Weight of Variable Geometry Wings

[Jane-DoH]

How is it that the X-5's swing wing mechanism weighed only 370 pounds and yet later swing-wing designs weighed so much more?

[PEI_3721]

How are components of a ‘swing wing’ design defined, thus what is considered in the weight?
I can only speculate that as a research aircraft the X5 was not stressed to such high g levels as subsequent combat aircraft. Also, that fatigue issues from a long service life and/or a severe operating environment, and with wing stores were not of great concern.

[Jane-DoH]

PEI_3721

What g-load was the X-5 designed to?

BTW: Do most swing-wing designs use a centralized pivot as well as tracks for the wing to sweep along? The X-5 if I recall used curved tracks for the wing to travel along as it swung from front to back

[ICT_SLB]

I believe the X-5's wing was ground-settable to a given sweepback NOT a fully variable geometry unit with actuators etc. plus it had no external hardpoints for stores.

[Kitbag]

From the NASA Dryden Research Centre website:
The X-5 was tested from 1951 until 1955 at the NACA High-Speed Research Station. Built by Bell Aircraft Company, the X-5's maiden flight was June 20, 1951. The X-5 was the first aircraft capable of sweeping its wings in flight and helped our understanding of wing-sweep angles of 20, 45, and 60 degrees at subsonic and transonic speeds.Results of the research program demonstrated that the variable-wing-sweep principle worked. With the wings fully extended the low-speed performance was improved for take-off and landing and when swept back the high speed performance was improved and drag reduced. The pilots found they could use the variable wing sweep as a tactical control to out-perform the
accompanying escort aircraft during research missions. The X-5 flight tests provided some of the design background for the
F-111 and the Navy F-14 tactical aircraft.Also worth looking at is this link (http://www.nasa.gov/centers/dryden/news/FactSheets/FS-081-DFRC.html), the last paragraph probably answers the original question: the system used worked, but it wasn't very practical, I guess later systems/mechanisms were more robust but the aerodynamic data gathered was still very useful.

As regards pivot points F14, MiG23/27,Su17 types use pivot points some way from the fuselage, the French AVG, European Tornado had pivots close in to the fuselage.

Also Grumman's Jaguar used a similar mechanism to the X5, no idea if that was why the type failed to enter service.

[theficklefinger]

I am by no means an expert, but I was wondering why we didn't have variable sweep wings in civilian aviation. So I took a look at some designs.

Turns out during some initial testing as the wings sweep back, center of pressure moves back as well, and they lost some planes that were 'nose heavy'.

Hence when you look at your variable sweep planes these days, they have that fixed wing portion that extrudes away from the fuselage. It creates lift at a fixed point, keeping center of pressure at a fixed point. Extended from that are the smaller variable sweep portions, that being out so far don't seem to affect center of pressure so much as that portion of the wing doesn't create as much lift(less camber/less lifting area/less induced drag)

I gather they worked on a variable sweep wing that as it swept back, the attachment point to the wing, moved forward, to keep the center of pressure in a flyable place.

Seems the moving wing thing might be for the history books for a couple of reasons.

New wing technology seems to have made the 'lower and higher limits' of the wing larger...basically more efficient.

I suspect also that the computer, training, hydraulics, weight, etc...might add up to being more of a pain, when the engines are getting more efficient to get the speed/range advantages.

In civilian world a variable sweep wing would be great to increase range and speed at altitude, but I don't see it happening right now. Considering the SJ30 is probably the most efficient corporate jet on the market and that company is pretty much sunk, it tells you that technology moves slow in the civilian world.

[Denti]

Variable geometry doesn't have to be variable wing sweep, some other concepts like for example variable wingspan or variable wing area were tested in civil aviation as well, granted, "only" glider planes, but still ;)

[Jane-DoH]

ICT_SLB

The P.1109 fit that description; it was a German research-plane which the X-5 was loosely based on


Kitbag

the last paragraph probably answers the original question: the system used worked, but it wasn't very practical, I guess later systems/mechanisms were more robust but the aerodynamic data gathered was still very useful.

Okay, so the wing pivoted and what would now be called the glove, would slide forward a little over two feet in order to keep the center of pressure in place.


theficklefinger

Turns out during some initial testing as the wings sweep back, center of pressure moves back as well, and they lost some planes that were 'nose heavy'.

Hence when you look at your variable sweep planes these days, they have that fixed wing portion that extrudes away from the fuselage.

I believe that structure is called a glove (at least it's called a glove on the F-14) -- it's a wing-body fairing that the wing fits into (like how a hand fits into a glove)

It creates lift at a fixed point, keeping center of pressure at a fixed point. Extended from that are the smaller variable sweep portions, that being out so far don't seem to affect center of pressure so much as that portion of the wing doesn't create as much lift(less camber/less lifting area/less induced drag)

I'm not sure if that is accurate, as the X-5 had a glove too. As far as I understand, the center of pressure was retained by designing the wing so that as it pivots aft, some of leading-edge slides out of the glove (lengthening the leading edge, increasing lift up front); some of the trailing-edge ends up slides inside the glove (shortening the trailing-edge, reducing lift in the rear).

I gather they worked on a variable sweep wing that as it swept back, the attachment point to the wing, moved forward, to keep the center of pressure in a flyable place.

On the X-5, the whole glove slides forward as the wings pivot back; on later wings it would appear that as the wing sweeps back, additional leading-edge would slide out of the glove, whereas the trailing edge would slide into the glove increasing lift up front, and decreasing lift in the back.

[theficklefinger]

I can only go by what I have read, on where they put the levers, cams, bearings...etc.

Doesn't matter, the issue is dealing with a moving center of pressure...you either move the wing forward as the wings angle back, or you create a lifting surface(F14) that provides a stable center of pressure. Your 'Glove' as you call it creates a lot of lift, like most wings nearer the root...so the outside part of the wing can move back and not affect stability as much.

Either way, maybe it's moot. Just build a skinny wing that goes fast, and add slats and flaps to create more lift at slower speeds.

[Mechta]

Barnes Wallis designed an RPV called Wild Goose which was tested at Predannack in Cornwall just post war. This used its swing wings for pitch and roll control too. Here it is on its launch dolly.
http://i282.photobucket.com/albums/kk279/Rocky_Roger/BWWG.jpg

Due to the huge loss of life on the Dambuster raid, Wallis insisted on testing with RPVs first, for fear of any further deaths of aircrew due to his designs.

Wild Goose led to the Swallow design which, needless to say, got cancelled:

http://27.media.tumblr.com/NAJN8JTZ6iwigv0q48AsFvKpo1_400.jpg

some other concepts like for example variable wingspan or variable wing area were tested in civil aviation

You could argue that when any modern airliner lands with its slats and flaps out, that it is making use of variable wing area.

[theficklefinger]

Idle ponderings on aircraft design aside, I just can't stand to sit in a slow aircraft anymore...most aircraft just seem so inefficient...so much induced and parasite drag that could be eliminated, not mention better thrust efficiencies.

Not hard for me to sit there and ponder the wings gong back 40 degrees, the airspeed increases 40 knots, the FMS shows that my trip will be 3 hours instead of 4...that would be so nice.

[Jig Peter]

Your wish for more speed ("40 kts more") would be getting you well into the "Sonic Cruiser" area - and Boeing found no takers, remember ?
There are lots of possible ways to reduce drag, as you will no doubt know, but all have weight, cost, maintenance and other disadvantages, so designers have to come up with the best average ....
Not that that makes long flights any less booooooringggg, I agree !

[theficklefinger]

Sonic cruiser?

The only thing keeping an aircraft from going faster are the rules of no super sonic flight over land, and aircraft manufacturers pandering to what the airlines want, pilots that can't handle fast aircraft, cost issues related to ticket prices and such.

I have no doubt if the laws were changed and pilots were up to the task we would be up into the Mach speed levels.

The ONLY reason the Concorde program is dead is because the pilots were over gross and decided to fly an aircraft that they should have rolled out on the ground.

It was a great plane and could have led to better designed and more efficient super sonic aircraft.

Why is the SJ30 dead in the water? Why can't a Citation X bust the speed of sound? We know the Falcon 10 can and did. Put some real engines on it and scoot.

What's going on in aviation is just plain ignorance and backwards thinking.

Personally it's hard for me to believe anyone with real hours on a long trip, can't imagine how to make his plane go faster...sure at what cost, but even so, just sitting there all day long gets me to thinking there has to be a better way.

[Jane-DoH]

theficklefinger

Doesn't matter, the issue is dealing with a moving center of pressure...you either move the wing forward as the wings angle back, or you create a lifting surface(F14) that provides a stable center of pressure. Your 'Glove' as you call it creates a lot of lift, like most wings nearer the root...so the outside part of the wing can move back and not affect stability as much.

So the gloves on later planes were indeed larger? I suppose you're right in that it does produce a steady source of lift in that area. Regardless, the fact that as the wing pivots, some of the leading edge comes out and some trailing edge goes in seems to reduce the effect of C of P shift in addition to the glove producing a stable C of P in the middle.

The only thing keeping an aircraft from going faster are the rules of no super sonic flight over land

What I'm wondering is, would hypersonic planes be allowed to go over land (once they were fully hypersonic)? It sounds odd, but hypersonic planes have shockwaves so highly swept back to the extent that they usually don't reach the ground (atmospheric conditions tend to keep the wave from reaching the ground). You would have to get away from land to accelerate from supersonic to hypersonic, but once up to speed you could fly over land without booming anybody as far as I know so long as you don't slow down.

pilots that can't handle fast aircraft

What would prohibit a pilot from handling a fast aircraft?

cost issues related to ticket prices and such.

Probably the biggest obstacle

[Jane-DoH]

I just thought of something. What about the XF10F Jaguar. It had a wing-sweep system similar to the X-5 whereby the wing pivoted aft and the roots traveled forward to keep the C/L in the right space.

Why was the X-5 light in weight, yet the XF10F Jaguar enormously overweight?


R.C.
"That being said, I'd like to remind everybody in a manner reminiscent of the SNL bit on Julian Assange, that no matter how I die: It was murder (even if there was a suicide note or a video of me peacefully dying in my sleep), and should I be arrested or framed for a criminal offense, or disappear entirely -- I think we all know who to blame for it"

[Harley Quinn]

Why was the X-5 light in weight, yet the XF10F Jaguar enormously overweight?

Perhaps some of the answer is the difference in purpose of the 2 aircraft; X-5 was a research aircraft, XF10 was meant to be the prototype of a combat aircraft. I found this (http://www.angelfire.com/space/grumman/aircraft/jaguar.html) which explains a lot.

[Jane-DoH]

Harley Quinn

If it is not classified, what g-loads was the X-5 stressed to?

[Jig Peter]

Remember the TSR2, anyone ? (and I think, the F-104, as well as the Buccaneer).
Way back then, the problem of getting good-enough low speed handling combined with high-speed performance was solved by flap blowing. Seems simple enough, till you think of all that interlinked pipework and the engine-out case, which could well have needed max. thrust on approach from the "good" engine and would probably not have been all that comfortable for the driver.
Tornado, the TSR2's "replacement", took the swing-wing approach, which seems to have been the better answer, despite the mechanical complication. Whether one or 'tother was the "best" solution in service; I leave to those who have experience of both, in flight and maintenance ...

Just a side-bar for the main thread ...

[Harley Quinn]

No idea if it is classified or not, and tbh 50 years after its retirement I would suggest its limitations cannot be regarded as a secret.
According to this paper (http://www.scribd.com/doc/36166740/NACA-Conference-on-Aircraft-Loads-1953) from 1953 the X-5 was designed with a load limit of 7.33g, which was I think, more or less industry standard at the time. Remember this aircraft was built to investigate the effects of variable sweep and as technology demonstrator to prove the concept of Bells sweep system, not as a prototype combat aircraft.

[Jane-DoH]

Jig Peter

Remember the TSR2, anyone ? (and I think, the F-104, as well as the Buccaneer).
Way back then, the problem of getting good-enough low speed handling combined with high-speed performance was solved by flap blowing.

That's correct, and as I understand it the TSR-2's takeoff (or landing, I forgot which) speed was around 140 kts despite it's heavy wing-loading.

If I recall correctly, and I don't know why this is so, the increase in lift is substantial, but roll authority doesn't increase in proportion with the increase in lift -- at least that's why I've been told it wasn't used as liberally on USN carrier planes though that could be some bullschite I was told (which makes it even less comprehensible that the USN didn't make more liberal use of it -- the USN did use blown flaps).


Harley Quinn

Okay, if it could pull 7.33g's I don't understand why there was any issue with producing a lightweight swing-wing mechanism...

What g-load was the XF10F-1 stressed to?

[PEI_3721]

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.

[Harley Quinn]

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 (http://history.nasa.gov/SP-468/reference.htm#r184), 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. http://history.nasa.gov/SP-468/p258a.jpg
http://history.nasa.gov/SP-468/p258b.jpg http://history.nasa.gov/SP-468/p258c.jpg (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. http://history.nasa.gov/SP-468/p259.jpg [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 (http://history.nasa.gov/SP-468/contents.htm) and 12. (http://history.nasa.gov/SP-468/contents.htm) 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 (http://history.nasa.gov/SP-468/reference.htm#r155) and 184 (http://history.nasa.gov/SP-468/reference.htm#r184).

[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.


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 :hmm:

[Jane-DoH]

PEI 3721

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

So the operational g-load could either be 7.33g or 5g?


Harley Quinn

No idea about the g loading, guessing 9g as load limit

Well, that is higher than 7.33g.

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.

When you say the cuff, you mean the glove right?

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.

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

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.

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.

[Jig Peter]

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 ...

[PEI_3721]

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).

[Jane-DoH]

PEI 3721

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.

Understood