fixed Cat III takeoff with no afterburner pitch down after gear up

[FoxTwo]

The issue occurs with a Cat III stores selected takeoff without afterburner. The airframe pitches down significantly after the gear is retracted. Without immediate pilot correction, the aircraft crashes into the ground.

 

This does not seem to occur when the aircraft takes off with afterburner, or if the switch is in Cat I.

 

I've included tracks from all 3 scenarios - Cat I with no AB, Cat III with AB, and Cat III without AB (which is where the problem lies).

 

I want to be clear, I may be putting the gear up too soon causing the flaperons to retract (which they do with the gear) and a corresponding loss of lift, however this should probably happen with the stores config in either Cat I or Cat III, so either way this is a bug just due to the inconsistency.

cat3_ab.trk

cat3_no-ab.trk

cat1.trk

Edited August 18, 2020 by FoxTwo

[smire666]

You' d better to use "Alt flaps" switch before take off. That holds TE flaps extended even wih gear retracted. After take off, over 200-250 Kts, return switch back...

[Dee-Jay]

You' d better to use "Alt flaps" switch before take off. That holds TE flaps extended even wih gear retracted. After take off, over 200-250 Kts, return switch back...

 

This is a workaround, not a fix. ;)

[Bouli306]

The issue occurs with a Cat III stores selected takeoff without afterburner. The airframe pitches down significantly after the gear is retracted. Without immediate pilot correction, the aircraft crashes into the ground.

 

This does not seem to occur when the aircraft takes off with afterburner, or if the switch is in Cat I.

 

I've included tracks from all 3 scenarios - Cat I with no AB, Cat III with AB, and Cat III without AB (which is where the problem lies).

 

I want to be clear, I may be putting the gear up too soon causing the flaperons to retract (which they do with the gear) and a corresponding loss of lift, however this should probably happen with the stores config in either Cat I or Cat III, so either way this is a bug just due to the inconsistency.

 

What is your AOA when selecting gear up?

[FoxTwo]

What is your AOA when selecting gear up?

 

~11 degrees.

 

Again I think the problem here is the inconsistency. Either it should do it or it shouldn't but it should do it regardless of where the switch is. AOA limits of Cat III wouldn't even let me pull extreme angles, this isn't that, this is letting you pull an angle, then you put the gear up and the aircraft noses down. If this should happen (and it probably should) then it should happen in either Cat I or Cat III.

[BIGNEWY]

There is a slight pitch down as the flaps come up as far as I can see.

 

You are raising the gear a little early and slow, but weather maybe a factor here also.

 

Can I ask you to try the instant action takeoff mission and see what results you get, attach the track replay after you have tried

 

Also, should you even be doing a CAT3 takeoff with no afterburner?

 

thank you

Edited August 18, 2020 by BIGNEWY

[FoxTwo]

I took a look at the flight manual and it didn't specifically mention anything about cat iii requiring ab.

 

Instant action behaved the same, it happens in any mission with cat 3 selected. Actual stores config does not seem to make a difference, it only happens when the switch is in cat 3. Taking off with the same weight/stores config and the switch in cat 1 doesn't pitch down even if you put the gear up as soon as they lift off the tarmac.

 

Like I said it should probably be pitching down but it should probably also be doing so regardless of the cat switch position.

[Bouli306]

~11 degrees.

 

Again I think the problem here is the inconsistency. Either it should do it or it shouldn't but it should do it regardless of where the switch is. AOA limits of Cat III wouldn't even let me pull extreme angles, this isn't that, this is letting you pull an angle, then you put the gear up and the aircraft noses down. If this should happen (and it probably should) then it should happen in either Cat I or Cat III.

 

Officially you put the gear up at or below 9 degrees aoa. I agree about the inconsistancy but in AB the acceleration is a lot more compared to MIL takeoff.

[Dee-Jay]

Hi!

Also, should you even be doing a CAT3 takeoff with no afterburner?

*You* can. This is allowed. Domestic/SOPs procedures may recommend AB takeoff as much as possible. MCH F-16 Vol3 is only saying this:

 

3.6.6. Make an afterburner takeoff anytime the computed MIL power takeoff roll exceeds 50 percent of the available runway.

 

So, anytime your ASDA is compatible with this, pilots are allowed to plan a dry takeoff if saving fuel is factor for the mission/flight regardless of your CAT or load configuration.

 

Regards.

[Nealius]

Is this still being investigated? In CATIII AB takeoffs, once the gear locks in the up position I get a major nose-down pitch moment. Not as bad as to cause a crash, but it does bump the FPM down a solid 2 degrees or so, and is jarring enough that you need to keep your cool to not bump the stick aft to (over)compensate. 

[BIGNEWY]

I have reported to the team to get feedback from them.

 

I will update this post when I have some information. 

 

thanks