Can a 747 go supersonic in level flight?

Patch

Patch

Pre-takeoff checklist
Joined
Apr 16, 2007
Messages
194
Location
Oklahoma
Display Name
Display name:
Patch
Engineering types (and those who fly commercial airliners), I pose the question. Can an airliner reach supersonic flight, level with pure thrust? And would the aircraft be controllable under such conditions?
 
The answer is probably yes, but MMO (Max Mach) for the airliners besides the concorde is usually in the .78-.88 range. As you enter the transsonic speed envelope the drag goes up dramatically, requiring a lot more thrust, then it decreases when supersonic. I believe (but don't know) that the Concorde required afterburners to accelerate but not sure if they were needed to maintain the supersonic cruise speed.

I know that the 737/8/9 sims I've flown give me the clacker (overspeed warning) at .85-86 mach, so that's the max speed.
 
I'm pretty sure yes, though like Tim said, there are some difficulties in the transsonic range. Mach tuck and compressor stalls, for instance. If the aircraft actually manages to go transsonic, there are going to be areas along the fuselage and especially in the engine where the local airflow is supersonic...this tends to do bad things inside turbine engines.

When I was jumping this weekend in a 757, we were at 83% N1 and probably only 75% EPRs and maintaining an easy .82 Mach at FL390. I find it hard to imagine that they couldn't have added a little extra power taken that thing well past Mmo (turbines best power comes above about 72%...everything below that is pretty much idle.
 
Last edited:
I suspect that it's possible to get supersonic flow over some portions of the 747's anatomy with full throttle and little load, but I also suspect that you'd run into serious (possibly fatal) aerodynamic problems well before actually achieving an aircraft velocity of Mach 1. Outside of anything else, I think the engines would blow lunch as intake air velocity reached sonic values without some sort of inlet flow management system (spikes, ramps, etc).
 
Patch said:
Engineering types (and those who fly commercial airliners), I pose the question. Can an airliner reach supersonic flight, level with pure thrust? And would the aircraft be controllable under such conditions?
Click to expand...

I think the answer is no for several reasons. One is that an airplane not designed for supersonic flight is likely to be uncontrollable in the trans-sonic range as the shockwave builds over lifting surfaces and migrates to the control surfaces. Another is the thrust required to "break" the sound barrier is way more (like at least twice as much) than what it takes to get near Mach 1 and I doubt (but don't know) that a 747 has that much excess power. Finally as Ron mentioned high bypass engines like the ones on a 747 don't work well when a supersonic shock wave penetrates the intake.
 
I've heard anecdotally that a 747-400 was taken slightly supersonic in level flight during the test program. Anyone else heard this, or have any data?
 
Ron Levy said:
I suspect that it's possible to get supersonic flow over some portions of the 747's anatomy with full throttle and little load, but I also suspect that you'd run into serious (possibly fatal) aerodynamic problems well before actually achieving an aircraft velocity of Mach 1. Outside of anything else, I think the engines would blow lunch as intake air velocity reached sonic values without some sort of inlet flow management system (spikes, ramps, etc).
Click to expand...
Is the issue more ram air than the engine can handle or disruption of airflow to the engine resulting in a stall?
 
I'm gonna go out on a limb here, since it's been over twenty years since I last studied this stuff.

My recollection about the engines are: As the airflow goes sonic there is an invisible bow wave (air disturbance) that begins to form ahead of the engine. This compressed region of air slows the flow behind it. So, I'm gonna bet that the engine will have choked flow and flame out at the higher trans-sonic flows.

Flow over the wings is normally trans-sonic with grounds speeds of M>0.7 (and is airfoil dependent). As the the flow velocity is increased the air ahead of the wing begins to compress and forms a wave. If enough thrust is available this wave further compresses to form a shock wave. The angle of this wave changes from a vertical wall like shape to more conical with increased speed. As was mentioned, the required thrust to continue compressing the wave is cubic function (? I think). So, to get thru the sonic barrier is gonna require lots more thrust.

The issue of it going sonic is loss of flow over the control surfaces due to the reduced airflow behind the shock wave. As the shock wave forms and begins to bend back into the conical shape the aircraft becomes closer to the wave and flow behind the wave is reduced. This reduced flow causes a loss of control effectiveness.

So, there's my not so technical recollection.

Rick
 
Last edited:
I believe it can go supersonic one time <g>. May have to dive a little to get there!

I have a friend that flew the SST for Braniff. Can ask him some questions if you have specific ones.

Best,

Dave
 
TMetzinger said:
I believe (but don't know) that the Concorde required afterburners to accelerate but not sure if they were needed to maintain the supersonic cruise speed.
Click to expand...

I was talking to a BA Concord Capt who told me they ran in afterburner all the way across the Atlantic.
 
As far as I know, without putting any time or research into the matter other than what I can pull out my a...brain: the F-22 is the only aircraft that can sustain supersonic flight in level or climbing flight without the use of afterburners; or as they call it: super cruise.
 
Teller1900 said:
As far as I know, without putting any time or research into the matter other than what I can pull out my a...brain: the F-22 is the only aircraft that can sustain supersonic flight in level or climbing flight without the use of afterburners; or as they call it: super cruise.
Click to expand...
Teller is almost correct -- the F-111F (the F-111 model with the big engines -- 50% more thrust than the original F-111A) can just barely supercruise on a very cold day at low altitude, but it's not like the F-22 for which supercruising is easy throughout the envelope, and it was never either a requirement nor an advertised capability. And Henning is correct that AB is needed for supersonic cruise in the Concorde, although at 67,000 feet, you're not going blowing fuel out the back nearly as fast in AB as you are at sea level. At that altitude, you're nearly a ramjet engine, like the SR-71's J58's with the spikes fully displaced.
 
I don't believe the SR-71 used afterburning to maintain SS flight, but I could be wrong. I know it was available to go trans-sonic. They also performed a manuver called the 'dipsy-doodle' to attain SS flight. When transonic zone is reached, the pilot pushes over into a slight dive to moderate the pressure wave on the wing/elevon. Once SS flight is reached, the level flight can be resumed.

It's all about the heat.

The OP said 'level flight' and I'm gonna go with no, can't be done with the high bypass fan engine as is. Now, getting it SS by diving, and then maintaining SS flight would be tricky but possible with some modifications as Ron mentioned to the intake of the compressor. As for the rest of the leading edges, well - it might fly for a few minutes, but heat will eventually distort and destroy the nose, leading edge of the wing, and everything else that's exposed to the direct force of the air.

The SR-71 grew about a foot due to heat expansion, and most of it happended just after SS speed. I suspect the 747, although a great plane, would disintegrate quickly.
 
docmirror said:
I don't believe the SR-71 used afterburning to maintain SS flight, but I could be wrong. I know it was available to go trans-sonic. They also performed a manuver called the 'dipsy-doodle' to attain SS flight. When transonic zone is reached, the pilot pushes over into a slight dive to moderate the pressure wave on the wing/elevon. Once SS flight is reached, the level flight can be resumed.

It's all about the heat.

The OP said 'level flight' and I'm gonna go with no, can't be done with the high bypass fan engine as is. Now, getting it SS by diving, and then maintaining SS flight would be tricky but possible with some modifications as Ron mentioned to the intake of the compressor. As for the rest of the leading edges, well - it might fly for a few minutes, but heat will eventually distort and destroy the nose, leading edge of the wing, and everything else that's exposed to the direct force of the air.

The SR-71 grew about a foot due to heat expansion, and most of it happended just after SS speed. I suspect the 747, although a great plane, would disintegrate quickly.
Click to expand...
Doc, the SR-71 also had variable cones on the engine inlets to control the shock waves. The swept back wings also kept the lifting body behind the fore wave.
 
docmirror said:
I don't believe the SR-71 used afterburning to maintain SS flight, but I could be wrong. I know it was available to go trans-sonic. They also performed a manuver called the 'dipsy-doodle' to attain SS flight. When transonic zone is reached, the pilot pushes over into a slight dive to moderate the pressure wave on the wing/elevon. Once SS flight is reached, the level flight can be resumed.
Click to expand...
Acceleration to SS speed in level flight in the SR-71 is performed at about FL250 by using min AB up to M0.9, then full blower up to M1.1. At that point, everything changes, and acceleration increases rapidly, with the possibility of 450 KEAS being exceeded. If that happens, the WARNING in the -1 says to "Reduce power (below Military, if necessary) to avoid high airspeeds."

The climb-and-descent method (Doc's "dipsy-doodle") is initiated at FL300 by using min AB to M0.9, then max AB while holding 300 KEAS to FL330 and leveling off to accelerate to M0.95. At that point, a pushover is initiated to a 2500-3000 fpm descent to accelerate quickly to M1.05 and then holding attitude to accelerate to 435 KEAS and initiating a pull at that speed to establish climb attitude at 450 KEAS.

Either way, the process of accelerating from M0.75 at FL 250 to SS operation above M1.0 takes about four minutes and 5500 lb of of the rather exotic JP-7 fuel the SR-71 uses. Also, once SS flight is begun and climb is initiated, the climb is continued up to "operational altitude" for SS cruise. In any event, once in SS cruise flight, the engines are retarded out of AB only after initiating the descent and deceleration to below M2.6, somewhere below FL700. In all SS cruise cases, AB is called for in the flight manual. Also, reducing power below AB in normal SS cruise would probably result in a very, very bad reaction from the engines.

Reference: SR-71A Flight Manual, T.O. 1-SR-71A-1
 
Last edited:
I'd seen the flight manual before on the SR-71, but didn't read the whole thing. I just recall the dive manuver from discussions with a Habu driver way back. I guess the AB memory was faulty. As for the 747, I still maintain it would come apart pretty quick.
 
Henning said:
I was talking to a BA Concord Capt who told me they ran in afterburner all the way across the Atlantic.
Click to expand...

I'd be interested to know who that Captain was.

Concorde used afterburners to accelerate on the initial climb, and then again to accelerate through the sound barrier, but once supersonic she cruised with the afterburners turned off. They didn't carry enough fuel to burn on afterburner the whole way :)

There was a wonderful article in the BA Pilot's Log, called The Orange Pip effect, which described 'squeezing a 747, like you would squeeze an orange pip between your fingers so it would shoot out at high speed and thus achieve supersonic flight. I belive it was theoretical only ;-)

Concorde's engines were fitted with doors just inside the intakes, which were adjustable in flight. They slowed the air down to subsonic rates which teh engines could handle. Details can be read here: http://www.concordesst.com/powerplant.html

Hope that helps
Geoff
Son of Senior Route Check Captain - Concorde Fleet
 
Tiggs said:
I'd be interested to know who that Captain was.

Concorde used afterburners to accelerate on the initial climb, and then again to accelerate through the sound barrier, but once supersonic she cruised with the afterburners turned off. They didn't carry enough fuel to burn on afterburner the whole way :)

There was a wonderful article in the BA Pilot's Log, called The Orange Pip effect, which described 'squeezing a 747, like you would squeeze an orange pip between your fingers so it would shoot out at high speed and thus achieve supersonic flight. I belive it was theoretical only ;-)

Concorde's engines were fitted with doors just inside the intakes, which were adjustable in flight. They slowed the air down to subsonic rates which teh engines could handle. Details can be read here: http://www.concordesst.com/powerplant.html

Hope that helps
Geoff
Son of Senior Route Check Captain - Concorde Fleet
Click to expand...
Geoff, Welcome to the board.

Ya had me going with this thread when I saw 20 posts but didn't recall it. The Concorde was a neat bird. It's sad to see it go but I guess it was never going to be a good money-maker for BA.
 
KennyFlys said:
Geoff, Welcome to the board.

Ya had me going with this thread when I saw 20 posts but didn't recall it. The Concorde was a neat bird. It's sad to see it go but I guess it was never going to be a good money-maker for BA.
Click to expand...

Thanks. Sorry about that - was googling something else and stumbled across it :)

Actually, once the development costs were written off, she was turning a tidy profit. But the airframe was getting to the end of its life and once the decision was made not to make any new parts her days were effectively numbered.
 
Ron Levy said:
That sounds a lot like, "Yeah, at that price, we lose money on each sale, but we make it up on volume.":rofl:
Click to expand...

It's more like a manager who's compensation depends solely on operating profit: "Don't make me expense that item, even though I buy a new one every year! How do you expect me to show an operating profit unless I capitalize that (and put that expense below the line)?"
 
Patch said:
Engineering types (and those who fly commercial airliners), I pose the question. Can an airliner reach supersonic flight, level with pure thrust? And would the aircraft be controllable under such conditions?
Click to expand...

Patch,
I am not much of an engineer type but I will try to give you a real world answer. The answer to both the thrust question and the controllibility question is a definate no. As you gain altitude (If I remember all of this correctly) the speed of sound decreases so you can fly at a higher Mach . Part of the problem is that the higher you go, the more power it takes to maintain a given criuse mach. This is why a heavy airliner will typically level off a few thousand feet below its final cruise altitude for a couple hours until it is light enough to climb and maintain cruise mach at its final altitude .
Another factor (The engineering types can help out with this one) is buffet onset speed. If I remember ground school correctly it is caused by air going supersonic across parts of the plane and it feels just like a stall buffet. If you were to continue to increase the speed past this buffet it would result in what I can only describe as a high speed stall and a loss of controll. A crew at a certain airline years ago oversped a 727 over Florida and they lost about 20 thousand feet of altitude before they regained controll.
Years ago when I was a punk ass newhire we used to have what Boeing called "Flight Conduct Charts" which would tell you your max speed and altitude based on wieght, ISA Dev, G loading , and max continious criuse power. For an example , on a given day you could criuse .82 at FL350 or .80 at FL370 etc. This was all a funtion of available power and the buffet onset speed. The chart would give you the maximum and minimum speeds at a given FL. The higher you go the closer these speeds get until they are only 40 KTS or so between the min manuvering speed and the pole at a typicall at criuse. Nowadays this is all figured out by squirels and an abicus behind the EFIS panel and it is displays on the FMS and the speed tape. Hope I didnt confuse you.
Frank
 
I thought one of the requirements for supersonic capability was a stabilator/"moving tail" (to work through the transonic shock waves)?

Does the 747 have a stabilator? I thought it was a horizontal stabilizer with elevators.
 
jshawley said:
Does the 747 have a stabilator? I thought it was a horizontal stabilizer with elevators.
Click to expand...

All airliners have a moving stabilizer and elevators. The leading edge of the stab is moved up or down for trim. The stab is trimed automatically on the Boeings as they accelerate through .63M (Or so depending on the model) for stability.
Frank
 
F.Baum said:
Patch,
I am not much of an engineer type but I will try to give you a real world answer. ...k
Click to expand...

Interesting (really not being a smart ass).


I wonder if Patch is now more of an expert than when he first asked this question as he is now flying supersonic aircraft?? :dunno:
 
Ron Levy said:
That sounds a lot like, "Yeah, at that price, we lose money on each sale, but we make it up on volume.":rofl:
Click to expand...

Ah, but it wasn't BA who were writing off the costs, they didn't pay to develop it, so were making profit all the way. Sorry to say it, but she was restricted more by US environmentalists than other factors (although there were issues over maximum range - but hey, this was a 1960s design!)

Concorde had an advantage, in that she operated on her own route with nothing above her to worry about, and the only thing coming the other way was the other Concorde, so they would let her climb as she burnt off fuel rather than be fixed to a specific FL. She also 'flew different', especially on the landing, as she was a delta configuration.
 
Worked a Swiss Air B747 Special once, I wanted to speed him up to get ahead of another aircraft, needed 20 miles intrail to JFK. He advised me that he was already at .91, I was surprised and asked him how fast he could actually go. He told me that someone at Swiss Air had it between .94 & .95 mach, but the aircraft began to buffet. He said the power was there to go faster but no one had ever tried it.
 
You must log in or register to reply here.
Back
Top