Challenge Questions PPL Sec 1.

These are the latest challenge questions, highest level PPL. But you would be surprised how many 'experienced' pilots won't be able to answer these. If you can't answer all of these, you might wan't to hit the books, this is basic knowledge, aerodynamics. Remember, you're not here to answer questions you already know the answer to, your hear to learn the answers to questions you don't know

Q 1. In what configuration in terms of attitude does weight become as thrust and thrust become as lift?

Q 2. What 3 elements are tested in determining the 'parasite drag' of an aircraft?

Q 3. The greater the size and strength of the net sum of vortices along the wing, the greater the down wash (not top be confused with another down wash responsible for lift). This down wash causes the lift vector to move slightly aft of perpendicular to the relative wind, creating an innate rearward lift component; this is un-avoidable for any airfoil. What is this rearward lift component called?

Q 4. A greater angle of attack denotes an increased negative pressure on top of the wing which further denotes an increase of what type of drag? Also by what value does this type of drag increase parallel to speed? Refer to subsonic speed (0.75 MACH) values only, as values increase once an aircraft enters above subsonic.

Q 5. Explain the cause of 'negative pressure lift' above the wing and 'positive pressure lift' below the wing. Refer to Newtons 3d law of motion, Bernoulli's principals of pressure and the Venturi model. Also, how does the design of the wings effect the further pressure differential above and below the wings, taking into account the local velocities of both sides.

Q 6. As airspeed nears stall speed one type of drag become greatest, same as when airspeed reaches terminal velocity another type of drag is predominant. Which is which? Also, what determines terminal velocity?

Q 7. In terms of 'slipping' and 'skidding', what is the relationship between 'centrifugal force' and the 'horizontal component' of lift?

Q 8. Angle of attack must increase as bank angle increases, in order to counteract the increased net weight of the aircraft due to centrifugal force. What other reasons are there?

Q 9. The wings can be brought in to an excessive angle of attack at any speed. True or false? Explain.

Q10. In order for dynamic stability to be realized, an aircraft must have 'positive static' stability. What would happen to the oscillations of an aircraft in the case of positive static stability and 'negative dynamic' stability?

Q11. In order to obtain an adequate restoring moment, where must the CP be in relation to the aircraft CG?

Q 12. Whats the difference between 'Servo Tabs', 'Anti Servo Tabs', 'Balance Tabs' and 'Anti Balance Tabs'...?

Q 13. The 'linear' velocity of a propeller increases along the length of the blade, while forward velocity stays the same, explain.

Q 14. What is the relationship between the helical path of a section of the propeller and the term 'geometric pitch'?

Q 15. How is it possible to execute a high speed stall?

I have a CPL/IR and I am not embarrassed to say that I couldn't answer every single question without looking it up, although I have definitely come across all of the subjects before ie. no trick questions.

It just proves again that we all need to continue learning and that complacency is never a good thing in aviation. The moment you think you know it all, you don't.

Thats very honest of you, The_Dream_Machine. You're quite right, 'complacency' is not an option for pilots. The Pilot's code, actually states in many ways - it is the duty of a pilot to guard against complacency. It must be obvious why.

Yap totally agree...We need to keep learning things and always ask "why" and "how",and this is a remind for myself...Sorry but i didn't have time to answer the questions....but i feel very lucky to have this forum and we can learn new things....

Q15.....

we can execute by mistake a high speed stall after a recover from a spin or a stall or in steep turn by pulling back the control column too hard...many people wonder why because they think that Stalling is a matter of Airspeed...this is what was confusing me years ago...Stalling is a matter of Angle Of Attack of the Wing....when the aerofoil reaches the Critical Angle of Attack (which is 16 degrees for most of training planes) then is Stall...a plane can stall at high speeds if the critical AOA is reached....an example that is coming to my mind is in a steep turn pulling 2G 's in 60 degrees bank angle....although you are in a full power with a speed 70 lets you can stall because you exceeded the angle of attack....

and also by personal experience with gliders you can have high speed stall in a winch launch when you pull hard to climb..you can still stall in 60 knots even if the glider stalling speed is 35 kt....so what i am trying to remind my self is dont rely on the speed but be careful with the angle of attack

This is a really brilliant answer

It may take you by surprise how many pilots cannot answer Q 15.

There is one more detail to the explanation which is missing, you have partly touched on it, but it is a matter of explanation. The part of the answer missing is in relation to 'what happens' to the relative airflow to the propeller/jet engine when pulling out of a high speed stall. Yes, the airfoils reach Aoa Crit, but - theres 'something else' which also reaches its critical angle. Does anyone know what this is?

Axial compressors rely on spinning blades that have aerofoil sections, similar to aeroplane wings. As with aeroplane wings in some conditions the blades can stall. If this happens, the airflow around the stalled compressor can reverse direction violently

You have established that compressor/propeller blades are also airfoils, with the same function as a wing - to stimulate airflow. There is still something missing, think - 'what does an airfoil like the wings or propeller and compressor blades require in order to function and stimulate aerodynamic force'? The answer can be found by determining what constitutes an Aoa.

Your very close!

yap ok angle of attack is the angle of the chord line relative with remote airflow....the airflow is reaching also a critical angle and the airflow become turbulent flow and the separation point moves forward....so the airflow eventually becomes turbulent flow...i hope i got your point

Nope, - it has to do with thrust. There are 2 vector quantities which create the aerodynamic motion over a propeller/compressor blade. When there is in imbalance between these 2 vector quantities, a stall will result. The high speed stall is one way in which these vector quantities will become imbalanced.

hello aviation ....sorry but i was very busy and i was also abroad for holidays....but i am back for more questions....so can you give us the answer for this subject to proceed to another question

Welcome back Kerveras

The specific answer to the question is -

As an aircraft pulls out of a stall, the momentum of the aircraft causes it to continue down in its original flight path before adjusting to the new attitude. While the aircraft is still traveling downwards, the relative airflow is no longer inline with the propeller causing it to become temporarily ineffective. The two vectors which constitute a propellers angle of attack are the relative airflow and the speed of the propellers rotation. If one of these is out of balance, the propeller becomes less productive or ineffective. During the pull out of a stall, these vector quantities are temporarily out of balance, until the momentum of the aircraft catches up with the new attitude.