As long as we're on the subject, what is the typical cooling drag as a percentage of the total airframe drag? My memory from undergrad aerodynamics is fading but it seems like it is in the 5 to 10% range. For the moment lets assume it is 7%.

Rob,

 

Diesels aside, "typical" isn't typical anymore.  I.E. Lancairs do not exhibit airframe drag anything like those that you studied.  With slick, efficient airframes and laminar flow wings, the relative impact of drag inducing components changes dramatically.  The reduction of cooling drag is free and contributes a great deal to performance.  Maybe we should assume a diesel scenario where the cooling drag contribution is more like 20% of the total drag.

 

The reduction of cooling drag is one of the ways that I can achieve the speeds that I do (exceeding 200 Kts with a 320 CI spark ignition engine). 

 

Gee, I once programmed 1950's era computers and they work the same way today, only they are a bit faster and smaller.  Your undergrad course, relating data from textbooks written in the middle of the last century, is merely an artifact, nay, even a relic from the dark past - before laminar plan forms, carbon fiber and polymer snot-slick coatings were widely available and used in or about every-man's airplane....

 

OK, let the diesel discussion continue apace.

 

Grayhawk