Ex. 12 - Stalls | Attempts: 461 - Quiz, Trivia & Questions

2.

What is washout, and what's the purpose of building it into the plane's design?

It is a tapering of the wing towards the trailing edge to ensure smooth airflow
It is a built-in increase in the angle of incidence as you go towards the wingtips to ensure they stall first while the rest of the wing is still flying normally
It is the a shallow bowl-shaped dip at the top of each wing, to "trap" turbulent air and delay a stall
It is the difference in the angle of incidence between the wing root and the wing tip, used to increase aileron effectiveness in stalls

Correct Answer

A. It is the difference in the angle of incidence between the wing root and the wing tip, used to increase aileron effectiveness in stalls

Explanation

B looks like a plausible answer, but it is reversed: in actuality, washout is the decrease of the angle of incidence towards the wingtips, so that they stall after the wing roots. This is done so that even if most of the wing is stalled, the wing tips are not. In other words, the wing tips are NOT yet at the critical angle of attack, so the increase in an angle of attack will produce an increase in lift, so ailerons will still work as expected. When the wing tips are actually stalled, the increase in an angle of attack would cause a decrease in lift, so turning the yoke to the left might actually make the plane roll to the right!

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3.

During a power-on stall practice, your right wing drops as the plane stalls. Which of the following actions would you immediately take to help remedy the situation? (Check ALL that apply.)

Apply left rudder
Turn yoke to the left
Pull the yoke all the way back to increase control effectiveness

Correct Answer

A. Apply left rudder

Explanation

Rudder is the most effective control surface in a stall, so that's what's used to correct a wing drop in a stall.
Your ailerons must stay NEUTRAL at the beginning of the stall recovery procedure: when the wing is stalled, they won't be very effective and in fact may make the wing drop worse, since they would more deeply stall an already stalled wing. Practice this during power-on stalls, because it will be critical at your next lesson - spins!
Pulling back on the yoke does not make sense - that's what got you in the stall in the first place - it just increases the angle of attack stalling the wings more deeply.

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4.

Assuming your plane is equipped with a properly functioning stall warning horn, in which cases will it likely fail to sound before the stall? (Check ALL that apply.)

In steep turns, because the plane will stall at much higher airspeed than normal
In severe icing conditions, because the plane will stall at a much higher angle of attack than normal
In any stalling situation which occurs above published stall speeds (turns, high-G manoeuvres etc.)
A properly functioning stall warning horn will always sound just before a stall since it detects the increase in airflow turbulence over the wing which occurs before every stall

Correct Answer

A. In severe icing conditions, because the plane will stall at a much higher angle of attack than normal

Explanation

A stall warning horn will sound when a certain angle of attack is exceeded (typically a few degrees below the critical angle of attack), no matter what airspeed you are flying at. To test it, ask your instructor to demonstrate a steep turn at a relatively low airspeed and note when the stall warning horn sounds - it will go off at a much higher airspeed than during normal stall practice.
In severe icing conditions, however, the whole aerodynamics of the wings changes, so that they will stall at a much lower angle of attack than normally. So a stall may occur well before the angle of attack increases sufficiently to actuate a stall horn. (This is just one of many reasons why flying with ice or frost anywhere on the control surfaces is extremely dangerous.)

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5.

How does power affect a plane's stalling characteristics?

A power-on stall will be "gentler" than a power-off stall, but it is dangerous because the engine noise may make it difficult to hear the stall horn
A power-on stall will occur at a higher airspeed than a power-off stall, but will be less dramatic and easier to recover from
A power-on stall will occur at a lower airspeed than a power-off stall, but will be more "aggressive" and is more likely to result in a wing drop
Power has no noticeable difference on stall characteristics

Correct Answer

A. A power-on stall will occur at a lower airspeed than a power-off stall, but will be more "aggressive" and is more likely to result in a wing drop

Explanation

A power-on stall will occur at a lower airspeed than a power-off stall, for a couple of reasons. First, the turning propeller will create additional airflow over the wing roots (which are normally supposed to stall first due to washout, remember?) This means the wing can avoid being stalled for a little bit longer. Another reason is that the thrust generated by the engine has a bit of an upward component, which acts as extra lift, which helps delay the nose drop.
However, because the wing root stall is delayed, once the stall occurs, the wing roots and the wing tips will stall at about the same time, which results in a more deeply stalled wing and thus a more dramatic stall. Moreover, if one wing ends up being a bit more stalled than the other, it will drop, so you are more likely to encounter a wing drop along with a nose drop in a power-on stall.
CAUSES CONTRIBUTING TO POWER-ON STALL DELAY:

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6.

We say that a plane always stalls at the same angle of attack (and in case of a straight unaccelerated flight this means the same airspeed). However, the wing's aerodynamics will vary based on the number of conditions, which affect the critical angle of attack and the stall speed. Which of the following factors INCREASE the stall speed? (Check ALL that apply.)

Forward centre of gravity
Aft centre of gravity
Higher weight
Lower weight
Steep bank angles
Power
Flaps

Correct Answer(s)

A. Forward centre of gravity
A. Higher weight
A. Steep bank angles

Explanation

See the CONSIDERATIONS slides in the Ex. 12 presentation for the explanations. (Or contact us if you are confused about this (or any other exercise!)

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7.

What accounts for buffeting (airframe shaking) you may experience as you approach a stall?

Engine roughness due to overheating because of insufficient cooling at high angles of attack
Aileron flutter
Turbulent airflow over the wings due to an increase in the angle of attack
Elevator oscillations due to insufficient air flow

Correct Answer

A. Turbulent airflow over the wings due to an increase in the angle of attack

Explanation

This is what happens with the airflow as the angle of attack increases (note that the actual angles will vary for different airplanes, though 17-18 degrees is a typical angle at which a light trainer like a Cessna 172 will stall):

It's no wonder you might experience some buffeting!
(Some planes are also equipped with a stick-shaker, which is a stall warning device that shakes the pilot's controls at the onset of stall - do not confuse this with buffeting, which is airframe shaking due to to turbulent airflow over the wings.)

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8.

True or false: to break a stall, you must reduce the plane's angle of attack by reducing back pressure (or pushing forward) on the yoke?

True
False

Correct Answer

A. True

Explanation

Correct! Lowering the nose by pushing forward on the yoke (or relaxing the back pressure) is in essence lowering your angle of attack, which equals destalling the wings.

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9.

On a recovery from a typical power-off stall, how far do you push the nose down?

As far down as it can go, to build up the airspeed faster
Well below the horizon, to build up the airspeed faster
Just sufficiently to unstall the wing (typically close to cruise attitude)
Barely a degree or two

Correct Answer

A. Just sufficiently to unstall the wing (typically close to cruise attitude)

Explanation

A common mistake student mistake on stall recoveries is to point the nose down far too much, producing a rapid dive which results in unnecessary airspeed build-up and considerable altitude loss. Your objective is to recover with minimum loss of altitude (since if you stall inadvertently, it will likely be close to the ground on take-off or landing), so you want to push the nose down enough to break the stall, but not so much that you end up in an unchecked high-speed dive. For a typical power-off stall in most trainer aircraft entered from straight and level flight, that would be just a bit below the horizon. Save your instructor's nerves, don't point the thing straight down! :-)

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10.

Ok, so as you recover from a stall, you put the nose down just enough to unstall the wings. What can you do next to prevent further altitude loss?

Immediately pull nose up
Add power (and turn carb heat off, if your plane has it!)
Lower flaps
Maintain best glide speed

Correct Answer

A. Add power (and turn carb heat off, if your plane has it!)

Explanation

Pulling the nose back up will only serve to stall the plane again! Lowering the flaps is actually dangerous because now that your plane is unstalled, it's gaining airspeed and you could easily overspeed the flaps, damaging them. Maintaining best glide speed will ensure you won't lose altitude too fast, but adding power will actually allow you to stop altitude loss and begin the climb. So, since your objective is to prevent altitude loss, don't wait too long before applying the power on recovery.

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Ex. 12 - Stalls

What is a stall in an airplane?

Quiz Preview

What is washout, and what's the purpose of building it into the plane's design?

During a power-on stall practice, your right wing drops as the plane stalls. Which of the following actions would you immediately take to help remedy the situation? (Check ALL that apply.)

Assuming your plane is equipped with a properly functioning stall warning horn, in which cases will it likely fail to sound before the stall? (Check ALL that apply.)

How does power affect a plane's stalling characteristics?

What accounts for buffeting (airframe shaking) you may experience as you approach a stall?

True or false: to break a stall, you must reduce the plane's angle of attack by reducing back pressure (or pushing forward) on the yoke?

On a recovery from a typical power-off stall, how far do you push the nose down?

Ok, so as you recover from a stall, you put the nose down just enough to unstall the wings. What can you do next to prevent further altitude loss?