T/O & Lndg Gains

Operating an F-16 on the ground or in the air - from the engine start sequence, over replacing a wing, to aerial refueling procedures
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Patriot

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Unread post10 Dec 2017, 14:46

Have a question.
How the T/O & landing gains (flcs mode set <400kts) affects the AOA, rool rate and yaw? Is the TO&L mode turned off as soon as the gear is up (in accordance with TEFs) or it stays on wehenever the jet is up to or below 400 knots?
Are CAT. III and Alt Flaps Mode independently put similar limitations to the airframe? I.e. AOA limit to 16-18 degs, roll rate cuted by half, yaw rate the same?
Any specific figures are welcomed!

ps. Does the alt flaps mode causes LEFs to be locked in place or not? Actually, does the alt flaps mode is operating under t/o&l gains or stand by ones?
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yooper65

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Unread post11 Dec 2017, 07:03

This is what little I recall.. the Flight Control System is placed into Takeoff and Landing Gains either with the Landing Gear Control Handle being down, or Alt Flaps in Extend (and below 400 knots), or Air Refuel switch in Open (and below 400 knots).
I believe the Stores Config switch has no effect with FLCS while in Takeoff and Landing Gains. And the Alt Flaps switch has no effect on the LEFs with FLCS in Takeoff and Landing Gains.
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Unread post11 Dec 2017, 10:10

Thank you for this clarification.

yooper65 wrote: And the Alt Flaps switch has no effect on the LEFs with FLCS in Takeoff and Landing Gains.

It goes with contrary with what Ive heard that using alt+flaps put LEFs in fixed position (either 15 or 25 degs supposingly).

Btw, Ive read somewhere on this forum that if a (Viper) pilot switches alt flaps to extend, he's already in trouble..
Therefore my question. Can an Alt Flaps by any means be refered to as an emergency or an abnormal flight condition/procedure? (...as this feature was put in the jet originally to cope with an actual emergency/lndg gear mal)
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bouliult

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Unread post11 Dec 2017, 15:26

Patriot wrote:Have a question.
How the T/O & landing gains (flcs mode set <400kts) affects the AOA, rool rate and yaw? Is the TO&L mode turned off as soon as the gear is up (in accordance with TEFs) or it stays on wehenever the jet is up to or below 400 knots?
Are CAT. III and Alt Flaps Mode independently put similar limitations to the airframe? I.e. AOA limit to 16-18 degs, roll rate cuted by half, yaw rate the same?
Any specific figures are welcomed!

ps. Does the alt flaps mode causes LEFs to be locked in place or not? Actually, does the alt flaps mode is operating under t/o&l gains or stand by ones?


The airspeed has nothing to do with being in Takeoff and landing gains. The jet is in these gains as said by putting the landing gear handle down, air refuel switch in OPEN, or the alt flaps switch in extend. Be aware that it only looks at the landing gear handle position. In landing gains the jet is not G/AOA rated as in cruise gains but is Pitch/AOA rated. This means that below 10 degrees AOA the jet is pitch rated (the jet wants to maintain pitch up/down attitude as inputed by the pilot opposed to cruise gains where it wants to maintain a constant G number untill app 12 degrees in CAT III and 20 degrees in CAT I) above 10 degrees AOA the AOA limiting is blended in. Also rollrate is limited.

The LEF’s are not affected by placing the alt flap switch in extend.

Alternate flaps may be used when you want to fly low airspeed with the gear up (slow mover intercept). But mostly it is used when there is something wrong. For example when for whatever reason you want to leave the gear handle in the up position. Or want to fly low airspeeds because of a canopy crack or a canopy that blew off.

The LEF’s will not schedule if there is a assimmetry between left and right LEF, when the the jet is operating in Standby gains or when they are placed in lock by the person in the cockpit.
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lamoey

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Unread post11 Dec 2017, 23:41

Patriot wrote:Have a question.
How the T/O & landing gains (flcs mode set <400kts) affects the AOA, rool rate and yaw? Is the TO&L mode turned off as soon as the gear is up (in accordance with TEFs) or it stays on wehenever the jet is up to or below 400 knots?
Are CAT. III and Alt Flaps Mode independently put similar limitations to the airframe? I.e. AOA limit to 16-18 degs, roll rate cuted by half, yaw rate the same?
Any specific figures are welcomed!

ps. Does the alt flaps mode causes LEFs to be locked in place or not? Actually, does the alt flaps mode is operating under t/o&l gains or stand by ones?


It's been a few decades now, but I believe the <400kts, under 10,000ft (not sure of accurate alt.) and a certain sink rate gives the T/O warning light, to warn the pilot that the gear is not extended. I know a Norwegian viper managed to land with gear up, partly blamed on a low altitude, high speed circle, which prevented the sink rate to go over the limit, hence he got no warning about the impending belly landing.
Former Flight Control Technican - We keep'em flying
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Unread post12 Dec 2017, 12:31

Guys, bouliult exceptionally (it seem like you had some hrs on the thing) thank you for these explanations. On the other hand..

Gums (an ex-Viper driver I believe) back in 2006 somewhere else on this forum wrote something like this:

BTW, only time I ever used ALT FLAPS was trying to stay slow enuf to get tail numbers off a Cessna that was violatin restricted airspace. What a hoot.......

If you have to try something like ALT FLAPS, you're already in trouble, IMHO.


So my only question remains, what he meant by "trouble" ? :whistle:
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bouliult

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Unread post12 Dec 2017, 12:42

It's been a few decades now, but I believe the <400kts, under 10,000ft (not sure of accurate alt.) and a certain sink rate gives the T/O warning light, to warn the pilot that the gear is not extended. I know a Norwegian viper managed to land with gear up, partly blamed on a low altitude, high speed circle, which prevented the sink rate to go over the limit, hence he got no warning about the impending belly landing.[/quote]

The T/O warn light illuminates (just like the gear warning horn) when airspeed is below 190kts, alt less than 10000ft and vvi is more than 250ft/min negative and the trailing edge flaps are not extended and/or nosewheel not down and lockeed.
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yooper65

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Unread post13 Dec 2017, 10:33

It appears during an Emergency Procedure that requires the Landing Gear Handle to be lowered but does not, the Pilot is to position the Alt Flaps Switch to Extend.
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saberrider

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Unread post14 Dec 2017, 09:26

Patriot wrote:Thank you for this clarification.

yooper65 wrote: And the Alt Flaps switch has no effect on the LEFs with FLCS in Takeoff and Landing Gains.

It goes with contrary with what Ive heard that using alt+flaps put LEFs in fixed position (either 15 or 25 degs supposingly).

Btw, Ive read somewhere on this forum that if a (Viper) pilot switches alt flaps to extend, he's already in trouble..
Therefore my question. Can an Alt Flaps by any means be refered to as an emergency or an abnormal flight condition/procedure? (...as this feature was put in the jet originally to cope with an actual emergency/lndg gear mal)
If F16 is in interception of an Cessna at @140knots AltFlap is used for lowering AoA and fly by next to the private plane.So No it is not emergency /abnormalities to drop the flaps .But fuel economy is important and why to fly with more drag if it is not required by mission or AR ?
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bouliult

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Unread post14 Dec 2017, 12:39

saberrider wrote:
Patriot wrote:Thank you for this clarification.

yooper65 wrote: And the Alt Flaps switch has no effect on the LEFs with FLCS in Takeoff and Landing Gains.

It goes with contrary with what Ive heard that using alt+flaps put LEFs in fixed position (either 15 or 25 degs supposingly).

Btw, Ive read somewhere on this forum that if a (Viper) pilot switches alt flaps to extend, he's already in trouble..
Therefore my question. Can an Alt Flaps by any means be refered to as an emergency or an abnormal flight condition/procedure? (...as this feature was put in the jet originally to cope with an actual emergency/lndg gear mal)
If F16 is in interception of an Cessna at @140knots AltFlap is used for lowering AoA and fly by next to the private plane.So No it is not emergency /abnormalities to drop the flaps .But fuel economy is important and why to fly with more drag if it is not required by mission or AR ?


Not to mention that flyng in landing gains the jet is much more limited in manoeuvrebility.
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Unread post14 Dec 2017, 14:15

Got it.

So, for example, situation: Flying in formation with slow mower at 200 knots (as in this pic below) in configuration likie this:
Handlingwise it would be better to stay in crusing gains and at considerably high AOA, or extend alt flaps and fly at lower AOA on t/o & l gains withh reduced maneuverbility?

Image


lamoey wrote:I know a Norwegian viper managed to land with gear up, partly blamed on a low altitude, high speed circle, which prevented the sink rate to go over the limit, hence he got no warning about the impending belly landing.


wasn't that it?


Image
Last edited by Patriot on 14 Dec 2017, 19:18, edited 1 time in total.
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saberrider

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Unread post14 Dec 2017, 15:47

Thinking of this aspect : if the a/c is in To/L gains with flaps down it will have half off the response rates and may sunk a little when maneuver if you're heavyweight then you must not be aggressive in flight .But if refueling in the air this sluggishness will help you while make little corrections.
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Unread post15 Dec 2017, 00:21

bouliult wrote:The airspeed has nothing to do with being in Takeoff and landing gains. The jet is in these gains as said by putting the landing gear handle down, air refuel switch in OPEN, or the alt flaps switch in extend.


You're saying that if I'd fly at say Mach 1.5 and put an air refuel switch to open the jet would go into takeof & landing gains?
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Unread post15 Dec 2017, 21:23

Patriot wrote:
bouliult wrote:The airspeed has nothing to do with being in Takeoff and landing gains. The jet is in these gains as said by putting the landing gear handle down, air refuel switch in OPEN, or the alt flaps switch in extend.


You're saying that if I'd fly at say Mach 1.5 and put an air refuel switch to open the jet would go into takeof & landing gains?
Limitations are present and flaps cannot stay down over speed limit of 370knots and gear over 300
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bouliult

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Unread post15 Dec 2017, 22:32

Patriot wrote:
bouliult wrote:The airspeed has nothing to do with being in Takeoff and landing gains. The jet is in these gains as said by putting the landing gear handle down, air refuel switch in OPEN, or the alt flaps switch in extend.


You're saying that if I'd fly at say Mach 1.5 and put an air refuel switch to open the jet would go into takeof & landing gains?


Affirm. That is it. Off course the speed limit is 400kts 0.85 mach fit selecting Air refuel open.
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