Some Airbus questions...
 

Can anyone help me with the following:

1) Why are the winglets different on A320 and A330/340?
2) Brake fans, why is there a limit of 150 deg fans on and 300 fans off prior To takeoff?
3) Can we cruise above max recommended altitude on progress page, and if so by how much?

Thanks for any help!

Hi,

I can only answers your number 2 question;

On A300600, last airbus that I flew, Brake Fans must be OFF prior to takeoff, and the Max Allowable brake temp. for take off is 300 degrees C. Having said that:

1. If prior to takeoff with Brake Fans ON, the brakes temp. exceeds 150 degrees, it is likely that the brakes temp. will exceed 300 degrees during Take Off roll as the Brake Fans is switched off.

2. If with Brake Fans OFF, the brakes temp. exceeds 300 degrees, take off is not allowed as the max allowable brakes temp. is 300 degrees, if exceeded, fuse melt could occur in the event of rejected take off.

Hope it helps.

As for your winglets Q, I am not good at aerodynamics, all I know they are there to reduce induced drag (i.e drag generated as a result of lift). But no idea as to why different shape.

SS

Maybe you CAN.

But I would strongly recommend not to do it....

Because it is a different wing design/construction.

ah.. call me mr bus man
 

i cant answer question 1 but..

2) half of silver spurs answer is correct
but the reason is not because of fuse plug its:

*quoted from the airbus330 FCTM

3) *also from the FCTM(busboy's best friend)

time to read your books sir.

Why are the winglets different? perhaps its some thing to do with the fact the A330 wing is a generation advanced from the A320 wing

1) The 320 wing is not robust enough to support larger winglets

Air Transport
DATE:10/10/06
SOURCE:Flight International
Airbus rethinks plan to put winglets on A320
By Max Kingsley-Jones

Airbus’s mid-life update for the A320 family has hit trouble with the revelation that it is unlikely to adopt new large winglets that were central to expected fuel burn improvements.
The manufacturer has been undertaking back-to-back tests of two winglet designs since April – one designed in-house and the other by US company Winglet Technology. Evaluations have been carried out on the prototype A320 as well as a production aircraft built for JetBlue, with a view to developing a retrofit programme, as well as for possible inclusion in the package of upgrades that Airbus is planning for the so-called “A320 Enhanced”. Other Enhanced improvements include an aerodynamic tidy-up (to the engine pylons, surge tank ducts and upper belly fairing), engine improvements, weight savings and a new cabin.
Airbus chief operating officer customers John Leahy said earlier this year that the aim of all the improvements was to reduce fuel burn by 4-5%, with the winglets alone expected to “get a couple of per cent” of this.
However, Airbus says that the “latest information on the A320 winglet testing is that the results indicate that although improvements were found in terms of cruise drag, the increase in structural weight that would be necessary to support the winglets largely offsets the gain”. However, it adds that “at this stage, it is too early to say that the winglet programme is over completely”.
Airbus says the other improvements announced for the A320 Enhanced, including the aerodynamic and engine improvements, continue to be worked on. The new cabin, which will offer a 50kg (110lb) weight saving, will enter service in mid-2007. Airbus had said earlier this year that it was aiming for a design freeze on the Enhanced before the end of 2006, with the aim “to provide most, if not all, of the improvements by 2008”.

The answer to question 2 is simply because the fans when in use cool the sensor as well, so the limit has to change to keep it correct.

An airliner in the US is (was?) flying around with larger winglets on the A320. Late last year Airbus were testing some blended winglets.

Photos: Airbus A320-232 Aircraft Pictures | Airliners.net

Greetings
[quote]2) Brake fans, why is there a limit of 150 deg fans on and 300 fans off prior To takeoff?
[quote].
In the FCTM, Airbus tackles the brake limitations, in a very dispersed maner, they jump from classic limitation as 150 , 300 deg with brake fan ON, skydrol flash point is the idea behind it, we may think, however, at a later stage Airbus goes on by addressing brake wear, with a hot brake long life type of description, but then; and it is the troubling part , Airbus acknowledges that they cannot guaranty a sucessfull RTO at high weight, if the brake temperature is at 150 Deg!!!
I pointed out that fact to the fleet office, and up to today AIrbus never came with a recommandation.
As far as I am concerned, if octopus, in the takeoff performance computations, was stating that the limitation was VMBE, or ASDA, then I would use the brake fans, to keep the brakes as cool as possible, and for other limitation, I would apply the 150, 300 deg, for the A330, that is.:ok:
Regards

Hi Cav-not-ok,

Thanks for correcting me, I can recall now it has to do with the skydrol (or whatever hyd fluid that is) flash point.

While we are on the subject, can you or any of you reading this explain the difference in aerodynamics properties between the 2 winglets?? i.e the one on the 330/340 and the one on the 320/310/300-600?


Regards

Let me ask then, what are the considerations/issues if a crew decides to take off with brake temps above 300C?

compressor stall;

The photo you posted is of a jetBlue A320.
From line 6 of the article I posted:

Evaluations have been carried out on the prototype A320 as well as a production aircraft built for JetBlue,

1) I can't remember what the difference is, but the A320 family (together with the A300-600R/A310-300 and the A380) have what are called 'Wing Fences', while the A330/A340 have 'Winglets'. In theory, the fences look after the spanwise outward flow on both the top and bottom of the wings, while the winglets do something different again (not too sure what exactly, but I believe, in the end, it's all much the same - reduce induced drag and thus save fuel/increase performance).

2) The brake fan issue is much simpler; because the brake temperature sensors only measure surface temperature, Airbus had to determine what the MAXIMUM difference between actual and indicated temperature would be with the brake fans ON (due to 'blowing' effect). They determined that the maximum difference was in the order of NOT MORE than 150 degrees. So, in essence, Airbus say that if - with brake fans ON - you see any brake temperature of 150 degrees, then the real temperature of that brake will not be more than 300 degrees.
And the reason 300 degrees is the 'true' limit is also straight-forward; it is the temperature at or below which hydraulic fluid is deemed to not be able to ignite if it were to come into contact with a surface at that temperature. It covers the case of a hydraulic leak in the wheel well, i.e. if under 300 degrees, then no wheel well fire.

3) Has already been answered. The license to go above REC MAX alt, is only to allow strategic decision making (allow a slightly higher altitude instead of having to descend to a much lower altitude in busy airspace if offered the choice by ATC). Having said that, I don't think I'd be very willing to go above what's shown in the PROG page except in 'unique' circumstances.

Hope that helps.

PJ2

One of the issues if the crew decided to take-off with brake temps in excess of 300 degrees would be how they would least-uncomfortably sit in their crew seats after the butt-kicking they should get for purposely (I assume) disregarding a limitation (A330 FCOM 3.01.32 P1)!

PJ2

Greetings

You have to realize that the brakes will not stop heating up, the temp will continue to rise, look at the brake temp after takeoff, and you will see that it is not 300 deg anymore. Brake temp will rise during the takeoff roll, due to the heat generated by the tyre's flexibility/friction.
Now after takeoff, the main problem is skydrol leak, leading to auto-ignite if the drop of hydraulic touches the brakes, in that case you will have a weel whell fire.(goto skydroll web site they published all temperatures)
During takeoff roll, if you need to abort, then, we have already lost 300 deg of energy absorbtion by the brakes. :eek:
Now the certification RTO was done with brake at ..... 150 deg
Look in the FCTM, you will see that Airbus doesnot guaranty a successfull RTO at max weights.:ouch:

kijangnim;

Yes, understand brakes will continue to heat up due tire flex. Thanks for the suggested link to skydrol - will take a look. Goodyear has a very good presentation on tire temperatures, taxiing, etc.

As we know, the 320 takeoff config warning for hot brakes, (>300C), is amber, not red. Some pilots have considered this a "cautionary" guide not a warning, that can be, in their judgement, ignored in some circumstances, (light takeoff, long runway, long delay for cooling after a long taxi in hot weather, etc).

We should be clear here - I am not advocating this nor do I agree with it for all the obvious reasons including the "oak chair" ones that RAD_ALT_ALIVE suggests, but it has happened more than a few times and I was interested in others' opinions. I know this is a tech forum so will avoid drift into other points.

Experiment.....
 

Gentlemen,

Next time, when you've nothing better to do.....:8

After landing, after arriving at the gate....without brake fans....brakes OFF (aircraft chocked)....note the brake temperatures....continue to note the
temperatures over a period of time....like for maybe an hour. Graph the temperatures vs. time. Maybe note the temps every five minutes for an hour period and graph the results.

I've done this.

As a result of my findings, I conclude:

1. Quick turns are not a good idea if you wish for a successful RTO.

2. Leave the XXX brake fans run. Don't turn them off if/when you leave the cockpit after the PARKING checklist is completed. Ask the mechanic to let them run for a bit before the next crew gets on board. (This adds new meaning to 'AS REQUIRED' on the Airbus PARKING checklist.)

A famous U.S. carrier (I don't need to name.) that boasts of quick turns rejected a takeoff several years ago due to bird ingestion and subsequent engine problems. The pilots performed the RTO flawlessly, but the aircraft ran off the end of the runway and into the grass.

Turns out, the brakes were hot.....maybe still within limits...but hot.

Doing one-hour segments....making that first turnoff after landing....quick turns....the brakes get hotter and hotter throughout the day. At some point, you become a test pilot if you need to do an RTO.

Over the years, I've discovered many little tidbits of information regarding aircraft performance vs. certification requirements...."stuff they don't want you to know" ....as the advertisements say...

In the case of the 150 degree limit on the SA Airbus brakes...this is one example. Yes, if you read the fine print, the accelerate-stop performance is guaranteed only if brake temps are no higher than 150 degrees. (Of course, there are other factors involved with this issue, as well.)

So, now, regarding the above-mentioned experiement. Cross reference your findings to this 150 degree figure.

Of course, the Airbus SOP states that, while taxiing out for takeoff, if the 'hat' is above one or more brake temps, you should run the fans during taxi out. (The hat pops up with a temp above 100 degrees.)

Fly safe,

PantLoad

A senior Airbus manager told me during the 1992 ILA in Berlin (where the A340 was making a visit during the initial flight test camapin) that intensive investigations has demonstrated the big A330/340 winglets to be not more efficient than the small A320 ones (taking into account additional weight etc.). However, several operators requested Winglets where they can put their logo on, so the passengers could see it all through the flight. Therefore it was finally decided to install the large ones.

On the topic of brakes, i was wondering why doesn't Boeing place such a big emphasis on brake temp as Airbus ? They don't come with brake fans and I've yet to see a boeing that needs brake cooling wheres for airbus it's almost every other day.
Here we use the portable air con truck to aid the brake cooling . And does it help to set parking brakes contrary to ECAM memo to aid the brake cooling ?

Greetings,
The B777 brake design, minimises excess heating :}