Delta Wing

[The Range]

Hi all,

Can somebody explain why some pure delta wing airplanes didn't need a horizontal stabilizer? What makes it unnecessary?
Thanks

[Mad (Flt) Scientist]

A horizontal stabilizer or tailplane does two things, usually - it makes the aircraft aerodynamically stable in pitch for the desired range of centres of gravity, and it provides a means to create variable pitching moment for aerodynamic control of the aircraft angle of attack.Thus it provides both "stability" and "control"

The former goal (stability) may be achieved instead by means of locating the centre of gravity relative to the wing (or vice versa) in such a fashion as to provide the required stability. Detail shaping of the wing in a spanwise sense may also help for a swept wing aircraft.
The latter (control) can be achieved by means of using trailing edge devices on the wing to create changing pitching moments for the same purpose of adjusting angle of attack.

Both are less efficient ways to achieve the specific goals, but if there are other compelling reasons to use the delta planform then these disadvantages may be acceptable to the overall design.

[The Range]

Thanks....

[tdracer]

To add a bit to what Mad Scientist wrote:
The flying wing (the extreme example of a delta wing) is not an inherently stable platform. As a result, the original flying wing bomber (YB-35) made a lousy bombing platform since it wasn't stable enough.
With the advent of FBW, and computers that can automatically adjust control surfaces many times per second, inherently unstable aircraft have become feasible - e.g. the B-2.

[turbidus]

Quite unlike the 737 MAX , no?

[pattern_is_full]

From a different angle - why a delta wing in the first place, and what reasons are there not to have an HS?

Delta wings are generally used for supersonic and high subsonic flight, because they have advantages regarding supersonic shock waves and reducing drag.

In that regime, the fewer the shock-producing surfaces and protrusions, the better. So it is advantageous to do away with a conventional HS, replacing it (as td and madscientist say) with elevons on the single wing. See also: Me 163, although that is a swept rather than a delta wing. but still lacks an HS.

Another point is that an HS can get caught in the shockwave off the wing, and end up with controllability problems at high speeds. While also being subject to a deep stall at slower speeds (HS being deprived of airflow by the "shadow" of the main wing at high AoA, and thus losing any effectiveness).

Additionally, a feature of long-deltas (e.g. Concorde) is that at lowish speeds, they can produce vortex lift at high AoA (tornados on top of the wings) - eliminating the need for high-lift devices (slats and flaps), and thus providing space on the wing for elevons.

Some deltas have canards to take the place of a HS, providing nose-up-lift at low speeds, and also handle the shifts in center-of-lift produced by shock-waves.

There is also the case of the Rogallo Delta often used for hang-gliders - where control is via the flexibility (warping) of the whole wing.

So it becomes a chicken-and-egg problem - which configuration or set of dependent features best suits the overall design goal of the particular aircraft? Does an HS cause more problems than it solves - or does eliminating an HS cause more problems than it solves?

[sandringham1]

There is also the case of the Rogallo Delta often used for hang-gliders - where control is via the flexibility (warping) of the whole wing.


Rogello hang-gliders and microlights are controlled by weight shift, the wing itself is designed to be neutral in pitch using a reflex wing section, the weight shift action being the control input although some have an adjustable trim function altered by changing the amount of reflex, other ingenious methods are used.

[Denti]

To add a bit to what Mad Scientist wrote:
The flying wing (the extreme example of a delta wing) is not an inherently stable platform. As a result, the original flying wing bomber (YB-35) made a lousy bombing platform since it wasn't stable enough.
With the advent of FBW, and computers that can automatically adjust control surfaces many times per second, inherently unstable aircraft have become feasible - e.g. the B-2.

It depends how the wing is designed. The Horten gliders in the 30ies (flying wings as well) were actually stable from the reports of those that were lucky enough to have flown them, especially the HO IV.

[stilton]

What about the ‘hybrids’ ?

Such as the Mig 21, even the F4 with delta wings and conventional horizontal tails ?


Why have both ?

[Jason Burry]

True supersonic deltas have a VERY low aspect ratio - Extremely chord-y, but very short span. This causes them to be quite inefficient in high alpha flight. Control inputs, especially elevator, are less efficient due to the single lifting surface having to provide for competing goals of lifting the nose and depressing the tail - Elevators effectively modify the pitching moment of the wing's airfoil rather than providing a simple down moment on a conventional tail, while the wing lifts, as ever. Flaps are impossible on a true delta, so approach visibility is very poor - The pilot is looking to the sky, the nose blocking the runway. High energy turns throw away ALOT of energy in induced drag.

The Mig 21 and F4 have semi-delta wings, and are significantly less chordy than most true deltas. This lessens the trade-offs the delta imposes, while maintaining much of its advantage in supersonic flight. The more conventional tail allows more conventional maneuvering loads, and allows for various flaps to be applied to the wing, reducing required alpha at low speed segments of flight. Much less energy is thrown away in a turning engagement.

Every airplane is a compromise, and wing planform holds a host of them.

J