FALLING LEAF

Has this aspect of the F18s flight been modelled.

See this extract from jet stream.

Thanks

Another question is whether the current version of software in FCS even allows the aircraft to enter falling leaf mode.

Falling leaf is now not possible with the latest fcs software update.

Falling leaf is now not possible with the latest fcs software update.

Not clear to me, do you mean it was possible before and not anymore since 2.5.3? And do you mean DCS, or what is FCS?

the FCS ( Flight Contol System ? ) is what is between your stick input and the control surfaces output, it is what limits the number of available G for exemple

=/= the Flight Model is what is between your control surface output and the way the plane behaves

it seems that the new FCS does not allow you to be drawn into a situation where the Falling Leaf syndrom appears ( the FCS won t allow enough AoA for ex )

Haha, I had it all backwards, but then I thought it was related to the OP and didn't see the point of the 2nd post :D

Time to study those systems then.

You can do falling leaf in DCS.

Prove it... Just saying you can do it doesn't mean ANYTHING at all.

You can do falling leaf in DCS.

Going to need a video of that. Haven't seen anyone manage to get into the falling leaf yet.

I have a few videos of departures in the DCS F/A-18C, I'll check through the tracks there was a couple of crashes and a recovery. You can get into a flat spin as well.:thumbup:

Are you referring to Falling leaf, as in the departure from controlled flight, made infamous by the F-16, or something else?

The falling leaf is when there is departure from controlled flight, where 3 axis of opposing input is forced at stall speed, which the FCS can't compensate for. The FCS's attempts to return controlled flight exacerbates this condition and the aircraft departs. The reason it's called the falling leaf, is because the aircraft mimics a falling leaf, rocking back and forward whilst falling out of the sky. The FCS (In the case of the F-16) continues to return the aircraft to controlled flight, but just worsens the problem. The aircraft can't return to controlled flight and none of the pilot's inputs have an effect to return from the departure. The F-16 (In BMS) is easy put in this state of departure; get slow, apply back pressure to nose up, hold the attitude then apply opposing roll and yaw input. If you do it correctly, you'll depart. Make sure you're at 20 000 - 25 000ft when attempting to the force the departure to practice recovery.

I've had several attempts to get the Hornet in this state, but have not had any success. I've accidentally put the Flanker in this type of departure. It's possible you simply can't put the Hornet in this departure, due to advances in the FCS. After all, the F-16 was the first proper go at FBW and I guess the Hornet's FBW is bit more advanced that the F-16, thus it can actually contend with 3 channels of opposing input and not depart in this manner. Or I could just be wrong.

I was surprised to the see the Flanker do it. Fortunately from Falcon 4/BMS experience caused me to immediately recognise the type of departure and I correctly assumed recovery would be the same as the F-16:

- Throttle idle

- FBW override

- Match the nose of up/down position with corresponding control input. I.e. when the nose drops down, push the stick down. When the nose rises, pull back on the stick.

- Continue this "sea-saw" rocking, until the nose drops, and stays pointed down - does not rise again.

- Allow IAS to increase until above stall speed, apply power, pull up to level flight.

- Re-engage FBW (disengage FBW override.)

You need a good 15 000ft to recover from this departure. It takes time to recover and you just need to be patient. If you're below 15 000ft when you enter this type of departure, eject.

To avoid confusion and misunderstandings, this is what the falling leaf looks like.

The recovery method is to release the controls and hope for the best or eject when you reach the minimum safe altitude.

NATOPS claims that the falling leaf has not been encountered during extensive testing since the software update, which I believe is present in our aircraft?

If it's possible to do I'd love to know how though, seems fun.

I have a few videos of departures in the DCS F/A-18C, I'll check through the tracks there was a couple of crashes and a recovery. You can get into a flat spin as well.:thumbup:

Yep it's actually pretty easy to put the Hornet into an intentional flat spin at high altitude.

Pull the stick all the way back into a stall. With left engine at idle add full left rudder and right engine to burner (or vice versa of course). Once established in the spin you can idle the right engine and neutralize controls and she'll pancake all the way down. To recover just firewall the left engine to counteract the rotation, the left wing will rise, nose will drop, and you'll be recovered.

I've never flown a real plane that's at risk of entering a flat spin so I honestly have no idea how closely this conforms to reality.

The FCS (In the case of the F-16) continues to return the aircraft to controlled flight, but just worsens the problem.

AFAIK, is not the FLCS. At High alpha(50° to 60°), the Lift center moves forward couple with the heavier tail (normal weight and balance of the aircraft) the aircraft get stuck at high alpha. That is why MPO is used, to further increase pitch down authority on the horizontal tail and help get the aircraft out of the high AOA.

Again, AFAIK, on the F/A-18 the canted vertical tails and the way the aircraft is balance avoids aircraft being stuck at High AOA, but creates this falling leaf effect.

MPO?

MPO?

Manual Pitch Override, is a F-16 thing.

Thanks.

I had a quick go trying to spin but didn't succeed even with spin mode engaged.

This is the technique for demonstrating spin characteristics with the 10.7 OFP

The following spin demonstration procedure is recommended for v10.7 Automatic Spin Recovery Mode Demonstration:

1) Stabilize wings level, 150 KCAS and 35,000 feet.

2) Slowly reduce both throttles to IDLE.

3) Set 15 to 20 degree pitch attitude and hold.

4) When AOA tone is present (approximately 35 AOA) smoothly apply full aft

stick while noting heading or ground reference.

5) Firmly hold full aft stick and smoothly increase thrust on left/right engine to

MAX with opposite engine at IDLE. Simultaneously apply full lateral stick and rudder pedal (full pirouette control inputs) into the direction of the throttle at IDLE.

6) Hold the control inputs for 1.5 turns while counting every half turn looking outside the cockpit.

7) After 1.5 turns, neutralize control stick and rudder pedal inputs - release the control stick and take feet off the rudders.

8) Automatic Spin Mode logic should activate within 1/4 turn.

9) Note the spin arrows, altitude, AOA, airspeed, and yaw rate.

10) Proceed with NATOPS spin recovery procedure: apply lateral stick in the

direction of the spin arrows.

11) Continue to look outside the cockpit.

12) When yaw rate ceases, neutralize the lateral stick.

13) Note when the spin arrows disappear.

14) Bring both throttles to IDLE and complete NATOPS Out-of-Control

Recovery procedures by waiting for AOA/yaw tones to be removed, side- forces to be subsided, and aircraft to increase through 180 KCAS prior to recovering from the nose low attitude.

From https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=3738&context=utk_gradthes

Thanks.

 

I had a quick go trying to spin but didn't succeed even with spin mode engaged.

''Spin mode'' is a manual FCS override to get you out of a spin, not into one.

Are you referring to Falling leaf, as in the departure from controlled flight, made infamous by the F-16, or something else?

 

The falling leaf is when there is departure from controlled flight, where 3 axis of opposing input is forced at stall speed, which the FCS can't compensate for. The FCS's attempts to return controlled flight exacerbates this condition and the aircraft departs. The reason it's called the falling leaf, is because the aircraft mimics a falling leaf, rocking back and forward whilst falling out of the sky. The FCS (In the case of the F-16) continues to return the aircraft to controlled flight, but just worsens the problem. The aircraft can't return to controlled flight and none of the pilot's inputs have an effect to return from the departure. The F-16 (In BMS) is easy put in this state of departure; get slow, apply back pressure to nose up, hold the attitude then apply opposing roll and yaw input. If you do it correctly, you'll depart. Make sure you're at 20 000 - 25 000ft when attempting to the force the departure to practice recovery.

 

I've had several attempts to get the Hornet in this state, but have not had any success. I've accidentally put the Flanker in this type of departure. It's possible you simply can't put the Hornet in this departure, due to advances in the FCS. After all, the F-16 was the first proper go at FBW and I guess the Hornet's FBW is bit more advanced that the F-16, thus it can actually contend with 3 channels of opposing input and not depart in this manner. Or I could just be wrong.

 

I was surprised to the see the Flanker do it. Fortunately from Falcon 4/BMS experience caused me to immediately recognise the type of departure and I correctly assumed recovery would be the same as the F-16:

 

- Throttle idle

- FBW override

- Match the nose of up/down position with corresponding control input. I.e. when the nose drops down, push the stick down. When the nose rises, pull back on the stick.

- Continue this "sea-saw" rocking, until the nose drops, and stays pointed down - does not rise again.

- Allow IAS to increase until above stall speed, apply power, pull up to level flight.

- Re-engage FBW (disengage FBW override.)

 

You need a good 15 000ft to recover from this departure. It takes time to recover and you just need to be patient. If you're below 15 000ft when you enter this type of departure, eject.

Not the same procedure for the Hornet, it does not depart like an F-16, when the spin recovery mode kicks in follow the directions on the MFDs/HUD. When in a vertical departure like you mentioned the Hornet pitches forward because of the CoG. So you won't be departing like that for long.

Falling leaf is essentially a stall so the fastest way to recover I've found:

Stick forward -nose down

afterburner

:thumbup:

''Spin mode'' is a manual FCS override to get you out of a spin, not into one.

Nope. SRM helps you get out of a spin, but it also removes any spin protection making you more likely to enter one if you're not already in out of control flight.

11.2.5.5.1 Spin Recovery Mode (SRM). Flight characteristics in SRM differ significantly from those

of the normal CAS mode. All FCS feedbacks, interconnects, and gain schedules are removed, leaving

the FCS in essentially a three axes DEL mode. Because the artificial yaw stability features of CAS are

not available in SRM, the directional stability is weak and the nose tends to wander. Because the

lateral control surfaces are not washed out with increasing AOA as they are in CAS, lateral stick can

generate excessive yaw. The aircraft is very susceptible to nose−slice departure with even small stick

deflection.

Falling leaf is essentially a stall so the fastest way to recover I've found:

Stick forward -nose down

afterburner

:thumbup:

That may work, but that's not what the manual says:

15.43.4 OCF Recovery Procedures

*1. Controls - RELEASE, FEET OFF RUDDERS, SPEEDBRAKE IN

If still out of control -

*2. Throttles - IDLE

*3. Altitude, AOA, airspeed and yaw rate - CHECK

If command arrow present -

*4. Lateral stick - FULL WITH ARROW

When command arrow removed -

*5. Lateral stick - SMOOTHLY NEUTRAL

When recovery indicated by AOA and YAW rate tones removed, side forces subsided, and

airspeed accelerating above 180 KCAS -

*6. Recover.

Why are people so eager to get into a departed flight :lol:

Some interesting departure/stall characteristics modelled shown here including an usual CoG type departure.:joystick: