PDA

View Full Version : LAPCAT and other hypersonics


tartare
12th Feb 2008, 00:34
Have been reading about Lapcat and various proposed hypersonic transport programmes.
The thing I wonder about is how pleasant it would be to pax on one of these things?
Acceleration and climb to altitude would be around +4g's I'd imagine?
The cruise would be ok.
But then another minimum 4g decceleration at least?
And you'd have to join straight in on a 30-40 mile final....???!!!
My point being, a combination of approved routes and climbs to, descents from altitude might mean they are less than optimal for passenger flights.
Any thoughts anyone?

chornedsnorkack
12th Feb 2008, 13:11
The thing I wonder about is how pleasant it would be to pax on one of these things?
Acceleration and climb to altitude would be around +4g's I'd imagine?
The cruise would be ok.
But then another minimum 4g decceleration at least?
And you'd have to join straight in on a 30-40 mile final....???!!!

Er, why? What would be the point?

Concorde, at full afterburner, has less than 0,4g thrust to weight at MTOW.

If you arrive at Mach 5 and decelerate at 4g, you will stop in 40 seconds, and cover 30 km over the time. Why not decelerate at 0,4 g over 7 minutes, covering 300 km in the meanwhile?

ChristiaanJ
12th Feb 2008, 17:11
Not to mention that for 4g acceleration the thrust in lbf needs to be at least 4 times the MTOW in lb of the aircraft (not even counting drag...).
Seems overkill to me. :rolleyes:

tartare, where did you get this notion?

And BTW, LAPCAT is an early study of advanced propulsion techniques, not an aircraft design.
The Reaction Engines A-2 is a paper exercise to give an idea what such an aircraft might look like in 25 years time.

tartare
12th Feb 2008, 20:35
Fair enough.
I guess the point I am trying to clarify is the minimum length of sector on which travelling at hypersonic speeds would be practicable.
Any links to studies or modelling done for hypothetical flight paths etc?

ChristiaanJ
12th Feb 2008, 21:48
tartare,
I have found myself staring at that question as well.
On what sectors does it become interesting to spend only three or four hours in the air, and sort out the 'timezone shift' on the ground?

Europe - Australia/NZ, possibly.
US West Coast - Asia and Australia, probably.
Europe - US East Coast (which would be about an hour's flight) ?

So much time is now spent on ground transport to and from the airport, "security" at the airport, taxying at the airport at 30mph, waiting in the take-off queue, then waiting in the landing queue and getting to the gate, disembarking, getting through immigration and getting one's luggage.....
Chopping a significant part off the 'in the air' time is only worth it over long distances.
And even then the time zone changes can negate much of the gain in travel time.

Look at Concorde. UK or France to the US you gained. In the other direction you still lost.

chornedsnorkack
13th Feb 2008, 10:03
I guess the point I am trying to clarify is the minimum length of sector on which travelling at hypersonic speeds would be practicable.

What were the New York-Miami hops like?

What would be faster: Concorde New York-Houston overland (subsonic) or the same route round Florida (supersonic)?