Flap

flamer = F = flarp

flap vt.

1. [obs.] To unload a DECtape (so it goes flap, flap, flap...). Old-time hackers at MIT tell of the days when the disk was device 0 and DEC microtapes were 1, 2,... and attempting to flap device 0 would instead start a motor banging inside a cabinet near the disk. 2. By extension, to unload any magnetic tape. See also macrotape. Modern cartridge tapes no longer actually flap, but the usage has remained. (The term could well be re-applied to DEC's TK50 cartridge tape drive, a spectacularly misengineered contraption which makes a loud flapping sound, almost like an old reel-type lawnmower, in one of its many tape-eating failure modes.)

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

Also used in the sense of UFO flap, i.e. a group of U.F.O. observations that are close in space and time.
For unknown reasons, it often happens that a lot of independent U.F.O. observations happen in a place during a given period of time that may be of weeks or months, and then disapperar. Such flaps may happen around military devices or maneuvres, or around nuclear power plants, or for no apparent reason at all. Such flaps happen all of the time, just go to any ufology web site and find out how many are witnessed all of the time.
Famous flaps in ufology were the ones in Hessdalen, Norway and the ones on Monte Orsa, Italy in the 70's.

The flap is the simplest high lift device used on a wing, consisting of a hinged portion of the trailing edge which can be lowered in order to increase the lift coefficient and thus the lift produced by the wing. Flaps are most commonly used during takeoff and landing, when additional lift is needed to get off the ground with a full fuel load or to land at a low speed while keeping enough lift to flare.

The increase in lift coefficient is due to an increase in the downward change in momentum caused by placing the flap in the airflow. This increases the circulation, thus increasing lift (by the Kutta-Joukowski lift theorem). The effect can also be viewed as a simultaneous increase in both camber and angle of attack, because the trailing edge is being moved so it is below the leading edge, causing the wing to appear pitched with respect to the flow, when in fact it is not.

There are a number of types of flaps, depending on the application. The simple flap described above is a trailing flap, which is used on smaller aircraft where a large lift boost is not needed and simplicity is of utmost importance. As needs increase for larger aircraft, more complex flap devices are used, such as the split, slotted, and Fowler flaps. Each of these offers a greater maximum lift coefficient than the previous design. Note that a wing with no flaps has a C_Lmax of about 1.4.

 C_L_max       _________________                        Trailing Flap
             _-                 ---------__________
   2.4      (______________________________________\
                                                    \
                                                     \


               _________________                        Split Flap
             _-                 ---------_____________
   2.6      (______________________________________\
                                                    \
                                                     \


               _________________                        Slotted Flap
             _-                 ---------______________
   2.9      (______________________________________/
                                                      \
                                                       \


               _________________                        Fowler Flap
             _-                 ---------_____________
   3.0      (______________________________________|__  O
                                                           \
                                                            \

So a wing with an extended Fowler flap, as you might find on an airliner at takeoff, could produce twice as much lift as it does at cruise. However, the extended flap incurs a significant drag penalty. By extending far out into the flow, the parasite drag of the wing is increased greatly, reducing not only the efficiency of the wing but also its maximum speed before stall. Thus, the pilot will retract the flaps fairly quickly after taking off in order to accelerate to cruising speed. On the other hand, this apparent drawback is a boon when attempting to land, because the increased drag will help slow the plane to a safe landing speed.

Flap (?), n. [OE. flappe, flap, blow, bly-flap; cf. D. flap, and E. flap, v.]

Anything broad and limber that hangs loose, or that is attached by one side or end and is easily moved; as, the flap of a garment.

A cartilaginous flap upon the opening of the larynx. Sir T. Browne.

2.

A hinged leaf, as of a table or shutter.

3.

The motion of anything broad and loose, or a stroke or sound made with it; as, the flap of a sail or of a wing.

4. pl. Far.

A disease in the lips of horses.

Flap tile, a tile with a bent up portion, to turn a corner or catch a drip. -- Flap valve Mech., a valve which opens and shuts upon one hinged side; a clack valve.

 

© Webster 1913.

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Flap, v. t. [imp. & p. p. Flapped (?); p. pr. & vb. n. Flapping (?).] [Prob. of imitative origin; cf. D. flappen, E. flap, n., flop, flippant, fillip.]

1.

To beat with a flap; to strike.

Yet let me flap this bug with gilded wings. Pope.

2.

To move, as something broad and flaplike; as, to flap the wings; to let fall, as the brim of a hat.

To flap in the mouth, to taunt. [Obs.]

W. Cartwright.

 

© Webster 1913.

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Flap, v. i.

1.

To move as do wings, or as something broad or loose; to fly with wings beating the air.

The crows flapped over by twos and threes. Lowell.

2.

To fall and hang like a flap, as the brim of a hat, or other broad thing.

Gay.

 

© Webster 1913.