747........Supersonic.....?

This was one of the first encounters with this previously unknown problem that all fighter aircraft manufacturers soon experienced. All fighters prior to the P-38 were required to demonstrate full-power vertical terminal-velocity dives from the service ceiling of the aircraft and to delay their pullout until below 7,500 feet. Because its greater engine power allowed it to start dives at much higher altitudes than previous fighters, the P-38 was the first military fighter to encounter this transonic Mach number phenomenon.

Flight testing the P-38 disclosed that whenever the airflow over the wing exceeded Mach 1.0, compressibility effects were encountered. This result was soon predictable when this slippery fighter accelerated in excess of 0.65 Mach in dive angles greater than 45 degrees at altitudes above 15,000 feet. Cockpit-installed Mach meters had yet to be invented.

www.24hourscholar.com...


The P-38 shown in this photo was one of the fighters built in the late 1930s and early 1940s that experienced compressibility effects. In steep dives, these aircraft could reach speeds above Mach 0.75 (called transonic). At transonic speeds, air in front of the wings became compressed and reached supersonic speeds as it flowed over the wings, forming a shock wave. This resulted in an increase in drag and a decrease in lift.


www.dfrc.nasa.gov...

Note the above is from NASA.


Powerful fighters such as the P-47 and P-38 were Hub Zemke with his P-47C, circa 1943.


Pilots were running up against compressibility and they were dying. P-47’s and P-38’s were being flown straight into the ground, or even breaking up in flight.


This is because as the plane continues down, the relative speed of sound goes up. Eventually, the aircraft’s Mach number will drop (although its actual airspeed does not) and the shock wave will dissipate


www.cradleofaviation.org...

See above speed of sound required at Sea level greater then higher altitude, thus same airspeed lets say 500 knots at 20,000 feet maybe Mach .95 while at 5,000 feet 500 knots may only be Mach .60

The denser the air, (hence the lower in altitude) the faster you have to go to break Mach. So P38 more powerful, higher operating ceiling, diving, breaks Mach, controls lock up or aircraft falls apart, dives down with no control inputs at terminal velocity, until lower altitude, denser air allows the control surface to operate and since denser air, aircraft is now traveling at a lower Mach speed.

So YES in deed the P38 were capable of breaking Mach 1.

Originally posted by jonititan

...any inversions are probably very high up and don't last too long...

Temperature inversions can happen at any altitude in the troposphere. When the KC-135A (which was an underpowered pig) was still flying, temperature inversions had to be considered in takeoff data. At heavy gross weights there existed the possibility that the aircraft would be unable to climb through an inversion which would be a problem if there were mountains or other high obstacles in the vicinity.

Robertfenix, No, they could not. Note the NASA source quoted states that these aircraft could reach speeds in excess of mach 0.75. If they exceeded mach 1 the NASA source would say so.

You are right that research in this field was going on elsewhere, in the UK the same sort of high velocity dives were being carried out by Griffon Spitfires and later Spitefuls, both much faster and more aerodynamically advanced (in the case of the Spiteful) aircraft than the P-38 and none of these passed mach 1 either. It was impossible due to the effects of compressibility and that rather big whirly thing on the front (intended).

I have posted quotes before where test pilots were required to dive Spitfires at the highest possible speed and then fire the guns to see if the wings came off (an unenviable job I'm sure you will agree) In one such test the nose of the aircraft buckled and the propeller detached at mach 0.9 due to the impossible strain. Incredibly the pilot recovered and glided in to a landing and I have a photograph of this very aircraft looking bent and sans propeller immediately after the event.

May I suggest that you have misinterpreted the information you have posted so that supersonic airflow over the wing has been read as meaning supersonic speed by the aircraft? The airflow over the wing is compressed and travels faster than the air beneath it, in this way lift is created, so in the transonic regime the airflow over the wing could indeed be supersonic in the right conditions while the aircraft itself remains subsonic.

post edited because I found the picture;

The Spitfire Mk. XI flown by Sqn. Ldr. Martindale, seen here damaged after its flight on 27 April 1944 during which it achieved a true airspeed of 606 mph.

[edit on 9-6-2005 by waynos]

look in my very recent avionics exam
all the equations for temperature at given altitude
different equations for different bits
but the troposphere had a linear lapse rate
if there are any inversions it had better have some funky reason why it's not taught on a university course where 1/3 of one module is all about air data systems and calculating different bits of air data from given quantites

jonititan;

Here is a link that explains temp inversions quite well.

Regards

There was no "over Mach" gauges at the time, so there is no way to tell. But in a powered dive from altitude, yes the P38 did break the speed of sound

But look what a 'mere' 600mph did to a spitfire! Clearly we disagree on this and we aren't going to convince one another so we should leave it there perhaps?

During testflights of the 747 they reached 0.9 mach and began to experience buffeting so they throttled back. If you pushed a 747 much beyond you would probably suffer a catastrophic structural failure. It's not stressed or aerodynamic enough to go past mach 1. If a BUFF were to go past Mach 1 it would probably disintigrate. They weren't designed for high speed flight, and again aren't stressed for it. Currently if you walk along the back of a BUFF you can feel the skin crinkling under your feet from the age.

My father was a B-52 mechanic at Castle AFB in the 60s, and they had an aircraft there, tail number 007, that had twisted the backbone during hard manuvers, so for the rest of its career it had to be flown with the rudder pedal on one side pushed all the way to the floor. Most non-fighter aircraft just aren't stressed or designed to break mach 1. They can come close to it, but they wouldn't be able to take the stress of breaking the sound barrier. That's why the Concorde, the US SST design, and the TU-144 are all very thin round fuselages. That shape can take the stress of breaking the sound barrier.

Oh yeah, and while were here, can the B2, or Harrier, for example, go supersonic? I mean ,again, being structually sound etc!

Am just curious, by the way!




[edit on 16-6-2005 by veritas 7]

Originally posted by Zaphod58
During testflights of the 747 they reached 0.9 mach and began to experience buffeting so they throttled back. If you pushed a 747 much beyond you would probably suffer a catastrophic structural failure. It's not stressed or aerodynamic enough to go past mach 1.

Actually, the reason they throttle back is to avoid mach tuck, which could lead to inadvertantly exceeding Mach 1.0. But as I stated in a previous post, just because a large commercial type aircraft exceeds mach 1 doesn't mean that it will instantaneously break apart in flight. It has happened before.

Originally posted by Zaphod58
If a BUFF were to go past Mach 1 it would probably disintigrate.

Again; it probably wouldn't

Originally posted by Zaphod58
My father was a B-52 mechanic at Castle AFB in the 60s, and they had an aircraft there, tail number 007, that had twisted the backbone during hard manuvers, so for the rest of its career it had to be flown with the rudder pedal on one side pushed all the way to the floor.

An aircraft that required continuous displacement of the rudder (especially all the way to the floor) would be unairworthy and therfore either repaired or taken out of service. No pilot would fly an aircraft in this condition except maybe only to ferry it for repairs or the boneyard. Incidentally, I went to Castle for KC-135 training and miss that place (It's now closed) It was a great assignment.

Originally posted by Zaphod58
Most non-fighter aircraft just aren't stressed or designed to break mach 1. They can come close to it, but they wouldn't be able to take the stress of breaking the sound barrier.

Like I said: it has happened before in a KC-135 (B-707) and the crew safely landed the aircraft.

Originally posted by veritas 7
Oh yeah, and while were here, can the B2, or Harrier, for example, go supersonic? I mean ,again, being structually sound etc!

Am just curious, by the way!




[edit on 16-6-2005 by veritas 7]

The answer is no for both, in the case of the Harrier it is partly because fuselage lenght/cross section is all wrong but mainly because of the exposed fan blades in those huge open air intakes. A McDonnell Douglas/ Rolls Royce Harrier based supersonic demonstrator was proposed under the designation AV-8SX (for Supersonic eXperimental) in 1981 but it was never built. It featured a greatly lengthened fuselage of the same cross section to accomodate a PCB pegasus test engine (the greater length helped with the transonic drag) and extended shrouded air intakes where the airflow into the fan could be controlled at high speeds.



In the case of the B-2 subsonic was chosen for many operational reasons to do with maintaining the integrity of its stealth characteristics but the aerodynamic reason for the B-2 itself is simply the fact that it is a flying wing, you will never see a supersonic plane that is wider than it is long, test that theory out with any plane you like

I've heard of a couple cases where a plane was flown where you had to have one rudder pedal pushed almost to the floor that they flew for several months, and just waited until the plane went to the Depot for scheduled maintenance. One of the reasons they kept 007 in service was that it was used almost exclusively as a training aircraft, and was a good example for the student pilots of what would happen to the airframe if you manuvered too hard, and how to keep a structurally "damaged" aircraft in straight and level flight.

I am not so sure about the B-2 my self, this thing is still shrouded in mystery and I do believe it's max speed is still classified, and rumors are that it was part of Project Aurora, all of these alledged designs were flying triangles able to go supersonic speeds and perhaps beyond, it might have been the least exciting Aurora plane, but i'm sure it's hiding some things, possibily a higher speed then led on, remember the B-1B is supersonic as well, that has been the trend.

The Harrier supposedly pushes Mach speeds, the Harrier FA2 GOES mach speed, Mach 1.25 at high altitude.

source

Originally posted by GrOuNd_ZeRo
I am not so sure about the B-2 my self, this thing is still shrouded in mystery and I do believe it's max speed is still classified, and rumors are that it was part of Project Aurora, all of these alledged designs were flying triangles able to go supersonic speeds and perhaps beyond, it might have been the least exciting Aurora plane, but i'm sure it's hiding some things, possibily a higher speed then led on, remember the B-1B is supersonic as well, that has been the trend.

source

The B-2 guys that I've talked to typically quote the 'high subsonic' range for the speed of their bird and once in a while will tag the top speed at altitude in the area of 450 kts...

As for the T-Bone, she is good for an advertised max of 1.25 Mach as opposed the original design that was good for about 2.3 Mach... Much of the degradation in performance being due to the change to fixed geometry inlets for the engines v. the variable geometry type on the B-1A...

Really an aircraft that is wider than it is long cant go supersonic? I never know that, is that true even if you put some monstrous engines on there with a lot of thrust.

The B-1A was actually a much lighter airframe than that B-1B. That's why it was so much faster. One of the big things with the B-1B is that they were only able to put three electrical generators on it, to help save weight so it could go supersonic, however because of this, it's horribly underpowered. On take off and landing they have to choose between deicing power, and enough systems power for other equipment. We had three out here one night that needed engine blade changes, and one engine change, because they didn't have enough power to deice taking off from Singapore, and took ice down the engines.

Originally posted by Zaphod58
I've heard of a couple cases where a plane was flown where you had to have one rudder pedal pushed almost to the floor that they flew for several months, and just waited until the plane went to the Depot for scheduled maintenance. One of the reasons they kept 007 in service was that it was used almost

Zaphod;

That's simply folklore; and here's why: When flying multi-engine aircraft, especially with wing-mounted engines, performance and control issues are often addressed within the context of "what if" and engine fails. In fact, takeoff planning is based on the assumption that an engine WILL fail. When an engine fails the pilot's ability to counteract the yaw caused by its failure depends on a number of factors, including how much rudder authority he has at his disposal.

For an aircraft that requires full, or even almost full, displacement of the rudder, the pilot would have virtually no ability to counteract an engine failure on the opposite side that the rudder is displaced. For instance; if significant right rudder was constantly required to fly straight, a failure of the left engine would necessitate even MORE right rudder. If the rudder is already mostly displaced to fly "straight" the pilot's only option would be to cut the operating engine(s) on the opposite side, or crash. This is why no pilot in his right mind would ever fly an aircraft with the condition you describe.

That said; I have flown both ancient (KC-135) and modern (B757/767) aircraft that sometimes required a couple spins on the rudder trim to make the aircraft fly coordinated. But there is always enough rudder authority to respond to an engine failure. There are limitations, however, how much trim is allowed. Beyond these limitations, the aircraft is grounded.

Originally posted by WestPoint23
Really an aircraft that is wider than it is long cant go supersonic? I never know that, is that true even if you put some monstrous engines on there with a lot of thrust.

Yes, its true. Long span, short chord relatively thick wings are efficient for subsonic cruising while to go supersonic you want short span, long chord very thin wings. To illustrate it simply look at how around, say, 1939 (and before) most aircraft had wingspans that were greater than their fuselgae length; ie Spitfire, Manchester, He-111, in fact almost everything. Then as speeds increased by the end of the war you began to see how wingspan shortened in relation to fuselage length. for one example of this look how the 600mph Meteor F4 had shorter wings but a longer fuselage than the preceding 490mph Meteor F.3. follow the progression through to the first supersonic fighters of the fifities and fuselage length continued to grow as wingspan receded, the ultimate example of this being the F-104. The best supersonic shape is a long and thin one. It is also why Concorde is long and thin with a narrow delta wing, its all about the aerodynamics of supersonic airflow and the absolutely huge drag rise experienced (simply put that for every increase in speed, drag increases by twice as much). You can look at any supersonic aeroplane that has ever been built and you will see that trend in design. Also, why do you think VG aircraft sweep their wings back for high speed flight? It certainly isn't for dramatic effect This is why the notion that something like the B-2 could be supersonic is nonsensical, as not only is the wingspan greater than the length, but hugely so and the B-2, if it could be propelled to such a speed would be so hopelessly uncontrollable that it would want to tumble end over end in a similar manner to a piece of cardboard if you threw it. This is what would cause the plane to disentegrate, not any inherent weakness in its structure but simply the immense stresses forced on the airframe from trying to make the wrong shape go too fast.

Just for a bit of fun I challenge anyone to prove me wrong with a supersonic plane with a wingspan greater than its own length as it would be interesting to see such a type.


Also, regarding the Harrier FA.2 (or any other model) The are distinctly subsonic in level flight at any altitude (despite wht that website may say) as the drag rise in the transonic region will not allow the tubby little wonder to pass the speed of sound, because the designers knew this full well (and dont forget the supersonic Harrier was a separate programme which was abandoned) the intakes are not designed or constructed to cope with supersonic airflow into the fan. Simple fact.

[edit on 17-6-2005 by waynos]

[edit on 17-6-2005 by waynos]