[AR] Re: P&W GTF
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 3 Apr 2020 23:48:28 -0400 (EDT)
On Fri, 3 Apr 2020, Ben Brockert wrote:
...Boom says that the final plane will use medium-bypass turbofans,
but their subscale model is pure turbojets. Even if they can take off
without afterburner they're still going to be comparatively loud.
The biggest noise issue usually is not the area right beside the airport,
but the areas under the long low departure paths. There is *some* benefit
to be had from using the higher thrust of a supersonic aircraft to shape
the trajectory for noise mitigation -- steeper climbs, and given suitable
airport geography, sharper turns to avoid noise-sensitive areas and
exploit over-water departure paths (Concorde did some of that). Enough to
help some, anyway.
One more subtle noise problem that any supersonic vehicle has (barring
extremely clever aerodynamic design to get rid of the shock wave), is that
you can't necessarily avoid sonic booms on land just by going supersonic
only over water. When you decelerate offshore, the shock wave you were
pushing in front of you separates from the aircraft when you slow down,
and carries on forward -- it weakens but doesn't instantly vanish.
Concorde sometimes boomed its destination that way, when air conditions
were unfavorable.
But for rockets there's sill a large space of easy return in pumps...
Gas turbines are extensively developed, expander cycles certainly
aren't. An all-aluminum expander engine is practical, no single crystal
regeneratively cooled micro EDM tungsten cowhide blisk needed.
As witness half a century of aluminum turbine blades in the RL10.
Henry
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