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The Northrop-Grumman B-2, a tailless-flying-delta-wing aircraft, has a set of flaps along its trailing edge, as seen (for instance) in this cutaway diagram:

B-2 diagram

(Image from Funker530.)

But tailless delta-winged aircraft (except for those few equipped with canards) can't generally use flaps, because a tailless canardless delta-winged aircraft has no way of countering the nosedown pitching moment produced by extended flaps.

How does the B-2 avoid pitching down uncontrollably when its flaps are extended?

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  • $\begingroup$ Doesn’t it simply cheat on the „tail-less“ part by deflecting the tail? $\endgroup$
    – Cpt Reynolds
    May 3, 2019 at 4:07
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    $\begingroup$ Other sources identify these surfaces as elevons. Are you sure they are actually flaps? $\endgroup$
    – Sanchises
    May 3, 2019 at 10:19
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    $\begingroup$ @Sanchises They are listed as elevons in How Stuff Works, with the "beaver tail" as a Gust Load Alleviation System. The B2 Spirit has clamshells at the trailing edges of its wing tips, which open top and bottom as airbrakes. These may act as "flaps" when used together, or "rudders" when used on side at a time. $\endgroup$
    – Robert DiGiovanni
    May 3, 2019 at 10:32
  • $\begingroup$ The Aeriane Swift ( en.wikipedia.org/wiki/A%C3%A9riane_Swift ) is a tailless aircraft that uses flaps. But, they appear to be located near the CG. $\endgroup$
    – quiet flyer
    Feb 9, 2021 at 14:27

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I don't think the flaps are used as high lift devices. Watch this video of a B-2 landing. Perfect view:

enter image description here

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I am sure the B-2 is an unstable aircraft meaning if it pitches up the pitching moment increases and the aircraft wants to further increase pitch. This is contrary to traditional design, but can be controlled through fly-by-wire. This increases the efficiency of a flying wing design as many of the things done to help flying wing stability hurt efficiency.

This means that when the flaps at the trailing edge deflect they are helping stabilize the aircraft. This means though that the angle of attack or relative angle of the wing to the incoming airflow cannot go negative. This is not a problem as the aircraft will always be pitched up with flaps deployed.

I am an aerospace engineer who is currently working on flying wing type aircraft.

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    $\begingroup$ "This means that when the flaps at the trailing edge deflect they are helping stabilize the aircraft.: -- does this really follow from your earlier comments? $\endgroup$
    – quiet flyer
    Feb 9, 2021 at 14:29
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First we consider the purpose of a "tail", more correctly Horizontal stabilizer, for pitch control. The classical set up for a straight wing is to have a tail for adequate pitch stability.

Proper design, especially for a bomber, calls for pitch stability to be stronger than all but the strongest control inputs, including flaps. You don't want to stall one of these.

The B-2 has enough pitch stability in its design not to need an extra tail sticking out the back. Any pitch down moment caused by flap deployment is not only counteracted by the aerodynamic stability of the aircraft, but also computer control of surfaces such as elevons and beaver tail.

The "tail" is hidden in the structure and the computer control. Finding the "tail" leads to an understanding of how it works. Swept wings lengthen the pitch axis just like a fuselage. Surface area at the trailing edge of a delta serves the same purpose as a horizontal stabilizer. Deltas are really blended wing-tails.

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    $\begingroup$ Since the trailing edge of the B-2 wing-- ignoring the large serrations-- is essentially a straight line running in the spanwise direction, it's unclear how deflecting the elevons would be an effective way to counter the nose-down pitching moment generated by deflecting any flaps that may be present. The elevons are operating at no greater a moment-arm, in the fore-and-aft sense, than the flaps are, $\endgroup$
    – quiet flyer
    May 3, 2019 at 22:49
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    $\begingroup$ "Proper design, especially for a bomber, calls for pitch stability to be stronger than all but the strongest control inputs, including flaps. You don't want to stall one of these."-- is this really an appropriate statement in the context of an aircraft with artificial computer-generated stability? $\endgroup$
    – quiet flyer
    May 3, 2019 at 22:51
  • $\begingroup$ Hey, long time no see. Please look at the above picture. They use clamshells to achieve the same effect as flap down elevon (or spoiler) up. And with dual rates, one can increase elevon (or elevator) throw if needed. $\endgroup$
    – Robert DiGiovanni
    May 4, 2019 at 1:01
  • $\begingroup$ Model B2s fly without computer control. The statement is appropriate as a design goal, whether it is achieved by passive aerodynamic stabilization (old fashioned) or by computer control, or by BOTH. And those serrations, in addition to being stealthy, provide MORE than a straight line of space for control surfaces. But no, they don't have traditional flaps, the diagram in the question was mis-labeled. $\endgroup$
    – Robert DiGiovanni
    May 4, 2019 at 1:10

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