Toe-in?
 

May I pick your brains please?

I was standing outside The Orange Tree in Richmond the other night getting rediculously drunk having just enjoyed England ... er ... putting the All Blacks to the sword. Anyway, every couple of minutes another plans passes over, and I couldn't help but notice that some 737's seem to have a large amount of toe-in at the front of the engines. Just to give a bit more technical help as to which 737's, it was the ones with the thin engines, not the fat engines!

On all the other planes coming over - as far as I could tell - the engines were pretty much lined up fore and aft. So why not on these 737's. Of course this was after a gallon of Guiness so I could have imagined the whole thing!

Thanks,

Yes, there is "toe-in" on jet aircraft engines. The nose of the aircraft generates a bow wave. By the time this wave reaches the engines, the airflow is at an angle to the fuselage. From memory, the engine angle for a 747 is only 2 degrees (either side), but if you can see toe-in on a 737, the toe-in angle for this aircraft is probably somewhat higher than this.

Rgds.
Q.

I guess this is the reason the DC9 had toe-out in the tail.
To meet the airflow dead on(poor terminology)and to direct the efflux more to the centre(reducing VMCA?),and engine out drag.:D