Is VMO an absolute aerodynamic limit ?
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Originally Posted by Re-Heat
I always thought that many speed limits were the limits at which significant damage to the structure could start to occur - clearly structural failure rarely happens immediately at any operational speed, and flying up to published limits would not break the aircraft at that point in time, but result in many structural repairs to prevent eventual failure at a later date under normal operating conditions??
Another problem would be gust, which can be quite challenging for the airframe at such air densities.
I would assume that for "good" configuration (lots of weight in the wings) and careful handling the VMO can be exceeded by a fair margin at low altitudes. Weather should be corresponding.
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Mmo is not purely for jets. Modern fast turboprops ( say the Dornier 328 ) will climb to 31,000' where permitted. Its limits from memory are 270 KIAS or Mach 0.56.
The Embraer 135/145 series limits are quoted as:
Mmo/Vmo M0.78 OR 320 knots from 37,000 feet to 10,000 feet, reducing in a straight line to 250 knots between 10,000 feet and 8,000 feet.
Below 8,000 feet it's a windshield limit. (In the U.K. it's normally an airspace limit of 250 knots below 10,000ft. anyway.)
The Manual states: Vmo/Mmo may not be deliberately exceeded in any regime of flight (climb, cruise or descent).
The Embraer will exceed its published limits straight and level. Below about 25,000 feet, 320 KIAS will be reached first. Above that level, it will be M0.78 reached first. Review your tech books for an explanation.
A Company will issue its Pilots with procedures regarding the reporting of overspeeds in consultation with the Manufacturer. It is likely that an overspeed will ground the aircraft until inspected. Information is held by Engineering regarding checks to be made on the aircraft. The aircraft is not likely to sustain any damage with short overspeeds- that's why the limits are set where they are.
The Embraer 135/145 series limits are quoted as:
Mmo/Vmo M0.78 OR 320 knots from 37,000 feet to 10,000 feet, reducing in a straight line to 250 knots between 10,000 feet and 8,000 feet.
Below 8,000 feet it's a windshield limit. (In the U.K. it's normally an airspace limit of 250 knots below 10,000ft. anyway.)
The Manual states: Vmo/Mmo may not be deliberately exceeded in any regime of flight (climb, cruise or descent).
The Embraer will exceed its published limits straight and level. Below about 25,000 feet, 320 KIAS will be reached first. Above that level, it will be M0.78 reached first. Review your tech books for an explanation.
A Company will issue its Pilots with procedures regarding the reporting of overspeeds in consultation with the Manufacturer. It is likely that an overspeed will ground the aircraft until inspected. Information is held by Engineering regarding checks to be made on the aircraft. The aircraft is not likely to sustain any damage with short overspeeds- that's why the limits are set where they are.
Last edited by fleecy; 18th Jul 2007 at 15:54.
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Some posters seem to be less than clear about the fact that VMO and MMO are certified limits.
The aircraft does not promptly come apart, but you start to compromise the "advertised" life of the airframe, when you exceed those limits.
To establish those limits, the aircraft has been flown to well beyond those limits in a carefully controlled manner. Concorde has an MMO of 2.04, but the certification aircraft went up to M 2.23. For those who know the Concorde story: it was one of the reasons the two cerification aircraft (201 and 202) never went into service in the end. It was extremely difficult to assess how much of the aircraft's "life" (in terms of fatigue cycles) had been used up by the certification flights to the edges of the envelope.
The aircraft does not promptly come apart, but you start to compromise the "advertised" life of the airframe, when you exceed those limits.
To establish those limits, the aircraft has been flown to well beyond those limits in a carefully controlled manner. Concorde has an MMO of 2.04, but the certification aircraft went up to M 2.23. For those who know the Concorde story: it was one of the reasons the two cerification aircraft (201 and 202) never went into service in the end. It was extremely difficult to assess how much of the aircraft's "life" (in terms of fatigue cycles) had been used up by the certification flights to the edges of the envelope.
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Originally Posted by BelArgUSA
If the US/FAA uses low altitude turkeys made in USA, they better come down here in Andes, and revise their certification standards. We have turbocharged condors here, probably fitted with O2 masks on their beaks, flying above 20,000 feet...
Originally Posted by Kiwiguy"
Next you'll be telling me they're IFR rated ?
No actually I read somewhere that the 757's windshield is rated to only 313 knots for birdstrike.
As mad scientist notes many aircraft are VMO limited by windscreens.
No actually I read somewhere that the 757's windshield is rated to only 313 knots for birdstrike.
As mad scientist notes many aircraft are VMO limited by windscreens.
Now bear with me a sec.
VMO is IAS, no?
Now (off the top of my head) 300 KIAS is over 500 KTAS at those altitudes.
And for impacts such as birdstrikes, it's TAS that defines the energy of the impact, not IAS, so the energy is about three times that at sea-level.
Oops.... do we have a problem?
Should we start fitting condors and vultures with TCAS?
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A VERY interesting exchange of facts, gentlemen (ladies?)… thanks much to all of you for that.
Of course, while I don’t know for sure the reason behind Kiwiguy’s original question, I would assume it was due to the significant contrast between JL’s reputation together with his absolute statements about the fact that airplanes simply could not have been involved in the 9/11 crashes (i.e., the airplanes wouldn’t have been able to stay in one piece – of course, I think his comments are primarily limited to the AA77 crash at the Pentagon) AND the “official” US government’s claims that this is exactly what happened. JL also is of the opinion that a “novice” pilot, like the one alleged to have been at the controls of AA77, simply could not have flown the airplane the way it would have to have been flown to match the government’s story - reference Kiwiguy’s quotes in his July 6th quotes of JL’s comments.
I’ll not go into the details of the “strange” theories that JL offers to counter the governments claim that AA77 struck the Pentagon. Suffice it to say that I, too, have had an opportunity to exchange “opinions” with JL, and have come away with much the same opinion as BelArgUSA. Up to this exchange I was completely unaware of his claims regarding UFOs, but, and without trying to offer specific criticisms of JL, that knowledge does explain a lot of what may be behind some of his “fringe” 9/11 theories.
Of course, while I don’t know for sure the reason behind Kiwiguy’s original question, I would assume it was due to the significant contrast between JL’s reputation together with his absolute statements about the fact that airplanes simply could not have been involved in the 9/11 crashes (i.e., the airplanes wouldn’t have been able to stay in one piece – of course, I think his comments are primarily limited to the AA77 crash at the Pentagon) AND the “official” US government’s claims that this is exactly what happened. JL also is of the opinion that a “novice” pilot, like the one alleged to have been at the controls of AA77, simply could not have flown the airplane the way it would have to have been flown to match the government’s story - reference Kiwiguy’s quotes in his July 6th quotes of JL’s comments.
I’ll not go into the details of the “strange” theories that JL offers to counter the governments claim that AA77 struck the Pentagon. Suffice it to say that I, too, have had an opportunity to exchange “opinions” with JL, and have come away with much the same opinion as BelArgUSA. Up to this exchange I was completely unaware of his claims regarding UFOs, but, and without trying to offer specific criticisms of JL, that knowledge does explain a lot of what may be behind some of his “fringe” 9/11 theories.
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ChristiaanJ: We flew Concorde to a Mmo of 2.00, I did know what Mach number the overspeed went off at but, along with an unbelievably huge amount of data painstakingly learnt over 6 months, I have sadly forgotten. RIP the highest achieving airliner ever built.
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Originally Posted by NW1
ChristiaanJ: We flew Concorde to a Mmo of 2.00, I did know what Mach number the overspeed went off at but, along with an unbelievably huge amount of data painstakingly learnt over 6 months, I have sadly forgotten.
As SLF I've been up to M 2.03, in the development sim at Filton I've been up to M 2.11... and no, I can't remember either anymore when the overspeed warning started....
RIP the highest achieving airliner ever built.
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<<Formal Mmo was 2.04>> Not if you wanted the type rating (ground school taught 2.00) ... 
But you would see more, and Mach #s in excess of Mmo for two reasons:
1) from the cabin the Marilake display was far from accurate (it had a big delay in it to stop it flaying around and on those hot days when we were struggling in the cruise climb a couple of hours of M1.98 would dissapoint the customers so it would read M2.00 - same for a "subsonic" charter - very common to see M1.00 on the Marilake if the true Mach had temporarily "bracketed" over the normal M0.95 subsonic cruise)
and 2) Concorde was designed to be flown right up to Vmo / Mmo at all times, and so small and regular excursions were common and part of the operation - it was not always easy to persuade the blunties running fleet audits that the overspeed warning was SOP and did not need an ASR, we'd have drowned in paperwork if so.....
Brgds
PS: O'Speed warning went off for:
Tmo +7 degrees C
Vmo +6kts
Mach >=0.95 with visor not locked up
Vc > 270kts with nose below 5 degrees
It didn't have a trigger for Mmo, but based itself on equivalent Vmo, FWIW
But you would see more, and Mach #s in excess of Mmo for two reasons:
1) from the cabin the Marilake display was far from accurate (it had a big delay in it to stop it flaying around and on those hot days when we were struggling in the cruise climb a couple of hours of M1.98 would dissapoint the customers so it would read M2.00 - same for a "subsonic" charter - very common to see M1.00 on the Marilake if the true Mach had temporarily "bracketed" over the normal M0.95 subsonic cruise)
and 2) Concorde was designed to be flown right up to Vmo / Mmo at all times, and so small and regular excursions were common and part of the operation - it was not always easy to persuade the blunties running fleet audits that the overspeed warning was SOP and did not need an ASR, we'd have drowned in paperwork if so.....
Brgds
PS: O'Speed warning went off for:
Tmo +7 degrees C
Vmo +6kts
Mach >=0.95 with visor not locked up
Vc > 270kts with nose below 5 degrees
It didn't have a trigger for Mmo, but based itself on equivalent Vmo, FWIW
Last edited by NW1; 19th Jul 2007 at 17:55.
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NW1,
"Max Cruise" was a nifty combination of Vmo = 530kts IAS, Mmo = M2.04 and Tmo = 127°C.
I should know, worked on it.
I know about the "cheating" on the Marilakes..... at some point recently there was a serious discussion about getting a few to work again so I went through the documentation. Unfortunately some of the digital protocols used seem to have been lost forever.
The Marilake never showed anything beyond M2.00.
And "my" Mach 2.03 was on a French Concorde.... no cheating Marilake, just a digital voltmeter calibrated in Mach straight from an ADC pot
As to the overspeed warnings, I'd have to dive into the doc, but I expect you're already quoting from doc, not memory, so no need to doubt your info.
"Max Cruise" was a nifty combination of Vmo = 530kts IAS, Mmo = M2.04 and Tmo = 127°C.
I should know, worked on it.
I know about the "cheating" on the Marilakes..... at some point recently there was a serious discussion about getting a few to work again so I went through the documentation. Unfortunately some of the digital protocols used seem to have been lost forever.
The Marilake never showed anything beyond M2.00.
And "my" Mach 2.03 was on a French Concorde.... no cheating Marilake, just a digital voltmeter calibrated in Mach straight from an ADC pot
As to the overspeed warnings, I'd have to dive into the doc, but I expect you're already quoting from doc, not memory, so no need to doubt your info.
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Well whatever.
Max Cruise mode on the BA aircraft flew the aircraft to M2.00 / Tmo (it didn't always do too well with the latter, but it did fly to M2.00 pretty well).
Max Cruise mode on the BA aircraft flew the aircraft to M2.00 / Tmo (it didn't always do too well with the latter, but it did fly to M2.00 pretty well).
Last edited by NW1; 20th Jul 2007 at 13:28.
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Originally Posted by NW1
Well; it hardly matters now really - and that's the shame.
But at least there are a lot of "flight simmers" (I'm not one, BTW) who still work on getting every last detail right, even now, so at least some of the memory lives on.
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Here is a quote from the Falcon 900EX AFM
“CAUTION
The maximum operating limitspeed VMO/MMO must not be deliberately exceeded in any regime of flight (climb, cruise, decent) unless a higher speed is authorized for flight test or pilot training.”
As VMO may be deliberately exceeded in some circumstances it can't be an absolute limit.
By the way, for those of you who have not had the pleasure, Dassault aircraft fly beautifully.
“CAUTION
The maximum operating limitspeed VMO/MMO must not be deliberately exceeded in any regime of flight (climb, cruise, decent) unless a higher speed is authorized for flight test or pilot training.”
As VMO may be deliberately exceeded in some circumstances it can't be an absolute limit.
By the way, for those of you who have not had the pleasure, Dassault aircraft fly beautifully.
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I believe similar wording exists in almost every flight manual.
Exceedence of Vmo to ensure the overspeed warning is properly active is a routine production flight test activity on many types, too.
Exceedence of Vmo to ensure the overspeed warning is properly active is a routine production flight test activity on many types, too.
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Just jumpin in to open up some more discussion...
I imagine mostly all of you are fighting to prove that 9/11 happened the way the govt says it did, so I'm not going to fight with you all. First I'd like to insist that you pull off of the John Lear bashing a little and concentrate on the aspects that bring him to his conclusions. Maybe exceeding VMO won't "bend wings" or cause "flutter." I don't know, never tried it... and if I did I certainly wouldn't admit it (looks around for FAA inspectors hehe), but going off of the structural damage that could be caused by an overspeed condition, maybe we could converse about how Center of Pressure (Lift) moves over the upper camber of the airfoil as speed is changed, especially in a swept-wing aircraft. I may be really tired right now and forgetting something, but I know this is where the term "Mach Tuck" comes into play. Also for you all talking about how jets fly up near MMO at cruise... OF COURSE THEY DO. What is the point of spending all that time and fuel (money) to climb to say FL350 (meaning 35,000 feet). Its definately not for the view! Air is thinner at altitude. As air thins, there is less resistance and the aircraft can penetrate the air with much less energy required, therefore giving you a faster ground speed. This is also why those "v speeds" are so much higher at altitude (minus the fact that there usually are no birds up there either, in the case of the 757). Also we have a problem called "Coffin Corner" at high altitudes... which comes from how the speed of sound (Mach) decreases and stall speed increases with altitude. It's a tiny window of airspeed that the pilot must stay within. Blow it and you're done. The higher you go, the smaller the room for airspeed fluctuation. Slow down too much, you stall the aircraft, speed up too much and you overspeed, which then results in "Mach Tuck." These are some reasons why jets fly near MMO all the time at cruise. Time and Safety. By climbing to high altitudes and flying fast, the jet is saving time and money and providing safety by keeping the aircraft away from a stall at altitude.
What about Parasite Drag at Sea Level vs FL350? At Sea Level, the very dense air going into the Pratt & Whitney 4062 turbofan blades would cause a lot of air to get jammed up like a dam at the engine inlet, in turn causing massive amounts of parasite drag. Throttle setting would also be a factor in this discussion... More throttle, more air being used, (less parasite drag?), less throttle, less air being used, (more parasite drag?). Also, there is such a dense amount of air going into the compressor section that the combustion would be hotter and faster, in return spinning the fans faster and causing detrimenal exceedances on the N1/N2 RPMs and Tempurature limits, which would then blow the blades off the turbines, causing the engine to lose mechanical power and burst into flames.
You can tear this up all you want, since I'm just pulling it out of what I know vs a logic thought process, (basically my ass, lol), but I know that if you put enough force on the blades of a compressor, it will blow apart, as in an instant explosive force "Wet Start" of a turbine engine and engine failure would occur. Of course, this would not be applicable for an engine that is descending and the RPM and force in increasing gradually. IF the force doesn't blow the engine apart... the overtemp would cause an engine fire which would be very visible to a video camera, though the pilots would still have power, which would deteriorate over time and eventually fail completely. I saw no fires on the 9/11 tapes until after the aircraft crashed. Forget "structural damage" due to overspeed... what about all the other things that we can damage by flying an aircraft out of its envelope?
How would our "novice" terrorist pilots be able to fly wide body aircraft beyond the limits on Boeing's test pilots without over stressing the aircraft while maneuvering anyway other than besides fluke? I've heard from 767 pilots that it maneuvers like a beached whale... intentionally maneuvering and positioning that aircraft into a 200 foot wide building at 450+ knots takes practice and skill. Just cause "terrorists" practiced flying 767s into buildings on Microsoft Flight Simulator doesn't give them the skillset required to achieve such an accomplishment in real life.
P.S. You can barrel roll a 747... I did it on flight simulator!
I imagine mostly all of you are fighting to prove that 9/11 happened the way the govt says it did, so I'm not going to fight with you all. First I'd like to insist that you pull off of the John Lear bashing a little and concentrate on the aspects that bring him to his conclusions. Maybe exceeding VMO won't "bend wings" or cause "flutter." I don't know, never tried it... and if I did I certainly wouldn't admit it (looks around for FAA inspectors hehe), but going off of the structural damage that could be caused by an overspeed condition, maybe we could converse about how Center of Pressure (Lift) moves over the upper camber of the airfoil as speed is changed, especially in a swept-wing aircraft. I may be really tired right now and forgetting something, but I know this is where the term "Mach Tuck" comes into play. Also for you all talking about how jets fly up near MMO at cruise... OF COURSE THEY DO. What is the point of spending all that time and fuel (money) to climb to say FL350 (meaning 35,000 feet). Its definately not for the view! Air is thinner at altitude. As air thins, there is less resistance and the aircraft can penetrate the air with much less energy required, therefore giving you a faster ground speed. This is also why those "v speeds" are so much higher at altitude (minus the fact that there usually are no birds up there either, in the case of the 757). Also we have a problem called "Coffin Corner" at high altitudes... which comes from how the speed of sound (Mach) decreases and stall speed increases with altitude. It's a tiny window of airspeed that the pilot must stay within. Blow it and you're done. The higher you go, the smaller the room for airspeed fluctuation. Slow down too much, you stall the aircraft, speed up too much and you overspeed, which then results in "Mach Tuck." These are some reasons why jets fly near MMO all the time at cruise. Time and Safety. By climbing to high altitudes and flying fast, the jet is saving time and money and providing safety by keeping the aircraft away from a stall at altitude.
What about Parasite Drag at Sea Level vs FL350? At Sea Level, the very dense air going into the Pratt & Whitney 4062 turbofan blades would cause a lot of air to get jammed up like a dam at the engine inlet, in turn causing massive amounts of parasite drag. Throttle setting would also be a factor in this discussion... More throttle, more air being used, (less parasite drag?), less throttle, less air being used, (more parasite drag?). Also, there is such a dense amount of air going into the compressor section that the combustion would be hotter and faster, in return spinning the fans faster and causing detrimenal exceedances on the N1/N2 RPMs and Tempurature limits, which would then blow the blades off the turbines, causing the engine to lose mechanical power and burst into flames.
You can tear this up all you want, since I'm just pulling it out of what I know vs a logic thought process, (basically my ass, lol), but I know that if you put enough force on the blades of a compressor, it will blow apart, as in an instant explosive force "Wet Start" of a turbine engine and engine failure would occur. Of course, this would not be applicable for an engine that is descending and the RPM and force in increasing gradually. IF the force doesn't blow the engine apart... the overtemp would cause an engine fire which would be very visible to a video camera, though the pilots would still have power, which would deteriorate over time and eventually fail completely. I saw no fires on the 9/11 tapes until after the aircraft crashed. Forget "structural damage" due to overspeed... what about all the other things that we can damage by flying an aircraft out of its envelope?
How would our "novice" terrorist pilots be able to fly wide body aircraft beyond the limits on Boeing's test pilots without over stressing the aircraft while maneuvering anyway other than besides fluke? I've heard from 767 pilots that it maneuvers like a beached whale... intentionally maneuvering and positioning that aircraft into a 200 foot wide building at 450+ knots takes practice and skill. Just cause "terrorists" practiced flying 767s into buildings on Microsoft Flight Simulator doesn't give them the skillset required to achieve such an accomplishment in real life.
P.S. You can barrel roll a 747... I did it on flight simulator!
P.S. You can barrel roll a 747... I did it on flight simulator!
GF
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Has anybody understood why this "AirmanDave" keeps waffling about "overspeed" and Mmo, and all that? If my 17-year old son (way back) could fly BOS-JFK IFR on the Atari 800 MS FS (two hours in the Cessna), and land properly at JFK, why couldn't a couple of terrorists, with basic flight training and a reasonable idea of the 767 cockpit functions and handling, aim at the WTC towers from miles away (VMC, IIRC) and hit them? I probably could.
Troll country, IMHO.
galaxy flyer,
The fact that you can barrel roll a 747 on MS FS proves nothing.... not even that it hasn't been done in real life!!
It's been done with enough other "big 'uns" (707, Vulcan, Concorde, for some of the definitely confirmed ones).
Would be interesting how many other ones have been quietly barrel rolled somewhere out of sight of prying eyes.....
Anybody for doing it with an A380 ?
CJ
Troll country, IMHO.
galaxy flyer,
The fact that you can barrel roll a 747 on MS FS proves nothing.... not even that it hasn't been done in real life!!
It's been done with enough other "big 'uns" (707, Vulcan, Concorde, for some of the definitely confirmed ones).
Would be interesting how many other ones have been quietly barrel rolled somewhere out of sight of prying eyes.....
Anybody for doing it with an A380 ?
CJ
Airman 'Dave' it is hard to know where to start addressing your incoherent aerodynamic babble.
'V speeds higher with altitude' ? 'flying at MMO to stay out of coffin corner'
'A 767 flying like a beached whale'
I have flown the 767 for 10 years and can state categorically it is one of the most responsive transport jets flying.
As to your other aeronautical 'theories' I suggest a little more research or stay with MS
'V speeds higher with altitude' ? 'flying at MMO to stay out of coffin corner'
'A 767 flying like a beached whale'
I have flown the 767 for 10 years and can state categorically it is one of the most responsive transport jets flying.
As to your other aeronautical 'theories' I suggest a little more research or stay with MS
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Kiwiguy, no vmo is not the absolute structural limit.he's talking nonsense.
There'd be a lot badly compromised aircraft out there otherwise.
I've been vne and a smidge higher in a prop driven craft numerous times on test flights and I'm still here.
Its a tad scary, the buffeting was quite bad.Would not want to go much harder.
There'd be a lot badly compromised aircraft out there otherwise.
I've been vne and a smidge higher in a prop driven craft numerous times on test flights and I'm still here.
Its a tad scary, the buffeting was quite bad.Would not want to go much harder.