Report Card for Donald Trump

[Warren Dew]

(01-16-2017, 03:13 PM)Mikebert Wrote:

(01-16-2017, 03:03 PM)Warren Dew Wrote:

(01-16-2017, 01:13 PM)SomeGuy Wrote:

Quote:Branson has been trying to provide supersonic service for some time; he tried to buy the remaining Concordes from British Air when British Air stopped flying them when the internet bubble burst.  That's why I view this as credible.  This company is connected to his Space Ship One venture, which is less likely actually to offer paid service, but which has relevant technology.

Don't get me wrong, I think all that stuff is cool, but I wonder what technology you'd think Space Ship One has that would translate into affordable supersonic commercial jets?

Composite materials suitable for the high temperatures of supersonic applications.

Actually this is interesting for another reason:  aerospace composites are a new technology, and Boeing already has a worldwide lead in them.  Since engineering is being done by a US team for this, it extends the US technology lead.  This is the kind of manufacturing I think the US can usefully emphasize:  emerging technologies where the US has a technical lead thanks to our strong University network.

Quote:

Quote:Supersonic flight is not inherently less fuel efficient on a per mile basis, just on a per hour basis.

Yes, it is.  Fuel use is largely a function drag, and drag is a function of speed.  In addition, the drag coefficient increases significantly after about Mach 0.8, pushing up fuel consumption dramatically.

It's not that it is impossible to fly past the sound barrier, I just question whether it is possible to do so cheaply.

But what would I know?

It's not that simple.  Drag coefficient increases substantially right at the sound barrier.  However, it then falls again at higher speeds.



If you're cruising at mach 2 or above, there's no fundamental reason why fuel economy has to be worse for supersonic flight.  There are differences due to much more research and development money being spent on optimizing engines for subsonic fuel efficiency, but that just means we ought to expect rapid improvement once fuel efficiency becomes a focus for supersonic engines.

Um yeah there is.  You are showing a plot of drag coefficient CD.  Drag force is proportion to CD and speed squared. Since work is force integrated over distance, fuel economy (i.e. work per distance) would be correlated with drag force.  So even if CD returns to its subsonic values, fuel economy at 1500 mph would still be nine times less than at 500 mph.

This is only true at constant altitude at subsonic speeds.

At supersonic speeds, the boundary layer speeds must remain subsonic due to speed of sound limitations, which changes how skin friction drag operates.

In addition, for both subsonic and supersonic speeds, higher speeds result in higher lift.  This permits aircraft to achieve adequate lift at higher altitudes where the air is thinner.  This in turn reduces drag.

Finally, at supersonic speeds, there is compressibility drag, but again, the compression wave can be used for lift.  This permits supersonic transports to cruise at much higher altitudes than subsonic transports, which again reduces drag relative to flying "in the soup".