747........Supersonic.....?

Oh, sorry missed the K, not used to dealing with Kilometers here in the US.

Originally posted by aerospaceweb
Most commercial airliners are capable of reaching reaching very low supersonic speeds in a shallow dive from high altitude where the pressure is low. The first plane to do so was a DC-8 that reached Mach 1 during a test flight in 1961 over Edwards AFB.

www.dc8.org...

However, the plane did so during a dive from over 52,000 ft and pulled out at 41,000 ft. Most airliners today have a service ceiling around 40,000 ft, so they probably wouldn't even be able to climb that high in the first place. Even so, the structure of an airliner ought to be able to withstand a brief excursion into supersonic flight so long as it was at high enough altitude. It is not recommended, of course, since these planes were not intended to be flown in the harsh aerodynamic environment near Mach 1.

I seem to remember that Tex Johnston accidentally got a Dash 80 through Mach when he pooched up a roll... I believe it was on his way to some demo on the East Coast...

I do know that he rolled the 80 twice at Gold Cup Race back in 1955, much to the dismay of Bill Allen, then president of Boeing...

Airliners, including the 747, can survive mometary excursions into the transonic region. The problem is the phenomenon called mach tuck. As the aircraft approaches mach 1.0 the shock wave that is begining to form blocks out airflow over the horizontal stabilizer. Natural stability causes the aircraft to nose down; thereby causing even more speed increase. If the speed increases too much the shock wave will completely block out the elevator rendering it completely useless in arresting the dive. A pilot could use trim (which controls the stabilizer) but if too much nose-up trim is applied the aircraft could Over-G and structurally fail when its speed falls below Mach 1.0. Therfore, the best way to recover is: Throttles-Idle; Speed brakes-deployed; and in extreme cases; Landing gear down (this may damage the gear).

As far as the 767 doing 1000Kph (540 Knots/621 Mph): At 39,000 feet; Standard temperature (-63C), that would be Mach .96. As a guy who has flown the 767, I can tell you that it won't go that fast in level flight. In addition, the pilots would be getting over-speed warnings. What the previous poster was reading on that display was ground speed which is basically TRUE Airspeed corrected for the wind. You must have had a tailwind along your route of flight.

Almost any plane is capable of breaking "mach" in a dive, the true question is whether or not it survives. I am sure you will find lots of data about the number of P-38's they lost in combat simulation training when the lightning went into a powered dive, exceed mach 1 then to have the G's tear the connecting structure apart resulting in the loss of the aircraft when the pilot tried to pull out of the dive.

Originally posted by robertfenix
Almost any plane is capable of breaking "mach" in a dive, the true question is whether or not it survives. I am sure you will find lots of data about the number of P-38's they lost in combat simulation training when the lightning went into a powered dive, exceed mach 1 then to have the G's tear the connecting structure apart resulting in the loss of the aircraft when the pilot tried to pull out of the dive.

Give over mate, this has been done to death and neither the P-38 nor any other piston fighter ever exceeded mach 1, even vertically. It just isn't possible, don't mistake exceeding the airframe limit for exceeding the sound barrier.

It was actually on a United Airlines display in the passenger cabin, I can't remember how fast it actually went, transonic sounds about right, we did had a tailwind since we were flying in a slipstream.

Like I said, when a plane passes 1000kph it is going super-sonic, Waynos is aboslutely right, but my statement is still not fully incorrect.

So, these planes definitly push Mach 1, but not completely, and techically I know that I could never HAVE traveled at mach one, but pretty damn close.

Just for your info, I have flown in:

Airbus, can't remember exact build, Anatolia Airlines, this plane traveled to Turkey
Boeing 747, probably 747-200 series but I am not sure, KLM for Martinair, traveled to Greece.
Boeing 767 to Canada and United States, Canada Air and United Airlines.
De Havilland Canada DHC-7 "Dash 7"connection flight.
BAC 1-11, another connection flight to Canada.
Sea King, Helicopter, this was a tour flight in the Netherlands.

So I had my fair share of flying in alot of interesting aircraft

Just sharing this for fun since this debating is a bit getting me on my toes and I don't mean to lash out on people...sorry...

My Mazda MX5 can go mach 90!, but only when the girlfriend drives the sodding thing, the most terrior ever. Forget Bin Larden she scares the crap out of ME!

E.g. going fast before she hits the speed bumps logic forget that TOO!

RAB :-)

i believe that parts of the airflow over the wing does go supersonic
their supercritical wing that boeing invented was designed to control this to prevent excesse drag
i suspect it can''t go supersonic and there's no way in my opinion it could survive breaking the sound barier
it's entirely possible the small portions of the wing might experience supersonic flow during high speed flight but that's not the same thing as the whole plane breaking the barrier

Originally posted by GrOuNd_ZeRo
It was actually on a United Airlines display in the passenger cabin, I can't remember how fast it actually went, transonic sounds about right, we did had a tailwind since we were flying in a slipstream.

Like I said, when a plane passes 1000kph it is going super-sonic, Waynos is aboslutely right, but my statement is still not fully incorrect.

So, these planes definitly push Mach 1, but not completely, and techically I know that I could never HAVE traveled at mach one, but pretty damn close.

Just for your info, I have flown in:

Airbus, can't remember exact build, Anatolia Airlines, this plane traveled to Turkey
Boeing 747, probably 747-200 series but I am not sure, KLM for Martinair, traveled to Greece.
Boeing 767 to Canada and United States, Canada Air and United Airlines.
De Havilland Canada DHC-7 "Dash 7"connection flight.
BAC 1-11, another connection flight to Canada.
Sea King, Helicopter, this was a tour flight in the Netherlands.

So I had my fair share of flying in alot of interesting aircraft

Just sharing this for fun since this debating is a bit getting me on my toes and I don't mean to lash out on people...sorry...

As has been mentioned before... there's a big difference between ground speed, which is what you observed in the display in the cabin, and airspeed...

One could have a ground speed well above 770 mph and an airspeed of 300...

Originally posted by jonititan
i believe that parts of the airflow over the wing does go supersonic
their supercritical wing that boeing invented was designed to control this to prevent excesse drag
i suspect it can''t go supersonic and there's no way in my opinion it could survive breaking the sound barier
it's entirely possible the small portions of the wing might experience supersonic flow during high speed flight but that's not the same thing as the whole plane breaking the barrier

Large jets can and have survived exceeding mach 1. It happened in a KC-135 (B-707) whereby a crew experienced severe turbulence in level cruise flight (I believe due to a thunderstorm), stalled the aircraft; and during the subsequent dive, exceeded Mach 1.0. I'll see if I can find a reference and post it here.

Indeed they have although I've not heard of a BUFF hitting Mach...

I was trying to find the reference for the incident that resulted in Tex Johnston exceeding Mach in the Dash 80...

If I recall correctly he dished out of a roll and exceeded Mach with the nose burried... The bird was a bit bent from the resultant recovery but it kept flying...

When I was on a flight to Eurpope once, with a strong tail wind, the pilot came on and annouced that we had exceeded the sea-level ground speed of sound. Of course, with the tail wind, our airspeed wasn't supersonic. Still cool, though.

yeah but what altitude where you at at the time?
the speed of sound varies enormously with altitude

Originally posted by jonititan
yeah but what altitude where you at at the time?
the speed of sound varies enormously with altitude

Actually; not to belabor minutia, but the speed of sound depends primarily on temperature--not altitude; though varying altitudes do affect Mach in a small way

Well... kinda... temperature is really a function of altitude, isn't it???

In the standard model for determining the speed of sound standard conditions at seal level are assumed, 29.92 inches of mercury and 60 degrees F or 15 degrees C...

The standard adiabatic lapse rate is three degrees Celsius per 1,000 feet so, bottom line... altitude, to a large degree, altitude determines temperature which determines the speed of sound!

This link is to a great little set of tables that provide the speed of sound v. altitude:

www.aerospaceweb.org...

Cheers!!!

Originally posted by CTO
Well... kinda... temperature is really a function of altitude, isn't it???

Temperature doesn't always decrease with altitude. Sometimes it increases with altitude which is a called a temperature inversion.

Here is a great link explaining the different factors that effect the speed of sound

Originally posted by CTO
In the standard model for determining the speed of sound standard conditions at seal level are assumed, 29.92 inches of mercury and 60 degrees F or 15 degrees C...

The standard adiabatic lapse rate is three degrees Celsius per 1,000 feet so, bottom line... altitude, to a large degree, altitude determines temperature which determines the speed of sound!

The atmosphere is rarely ever "standard". I again defer to the reference page above. Incidentally, the standard lapse rate is 2 Degrees celsius/1000 feet and 3 degrees F/1000 feet.

Great topic

gah
look

A= sqrt(R*T*lamda)
A= local speed of sound
R= gas constant
T= static temperature
lamda = the ratio of the specific heat capacity of air at constant pressure/the specific heat capacity of air at constant volume = 1.4 for air
in the tropopause the temperature lapse rate is constant
then it has a wacky kind of variance beyond that which i cna't be bothered to explain but take it from me it just gets colder
any inversions are probably very high up and don't last too long
Edit:if you want to know how it varies beyond tropopause don't ask me because i''m supposed to be revising

[edit on 9/6/05 by jonititan]

Humm... I may well be mistaken but I thought the dry adiabatic lapse rate was 1 degree C per 100 meters, just about 3 degrees C per thousand feet or 5 1/2 degrees F per 1000...

Whatever it is... altitude seems to have more to do with the speed of sound as opposed to temperature but, none the none, they are inexorably linked!!!

Good discussion!

Could a 747 go supersonic?

Well i have no idea, BUT would you really want to be on board a flying elephant
going THIS fast?????

I know i wouldnt!



[edit on 9/6/2005 by MickeyDee]

Originally posted by CTO
Humm... I may well be mistaken but I thought the dry adiabatic lapse rate was 1 degree C per 100 meters, just about 3 degrees C per thousand feet or 5 1/2 degrees F per 1000...

Whatever it is... altitude seems to have more to do with the speed of sound as opposed to temperature but, none the none, they are inexorably linked!!!

Good discussion!

You're correct. But when discussing the "standard" atmosphere the lapse rates they are as stated in my previous post.