Drag Reduction and Total Drag

Question 1

what are the two formlae for aspect ratio?

Answer 1

AR = span(squared) / area,

or AR = span / mean chord

Question 2

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

Answer 2

high

smaller

Question 3

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

Answer 3

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

Question 4

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

why is this?

Answer 4

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

Question 5

what is geometric washout?

what does it achieve?

Answer 5

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

Question 6

what is aerodynamic washout?

Answer 6

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

Question 7

what is wing taper ratio?

will always be less than …

Answer 7

tip chord / root chord

1

Question 8

what is the effect of lowering flaps on induced drag?

Answer 8

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

Question 9

what are the three main factors that affect induced drag?

Answer 9

aircraft gross weight, aspect ratio and angle of attack

Question 10

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

Answer 10

lift/drag ratio

Question 11

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

Answer 11

4

efficiency

Question 12

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

Answer 12

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