T/O & Lndg Gains

[Patriot]

Thank you bouliult! I've almost got my head arround this topic finally. Would you please for the last time refer to situation below and share your thoughts... I'd also like to hear the opinion of Gums or Johnwill if they're arround.

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?

[johnwill]

Patriot, it's been a long long time since I looked at this, but I believe the comment saberrider made about flaps not down above 370 kt and gear not down above 300 kt may be a little misleading. I could easily be wrong here, but I believe the alt flap is automatically scheduled between 300 kt (maybe?) and 370 kt. Meaning with alt flap down, below 300 kt the flaps will go full down, but as speed increases above 300, they will gradually retract until at 370, they are fully retracted. The full down flaps loads are ok at 370, but if the pilot chose to do a 9g turn at that time the wing torque loads would likely be excessive. Also the gear down limit speed is 300 kt, but it is not an automatic limit, it is a pilot observed limit. Limiting factor for gear down is of course the gear doors departing and probably causing serious damage to the airplane.

[saberrider]

Of course , Johnwill you're right about flaps up programing because retraction is not instantaneous and a/c gain some speed in @7 second's until they are up and gear limits .Thing is if you try to lowering flaps when you're flying above speeds limitations they don't go down due actuator's I believe or ignored electrical comand .

[bouliult]

Of course , Johnwill you're right about flaps up programing because retraction is not instantaneous and a/c gain some speed in @7 second's until they are up and gear limits .Thing is if you try to lowering flaps when you're flying above speeds limitations they don't go down due actuator's I believe or ignored electrical comand .

If the Alternate flap switch is positioned in ALT Flaps and the jet is going to fast for the extension of the Flaps they will simply not extend, however the jet will be in landing gains.

When lowering the speed and the ALT flaps switch is still in extend the Flaps will gradually come down. Max gear extend speed is 300kts. So when loweirnf the gear teh flaps will extend and gradually come down more during decelaration.

[bouliult]

Thank you bouliult! I've almost got my head arround this topic finally. Would you please for the last time refer to situation below and share your thoughts... I'd also like to hear the opinion of Gums or Johnwill if they're arround.

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?

Flying with a slow mover below 200kts handling wise it will NOT be better to stay in cruise gains because the jet is not made to fly long times at those speeds. The pilot will be more 'in control'flying at very low speeds in landing gains. Be aware that flying at very low speeds in cruise gains will not leave the jet more agile compared to cruise gains suimply because the airflow is to little over the wings and flight controls. In landing gains the jet will be more forgiving. Typically when intercepting slow movers they will have the same problems as the Viper flying at low airspeeds.

[saberrider]

Of course , Johnwill you're right about flaps up programing because retraction is not instantaneous and a/c gain some speed in @7 second's until they are up and gear limits .Thing is if you try to lowering flaps when you're flying above speeds limitations they don't go down due actuator's I believe or ignored electrical comand .

" If the Alternate flap switch is positioned in ALT Flaps and the jet is going to fast for the extension of the Flaps they will simply not extend, however the jet will be in landing gains".

When lowering the speed and the ALT flaps switch is still in extend the Flaps will gradually come down. Max gear extend speed is 300kts. So when loweirnf the gear teh flaps will extend and gradually come down more during decelaration.

Flaps they will simply not extend, however the jet will be in landing gains you tell me BUT in Take off Landing gains flaperons moves only SINGLE ONE UP if AILERONS COMMAND another one IS LOCK IN DOWN 20 DEGREES. SO IF YOU SEE MY DRIFT , NOW HOW IS TAKE OFF GAINS NOT ignored IF FLAPERONs ARE BLOWN UP BY excessive speed?

[bouliult]

Of course , Johnwill you're right about flaps up programing because retraction is not instantaneous and a/c gain some speed in @7 second's until they are up and gear limits .Thing is if you try to lowering flaps when you're flying above speeds limitations they don't go down due actuator's I believe or ignored electrical comand .

" If the Alternate flap switch is positioned in ALT Flaps and the jet is going to fast for the extension of the Flaps they will simply not extend, however the jet will be in landing gains".

When lowering the speed and the ALT flaps switch is still in extend the Flaps will gradually come down. Max gear extend speed is 300kts. So when loweirnf the gear teh flaps will extend and gradually come down more during decelaration.

Flaps they will simply not extend, however the jet will be in landing gains you tell me BUT in Take off Landing gains flaperons moves only SINGLE ONE UP if AILERONS COMMAND another one IS LOCK IN DOWN 20 DEGREES. SO IF YOU SEE MY DRIFT , NOW HOW IS TAKE OFF GAINS NOT ignored IF FLAPERONs ARE BLOWN UP BY excessive speed?

The flaps are not blown up by excessive speed they are commanded up by the Air Data Converter. The jet is still in landing gains even if the flaps are commanded more up because of airspeed.

[saberrider]

But in To/L .gains flaps(flaperons) only rice one at the time if the aileron's are apply (rolling)?That mean one is riced above the wing line and another one is not down at any degree. This is not possible.

[johnwill]

I think your understanding of the aileron command with TO/L gains is incorrect. In fact, aileron command sends equal and opposite command to the flaperons at all gains, normal or TO/L. Let's look at some numbers to help understand it better. At a speed of 200 kt, with flaps down they will be at 20 deg. If a right roll 5 degree aileron command is sent, left flaperon is commanded to 25 deg down, but 20 deg command limiter prevents it from moving. The right flaperon moves to 15 deg down.

Next increase speed to about 350 kt and the flaperons move to 5 deg down. Then apply the +/- 5 deg aileron command, so the left flaperon is commanded to 10 deg down and the right to 0 deg.

So you can say flaperon position with any gain is flap command +/- aileron command, limited to +/-20 deg.

[saberrider]

Thanks for clarification . I believed that if in To/L gains flaperons will stay only down position (20*)then with increase in speed rice up with no stoops between 20degrees down and 0 degree (once command up position will go to the 0 *).So if the speed is more than 300kts any position form 20 -0 is possible to have and applying aileron command is symmetrical up/down till20*max. down .That may be never20 up/20down aileron's in the slowly flight even though 23/21*is max. Cruise Gain because not need anything closely .

[saberrider]

Not to mention that flyng in landing gains the jet is much more limited in manoeuvrebility.[/quote]Half of roll rate , 17 max AOA.

[saberrider]

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

So if you have any AoA with the Alt Flap / or gear down setting then LEF's are deployed always more 15 degrees?

[ljqc]

I'll try to answer OP's question axis by axis using the DFLCS control block diagram for a block25 testbed aircraft.
There're two related logic switches in the diagram: Note 1 and Note 5. Note 1 is mainly related to take-off & landing gains, and Note 5 is mainly related to TEF and LEF logic.

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NOTE 1. Switch activates by ANY of the following methods:

LG Handle in DOWN position,
Not Standby Gains & [Fwd or Aft ALT FLAPS Switch in EXTEND position] & qc < 600psf (airspeed < 400 kts),
Not Standby Gains & [Air Refuel Switch in OPEN position] & qc < 600psf (airspeed < 400 kts).


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NOTE 5. Switch activates by ANY of the following methods:

LG Handle in DOWN position,
Fwd or Aft ALT FLAPS Switch in EXTEND position.


I've highlighted the above switches in green in the diagrams.

Pitch Axis:

Basically the changes in pitch axis are:
1. pitch-rate * 0.5 is used as main feedback instead of (load factor - 1.0), as the portion of variable Y and Z is changed, which is switched by Note 1. So that the system is a pitch-rate command system, and the aircraft will try to maintain zero pitch-rate hands-off. The maximum pitch-rate command is 8.3 x 2 = 16.6 deg/s, whereas in cruise gains, the maximum g command is 8.3 + 1.0 = 9.3g.
2. An additional (filtered AOA - 10) * 0.X05 (too blurry to read), limited to positive values, is added to the pitch-rate feedback. This means if AOA is greater than 10 deg, the DFLCS will receive a (fake) positive pitch-rate feedback, which is equivalent to a pitch-down command. It will also result in a decreased AOA limit. The logic in CAT Limiter block however is unchanged.
3. All CAT III logic switches are ignored or overrided, meaning switching to CAT III will not affect anything in take-off & landing gains or will follow the logic in CAT I. For example in pitch axis, the roll-rate feedback is introduced into the CAT Limiter to further increase the received AOA feedback, in order to suppress the inertia roll-coupling moment developed. In this case, switching to take-off and landing gains has the same effect as in CAT I.
4. An additional pitch structural filter is applied after the combined command and feedback.

Roll Axis:

1. Maximum roll rate command is hard limited to 167 deg/s, which means any stick command more than 167 deg/s is ignored.
2. CAT switch has no effect in take-off and landing gains.

Yaw Axis:
Not yet to spot any logic switches related to take-off and landing gains in the yaw axis.

TEF:

1. The TEF is switched by Note 5. Unlike Note 1, it's unrelated to the Air Refuel Switch so that the flaps won't deploy when doing AAR.
2. TEF has a N10 gain scheduled by dynamic pressure, which will gradually retract the flaps when dynamic pressure is in between 200 and 500 psf (equivalent airspeed between 240 and 370 kts). This schedule is only activated if Note 5 is satisfied.

LEF:

The LEF will be locked to 15 degrees only when Note 5 is satisfied AND the DFLCS is in standby gains. Otherwise it has a normal schedule as in cruise gains.