-
Please take a moment and update your account profile. If you have an updated account profile with basic information on why you are on Air Warriors it will help other people respond to your posts. How do you update your profile you ask?
Go here:
Edit Account Details and Profile
aviation information section
- Thread starter JIMMY
- Start date
IrishNavy05 said:
AHHH! I stared at this way too long, I was thinking it said induced drag, not no induced drag. I agree with C. Again...
arguing with an expert? there are like 5 of us on here with MS's in aerospace engineering
an "airfoil" by definition is infinite, because "airfoil" refers only to the 2-D cross section...that is why there are corrections to account for finite wings
as for the "lift forces pointing in opposite directions, creating no net lift" theory, the definition of lift is the sum of all aerodynamic forces perpendicular to the direction of flow...there is no pressure differential between upper and lower surfaces of an airfoil, so the sum of all forces is 0....so there is ZERO LIFT.
we can argue semantics all day, but from the sounds of it everyone who's thought this through realizes that C is the answer
an "airfoil" by definition is infinite, because "airfoil" refers only to the 2-D cross section...that is why there are corrections to account for finite wings
as for the "lift forces pointing in opposite directions, creating no net lift" theory, the definition of lift is the sum of all aerodynamic forces perpendicular to the direction of flow...there is no pressure differential between upper and lower surfaces of an airfoil, so the sum of all forces is 0....so there is ZERO LIFT.
we can argue semantics all day, but from the sounds of it everyone who's thought this through realizes that C is the answer
sevenhelmet said:
a wing is not an airfoil. a wing uses the 2-D cross section of an airfoil, but the wing itself is not an airfoil
2x maxims of Naval Aviation:
1. Never underestimate the ability of the Navy to use the least technically correct answer for the purposes of testing entry level applicants for a commissioning program.
2. Never underestimate the ability of a bunch of engineering dorks to completely over-think (and subsequently fvck away) the most simple propositions at every possible opportunity. Ever heard of Occam's razor, boys?
As soon as I saw this thread pop up, I knew all you Poindexters would be on this like monkeys trying to fvck a football.
Brett
1. Never underestimate the ability of the Navy to use the least technically correct answer for the purposes of testing entry level applicants for a commissioning program.
2. Never underestimate the ability of a bunch of engineering dorks to completely over-think (and subsequently fvck away) the most simple propositions at every possible opportunity. Ever heard of Occam's razor, boys?
As soon as I saw this thread pop up, I knew all you Poindexters would be on this like monkeys trying to fvck a football.
Brett
I am agreeing with my fellow Aeronautical Engineers. The correct answer is C.
Reasons other answers are wrong:
A. AOA vs. CL graph for symmetric airfoil has a point a 0,0 (Like stated earlier). To conceed points to the naysayers, yes there is a pressure distribution across the airfoil, however, lift is defined as "Lift consists of the sum of all the fluid dynamic forces on a body perpendicular to the direction of the external flow approaching that body." (from Wikipedia http://en.wikipedia.org/wiki/Lift_(force) quickest site that could give me the answer). So since there are internal forces that cancel out, the Lift = 0 and Drag = (some number). So that nixes answer A.
B. Form Drag as stated here is caused on all surfaces by moving air. Thus nixing this answer.
D. Drag is some number, thus aerodynamic forces are not equal to 0. Say bye bye to this answer.
Reasoning of correct answer:
C. As stated before, induced drag is produced by Lift over an airfoil. Since there is no Lift (due to CL = 0 @ AOA = 0) there is no induced drag. Which yields the correct answer.
Kobyra
P.S. For further information please register yourself in a 4-year Aero Engineering Undergrad program, the above topic would probably be discussed in the first 2 years of your classes (For you fast learners out there maybe the first year, for others just keep going, you'll eventually get it.)
Reasons other answers are wrong:
A. AOA vs. CL graph for symmetric airfoil has a point a 0,0 (Like stated earlier). To conceed points to the naysayers, yes there is a pressure distribution across the airfoil, however, lift is defined as "Lift consists of the sum of all the fluid dynamic forces on a body perpendicular to the direction of the external flow approaching that body." (from Wikipedia http://en.wikipedia.org/wiki/Lift_(force) quickest site that could give me the answer). So since there are internal forces that cancel out, the Lift = 0 and Drag = (some number). So that nixes answer A.
B. Form Drag as stated here is caused on all surfaces by moving air. Thus nixing this answer.
D. Drag is some number, thus aerodynamic forces are not equal to 0. Say bye bye to this answer.
Reasoning of correct answer:
C. As stated before, induced drag is produced by Lift over an airfoil. Since there is no Lift (due to CL = 0 @ AOA = 0) there is no induced drag. Which yields the correct answer.
Kobyra
P.S. For further information please register yourself in a 4-year Aero Engineering Undergrad program, the above topic would probably be discussed in the first 2 years of your classes (For you fast learners out there maybe the first year, for others just keep going, you'll eventually get it.)
JIMMY
Registered User
hey guys,
wow thx for all the responses
. didnt mean to start any wars
the question is from the acro military flight aptitude tests study guide (f-16s on the front). its actually in the AFOQT section. I was studying for the ASTB and I figured id study the aviation section in the AFOQT section just for some extra questions, and of course i was like wtf? when i saw that one.
hey for the aeronautic MS guys, where did you happen to get them from? anyone do the ERAU extended learning program?
thx again,
wow thx for all the responses
. didnt mean to start any wars the question is from the acro military flight aptitude tests study guide (f-16s on the front). its actually in the AFOQT section. I was studying for the ASTB and I figured id study the aviation section in the AFOQT section just for some extra questions, and of course i was like wtf? when i saw that one. hey for the aeronautic MS guys, where did you happen to get them from? anyone do the ERAU extended learning program?
thx again,
I've heard that if you're a pilot with a masters your plane has more drag. This is due to all the hot air being created in the cockpit which leaks out into the slipstream. This in turn creates a point of lower pressure causing flow reversal and in turn creating more drag.
In conclusion, thinking too much makes the plane crap.
In conclusion, thinking too much makes the plane crap.
danthaman
The right to keep and bear arms
The answer is infact "A". In an average wing you get approximately 75% of your lift from bernoulli's effect (the camber of the airfoil) and 25% from newton's third law of motion (for every action there is an equal and opposite reaction). Air is deflected downward under the wing, which creates an opposite reaction of pushing the wing upward. A symmetrical airfoil gives you no bernoulli effect therefore reducing the amount of lift by 75% or more compared to a cambered wing. This is straight from an aerodynamics class I took in college.
danthaman said:
Well, sh!t if you took an aero class in college, A must be the right answer.
While, I agree that A is probably the correct answer in the context of the study book from which the question came, there is no way that your aero class trumps the the theoretical/technical answers of the individuals with Masters' in aero. Unless your aero class was a prep course for the ASTB/AFOQT.
It is becoming obvious that the question's meaning of airfoil is different than the aero engineering community's standard definition.
jpaviator said:
Got mine from the University of Bath in the UK on a Marshall Scholarship in 2004. But, I know a lot of guys that did/are doing the ERAU program and it seems pretty good, as long as you have someone around you that can sit down with you and explain stuff when the shiznet hits the fan.
danthaman said:
On a symmetrical airfoil the amount deflected down is the same as the amount deflect up since its identical on top and bottom, cancelling the effect out. That is assuming that air is "deflected," which I haven't heard before. Its more of a pressure differential due to the speed of the air. But I am the last person to claim I know it all...