india DGCA ATPL exam

[CaptGalaxy]

Doubt_Principles of flight

Hi Folks, i was going through the Oxford ATPL, Principles of flight and found a few statements which, i cant seem to understand. I feel they contradict each other so please advice if i'm reading it wrong.

1. Chapter- Drag > Parasite drag> skin friction
"Because of the adverse pressure gradient existing on a curved surface, the transition point will be further forward than if the surface was flat"

2. Chapter- High Lift Devices> Leading Edge Flaps
"On high speed aerofoil sections the leading edge may have very little camber and have a small radius. This can give flow separation just aft the leading edge at quite low angles of attack"

Now which of the above is right and is there something i'm missing in the above concepts?

Also - i dont seem to see the definition for Form drag : "Because of separation there will be a lower pressure at the trailing edge than the leading edge. An aerodynamic force will act in the direction of the lower pressure - form drag"
How would this be a drag if there is airflow from the leading to the trailing edge? wouldnt this infact contribute to the thrust for the aerofoil?
I understand the concept of adverse pressure gradient but the above reason has been quoted as a separate factor.

thanks in advance.

cheers,
P

[pilot2612]

thanks buddy

thanks WINGSOFFIRE...
i have to give NAV & RAD AIDS both together!!!!
what should i expect????



also...CAN THEY PASS ME IN 1 AND FAIL ME IN ANOTHER????



help appreciated

[wings of fire]

@pilot2612

If u r giving both your orals together, they will either pass you on both the subjects or they will fail you on both. Never heard if they just pass on one if u r giving both the orals together. That's from my experience. Any ways do inform us how your oral goes.
For General Navigation - you should have mastery over maps and charts.

[wings of fire]

@ puneeth

Thrust acts in the forward direction. Drag acts in backward direction.


Form drag: Because of the adverse presuure gradient behind the transition point, there is decrease in kinetic energy of lower levels of boundary layer.Whereas the upper level of boundary layer overrun at this point(called seperation point). Because of seperation, Pressure at trailing edge < Pressure at leading edge. This force acting backward is form drag.

Thrust is a force and force=ma. In case of form drag, kinetic energy of lower boundary layer decreases. so acceleration is reduced and therfore thrust gets reduced.

[wings of fire]

@puneeth

Also see page 7-11. Your concepts will be much clear by reading stalling chapter thoroughly.

Generally sharper the nose , thinner the aerofoil section, the more sudden will be the stall.

Also there are 4 reasons of stall(or seperation)
1)leading edge radius
2)Camber
3)Thickness to chord ratio
4)Chordwise location of maximum thickness and max camber

Transition pt. is the point where airflow changes from laminar to turbulent.

As AOA increases, adverse pressure gradient increases and transition point will move forward.

Statement: 2. Chapter- High Lift Devices> Leading Edge Flaps
"On high speed aerofoil sections the leading edge may have very little camber and have a small radius. This can give flow separation just aft the leading edge at quite low angles of attack"

High speed aerofoils can stall at low aoa (that means when their speed is high). Just imagine if leading edge flaps are not put in those aerofoils, then how will these a/c's slow speed and land at the airport(as they will require high AOA during landing.)

[pilot2612]

thank you very much sir

thanks for the reply and the message... really appreciate it.
will post the questions i get...

im in charter flying these days... any difference in orals???

u think they would concentrate on my airplane????


thanks a lot again..

[CaptGalaxy]

@wings of fire

Thanks for the attempt to clarify, but i do understand all the concepts you're explaining, my question however was completely different.

I meant to say that the first two statements i mentioned seem to contradict themselves because one says the transition point/separation point would be much further ahead since the aerofoil is not a flat surface (translating to flatter the aerofoil/ surface more aft the separation )
The second says the separation is just aft the leading edge because the surface has less curvature. This would imply if the aerofoil had more curvature, the separation would be much further aft (hence contradicting the first statement)

I do understand the thrust and drag definitions but when there's a force acting from the leading edge toward the trailing edge - how would that be a drag?

thanks again in advance.

cheers,
P

[flyboyaviatior]

hi
im giving my first ATPL exams in october session. And was wondering which ATPL subject contains principles of flight!
is it Nav, met or radioaids?
It might be a silly question but still i want to know because i never came across this topic in CPL Navigation.

[13R]

ATPL oral - Radio Aids

Hey Guys!

I am appearing for Radio Aids ATPL oral exam for the first time, So can you tell me what type of questions they ask in the oral.
Your help would be greatly appreciated!!!!

Thanks!!

[amar anand]

charts

hi guys ..
if u r apeearing for nav orals in delhi then be preapared for the jeppssen charts ...rnav ...
for radio aids he might ask u gps ...adf ...ils ...radio altimeter .
all the best .

[mike_sierra]

question

I was asked this question in the orals..
The reference signal is 90deg, variable signal is 240deg. What is the phase difference ?
(please do not say it's 150deg)

I would appreciate if anyone presents a solution to this one..(it's using the graph).
I couldn't fgure it out in my Class 11 either

[golfpapa]

i think the answer is 90 plus 180 minus 240 = 30deg.

always subtract variable signal from reference signal and anytime reference signal is smaller than variable add 180 to reference signal and then subtract.

I am not sure if this method is correct just an inference i hv drawn after seeing the correct answers to these type of numericals

[AVIATROZ]

@ golfpapa

Even i would like yo clear my doubt on this............as according to me it was 360 degree + 90 degree -{minus} 240degree=210 degree...........please correct me on this if i going for the wrong concept

thanks

[golfpapa]

OMG so sorry guyzzz
honest mistake there.....

Of course its 360 and not 180....i got a lil confused considering its been long tym since i did these questions

thank you aviatroz

sorry again mike sierra

[skybuster7]

theres a way to remember doing this :


if phase_diff > +180 then
phase_diff = phase_diff-360

else if phase_diff <-180 then
phase_diff = phase_diff+360

else
phase_diff = phase_diff

in this phase_diff= ref - variable= 90-240= -150

-150 is less then -180

so phase diff= -150+360=210

[mike_sierra]

gracias fellas

[matthewgamm]

INS Qs

1. At the second stage of integration, E/W speed is converted to E/W distance gone. To convert this departure into change of longitude, it has to be:
a. Multiplied by the Secant of the latitude
b. Divided by the tangent of the latitude

2. The amber ALERT light on an INS Control and display unit:
a. illuminates steadily for 2 minutes before reaching the next waypoint
b. start flashing 2 minutes before reaching the next waypoint and goes out at 30 secs to run.

[sonsal]

@matthew
1- a
2-a

[keith williams]

The answer to the first question can be derived from the Departure equation.

Departure = Change in longitude x cosine of latitude.

Dividing both sides by cosine of latitude gives

Departure / cosine of latitude = Change of longitude

The secant of an angle = 1/cosine, so dividing by the cosine is the same as multiplying by the secant.

So departure x secant of latitude = Change of longitude.

Deriving answers is this way will enable you to develop a far better understanding of the subjects.

[AVIATROZ]

gen. navigation Q

Q1. A great circle has its North vertex at 70N130E, at what longitude and in what direction would the great circle cross the equator assuming:

a. Initial direction is east from the northern vertex{ans-140W 160{T}}

b. Initial direction is west frm northern vertex{ANs-040E200{T}}

Q2. Given that the compression value of the earth is 1/297 and that the semi major axis of the earth,measured at the axisof equator is 6378.4km,what is the semi major axis of the earth measured at the axis of the poles?
ans- 6356.9km