Module 8: Basic Aerodynamics5 Sep 2026

minimum drag speed doesnt make sense to me

Exam question

Minimum total drag of an aircraft occurs

A.at the stalling speed
B.when profile drag equals induced dragCorrect
C.when induced drag is least

Explanation

Sketch the drag curves (drag against speed). Induced drag decreases exponentially with speed. Profile drag increases exponentially with speed. Vmd (minimum drag speed) is where they meet.

Amira

asked · 5 Sep 2026

Author

ok so i thought minimum total drag would just be wherever induced drag is at its lowest point but the answer key says its actually where induced drag EQUALS profile drag which is a completely different point on the graph?? like why would you add two things together and the minimum of the total isnt just the minimum of one of them. i think i get it but can someone check my thinking

Discussion1

Part66Exams team

5 Oct 2026

your close but the minimum of the total isnt the minimum of one part. induced drag keeps falling as you speed up, it never really bottoms out, so "where induced drag is least" would be at max speed. profile drag does the opposite and keeps climbing. total drag is the two added together and the lowest point of that sum is where they cross, ie where induced = profile. go a bit slower and induced grows faster than profile shrinks, go a bit faster and profile grows faster than induced shrinks. so the bottom of the total curve sits right at the crossover, thats Vmd. sketch the two curves and add them up and youll see it straight away