'Sonic cruiser' claims

[PaperTiger]

"The plush superjet is expected to knock up to 75 minutes off journey times between London and New York"

Can somebody help a poor non-tekkie understand how ?

Mach 1 = 658kts = 758mph (SA value)
LHR-JFK = 3451 miles
3451 at M0.95 = 4.79hrs = 4:47
3451 at M0.82 = 5.55hrs = 5:33
max saving = 0:46, and that's assuming M0.95 sustained for the entire block (not true) and flying a true GC (also not).

Is my math faulty ? Where's the 75 minutes ?
Genuine questions.

[Squawk 8888]

Well, if it climbs faster it will get to M0.95 a lot sooner than the other jets get to M0.82. Add in the fact that it's above all the other traffic and that's probably where they expect the saving.

------------------
Per dementia ad astra

[Zeke]

Mach 1 at 40000+ ft (stated/desired crusing level) is 573 knots.

You have to allow for wind which can be significant.

[Lucifer]

And Mach 0.95 is a higher ground speed at a higher altitiude.

[PaperTiger]

Yes something's obviously missing from my equation, but I can't seem to get my head round this.
If this SC thing cruises say 1/9th faster than yer average Boebus, then to achieve a 1 hour saving the current flight time has to be at least 9 hours (which LHR-JFK is not).
Or don't I have a clue ?

[Frederic]

Didn't they mean LHR-JFK-LHR instead of just LHR-JFK?

[Pielander]

Lucifer etc...

The speed of sound is lower at a higher altitude hence the speeds that you are all quoting are far too high. (hence the times, and thus, also, the time saving will be considerably greater than your estimate).

I don't have the ISA data in front of me, so this is only a generalisation, but I have it at home, so If you're really interested I will "do the math"

[Zeke]

The Mach 1 (speed of sound) at FL350 in ISA conditions is 576.6 kt, above FL361 Mach 1 is 573.8 (up to about FL850).

Normal cruise for todays jets is around M0.82, in the FL350-FL400 region.

FL350 M0.82 = 473 KTAS (353 KEAS) FL400 M0.82 = 471 KTAS (331 KEAS)


Sonic cruiser (#1), design cruise at FL400-FL450 M0.95

FL400 M0.95 = 545 KTAS (384 KEAS) FL450 M0.95 = 545 KTAS (362 KEAS)


Sonic cuiser (#1) is 15% faster at FL400 than a current jet at FL350, 16% faster than a current jet at FL400.

Sonic cuiser (#1) is 15% faster at FL450 than a current jet at FL350, 16% faster than a current jet at FL400.

Sonic cuiser (#2) design cruise at FL400-FL450 M1.2

FL400 M1.2 = 689 KTAS (485 KEAS) FL450 M1.2 = 689 KTAS (457 KEAS)


Sonic cuiser (#2) is 46% faster at FL400 than a current jet at FL350, 46% faster than a current jet at FL400.

Sonic cuiser (#2) is 46% faster at FL450 than a current jet at FL350, 46% faster than a current jet at FL400.

:rolleyes:

Edit : thanks babble silly mistake the numbers didn't even look close !

[This message has been edited by Zeke (edited 15 May 2001).]

[Pdub]

<font face="Verdana, Arial, Helvetica" size="2">
The F-22 engines already allow super cuise at M2.0+ without afterburner, the engine technology exists.
</font>

So do the engines in Concorde - The technology has existed for a long time, just takes the military a little while to catch up ;)

edited for getting the quotes right

[This message has been edited by Pdub (edited 15 May 2001).]

[Zeke]

Pdub,

F-22 engines don't have reheat, low fuel burn for M2.0+ cruise.

:rolleyes:

[Captain Noodle]

Hurricane Harry??????

[babble]

Zeke, er... not quite right!

Your ISA speeds of sound are correct, but you need to multiply your mach numbers by the speed of sound to get TAS, then calculate the EAS for the pressure altitude.

[PaperTiger]

Zeke et al

Thanks for the education. A 16% increase in cruise speed is close enough to the claimed 1:15 LHR-JFK.
And here I thought the Bearded One was talking through his APU again.

[foghorn]

pdub

Concorde's engines were developed for the military - they were designed for the TSR2 which had Mach 2 supercruise capabilities in the mid-1960's. A truly superlative aircraft which was sadly doomed due to idiotic politicians.

cheers!
foggy.