Maximum Speed of Airliner At Low Altitude

[Roger Helbig]

Airline or Military transport pilots .. I would like to ask you some =
questions about the maximum speed that an airliner like a B-767 or 757 =
can travel at low altitude. Someone claims that the speed at altitude =
is much higher than that at low altitude because the drag of the wide =
body limits the maximum speed at low altitude. Can any of you comment =
on that?

Thank you.

Roger Helbig



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[Mortimer Schnerd, RN]

Ian MacLure wrote:
> Operationally its irrlevant because the FAA limits speed below 10K
> ft to 250Kts IIRC.
> As to the actual max speed attainable at low altitude, I believe you
> have it correct.


Agreed. Thicker air equals lower speed. FAA equals even lower speed.




--
Mortimer Schnerd, RN


http://www.mortimerschnerd.com

[Andy Bush]

Each aircraft may well have a different low altitude max speed...this will
be given in knots of Indicated Airspeed (IAS)...and typically is about
350-400 knots for passenger aircraft. At low altitude, IAS and True Airspeed
(TAS) are pretty much the same. While the low altitude max speed is
expressed in knots IAS, the high altitude max speed is expressed as a Mach
number. Passenger jet max mach numbers vary from around .8M to close to .9M.

At high altitude, IAS and TAS often are quite different, with TAS being the
larger value.

The low altitude max speed limitation is an airframe limit and not a drag
limit. In most cases, the jet could go faster but for various aerodynamic
reasons, is restricted from doing so.
"Roger Helbig" > wrote in message
news:40ccdcd9@hughey...
Airline or Military transport pilots .. I would like to ask you some
questions about the maximum speed that an airliner like a B-767 or 757 can
travel at low altitude. Someone claims that the speed at altitude is much
higher than that at low altitude because the drag of the wide body limits
the maximum speed at low altitude. Can any of you comment on that?

Thank you.

Roger Helbig



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http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----= Over 100,000 Newsgroups - 19 Different Servers! =---

[Robey Price]

After an exhausting session with Victoria's Secret Police, "Roger
Helbig" confessed the following:

>Airline or Military transport pilots .. I would like to ask you
> some questions about the maximum speed that an airliner
>like a B-767 or 757 can travel at low altitude.

Since I have a checkride coming up...Vmo is 340 KIAS for the 757 I
fly. "Clackers" start going off if you hit 340...ahem, I have seen
this in an Idle thrust descent.

The 757 is a very "clean" airframe. It does not like to slow down. If
a pilot turned the autothrottles off and simply firewalled the
throttles it would haul ass in the traffic pattern. How fast? Not
supersonic, but it requires surprisingly low thrust to hold the FAA
250 KIAS limit beow 10k'. I should have taken notes today (TIC).

Ramp down from altitude, it would probably scare the islamist ****
terrorist with all the warning noise from an overspeed (340+ KIAS). I
mean scare in terms of, "holy allah will this infidel made machine
hold together?"

Robey

[Cub Driver]

I believe the max for any aircraft is 250 knots.

The restriction is lifted in certain cases, for example: military jets
doing a Missing Man at Arlington National Cemetery.

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! www.vivabush.org

[Tamas Feher]

>Operationally its irrlevant because the FAA limits speed
>below 10K ft to 250Kts IIRC.

And Mohamed Atta conveniently ignored this rule. The 9/11 planes went so
fast and so low that they were expected to fall apart in-flight. Boeing
made them too sturdy, however. I wonder if some legal-savvy widows will
sue Boeing for building too good planes and thus causing 2800+ deaths.

[Robey Price]

After an exhausting session with Victoria's Secret Police, Cub Driver
confessed the following:

>I believe the max for any aircraft is 250 knots.
>
>The restriction is lifted in certain cases, for example: military jets
>doing a Missing Man at Arlington National Cemetery.

Mil jets are not limited to 250 KIAS "due to operational need," as in
a routine Dash 1 procedure (eg 350 KIAS up Initial for the RF-101, 300
KIAS for the F-4, F-16, F-15). But in the radar traffic pattern we
held it down to 250 KIAS.

But Roger's question has to do with the physical limitation of the 757
not something written in an FAR.

Robey

[Peter Stickney]

In article >,
"Mortimer Schnerd, RN" > writes:
> Ian MacLure wrote:
>> Operationally its irrlevant because the FAA limits speed below 10K
>> ft to 250Kts IIRC.
>> As to the actual max speed attainable at low altitude, I believe you
>> have it correct.
>
>
> Agreed. Thicker air equals lower speed. FAA equals even lower speed.

Not necessarily - thicker air also = much more thrust. It's all pretty
much a wash, with a transonic airplane. Usually the TAS in units/time
(mph, kts, km/hr) is higher, but the Mach Number's a bit lower. *The
Speed of Sound is proportional to absolute temperature. It's warmer
near the surface, so there's more mph/Mach Number.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[Cub Driver]

> I wonder if some legal-savvy widows will
>sue Boeing for building too good planes

Now you've done it!

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! weblog www.vivabush.org

[John Carrier]

Generally not true. Indicated airspeed top end is usually highest at low
altitude, but true airspeed capability will rise with increased altitude.
This all assumes no airframe structural limit, which is frequently below the
aircraft's capabilities in commercial designs.

R / John

"Peter Stickney" > wrote in message
...
> In article >,
> "Mortimer Schnerd, RN" > writes:
> > Ian MacLure wrote:
> >> Operationally its irrlevant because the FAA limits speed below 10K
> >> ft to 250Kts IIRC.
> >> As to the actual max speed attainable at low altitude, I believe
you
> >> have it correct.
> >
> >
> > Agreed. Thicker air equals lower speed. FAA equals even lower speed.
>
> Not necessarily - thicker air also = much more thrust. It's all pretty
> much a wash, with a transonic airplane. Usually the TAS in units/time
> (mph, kts, km/hr) is higher, but the Mach Number's a bit lower. *The
> Speed of Sound is proportional to absolute temperature. It's warmer
> near the surface, so there's more mph/Mach Number.
>
> --
> Pete Stickney
> A strong conviction that something must be done is the parent of many
> bad measures. -- Daniel Webster

[Peter Stickney]

In article >,
"John Carrier" > writes:

<Top Posting fixed, to improve following teh context >

> "Peter Stickney" > wrote in message
> ...
>> In article >,
>> "Mortimer Schnerd, RN" > writes:
>> > Ian MacLure wrote:
>> >> Operationally its irrlevant because the FAA limits speed below 10K
>> >> ft to 250Kts IIRC.
>> >> As to the actual max speed attainable at low altitude, I believe
> you
>> >> have it correct.
>> >
>> >
>> > Agreed. Thicker air equals lower speed. FAA equals even lower speed.
>>
>> Not necessarily - thicker air also = much more thrust. It's all pretty
>> much a wash, with a transonic airplane. Usually the TAS in units/time
>> (mph, kts, km/hr) is higher, but the Mach Number's a bit lower. *The
>> Speed of Sound is proportional to absolute temperature. It's warmer
>> near the surface, so there's more mph/Mach Number.

> Generally not true. Indicated airspeed top end is usually highest at low
> altitude, but true airspeed capability will rise with increased altitude.
> This all assumes no airframe structural limit, which is frequently below the
> aircraft's capabilities in commercial designs.

John, I have to respectfully disagree. While I don't have the
specifics for a 757 or 767, here's a list of the thrust/drag limits
(Which often exceed the published flight limits) for a number of
similarly performing transonic military aircraft. The data sources
are teh Standard Aircraft Characteristics for each aircraft, which
uses the same flight test data used to create the Pilot's Handbooks
and NATOPS.
All are Standard Day conditions

Sea Level 35,000' Notes
Vmax Vmax Mmax Vmax Vmax Mmax (Placard Limits, etc.)
KTAS KEAS KTAS KEAS
F-86H 600 600 0.91 545 304 0.94
B-47E 545 545 0.83 485 270 0.85 Lim. 425 KEAS/M 0.86
B-57B 521 521 0.79 475 262 0.83 Lim. 500 KEAS/M 0.83
A-3A 545 545 0.83 510 284 0.89
AV-8B 575 575 0.87 528 294 0.92
S-3A 430 430 0.65 443 324 0.72 Vmax is at 20,000'

Of all the examples, the S-3 comes eth closest to, say, an airliner,
with its fat body and high bypass engines. Even so, there isn't much
difference. The thing driving drag the most is Mach Number. (The drag
rise due to compressibility getting going) Since Mach 1 is about 85
Kts lower at 35,000' than it is at Sea Level, It's not too surprising
that you'll have more knots in hand at low altitudes.


--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[Cub Driver]

On Tue, 15 Jun 2004 17:22:32 -0400, (Peter
Stickney) wrote:

> Sea Level 35,000' Notes
> Vmax Vmax Mmax Vmax Vmax Mmax (Placard Limits, etc.)
> KTAS KEAS KTAS KEAS
>F-86H 600 600 0.91 545 304 0.94

Amazing. Is the same true at an intermediate altitude, say 20,000 ft?

This reverses the WWII piston-engine experience, where the max
airspeed was always at higher altitudes (though falling off well below
35,000).

Indeed, one of the hopes for the jet engine was that speed would
increase (and fuel burn decrease) as the planes went higher and
higher. Whittle believed that. Or at least I believed that he believed
it. http://www.warbirdforum.com/whittle.htm

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! weblog www.vivabush.org

[John Carrier]

Clip, clip clip ... is everybody happy?

> >> > Agreed. Thicker air equals lower speed. FAA equals even lower
speed.
> >>
> >> Not necessarily - thicker air also = much more thrust. It's all pretty
> >> much a wash, with a transonic airplane. Usually the TAS in units/time
> >> (mph, kts, km/hr) is higher, but the Mach Number's a bit lower. *The
> >> Speed of Sound is proportional to absolute temperature. It's warmer
> >> near the surface, so there's more mph/Mach Number.
>
> > Generally not true. Indicated airspeed top end is usually highest at
low
> > altitude, but true airspeed capability will rise with increased
altitude.
> > This all assumes no airframe structural limit, which is frequently below
the
> > aircraft's capabilities in commercial designs.
>
> John, I have to respectfully disagree. While I don't have the
> specifics for a 757 or 767, here's a list of the thrust/drag limits
> (Which often exceed the published flight limits) for a number of
> similarly performing transonic military aircraft. The data sources
> are teh Standard Aircraft Characteristics for each aircraft, which
> uses the same flight test data used to create the Pilot's Handbooks
> and NATOPS.
> All are Standard Day conditions
>
> Sea Level 35,000' Notes
> Vmax Vmax Mmax Vmax Vmax Mmax (Placard Limits, etc.)
> KTAS KEAS KTAS KEAS
> F-86H 600 600 0.91 545 304 0.94
> B-47E 545 545 0.83 485 270 0.85 Lim. 425 KEAS/M 0.86
> B-57B 521 521 0.79 475 262 0.83 Lim. 500 KEAS/M 0.83
> A-3A 545 545 0.83 510 284 0.89
> AV-8B 575 575 0.87 528 294 0.92
> S-3A 430 430 0.65 443 324 0.72 Vmax is at 20,000'
>
> Of all the examples, the S-3 comes eth closest to, say, an airliner,
> with its fat body and high bypass engines. Even so, there isn't much
> difference. The thing driving drag the most is Mach Number. (The drag
> rise due to compressibility getting going) Since Mach 1 is about 85
> Kts lower at 35,000' than it is at Sea Level, It's not too surprising
> that you'll have more knots in hand at low altitudes.

The problem with your comparison is that it shows only SL and 35K
(tropopause) speeds. An examination of PsubS curves would show zero PsubS
increases slightly with altitude to a point (well below tropopause) and then
suffers the mach effect as you describe giving slightly slower speeds in the
stratosphere. The issue is engine efficiency versus transonic drag effects
and normally produces results as the S-3 illustrates. While most of my high
speed experience (approaching placard etc) is in supersonic aircraft
(different rules, different PsubS curves), I recall the A-4 exhibited a
similar behavior ... faster at mid altitudes than either very low or very
high.

I'd like to know who the brave soul was that pushed a B-47 120 knots over
its airframe limit ... funny structural things happen in such cases.

R / John

[Peter Stickney]

In article >,
"John Carrier" > writes:

<Yesterday I wrote:>
>> John, I have to respectfully disagree. While I don't have the
>> specifics for a 757 or 767, here's a list of the thrust/drag limits
>> (Which often exceed the published flight limits) for a number of
>> similarly performing transonic military aircraft. The data sources
>> are teh Standard Aircraft Characteristics for each aircraft, which
>> uses the same flight test data used to create the Pilot's Handbooks
>> and NATOPS.
>> All are Standard Day conditions
>>
>> Sea Level 35,000' Notes
>> Vmax Vmax Mmax Vmax Vmax Mmax (Placard Limits, etc.)
>> KTAS KEAS KTAS KEAS
>> F-86H 600 600 0.91 545 304 0.94
>> B-47E 545 545 0.83 485 270 0.85 Lim. 425 KEAS/M 0.86
>> B-57B 521 521 0.79 475 262 0.83 Lim. 500 KEAS/M 0.83
>> A-3A 545 545 0.83 510 284 0.89
>> AV-8B 575 575 0.87 528 294 0.92
>> S-3A 430 430 0.65 443 324 0.72 Vmax is at 20,000'
>>
>> Of all the examples, the S-3 comes eth closest to, say, an airliner,
>> with its fat body and high bypass engines. Even so, there isn't much
>> difference. The thing driving drag the most is Mach Number. (The drag
>> rise due to compressibility getting going) Since Mach 1 is about 85
>> Kts lower at 35,000' than it is at Sea Level, It's not too surprising
>> that you'll have more knots in hand at low altitudes.
>
> The problem with your comparison is that it shows only SL and 35K
> (tropopause) speeds. An examination of PsubS curves would show zero PsubS
> increases slightly with altitude to a point (well below tropopause) and then
> suffers the mach effect as you describe giving slightly slower speeds in the
> stratosphere. The issue is engine efficiency versus transonic drag effects
> and normally produces results as the S-3 illustrates. While most of my high
> speed experience (approaching placard etc) is in supersonic aircraft
> (different rules, different PsubS curves), I recall the A-4 exhibited a
> similar behavior ... faster at mid altitudes than either very low or very
> high.

Ah - that was a simplification on my part, to keep the table a
manageble, and understandable size. If you like, I could give you the
full PsubS curves for all of them, verified to be within 2%, but
that's not really relevant. Given the usual shpae of the thrust and
drag curves, peak Mach Number will occor at the Tropopause. While the
thrust is decreasing with altitude, the drag's decreasing too, and,
until the air temperature stabilizes, (The definition of the
Tropopause), the thrust decays more slowly. (Note that there are some
thrust curves that do bias the altitude where T-D=0 downward - High
Bypass Turbofans tend to have a lot of Ram Drag, and thus don't like
high Mach Numbers. - that's why I think the S-3 is the best match from
the data above. (And, in fact, it does show teh behavior that you
note - I listed Vmax for 20,000' in that case, rather than 35,000'.
The 35,000' numbers for the S-3A are: 420 KTAS, 232 KEAS, Mach 0.73.

For all the others, it's Vmax in Kts is a Sea Level, Mmax is at
35,000. I'll be glad to send the Vmax graphs from the SAC Charts if
you like. All airplanes are different, of course, and for a transonic
jet, the thing that will drive what Vmax is more than anything else is
Mach Number. The drag rise can get pretty steep for many shapes above
Mach 0.7, depending on the wing sweep, airfoil thickness/chord ratio,
and the area distribution. This can lead to a situation where, as
altitude increases, the drag is, in fact, increasing faster than the
thrust. An A-4, with its moderate sweep, and fairly blunt body may
very well behave that way. When you were flying the A-4, did you ever
fly it without external tanks? Those will make a big difference on
something as small as a Scooter, especially in terms of the point
where the drag rise accors, adn the magnitude of the increase in drag.

>
> I'd like to know who the brave soul was that pushed a B-47 120 knots over
> its airframe limit ... funny structural things happen in such cases.

I don't think anyone ever did - 545 KTAS is the point where the thrust
curve and the drag curve cross at Sea Level. After all, teh original
question was about what was "theoretically possible", ignoring
airframe limits. If somebody were to really have taken one that fast,
they'd have had all sorts of lateral control problems - the 425 KEAS
limit was due to wing flex when the ailerons deflected, leading to no
roll control at 425 KEAS, and reversal at some point above that speed.
Bailing out wouldn't have been much of an option - the airflow over
the canopy would have had a local Mach Number of around 1.2-1.3, by my
calculations.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[Peter Stickney]

In article >,
Cub Driver > writes:
> On Tue, 15 Jun 2004 17:22:32 -0400, (Peter
> Stickney) wrote:
>
>> Sea Level 35,000' Notes
>> Vmax Vmax Mmax Vmax Vmax Mmax (Placard Limits, etc.)
>> KTAS KEAS KTAS KEAS
>>F-86H 600 600 0.91 545 304 0.94
>
> Amazing. Is the same true at an intermediate altitude, say 20,000 ft?

Pretty much so, depending on the shapes of the thrust and drag curves
of that particular airplane. I've got a longer, (and possibly
Caffeine-Deprived) reply to John Carrier's reply that goes into more
detail.

> This reverses the WWII piston-engine experience, where the max
> airspeed was always at higher altitudes (though falling off well below
> 35,000)

That's due to something a bit different. The piston engines on WW 2
airplanes are, of course, all supercharged, so that they produce their
maximum power at some point above Sea Level. This means that the
thrust produced by the propeller doesn't decay. Propeller Thrust is
((Engine Horsepower/True Airspeed) * Propeller Efficiency) 1,000 HP
is 1,000 HP, whether it's at Sea Level, or 20,000'. With a
controllable pitch propeller, the prop's going to vary its pitch so
that the force exerted on the air is equal to the torque by the engine
at some particular RPM. This gives the same thrust for a particular
airspeed regardless of altitude - until the engine is at a higher
altitude than the supercharger can deliver its full output, and power
(torque) drops off.
(Torque is proportional to Manifold Pressure.
On an airplane with a controllable prop, the prop controls RPM, and
the Throttle controls MAP (Torque). Constant speed props use
governers to automatically vary the prop pitch to match the RPM
commanded by the Pilot or Flight Engineer operating the engines. (Much
easier workload))

The drag decreases with the decrease in air pressure as you increase
altitude. So, if the power remains constant, and you've got less
drag, you can go faster. The rub is that since thrust is proportional
to Power / Speed, teh faster you go, the less thrust you have.
1 HP = 3.75 # of thrust at 100 mph, 1.88# of thrust at 200 MPH, 1.35#
of thrust at 300 MPH, 0.94# at 400 mph, and 0.75# at 500 mph.
This means that using a propeller to fly fast requires bucketloads of
horsepower, with the increases in engine size and fuel burn that go
with it. When you factor in teh decrease in propeller efficiency as
the airflow over teh prop goes supersonic, you can see that props
aren't very good for poing anywhere fast. But they do produce buckets
of excess thrust at low speed, which is good for takeoff adn climb
performance.

>
> Indeed, one of the hopes for the jet engine was that speed would
> increase (and fuel burn decrease) as the planes went higher and
> higher. Whittle believed that. Or at least I believed that he believed
> it. http://www.warbirdforum.com/whittle.htm

That's becasue a jet produces a fairly constant thrust across teh
speed range, instead of constant power. This means that teh faster
you go, the more power you have. Since the thrust of a jet decreases
more slowly with altitude than the drag is decreasing, you get a
higher top speed (discounting transonic effects) the higher you go.

Whittle wasn't teh only one who believed it - others did as well.
There's a report on the feasibility and tradeoffs of jet proulsion
from 1924 on the NACA Tech Reports server:
Jet propulsion for airplanes
Buckingham, Edgar , National Bureau of Standards (Washington, DC,
United States)
NACA Report 159, 18 pp. , 1924
This report is a description of a method of propelling airplanes by
the reaction of jet propulsion. Air is compressed and mixed with fuel
in a combustion chamber, where the mixture burns at constant
pressure. The combustion products issue through a nozzle, and the
reaction of that of the motor-driven air screw. The computations are
outlined and the results given by tables and curves. The relative fuel
consumption and weight of machinery for the jet, decrease as the
flying speed increases; but at 250 miles per hour the jet would still
take about four times as much fuel per thrust horsepower-hour as the
air screw, and the power plant would be heavier and much more
complicated. Propulsion by the reaction of a simple jet can not
compete with air screw propulsion at such flying speeds as are now in
prospect.

http://naca.larc.nasa.gov/reports/1924/naca-report-159/
Updated/Added to NTRS: 2003-08-19

So - the potentials were understood, and there were people working on
the problem for quite a while - notably Dr. Griffith of teh Royal
Aircraft Establishment. Griffith was big on producing complicated,
baroque designs that were well beyond the ability of anyone in the
1920s and 1930s to build - multispool contrarotating reverse-flow
axial compressors, for example. Whittle determined that things could
be much, much simpler, and came up with his simple centrifugal
designs. They weren't theoretically the most efficient, but they were
simple, and tolerant of off-design conditions. When Whittle first
presented his ideas to the RAF and the RAE, they consulted their tame
expert, Griffith, who advised them that Whittle's ideas were
impracticable. Whether this was due to personal jealousy, or Griffith
being unable to wrap his mind around the idea that the complicated
solutions to the problem that he was working on were unnecessary is
something I havent' been able to figure out.
With a bit more researchm, there could be a story, there.

Whittle adn von Ohain weren't the first to run Gas Turbines, btw. The
credit for that goes to Brown-Boverei Engineering in Switzerland, who
began building stationary Gas Turbines for use as industrial
powerplants in the 1920s. This didn't give them any insight into
aircraft Gas Turbines, however. Allis-Chalmers, which was
Brown-Boverei's licensee in the U.S. was a notable failure in the Jet
Race, completely dropping the ball on their homegrown turbofan
development begun in 1941, and in their licensed production of teh
DeHavilland Goblin as the J36 later in the War. Luckily, we had GE and
Westinghouse on the ball.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[John Carrier]

Just out of curiosity, what is the source for all your PsubS data?

A-4F always clean. TA-4J on occasion clean.

R / John

[John Carrier]

After some research concerning those aircraft that were decidedly subsonic
in level flight (no pushover from altitude to gain greater speed), it would
appear mach effect is the overriding concern. The last low altitude record
before the transition to high (F-100, with several ... F-86, F-4D ...
previous to that) were all done at the Salton Sea. Hi temp (higher TAS for
mach) and low altitude (-227 MSL), delayed transonic drag rise.

The PsubS bulge doesn't occur until you get into the cleraly supersonic
designs. Then it behooves a "low altitude" record to occur as high above
MSL as possible. Hence the sageburner and later Greenamyer efforts in the
high desert (less IAS, more TAS, 988 mph for Darryl ... great film by the
way).

Bottom line, in our running discussion, I now find your argument compelling.
I was incorrect.

R / John

[Krztalizer]

>
>Bottom line, in our running discussion, I now find your argument compelling.
>I was incorrect.

Psst, John....Uhhh, this is RAM - all arguments / disagreements are required to
last indefinitely, with neither side budging an inch. You're breaking ALL the
rules!

D says hi and asks about you often.
v/r
Gordon

[Guy Alcala]

Krztalizer wrote:

> >
> >Bottom line, in our running discussion, I now find your argument compelling.
> >I was incorrect.
>
> Psst, John....Uhhh, this is RAM - all arguments / disagreements are required to
> last indefinitely, with neither side budging an inch. You're breaking ALL the
> rules!

Shouldn't we cut a corner off his membership card for committing such a flagrant
violation of protocol? ;-)

Getting back to Pete's point, was the MiG-17's top level speed altitude (usually
given as 13,000 feet) likely because of engine temp limits at lower altitude plus
the use of A/B up higher, or for the reasons you mention in this thread? The other
swept-wing subsonics sans A/B all seem to be fastest on the deck. I wonder if the
F-86D/K/L Sabre's top speed graph was similar to the MiG-17's, owing to the A/B --
Walt? I think the only F-86 graphs I have are for navy Furies and the F-86H.

Guy

[Guy Alcala]

John Carrier wrote:

> After some research concerning those aircraft that were decidedly subsonic
> in level flight (no pushover from altitude to gain greater speed), it would
> appear mach effect is the overriding concern. The last low altitude record
> before the transition to high (F-100, with several ... F-86, F-4D ...
> previous to that) were all done at the Salton Sea. Hi temp (higher TAS for
> mach) and low altitude (-227 MSL), delayed transonic drag rise.

<snip>

And in between the F-86 and F-100 records, ISTR the Brits took a Hunter to Libya
for the same reason.

Guy

[Peter Stickney]

In article >,
"John Carrier" > writes:
> Just out of curiosity, what is the source for all your PsubS data?

In the case of the numbers I posted, the inital data comes from teh
Standard Aircraft Characteristics for the particular aircraft. Using
the characteristcs of teh engine, I generate the thrust curve for that
altitude & speed range, which gives me the total for Drag. (For the
engine, I can dope it out with Sea Level Static Thrust & SFC data, the
bypass ratio, and overall pressure ratio.) Then come the fun part,
breaking the drag numbers down to the individual contributions, and
fit them into a predicticed curve for total drag coefficient.
Then I test vs. certain point conditions - Vmax at Sea Level, and
various altitudes for Vmax values, and PsubSmax at Sea Level, (Rate of
Climb), and the altitude at which PsubSmax = 100 ft/minute (Service
ceiling). If the numbers are within reason, then it gets plugged into
teh flight model section of the Mighty Wurlitzer to deliver a PsubS
matrix for all acheivable speeds and altitudes. (Much repetitive
work, let teh computer do it!) While that's crunching away, I'm
running mathematicl models of teh airplane geomety through LDstab and
VLM to get the stability derivitives and the control moments.
So far, I've got things tuned to deliver numbers with a nominal 3%
accuracy to the flight test data, which is less than the variation
that you'll find in a squadron-sized group of airplanes.

> A-4F always clean. TA-4J on occasion clean.

Thanks, John. I don't have any good Skyhawk numbers yet, but it seems
that on a little jet like that, the tanks would make a big difference,
wrt drag.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[Peter Stickney]

In article >,
"John Carrier" > writes:
> After some research concerning those aircraft that were decidedly subsonic
> in level flight (no pushover from altitude to gain greater speed), it would
> appear mach effect is the overriding concern. The last low altitude record
> before the transition to high (F-100, with several ... F-86, F-4D ...
> previous to that) were all done at the Salton Sea. Hi temp (higher TAS for
> mach) and low altitude (-227 MSL), delayed transonic drag rise.

Quite so - they discovered that a pushover into teh course for teh
records didn't make any difference - the drag increase was so great
that it just didn't matter. We weren't teh only ones to use this -
The Brits made a record attempt with a slightly modified Hunter over
the Dead Sea. IIRC. That would be the only Speed Record set below Sea
Level.

> The PsubS bulge doesn't occur until you get into the cleraly supersonic
> designs. Then it behooves a "low altitude" record to occur as high above
> MSL as possible. Hence the sageburner and later Greenamyer efforts in the
> high desert (less IAS, more TAS, 988 mph for Darryl ... great film by the
> way).

I agree. The biggest deal there is that an afterburning turbojet
really denifits from Ram Compressionwhich gets really large above Mach
1. You get a lot more thrust, without the penalty of more Ram Drag.

> Bottom line, in our running discussion, I now find your argument compelling.
> I was incorrect.

I don't think that we were disagreeing on all that much, really.
Sometimes in my efforts to put things into non-technical terms, I
over-simplify. If you think I'm off, or not explaining properly,
please do jump in with a correction or an improved explanation.
Thank you for the questions, and helping me to improve my focus.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[Peter Stickney]

In article >,
Guy Alcala > writes:


> Getting back to Pete's point, was the MiG-17's top level speed altitude (usually
> given as 13,000 feet) likely because of engine temp limits at lower altitude plus
> the use of A/B up higher, or for the reasons you mention in this thread? The other
> swept-wing subsonics sans A/B all seem to be fastest on the deck. I wonder if the
> F-86D/K/L Sabre's top speed graph was similar to the MiG-17's, owing to the A/B --
> Walt? I think the only F-86 graphs I have are for navy Furies and the F-86H.

As it just so happens, I have my F-86D Dash-1 (Flight Handbook) to
hand. And it does have a Vmax curve. In the case of a clean
airplane, 16,000# weight, in AB, the Vmax curve looks something like
this:
Alt Mach Vmph VKTAS
0 0.91 692 601
10,000 0.93 677 588
20,000 0.94 659 572
30,000 0.94 634 550
40,000 0.93 611 530

So, in the Dogship's case, it still holds to the pattern where teh
maximum absolute speed it greates at Sea Level. (Airframe limits are
610 KIAS, no Mach Limit without external tanks.)

I've often wondered about the MiG-17's numbers as well. The guy to
ask, if he's monitoring, is Dave Sutton. It's kinda hard to argue
when he can walk out into the hangar and check. I've suspected that
its some sort of Q limit. My main suspect would be wing flex at high
speeds reducing roll rate, like what happens with a B-47. At those
speeds and altitudes, there's usually not enough temperature rise due
to ram compression for that to be a factor.
I've heard some funny stories about the teh flight limits on Soviet
airplanes. Apparently, the Soviets were very conservative about the
limits they placarded for their export airplanes. (I don't know about
their domestic stuff) This may have been due to an, erm, "mistrust"
in the levels of training received by their clients. I do know that
when the Indian Air FOrce adopted the MiG-21 and Su-7. that they were
very disappointed with the transition training that they received.
But then, at that time, the IAF still had close ties with the RAF, not
only having flown Brit equipment (Vampires, Hunters, and Gnats), but
also having their pilots trained "RAF Style" in India, and arranging
advanced training at the Fighter Leader's School and Empire Test
Pilot's School. The IAF rewrote the handbook for the MiG-21 and Su-7,
and in the process, opened up the flight envelopes a great deal. The
Su-7 was surprising - it turned out to be much faster, adn with much
better PsubS than th handbook limits had indicated. The biggest
problems were that the control system was set up for Soviet Weight
Lifters (I've never heard of anyone over-Ging an Su-7), and it would
run itself out of gas in sight of its own airfield.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[John Carrier]

> Quite so - they discovered that a pushover into teh course for teh
> records didn't make any difference - the drag increase was so great
> that it just didn't matter. We weren't teh only ones to use this -
> The Brits made a record attempt with a slightly modified Hunter over
> the Dead Sea. IIRC. That would be the only Speed Record set below Sea
> Level.

Actually, pushovers not allowed. The aircraft was prohibited from exceeding
300 meters altitude for the duration of the flight and had to be at 100
meters or less for the 4 passes on the 3-5 km course. Salton Sea is
slightly below sea level if my sources are correct.

R / John

[David Lednicer]

Go to the FAA Type Certificate database at:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet

Each type certificate lists the maximum operating airspeed and Mach
number. The airspeed is the limit until an altitude is reached at which
the Mach number listed equals the airspeed. Then, the Mach number
limits the aircraft. Be careful - some type certificates list the
airspeed in Knots Indicated Airspeed (KIAS), some in Knots Calibrated
Airspeed (KCAS), some in Knots Equivalent Airspeed (KEAS) and some in
Knots True Airspeed (KTAS).

[Guy Alcala]

Peter Stickney wrote:

> In article >,
> Guy Alcala > writes:
>
> > Getting back to Pete's point, was the MiG-17's top level speed altitude (usually
> > given as 13,000 feet) likely because of engine temp limits at lower altitude plus
> > the use of A/B up higher, or for the reasons you mention in this thread? The other
> > swept-wing subsonics sans A/B all seem to be fastest on the deck. I wonder if the
> > F-86D/K/L Sabre's top speed graph was similar to the MiG-17's, owing to the A/B --
> > Walt? I think the only F-86 graphs I have are for navy Furies and the F-86H.
>
> As it just so happens, I have my F-86D Dash-1 (Flight Handbook) to
> hand. And it does have a Vmax curve. In the case of a clean
> airplane, 16,000# weight, in AB, the Vmax curve looks something like
> this:

<snipperoo>

Thanks for the data, Pete. Sorry for the delayed reply.

Guy

[Alan Minyard]

On Wed, 16 Jun 2004 11:49:47 -0500, "John Carrier" > wrote:

>Just out of curiosity, what is the source for all your PsubS data?
>
>A-4F always clean. TA-4J on occasion clean.
>
>R / John
>
You flew a scooter without the "auxiliary landing gear"? You,
Sir, are a brave soul!!!

Al Minyard