Dihedral

[Ministry_Cork]

All,
A question that has come up in preperation for the ppl exams:

Wing Dihedral
A: Increases from Root to Tip
B: Decreases from Root to Tip
C: Gives Lateral Stability
D: Gives Directional Stability

My understanding is that dihedral gives lateral stability and therfor C should be correct however the correct answer has been given as A. I cannot find any reference to wing dihedral increasing from root to tip as i would assume (probably incorrectly) that the wing angle remains almost contstant from root to tip with referene to the horizontal on light aircraft? Looking at the A380 however it looks like dihedral decreases from root to tip?

Does anyone have a clear definition of Dihedral with specific reference to the anlges?


Thanks in advanace.
M

[Re-Heat]

Wikipedia has a very detailed entry.

http://en.wikipedia.org/wiki/Dihedral_(aircraft)

[Ministry_Cork]

Thanks Re-Heat,
As detailed as it is however it cannot answer the question.

[olliew]

The definition of dihedral as according to L.J. Clancys Aerodynamics is: 'The angle between the plane of each wing and the horizontal'. I would consider your question source as answer C is correct.

[Lightning Mate]

...."in preperatipon for the ppl exams"....

good grief.....

[Re-Heat]

Well, it does answer it indirectly if you read through it - you're not going to find the answer printed directly on a website anywhere!

Think about how it resolves minor upset flight and the mechanics of it doing so.

[GOLF_BRAVO_ZULU]

How about keeping it simple as per AP3456?

Vol 1, Pt 1, Sect 1, Ch 14:

73. The factors affecting static lateral stability are:
a. Wing contributions due to:
(1) Dihedral.
(2) Sweepback

The answer option A would give a dihedral angle that increased towards the tip; so the wing would curve up. Option B would be a curve in the opposite direction. You don't see many aeroplanes with either characteristic.

The question was probably written by a Quantity Surveyor with English as a second language.

[Ministry_Cork]

Thanks re-heat, but i find the following site addresses the questions in my initial post more accurately. i.e it discussus the angle of dihedral.


Airfield Models - Calculating the Dihedral of a Wing

[Ministry_Cork]

Thanks GBZ, thats exactly what i was thinking, and why i mentioned the A380, if you look at it head on it appears that the angle of the wing with reference to the horizontal reduces from root to tip.?

[Ministry_Cork]

Maybe a little too complex for ppl level Lightning - I suppose its really in prep for the ATPLs but need to get these out of the way first :-)

[ClippedCub]

Wings deform under one g load once airborne. On the ground, the A380 appears to sag, but aerodynamically, once airborne, under one g, the wing bows upward. That's what is felt by the airplane in operation, producing 'C'.

[Ministry_Cork]

Thansk CC, it seems that wing Dihedral is an angle raising the centerline of the wing tip above the centerline of the wing root. It can also be expressed as a measurement of length. given this definition it seems that any curve of the wing is irrelevant as the measurement is from root to tip and alonh the horizontal - a diagram for which would produce a triangle. then wingspan * sin of the angle gives the valiue for dihedral. If i come across the question in the exams i think i will go with - "Gives lateral stability"


Thanks for your input.

[wheelbrace]

Are you-understandably-thinking too much into the question?

I would take this question at face value - it is asking what wing dihedral is, not its effect. The wikipedia reference answers the former and (maybe unhelpfully?) expands on it to explain the latter. Look up anhedral for the reverse.

Just a thought. As for ATPL preparation, you will need a first class degree(with Hons.) in second guessing and bull**** before even contemplating opening that shiny package from BGS

[Ministry_Cork]

Wheelbrace - looking formward to that shiny package and yes, it will indeed be from BGS but not for 12 months or so. are you saying you would go with A or C then?

[Lightning Mate]

Ministry Cork,

Which book is giving you that answer?
I teach this stuff to ATPL and university degree level, and some of the books out there do give incorrect answers.

Dihedral is a contributing factor in static and dynamic lateral stability.

LM

[Ministry_Cork]

Lightning Mate,
It was given to me by my instructor in a sample paper so i do not know the source- i havent looked through any of the books for that specific question yet. not to drift off the subject but tere were a few ambiguous questipons in there e.g what advantge does an alternator offer over a generator? two of the possible answers were a: its lighter b: it produces power at low rpm. I answered b but was told that in fact a was correct.

We were told that there will be a few questions in the real exam like this where they could be as GBZ said earlier "probably written by a Quantity Surveyor with English as a second language." While im confident that i understand the subject i am inclined to agree and move on. but having said that i think i will make good use of the note paper in the exam if i come across such questions!

M

[Re-Heat]

It is possible for it to do either A or B depending upon design, so they are clearly not the answer. The answer is C.

[ClippedCub]

B: Decreases from Root to Tip

Is termed Anhedral.

[Re-Heat]

No, ClippedClub - it is polyhedral (though likely to be anhedral at the root, I admit...), as is A. See a 777 wing in flight for example.

[ClippedCub]

though likely to be anhedral

Based on high wing transports.