winglets
 

Pardon my ignorance- could a professional engineer/ pilot explain why, for example , BA 747-400's have winglets and their B777s do not. Were the former built with them. I recently flew South West-Tampa to New Orleans and the B737 -700 out had winglets but the 300 version back did not.Apologies if this is all obvious. Thanks.

The 777 has a more advance wing development within the category of fuel emission. This is where you will see that the 787/747-8 will have wing constructions as on the current 777.
737-200/400/500/600 do not carry winglets for the time being. Usually aircraft carry winglets are there to save fuel, and for your case when you flew back, SW probably have not had that aircraft fitted yet, but most likely further on it will. Hope I answered your question.:hmm:

Maybe someone else could explain in a bit more detail if they wish.

Although not a proffessional pilot I can offer you an explanation from my PPL technical book.

Modified wingtips [winglets] can reduce the amount of leakage of the airflow around the wingtip and therefore reduce the formation of induced drag.

Not very detailed however aircraft with wingtips are more efficient, both aerodynamically and in terms of fuel burn.

B744 built with winglets; B777 not due to more efficient wing design as mentioned.

B737 Classics not originally designed with winglets but 737-NG's were thus the difference you observed on your SWA flight. I believe SWA are retrofitting their classics though as I'm certain I flew on a 733 recently with winglets. BA did same with B757 for the Openskies operation as have United/Continental, US Airways and others.

winglets
 

Many thanks to all for taking the trouble to reply- very much appreciated

Just to add, the only member of the 737NG family that was designed with winglets is the 737-900ER, earliest versions of the 736, 73G, 73H and 739 didnt come with the winglets (added at a later date, although new builds seem to all include winglets nowadays).

winglets
 

Many thanks Graham