×
Welcome to the CPL Aerodynamics question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.
Drag Formula and Variable 'S'
Eternity
Topic Author
Eternity created the topic: Drag Formula and Variable 'S'
Hi
An exam question for CADA went something like:
What does 'S' stand for in the drag formula:
(a) Maximum Surface Area
(b) Mean Surface Area
(a) Maximum Frontal Area
(b) Mean Frontal Area
As far as I can tell from research on the internet the best answer seems to be either Mean Surface Area or Mean Frontal Area, but I am not certain (particularly as both these options were available in the exam) as it seems to vary depending upon the frame of reference used (eg NASA*) or preferred by the manufacturer. Some seem to use the Surface Area so a direct comparison with the Lift formula can be made, but then others talk about it being the cross-section of the wing which is determined by the squaring the chord (eg. Wikipedia**)
In the Aviation Theory Centre CPL Aerodynamics book in its glossary it says that 'S' = Frontal Area, but doesn't seem to amplify whether Mean or Max. In the Day VFR syllabus at 2.6.5.1(c) it seems to indicate the 'S' is Surface area for BOTH Lift and Drag formula.
Hence my confusion, which I am hoping you may be able to help clarify.
Richard replied the topic: Drag Formula and Variable 'S'
Hi Eternity,
On page 52 of the 12th Edition of "Mechanics of Flight" by Kermode discusses drag and talks about the "maximum frontal area" or "maximum cross sectional area" which we represent as S in the drag formula. The answer to your question should be "(c) Maximum Frontal Area" in that case.
