Airspeed is decreased during a turn, What would you do to maintain level flight? (FAA Question that most people get it wrong.)

10 Answers

1. 
   

   
   

   Kris Kortokrax on Oct 10, 2013

   Are you asking because you missed the question on the test and don’t understand why?
   Or, are you playing stump the people on the forum?
   If you are a physicist, one would think you would be able to find the answer

   There is not enough information in the question to pick between A and C as being the correct answer.

   Based upon the lift equation, there is a tradeoff between velocity and Coefficient of Lift.
   If speed decreases, then angle of attack would need to be increased to keep the equation in balance.

   If the aircraft is already flying close to the critical angle of attack, then the bank angle would need to be decreased and then the angle of attack increased.

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2. 
   

   
   

   Physicist on Oct 10, 2013

   Well, If you are taking a ATPL test, would you answer “There is not enough information to answer the question”?

   It is correct to increase the angle of attack in theory.

   By raising a chord line that meet the relative wind you can increase the angle of attack. However, in reality wouldn’t you end up losing more airspeed if you try to increase the angle of attack by adjusting an aircraft’s nose high?

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3. 
   

   
   

   Kris Kortokrax on Oct 10, 2013

   I don’t design the questions. If I had a problem with the question, I would take it up with the people in the FAA who design the questions. Apparently, they have not read the section in the Instructor’s Handbook that deals with designing good test questions.

   I am making the assumption that speed has decreased because the angle of attack was increased to maintain altitude because the power was not increased.

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4. 
   

   
   

   Physicist on Oct 10, 2013

   I am trying to understand this tricky question what the assumption behind of the question is.

   Premise:
   When Airspeed is decreased in a turn, what must be done to maintain level flight?

   Common Knowledge:
   We normally observe an airspeed decreasing in a turn because an aircraft’s pitch is high without thrust compensation. But then in oder to recover, why would you want to increase the angle of attack when it’s already high enough to bleed out speed?

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5. 
   

   
   

   Kris Kortokrax on Oct 10, 2013

   There lies the ambiguity in the question.

   Did the speed decrease as a result of an increase in angle of attack without an increase in power or

   Was the speed reduced during the entry to the turn by decreasing power?

   There was no mention in the question concerning recovering any speed, only maintaining level flight.

   If I had to pick the least wrong answer (one that would cover any potential situation), I would probably pick answer A.

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6. 
   

   
   

   Physicist on Oct 10, 2013

   Yes, A is indeed least wrong answer. Like you explained earlier, in Total Lift Equation,
   Lift = Coefficient Lift x Wing Area x Square (Velocity of Air)/2 x Density of Air/2

   In theory, when airspeed (Velocity of Air) decreases, it needs to be compensated with Coefficient Lift (AoA). But then according to Coefficient Lift and Airspeed graph, more you increases the Coefficient Lift (AoA), more drag is being produced resulting further dropping Velocity of Air (Airspeed). Drag is a price that is paid for a lift.

   In practice though, you put your plane into a turn and next thing you see is airspeed dropping, Would you want to push the throttle and “Decrease” the pitch attitude to gain an airspeed unless you are flying a jet?

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7. 
   

   
   

   Bob Watson on Oct 11, 2013

   This is similar to the question about the relationship between airspeed and angle of attack–the answer has to do with the degree that things change.

   If your airspeed is reduced in a turn (which sounds like a deliberate action as it’s phrased in the question) and you wanted to maintain level flight, you would either reduce the bank and/or increase the AOA. This might reduce the airspeed a bit more, but its more likely to arrive at the desired equilibrium (level flight at some, perhaps slightly lower, stable airspeed) than result in a continually degrading situation of less airspeed, less AOA, etc. (There are, of course, points on the L/D curve where increasing the AOA could cause this).

   You could also add power, but that wasn’t an option presented in the test question as that would solve the problem by increasing airspeed (through more thrust).

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8. 
   

   
   

   Kris Kortokrax on Oct 11, 2013

   You appear to want to dwell on the theoretical.

   I deal with the practical.

   If I am making a turn, I use ailerons (or cyclic in a helicopter) to bank the aircraft and rudder for coordination in an airplane.
   I use elevator in an airplane to raise the nose to an altitude which will maintain level flight, if that is my aim. I also add power to maintain my speed, if necessary. In a helicopter, I raise collective, which increases the AOA on the rotor blades. The correlator increases power as the collective is raised.

   I will leave the theoretical exercises to you. Aerodynamics for Naval Aviators is a good reference text.

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9. 
   

   
   

   Lion on Oct 11, 2013

   The correct answer is “A”. The question seems clear for me. It says if the IAS decreased (not decreased AND maintained). When the IAS drops, we can’t maintain level flight except by three ways:
   1. Increasing power/thrust (not an optioned in this question)
   2. Decreasing the turn and or
   3. Increasing the AoA

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10. 
    

    
    

    Brian on Oct 11, 2013

    With questions like this it’s a no wonder pilots are stumped whenever someone presents an accurate analysis of physical events. “When airspeed is decreased in a turn.”

    How about, “Why was airspeed decreased in a turn?” That is far more valuable if you care to grasp the relevant concepts. The airspeed decreased in the turn because the angle of attack was increased to maintain level flight, NOT the other way around; as this question would have you believe.

    —

    Physicist, this is why you’re confused when you attempt to logically analyze the presented scenario. You, like the author of this question, is skipping over the most important question, the one this question fails to acknowledge:

    Why did the airspeed go down in the first place? You might immediately think, well drag, right? Ok, let’s go with that. So what caused the drag to increase? Quickly you’d think, well drag increases in a turn because lift increased. Ok, so what increased lift? Finally, answering this question, you get to the roots: lift increased because AOA increased, causing drag to increase, and causing the decrease in airspeed.

    Do you see the analytical mess this question puts you in? No answer is analytically correct because they all include an action that’s already happened. That action is the change in AOA, which is what caused the airspeed to decrease in the first place. The only accurate assumption we can draw from this is that the pilot increased AOA, but not enough. That resulted in a decrease in airspeed, but insufficient action to maintain level flight. In other words, imagine the same set of answers but with this question:

    The pilot enters a turn, increasing lift by pulling back, as a result losing airspeed. The pilot’s actions fail to maintain level flight, what must the pilot do to accomplish level flight?

    Assuming this is the question, your analysis would be accurate. The pilot can either pull back harder, increasing AOA and losing more airspeed or reduce bank angle.

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