The purpose of the part in front of the wing

Always wondered why the F-16 has a tailhook, or how big a bigmouth F-16's mouth really is ? Find it out here !
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deadseal

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Unread post21 Feb 2009, 00:31

verbatim outta dash one...im lookin at it......altitude/mlg..unless they r lying to confuse pilots :)
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MVSGas

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Unread post21 Feb 2009, 05:43

http://www.patricksaviation.com/videos/SUPERGT/2872/
For you guys that have never seen this before.You can really see the LEF operating on this video. at 1:23 the nose comes off the ground and no LEF activity while by 1:24 you can see them come down. Good video to see what the LEF do during maneuvers
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Raptor_claw

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Unread post21 Feb 2009, 08:39

At the risk of getting too nit-picky, or too much into the weeds, lemme throw out a couple points. (I've attached JW's graphic for reference).

- The LEF maximum deflection is 25 degrees. At least that's the upper limit on the command coming from FLCS.

- The lower limit of -2.0 degrees is not quite as simple as the diagram would indicate, and this is where some of the complexity (and the altitude functionality) comes in.
---- The lower limit applied to the basic schedule is a function of altitude. This limit is -2.0 at altitudes of 15,000 feet and above. The limit is 0.0 at 10,000 ft and below (it fades between the two values between 10k and 15k.)
---- The supersonic -2.0 command is in a different path, and is not affected by the variable limit from the previous bullet. BUT, there is an altitude functionality here as well. This path is selected if Mach is greater than 0.998, but only if altitude is above (roughly) 19,600 feet. So, if you are at 19k feet and supersonic, you stay on the basic Mach/AOA schedule with the limit computed as above - you don't automatically go to -2.0, as you would if you were at 21,000 feet.
---- The switch that selects a constant -2.0 command while supersonic (and alt>19600) also sets the -2.0 command on the ground, based on either WOMG OR wheel spin up greater than 60 knots at idle power.

- The other slightly complicating altitude functionality applies to the Mach/AOA schedule lines as shown in the graphic. At sea level, the Mach going into the calculations is capped at 0.7. In other words, no matter how much faster you go than Mach 0.7 at sea level, the schedule is computed as if you were still at 0.7. This "cap" increases as a function of altitude, such that it hits 0.998 at 20,000 feet. (This makes sense, because if you proceed above 0.998 while above 20,000, you don't need the schedule - you would be switched to the constant -2.0).

- Just for reference, and refering to the diagram, the Mach 0.6 schedule line crosses 0 (LEF) at just about 1 degree of AOA. Also, the slope of the lines is 1.377 (you get a 1.377 degree increase in LEF for every 1.0 deg of AOA).
- Final point (and this really is nit-picky). Mach number is not actually used in schedule computations. The schedules are based on qc/Ps (dynamic pressure (calibrated) divided by static pressure). There is a one-to-one relationship between Mach and qc/Ps, but it is not linear. So if you were to use a graph based on Mach (such as the one below) you would get the right answer as long as you stayed on the provided Mach lines, but if you tried to interpolate between Machs, your answer would be off, not a lot, but off nonetheless.
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lef_360.jpg
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MVSGas

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Unread post21 Feb 2009, 08:48

Grate post Raptor_claw, than you.
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falconfixr1

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Unread post21 Feb 2009, 16:27

all -- the video i posted of the T/O wasn't to prove my point....i can actually see the LEFs drive down when MLG's come up...i just thought it was a good shot of it.

If you have a -1 or a 34 FI...please let me know when AOA indication occurs...maybe that was with nose wow...
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deadseal

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Unread post21 Feb 2009, 17:34

Now i know where your getting the NLG wow thing. AOA indexer, aoa indicator, and hud aoa bracket are connected to the NLG wow for accurate two point aero braking....once the nose comes down (about 110-100 pending how good an aero brake you get) the flcs sets everything to zero.
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johnwill

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Unread post21 Feb 2009, 17:51

Quite evidently, my LEF schedule is outdated. That was the schedule used through block 30, but it seems the digital FLCS gave them the capability to develop a more refined and complex schedule. Thanks, RaptorClaw. Can you tell me if the new schedule was retrofitted to the analog airplanes?
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Raptor_claw

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Unread post24 Feb 2009, 09:49

johnwill wrote:Can you tell me if the new schedule was retrofitted to the analog airplanes?

From what I can tell at least part of the altitude functionality has been in all along. I dug out an A/B FQ report from FSD (circa 1979). It has the same basic Mach/AOA schedule that we have been looking at, with a block of text inserted onto it describing exact same lower limit vs altitude function (-2.0 at 15k+, 0.0 at 10k-) that is still in there. There is no mention that I could see of the other altitude function (the limiting of Mach into the schedule lookup), but there really isn't much detail, so I'm not sure what that really means (there is also no mention of the on-ground schedule switch logic at the time).
As far as the general question as to what might have been retrofit back into analog through the years, I have no idea, although I would guess "not much".
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johnwill

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Unread post24 Feb 2009, 15:16

Thanks, Raptor claw. The part about altitude affecting the max up position would have been very important to the airload felt by the LEF. About 1/3 of all the lift on the wing is developed on the LEF at the worst case (0.8 mach / low altitude). 2 degrees would have made a significant difference in the LEF load.
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mirazmircan

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Unread post02 Mar 2009, 01:07

Hi All, I'm mechanical engineering student and I'm last class student. I have a graduate projection. It's modelling of wing structure of F-16. I have to found dimension of wing stucture (rib, skin, and spar). If I found this information, I can make my graduate projection. I'm use this information at CATIA and ANSYS programmes. Please help me. Do you have any information of wing of F-16? If there are any information, pls send me a message. It' very important for me.

Thank you for all
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mitchell_

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Unread post27 Oct 2009, 14:35

...so in the end, what I understand - please correct me if I'm wrong - is that the FLCS has full authority on the LEF's and taileron's while TEF's - in their flaperon function - responds only to the Gear down handle input?

Sorry guys, I know this is an old topic but it's extremely interesting...plus I'd like to have a clear idea of how this thing works... :wink:

Thanks to the F-16.net Staff for the great job he's been doin' for all these years and to all of you guys for these great posts and topics!

Greetings from Italy...
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johnwill

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Unread post27 Oct 2009, 19:13

Mitchell, welcome to F-16.net!

The trailing edge flaps or flaperons are totally controlled by the FLCS. The FLCS receives a signal from the gear handle to move the flaps down 20 degrees for takeoff and landing. There is also an alternate flap switch to do the same thing in case the gear handle malfunctions. In supersonic flight, the FLCS moves the flaps up 2 degrees. All of those commands are symmetric, same to left and right flaps.

There is an automatic function to reduce symmetric flap extension between 250 kcas and 370 kcas, so there is no flap extension above 370 kcas from gear handle or alternate flap commands.

Pilot roll commands (stick and trim) are sent to the FLCS, which moves the flaps asymmetrically, left opposite from right.
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mitchell_

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Unread post27 Oct 2009, 19:44

Hi johnwill! Thanks a lot for your answer dude...could you tell me what's the LEF's maximum extension up and down?

Thanks again for the welcome john!
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vegasdave901

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Unread post27 Oct 2009, 22:36

Hey, johnwill. If you've got a couple hours to kill would you label all the moving surfaces of the F-14 for me :twisted:
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fifel144

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Unread post28 Oct 2009, 00:32

ViperDude wrote:That minus 2 degrees on the LEF is about 1 3/4 to 2 inches when measured, as I would just put my index finger up there and measure from the tip of my finger to the 2nd joint...lol.

Here is one for you Johnwill, the first time I climbed in the F-16 XL I noticed these 4 letters on the flight control panel..L E A F, bring back any memories?

Cheers,

ViperDude


-2 is 21/32" - 1" whats an inch? :wink:

:cheers:
Fife
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