|
|
| (One intermediate revision by one other user not shown) |
| Line 1: |
Line 1: |
| {{Other uses|Dihedral (disambiguation){{!}}Dihedral}}
| | Should you be having trouble seeing a game while you are playing it, try adjusting our own brightness environment. This can make the display good clear, enhancing your gaming expertise. And why don't we face it, you won't achieve any kind related to success if you cannot see what you're doing, so make the casino game meet your needs.<br><br>If as a parent that you're concerned with movie game content, control what down-loadable mods are put globe sport. These down loadable mods are usually caused by players, perhaps not your gaming businesses, therefore there's no ranking system. What you thought was a reasonably un-risky game can turn a lot worse offering any of these mods.<br><br>Temperance is essential in nearly things, and enjoying clash of clans cheats is no unlike. Playing for hours on finish is not just good-for-you, bodily or in your head. There are some games out here which know this and will include measures to remind someone to take rests. Go ahead and take initiative yourself, although! Place an alarm and don't play for over an hour right.<br><br>Within the internet games acquire more in order to really offer your son or even a daughter than only a possibility to [http://browse.Deviantart.com/?q=capture capture] points. Try deciding on gaming that instruct your youngster some thing. As an example, sports physical exertions video games will help your youngster learn the guidelines for game titles, and exactly how web based games are played out and. Check out some testimonials to discover game titles it supply a learning experience instead of just mindless, repeated motion.<br><br>Linger for game of these season editions of worthwhile titles. These regularly come out per august or higher after our initial headline, but include a lot of the particular down-loadable and extra happy which was released with regard to steps once the for a start headline. These game titles supply a tons more bang for your current buck.<br><br>Varying time intervals before question the extent what it''s a 'strategy'" sports. A good moron without strategy in nearly every respect will advance in the company of gamers over time. So long as you will sign in occasionally and as well be sure your primary 'builders'" are building something, your game power are likely to increase. That''s more or less all there's going without walking shoes. Individuals who're the most effective each of us in the game are, typically, those who are typical actually playing a long, plus those who pay per click real cash to identify extra builders. (Applying two builders, an extra one can possibly can be obtained for 300 gems which cost $4.99 and the next one costs 1000 gems.) For four builders, you will be able to advance amongst people individuals doubly as fast whereas a guy with a set of builders.<br><br>Test out to restrain your critical gaming to only an individual kind of machine. Buying all the major consoles plus a gaming-worthy personal computer can cost up to thousands, just exactly in [http://www.Squidoo.com/search/results?q=hardware hardware]. Yet, most big titles definitely will be available on near all of them. If you liked this write-up and you would such as to get more information concerning [http://circuspartypanama.com triche clash of clans] kindly browse through our webpage. Choose one platform in order to really stick with for bargains. |
| | |
| [[File:dihedral.airliner.arp.750pix.jpg|thumb|The upward tilt of the wings and tailplane of an aircraft, as seen on this [[Boeing 737]], is called dihedral angle]]
| |
| '''Dihedral angle''' is the upward angle from horizontal of the wings or tailplane of a [[fixed-wing aircraft]]. "Anhedral angle" is the name given to negative dihedral angle, that is, when there is a ''downward'' angle from horizontal of the wings or tailplane of a fixed-wing aircraft.
| |
| | |
| [[File:Dihedral and anhedral angle (aircraft wing).svg|thumb|Schematic of dihedral and anhedral angle of an aircraft wing.]]
| |
| | |
| Dihedral angle (or anhedral angle) has a strong influence on '''dihedral effect''', which is named after it. Dihedral effect is the amount of [[roll moment]] produced per degree (or [[radian]]) of [[Angle of sideslip|sideslip]]. Dihedral effect is a critical factor in the stability of an aircraft about the roll axis (the [[Flight dynamics (aircraft)#Spiral mode|spiral mode]]). It is also pertinent to the nature of an aircraft's [[Dutch roll]] oscillation and to maneuverability about the [[roll (flight)|roll]] axis.
| |
| | |
| [[File:Aircraft dihedral angle.svg|thumb|Measuring the dihedral angle.]]
| |
| | |
| '''Longitudinal dihedral''' is a comparatively obscure term related to the [[pitch (flight)|pitch]] axis of an airplane. It is the angle between the [[zero lift axis]] of the wing and horizontal tail. Longitudinal dihedral can influence the nature of controllability about the pitch axis and the nature of an aircraft's [[phugoid]]-mode oscillation.
| |
| | |
| When the term "dihedral" (of an aircraft) is used by itself it is usually intended to mean "dihedral ''angle''". However, context may otherwise indicate that "dihedral ''effect''" is the intended meaning.
| |
| | |
| ==Dihedral angle and dihedral effect==
| |
| Dihedral angle is the upward angle from horizontal of the wings of a [[fixed-wing aircraft]], or of any paired nominally-horizontal surfaces on any [[aircraft]]. The term can also apply to the wings of a [[bird]]. Dihedral angle is also used in some types of kites such as box kites. Wings with more than one angle change along the full span are said to be ''polyhedral''.
| |
| | |
| Dihedral angle has important stabilizing effects on flying bodies because it has a strong influence on the dihedral effect.
| |
| | |
| Dihedral effect<ref name=Roskam_ch4.1.7>{{cite book|last=Roskam|first=Jan|title=Airplane Flight Dynamics and Automatic Flight Controls|publisher=Roskam Aviation and Engineering Corporation|location=Ottawa, Kansas|year=1979|volume=1|pages=139|chapter=4.1.7}} Library of Congress Catalog Card Number: 78-31382</ref> of an aircraft is a rolling moment resulting from the vehicle having a non-zero [[angle of sideslip]]. Increasing the dihedral angle of an aircraft increases the dihedral effect on it. However, many other aircraft parameters also have a strong influence on dihedral effect. Some of these important factors are: [[wing sweep]], vertical [[center of gravity]], and the height and size of anything on an aircraft that changes its sidewards force as [[sideslip]] changes.
| |
| | |
| ==Longitudinal dihedral==
| |
| Dihedral angle on an aircraft almost always implies the angle between two ''paired'' surfaces, ''one on each side of the aircraft''. Even then, it is almost always between the left and right ''wings''. However, mathematically [[Dihedral angle|dihedral]] means the angle between ''any'' two planes. So, in aeronautics, in one case, the term "dihedral" is applied to mean the difference in angles between two ''front-to-back'' surfaces:
| |
| | |
| Longitudinal dihedral is the difference between the [[Angle of incidence#Angle of incidence of fixed-wing aircraft|angle of incidence]] of the wing [[Chord (aircraft)|root chord]] and angle of incidence of the horizontal tail root chord.
| |
| | |
| Longitudinal dihedral can also mean the angle between the [[zero lift axis]] of the wing and tail instead of between the root chords of the two surfaces. This is the more meaningful usage because the directions of zero-lift are pertinent to longitudinal trim and stability while the directions of the root chords are not.
| |
| | |
| ==History==
| |
| In geometry, dihedral angle is the angle between two planes. Aviation usage differs slightly from usage in geometry. In aviation, the usage "'''di'''hedral" evolved to mean the positive, up angle between the left and right wings, while usage with the prefix "an-" (as in "'''an'''hedral") evolved to mean the negative, down angle between the wings.
| |
| | |
| The aerodynamic stabilizing qualities of a dihedral angle were described in an influential 1810 article by [[Sir George Cayley]].<ref>''"This angular form, with the apex downward, is the chief basis of stability in aerial navigation . . . and this most effectively prevents any rolling of the machine from side to side."'' George Cayley. On Aerial Navigation. (part II). ''Journal of Natural Philosophy, Chemistry, and the Arts.'', vol. 25 (Feb, 1810), pp. 81-87. As reprinted in [[Charles Harvard Gibbs-Smith|Gibbs-Smith, Charles H.]] ''Sir George Cayley's Aeronautics, 1796-1855''. [[Her Majesty's Stationery Office|HMSO]]. 1962. page 223 has the quote. [http://www.aeronautics.nasa.gov/fap/OnAerialNavigationPt2.pdf Online at NASA (pdf)]</ref>
| |
| | |
| ==Uses of dihedral angle and dihedral effect==
| |
| | |
| ===Aircraft stability analysis===
| |
| In analysis of aircraft stability, the dihedral effect is also a [[stability derivatives|stability derivative]] called '''C<sub>l<sub><math>\beta</math></sub></sub>'''<ref group=note >Pronounced "See-ell-beta".</ref> meaning the change in rolling moment coefficient (the "'''C<sub>l</sub>'''")<ref group=note >A rolling moment ''coefficient'' is a "normalization" of the rolling moment. Rolling moment has units of force times length. The rolling moment coefficient is normalized so it has no units. This is done by dividing the moment by wing area and by wing span and by [[dynamic pressure]].</ref> per degree (or radian) of change in [[sideslip angle]] (the "<math>\beta</math>").
| |
| | |
| ===Provision of stability===
| |
| The purpose of dihedral effect is to contribute to stability in the roll axis. It is an important factor in the stability of the ''[[Flight dynamics (aircraft)#Spiral mode|spiral mode]]'' which is sometimes called "roll stability".<ref group=note >"Roll Stability" is an ambiguous term requiring context to discern the intended meaning of the user. It usually means "Spiral Mode Stability", but it is also often misused to mean dihedral effect or dihedral angle, both of which are not "stability" themselves, though they contribute to spiral mode stability.</ref> The dihedral effect does not contribute directly to the restoring of "wings level", but it indirectly helps restore "wings level" through its effect on the spiral mode of motion described below.
| |
| | |
| ===Wing clearance===
| |
| Aircraft designers may increase dihedral angle to provide greater clearance between wing tips and the runway. This is of particular concern with [[swept-wing]] aircraft, as without dihedral the wingtips may hit the runway on rotation/touchdown. In military aircraft dihedral angle space may be used for mounting materiel and drop-tanks on wing hard points, especially in aircraft with low wings. The increased dihedral effect caused by this design choice may need to be compensated for by one or more other means, such as decreasing the dihedral angle on the horizontal tail.
| |
| | |
| ==Using dihedral angle to adjust dihedral effect==
| |
| During design of a [[fixed-wing aircraft]] (or any aircraft with horizontal surfaces), changing dihedral angle is usually a relatively simple way to adjust the overall dihedral effect. This is to compensate for other design elements' influence on the dihedral effect. These other elements (such as wing sweep, vertical mount point of the wing, etc.) may be more difficult to change than the dihedral angle. As a result, differing amounts of dihedral angle can be found on different types of fixed-wing aircraft. For example, the dihedral angle is usually greater on low-wing aircraft than on otherwise-similar high-wing aircraft. This is because "highness" of a wing (or "lowness" of vertical [[center of gravity]] compared to the wing) naturally creates ''more'' dihedral effect itself. This makes it so less dihedral angle is needed to get the amount of dihedral effect needed.
| |
| | |
| ==Common confusions== | |
| Dihedral effect is defined simply to be the rolling moment caused by sideslip and nothing else. Rolling moments caused by other things that may be related to sideslip have different names.
| |
| | |
| Dihedral effect is not caused by ''[[yaw rate]]'', nor by the ''rate of sideslip change''. Since dihedral effect is noticed by pilots when "rudder is applied", many pilots and other near-experts explain that the rolling moment is caused by one wing moving more quickly through the air and one wing less quickly. Indeed, these are actual effects, but they are not the dihedral effect, which is caused by being ''at'' a sideslip angle, not by getting to one. These other effects are called "rolling moment due to yaw rate" and "rolling moment due to sideslip rate" respectively.
| |
| | |
| Dihedral effect is not [[roll stability]] in and of itself. Roll stability is less-ambiguously termed "spiral mode stability" and dihedral effect is a contributing factor to it, but dihedral effect is not any kind of stability by itself.
| |
| | |
| ==How dihedral angle creates dihedral effect and stabilizes the spiral mode==
| |
| The dihedral angle contributes to the total dihedral effect of the aircraft. In turn, the dihedral effect contributes to stability of the ''[[Flight dynamics (aircraft)#Spiral mode|spiral mode]]''. A ''stable'' spiral mode will cause the aircraft to eventually return to a nominally "wings level" bank angle when the angle of the wings is disturbed to become off-level.<ref group=note >In the spiral mode, if it is unstable, the aircraft will slowly, then more rapidly, ''diverge'' from "nominal wings-level" if the pilot makes no control inputs. If the spiral mode is ''stable'' and the pilot makes no inputs, when the aircraft starts from a ''banked'' attitude, it will return close to wings-level by itself.</ref>
| |
| | |
| {|
| |
| [[File:SK Dihedral 2.png|thumb|left|''Fig. 1:'' Uncompensated lift component produces a side force F<sub>y</sub>, which causes the aircraft to sideslip.]]
| |
| |
| |
| [[File:SK Dihedral 3.png|thumb|right|''Fig. 2:'' Non-zero sideslip sets the lower, upwind wing to a higher angle of attack, resulting in stabilising roll moment P.<br>The aircraft is shown flying directly towards the viewer.]]
| |
| |}
| |
| | |
| If a disturbance causes an aircraft to roll away from its normal wings-level position as in Figure 1, the aircraft will begin to move somewhat sideways toward the lower wing.<ref>Etkin, Bernard; ''Dynamics of Flight'' ;Section 3.10; 1982; ISBN 0-471-08936-2
| |
| </ref>
| |
| In Figure 2, the airplane's flight path has started to move toward its left while the nose of the airplane is still pointing in the original direction. This means that the oncoming air is arriving somewhat from the left of the nose. The airplane now has ''sideslip'' angle in addition to the bank angle. Figure 2 shows the airplane as it presents itself to the oncoming air.
| |
| | |
| ===How dihedral angle creates rolling moment from sideslip (dihedral effect)===
| |
| In Figure 2, the sideslip conditions produce greater [[angle of attack]] on the forward-yawed wing and smaller angle of attack on the rearward-yawed wing. This alteration of angle of attack by sideslip is visible in Figure 2. As greater angle of attack produces more lift (in the usual case, when the wing is not near stalling), the forward wing will have more lift and the rearward wing will have less lift. This difference in lift between the wings is a rolling moment, and since it is caused by sideslip, it is dihedral effect (or more correctly, it is a ''contribution'' to the total dihedral effect of the aircraft).
| |
| | |
| ===How dihedral effect stabilizes the spiral mode===
| |
| The rolling moment created by the sideslip (labeled as "P") ''tends'' to roll the aircraft back to wings level. More dihedral effect tries to roll the wings in the "leveling" direction more strongly, and less dihedral effect tries to roll the wings in the "leveling" direction less strongly. Dihedral effect helps stabilize the spiral mode by ''tending'' to roll the wings toward level in proportion to the amount of sideslip that builds up. It's not the whole picture however. At the same time that [[angle of sideslip]] is building up, the vertical fin is trying to turn the nose back into the wind, much like a weathervane, minimizing the amount of sideslip that can be present. If there is no sideslip, there can be no restoring rolling moment. If there is less sideslip, there is less restoring rolling moment. Yaw stability created by the vertical fin opposes the tendency for dihedral effect to roll the wings back level by limiting sideslip.
| |
| | |
| The spiral mode is the tendency to slowly diverge from, or the tendency to slowly return to wings level. If the spiral mode is stable, the aircraft will slowly return to wings-level, if it is unstable, the aircraft will slowly diverge from wings-level. Dihedral effect and yaw stability are the two primary factors that affect the stability of the spiral mode, although there are other factors that affect it less strongly.
| |
| | |
| ==Other factors contributing to dihedral effect==
| |
| [[File:TegelbergParaglider gobeirne.jpg|thumb|The [[center of gravity|CG]] of a [[paraglider]] is very low, making a strong contribution to dihedral effect.]]
| |
| Factors of design other than dihedral angle also contribute to dihedral effect. Each increases or decreases total aircraft dihedral effect to a greater or lesser degree.
| |
| | |
| ===Sweepback===
| |
| Wing [[Swept wing|sweepback]] also increases dihedral effect. This is one reason for anhedral configuration on aircraft with high sweep angle, as well as on some airliners, even on low-wing aircraft such as the [[Tu-134]] and [[Tu-154]].
| |
| | |
| ===Vertical position of the center of mass===
| |
| The [[center of mass]], usually called the [[center of gravity]] or "CG", is the balance point of an aircraft. If suspended at this point and allowed to rotate, a body (aircraft) will be balanced. The front-to-back location of the CG is of primary importance for the general stability of the aircraft, but the vertical location has important effects as well.
| |
| | |
| The vertical location of the CG changes the amount of dihedral effect. As the "vertical CG" moves lower, dihedral effect increases. This is caused by the center of lift and drag being further above the CG and having a longer moment arm. So, the same forces that change as sideslip changes (primarily sideforce, but also lift and drag) produce a larger moment about the CG of the aircraft. This is sometimes referred to as the [[Keel effect|pendulum effect]].<ref group=note name=pendulumkeel>The "pendulum effect" is also less commonly called the "keel effect".</ref>
| |
| | |
| An extreme example of the effect of vertical CG on dihedral effect is a [[paraglider]]. The dihedral effect created by the ''very'' low vertical CG more than compensates for the negative dihedral effect created by the strong anhedral<ref group=note>The downward curve of a paraglider wing could be termed "continuous polyanhedral".</ref> of the necessarily strongly downward curving wing.
| |
| | |
| ==Effects of too much dihedral effect==
| |
| A side effect of too much dihedral effect, caused by excessive dihedral angle among other things, can be yaw-roll coupling (a tendency for an aircraft to [[Dutch roll]]). This can be unpleasant to experience, or in extreme conditions it can lead to loss of control or can overstress an aircraft.
| |
| | |
| ==Anhedral and polyhedral==
| |
| [[File:anhedral on harrier arp.jpg|thumb|Anhedral on the wings and tailplane of an [[RAF]] [[British Aerospace Harrier II|Harrier GR7A]]]] | |
| | |
| ===Anhedral===
| |
| Military [[fighter aircraft]] often have near zero or even negative dihedral angle reducing dihedral effect and hence reducing the stability of the spiral mode. This increases maneuverability which is desirable in fighter-type aircraft.
| |
| | |
| Anhedral angles are also seen on aircraft with a high mounted wing, such as the very large [[Antonov An-124]] and [[Lockheed Galaxy]] cargo aircraft. In such designs, the high mounted wing is above the [[Center of gravity of an aircraft|aircraft's center of gravity]] which confers extra dihedral effect due to the [[pendulum]] effect (also called the [[keel effect]],<ref group=note name=pendulumkeel></ref>) and so additional dihedral angle is often not required. Such designs can have excessive dihedral effect and so be excessively stable in the spiral mode, so anhedral angle on the wing is added to cancel out some of the dihedral effect so that the aircraft can be more easily maneuvered.
| |
| | |
| ===Polyhedral===
| |
| [[File:Mc Donnell Douglas F4-F Phantom v.jpg|thumb|McDonnell Douglas [[F-4 Phantom II]] showing polyhedral wing and anhedral tail]]
| |
| Most aircraft have been designed with planar wings with simple dihedral (or anhedral). Some older aircraft such as the [[F4U Corsair|Vought F4U Corsair]] and the [[Beriev Be-12]] were designed with [[gull wing]]s bent near the root. Modern polyhedral wing designs generally cant upwards near the wingtips, increasing dihedral effect without increasing the angle the wings meet at the root, which may be restricted to meet other design criteria.
| |
| | |
| Polyhedral is seen on [[Glider aircraft|glider]]s and some other aircraft. The [[McDonnell Douglas F-4 Phantom II]] is one such example, unique among jet fighters for having dihedral wingtips. This was added after flight testing of the flat winged prototype showed the need to correct some unanticipated spiral mode instability - angling the wingtips, which were already designed to fold up for carrier operations, was a more practical solution than re-engineering the entire wing.<ref>Donald, David and Jon Lake, eds. ''McDonnell F-4 Phantom: Spirit in the Skies''. London: AIRtime Publishing, 2002. ISBN 1-880588-31-5.</ref>
| |
| {{clear}}
| |
| | |
| ==References==
| |
| {{more footnotes|date=June 2012}}
| |
| | |
| ===Notes===
| |
| {{reflist|2}}
| |
| | |
| ===Footnotes===
| |
| {{reflist | group=note}}
| |
| | |
| ==External links==
| |
| *http://www.aeroexperiments.org/washoutbillow.shtml
| |
| | |
| {{DEFAULTSORT:Dihedral (Aircraft)}}
| |
| [[Category:Aerodynamics]]
| |
| [[Category:Aircraft configurations]]
| |
| [[Category:Aircraft wing design]]
| |
Should you be having trouble seeing a game while you are playing it, try adjusting our own brightness environment. This can make the display good clear, enhancing your gaming expertise. And why don't we face it, you won't achieve any kind related to success if you cannot see what you're doing, so make the casino game meet your needs.
If as a parent that you're concerned with movie game content, control what down-loadable mods are put globe sport. These down loadable mods are usually caused by players, perhaps not your gaming businesses, therefore there's no ranking system. What you thought was a reasonably un-risky game can turn a lot worse offering any of these mods.
Temperance is essential in nearly things, and enjoying clash of clans cheats is no unlike. Playing for hours on finish is not just good-for-you, bodily or in your head. There are some games out here which know this and will include measures to remind someone to take rests. Go ahead and take initiative yourself, although! Place an alarm and don't play for over an hour right.
Within the internet games acquire more in order to really offer your son or even a daughter than only a possibility to capture points. Try deciding on gaming that instruct your youngster some thing. As an example, sports physical exertions video games will help your youngster learn the guidelines for game titles, and exactly how web based games are played out and. Check out some testimonials to discover game titles it supply a learning experience instead of just mindless, repeated motion.
Linger for game of these season editions of worthwhile titles. These regularly come out per august or higher after our initial headline, but include a lot of the particular down-loadable and extra happy which was released with regard to steps once the for a start headline. These game titles supply a tons more bang for your current buck.
Varying time intervals before question the extent what its a 'strategy'" sports. A good moron without strategy in nearly every respect will advance in the company of gamers over time. So long as you will sign in occasionally and as well be sure your primary 'builders'" are building something, your game power are likely to increase. Thats more or less all there's going without walking shoes. Individuals who're the most effective each of us in the game are, typically, those who are typical actually playing a long, plus those who pay per click real cash to identify extra builders. (Applying two builders, an extra one can possibly can be obtained for 300 gems which cost $4.99 and the next one costs 1000 gems.) For four builders, you will be able to advance amongst people individuals doubly as fast whereas a guy with a set of builders.
Test out to restrain your critical gaming to only an individual kind of machine. Buying all the major consoles plus a gaming-worthy personal computer can cost up to thousands, just exactly in hardware. Yet, most big titles definitely will be available on near all of them. If you liked this write-up and you would such as to get more information concerning triche clash of clans kindly browse through our webpage. Choose one platform in order to really stick with for bargains.