Boeing 767 Low-altitude Top Speed Options

[amazed!]

The better question IMO, is can an autopilot fly the airplane at speeds over Vmo?

My bet is YES.

[dMz]

"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."

Has anyone seen a source to verify the 2.5 factor above? It seems a bit "ambitious" for commercial passenger transport type, and a bit conservative for many military airframes to me. I didn't see it anywhere in the FAR (but I posted the 1.5 safety factor and FAR source here).

The anonymous "friend" doesn't seem to differentiate very well between airframe design specifications, certification/test limits, and physical/structural limits IMHSO. O892 probably has some input here, I'll hypothesize.

EDIT:
"The maximum operating limit speed (VMO/MMO airspeed or Mach Number, whichever is critical at a particular altitude) is a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent), unless a higher speed is authorized for flight test or pilot training operations."

[Bold emphasis mine- d]

[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".

[dMz]

But we acctually flew (B.727 by the way) at up to 390 kias as low as a 1000 feet. (Yes one thousand feet) CRAZY.
What I´m trying to say, basically is, there´s no problem with those airplanes going up to max speed at any altitude.

Hello fransan,

FAA type data sheet for B727 says:

http://rgl.faa.gov/Regulatory_and_Guidance...1C?OpenDocument

http://rgl.faa.gov/Regulatory_and_Guidance...6;FILE/A3we.pdf

"Airspeed limits: VMO/MMO - 390/0.9 (KEAS), Dual Mode 390/350/0.88 (KEAS)
For other airspeed limits see the appropriate FAA approved Airplane Flight Manual."

390 kts is right at V_mo, not ~150 knots over V_mo. (~142% of V_mo for B767-200 in the OCT "UA175" case).

My $0.02, and I'm still looking for sourced turbofan engine overspeed survivability evidence (refer to my air density vs. altitude post above).

[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]

Of course ships don't normally dive to achieve an increase in speed.

Umm, I think some ships['boats'] do (but I'm trying to stay in the graces of the USN here). (IMG:http://pilotsfor911truth.org/forum/style_emoticons/default/whistle.gif)

[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

[fransan]

Hello. I insist the actual limit of the airframe must be around MACH 1. A non supersonic design will suffer too much stress and probably start to fail when passing the sound barrier. It could start braking up at different places.
I mentioned an incident that happened with an AAB727 many years ago where there even was speculation that they had gone supersonic for a while. Nobody has made any coment on that.
As far as the engines, I don´t think there´s any problem there. You occationally would get a compresor stall when being too quick on the throtles in the past, but now with "fadecs" it´s much harder to do. (Full authority digital engine control.)

[rob balsamo]

Hello. I insist the actual limit of the airframe must be around MACH 1.

"Insist" is not data. Please provide source for your claims. Preferrably from Boeing wind tunnel tests.

I mentioned an incident that happened with an AAB727 many years ago where there even was speculation that they had gone supersonic for a while. Nobody has made any coment on that.

Yes we have, you just didnt read it. So it will be repeated. A 727 is not a 757 and you admit speculation. Speculation is not fact.

As far as the engines, I don´t think there´s any problem there.

Your opinion noted. Unfortunately, you only have opinion and no facts.


Fransan, if you continue to insist fact without source, warnings will commence and you will join your "friend" carlos on the sidelines.

[Omega892R09]

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.

That Tomcat shot comes from a sequence where shortly after that the Tomcat breaks up.

If not that one then is is one similar and here it is:

http://www.youtube.com/watch?v=7qMtnFtB38I&NR=1

What was I saying about it being easy to break an F4 Phantom by flying outside of the flight envelope, that is why there are flight envelopes, flight envelopes being the result of brave test pilots these days assisted by computer models but back in the 1960s test pilots were still pretty much pushing the envelope themselves.

This post has been edited by Omega892R09: Aug 18 2008, 11:45 AM

[fransan]

Hey, hey, easy there Rob. Sorry for voicing my humble opinion on a subject, as I thought everyone was entitled to do. From now on I´ll try not to write anything that has not been "prooven" or that is " A FACT".
But I´ll say this. I´ve seen lots of speculation all over these threads on all kinds of subjects, but you jump on me like I´m Mark Roberts or something. I think you are overreacting.

[dMz]

OK, here's a little on the [off-topic, red herring, irrelevant] McDonnell-Douglas DC10, MD-10, and MD-11 variants (although we really would rather discuss Boeing B767-200's on this thread, I think).

http://www.aftd.com/TCDS_PDFS/A22WE_8.pdf

This is interesting:
---
"Engine Limits:

Maximum permissible engine rotor operating speeds
N1 (Low Compressor) 3810 rpm (111%)
N2 (High Compressor) 9925 rpm (101%)

...

Airspeed Limits:
(CAS)
VMO/MMO (Maximum Operating) With SB 37-87 Without SB 37-87
At Sea Level 350K 350K
At 10,000 ft 350K 376K
At 24,820 ft 350K 376K (M=0.88)
At 28,310 ft 350K (M=0.88) 350K (M=0.88)
At 42,000 ft 258K (M=0.88) 258K (M=0.88)
VA (Maneuvering) See FAA Approved Airplane Flight Manual"

[Can we get back to VERIFIABLE, SOURCED Boeing information now??] (IMG:http://pilotsfor911truth.org/forum/style_emoticons/default/rolleyes.gif)

[Seatnineb]

Ok...this may not be a 767....but the laws of aerodynamics still apply

(IMG:http://i11.photobucket.com/albums/a159/Make7/excessvne.jpg)

(IMG:http://edit.81x.com/Authors/TruthExplosion/vneexcess.jpg)

(The Air Pilots manual)
The Aeroplane Technical
By Peter D Godwin
Published by AirPilot Publishing
(2006)
ISBN : 1843660683

This post has been edited by Seatnineb: Aug 18 2008, 03:09 PM

[dMz]

Thanks S9B- sourced aerodynamics information is always welcome to me- several of those books are out of print and/or quite expensive and difficult to find. V_ne is more for smaller aircraft, with V_mo/M_mo being more applicable to the "Big Boeings." That diagram of V > V_ne [or V_mo] effects is still very relevant here, too.

Instead of speculating about what the speed "could" be, let's talk about what the data suggests it "WAS," in absence of SSFDR and CVR's. This is from something I posted earlier on a ["limited" by necessity] thread here:

"1. My preliminary analysis of USAF 84 RADES data shows UA175 pitching down from 8-15 degrees during the last minute of flight (based upon arc tan(ModeC "v_y" /GS "v_x" ) spherical Law of Cosines approximation- see UA175 section...)

2. My RADES analysis shows UA175 approximate GS of 471.344 knots at 2200 feet aMSL ModeC at 13:02:23.660 Zulu time (GMT) or 9:02:24 EDT (the final radar return). [FEMA and FAA put it about 512 kts, NIST at 475 kts, and I'm not sure whether they meant TAS, IAS, CAS, or GS here]

3. My RADES analysis shows approx. AA11 GS of 421.81 knots at 2000 feet aMSL "height" at 12:45:48.445 Zulu or 8:45:48 EDT (final RADES return, no transponder or secondary radar info).

I have used approximation techniques to derive GS velocity from the RADES lat/lon data (more info in AA11 and UA175 Aircraft sections if needed here).

Unfortunately, I reached a standstill without verifiable, documented structural B767-200 data/specifications or better WTC mass distribution numbers. I also have yet to see any FAA radar data 6 years later, or WTC2 South blueprints for that matter. There has been considerable speculation and ambiguity about the WTC 1,2, and 7 construction particulars as well. Apparently ASCE, FEMA, NIST, and FBI/NTSB were able to draw their conclusions without any of this information that I still seek...

For AA11, my research says:
B767-223ER #N334AA B# 22332, GE CF6-80A2, Mode 3A 1443 off 08:20:38 EDT

For UA175:
B767-222 #N612UA B# 21873, PW JT9D-7R4D, Mode 3A 1470 > 3020 > 3321 "

[Omega892R09]

On lack of data.

What puzzles me about all this is that there is so little coming from anybody working with commercial airlines.

Maybe I am being naive here but military aviation types know about pilots notes and stuff that informs on the limits of their aircraft and propulsion systems, is there nothing similar in commercial aviation?

I would have thought that there are numerous copies of such technical literature in circulation and yet we seem unable to come up with any either from pilots or ground engineers neither of whom could do their jobs without this stuff.

Of course in my day this stuff was all on paper, maybe times have changed so much that this information is tightly sequestered by IT.

Dropped that second r in aircraft again, seems to be a habit for some reason ATM! Must be the Chinese Olympics - trouble with 'rs'.

This post has been edited by Omega892R09: Aug 19 2008, 02:20 PM

[rob balsamo]

Limitations are learned during initial training, are published in a limitation manual carried with the pilot in his flight bag, are directly on the instrument (barber pole, red tape on EFIS, etc) and most times placarded on the panel.

Pilots are not privy to airframe structural limitations/failure speeds because pilots stay within the limits learned as described above, which are of course lower than actual structural failure limits. What we need are wind tunnel data from Boeing, however we've been hitting nothing but brick walls.

[amazed!]

The vast majority of limitations can be exceeded with no huge penalty. Yes, you might damage something in terms of something not making it to overhaul, but exceeding limitations does not necessarily do anything. The airplane is still flying, but certain of the limitations are not being met.

[Seatnineb]

Thanks S9B- sourced aerodynamics information is always welcome to me- several of those books are out of print and/or quite expensive and difficult to find. V_ne is more for smaller aircraft, with V_mo/M_mo being more applicable to the "Big Boeings." That diagram of V > V_ne [or V_mo] effects is still very relevant here, too.

Instead of speculating about what the speed "could" be, let's talk about what the data suggests it "WAS," in absence of SSFDR and CVR's. This is from something I posted earlier on a ["limited" by necessity] thread here:

"1. My preliminary analysis of USAF 84 RADES data shows UA175 pitching down from 8-15 degrees during the last minute of flight (based upon arc tan(ModeC "v_y" /GS "v_x" ) spherical Law of Cosines approximation- see UA175 section...)

2. My RADES analysis shows UA175 approximate GS of 471.344 knots at 2200 feet aMSL ModeC at 13:02:23.660 Zulu time (GMT) or 9:02:24 EDT (the final radar return). [FEMA and FAA put it about 512 kts, NIST at 475 kts, and I'm not sure whether they meant TAS, IAS, CAS, or GS here]

3. My RADES analysis shows approx. AA11 GS of 421.81 knots at 2000 feet aMSL "height" at 12:45:48.445 Zulu or 8:45:48 EDT (final RADES return, no transponder or secondary radar info).

I have used approximation techniques to derive GS velocity from the RADES lat/lon data (more info in AA11 and UA175 Aircraft sections if needed here).

Unfortunately, I reached a standstill without verifiable, documented structural B767-200 data/specifications or better WTC mass distribution numbers. I also have yet to see any FAA radar data 6 years later, or WTC2 South blueprints for that matter. There has been considerable speculation and ambiguity about the WTC 1,2, and 7 construction particulars as well. Apparently ASCE, FEMA, NIST, and FBI/NTSB were able to draw their conclusions without any of this information that I still seek...

For AA11, my research says:
B767-223ER #N334AA B# 22332, GE CF6-80A2, Mode 3A 1443 off 08:20:38 EDT

For UA175:
B767-222 #N612UA B# 21873, PW JT9D-7R4D, Mode 3A 1470 > 3020 > 3321 "

It was not just that fl175 flew at 500+mph at 700 feet......it also dove and turned at the same time:

(IMG:http://img240.imageshack.us/img240/1309/wb11li1.gif)
(IMG:http://www.911research.dsl.pipex.com/ggua175/foreman_time_lapse_panoramic_merged.jpg)

(IMG:http://www.freewebs.com/joecraine/NSAFligth175altitude.jpg)

unreal...

[Omega892R09]

The vast majority of limitations can be exceeded with no huge penalty.

But not when heading into the transonic flight regime in an aircraft not designed for it.

Sure here I am assuming that a 757 or 767 is not designed for that. I am reasonably certain, based on my knowledge of the special design features that are required for transonic flight such as overcoming control reversal that they are not. Do 757s or 767s have stabillity augmentation and all-flying tailplanes for example?

This post has been edited by Omega892R09: Aug 20 2008, 12:15 PM

[dMz]

It was not just that fl175 flew at 500+mph at 700 feet......it also dove and turned at the same time:
...
unreal...

Agreed S9B,

You all knew that I was only listing a speed (0.7176M for "UA175" if anyone is interested BTW) for the last 12 seconds of "UA175" RADES data in #2 above, right?

The errr.... "interesting" parts of the RADES data I posted a few months ago at post #6:

http://pilotsfor911truth.org/forum//index....&p=10742683

Does anyone care to explain those "UA175" ground speeds to me, and exactly how they were achieved with what type of propulsion?