Delta wings and tailplanes
Discussion
Adding reflex to an aerofoil reduces it's maximum lift coefficient and, since this is what you need to do to a tailless aircraft to generate a positive pitching moment, just when you need a high lift coefficient you reduce it by trying to access it (with up elevon)
The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
AER said:
Adding reflex to an aerofoil reduces it's maximum lift coefficient and, since this is what you need to do to a tailless aircraft to generate a positive pitching moment, just when you need a high lift coefficient you reduce it by trying to access it (with up elevon)
The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
Sounds good, must admit I have no idea what it means.The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
Deltas are a very good shape for the high speed (transonic and supersonic) flight regimes. They have some disadvantages at slower speeds. The problem as AER is explaining, is to do with pitch authority i.e, the ability to move the nose up and down.
On a conventional aeroplane, that pitch is normally provided by elevators attached to the separate tailplane or sometimes by moving the entire tailplane in its entirety. Roll control is normally exercised by having ailerons on the wing.
On a delta, there are no elevators as such but "elevons" which are a combination of elevator and aileron. Working together they act as elevators and working in opposition, they work as ailerons.
Delta winged aircraft don't always have landing flaps. This means that they need to adapt a fairly high pitch angle to maintain lift at low speed (look at shots of Concorde when it is landing).
For a fighter aircraft where manoeuverability is usually required, deltas can produce a lot of drag when the aircraft is performing tight turns so speed can be lost very quickly. This is not always a bad thing but fighter tactics using a pure delta winged aircraft have to be adapted to these characteristics.
If you look at the evolution of delta winged aircraft, you can see that early designs were often a simple triangle but as the concept was tested and the shortcomings became known, you can see that the delta shapes became more and more complex. Look at the difference between the wing of the prototype Avro Vulcan and the final B2 version -
On a conventional aeroplane, that pitch is normally provided by elevators attached to the separate tailplane or sometimes by moving the entire tailplane in its entirety. Roll control is normally exercised by having ailerons on the wing.
On a delta, there are no elevators as such but "elevons" which are a combination of elevator and aileron. Working together they act as elevators and working in opposition, they work as ailerons.
Delta winged aircraft don't always have landing flaps. This means that they need to adapt a fairly high pitch angle to maintain lift at low speed (look at shots of Concorde when it is landing).
For a fighter aircraft where manoeuverability is usually required, deltas can produce a lot of drag when the aircraft is performing tight turns so speed can be lost very quickly. This is not always a bad thing but fighter tactics using a pure delta winged aircraft have to be adapted to these characteristics.
If you look at the evolution of delta winged aircraft, you can see that early designs were often a simple triangle but as the concept was tested and the shortcomings became known, you can see that the delta shapes became more and more complex. Look at the difference between the wing of the prototype Avro Vulcan and the final B2 version -
AER said:
Adding reflex to an aerofoil reduces it's maximum lift coefficient and, since this is what you need to do to a tailless aircraft to generate a positive pitching moment, just when you need a high lift coefficient you reduce it by trying to access it (with up elevon)
The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
If you have washout at the wing tips you don't need a reflexed section. Washout still adds drag and makes the wing less efficient though.The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
Dr Jekyll said:
What's 'reflex' and 'washout'?
Reflex is a slighly upturned training edge.Washout is having the tips at a lower angle of incidence than the root. It needs to be applied to delta or swept wings though.
Both have the effect of preventing the wing from tucking under; Reflex by modifying the lift curve (as AER explained), washout by effectively making the wingtips elevators (because they are behind the centre of lift position - as the tips get pushed down, the nose gets pushed up).
Krikkit said:
Yertis said:
What was the thinking behind the 'notched delta' on the EE Lightning?
That's not designed as a delta, but the earliest solution to transonic flight - the MiG19 is the same thing. Swept wings and a tailplane above/below it.Dr Jekyll said:
Krikkit said:
Yertis said:
What was the thinking behind the 'notched delta' on the EE Lightning?
That's not designed as a delta, but the earliest solution to transonic flight - the MiG19 is the same thing. Swept wings and a tailplane above/below it.z06tim said:
Dr Jekyll said:
Krikkit said:
Yertis said:
What was the thinking behind the 'notched delta' on the EE Lightning?
That's not designed as a delta, but the earliest solution to transonic flight - the MiG19 is the same thing. Swept wings and a tailplane above/below it.AER said:
Adding reflex to an aerofoil reduces it's maximum lift coefficient and, since this is what you need to do to a tailless aircraft to generate a positive pitching moment, just when you need a high lift coefficient you reduce it by trying to access it (with up elevon)
The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
So a canard allows the delta to do its job efficiently and leave pitch/roll control to this control surface, but you needed modern control systems to make a possibly inherently unstable pitch control system work ?The net result is you wind up carrying around waaay more wing area than you'd otherwise need to. Wing area is drag, especially at high speeds.
And being ahead of the centre of lift makes the plane even more responsive ?
Never studied aerodynamics
Gary C said:
So a canard allows the delta to do its job efficiently and leave pitch/roll control to this control surface, but you needed modern control systems to make a possibly inherently unstable pitch control system work ?
And being ahead of the centre of lift makes the plane even more responsive ?
Never studied aerodynamics
It's the hardest "easy" subject I ever studied, because everything seems easy initially but it very rapidly takes a turn for the worse once you "think" you have an understanding (you don't) and then you have to relearn everything you thought you knew. And being ahead of the centre of lift makes the plane even more responsive ?
Never studied aerodynamics
IanH755 said:
It's the hardest "easy" subject I ever studied, because everything seems easy initially but it very rapidly takes a turn for the worse once you "think" you have an understanding (you don't) and then you have to relearn everything you thought you knew.
You mean you get to a point where you know enough, to know you don't know enough, to know enough, to know the subject?Eric Mc said:
And you could claim that variable sweep wing aircraft become virtual deltas when the wings are fully swept back.
Especially on airframes like the F14 that use pneumatic inflating or spring loaded fairings to attempt to keep the wing blended into the fuselage at all sweep angles!http://www.anft.net/f-14/f14-detail-wingsweep.htm
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