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

Forward Swept Wings :: History + Details

Discussion in 'Scratchbuild Talk' started by Dredogol, Mar 23, 2009.

  1. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    Okay, so I will start this topic by giving a brief history of forward swept wings, then jump into the details everyone is interested in:

    History:
    The concept was actually first proposed by the Germans during WWII (1936).
    (Yes, the Germans were usually first at making revolutionary aviation tech, including the flying wing bomber designs.)
    Anyways, the first prototype was created and flown in 1944. The designation was the Junkers JU-287, which was basically created by scraps from other JU planes. This design was to be a turbo-jet Bomber. The main reason for the forward-swept wings was to provide extra lift during low speeds, and provide extra wingtip stability at transonic speeds (Mach 0.8 - 1.2).
    An improved second prototype was being created, but the Junkers factory was sacked by the Soviet Union.

    [​IMG]
    [​IMG]Image #2 :: http://img369.imageshack.us/img369/9687/type1312768916mh8.jpg

    After the war, The Soviets continued working on the JU-287, and ended up creating the "OKB-1 EF 140". This design transformed into a scout design rather than a bomber. After the first prototype was created, the entire project was canceled.

    [​IMG]

    At roughly the same time (~1946), Bell Aircrafts attempted to attach forward-swept wings onto the Bell X-1 super sonic project plane, but found the wingtips twisted too much. Technology at the time could not provide sufficient structural integrity without greatly increasing size and weight of the plane.

    During the 1970s, the birth of composite materials and computer assisted flight controls (fly-by-wire) technologies opened the doors once again to forward-swept wing experiments. This was done by the Grumman X-29 prototype. Two test planes were created; the first flew in 1984. The X-29 performed excellent until 45-degrees AOA (angle of attack), but was able to achievea maximum of 67-degrees AOA. Such high numbers are pretty close to the maximum AOA of military fighters today.

    [​IMG]

    The only other military fighter jet to incorporate forward-swept wing designs is the Russian Sukhoi SU-47 "Berkut". This plane first flew in 1997 at the Paris Air Show. The principles and design are pretty similar to the Grumman X-29, but with greater agility and speed. This fighter is entirely created with composite materials (unlike the X-29 which used them only around the wings). However, this fighter has yet to be in production, and is rumored it will not enter production.

    [​IMG]

    The are several civilian gliders and jet aircraft to incorporate this design, but they will not be covered here...
    Kiko12 likes this.
  2. Dredogol

    Dredogol M0DERATOR - (aka "Dred")

    Posts:
    998
    Likes:
    4
    Points:
    0
    Design Theory / Benefits:

    Why did people even consider this odd shape in the first place?
    First, we must discuss the Pros and Cons of a regular backward-swept wing (Aft Swept Wing = ASW) before we move on to forward-swept wing designs (FSW).

    The main benefits of ASW are the following:
    1) Lower wave drag at transonic speeds (Mach 0.8 - 1.2)
    2) Less energy to break the sound barrier caused by wave drag.
    3) Provides extra stability at subsonic / transonic flight.
    4) At transonic / supersonic speeds, the chord length becomes up to 1.4 times greater than the actual chord length due to drag properties.
    5) Design wise, allows for supersonic lift without the use of sharp leading edge wings.
    6) At supersonic speeds, the air does not have time to conform to the wing shape, thus passes right over in a near straight line over the wing.

    Now, let us look at the disadvantages of regular ASW designs:
    1) At subsonic / transonic speeds, air has time to conform to the wing shape. Thus, the airflow at the leading edge points sideways (inwards) as it nears the wingtips. Such airflow destroys lift and increases drag.
    2) Due to sideway airflow near the wingtips, (airflow also reaching the wingtips last) air separates at the wingtips first.
    Also, the wingspan decreases at the wingtips (less surface area). All of this produces stalling behavior at the wingtips first (aka: wingtip stall).
    3) At landing speeds, the center of lift (CL) is further forward then the wingtips, which causes the nose to pitch up. As the AOA increases this behavior increases (aka Sabre Dance).



    Those are the basic Pros and Cons of a regular ASW.
    Now, we may continue with the discussion of forward-swept wings (FSW).
    The basic behavior of a FSW design is very similar to that of an ASW design.
    "Both designs have an equal amount of drag reduction" (one would thing FSW has more drag).

    However, the major difference between the two is HOW airflow moves over the wing surface.

    [​IMG]
    Above is an image of how airflow moves across the wing at high AOA for an ASW and FSW design. As one will notice, airflow over the wingtips on FSW designs reach the ailerons first, and the wing root last. This causes the stalling (air / surface separation) to occur at the rear wing root first. For the ASW design, air/surface separation occurs at the wingtips first.

    Simply put, ASW designs have wingtip stalling first, while FSW have rear wing-root stalling first. For control purposes, wingtip stall = loss of aileron controls. Because ailerons control the roll of the aircraft, this can be a bad thing. For FSW, most elevon / flap controls are near the wing roots. This will lead to pitch loss control, but is not as terrible as wingtip stalls. The main reason root stall is better, is because the wing-root has a larger wingspan (chord), thus having greater lift at the root compared to the wingtip.

    Another major difference between the two designs is how the wing "twists". For ASW designs, as the AOA increases, the wing tips "twist" in the opposite direction of the lift force. For this reason, ASW designs require greater strength at the wingtips to prevent them from snapping.
    For FSW designs, as the AOA increases, the wing tips "twist" in the same direction of the lift force. As the AOA increases even further, the twisting force becomes even greater. This is the main reason why older designs were unable to design FSW planes. The metals (materials) at the time did not allow such flexing properties with aircraft weight in mind. This is where composite materials come into play for FSW designs. Because composites are strong, light, and flexible, less material is needed to maintain structural
    integrity (less material weight).


    Another difference between ASW and FSW is the energy required to break the sound barrier. The theory is that FSW designs require slightly less energy to reach supersonic speeds:


    [​IMG]


    This theory has yet to be completely proven due to two identical planes planes of the same shape and mass with only the wing direction being different. This is almost impossible due to natural differences between the two designs. FSW require the wing placement to be further back to offset the center of lift (CL) being further forward than where the wing is. This design difference alone makes it impossible to accurately test supersonic boundary layers with the same aircraft of FSW and ASW variants.




    -- 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.
    Kiko12 likes this.
  3. ivan_chan

    ivan_chan Rookie

    Posts:
    14
    Likes:
    0
    Points:
    0
    Thanks for the very good explanations. I have been thinking of building one forward-swept wing for some time.
  4. lawrenceb

    lawrenceb Cadet

    Posts:
    66
    Likes:
    31
    Points:
    18

    I thought this would be outward not inward?(disadvantages of ASF #1)
  5. gm3

    gm3 Top Gun

    Posts:
    2,210
    Likes:
    516
    Points:
    133
    i built an su 47 and it flew great. i personally dont like the forward swept wings because the twist is hard to stop in parkjet form.
  6. whatmovesyou

    whatmovesyou Ace Pilot

    Posts:
    1,746
    Likes:
    339
    Points:
    83
    I did something different. I combined the aft swept wing and the forward swept wing into one plane by the use of two servos. Even NASA has not done that!! (Cg was a big problem)
    How it flies is you take off with wings perpendicular to plane, flip mode so as throttle goes forward, wing goes aft(+45) (used heli mode) and moves real fast, and then back at 1/2 throttle, flip to another mode and use a slider to move wing forward to about -31 degrees and slow fly it.

    forward aft wing 006.JPG

    forward aft wing 008.JPG

    It really looks weird and different when you fly it.
  7. gm3

    gm3 Top Gun

    Posts:
    2,210
    Likes:
    516
    Points:
    133
    I built that f14 and it was fun. I'm now using the same sweep method in a b1 b lancer that I designed
Similar Threads
Forum Title Date
Scratchbuild Talk Swept Forward Wing SU 47 Version 2 Jun 15, 2012
Scratchbuild Talk SU 47 (without canards) Swept Forward Wing May 7, 2012
Scratchbuild Talk Forward-swept vertical stabilizers Jun 30, 2010
Scratchbuild Talk Forward swept wings Feb 11, 2010
Scratchbuild Talk Swept Forward Wing Dec 22, 2009
Scratchbuild Talk forward swept aircraft CG Jul 17, 2009

Share This Page

string(1) "1"