ATPL Aerodynamics question.

[Shaun-356]

Hi everyone, just a ATPL question I'm wrestling with! :ugh:

When an aircraft is making an approach to land, the use of spoilers is to increase?

a) drag coefficient by controlling cordwise flow.
b) drag coefficient by controlling spanwise flow.
c) lift coefficient by controlling cordwise flow.
d) lift coefficient by controling spanwise flow.


Many thanks.

[Bladeangle]

Hey there, spoilers are designed to create turbulent flow over the wing which can decrease lift/increase drag either for a steeper approach or once touched down spolis lift to allow more weight on the gear for max effective braking. In answer to your question they would increase the drag CL by affecting chordwise flow.

[411A]

Considering the question, with the proviso that the answer might be applied to the L1011, which is equipped with DLC, the correct answer could well be...answer C.
However, 'increased' would better be changed to 'alter.'

And, I would be quite prepared to argue the fact if marked wrong.:}

[Lightning Mate]

once touched down spolis lift to allow more weight on the gear for max effective braking.

Just how spoilers increase aircraft weight is beyond me. Their purpose on touchdown is to increase aerodynamic drag.

The answer to the original question is a.

If I were to reveal my profession you might believe me.

[TheBeak]

I don't want to start a debate with someone who possibly (and probably) knows better than me but my thoughts are:

No the purpose is to PUT the weight on the wheels to allow best brake performance. He or she did not say increase weight full stop, he or she said 'to allow more weight on the gear'.

Yes the spoilers do increase aerodynamic drag and 'dump' the lift but their purpose on the ground is to put the weight on the wheels. In the air they represent poor planning! If they don't deploy on the ground, braking can and will take alot longer as seen with the American Airlines MD80 crash in Texas.

They certainly do not increase lift coefficient so it's a or b - they increase parasitic drag. Would you mind explaining why it is chordwise and not spanwise please? I can see it being Spanwise and chordwise! Induced drag comes in the form of vortices off the wing tips (amongst other places) from a spanwise flow. If you reduce lift surely you affect spanwise flow and thus 'control' it?

Apologies for the range of colours, it went funny when I tried to quote the previous post!

[Mister McDoo]

Hello Lightning Mate,

Once the spoilers deploy, the lift generated by the wing reduces. The lift vector is not as great as for the clean wing, so the proportion of lift to weight reduces. The actual weight itself obviously is unchanged, but the effective weight increases.

[Donalk]

As with just about everything in aviation there can be more than one correct answer to a specific question. The beak is correct in saying that spanwise flow, defined as flow that travels along the span of the wing from the root to the tip, more or less parallel to the leading edge, is altered. However chordwise flow is altered to a greater extent as the spoiler dumps lift by creating a controlled stall in that part of the wing directly behind it.

Since a stalled or partially stalled airfoil is most commonly linked to chordwise flow I would go with A.

[Lightning Mate]

I give up. ByeBye.

:ugh::ugh::ugh:

[TheBeak]

What are you giving up on? How dare we offer our opinions or ask for your explanation.

[Donalk]

Lightning - If you feel you have a more comprehensive opinion or explanation based on qualifications or experience I would be genuinely interested to hear it.

It's always good to keep learning.