Use of speed brakes in flight
 

Hello all. I think this might be my first post here.

So a tiny bit about me first of all. I am called Colin. I am 15 live in Glasgow, Scotland. And love planes.

I have a question regarding the use of speed brakes in flight and on approach.

What are the real life limitations apart from speed for not using speed brake in flight?

Is there any point in which it is forbidden as so to speak to release and use the spoiler in flight?

Is it really advisable to use speed brakes in flight unless it is absolutely necessary?

Thanks,
Colin

G'day Col,

Different aircraft have different limitations. I can't think of one right now which requires you to be below a certain speed in ordr to use. The speedbrake is there so if you reach the high speed limit(Mmo) you can pop them out and slow down............hence "speed brakes", they also help you increase the drag in the L/D equation thus increasing the descent profile(particularly useful with say a depressurisation or uncontained cabin fire). Some aircraft require they not be deployed when flaps are set greater than ten degrees and many operators do not allow them to be used below 1000 ft(as standard operating procedure rather than an airframe limitation).
Hope this helps

Thank you very much. That has answered my question fairly well.

If anyone has any specifics on the 767 I would be overjoyed however.

Thanks,
Colin.

And they are also used for landing (or rejected take-off) to decrease lift on the wing and therefore increase weight on the wheels to make the wheel braking system more effective.

One regularly hears the terms "speed brakes", "spoilers", and "lift dumpers" and I am never really sure if these are all different things or fundamentally the same. I used to fly a (light) aircraft that had airbrakes on the underside of the wing. I'm guessing that's not the case on a commercial jets though.

Technically speaking the panels on top of the wing on most if not all modern jets are "spoilers". They are used for various functions such as:

"Speed Brake" - symmetrical variable deployment of some or all pairs of spoilers to increase drag and reduce lift. Often the most inboard pairs are not used for this function.

"Ground Spoiler" - sometimes called Lift Dump - symmetrical deployment of all pairs to max position in order to disrupt lift and put the weight on the wheels to improve braking on landing or in the case of a rejected take off.


"Roll spoiler" - Asymmetric variable deployment to assist or completely control roll.

"Direct Lift Control" - Symmetrical variable deployment coupled to elevator or stabilizer input in order to "Directly control the lift" as apposed to indirect lift control by virtue of varying pitch and therefore AOA.

"Maneuver Direct Lift Control" - symmetrical automatic variable deployment of some or all pairs in order to reduce load factor during high speed maneuvers.

Did I miss any?

In general for most airplanes their speed brakes are useable at any speed. The 737 does have a limitation at most carriers preventing speed brake use with flaps at the same time.

I want to thank you all for these answers.

Especially FE Hoppy I have now learned a lot I never knew about the wing.

Speed brakes
 

Hi cosie
the speed brakes are the only fly by wire on the B767, when you pull the handle out of its detent, the speed brakes will pop up and create a slight a short pitching moment, and it takes a little bit of practice to master.
Once I had to diverte (due to a pax weird behavior), the weight was above max landing weight and no jetisson, I cruised with speed brakes slightly out to increase the drag,thus the fuel flow, without compromising the speed. I landed at the max landing weight.
regards

Colsie, there are other factors of interest. Speedbrake causes vibration throughout the aeroplane. With flaps extended it gets worse. It can be quite sobering to sit behind the wing and see what speedbrake does to the flaps. That is the reason the use of speedbrake is not recommended beyond a certain level of flap. Flap 5 on the 737 and full speedbrake is not a nice combination!

Another reason is that you are throwing away efficiency, and I view it as an admission that you have misjudged the descent if you need to use speedbrake except where you are having to obey ATC instructions. If you have free reign over your descent and use speedbrake, you are throwing away energy, hence you have wasted fuel. It comes with practice!

Another factor may interest you- using partial speedbrake on the 737 is not recommended because it affects the roll control and makes the aileron control more sensitive. However I don't like using full speedbrake, especially when any flap is out, so I only use what I need and take care with very gentle controls.

Right- are you ready for your exam?

(May I say how nice to see such a well phrased query? You are very welcome to ask more! Do you have a further interest in aviation?)

FE Hoppy has given you superb information, Colin, but he forget to mention one rather important item...

These functions of the spoilers are found only on one type of civil jet transport. And, they are fully automatic, requiring no separate pilot action.
It was manufactured by the Lockheed California Company at Palmdale California, and is called...the Lockheed L-1011 TriStar.




Sorry folks...but it's true.
Lockheed...far far ahead of everyone else, at the time.

Again I would like to thank you all for these very informative and most importantly educational answers.

Rainboe my main interest in aviation is with the good old (well modern actually), airbus aircraft. I do however like the Boeing 767's and 727's. Actually anything which is vintage is a big go in my book.

Unfortunately any career in the skies is out of my reach, this due to my poor eye sight. So I need to suffice and aim for a job in the airport.

It is nice to be welcomed into such as good community. I hope you look forward to more of my questions.

Thanks,
Colin

Colin,

As you ask about the 767:

There is no limitation on its use in terms of speed. Part of the drill for an overspeed condition is t deploy speed brakes first before retarding the thrust levers. This does two things, one increase drag and two cause the nose to pitch up as the centre of pressure (the point through which lift acts) moves. Nose goes up, reducing speed rapidly.

Company SOP is no speedbrake use beyond Flap 20.

On the 757s we have fitted with winglets there is a limitation on full speed brake deployment - 330 Knots Indicated Airspeed. Maximum of 50% deployment only is permitted beyond this speed. There is an auto stow facility which limits the spoiler movement above this speed. This limit is to do with the bending of the wing caused by the winglets combined with the loss of lift at the root of the wing at such high speeds. Winglets place a greater bending force on the outer portion of the wing upward than on aircraft without therefore when you deploy the spoilers at the centre of the wing you effectively increase this bending force placing extra stress on the structure. This is not desirable at such speeds.

The speedbrakes on the 757 are not that effective at low speeds with the aircraft being so overpowered. At lower speeds 220kts or so it is little more than a rumble maker.

Yes it is! Unnecessary use of the speedbrake and I throw a tantrum! Waving a rolled-up newspaper around and shouting 'you're wasting my fuel! Have you ever REALLY been short of fuel in your miserable short existence?' sort of question. Far too many young pilots use speedbrake almost every flight- it's almost a dummy for them, and they'll use it happily knowing that they will probably have to fly level later, but such is their horror of being high they overuse it badly. 200 up to MCT is an ATC requirement- it is using it when planning and foresight would have prevented it that annoys me. I used to fly 747s. The potential to really waste a large amount of fuel through poor planning instilled discipline!

Colsie- good luck with your eventual entry into aviation. You have a very good understanding from your question. Airbus needs you! Work hard.

Again I would like to say thank you all for the replies. And now the interesting informative following discussion.

Oh and Rainboe as for Airbus needing me, Airbus need anything.

Colsie-I'd recommend you read "Handling the big jets" by D P Davies. Published by the Civil Aviation Authority. Don't know if it is still in print but your library or Amazon should have one.

Thank you for that advice. I shall look into this book.

Reminds me of the story (possible read somewhere on PPrune) of the pilot who is being nagged repeatedly to expedite descent by ATC. "Don't you have speed brakes?" says the ATCO with exasperation. "Yes" comes the reply "But those are for my mistakes not yours."

.. hence PECL .. pilot error correction lever ....

411A.

Not entirely true anymore.

The little E-jet 170 uses DLC for steep approach. More for drag than lift control but it works in exactly the same way.

:-)