lovely aircraft and the aerodyanmist at Toulouse on Tuesday pointed out that his boss had patented the strakes on the nose and got lots of lolly from M.D..
Reason why Toulouse got the money I guess.
The shedding of vortices from the forward portion of long and slender fuselages at incidence can cause lateral instability which is aggravated if the aircraft is flying at small angles of yaw. This condition only occurs at low speed and few aircraft have a sufficiently high overhang ratios (the ratio of length of fuselage ahead of the centre of gravity to fuselage diameter) to give a problem. The rear-engined DC-9-50 has an overhang ratio of about 6:1, very similar to that of the long-bodied, wing-engined DC-8-61/63, which was not fitted with strakes. Small, very low- aspect-ratio forward fuselage strakes act to prevent any lateral instability by fixing the vortex pattern. Concorde is the only other airliner to make use of such strakes and the DC-9-50 is the first subsonic airliner to follow suit.
The DC-9 strakes are probably insufficient in area to provide anything but a minimal nose-up pitching moment or contribution to lift during low-speed flight and therefore serve a completely different purpose from that of the retractable foreplanes on the Tu-144. The primary role of the latter is to provide a trimming force which also contributes to lift. The strakes were not shown on earlier general-arrangement drawings of the DC-9-50 (although they have been apparent on drawings of the longer DC-9-60 project shown to airlines) and were probably added after wind-tunnel testing.