Warning! This site requires Javascript. Learn how to enable it here.

Anhedral Wings :: Detailed explanations of anhedral plane designs

Discussion in 'Scratchbuild Talk' started by Dredogol, Feb 15, 2009.

  1. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    This post will be dedicated to ALL information related to Anhedral planes!

    I will be doing the first installment of information for this post, then Dave and other members can add to this post.
    All useful information gathered in this topic will be updated and copied to the top of this page. There will be a date-stamp to let everyone know when this top post was last updated.
    (Last updated: Feb 16, 2009)



    ========== PAGE 01 ==========

    Contnets:
    1) What is an Anhedral wing?
    2) Why use anhedral wing designs?
    2_Q1) What is the "Keel Effect", and how does anhedral help?
    2_Q2) Why do most cargo-planes have their wings so high up?
    2_Q3) What is the reason for anhedral wings on military fighter jets?
    2_Q4) Do "swept-back wings" have anything to do with anhedral wings?
    2_Q5) What is a "Dutch Roll", and how does anhedral prevent it?
    2_Q6) ?
    3) Does my plane design require anhedral wings?



    Section 01 -- What is an Anhedral wing?
    For detailed information on what anhedral is, please click on the link below, and proceed to Section #18 where we explain what anhedral is:
    http://www.rcpowers.com/forum/showthread.php?t=91/



    Section 02 -- Why use anhedral wing designs?
    If you read Section 01, you should have a general idea as to when to use dihedral and anhedral wing designs. However, you may not fully understand the real practical use of anhedral wings. To fully understand and appreciate the anhedral wing design, we will list several issues in aviation today, and see how anhedral helps solve these issues.

    Q)What is the "Keel Effect", and how does anhedral help?
    A) The Keel effect (aka Pendulum Effect) is when the aircraft naturally wants to resist banking (rolling out of level wings condition). When the plane banks its lift force vector diverges from vertical to one side which causes a side force and the plane starts to side-slip. If the wings are mounted above the CG the sideways drag component of the wings creates a roll torque that tries to level the wings. To prevent this condition, aeronautical engineers decided to angle the wings downward. When the plane begins to bank and side-slip the wing which is rising upwards has a greater angle of attack compared to the lowering wing. This causes the rising wing to produce more lift and in the case of high mounted wings counteract the tendency to automatically level the wings.


    Q)Why do most cargo-planes have their wings so high up?
    A)
    Since cargo planes are so large and heavy, they need a lot of engines to produce sufficient thrust to stay in the air. All heavy cargo planes require at least 4-engines to keep them airborne, so they must be placed below the wings (space reasons). Because of all the excess weight on the wings of the plane, they require several feet of wing flex (up and down) to prevent them from breaking. If the wings are not placed high enough, the wing flex would cause the engines to slam into the ground during landings. This is the main reason why cargo planes have their wings so high up on the fuselage.
    C-17 ::
    http://upload.wikimedia.org/wikipedia/commons/3/36/C17_aircraft_alt.jpg
    AN-225 :: http://www.thetoptenblog.com/wp-content/uploads/2007/10/antonov-an-225.jpg


    Q)What is the reason for anhedral wings on military fighter jets?
    A)
    Unlike heavy cargo planes, fighter jets are actually fairly light, produce a lot of thrust, and highly maneuverable. There is no real need for the plane to have anhedral wings to better stabilize it. The reason fighter jets incorporate anhedral wing designs is to make them MORE unstable then what they already are. To win a dogfight against another plane, it needs to be more maneuverable than the other. This means faster turn and climb rates to get behind the other plane quicker. By adding anhedral wings, it allows the plane to bank (roll) much faster, thus increasing maneuverability.
    Harrier ::
    http://www.richard-seaman.com/Aircraft/AirShows/Yuma2005/Flying/HarrierNearGround.jpg
    F-22A :: http://www.aetc.af.mil/shared/media/ggallery/hires/AFG-060705-005.jpg


    Q)Do "swept-back wings" have anything to do with anhedral wings?
    A)
    Actually, the answer is YES! The MORE swept-back a wing is (more 'V' shape it has), the more stable the plane becomes on the ROLL axis. The spanwise flow (flow component along the chord; doesn't produce lift) on a swept back wing is directed outwards and it increases towards the tip. Side-slip caused by banking decreases spanwise flow on the lower wing and increases it on the higher one and the lift difference tries to level the wings..
    [​IMG] _ [​IMG]


    Q) What is a "Dutch Roll", and how does anhedral prevent it?
    A) Dutch roll is a particular aircraft movement, where it does 3 different things: 1) Tail yaws back and forth, 2) Plane rolls back and forth, 3) Plane pitches and rolls in a circular shape. This condition is not very noticeable on small and light aircrafts, but become more apparent in larger and heavier ones. For larger aircraft, this condition is more noticeable at lower air-speeds. If wings are place very high on the fuselage (wings above CG), have very high swept-back angles, and/or have dihedral angled wings, they all increase the effect of Dutch Roll. Below are the steps in which dutch roll occur:
    1) Low directional stability (tendency for plane to align itself with direction of motion) causes a slide-slip (aka fish-tail effect).
    2) High lateral stability (tendency for plane to reduce current motion) restores plane back to level flight.
    3) Low directional stability again attempts to correct current slide-slip with new lateral stability corrections.
    4) Lag in correction time causes the tail to slip sideways, and the roll angle of the plane to oscillate.
    Student pilots are taught various techniques to help them avoid this common condition. So, to help avoid this condition, engineers implement some form of anhedral to planes which are likely to have this condition to occur on a regular basis.
    Wikipedia :: http://en.wikipedia.org/wiki/Dutch_roll/




    Q) ?
    A) x



    Section 03 -- Does my plane design require anhedral wings?
    x




    -- I hope members who are new to airplanes find this information useful.
    -- If you find any errors, please let me know, and I will fix them.
  2. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    (Last updated: Feb 15, 2009)

    ==========
    PAGE 02 ==========

    Contents:
    x)
    x)
    x)

  3. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    (Last updated: Feb 15, 2009)

    ==========
    PAGE 03 ==========

    Contents:
    x)
    x)
    x)

  4. DevinDude

    DevinDude Rookie

    Posts:
    30
    Likes:
    0
    Points:
    0
    Heres a link of a dutch roll.

  5. DevinDude

    DevinDude Rookie

    Posts:
    30
    Likes:
    0
    Points:
    0
    This excerpt talks about the F-4's complex dihedral/tail anhedral set up.

    Wind tunnel testing had revealed lateral instability requiring the addition of five degrees dihedral to the wings.[28] To avoid redesigning the titanium central section of the aircraft, McDonnell engineers angled up only the outer portions of the wings by 12 degrees which averaged to the required five degrees over the entire wingspan. The wings also received the distinctive "dogtooth" for improved control at high angles of attack. The all-moving tailplane was given 23 degrees of anhedral to improve control at high angles of attack while still keeping the tailplane clear of the engine exhaust"

    http://74.125.47.132/search?q=cache...-F.htm nasa anhedral&hl=en&ct=clnk&cd=1&gl=us
  6. F-111A John

    F-111A John Cadet

    Posts:
    144
    Likes:
    2
    Points:
    18
    The reason why cargo aircraft have their wings so high up is because they need to have the entire fuselage open for cargo. There is a very large structure called the wing box that transfers the loads from the fuselage to the wings, and one or more main wing spars that pass from one wing to the other.

    Were the wings near the middle of the fuselage, this would put the wing box and spar in the middle of the cargo hold area. On most commercial jetliners, the wings are in the lower third of the fuselage, and indeed cuts the lower cargo hold into two sections, but leaves the upper two thirds of the fuselage open for passenger seating.

    For most cargo aircraft, there is no 'lower hold', the cargo load floor being almost at the bottom of the fuselage. So this leaves only two places to place the wings: Either under the fuslage, or on top of the fuselage.

    If the wings were mounted under the fuselage, then the aircraft would have to be mounted on tallish landing gear to clear the engines hanging underneath.

    For rear ramp equipped cargo aircraft, it is advantageous to have the load floor of the aircraft as close to the ground as possible, so the ramp angle isn't too great for roll on-roll off cargo. This leaves only one possibility for placing the wings: On top of the aircraft.

    Every cargo aircraft with a rear loading ramp, from the small Shorts C-23 Sherpa two engine turboprop to the giant Antonov An-225 six engine turbofan aircraft have high mounted wings, and for the same reason; to maximize cargo volume within the fuselage, and minimize cargo load floor height.
Similar Threads
Forum Title Date
Scratchbuild Talk F4 rear Elevator design (why it's anhedral) Mar 2, 2009
Scratchbuild Talk F-4 Phantom Anhedral Horizontal Tail Mar 1, 2009
Scratchbuild Talk Alpha Jet--high alpha, hovering, no rocking wings Apr 30, 2013
Scratchbuild Talk below one wingspan Apr 13, 2013
Scratchbuild Talk Maiden flight of a 5,5m wingspan SB-10 Feb 25, 2013
Scratchbuild Talk Hawk sky speed wings Aug 19, 2012

Share This Page

string(1) "1"