Maximum Speed of Airliner At Low Altitude

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

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

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

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

Go to the FAA Type Certificate database at:
http://www.airweb.faa.gov/Regulatory...e?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).

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

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