Epic Forum Thread on Concorde (2010)

http://www.pprune.org/tech-log/423988-concorde-question.html

by idlewords • 12 years ago

115 49 12 years ago

idlewords6• 12 years ago

This starts off as a discussion of APUs but turns into a Q/A with participation by Concorde pilots, designers, and even a flight attendant who all clearly pine for their favorite plane ever. I couldn't pick one of the many anecdotes to highlight, so I posted a link to the entire monster thread. It rewards digging.

brianbreslin• 12 years ago

What was an APU?

jzwinck• 12 years ago

On the Concorde, the APU did not exist. On both contemporary and modern planes, the APU is the Auxiliary Power Unit, which is a fancy way of saying electric generator. Basically a moderate-size internal combustion engine (relative to the plane; big planes have big APUs) with the usual arrangement to generate electricity.

Why? Well, it's handy if a plane can start its own engines, and big engines can't usually be started by batteries, so batteries start the APU and the APU starts the turbines. The APU is also used to drive climate and entertainment systems when on the ground (and not connected to the Ground Power Unit, also mentioned early in the thread).

Finally, the APU can provide fault tolerance: if the turbines are disabled in flight, the APU can provide hydraulic pressure for the control surfaces, as well as electricity for safety systems and the potential to restart the turbines. There is some correlation in turbine failures (flying through something, fire, one turbine blade flies out and destroys a second engine), but the APU is inside and less likely to fail at the same time.

Related is the Ram Air Turbine, which is basically a small wind generator that can pop out of the fuselage if needed to provide some power to critical system when really nothing is working.

creamyhorror• 12 years ago

Enjoyable, nostalgic thread. Later on one member (age 78) of the core Concorde design team even appears. Here's an amusing anecdote from early in the thread:

========

Whilst on the Concorde conversion course at Bristol, occasionally crews would have the privilege of meeting some of the original design engineers and draughtsmen who had worked on the Concorde project.

...

Suffice to say that the senior fire officer who misread litres-per-minute as gallons-per-minute during an Olympus water ingestion test probably would not want any further publicity, likewise the apprentice who didn’t defrost the chicken before firing it into an engine running at full power in the bird ingestion test. My favourite was the supersonic hailstone story, fired as part of a hailstone ingestion test, but with uncertain results, the final resting place of said hailstone still being slightly obscure to this day. If anyone in the greater Bristol area got hit by a particularly hard snowball in the early sixties, the Filton test engineers are very sorry, and would like to apologise!

However, it is often the little insights into the past that amuse one the most and stick in one’s mind. During one such conversation, with a couple of thermodynamicists, I ventured to ask how they had settled on the (rather difficult to memorise) various temperature limits associated with Concorde.

For instance, why a nose temperature limit of +127°C, why not +130°C, much easier for a pilot to remember?

“Isn’t it obvious?” one replied politely, genuinely puzzled by my question.

“Computer generation,” replied his colleague to him, pointing his pipe stem at me.

“Ah yes,” said the first, “that would be it.”

They then went on to explain, in ever such a kindly manner, that, in thermodynamics, apparently the square, and the square root, of the absolute temperature of a material are terms used in many equations. Being armed mostly only with slide rules (and as they were in the vicinity of 120°C to 130°C as a limit anyway) it had been decided to make life easy and settle on +127°C as the limit, a temperature for which they could easily calculate the square and square root in their heads.

Noticing my bewilderment at the thought that anyone might be able to calculate the square or the square root of 127 in their heads, they proceeded to explain it to me still further, very slowly; in the manner that one would speak to an aged and rather deaf great aunt!

    • Absolute zero = -273°C = Zero Kelvin = 0K
    • Max Nose temp = +127°C equal to 400K
    • √400 = 20
    • 400² = 160,000.

These are the people with the amusing stories to tell!

spiritplumber• 12 years ago

I thought it'd be 127°C to avoid 8 bit signed overflow...

pgeorgi• 12 years ago

That was my first thought, too. Gives the "Computer generation" pejorative a new meaning…

mmaunder• 12 years ago

If you're wondering why the air isn't full of supersonic passenger aircraft, one of the main reasons is that high bypass turbofan engines are much more efficient than turbojet engines like the Olympus engines in the concord. (And way quieter)

Turns out a lower volume or air in a gas turbine engine moving at supersonic speed is much less efficient than a large volume of air moving at lower speed.

idlewords6• 12 years ago

Each engine type has a range where it's superior. Turbojets are much more efficient at high speeds, while high-bypass turbofans are better at low speeds. The Concorde burned remarkably little fuel at Mach 2, but used up ludicrous amounts of fuel at idle, taxi and takeoff. Read the thread, it's all in there.

Tloewald3• 12 years ago

If you read further into the thread, a pilot says that the high fuel consumption during takeoff was a consequence of the aircraft's weight being higher, and higher air density at lower altitudes -- the engines were not more efficient at higher speeds as an earlier post suggested.

Note that the idle fuel consumption (1t/hour; not sure whether that figure was per engine or for the entire plane) was not higher than cruising (4-6t/hour) -- it was just high in absolute terms.

RachelF• 12 years ago

An enjoyable thread, so much good discussion, no trolls or stupid comments, mostly professionals and interested amateurs discussing a topic they love, and know lots about.

rodgerd• 12 years ago

Really, it had a great deal more to do with politics: specifically, the Europeans had a supersonic airliner and the US didn't, so there was no way in hell the US government was going to do anything other than make it as difficult to use as possible.

hollerith• 12 years ago

Do you have any specific reasons to believe that the USG ever stopped or even simply tried to discourage the Concorde from flying to airports on the U.S. East Coast?

As for flying over populated parts of the U.S. at supersonic speeds, not even the U.S. Air Force gets to do that. (Source: https://news.ycombinator.com/item?id=8209976)

jpatokal• 12 years ago

I take it you're referring to the "no sonic boom in my backyard" shenanigans that hampered flights to/from/over the US in the early days? These were sorted out for the key NY-Europe routes by 1977, just over a year from first commercial flight.

https://en.wikipedia.org/wiki/Concorde#Operational_history

bootload2• 12 years ago

the Europeans had a supersonic airliner and the US didn't

Technically no, but the 747 is fast, almost too fast in these days of fuel economy.

The 747 was designed by Boeing to do M.87 (Pan Am wanted M.9) , though it now sits around M.855 (913 km/h) [1] due mainly to the requirement of fuel efficiency over raw speed. Almost Mach 1. How did Boeing designers get this speed? Hint: The hump and area rule (min drag > M.8) [2] Now a DC8 was pushed to M1.012 under special conditions. [3] And as a point of interest, Air Force One (VC-25A) is rated at M0.92 (1015 km/h). [4]

[1] http://www.boeing.com/boeing/commercial/747family/pf/pf_400e...?

[2] http://www.aerospaceweb.org/question/performance/q0150a.shtm...

[3] https://en.wikipedia.org/wiki/Douglas_DC-8#Production_and_te...

[4] https://en.wikipedia.org/wiki/Boeing_VC-25#Specifications_.2...

vermontdevil• 12 years ago

Really?

I saw the Concorde at OshKosh Air Show. Doubt they had problems flying there, landing, and setting up for viewing plus several demonstration flights. After that, I recall they were set to fly out west coast for another show.

Don't think the USG had any issues with the plane.

Not to mention the flights from JFK to Heathrow and Paris.

svdree• 12 years ago

Another reason might be that supersonic flying doesn't really gain you all that much. You still have to spend time getting to the airport, being there a couple of hours in advance, go through all the security measures etc, and jump through similar hoops upon arrival. Cutting your flight time in half sounds nice, but the effect on your actual travel time is a lot smaller.

cstross• 12 years ago

Please note that the Concorde requirement was set circa 1958-60, and the plane first flew in 1969; airlines were placing orders in the early 1970s.

Back in those days, airline security was a lot more relaxed: despite numerous hijackings nobody had yet figured out that a couple of hundred tons of airliner and jet fuel made a potent self-guided cruise missile, so the usual ending of a hijacking was on the ground with a negotiated hand-over. It was still possible to get from drop-off at the airport to the Concorde departure lounge in under 30 minutes; and for the trip from Arrivals at JFK to Wall Street ... well, that's what helicopters are for. (If you can afford a Concorde ticket you can afford a helicopter limo service!)

The immediate aftermath of 9/11 pushed the suggested minimum check-in time for trans-Atlantic flights up from 30-40 minutes to 3 hours, for everyone, VIP's included. So the folks who could afford a first class ticket -- the only kind of seat available on Concorde -- decamped for NetJets and other bizjet services, because the civil aviation security regulations didn't apply to private jets and you could still do the 30 minute from door-to-plane thing.

(And then Airbus refused to renew Concorde's type certification at the 30 year mark, allegedly just as they were discussing development of a new second-generation SST with a large Japanese corporation ...)

SpacemanSpiff• 12 years ago

From page 2 of the discussion: "Anyway, back to some figues; at Mach 2, 50,000', the typical fuel burn per engine would be around 5 tonnes/hour, falling to around 4.2 tonnes/hour at 60,000'." So at 60,000 feet, total fuel flow would be: 4.2 tonnes/hour * 4 engines = 16.8 tonnes/hour 16.8 tonnes/hour * 326 gallons per tonne = 5477 gallons/hour 5477 gallons/hour * 1/1320mph = 4.15 gallons/mile, 0.24 miles/gallon 0.24 miles/gallon * 120 passengers = 28.8 passenger miles/gallon

The 787 boasts around 120 passenger miles per gallon. So the Concorde uses 4x this much at highest efficiency. Not bad for 60's engineering at mach 2! I can see why it was not profitable to operate however, due to the increases in fuel cost since the aircraft was designed.

imaginenore• 12 years ago

So it's 4x less fuel-efficient. Fuel is a small percentage of the ticket price:

http://www.darinlee.net/fuel/fuel_widget.html

But even if fuel represented 100% of the ticket price, these supersonic flights could catch all of first- and business-class market. Rich people and businessmen value their time.

serf• 12 years ago

that's a cool thread, and a cool website to discover. Thank you.

aburan28• 12 years ago

Here is a thought, Imagine if a Concorde got hijacked? An F16's top speed is approx 1320 mph and the Concorde's is 1350 mph per wikipedia. I feel like there might have been some government pressure to take this plane out of service with all the fear mongering post 9/11

zhte415• 12 years ago

You may be interested in the movie http://www.imdb.com/title/tt0078740/plotsummary?ref_=tt_ov_p... where a Concorde isn't quite hijacked, but has some chase scenes between a Concorde and various rouge missiles and airforces.

oh_sigh• 12 years ago

A concorde going 1350 mph still has less kinetic energy than a 747 going 600mph. Also, I'm not positive, but I'd suspect that the concorde couldn't hit 1350mph at only a few hundred feet due to the really soupy atmosphere down here.

masklinn• 12 years ago

A concorde going 1350 mph still has less kinetic energy than a 747 going 600mph.

Not really no. Remember that Ek grows with the square of speed, so you need 4.5g of 747 for each gram of Concorde, something you only get when closing in on a 747 at MTOW (400t for a -400, 440t for a -8i) and a completely empty Concorde (80t).

Comparing the 747-400 and Concorde using maximum takeoff weights, the 747 comes out at 15GJ[0] when Concorde is 33GJ[1]. Using empty weight has roughly the same ratio. Even swapping the -400 for a -8i yields only marginal improvements to 17GJ[2].

With a loaded but dry plane (simulating the arrival at the end of a flight, under the assumption that fuel is a much bigger part of a Concorde than a 747) and maximum fuel load at takeoff, Concorde comes out at 16GJ[3] and the 8i at 10GJ[4].

Even if we use the same route, halve the 8i's fuel load (to account for twice the range) and replace it all with additional payload (which I'm not sure makes any sense), it's still only 13GJ.

Going back to the first paragraph, fully loaded 747's 15~17GJ[0][2] would indeed beat a completely empty Concorde's 14GJ[5], but that's about it.

[0] http://www.wolframalpha.com/input/?i=1%2F2+*+396890+kg+*+%28...

[1] http://www.wolframalpha.com/input/?i=1%2F2+*+185000+kg+*+%28...

[2] http://www.wolframalpha.com/input/?i=1%2F2+*+442253+kg+*+%28...

[3] http://www.wolframalpha.com/input/?i=1%2F2+*+%28185000+-+956...

[4] http://www.wolframalpha.com/input/?i=1%2F2+*+%28442253+-+216...

[5] http://www.wolframalpha.com/input/?i=1%2F2+*+78700+kg+*+%282...

rjsw• 12 years ago

An English Electric Lightning could catch a Concorde.

z303• 12 years ago

With a stern conversion intercept no less http://www.lightning.org.uk/oct04sotm.html

Curmudgel2• 12 years ago

A Concorde could not outrun an F-15, which has a maximum speed of more than Mach 2.5 at the cruising altitude of a Concorde. And an F-16 would only need to get close to a Concorde in order to shoot it down with missiles.

Scramblejams• 12 years ago

Still, you'd be surprised how a fast target shrinks missile envelopes. I spoke with a guy who spent a few minutes chasing a MiG-21 over Vietnam in a Navy F-4. They were both supersonic -- don't know how fast, but they were in the weeds and IIRC even in the 80s the Tornado IDS doing M1.2 at sea level was about the fastest thing at that altitude -- and from 7 miles astern, his Sparrows just didn't have the range to do it. That from a missile that we think of as a 30+ mile range weapon.

Similar story with today's weapons. I've read about frustrated F-15 drivers saying all an F-22 has to do in a mock dogfight is change his heading by 10 or 20 degrees and the F-15's beyond-visual-range missile solution goes out the window, such is the F-22's usual speed advantage with supercruise.

aidenn03• 12 years ago

The Soviets could shoot down an SR-71 that invaded their airspace by 1980 (I can't find a reference ; it seems likely we could shoot down a Concorde if needed. (I say likely rather than definitely, since a large part of the USSR deterrence involved scrambling interceptors before the SR-71 reached their airspace, and by 9/11 we no longer had a plane capable of launching an AIM-54 which could almost trivially shoot down a Concorde).

genericacct• 12 years ago

Wasnt that a U2?

jimmcslim• 12 years ago

I lived in London in the early 2000's before Concorde stopped flying; I was in Fulham so happened to be under one of the Heathrow approach flight paths.

I remember seeing and HEARING the Concorde coming in for landing at Heathrow. Absolutely the loudest thing in the sky! (apart from the occasional RAF flyover for Her Maj's birthday or some such...) You couldn't mistake it for anything else.

Erwin• 12 years ago

The Concorde engines were apparently based on the Vulcan Bomber's engines. There's still one of those that flies, and you can see it at airshows in Britain once in a while. I saw it at this year's Farnbourough which was an awesome experience (as was seeing the Airbus A380 take off at an extremely short distance -- when it's not loaded with fuel and cargo it's incredibly powerful and agile). The Vulcan was load, and has an incredible "howl": https://www.youtube.com/watch?v=H_ARSE8jEHQ

owenversteeg• 12 years ago

I noticed in the second post how the MEPU was developed by Sundstrand - the same company that made calculators in the 70s. (I, as a vintage calculator collector, actually have one.) On HN we hear about pivots all the time, typically not too drastic, but imagine going from manufacturing MEPUs for the Concorde to manufacturing calculators!

b_emery• 12 years ago

From wikipedia:

"The only thing that tells you that you're moving is that occasionally when you're flying over the subsonic aeroplanes you can see all these 747s 20,000 feet below you almost appearing to go backwards, I mean you are going 800 miles an hour or thereabouts faster than they are. The aeroplane was an absolute delight to fly, it handled beautifully. And remember we are talking about an aeroplane that was being designed in the late 1950s – mid 1960s. I think it's absolutely amazing and here we are, now in the 21st century, and it remains unique." —John Hutchinson, Concorde Captain, "The World's Greatest Airliner" (2003)[114]

I really hope we get to fly in one of these, or a modern version, someday.

Epic Forum Thread on Concorde (2010)

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