John Lear vs. Ryan Mackey on Flying Boeing

767s Really, Really Fast Near Sea Level

by

John Lear

Posted September 24, 2008

Editor's note: this email exchange below from August 28, 2008 provides some important information on the question of whether a Boeing 767 could really fly at 542+ mph near sea level as NIST and other official/media/propaganda sources say it did on 9/11, based on the study of [fake] videos. 

Anthony [Lawson, allegedly a British ex-pat and director/producer of TV commercials]:

Well, well, well!
 
Ryan Mackey's piece confirms the research done for my video:  "Impossible Speed and Impact -- Busted!"  
 
 
John Lear, retired airliner pilot and son of Bill Lear of Motorola and Learjet fame:

Good afternoon Anthony,
 
My comments are in blue.

 
Ryan Mackey [allegedly a NASA research scientist] wrote:

That discussion is actually repellent in its stupidity.  I refuse to read it point-by-point, but will only state a few very obvious things that leave little doubt as to its accuracy:

   1.  Turbofans are in service on some of the fastest aircraft in the world, including the F-15 Eagle, and the F-22 Raptor, which is famous for its supercruise ability.
Mackey needs to clarify that his statement only refers to "low bypass ducted turbofans" which are used on fighters. Someone might think that there are high bypass turbofans used on airliners which might go 900 mph. (Mackey uses 'fastest aircraft in the world' instead of fastest 'fighters' in the world.)

   2.  Turbofans are used by the fastest (known) aircraft at sea level, the Panavia Tornado (http://www.aerospaceweb.org/aircraft/bomber/tornado_ids/), which claims > 900 miles per hour on the deck.  This is important as the Tornado's original design called for extreme high-speed and low-altitude horizontal bombing of enemy airfields, and low-level dash speed was a crucial requirement.  Clearly the turbofan was not a limiting factor here.
I'm not sure if Ryan Mackey means that if a Panavia Tornado which he claims goes 900 miles per hour on the deck then certainly a Boeing 767 should be able to do at least 600 but the differences in these airplanes are manifold. His attempt to compare the relative speeds of a high bypass turbofan (Boeing 767) with a low bypass ducted turbofan (Panavia Tornado), two completely different types of engines and two completely different types of airplane, is ridiculous.
Fighter jets such as the Panavia Tornado are designed for very high speed and use an aspect ratio for the wing (that is the fineness ratio of the wing, or proportion of the span to the average chord), in addition to wing sweep, which in the case of the Panavia can be selected to 25 degrees, 45 degrees and 67 degrees depending on the speed and regime in which they are operating, to obtain those high speeds.
The aspect ratio is variable on a variable sweepback wing but less than 4 as an average.
The thrust to weight ratio of a Panavia Tornado is 1 to 1.6.
Let's compare all of this with a Boeing 767.
The aspect ratio of a Boeing 767 is 8 and the sweepback is 31.5 degrees. Twice the aspect ratio of a Panavia Tornado and a sweepback less than half. The Boeing 767 is designed with a completely different wing, a supercritical wing, also called an 'aft loaded wing' which delays the onset of compressibility, enabling the airplane to cruise, economically at a higher airspeed which is about .82 Mach.
The thrust to weight ratio is 1 to 3.26.
So comparatively, the Boeing 767 with a thrust to weight ratio of 3.26 which is twice that of a Panavia, a sweepback less than half and an aspect ratio twice that of a Panavia Ryan Mackey would have us believe that it is possible for a Boeing 767 to achieve 600 mph under any conditions? Is he kidding?
Somebody here does not understand parasite drag or parasite power coefficients both of which, even separately, prevent an airspeed of 600 mph. Not to mention no high bypass turbofan is going to go 600 mph at sea level. Not to mention the fact that we wonder how an Arab hijacker is going to counteract the 'pitch up' of an increase in speed of 180 mph.
 
3.  The discussion misses the point entirely.  Nobody has claimed a 767 could maintain 600 MPH FLAT AND LEVEL, INDEFINITELY.  The actual speed claimed is only 542 MPH, and this is after diving from 20-odd thousand feet.  If you dive steeply enough, it doesn't matter whether the aircraft uses turbofans or turbojets, or if the engines are even running. Gravity provides up to a 1.0 thrust-to-weight ratio Gravity provides up to a 1.0 thrust-to-weight ratio, far exceeding any jetliner engine performance at any altitude, and besting even some fighter aircraft engines, including the (turbojet powered) MiG-25 Foxbat (and its replacement, the turbofan-powered MiG-31).
 
I googled the statement "Gravity provides up to a 1.0 thrust-to-weight ratio far exceeding any jetliner engine performance at any altitude", (this is sheer, unadulterated gobbledygook. It's nonsense.) to see if the statement had any basis in fact. It did not. The only google reference was to the Mackey statement itself. If an airplane is flying, it is overcoming gravity, that is why it is flying and not dropping out of the sky.
Mackey uses 'thrust-to-weight ratio' in referring to 'gravity provides', completely out of context. A thrust to weight ratio means the ratio of the thrust, in the case of the Boeing 767, 126,000 pounds of thrust, to its weight, 410,000 pounds. You divide weight by thrust and you get a thrust to weight ratio of 1 to 3.25 or for every pound of thrust there is 3.25 pounds of airplane weight. The Panavia Tornado has a thrust to weight ratio of 1 to 1.6 which means that for every pound of thrust you have 1.6 pounds of airplane weight. (Different models vary in thrust but the basic all up weight is about 60,000 pounds and 2 after-burning Turbo Union Rb199's have about 18,000 pounds of thrust each.)
The statement "If you dive steeply enough, it doesn't matter whether the aircraft uses turbofans or turbojets, or if the engines are even running" ignores drag rise due to parasite drag, parasite power, and if the engines are not running an additional frontal area drag of approximately 100 sq. ft of flat plate area. (Helllllllloooooooo!)
If this were not a limiting factor then military aircraft would not need Dr. Richard T. Whitcombs 'area rule' in the transonic or supersonic range. The lack of 'area rule' in the Boeing 767 is what enables it to meet Title 14 CFR 25.253 High Speed Characteristics in which the airplane is placed in a dive and may not exceed 420 kts (VD) by preventing it from exceeding that airspeed by specific design. And an Arab hijacker made it go 115 mph faster? Is that a joke?
To suggest that a pilot might dive past Vmo in excess of 180 mph without any trim change is to not fully understand what pitch trim is used for and why. To suggest that this was overcome by an inexperienced hijacker who could toggle the pitch trim switch in the right direction and for the correct amount of time is ludicrous. To suggest that an alleged hijacker held the wheel forward without trim during a 180 mph increase in speed is to be ignorant of the facts. To suggest that Boeing would design a trim system to allow the pilot to trim out pitch forces of an airspeed exceeding Vmo by 180 mph is not only ignorant. Its plain stupid.
Every transport category aircraft has to meet the same out-of-trim characteristics in 14 CFR Part 25.255.

What actually happened is the Boeing dived, starting at cruising altitude and speed, possibly at full power.  It would have slowed down only slightly in the last few seconds as it leveled off. There is nothing even faintly remarkable about a 767 exceeding 542 MPH under such conditions.  The engine is not the limiting factor.  It's like saying a VW beetle cannot exceed 80 MPH even if you drive it off a cliff -- nonsense.
 
To say that an engine, specifically the Pratt & Whitney JT9D 4062 is not a limiting factor in allegedly attaining 542 miles per hour in a dive is to completely misunderstand the effects of aerodynamic drag and the limitations of a high bypass turbofan engine. Here are some facts about the high bypass turbofan.
The high bypass ratio of the Pratt and Whitney and SNECMA Boeing 767 engines is 4.5 to 5.0 and compressor ratios of 23 to 25. The bypass ratio of an Rb199 is 1.3 and 23. That's why JT9D's and CF-6's were designed, for hi bypass, more fuel economy. Low bypass engines were designed for extremely high speed and don't have to turn an 8 foot diameter 'propeller' (fan) on the front of the engine.
The high bypass turbofan was designed with a huge 'propeller' or fan, the diameter of which is 8 feet, in front of the engine to take in huge amounts of air at sea level at slow speeds and accelerate it to produce huge amounts of thrust for takeoff. At altitude, this huge 'fan' can take the air, which is one third as dense, and accelerate it to produce a cruising speed of over 500 mph.
What the high bypass turbofan cannot do is produce the same thrust, using air that is three times as dense (sea level), at speeds much over 360 knots. The engine simply cannot use and/or bypass the amount of air it is being asked to accept at those high speeds at sea level.
The high bypass engine was specifically designed to produce enormous amounts of thrust with dense air at low speeds or thin air at high speeds. But it cannot produce these enormous amounts of thrust with air three times as dense being rammed in the intake at high speed at sea level.


Just so I can provide something useful, the difference between turbojets and turbofans is not night and day, particularly in the case of a low-bypass ducted turbofan.  Both of them require the air reaching the inlet to slow -- if the aircraft is traveling at supersonic speed, there will be a fixed shock at the inlet, and inside the air will be flowing subsonically, unlike a scramjet.  The major differences are simply as follows:

   a)  The turbojet compresses all inlet air and passes it through the core, whereas the turbofan "bypasses" some of the inlet air around the core
   b)  As a result, the turbojet's exhaust speed is hotter and faster, whereas the turbofan (by mixing with the bypassed air) pushes a larger volume of cooler and slower gas
   c)  This makes the turbofan more efficient, much as a gasoline engine is more efficient at lower RPM

Mackey's statement 'something useful' here is somewhat misleading. He has cut and pasted several sentences which don't apply to this discussion. The difference between a high bypass and low bypass jet engine is that the high bypass engines are more economical in terms of fuel consumption and have a larger fan, because they are used on heavier airplanes; whereas the low bypass in more interested in speed at the expense of increased fuel consumption and has a small diameter fan because fighter jets are smaller. These are a few of the reasons why fighters use low bypass engines and why airliners use high bypass engines.
To suggest that there is no 'night and day' difference between turbojets and turbofans is to suggest that there is no difference between the 2 most important developments in jet engines since its original design (single stage centrifugal compressor-single stage turbine).

  d)  The turbojet is *sometimes* the more efficient *system* at very high speed, mostly because it is narrower in profile, partly because the higher exhaust speed can lead to a cleaner wake.

I googled 'cleaner wake' to see if I could figure out was Mackey was talking about but the best I could come up with was "Dry Cleaner, Clothing Alterations, Custom Embroidery, Wake Forest, NC <http://www.triangledrycleaners.com/> .
 
But the speeds in question here are not "high" by aircraft standards -- 600 MPH is only about Mach 0.8, not nearly enough to pose a problem for any engine.  Above Mach 2 the question is more pertinent, and even there inlet design is at least as crucial as the engine type.
 
By stating that "600 mph and .8 Mach are not nearly enough to pose a problem for any engine" and assuming he is talking about sea level operations of a high bypass turbofan Mackey is simply wrong. Low bypass engines would have no problem but a high bypass turbofan engine simply cannot attain that speed. Compare a Pratt & Whitney JT9D with a fan diameter 8 feet to a Panavia Tornado Rb 199 with an overall diameter of 870 millimeters or about 34.25 inches. That's right! A fan diameter of 870 millimeters (34 inches)! So Mackey proposes an airliner with 2 eight foot diameter high bypass fans going 600 mph at sea level? Not in Earth's atmosphere at sea level it's not.
 
Mr. Lear at least had the good sense to drop this line of argument and instead focus on control issues;
 
I am not sure which line of argument Mackey is alleging I have dropped.
 
while there is no reason to suspect a Boeing would be uncontrollable at this speed, it is at least getting close to the edge of the envelope.  The control argument is merely wrong,
 
Control stability Vfc is 390 kts. And that is the maximum speed at which it must be demonstrated. To state: "there is no reason to suspect a Boeing would be uncontrollable at this speed (600 mph)" is to assume that there would be no change in stability 150 mph above maximum demonstrated speed. Mackey may be a rocket scientist but he is most certainly not an aeronautical engineer.
Oh, and the envelope Mackey talks about getting close to? That envelope was sealed at 420 knots (VD).
 
whereas the turbojet/fan argument can only be the product of arrogance untempered by any technical expertise whatsoever.  I see no reason not to ignore such nonsense completely.
 
I am not sure what specific argument Mackey is referring to as being the product of arrogance untempered by any technical expertise 'whatsover' but I would be happy to address the issue if he would outline it.
And as to his suggestion to 'ignore such nonsense completely' I would request his indulgence in carefully reading the above and responding.
If I could find who Mackey's supervisor was at NASA I would write and ask him two questions:
Is Mackey really a 'rocket scientist"?
Does NASA stand behind Mackey's aeronautical statements of nonsense?
 
John Lear

Editor's note: Ryan Mackey, Anthony Lawson--no one has ever replied to this Lear email Silencio, that's what we hear from these plane huggers. What can they say--"We've been exposed?"