Consider the following statements:

Question

1. When the airfoil is at conditions, separation takes place around 85-90% of the chord.

2. The rapid increase in drag after a certain angle of attack is due to the fact that transition moves forward.

Select the answer that matches:

Only statement 1 is true

Only statement 2 is true

Both statement 1 and statement 2 are true

Neither statement 1 nor statement 2 is true

Answer 1

To evaluate the truth of the two statements provided:

1. The first statement refers to the conditions of airflow over an airfoil. It suggests that separation occurs around 85-90% of the chord. This can be context-dependent, but in many cases, for certain airfoil designs and at higher angles of attack, flow separation typically happens around the rear part of the airfoil (often between 70% and 90% of the chord). Therefore, this statement can be considered true in many situations involving airfoils at high angles of attack.

2. The second statement claims that the rapid increase in drag after a certain angle of attack is due to the fact that transition moves forward. In aerodynamics, the rapid increase in drag (often referred to as "drag increase" or "stall") is generally associated with flow separation and turbulence rather than the position of the transition point moving forward. Transition may affect drag, but it is not the direct cause of the rapid increase during stall. Therefore, this statement is not entirely accurate.

Based on this evaluation:

• Statement 1 is true.
• Statement 2 is false.

So the correct answer is: Only statement 1 is true.