A321: tail clearance Flap 3 versus Full

[ShotOne]

I've been told, and the manuals seem to confirm that landing Conf 3 improves tail clearance on the A 321. This seems counterintuitive. Can any clever folk confirm a) if it's really the case and b) why ?

[flybas]

Due to the double slotted flap-design there is almost no difference in pitch-angle during the approach and landing between Flaps 3 and FULL.

So Flaps 3 does not improve tail clearance for landing.

[Capt Scribble]

Flap 3 is 22/21 deg S/F and full is 27/25 deg in the 321. If I remember correctly there is a lot more flap at full in the 320.

[vilas]

It is 27/35 for A320 for CFM engines and even more for IAE 40 I think.

[Cough]

Full marks Vilas. However, back to the thread, I seem to remember the 321 having a marginally higher nose up attitude on final when F3 compared to Flap full, only by either a half or whole degree...

[vilas]

I think flap3 improving tail clearance is difficult to imagine but may be it doesn't aggravate from flaps full.

[MD83FO]

i loved to land the 321 with flaps 3, its ideal, it does increase tail clearance because of the relationship flaps slats is different from the 320.

[Lantirn]

In terms of pitch geometry limits there is absolutely no difference in tailstrike clearance between flap settings. The tail will scratch the ground at the same angle.

The question is what pitch and speed (AOA actually) is required to support the lift you need between flap settings.

You will need more pitch and speed in a conf3 landing to arrest a downdraught or a high rate of descent close to the runway. Thus you cannot ask for this pitch comfortably as you would with conf full. This is how you become somewhat limited.

[stilton]

Proper response to a high rate of descent close to the ground is a significant increase
in thrust to stop the unplanned sink rate, if in doubt go around being careful with the pitch until well clear of the runway.


Raising the nose in this situation is the wrong response in any aircraft, will often lead
to a hard landing and quite possibly a tail strike.

[Lantirn]

True. For explanation purposes

[ShotOne]

It may be true but doesn't touch on the issue of conf 3 vs full. There doesn't seem to be any unanimity In the responses. Clearly the physical geometry of the landing gear isn't changed by flap setting. Is perhaps my informant getting at a slightly lower deck angle with conf3, because of the higher approach speed?

[vilas]

Proper response to a high rate of descent close to the ground is a significant increase in thrust to stop the unplanned sink rate, if in doubt go around being careful with the pitch until well clear of the runway.

Salvaging a landing with a significant thrust increase is not a normal or recommended technique but early flare is what FCTM recommends. If that is not sufficient then a GA.



From stabilized conditions, the flare height is about 30 ft.
This height varies due to the range of typical operational conditions that can directly influence the rate of descent.

[FlightDetent]

ShotOne: There was an paragraph somewhere in the AB library, stating that on A321 use of CF3 enhances the tailstrike margin for landing.

I've devoted last half hour trying to find it, but no luck. And went to some very deep corners of my harddrive

[misd-agin]

You can, and should, pull the nose up if it's necessary, especially to avoid a hard landing. Obviously there's a limit that will generate a tail strike. I think it's seven degrees.

I thought there was a comment in the manual about a .5(?) change in pitch attitude between F3 and Ffull? If you have to worry about .5 degrees of pitch - go around.

Fly the plane within its limits, realize that different configurations slightly improve, or worsen, flying and landing qualities, and it's a non event.

[KayPam]

Originally Posted by ShotOne

It may be true but doesn't touch on the issue of conf 3 vs full. There doesn't seem to be any unanimity In the responses. Clearly the physical geometry of the landing gear isn't changed by flap setting. Is perhaps my informant getting at a slightly lower deck angle with conf3, because of the higher approach speed?

This is exactly what could explain a better tail clearance.
Higher speed -> less aoa and less pitch angle required.

However, I'm currently wondering if we do or do not take the chord line to be the line joining the the trailing edge to the leading edge, including flaps and slats.
If we did, then the chord line would be at a varying angle when compared to the reference fuselage horizontal line.

I believe that this is what leads to a higher nose up attitude when landing a light aircraft (no slats) with no flaps (despite the higher approach speed)

Based on the values given by Capt Scribbles (Flap 3 is 22/21 deg S/F and full is 27/25), this would be consistent : flaps 3 could have a chord line more pitched up than flaps full, which could in turn lead to a higher tail clearance (that sounds improbable, but maybe when coupled with speed increase it could lead to this surprise)

You really are looking at the Airbus aero data (Cl as a function of alpha for all configurations and all speeds) and geometrical data (for the tail clearance + maybe the chord line angle thing)

[stilton]

Pulling the nose up to prevent a hard landing is self defeating if you are in a high sink situation close to the ground, that is light aircraft thinking.


You will just hit harder with a higher attitude significantly increasing your chances of a tail strike, adding thrust is the answer, even in an AB.

[vilas]

You begin early flare to reduce the high ROD. If you need substantial thrust increase means it's a destabilised condition and you should continue the thrust increase to TOGA and go around. Can you give some reference that recommends completing a landing with high thrust increase during flare? What is the stabilization criteria of your airline?

[Sprinkles]

Full marks Vilas. However, back to the thread, I seem to remember the 321 having a marginally higher nose up attitude on final when F3 compared to Flap full, only by either a half or whole degree...

I'd actually disagree Cough.

In my experience I'd say the 321 in Config 3 actually has a slightly lower nose attitude than in Config Full. Thus increasing the tail strike margin! which would agree with the original question.

An old GB airways capt once said its a nicer A/C to land than the 319/320 and I agree with him. Double slotted flaps make a big difference. His logic on why there's a lower nose attitude made sense to me.

Forgive my basic aerodynamic explanation! It might not be perfect!

Less flap = slightly higher approach speed (VAPP) to produce comparable lift as in Config Full and maintain 3 degree slope.

The only way you're going to maintain a G/S at higher speeds is to lower the nose and increase the ROD.

It made sense to me and it seems to prove correct in the A/C.

I'm sure the differences are negligible (half - 1 degree) and the difference between Config 3/Full on a 321 are far less obvious than on the 319/320. Our outfit doesn't allow Config 3 on the 320 for normal ops.

I can't really comment on whether I flare any differently between the two Configs. It becomes rather subconscious after a while. Config 3 is a bit faster so its easier to over-do it and float a bit. Especially with a healthy h/wind.

Always interesting watching the cadets start the flare at 30 feet, fly level and wondering what's going on!

[Fursty Ferret]

Originally Posted by Sprinkles

I'd actually disagree Cough.

In my experience I'd say the 321 in Config 3 actually has a slightly lower nose attitude than in Config Full. Thus increasing the tail strike margin! which would agree with the original question.

An old GB airways capt once said its a nicer A/C to land than the 319/320 and I agree with him. Double slotted flaps make a big difference. His logic on why there's a lower nose attitude made sense to me.

Always interesting watching the cadets start the flare at 30 feet, fly level and wondering what's going on!

I agree, if conditions suit will always choose to land the A321 flap 3. You have to be slightly wary with tailwinds and an aircraft close to max landing weight due to the high Vapp and subsequent high rates of descent, but in general it's pretty forgiving.

The only occasions I've seen a high nose attitude on the A321 is flap full and an early flare. Flap 3 it will land, just firmly, where IMHO flap full leads to a float and a very firm touchdown with high pitch.

Cutting the power going through about 40 feet from a stable approach followed by a flare at about 30 feet is generally pretty foolproof thanks to the ground effect on a heavy 321.

[Cough]

Can only say its my memories... F3 in the 321 was my preferred setting anyhow (even in a minor tailwind - Thanks to the already mentioned double slotted flaps!)

I defer to those more current!