Position of Elevators at T/O - A-320
 

Hi all,

To offset the effect of thrust application at T/off, FCOM recommends moving elevators halfway down till reaching 80kts and full down in case of tailwind or crosswind in excess of 20 kts. Why the difference and does it really prevent the nose from coming up when T/Off power is applied???

What is your tailwind limitation?

Mutt

To clarify: the recommendation is for the event of any tailwind (up to limit (A320) of 10kts) or crosswind in excess of 20kts.

I thought it was only up to 10 kts? I wouldn't be too happy departing with a tailwind in excess of 20kts.

I think you'll find the FCOM might say "in a tailwind or in a crosswind in excess of 20kts" - they just forgot the comma after tailwind. Meaning you do this in ANY tailwind, AND in crosswinds exceeding 20kts. I don't think you can takeoff in tailwinds of greater than 10 in the bus. Have just started though, so could be wrong.

Why don't companies understand the importance of punctuation?:mad:

The answer to your question, I personally believe it does make a difference, and does stop the nose coming up excessively on the t/o roll. It also allows for better directional control as you roll down the rwy. So though it sounds a little stupid, I think it's quite effective.

1234

Haven't seen it myself, but TP mates have told tales of T/W increase trials with aircraft sitting on their tails when the brakes are released ...

Can't see any reason to increase separation as same dynamic would apply to the following departure,,,therefore same separation standard.

To clarify the topic further Airbus ask you to

- input half forward stick for normal take offs which results in full elevator down at roll start and progressive decrease of this deflection until the sitck is gradually released to reach neutral by 100 kt
- input full forward stick for all tailwind take offs and also if x-wind is above 20 kt. This results in full down elevator all the way until the stick is gradually released to reach neutral by 100 kt

The reasoning behind I was told is to increase load on NLG for better control.

Yours,
FD (the un-real).

My apologies for the confusion which seem to have
resulted because of my missing a miserly comma somewhere. Hopefully any 320 driver after reading my post would understand that it is half elevator down in normal case and full elevator down in case of any amount of tailwind( I do know that the tailwind limit is 10 kts) or crosswind in excess of 20 kts.

With this clarification, I am still hoping someone experienced on the 320 will be able to clarify as to why this difference? Really interested in the aerodynamic effect.

Grateful to all those who have contributed so far

FD
Surely half stick gives half elevator deflection?

In theory, but have a look at the FLT CTRL page next time you do it!

You don't need a comma here. The phrase is written correctly.

Not on an A320 (or other Airbuse FBW aircraft) stick position has no bearing on surface position. When the stick is moved the computers position the surface where it should be for the current conditions.

Or maybe it is to over come the effects of the horiziontal stabilizer which is trimmed for takeoff, preventing premature rotation.

But on the ground, during the take-off roll the flight control system is in direct law so stick position is directly related to control surface position.

Correct "Max Angle" (You beat me to it)
Plus, just to be a pedant. Some of the A320/1 series have a 15kt tailwind limit for takeoff! (MSN [for 321]around 2000 & below, if memory still works)

You Airbus guys can't take a joke?

Sidestick command is mapped similarly for nose-up and nose-down inputs, so that you don't get twice the sensitivity when applying a nose-down input (since nose-down travel is 1/2 that of nose-up: 15 degrees vs. 30). Similarly, when you apply half nose down stick, you are commanding half of 30 degrees, or 15, which is full nose down elevator. Simple, really :)

P.S. Nothing is ever what it seems on the Bus! :p

Thanks guys, but still hoping for a definite answer to this one. I am sure there is a experienced A-320 hand out there, ready with the answer.

First why the difference in sidestick position and secondly what does it actually achieve. Does the jet exhaust go and hit the elevator and as a result push the nose down.

I am sure the THS position has nothing to do with it.

it counters the nose up effect of setting engine takeoff thrust

one point of note, if you look at the FCTL ECAM pg as you do the flt control checks, half stick down already gives full elevator deflection; hence full stick is not actually achieving anything.
changing from half to full stick down in the conditions on topic, I am told, is a procedure that all Airbus perform, and on the 330, there is a difference, but not on the 320. A 330 jock may be able to shed some light on this information.

...but to play devil's advocate, at the start of the roll there's no airflow over the elevator, so it's not doing anything. By the time there is some useful airflow over the aeroplane, (e.g. 80kts) you release the stick to neutral! Your point about the F/CTL page is what I was getting at.

So, what function does the elevator do at low speed? Is the jet exhaust enough to make a difference?

that's simply what it says in the SOPs
as to the reasoning, obviously there is no aerodynamic influence of the elevator position from a standing start, I'll give you that
it really doesn't appear to be entirely logical, and I can only surmise it is more logical for a rolling take-off where the power is set at a higher speed where there will then be some tailplane effectiveness.
as to what the speed is where it has an influence, Airbus do not publish that with the manual set.