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Flashcards in Drag Reduction and Total Drag Deck (12):

what are the two formlae for aspect ratio?

AR = span(squared) / area,

or AR = span / mean chord


A long wing with a short chord will give a ... aspect ratio and produce ... wingtip vortices




a low aspect ratio wing has a great critical alpha than a high aspect ratio wing. Why is this?

a low AR wing produces bigger wingtip vortices, increasing downwash and reducing effective alpha, therefore allowing a larger criitcal alpha



a low AR wing produces more or less lift for a given alpha than a high AR wing?

why is this?

produces less lift for a given alpha because the increased wingtip vortices and downwash reduce effective alpha

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what is geometric washout?

what does it achieve?

wing twisted along its length, so giving a wing with a higher alpha at the root that at the tip

With the lower alpha at the tip, less lift will be created here and therefore less spillage of air around the tip, giving us smaller wingtip vortices and consequently less induced drag


what is aerodynamic washout?

changing the aerofoil section to a less effective profile at the tip by reducing the camber of the section 


what is wing taper ratio?

will always be less than ...

tip chord / root chord



what is the effect of lowering flaps on induced drag?

With inboard flap down the aircraft will fly at a lower nose attitude for the same lift, so the outboard section and tips will have a lower alpha

This should reduce the tip effect but whilst parasite drag goes up, induced drag is not significantly changed by flap extension at a constant speed


what are the three main factors that affect induced drag?

aircraft gross weight, aspect ratio and angle of attack


the point at which drag is at a minimum (Vmd) is also where we are flying with the best possible ...

lift/drag ratio


optimum alpha is normally found at around ... degrees and here the wing is performing with max ...




how does IAS and TAS vary with Vmd with increasing altitude?

Vmd will occur at the same IAS with increasing altitude, because Q (1/2RhoV(squared) is unchanged

However, the reduction in density is compensated for by an increase in TAS (V), so Vmd expressed as a TAS will increase with altitude