Dihedral
Ministry Cork,
Perhaps the question is referring to the distance between the wing and the horizontal. Assuming a constant dihedral angle would still result in the distance between the plane of the wing and the horizontal plane increasing from root to tip which would give A as the correct answer.
A rather ambigious question. I went for C initally too.
Perhaps the question is referring to the distance between the wing and the horizontal. Assuming a constant dihedral angle would still result in the distance between the plane of the wing and the horizontal plane increasing from root to tip which would give A as the correct answer.
A rather ambigious question. I went for C initally too.
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Oh dear. Dihedral; tips are higher than the root. Anhedral; tips are lower than the root. Polyhedral; differing degrees of dihedral or anhedral; or both as in a gull wing or cranked wing. The options A and B in the exam question imply polyhedral, as it is written.
In most simple wings, the dihedral is constant. It does not increase towards the tip. If it did it would be a positive polyhedral.
In most simple wings, the dihedral is constant. It does not increase towards the tip. If it did it would be a positive polyhedral.
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GBZ - Do you agree with the following to calculate the value of dihedral for a given wing?
Wingspan = 60" (note that we will be using half the wingspan)
Dihedral angle = 5°
Dihedral measurement = Unknown
1) find the Sine of the angle:
Wingspan = 60" (note that we will be using half the wingspan)
Dihedral angle = 5°
Dihedral measurement = Unknown
1) find the Sine of the angle:
Ø = 5°
Sine 5° = 0.087156
2) Plug in the answer above to find the opposite side of the triangle.Sine 5° = 0.087156
0.087156 = Dihedral ÷ 30"
Dihedral = 30" x 0.087156
Dihedral = 2.6" (under each tip)
Dihedral = 30" x 0.087156
Dihedral = 2.6" (under each tip)
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According to my trusty Casio fx-20, yes; except the dihedral is expressed as 5 deg. The wing tip datum would, indeed be 2.615" above root datum, though. That's got to be a model!
I don't recall seeing dihedral expressed as a gradient or tip height above root; hence my earlier reference to Quantity Surveyors. I may have had a sheltered life, though.
I don't recall seeing dihedral expressed as a gradient or tip height above root; hence my earlier reference to Quantity Surveyors. I may have had a sheltered life, though.
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the funniest thing here is that question which i recognise from my ppl days is in (or at least was in) the Irish ppl question bank which is jaa and can also come up in uk etc.. its just one of those ones where you learn the answer because somebody wrote a ****e question...
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Wing Dihedral
A: Increases from Root to Tip
B: Decreases from Root to Tip
C: Gives Lateral Stability
D: Gives Directional Stability
I think A & B are there as to confuse you with washout. i.e. the angle decrease from root to tip in order to make the root of the wing stall before the tip an subsequently the ailerons aft of the wing tip leading edge.
So after disregarding A & B you’ll be left with C & D, basics of the Tec notes will tell you that the fin gives you directional stability (around the normal axis – movement is given by the rudder in a yaw motion).
So you’re only left with C and ‘Lateral Stability’ is gained by having dihedral as seen on most low wing aircraft, or adhedral as seen on some high wing aircraft like a BAe146 or a Harrier Jet. Lateral stability is to stop the aircraft from sideslip.
By having dihedral (as mentioned in the answers) the lower wing in a sideslip will experience a greater angle of attack than the raised wing thus giving greater lift and regaining control of the aircraft so to speak.
… I think that makes sense?
A: Increases from Root to Tip
B: Decreases from Root to Tip
C: Gives Lateral Stability
D: Gives Directional Stability
I think A & B are there as to confuse you with washout. i.e. the angle decrease from root to tip in order to make the root of the wing stall before the tip an subsequently the ailerons aft of the wing tip leading edge.
So after disregarding A & B you’ll be left with C & D, basics of the Tec notes will tell you that the fin gives you directional stability (around the normal axis – movement is given by the rudder in a yaw motion).
So you’re only left with C and ‘Lateral Stability’ is gained by having dihedral as seen on most low wing aircraft, or adhedral as seen on some high wing aircraft like a BAe146 or a Harrier Jet. Lateral stability is to stop the aircraft from sideslip.
By having dihedral (as mentioned in the answers) the lower wing in a sideslip will experience a greater angle of attack than the raised wing thus giving greater lift and regaining control of the aircraft so to speak.
… I think that makes sense?
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I may be wrong here but doesn't the aircraft pitch about the lateral axis, roll about the longitudinal axis and yaw about the normal/vertical axis, dihedral therefore increases longitudinal stability not lateral stability? Therefore C can't be correct,Its been a while since i took the aero exam so like I said I may be wrong.
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And thinking about it all the question wants to know is that you know the difference between Anhedral and Dihedral, its one of those questions thats not worded the best. Dihedral means the tip is higher than the root, answer is A, C and D are there to trick.
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AVIATOR1982,
Bit of confusion here I think buddy!
Have a good think back to when you studied PoF, and hopefully you'll recall that -
In terminology used when discussing stability, you are referencing to the movement of an axis, not movement around an axis.
Hence lateral stability is the stability of the aeroplane in roll, i.e. when rolling the lateral axis is moving, whereas the longitudinal axis remains stationary. (Well ok, it's rolling too, bit think of what you can actually see moving.)
Lateral stability - Stability in roll.
Longitudinal stability - Stability in pitch.
I used to find it helpful to imagine the longitudinal axis like a boat. Smooth water and it's stable. Rough sea and it's unstable (longitudinally).
Hope this helps
Bit of confusion here I think buddy!
Have a good think back to when you studied PoF, and hopefully you'll recall that -
In terminology used when discussing stability, you are referencing to the movement of an axis, not movement around an axis.
Hence lateral stability is the stability of the aeroplane in roll, i.e. when rolling the lateral axis is moving, whereas the longitudinal axis remains stationary. (Well ok, it's rolling too, bit think of what you can actually see moving.)
Lateral stability - Stability in roll.
Longitudinal stability - Stability in pitch.
I used to find it helpful to imagine the longitudinal axis like a boat. Smooth water and it's stable. Rough sea and it's unstable (longitudinally).
Hope this helps
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I'm still sticking with 'C' but due to the question not being very detailed it could very well 'A' also. As you said the wing tip is higher than the root. 
I've been in a similar situation when doing PoF exam and it asked where the oil pressure sensor is situated in a dry sump engine. Knowing that you want to measure the pressure before it enters the engine it would need to be between the pump and engine. But answers were 'Outer side of the pump' or 'In-side of the pump'? Do you take it the oil pump is pumping the oil out to the engine or in to the engine?
I put the answer as In-side thinking outside would be the oil tank and filters etc. I had it wrong
The pump sucks the oil from the inside the tank and pushes it outside to the engine 
I've been in a similar situation when doing PoF exam and it asked where the oil pressure sensor is situated in a dry sump engine. Knowing that you want to measure the pressure before it enters the engine it would need to be between the pump and engine. But answers were 'Outer side of the pump' or 'In-side of the pump'? Do you take it the oil pump is pumping the oil out to the engine or in to the engine?
I put the answer as In-side thinking outside would be the oil tank and filters etc. I had it wrong
The pump sucks the oil from the inside the tank and pushes it outside to the engine
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I'm still sticking with 'C' on this one, reason being -
The way the question is phrased (if indeed the OP has copied it word for word), if you choose answer 'A', what you're saying effectively is that dihedral increases from root to tip. Not the height of the wing above the horizontal plane, but the dihedral. So you'd end up with a wing shaped like a banana, which in essence isn't completely incorrect. However, as somebody previously mentioned, the A380, and I'm sure other aeroplanes, displays polyhedral characteristics. On the ground, fully fuelled, I'm sure there's a measureable degree of anhedral, but once the wings are load bearing, this is transformed into dihedral.
So, in essence, if you take a very broad view of the wording in the question, A and B could both be considered correct, but are opposite answers and can therefore be disregarded.
Personally I think the question should be, very simply, 'C'! Certain words or phrases in aviation jump out hand in hand to me, and 'dihedral' and 'static lateral stability' are two of them!
The way the question is phrased (if indeed the OP has copied it word for word), if you choose answer 'A', what you're saying effectively is that dihedral increases from root to tip. Not the height of the wing above the horizontal plane, but the dihedral. So you'd end up with a wing shaped like a banana, which in essence isn't completely incorrect. However, as somebody previously mentioned, the A380, and I'm sure other aeroplanes, displays polyhedral characteristics. On the ground, fully fuelled, I'm sure there's a measureable degree of anhedral, but once the wings are load bearing, this is transformed into dihedral.
So, in essence, if you take a very broad view of the wording in the question, A and B could both be considered correct, but are opposite answers and can therefore be disregarded.
Personally I think the question should be, very simply, 'C'! Certain words or phrases in aviation jump out hand in hand to me, and 'dihedral' and 'static lateral stability' are two of them!
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Dihedral
Dihedral is the V shape formed when looking at the wings from the front so the dihedral would increase from the wing root to the tip. The opposite in aircraft wing is Anhedral and the Anhedral would decrease from wing root to wingtip.
I believe Mad(flt)Scientist expanded considerably on this subject a while ago,...but the short answer is 'helps the plane recover from side slip'=="lateral stabilty",..but in terms of pure geometry it's A V-shaped the legs on the V go-up
is this a trick question
is this a trick question
Last edited by Pugilistic Animus; 30th Oct 2009 at 19:01.
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I can see your point, but am misunderstanding something here -
If the answer is in fact 'A', I still think it's very badly worded - the dihedral does not increase from root to tip, it is the distance of the wing segment from the horizontal plane of the aircraft that increases with increasing distance from the root (in the case of dihedral).
Dihedral (or anhedral), is simply an expression for the angle formed between the wing and the lateral axis.
Or can somebody correct me?
If the answer is in fact 'A', I still think it's very badly worded - the dihedral does not increase from root to tip, it is the distance of the wing segment from the horizontal plane of the aircraft that increases with increasing distance from the root (in the case of dihedral).
Dihedral (or anhedral), is simply an expression for the angle formed between the wing and the lateral axis.
Or can somebody correct me?
http://www.pprune.org/tech-log/30735...light=anhedral
actually this guy does it better than me but I mean 'lateral stabilty' more in ol' colloquial pilot horse hooey whereas MFS is talking like an experienced engineer
except further discussion of roll helix angle and acceptable/ unacceptable roll stabilty is in order
PA
actually this guy does it better than me
but I mean 'lateral stabilty' more in ol' colloquial pilot horse hooey whereas MFS is talking like an experienced engineerexcept further discussion of roll helix angle and acceptable/ unacceptable roll stabilty is in order
PA
