

Epic Forum Thread on Concorde (2010) - idlewords
http://www.pprune.org/tech-log/423988-concorde-question.html

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

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

------
idlewords
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
What was an APU?

~~~
jzwinck
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.

~~~
robryk
Minor addition: engines need compressed air to start and APU provides that,
too (used for engine starting, cabin pressurization and some anti-icing
systems).

------
mmaunder
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.

~~~
rodgerd
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.

~~~
bootload
> 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...](http://www.boeing.com/boeing/commercial/747family/pf/pf_400er_prod.page)?

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

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

[4]
[https://en.wikipedia.org/wiki/Boeing_VC-25#Specifications_.2...](https://en.wikipedia.org/wiki/Boeing_VC-25#Specifications_.28VC-25A.29)

~~~
idlewords
The high speed of the 747 is a function of its wing sweep. The hump and area
rule have nothing to do with it.

~~~
bootload
_"... The fastest airplane out there today is the 747. Not one of them has
been able to match the cruise speed of the 747. That indicates to me that it’s
a high-technology airplane ..."_ Joe Sutter [0]

wing sweep alone doesn't explain why the 747 is the fastest subsonic transport
to date. If it did, competitors would have copied the idea. I'm curious why?
Boeing describe it as a combination of wing design, engine, electro-mechanical
systems. Maybe I should ask Boeing.

[0]
[http://www.boeingblogs.com/randy/archives/2006/08/father_kno...](http://www.boeingblogs.com/randy/archives/2006/08/father_knows_best.html)

~~~
idlewords
Because the penalty for that speed is higher fuel burn. That's why Boeing is
having trouble selling the 747-8, and why four-engine airliners in general are
getting phased out.

My source for the wing sweep thing is also Joe Sutter, in his wonderful book.
Also highly recommend Widebody, by Clive Irving, which is sadly out of print.

------
jimmcslim
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
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](https://www.youtube.com/watch?v=H_ARSE8jEHQ)

------
b_emery
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.

------
owenversteeg
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!

------
aburan28
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

~~~
oh_sigh
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
> 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...](http://www.wolframalpha.com/input/?i=1%2F2+*+396890+kg+*+%28988+km%2Fh%29%5E2)

[1]
[http://www.wolframalpha.com/input/?i=1%2F2+*+185000+kg+*+%28...](http://www.wolframalpha.com/input/?i=1%2F2+*+185000+kg+*+%282158+km%2Fh%29%5E2)

[2]
[http://www.wolframalpha.com/input/?i=1%2F2+*+442253+kg+*+%28...](http://www.wolframalpha.com/input/?i=1%2F2+*+442253+kg+*+%28988+km%2Fh%29%5E2)

[3]
[http://www.wolframalpha.com/input/?i=1%2F2+*+%28185000+-+956...](http://www.wolframalpha.com/input/?i=1%2F2+*+%28185000+-+95680%29+kg+*+%282158+km%2Fh%29%5E2)

[4]
[http://www.wolframalpha.com/input/?i=1%2F2+*+%28442253+-+216...](http://www.wolframalpha.com/input/?i=1%2F2+*+%28442253+-+216840+*+0.81%29+kg+*+%28988+km%2Fh%29%5E2)

[5]
[http://www.wolframalpha.com/input/?i=1%2F2+*+78700+kg+*+%282...](http://www.wolframalpha.com/input/?i=1%2F2+*+78700+kg+*+%282158+km%2Fh%29%5E2)

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

