747 Focal and avioniker:
Close, but not quite correct. The strakes are aerodynamic in nature. At high angles of attack crossflow on the forebody of a fuselage is substantial. The large moment arm between the forebody and the center of gravity results in that side force creating large yawing moments. When McDonnell Douglas stretched the DC-9-30 to the DC-9-50 the strakes were added to offset the change in directional stability caused by the increased fuselage length ahead of the center of gravity. They were kept in the MD-80 and MD-90. The difference in the MD-80 and MD-90 strakes is that the MD-80 strakes are pneumatically heated while the MD-90 strakes are electrically heated. The reason for the heating is as 747 Focal says.
I wish I had my old MD-80 manual because there is a brief description for the reason of the strakes. I believe it said something to the effect of reducing the fuselage vortex at high angles of attack. Someone with a manual care to dig that up ?
I guess the 717-300 will have the longer fuselage therefore it will require the strakes.
Typhoonpilot
Last edited by typhoonpilot; 10th August 2003 at 01:45.