Takeoff with light quartering tailwind
 

What should be aileron position if you are taking off in light quareting tailwind? What i learned in CPL Days was...
for taxiing in light quartering tailwind (say from left) hold control wheel to the right so that my left ailerons are down and right ailerons are up. Does same thing hold good for takeoff also?

No. Into wind for t/o.

always into the wind.

Don't know what airplane you are flying, but beware of the fact that if you displace the yoke to far into the wind -> your spoilers will also come up -> causing more drag.

Further info
 

Referring to this webpage http://freepilotinfo.********.com/20...wind-taxi.html shows POH diagram for taxiing with tailwind. It says left quartering tailwind left aileron down. So why would it be different for takeoff?

If it is b737 what will be aileron position with light quartering tailwind?
Note: just insert word b-l-o-g-s-p-o-t in above weblink without dashes

Sure, always into the wind, why would it be different?

Once the take off run is commenced then you do not have a tailwind in any real sense. The ground speed will be higher than your airspeed, but there is not wind coming from behind, and over, the tail and wings.

Control displaced when taxiing light aircraft can be "reversed", because at that stage there may be wind coming from behind, but this is quite different.

Wally.

Thats a good way of explaining it Wally :)

True ifly, but how far is 'too far' ? If you are looking at the aileron trim markings on the yoke in front of you, how many before the spoilers rise?

Went through the trouble of checking the AMM about this a while back for the 737, If I remember correctly the spoilers start to come up at 1.6 units on the yoke. Still - this is not a reason to limit aileron inputs if they are required...

This is from a 737 FCTM. Two things stand out to me. 1/Many pilots I fly with don't start the roll with the control wheel approximately centered and increase it as it is required. And 2/ What is "excessive" control wheel displacement?

Can you tell me which model 737 FTCM you are quoting from.

Thanks

From an 800 model.

In the 727, the spoilers come up after the yoke is rotated 10 degrees. In the 747 for dummies manual I've got with me, it doesn't give a number, it just says the ailerons and spoilers work together for roll control. Hey, if it's not in the book, they can't ask about it on the oral.

In most transport airplanes you are limited to a 10 knot tailwind. You're going to change that around to a headwind before the power is even half way set.

That was the procedure taught in J3 cubs and light aircraft, not airliners. They don't get flipped over by gusts like the light stuff unless you are really stupid.

Why are you increasing control wheel displacement as airspeed increases? If this theory were to hold true than you would have a large amount of aileron deflection as they become effective, leading to worse problems than a tailwind <10 kts.

You should start with it deflected and return to neutral as the airspeed increases so that you leave the runway wings level.

I haven't flown the 727, does it have markings indicating when you've reached 10 degrees rotation?

Thats not what boeing say. I see quite a few pilots starting with it already deflected and working backwards to somewhere thats hopefully right. If you do it like the book says it works nicely, you never end up with too much aileron. Do you ease off the aileron as the airspeed increases and then during rotation change direction and increase the aileron input again in order to maintain the wings level during rotation?

Framer
I think you may have mis-read the book or are reading from the landing section where you increase aileron deflection as the speed decreases and the ailerons become less effective.

I find it hard to believe that Boeing would publish something like this. If you start at neutral and work into the wind as the airspeed increases you're trying to roll the airplane while it's still on the ground. This puts extra stresses on the landing gear and really stresses that work their way back to the wing root. Not to mention differential drag on the main landing gear causing a yaw in the direction of aileron deflection. So that takes care of the problems on the ground.

Now for the problems in the air. The ailerons work by changing the lift on the individual wings. Aileron down, increased angle of attack, more lift and vice versa. So as you get closer to Vr one wing will be making the lift required for rotation before the other. You can see where this is going. Now you have one wing flying and the other one...well...not. And since both wings are connected, with asymmetrical lift one goes up, the other goes down. And it's not long till the tip of the wing meets concrete and the insurance rate begins to climb.

The procedure for takeoff (this could be different in the bigger jets with roll spoilers and all that stuff, the biggest thing I've ever flown is a King Air) is to start with the ailerons deflected fully into the crosswind, whether it's a headwind, or tailwind, that doesn't matter, because like someone else said the tailwind is gone by the time the engine is halfway to takeoff power. As the airspeed increases you'll feel the control forces increase (hydraulic controls too? I think, dunno, never flown 'em) so you slowly "give in" to the suggestion the airplane is giving you and begin to return the control wheel to neutral. The goal should be to hit neutral just before rotation speed, pull the airplane off the runway, and adjust bank angle as appropriate.

My goodness you're authoritive for someone who has never flown the aircraft you are giving advice on.

Different machinary, different techniques required. Boeing did publish that,it is a direct cut and paste from the latest update :)

That aint gunna be pretty in a 737.

Interesting. From the Flight Crew Training Manual for the 737-200 dated in 2005, it says simply "maintain wings level during the takeoff roll by applying control wheel displacement into the wind".

An old instructor, ex RAAF - eccentric but a gifted instructor, taught that the ailerons are for roll control.

Therefore, if barrelling down the runway and the wind is not sufficient to cause any roll, leave ailerons neutral. If the wind is causing some roll (there won't be much because the darned thing's on the ground) only use enough aileron to keep wings level (ie, use the natural horizon).

Simple. :ok:

Yes it does.

That would be handy. I wonder why they did it for the 727 and not the 737?

As I said, thats approximately 1.6 units as indicated on the yoke on the 737 if memory serves me right.

When it comes right down to it, no. All airplanes fly the same, from a J3 to an A380. Pull back the houses get smaller, push forward they get bigger. (for the Airbus I guess I apparently have to make the disclaimer that it's in it's "normal flight mode" or whatever the technical term is for it.)

No I'm using common sense and thinking about what would happen if you lift off the runway with full aileron deflection.

Thank you for all those insights.
In fact, I would avoid taking off with a tailwind, but if it cannot be avoided, then, as Captain Claret wisely said, ailerons are for roll control!
You use the tiller (is that right? I mean using the nose wheels orientation) , at the start of the take off roll, then remember that what is important is acceleration, to V1 and Vr...putting weight on one main landing gear by using ailerons is not, I beleive, a good idea, especially as the wind is "light", by the topic"s description. Use slight rudder inputs afterwards to keep the airplane centered, and rotate with the ailerons still neutral. I am always surprised to find that now, everything needs to be written and explained, when in fact, there are so many different conditions which cannot be all adressed. It is, in fact, state of the art piloting...I learnt by looking at (and admiring...) how the old hands did it, then later shared it with the younger ones...No need to cut entire forests to write that in the SOPs...

framer, your are correct mate.

Same general wording as my 747-400 manual.

They don't want you barreling down the drag strip with the spoilers up on one wing, eating up tarmac, reducing lift, reducing tailstrike margin...etc etc.... when ultimately, only a smidgen of into-wind yoke may be needed.

Maybe full aileron in a small/light aircraft without spoilers would be appropriate. As has been said...different methods for different machines.

One should not be misled by this quote. There can be significantly different ways of flying different aircraft. For example. from what I have been told, using control wheel after an engine failure in an MU2 can be very dangerous.

Bottom line....When it comes right down to it, not all airplanes fly the same.

Crashdriver
Someone tell you that in the hangar Crashdriver? Or the result of years of research flying many types in the exact same fashion? It sounds quite good,gives you an air of experience and wisdom, but it's not true.

If you started your roll on a 737 with full aileron and reduced it so that you rotated with ailerons neutral in a stiff crosswind, it would be an almighty cock-up. Simple as that really. If you did it in your B200 it might work pretty well......it's starting to look like is just a convenient saying.
If anyone reads this thread for advice I'd suggest they be rather judicious about who they take it from, better yet, follow the manufacturers guidelines.
STBYRUD I'd be really interested in nailing that figure down. Have you still got access to the AMM?

No actually it was a university professor in aeronautical physics. And the physics of your explanation is what I have trouble believing. Before I spend the next 3 hours flaming, I will leave it at that and leave you to your own devices, since an academic conversation cannot be completed here.

Ahhh come on Crashdriver, we were on the verge of learning something then. Lets get to the bottome of it :ok:

He should get in touch with Boeing and tell them their FCTM is incorrect and that the same crosswind departure technique as the J3 Cub will suffice.
My favourite part of the acedemic conversation thus far has been

framer: Tell you what, I will do some empirical testing during the next flight control check, aided by either the ACMS or the sys page if the bird has the flight control display - don't have access to the AMM at the moment unfortunately :(

Good idea STBYRUD, I look forward to the results.

All airplanes fly the same, from a J3 to an A380

I think one might choose a Type a little more modern than the Cub. However, with that caveat, it is not unreasonable to suggest that Types certificated to modern Standards - FAR23/25, for instance, generally will fly in reasonably predictable and similar manner.

That is not to suggest that different Types won't have specific differences, of course.

I suspect that the original statement would have been somewhat along such lines. Certainly, I have heard much the same comment from a variety of competent folk over the years.

Back to the crosswind stuff. Seeing as most aircraft seem to use a technique of reducing aileron into wind as airpeed increases on the takeoff roll, can we get any confirmation on this idea that Boeing is suggesting the opposite.

This is my take on it and I'm happy to be corrected by folk more knowledgable/ more experienced than me;

When you are rolling along the runway at speeds where the rudder is effective during a crosswind departure, you want to control your direction with your rudder while preventing the upwind wing from creating more lift than the downwind wing. If you end up in the situation where the aileron input is creating a drag towards the upwind side of the runway, then the opposite rudder you will need isn't to counter the wind, it's for the aileron/spoilers.
I have a feeling this happens quite a bit.
I think Boeings technique is designed to prevent excessive control inputs.

PS Jammed Stab,
I don't think Boeing are suggesting that the inputs continue as the airspeed increases. I'l paste below so it's easy to reference;

So what happens is that aileron goes in as required until the point is reached where it is sufficient and then it is held. (this is normally only a very small input) My experience is that as the airspeed increases and slightly less rudder is needed then the aileron is reduced a fraction with the rudder..... almost like they are connected really. Until rotation of course when the into wind aileron is pretty much doubled or trippled in order to keep the wings level.

All airplans fly the same? To some degree yes, to some degree no.

Anyone think a swept wing, hard wing fighter would react differently to a rudder input at high AOA, like landing, than a Piper Cub?

Ailerons are neutral and only enough input is needed to keep the wings level during takeoff roll.

In strong crosswinds the plane typically doesn't 'lean' until it's moving fairly quickly so a small, or perhaps moderate, amount of roll input might be needed but that will gradually be reduced as speed, and thereby roll effectiveness, increases.

Hello guys,

I was briefed during my type rating that the Boeing technique for crosswind take-off has to do with the swept wing.

Not 100% sure about this but I think it was this.
The wing which is on the crosswind side gets air over the wings at an higher angle (closer to perpendicular) than the wing on the other side (closer to parallel). So the wing on the crosswind side is creating more lift and this needs to be countered by applying aileron into the wind. As speed increases the effects gets bigger, so more aileron needed.

The 737-200 has markings on the yoke to show degrees of control wheel displacement.

Boeing has stated what they expect a pilot in their aircraft to do. They do not say "keep the wings level". They say "approximately level."

They are more concerned with drag by excess control wheel displacement vs. not being perfectly level.

Using control wheel inputs in a jetliner that are appropriate for light aircraft flying shows a failure to understand what you're doing with the control wheel(drag) vs. how jet performance is calculated.