44
Reply 1, posted (5 years 5 months 4 weeks 1 day 15 hours ago) and read 11416 times:

In a nut-shell:

On the F-16 the flaps are deployed when the gear is down. This flap selection is an automatic selection (not a pilot input). When becoming airborne after takeoff wing camber is initially augmented by drooping the leading edge flaps (which on the ground remain fixed at + 2 deg. up). The drooping of the leading edge flaps is also automatic by air data computer (ADC) aerodynamic input.

When airborne as gear is retracted the flaps (actually flaperons) will retract. The leading edge flaps will remain drooped depending on airspeed, aoa and maneouvring. When conditions are stable the leading edge flaps will retract to a flush, 0 deg. position.

During approach things are reversed, leading edge flaps are drooped depending on aerodynamic conditions and when the gear is lowered the flaps will extend to the same fixed position as on the ground or takeoff. As the flaps are basically flaperons, they will not remain symmetrically in down position with a roll input. The flaperon in the direction of the roll will retract depending on the amount of input and will extend to the fixed position when input is returned to neutral. At touchdown the flaps will remain extended and the leading edge flaps will return to their + 2 deg. up position.


Starglider


User currently offlineLarshjort From Denmark, joined Dec 2007, 1351 posts, RR: 0
Reply 2, posted (5 years 5 months 4 weeks 1 day 10 hours ago) and read 11377 times:



Quoting Starglider (Reply 1):
On the F-16 the flaps are deployed when the gear is down. This flap selection is an automatic selection (not a pilot input). When becoming airborne after takeoff wing camber is initially augmented by drooping the leading edge flaps (which on the ground remain fixed at + 2 deg. up). The drooping of the leading edge flaps is also automatic by air data computer (ADC) aerodynamic input.

I remember something about the LEF going to -2 deg inflight, I can't remeber if it was a speed setting or if it was when afterburner was selected? Can you help me to remember?

/Lars



139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4
User currently offlineMidEx216 From United States of America, joined Jun 2005, 651 posts, RR: 4
Reply 3, posted (5 years 5 months 4 weeks 1 day 5 hours ago) and read 11328 times:

So essentially, as long as wheels are down, so are (trailing edge) flaps, and always in the same position? And unless I understand wrong, that would mean that there's also no steps during the landing sequence involving lowering flaps (just making sure I understand clearly)?

Does that mean that the stall speed in landing configuration on an F-16 is essentially the same as the stall speed in takeoff configuration...because the two configurations (except for the leading edge flaps) are the same?



"Cue the Circus Music!"
User currently offlineStarglider From Netherlands, joined Sep 2006, 667 posts, RR: 44
Reply 4, posted (5 years 5 months 4 weeks 1 day 3 hours ago) and read 11305 times:



Quoting Larshjort (Reply 2):
I remember something about the LEF going to -2 deg inflight, I can't remeber if it was a speed setting or if it was when afterburner was selected? Can you help me to remember?

LEF position moving from +2 deg. to 0 deg (that is a -2 deg. difference) is a function of weight on wheel switches if i recall correctly (it has been a few years since I worked on them). 0 deg. position places the LEF leading edge position at the wing root flush with the fuselage strake. When airborne, the LEF position obviously varies at low speeds or while manoeuvring but will be flush (0 deg.) during level, stable flight at cruising- or higher speeds. When the aircraft is on the ground the + 2 deg. position is easily recognized with the LEF leading edge position slightly above the fuselage strake at the wing root.

Quoting MidEx216 (Reply 3):
So essentially, as long as wheels are down, so are (trailing edge) flaps, and always in the same position? And unless I understand wrong, that would mean that there's also no steps during the landing sequence involving lowering flaps (just making sure I understand clearly)?

Does that mean that the stall speed in landing configuration on an F-16 is essentially the same as the stall speed in takeoff configuration...because the two configurations (except for the leading edge flaps) are the same?

Trailing edge flaps are always down with gear down (with electrical- and hydraulic power on) but they will also come down with gear up at a defined low airspeed depending on ADC input. And there are no steps, there is one flaps down position. In normal flight with gear up the flaperons function as ailerons and will be flush (neutral) with the wing trailing edge. In this configuration the flaperons can move up and down like ailerons.

Stall speed basically depends on aircraft weight. With the aircraft in stable landing (gear down) configuration, provided there is no roll input, the flaps will be in a single, fixed, down position (same position for take-off and landing configuration). The LEF will schedule according airspeed, aoa and any vertical (g) acceleration. Any roll input in the landing configuration will move a flaperon up in the direction of the roll in conjunction with the stabilators (horizontal stabilizers) which also provide roll control, while the flaperon on the other wing will remain in its fixed, down position. The flaperon essentially assists in wing drop in the direction of the roll while the flaperon on the other wing retains its function as high lift device.


Hope this helped,

Starglider


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