Supersonic 747

[18-Wheeler]

If you got a couple of brave chap(ette)s and strapped them into a 747, got it up nice & high and then stuck the nose far down with max thrust and hung on ..... would it -
- Go supersonic.
- Be controllable.
- Hang together.


From a discussion on another forum.

[Dop]

I'm no aviation expert, but I find the phrase 'Crash Horribly' comes to mind.

[5150]

With a decent tailwind you'd get a supersonic groundspeed out of it. . . . does that count??! :E

[Bearcat]

i believe on the flight tests during dives well into the mach .9s were achieved. Also there was a major incident with a far east (china?) 747 yrs ago where they made a balls up of an engine flame out on the pacific.....between the farting around and doing nothing the aircraft ended up in a spiral dive and they reckon some of the control surfaces went supersonic.

[SR71]

Vne = 0.92 I believe.

Then you'd nose over into irrecoverable(?) Mach Tuck if its anything like the 737.

[chornedsnorkack]

One DC-8-4X did reach Mach 1,012 already in 1960-s and recovered. A shallow dive as a part of deliberate flight testing.

They also had water ballast tanks AND pumps installed in the cabin to resist Mach tuck.

Can any subsonic plane recover from a Mach 1,000 dive without ballast pumps?

Which ones? Is 747 among them?

[Capt Fathom]

Vne = 0.92 I believe

Well it's only another 30kts indicated from there to Mach One! :ok:

[SR71]

You first!

:ok:

[18-Wheeler]

Boeing tested the prototype up to M 0.991. I can't find anything that confirms for sure that the China Airlines SP went supersonic, in fact it seems more likely that it didn't.
The other thing that was talked about is that the engines would likely flameout.

[Meikleour]

To the best of my recall, the B747 is not fitted with a Mach Trimmer (cf the B707) therefore if the certifying authorities deemed it unnecessary then I presume that the handling at high mach nos` is benign. Remember also that demonstrated Vmd is quite a bit higher than Vne. Never was a problem demonstrating it in the sim on conversions however fidelity may be an issue here.

[mrcabbage]

Link to video:
http://www.liveleak.com/view?i=e9f_1180909211

[wotan]

if its worth anything the GIV went supersonic in a dive during initial flight testing, or so i'm told

[PyroTek]

mmm.. if one was to attach some trent 900 engines instead of the Rolls 747 engines (provided they'd fit properly), add structural strength AND install some disposable, but strong rockets on the fuselage, could be a fun experiment!

(don't try this at home kids)

[mustangsally]

Why would any pilot want to take an aircraft beyond it's defined envelope?

During acceptence flights, I've taken the Classic to Vmo/Mmo, 392 KIAS/0.92 M. Between FL 26 and 29 in level flight advance to maximum rated thrust and accellerate. This usually produces something about 380KIAS. A slight push over will result in the 392/.92 rather quickly, with the over speed warning within 3 kts and .01 M. And thats what we want to see. Every once and a while you get a very slight burble or low rumbel as the air starts to go supersonic somewhere above the flightdeck.

Generally the intake airspeed of a jet engine does not like supersonic airflow. I would hate to see the dampage on the N1 rotors after any lengthy exposure to this rate of airflow and the boundary separation that would be occurring. As the airflow entered the N2 the engine would likely fail.

Want to go supersonic in a 747, go fly down wind in the jet stream, as previouly suggested.

[nosefirsteverytime]

Why would any pilot want to take an aircraft beyond it's defined envelope?



You don't watch Top Gear then? :)

[tightcircuit]

I have been supersonic a couple of times in a/c that had the airframe capability but not the thrust (no re-heat). I takes a lot of oomph to get throught the barrier. In both of the types the technique was to climb to fl450 then with full power roll inverted, pull the nose to 45 degrees down then roll right way up again. You were supersonic just long enough to say "wow hasn't it gone quiet and smooth" before pulling like hell to avoid making a bid hole and a nasty mess. G capability is much reduced when supersonic due reduced lift. Bearing this in mind I think the chances of getting a 747 supersonic and surviving it are pretty slim.

[Milt]

The Mythbusters will probably come up with the answer!!

Incidently if you ever achieve Mach tuck with the stick hard back and the pitch down continues, let it go under and roll out the other side - better than making a big hole in the ground.

[hoggsnortrupert]

Not that I've ever flown the thing but?
Surely the thing would "take a dive" Cof P Where?( considering of course it had the thrust to push it through/displace the bow wave).
H/Snort

[Capt Fathom]

Why would any pilot want to take an aircraft beyond it's defined envelope?

Want to go supersonic in a 747, go fly down wind in the jet stream, as previouly suggested.

I don't believe anyone has suggested taking a 747 supersonic!

It's an interesting discussion though. I seem to recall it got a mention in the book, 'Handling The Big Jets'.

From what you posted Mustangsally, you're the only one here who has nudged the envelope! :)

[18-Wheeler]

From what you posted Mustangsally, you're the only one here who has nudged the envelope!

Me too.

http://www.billzilla.org/highindicated.jpg

http://www.billzilla.org/reallyhighmach.jpg

The aeroplane handled just fine at those speeds.
The stabiliser trim should have more than enough authority to counter mach tuck - there's usually only about 4 units set in the cruise, with 9.0 available.

[airseb]

for what it's worth (and i'm not comparing the two machines) they pushed the a380 to M0.937 during the testing. and that's where they stopped.
i guess it took a lot of breakers being pulled out...

seb

[Condor66]

If you put a 747 into a fairly steep nose down attitude, you might be able to achieve a speed higher than mach .85 which is its cruise speed, but the wings and airframe were never designed to withstand those kinds of speeds. The airfoil is considered " subsonic" which means that it flies optimally below the speed of sound. I expect if you attempted to fly it beyond its specified design parameters, the wings would buffet violently, creating tremendous drag and possible structural deformation if it continued unabated. For an airplane to come close to the speed of sound (transonic) or beyond the speed of sound (supersonic) the airfoil must, among many other factors, have a high degree of sweep - like the Concorde. The airfoils currently on all modern jetliners, as remarkably advanced and efficient as they are, are simply not designed to deal with those kinds of speeds. They fly most efficiently between speeds of mach .74 and mach .85. Hope that helps you out!!!

[Pugilistic Animus]

---I would think think the failure mode would be flutter or divergence, as the 747 exhibited a Mdf of M 0.998 [flown by the OEM] so it does have a controllability at high Mach numbers.

as mentioned above the DC-8 was the first civilian airliner to go sonic [which is actually extends a little above Mach 1.000]. this was done in a high speed dive from 50000 ft. in {I believe ] 1953

The Boeing 727 also had an interesting excursion to Mach 1.?? after someone tried to emulate Ol' Tex

[Loose rivets]

I was just going to mention that. When they dumped the gear, the passing breeze modified the airframe. Just shows what one is up against when you try to get home early.


I flew past Geneva one day, and anouced to my pax that we had a ground speed greater than the speed of sound at our height. I wonder if there was one SOB that understood.

[AAIGUY]

I have done .92 before in a Classic. No instabilty issues.

[CR2]

18W, were you flying right-seat when you took that photo?

[18-Wheeler]

18W, were you flying right-seat when you took that photo?

Yep. It was at the end of the 2002 Hajj, we were handing back a 747-300 to the owners at the end of the contract and had to perform a flight test, etc.

[Mr Good Cat]

Correct me if I am wrong, but in a normal cruise on the 747 doesn't the big hump at the front travel supersonically anyway? I believe the pronounced camber of the upper deck at that point results in the air above it travelling supersonically...

[ChristiaanJ]

The quoted Mdf of 0.998 for the 747 makes me smile.

First because it's only about 1 kt below Mach 1, secondly because an accuracy of 0.2% so close to Mach 1 is unlikely (think Machmeter and VSI "jump").
I would think they probably "hit" Mach 1 and a bit, but didn't want to write that in the final report :)

Oh, and to add another "airliner" to the Mach 1 club:
The RAF VC10s have the shorter fuselage of the early model VC10, but the more powerful engines of the later models.
It is told (but never confirmed officially AFAIK) that when empty and with most of the fuel burned off, they actually could reach and exceed Mach 1 in level flight at altitude......

Condor66,
I'm afraid you're barking up all the wrong trees.
- Jetliners are designed to withstand that sort of speed. The DC-8 supersonic dive was part of the flight test programme.
They are not designed to operate at that speed, because of the drag rise.
- There is no "tremendous buffet". We left that behind in the '50s.
- You don't need a Concorde-like sweep to reach and exceed Mach 1. The Sabre, the Hunter, the Mig-15 all had 30° to 35° sweep, and all were supersonic in a dive.
- You don't need a "supersonic" airfoil either to go supersonic. The aircraft cited above do not have "supersonic" airfoils, and neither does the DC-8.

[chornedsnorkack]

secondly because an accuracy of 0.2% so close to Mach 1 is unlikely

Distinguishing between 0,998 and 1,000 ought to be easier than distinguiching between 1,010 and 1,012 - and the latter is the known speed of DC-8. After all, it is precisely at Mach 1,000 that the shocks propagate indefinitely into undisturbed airflow? Finding how far from the plane the shocks terminate would indicate what is Mach 0,998, Mach 0,9990 or Mach 0,9950...

[ChristiaanJ]

chornedsnorkack,
Thanks for demonstrating your ignorance... once more.

[spannersatKL]

Meikloer (post on Previous page) sorry poor spelling of your handle.
B747 Does have Mach Trim....its part of the Stab Trim Screw Jack assembly.

[Melax]

I don't think the FEDEX DC-10 broke the sound barrier but if I recall well one or more 727 did so for a short period of time during a flight upset.

[Pugilistic Animus]

Melax, I think I know the incident you're speaking about???

a 727 departed controlled flight and entered a high speed upset, due to a TS encounter---but I don't know more--- i hope someone can enlighten us both further on the flight----in the same incident, I also believe and the had to wait until a much lower altitude to regain control due to high Mach or stab jamming??----sure seems people love to pull 'Chuck Yeagers' with the 727, however she's a tough one:E

jets can easily be pushed to their or past Vdf value while in a gentle climb at relatively low altitudes or---- way past Mmo to perhaps very close to Mdf at higher levels on thrust alone no dive needed!!!

Merry Christmas y Feliz Navidad, Happy Chanukah, Happy Kwanza---To all the wonderful contributers on Pprune---PA

[Shanwick Shanwick]

Mach .95 in a 744 a couple of years ago in mountain wave with the thrust levers at idle. Didn't cause any handling problems but the buffet noise above the flightdeck was rather alarming!

[stilton]

.92 in a 727 200 a few years back, right at Mmo, very stable, bit noisy though!

Sweet machine.

[PBL]

For an airplane to come close to the speed of sound (transonic) or beyond the speed of sound (supersonic) the airfoil must, among many other factors, have a high degree of sweep

Dear me. Like the Bell X-1, I suppose.

PBL

[Brian Abraham]

Or an F-104 :=

[False Capture]

The Pacific Southwest Airlines (PSA) BAe146 (reg: N350PS) achieved M1.2 before it broke up follwing a dive from 29 000ft to 13 000ft. This was the terrible hijacking in December 1987 when a disgruntled ex-employee shot both pilots and put the aircraft into a steep dive which killed all 44 people onboard.

[Mac the Knife]

http://upload.wikimedia.org/wikipedia/commons/3/33/Bell_X-1_color.jpg

[Iceman49]

Our squadron had a C-141 that had a yaw damp problem at 410, did a split-s and recovered at 12000, supposedly went mach1+ in the dive.

[Meikleour]

SpannerKL

Thanks for your input however are you sure that this is active? Re-reading my copy of `Handling the Big Jets` page 266 where DP Davies the then CAA Chief Test pilot discusses the B747 certification flying programme he says that the Stab Trim Brake mechanism was made to be compatible with a Mach Trimmer however that was deleted from the final design. Also the flighdeck has no such controls and the MEL makes no mention of a Mach Trim system therefore I assume that it is not in fact installed. The aircraft exhibits a natural pitch-up at M0.94

[ChristiaanJ]

Bell X-1 and F-104 have straight wings, yes, but they DO have thin airfoil profiles (which doesn't help with low-speed performance... the F-104 has blown flaps to at least mitigate that effect).

To go back a moment to the initial question, I think we can state.... :
yes, most or all of the big 'uns (and probably most of the smaller spamcans) CAN reach Mach 1 and slightly over. Some have done so deliberately (such as the DC-8), some due to circumstances outside their volition....

Just don't try this at home, kids. You may end up having to explain a bent airframe.

And while we're on the subject...
I suppose you know that the critical Mach number of the Spitfire is M0.92?
And that it's quite plausible that at least one Me-262 broke the sound barrier towards the end of WWII?
And that it's most likely that George Welch went over Mach 1 in the XP-86 Sabre, weeks before Chuck Yeager did the "Right Stuff" ?

I like cans of worms....

[EDML]

Aerodynamically it makes sense to have swept back wings below M 1.0
(in the transsonic range) to avoid the onset of Mach effects on certain
parts of the airframe.

Once you are above M 1.0-1.1 that does not matter anymore as everything
is supersonic anyway.

Furthermore there are even people around claiming that the drag of a
straight wing at full supersonic speeds (> M 1.3-1.5) is even lower than
that of a swept back wing - however I do not fully believe that.

EDML

[CV880]

You can read a Douglas press release and an extract of the flight test report for the supersonic DC8 flight at www.dc-8jet.com. The attached photograph indicates it was a Canadian Pacific DC8-40 series with RR Conways that was testing a revised wing design (Since Douglas increased the chord of the DC8's leading edge to improve cruise performance at some point in production I guess this was a part of the testing of that production change).

[Pugilistic Animus]

CV88: I was happy to see that Douglas report--- It seems I have the year wrong in my post---DC-8 Supersonic 1961:O--- still the first!

ChristaansJ: actually I believe the Boeing figures were TMN not IMN---so position error and compressibility errors were accounted for were accounted for

--- the account I read of the test was from Davies' "Handling the Big Jets", I have to take a look

[Brian Abraham]

And that it's quite plausible that at least one Me-262 broke the sound barrier towards the end of WWII?
And that it's most likely that George Welch went over Mach 1 in the XP-86 Sabre, weeks before Chuck Yeager did the "Right Stuff" ?

It has been recognised that George Welch was the first. Chucks claim to fame is being the first to do it in level flight (Mach 1 that is). As to the 262, the claim that it did,or may have, has been put to rest as a no. There is a comprehensive post war test report done in the US somewhere on the web.

[Anotherflapoperator]

That 146 incident must have been pretty hairy up to the point of failure...the poor old thing only has a VNe of 305kts or .72M on the -300 model. The 146 is a slow boat, and the thick slow speed wing is not happy at high speed at all. -200s tend to have a little hump or tuck at .67 but the memory's fading away nowadays.

[ChristiaanJ]

As to the 262, the claim that it did,or may have, has been put to rest as a no. There is a comprehensive post war test report done in the US somewhere on the web.There's Hans Guido Mutke's story, and there's "circumstantial evidence" in the "Me-262 Pilot's Handbook", which is the report you refer to (has been around for years, I have a facsimile copy somewhere).
See http://mach1.luftarchiv.de/mach1.htm.
I've seen better write-ups, that's just the first one, with most of the details in one place, that I pulled off Google for this reply.

My own opinion: certainly possible, quite possible, not proven.