Weight of Variable Geometry Wings
If 7.33g load limit was interpreted in engineering terms as ‘limit load’, then this could be 1.5 times higher than the allowed operational load depending on the chosen safety factor, e.g. the aircraft limit was approx 5g. This is less than the then state-of-the-art operational aircraft at approx 6g, and perhaps without fatigue considerations – cf #2.
No idea about the g loading, guessing 9g as load limit, but this extract from a NASA publication gives a clue to the issue, the chosen mechanism was cr@p and differs from that used in current VG types:
Quest for Performance: The Evolution of Modern Aircraft Part II: THE JET AGE Chapter 10: Technology of the Jet Airplane Wings and Configurations for High-Speed Flight
Aircraft with variable sweep wings have been discussed since the concept of wing sweep was first introduced. Some of the aerodynamic problems introduced by the variable sweep concept together with possible solutions, based on material contained in reference 184, are illustrated in figure 10.15. Figure 10.15(a) shows a wing that changes its sweep angle by rotating about a single inboard pivot located on the fuselage center line. At the bottom of the figure the rearward movement of the wing center of lift with increasing sweep angle is shown for both subsonic and supersonic speeds. The slight rearward shift of the aircraft center of gravity is caused by the rearward shift of the wing weight. Indicated by the cross-hatching is the distance between the center of gravity and the center of lift. This distance is a measure of the longitudinal stability of the aircraft and greatly increases as the sweep angle increases. A small amount of longitudinal stability is highly desirable, but the large increases with sweep angle shown in figure 10.15(a) cause reductions in aircraft maneuverability and large increases in trim drag. (Trim drag is associated with the large negative lift load that must be carried by the tail to balance the pitching moment induced by the distance between the centers of gravity and lift.) A single pivot wing of the type shown in figure 10.15(a) is accordingly unacceptable, and no aircraft utilizing this concept has ever been built. A solution to the problem highlighted in figure 10. 15(a) is illustrated in figure 10.15(b). Here, the wing translates forward as the sweep angle increases so that the stability remains essentially the same at all sweep angles. The increase in stability at supersonic speeds is not related to variable sweep but is characteristic of all wings as they pass from subsonic to supersonic speeds. The rotating and translating variable-sweep wing has been explored on two experimental aircraft. First was the Bell X-5 research airplane, which made its initial flight in 1951. The sweep angle on this aircraft could be varied from 20 to 60, as shown by figure 10.16. No problems were encountered with the variable-sweep mechanism on the X-5, and flight characteristics of the aircraft were fairly good at all sweep angles. At a somewhat later date, the Grumman XF10F variable-sweep fighter entered flight testing. Like the X-5, the Grumman fighter had a wing that combined rotation and [258] translation to control the relationship between the centers of lift and gravity. Because of problems entirely unrelated to the variable-sweep feature, the XF10F was not a success and was never put into production. Both the X-5 and the XFIOF were subsonic aircraft in which the variable-sweep feature was intended to increase, as compared with a fixed-wing aircraft, the critical Mach number at high-subsonic speeds and reduce the landing speed at the other end of the scale. These goals were accomplished in both aircraft. The translating and rotating variable-sweep wing, however, is heavy and leads to undesirable mechanical complications. Shown in figure 10.15(c) is the basic solution to the variable-sweep stability problem employed in the design of all operational variable-sweep aircraft in use today. The wing pivot is located outboard of the fuselage with a highly swept cuff extending from the pivot to the side of the fuselage. In this concept, developed at the NASA Langley Research Center, the fixed and movable components of the wing are configured so that the wing span-load distribution varies with sweep angle in a manner to minimize the rearward shift in the center of lift. As illustrated in figure 10.15(c), the distance between the centers of lift and gravity are the same at subsonic speeds for two sweep angles - one low and one high.
(a) No wing translation.
(b) With wing translation.
(c) No wing translation.
Figure 10. 15 - Aft movement of center of lift with increasing sweep angle for three variable-sweep concepts.
[259] Figure 10.16 - Bell X-5 research aircraft equipped with variable-sweep wings. [NASA] Three variable-sweep aircraft employing the outboard pivot concept are in operational use or under development in the United States today. These are described in chapters 11 and 12. Several variable-sweep aircraft are also in operational use in Europe. Interesting accounts of the development of' variable-sweep concepts and aircraft are contained in references 155 and 184.
Quest for Performance: The Evolution of Modern Aircraft Part II: THE JET AGE Chapter 10: Technology of the Jet Airplane Wings and Configurations for High-Speed Flight
Aircraft with variable sweep wings have been discussed since the concept of wing sweep was first introduced. Some of the aerodynamic problems introduced by the variable sweep concept together with possible solutions, based on material contained in reference 184, are illustrated in figure 10.15. Figure 10.15(a) shows a wing that changes its sweep angle by rotating about a single inboard pivot located on the fuselage center line. At the bottom of the figure the rearward movement of the wing center of lift with increasing sweep angle is shown for both subsonic and supersonic speeds. The slight rearward shift of the aircraft center of gravity is caused by the rearward shift of the wing weight. Indicated by the cross-hatching is the distance between the center of gravity and the center of lift. This distance is a measure of the longitudinal stability of the aircraft and greatly increases as the sweep angle increases. A small amount of longitudinal stability is highly desirable, but the large increases with sweep angle shown in figure 10.15(a) cause reductions in aircraft maneuverability and large increases in trim drag. (Trim drag is associated with the large negative lift load that must be carried by the tail to balance the pitching moment induced by the distance between the centers of gravity and lift.) A single pivot wing of the type shown in figure 10.15(a) is accordingly unacceptable, and no aircraft utilizing this concept has ever been built. A solution to the problem highlighted in figure 10. 15(a) is illustrated in figure 10.15(b). Here, the wing translates forward as the sweep angle increases so that the stability remains essentially the same at all sweep angles. The increase in stability at supersonic speeds is not related to variable sweep but is characteristic of all wings as they pass from subsonic to supersonic speeds. The rotating and translating variable-sweep wing has been explored on two experimental aircraft. First was the Bell X-5 research airplane, which made its initial flight in 1951. The sweep angle on this aircraft could be varied from 20 to 60, as shown by figure 10.16. No problems were encountered with the variable-sweep mechanism on the X-5, and flight characteristics of the aircraft were fairly good at all sweep angles. At a somewhat later date, the Grumman XF10F variable-sweep fighter entered flight testing. Like the X-5, the Grumman fighter had a wing that combined rotation and [258] translation to control the relationship between the centers of lift and gravity. Because of problems entirely unrelated to the variable-sweep feature, the XF10F was not a success and was never put into production. Both the X-5 and the XFIOF were subsonic aircraft in which the variable-sweep feature was intended to increase, as compared with a fixed-wing aircraft, the critical Mach number at high-subsonic speeds and reduce the landing speed at the other end of the scale. These goals were accomplished in both aircraft. The translating and rotating variable-sweep wing, however, is heavy and leads to undesirable mechanical complications. Shown in figure 10.15(c) is the basic solution to the variable-sweep stability problem employed in the design of all operational variable-sweep aircraft in use today. The wing pivot is located outboard of the fuselage with a highly swept cuff extending from the pivot to the side of the fuselage. In this concept, developed at the NASA Langley Research Center, the fixed and movable components of the wing are configured so that the wing span-load distribution varies with sweep angle in a manner to minimize the rearward shift in the center of lift. As illustrated in figure 10.15(c), the distance between the centers of lift and gravity are the same at subsonic speeds for two sweep angles - one low and one high.
(a) No wing translation. (b) With wing translation.
(c) No wing translation.
Figure 10. 15 - Aft movement of center of lift with increasing sweep angle for three variable-sweep concepts.
[259] Figure 10.16 - Bell X-5 research aircraft equipped with variable-sweep wings. [NASA] Three variable-sweep aircraft employing the outboard pivot concept are in operational use or under development in the United States today. These are described in chapters 11 and 12. Several variable-sweep aircraft are also in operational use in Europe. Interesting accounts of the development of' variable-sweep concepts and aircraft are contained in references 155 and 184.
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Roll authority
On TSR2 at least, and probably other flap-blowers, roll authority was obtained from the differential movement of the tailplane, plus the effect of the all-moving vertical tail; the wing as a whole being used to provide the necessary lift and the tail assembly the control in roll and yaw.
Pause for slight rant
A neat solution, unfortunately consigned to the "might have beens" by the then British government's "slash and burn" approach (so what's new ?)
Rant mode OFF
Pause for slight rant
A neat solution, unfortunately consigned to the "might have beens" by the then British government's "slash and burn" approach (so what's new ?)
Rant mode OFF
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PEI 3721
So the operational g-load could either be 7.33g or 5g?
Harley Quinn
Well, that is higher than 7.33g.
When you say the cuff, you mean the glove right?
So the glove produces the more lift when the wings are swept, and less when the wings are out? I also would almost swear that the pivot was also designed so that more leading-edge came out of the glove, and more trailing edge went into it -- am I wrong?
Did this wing design tend to weigh more or less than the earlier one?
Jig Peter
Yeah, but did the Buccaneer have an all moving tail, and differential tail-plane movement? Regardless, I'm pretty sure it didn't have an all moving tail, and it served with the RN FAA.
If 7.33g load limit was interpreted in engineering terms as ‘limit load’, then this could be 1.5 times higher than the allowed operational load depending on the chosen safety factor, e.g. the aircraft limit was approx 5g. This is less than the then state-of-the-art operational aircraft at approx 6g, and perhaps without fatigue considerations
Harley Quinn
No idea about the g loading, guessing 9g as load limit
Shown in figure 10.15(c) is the basic solution to the variable-sweep stability problem employed in the design of all operational variable-sweep aircraft in use today. The wing pivot is located outboard of the fuselage with a highly swept cuff extending from the pivot to the side of the fuselage.
In this concept, developed at the NASA Langley Research Center, the fixed and movable components of the wing are configured so that the wing span-load distribution varies with sweep angle in a manner to minimize the rearward shift in the center of lift.
Did this wing design tend to weigh more or less than the earlier one?
Jig Peter
On TSR2 at least, and probably other flap-blowers, roll authority was obtained from the differential movement of the tailplane, plus the effect of the all-moving vertical tail; the wing as a whole being used to provide the necessary lift and the tail assembly the control in roll and yaw.
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@ Jane Doh
Re: Buccaneer
No all-moving tail But a biiig chage of incidence, on the Buccaneer, but a "whole lotta blow" (IIRC). It also served with the RAF, with its area-ruled fuselage and some pretty high Mach down "among the weeds". Although a capable aircraft, it was pushed by political pressure from an influential admiral and royal relative who used as much of his influence as he could to "kill" TSR2.
OK, thread drift, so back to you ...
No all-moving tail But a biiig chage of incidence, on the Buccaneer, but a "whole lotta blow" (IIRC). It also served with the RAF, with its area-ruled fuselage and some pretty high Mach down "among the weeds". Although a capable aircraft, it was pushed by political pressure from an influential admiral and royal relative who used as much of his influence as he could to "kill" TSR2.
OK, thread drift, so back to you ...
So the operational g-load could either be 7.33g or 5g?
With the inference of a limit load of 7.33g, then for the piloting community the aircraft would have been limited to 5g for flight testing.
However, IMHO (a gut feeling and not much more), a research aircraft might have been limited to 4.5g if load measurement was not the primary objective of the tests: – mainly swing wing aerodynamics?
Early flights may have had even lower limits, like any new aircraft type, and if the total flying achieved in testing is low, a research aircraft might never experience the aircraft limit; - pure supposition (5 years with RAE).
With the inference of a limit load of 7.33g, then for the piloting community the aircraft would have been limited to 5g for flight testing.
However, IMHO (a gut feeling and not much more), a research aircraft might have been limited to 4.5g if load measurement was not the primary objective of the tests: – mainly swing wing aerodynamics?
Early flights may have had even lower limits, like any new aircraft type, and if the total flying achieved in testing is low, a research aircraft might never experience the aircraft limit; - pure supposition (5 years with RAE).
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PEI 3721
Understood
With the inference of a limit load of 7.33g, then for the piloting community the aircraft would have been limited to 5g for flight testing.
