The Basket
Senior Master Sergeant
- 3,712
- Jun 27, 2007
BAe 146 may have gone supersonic in a vertical dive.
Question about airliners
- Thread starter Thorlifter
- Start date
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BAe 146 may have gone supersonic in a vertical dive.
Did it land? I read six of these have been lost for various reasons, nice plane to be a passenger on though.
The Basket
Senior Master Sergeant
- 3,712
- Jun 27, 2007
Yes I like the 146.
See them flying over my head on my drive to work coming in to land.
146 did land. Kinda.
Pacific Southwest Airlines Flight 1771 - Wikipedia, the free encyclopedia
That must be one of the 6 I read about, as I remember not one was to do with the actual plane. It does say that it disintegrated, cant think of a modern plane that looks less likely to break the sound barrier than a 146. Wide body and engines hanging all over the place
The Basket
Senior Master Sergeant
- 3,712
- Jun 27, 2007
Certainly disintegrated when it hit the deck.
fastmongrel
1st Sergeant
The Hawker Siddeley Trident was one of the fastest subsonic passenger jets designed to cruise at up to mach 0.88 and have a critical mach 0f 0.93. I wonder if it could have broken the sound barrier if the pilot had accidentally let the nose drop in a high speed turn.
The Basket
Senior Master Sergeant
- 3,712
- Jun 27, 2007
The only airliners that could have gone supersonic did it in graveyard dives.
DC8 is the exception.
I plumbed the DC-8 for awhile, and the thing that amazed me about that 45 year old airplane was how smooth it was. You could look down the side of the fuselage and it was as smooth as glass, no ripples, crinkles, or any other perfections. Loud, fast, and thirsty! They don't make them like that anymore...
Jabberwocky
Staff Sergeant
Almost everything in commercial aviation at the moment is geared around generating maximum fuel efficiency, because fuel is typically 35-45% of the cost of running an airline. Airliner wings are designed for a pretty narrow optimum cruise speed range. Too fast or too slow and it really eats into the fuel consumption.
Typically a commercial aircraft will cruise at .80-.86 Mach. Despite more aerodynamically efficient aircraft entering service - 787, A350, A380, 747-8 ect - operational cruising speeds have actually been static or decreasing a little.
The latest version of the 747 cruises at .85 Mach, a little slower than the earlier 747-400, which cruises at .855-.86. This is despite the 747-8 having an extra 10,000 lb of thrust available, per engine.
I know Southwest Airlines has chopped 10 to 20 knots off average cruising speeds for their 737NGs in the last five to six years. Ryanair, also a 737NG operator, has also cut its cruising speeds back in the last 12 months. The result is $400-500 in fuel saved per flight.
Doesn't sound like much, but if you're Southwest and you're running a fleet of nearly 600 aircraft, and each aircraft operates an average of six flights per day, you're talking millions of dollars.
Typically a commercial aircraft will cruise at .80-.86 Mach. Despite more aerodynamically efficient aircraft entering service - 787, A350, A380, 747-8 ect - operational cruising speeds have actually been static or decreasing a little.
The latest version of the 747 cruises at .85 Mach, a little slower than the earlier 747-400, which cruises at .855-.86. This is despite the 747-8 having an extra 10,000 lb of thrust available, per engine.
I know Southwest Airlines has chopped 10 to 20 knots off average cruising speeds for their 737NGs in the last five to six years. Ryanair, also a 737NG operator, has also cut its cruising speeds back in the last 12 months. The result is $400-500 in fuel saved per flight.
Doesn't sound like much, but if you're Southwest and you're running a fleet of nearly 600 aircraft, and each aircraft operates an average of six flights per day, you're talking millions of dollars.
I never worked on the DC-8, a little before my time, but they were/are a most underestimated aeroplane. Throughout the 70s and 80s, the DC-8 crossed the Atlantic on a daily basis more often than any other type until the arrival of the 767 in large numbers. It wasn't without its problems, though. In the beginning Douglas got the wing design wrong and it cost the company enormously, since it didn't make its range/payload performance figures. Granted it was fast, but the Convar 880 and 990 were faster (they might have been able to break the sound barrier in a dive and hold it together), but they were too costly and also didn't make their range/payload figures, which killed them off. The secret to the success of the DC-8 was in the fact that its undercarriage and structural design meant it could be stretched and fitted with engines of bigger power output - high bypass fans. The 707 couldn't be stretched in the same way because of its undercarriage design, although it too, in the KC-135R with CFM-56s had big fans, although the commercial pax variants never had the high bypass fans, just low bypass ones. Boeing had a different philosophy; build different airframes with common features - the 727, 737 and 707 all shared the same fuselage width, cockpit and windscreen layout, but were different aircraft to fit different requirements. The DC-8 was stretched and re-engined and the many improvements it was subject to could be retrofitted to almost all variants. There are no DC-8s in pax service, but world wide they still provide freight services. Great aircraft.
In the past I flew (as a passenger, of course) on Alitalia's DC8s, and still remember the comfort, the smoothness of the fly and the lack of vibrations ..... very different from the "nervous" behaviour of today's airliners.
Probably this was depending from the fact that once an aeroplane was designed to fly "all alone" once trimmed, while today the design of an airplane is optimized (wing profiles, position of CoG etc.) to save fuel, as a computer will take care of the fly.
Probably this was depending from the fact that once an aeroplane was designed to fly "all alone" once trimmed, while today the design of an airplane is optimized (wing profiles, position of CoG etc.) to save fuel, as a computer will take care of the fly.
Too a degree; automated systems only go so far. When the proverbial hits the fan, that's when the pilot earns his pay packet.
One speedster not specifically mentioned is the 747-400, still the fastest airliner around; could leave anything in its wake, including a 727, which was no slouch.
Of course: this is the very reason for there is a reduntant system with two or three of them inside an airliner....
But, after the Malaysian B777, someone is probably thinking different things.....
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Lucky13
Forum Mascot
Ramjet?
davparlr
Senior Master Sergeant
Typically, fixed supersonic inlets have limited max mach capability, around 1.6 mach, whereas variable inlets allow efficiency over a larger mach range. It operates by controlling oblique shock waves (angled), which allows better control and efficiency of supersonic to sonic airflow. The super hornet does not have a high max mach speed over the hornet which I don't understand. Perhaps it is for efficiency or possibly more efficiency at mach speeds.
GregP
Major
According to friends of mine who flew them, the Boeing 727 could go supersonic without too much fanfare, but the fuel efficiency went to pot and they were not authorized to do so anyway. The ones that DID go supersonic didn't hit any large mach numbers, they stopped at Mach 1.03 or so since that was above design speed anyway.
Not being rated in a Boeing 727 myself, I cannot make a comment for or against the assertion, but I've heard it from at least a half dozen former 727 pilots. Supposedly they were running the engines at quite low settings while at cruise. Again, I have no first-hand knowledge of the settings, but could ask if anyone is interested.
They know for sure the one that did an uncommanded barrel roll over Detroit and lost the flaps on the way down went supersonic and was recovered by lowering the landing gear. It was repaired and returned to service where no further supersonic flight was officially recorded. I think that airframe is now out of service along with most other B-727s other than those in private hands or still running freight.
Not being rated in a Boeing 727 myself, I cannot make a comment for or against the assertion, but I've heard it from at least a half dozen former 727 pilots. Supposedly they were running the engines at quite low settings while at cruise. Again, I have no first-hand knowledge of the settings, but could ask if anyone is interested.
They know for sure the one that did an uncommanded barrel roll over Detroit and lost the flaps on the way down went supersonic and was recovered by lowering the landing gear. It was repaired and returned to service where no further supersonic flight was officially recorded. I think that airframe is now out of service along with most other B-727s other than those in private hands or still running freight.
Yep, all supersonic aircraft need what's called a convergent/divergent duct as an intake. This configuration slows the airflow down and prevents the formation of shock waves at the compressor face. In a fixed inlet geometry supersonic inlet, the supersonic air slows to roughly mach-1 within the convergent section by air compression and the formation of shock waves at the intake's throat and when entering into the divergent section the air then slows even more, but pressure builds before entering the compressor.
In a variable inlet, or supersonic diffuser inlet creates a shock wave at the mouth of the intake to reduce air velocity - as in a fixed inlet, but with a variable convergent/divergent shape is able to meet various flight conditions from take off to cruise more efficiently than a fixed inlet. In supersonic speeds, the throat area is reduced at the intake face, creating the convergent condition to enable the formation of shock waves at the intake mouth and dump and spill valves open to vent excess airflow. At subsonic speed, the convergent section is wider and enables a greater flow of air to the compressor, with dump valves open to increase air flow into the intake.
On the subject of supersonic intakes, here's some info on the SR-71's intake spike that I put in my thread on the Blackbird walkaround:
The starboard engine intake spike. These were moveable, travelling 26 inches between fully retracted and extended. At full extension speeds of up to Mach 1.6 were capable with full retraction at Mach 3. Correct operation of these spikes was crucial to maintain the correct flow of air to the compressor and an electronic Digital Automatic Flight and Inlet Control System was developed by Honeywell for controlling the inlets and also the aircraft's stability augmentation system and autopilot after severe problems encountered when pilots attempted this manually. If the spikes were not positioned correctly, the shock wave that forms at supersonic speeds at the lip of the engine intake would be expelled from the inlet, resulting in what became known as an 'unstart'. The result was a lack of air to the compressor, high exhaust gas temperatures and no thrust from the unstarted engine, which caused violent yawing to one side. At three times the speed of sound, this was decidedly hazardous.
See here: http://www.ww2aircraft.net/forum/wa...alkarounds-nuuumannn-36981-4.html#post1059302
The starboard engine intake spike. These were moveable, travelling 26 inches between fully retracted and extended. At full extension speeds of up to Mach 1.6 were capable with full retraction at Mach 3. Correct operation of these spikes was crucial to maintain the correct flow of air to the compressor and an electronic Digital Automatic Flight and Inlet Control System was developed by Honeywell for controlling the inlets and also the aircraft's stability augmentation system and autopilot after severe problems encountered when pilots attempted this manually. If the spikes were not positioned correctly, the shock wave that forms at supersonic speeds at the lip of the engine intake would be expelled from the inlet, resulting in what became known as an 'unstart'. The result was a lack of air to the compressor, high exhaust gas temperatures and no thrust from the unstarted engine, which caused violent yawing to one side. At three times the speed of sound, this was decidedly hazardous.
See here: http://www.ww2aircraft.net/forum/wa...alkarounds-nuuumannn-36981-4.html#post1059302
Jabberwocky
Staff Sergeant
The 747-400 typically cruises at .83 to .855, which probably makes it the fastest in service at the moment. Most other jets are .80-.83.
The fastest sub-sonic commercial jets were probably the Convair 990 or the Boeing 747SP, where the SP stands for Special Performance. Both used to cruise at .86 to .88.
