Boeing 767 Low-altitude Top Speed Options

[Guest_Ningen_*]

Does anyone know how fast a Boeing 767 can fly at low altitude? The top speed at cruising altitude is over 500 mph, but I've heard the following about flight at 700 feet altitude:

The power plant will max out at 330 mph.

The plane will begin to shake itself apart at over 220 mph.

At 700 feet altitude, the air is so thick that if you go too fast you max the rotation of the turbines, the engines can't suck in air, and the engine starts acting as a brake.

Does this make sense?

Where could I get more detailed information about flight limitations (or whatever you call it) of the Boeing 767?

Thank you.

This post has been edited by Ningen: Sep 2 2007, 04:19 AM

[alfonslof]

Does anyone know how fast a Boeing 767 can fly at low altitude? The top speed at cruising altitude is over 500 mph, but I've heard the following about flight at 700 feet altitude:

The power plant will max out at 330 mph.

The plane will begin to shake itself apart at over 220 mph.

At 700 feet altitude, the air is so thick that if you go too fast you max the rotation of the turbines, the engines can't suck in air, and the engine starts acting as a brake.

Does this make sense?

Where could I get more detailed information about flight limitations (or whatever you call it) of the Boeing 767?

Thank you.

I am not sure how to use this thing, so sorry if this is wrong.

I am working on a similar project, video to come, and so far I made this page.
Top speed for a 767 is 898 kph/558 mph and that is at an altitude of about 30,000 feet, source: http://www.zap16.com/civ%20fact/civ%20Boeing%20767-200.htm at 30,000 feet the atmosphere is 1/3 the thickness of atmosphere at 700 feet. This would cause approximately 3 times as much drag so the top speed would be about 1/3 of the top speed at 30,000 feet, or about 200 to 300 mph at best, and that is with no wind.

In a youtube video 175 travels 720 feet in 1.06 seconds = 720 Feet per Second = 490.90 Miles per Hour
http://www.v911t.org/175Velocity.php and therefore that plane is likely not a 767. It may not be a real plane at all.

Alfons v911t

[streetcar304]

Top speed for a 767 is 898 kph/558 mph and that is at an altitude of about 30,000 feet, source: http://www.zap16.com/civ%20fact/civ%20Boeing%20767-200.htm at 30,000 feet the atmosphere is 1/3 the thickness of atmosphere at 700 feet. This would cause approximately 3 times as much drag so the top speed would be about 1/3 of the top speed at 30,000 feet, or about 200 to 300 mph at best, and that is with no wind.

Is there an aeronautical principle you are quoting here or are these just your thoughts?

I asked an old friend who has been flying MD-10's for FED EX for the past 25+ years about this "How fast...?"question. I asked, verbatim:

Got a question for you. How fast do you think a 767 or 757 (or some current airliner) could go at, say, in a low altitude environment? By low I mean 1000 feet or something along those lines. Forget about 250 knots below 10k and whatever structural limitations are published – if you just went balls to the wall, full throttle, all that jazz.

Bottom line, a 757-sized aircraft will be able to exceed 450 knots easily at low altitude.

I am somewhat surprised that a website such as this with as many "pilots" as they claim to have, nobody has opined on this topic with this sort of information before and that none of your "pilots" have provided a detailed analysis of low-altitude/high-speed performance capabilities.

What about you, Rob? You are an "airline pilot". What about the experience you claim this board has in aircraft such as the MD-88, CRJ, 737, 757, 767, 747, DC-10? Where are all those pilots and their experience/expertise in low-altitude/high-speed flight? Where is Wittenberg? Where is Aimer? Where is Field McConnell? Where is Trood? Where is Mustanich? All these pilots - you'd think SOMEONE would come up with a definitive opinion on 7x7-class aircraft low altitude/high speed flight capabilities.

Guess not.

Here is my friend's answer, in full:

Well............Let me make a few statements that will qualify what I am about to say. As you are probably well aware, commercial aircraft don't have the forward throttle stops that military tactical aircraft have...........meaning, jamming a throttle full forward, to the stops, on a fighter aircraft is common practice and is routinely done. For example, on takeoff, climb-out, and especially
during a dogfight those throttles are bent forward to 100% RPM (or slightly under). The fuel control unit (military) will not allow that engine to overspeed and self distruct, if properly rigged. ( a guy's got to have means to get home after wrenching a kill on the enemy)

On commercial aircraft, the throttle must be set for takeoff and continually monitored and adjusted during climb by the pilot(s) or auto-throttles, if one's lucky enough to have them. The only time a throttle is bent forward on a commercial a/c is if ground contact appears imminent and it ain't a runway of intended contact. ie, the "escape" maneuver when an a/c is about to hit a mountain. It's firewall power, pull the nose up into buffet, and climb to the moon to clear any obstacle. Should a guy get himself safely on the ground somewhere thereafter, it is mandatory engine inspection and probably all engine removal and replacement. The engines will have been oversped and overtemped with possible other mechanical damage.

So.............of the arecraft of which I am familiar, the redline speed of an MD-10 at 10,000' is 375 KIAS. At sea level, it is 350 KIAS. ( the MD-11 is less than these speeds for a number of reasons that would only get boring) I'm quite sure the 757 and the 767 have very similar max speeds give or take 20-30 knots.

Interestingly, if a pilot didn't pull the throttles back to "cruise" settings (on a commercial a/c) when he leveled off at altitude, the aircraft would accelerate right thru redline on it's way to possible self destruction...........the engines are that powerful.

You know that the safety factors built into aircraft are 1.5 for structural components (wings, fuselage,etc.) and 2.5 safety factor for engines and landing gear, and control surfaces. Don't quote me on these exact components..........this is from memory from years ago. But it means that the design limits imposed by the manufacturer are what are safe to fly with, ie the speeds listed above and the "g" loadings. In reality, the aircraft has to be able to withstand 1.5 times the "g" loading design limits in order to be certified. I'm not sure if the same is true of the speeds, but I feel reasonably sure it is true as well. What this means is........ an aircraft will not show signs of destruction until it reaches the 1.5 times the design speed limit or its "g" limit. At least that is what the manufacturer guarantees, as required by the FAA. So..........

If I were to level off at 5000' (or 1000') and leave the throttles set at climb power, this aircraft would exceed the 350 KIAS (knots, indicated air speed) design limit. But it probably wouldn't come apart............yet. I don't know how fast it would ultimately go because I've never done that in a commercial airplane. We are not allowed to do that. But I do know that if a pilot then pushed the throttles up to the physical limits (stops), exceeding all the engine redline limits and warnings, the engines would accelerate and eventually self destruct as would the airframe itself..........say around 1.5 times 350 knots or 525 KIAS. Reasonably, I would guess the aircraft would start shedding pieces as it approached 500 KIAS.

In answer to your question...............a 757, or a 767, or an MD-11 can easily do 450 KIAS at low altitude at least once and maybe many times before it would show signs of damage and could do well beyond that if it were meant to be total destruction.

I look forward to comments on this information.

[dMz]

Is there an aeronautical principle you are quoting here or are these just your thoughts?

I look forward to comments on this information.

Yup, one is often called air density at altitude. Alfons wasn't quoting me specifically, but his post jibes quite well with my calculations based upon NOAA/USAF/NASA US Standard Atmosphere data- try post #18:

http://pilotsfor911truth.org/forum//index....&p=10592382

Another relevant "aeronautical principle" is transonic wave drag- you might want to read up on that a bit, then perhaps come back with some verifiable, non-anonymous sources... (IMG:http://pilotsfor911truth.org/forum/style_emoticons/default/rolleyes.gif)

http://en.wikipedia.org/wiki/Wave_drag
-----
"Wave drag is caused by the formation of shock waves around the aircraft. Shock waves radiate away a considerable amount of energy, energy that is experienced by the aircraft as drag. Although shock waves are typically associated with supersonic flow, they can form at much lower speeds at areas on the aircraft where, according to Bernoulli's principle, local airflow accelerates to supersonic speeds over curved areas. The effect is typically seen at speeds of about Mach 0.8, but it is possible to notice the problem at any speed over that of the critical Mach of that aircraft's wing. The magnitude of the rise in drag is impressive, typically peaking at about four times the normal subsonic drag. It is so powerful that it was thought for some time that engines would not be able to provide enough power to easily overcome the effect, which led to the concept of a "sound barrier".

[Omega892R09]

Another relevant "aeronautical principle" is transonic wave drag- you might want to read up on that a bit, then perhaps come back with some verifiable, non-anonymous sources... (IMG:http://pilotsfor911truth.org/forum/style_emoticons/default/rolleyes.gif)

Right I try this again my last effort having been lost due to net connection dropping out - again. (IMG:http://pilotsfor911truth.org/forum/style_emoticons/default/angry.gif)

On the ball as ever dMole. (IMG:http://pilotsfor911truth.org/forum/style_emoticons/default/smile.gif)

Many places of an aircraft can reach transonic speed ahead of the remainder of the structure. And I would like to put a spotlight here on the performance of the fan blades - as the aircraft forward speed builds so the effective tip speeds climb for any given rpm. Note that the tips airspeed is substantially greater than that of the root - this is why turbofans, and props, have washout (reducing incidence from root to tip). This, speed limit of the tips (combination of rotational velocity and forward motion velocity) WRT prop driven aircraft is what ultimately limited forward speed and the same will apply to the turbofans of the large diameter type fitted to commercial jets of the type under discussion.

By not being in the industry or involved with the type of engines under discussion I have no data but the essential principles underpinning my judgement here are sound.

Have you (not you dMole but those who cannot grasp the essential here I know you get this) ever seen aircraft displaying at about 450 - 500 knots, on the deck, in humid conditions with moisture condensing as the air around the aircraft is condensed by the shock waves such that the aircraft appears to be flying in its own cloud. Next time you see anything like this watch carefully and note where the air is condensing.

Aircraft that are designed to fly in the transonic flight regime, a much more demanding regime than once supersonic, at least until kinetic heating becomes a significant factor, are built using quite different design parameters to civil wide body passenger jets. Indeed aerodynamic limitations are reached before structural ones although aerodynamic forces generated at near transonic speeds can cause structural limits to be approached much more rapidly. This has been demonstrated a number of times with tragic consequences particularly during the early history of jet aircraft and examples are not hard to find.

This is why aircraft have flight envelopes. A velocity safe in level flight would destroy that same aircraft as G was increased - once again why military jets differ in construction to civil jets, having said that, it is very easy to break an F4 Phantom without trying too hard if one moves outside the flight envelope.

As for performance, any vessel that moves through a fluid will experience the law of diminishing returns as the wave drag kicks in and the denser the fluid the lower the max’ speed. Take for example a particular cruiser type (warship), I have data here that informs that this cruiser can sign along at 20 knots on 9000 S.H.P. (shaft horse power) but to reach 28 knots it needs 40000 S.H.P. This scenario is typical of vessels that move through the water rather than plane and skim the surface. Of course ships don't normally dive to achieve an increase in speed.

Reason for edit: Minor syntax error

This post has been edited by Omega892R09: Aug 19 2008, 07:04 AM

[dMz]

Have you (not you dMole but those who cannot grasp the essential here I know you get this) ever seen aircraft displaying at about 450 - 500 knots, on the deck, in humid conditions with moisture condensing as the air around the aircraft is condensed by the shock waves such that the aircraft appears to be flying in its own cloud. Next time you see anything like this watch carefully and note where the air is condensing.

Thanks O892,

Here's a great page on Prandtl-Glauert condensation clouds with info, photos, and video:

http://wilk4.com/misc/soundbreak.htm

Unfortunately, many of the links are broken, but well worth a look anyway.

EDIT: Here's the video link that's a little hard to find:

http://www.youtube.com/watch?v=wHrwgRsX0BI