1 Lensjet

An acceleration jet needs more low velocity thrust to be
useful in the boost role than on the high end where the
high altitude rocket engines can be expected to take over.
This implies a higher compression ratio than the introductory
model in the first post while retaining lightness and simlicity.
Also it implies a requirement to make certain that the total
combustion burn can be done in the main chamber.

Mod 1 of the orriginal adds another sealing ring at about
25 degrees latitude north and south for both contrarotating
turbocompression lenses. The new structure is hub from the
poles to 70 degrees latitude, compressor blading from 70 to
25 degrees, seal/structural ring at 25 degrees, compressor
blading from 25 to 10 degrees latitude, seal/structural ring
at 10 degrees, and turbine blading from 10 dgrees north to
10 degrees south of the equator of the lens.

The modified flow routing starts with the air entering the low
pressure compressor between the hubs and 25 degrees
latitude on both north and south sides of the lens. The
compression through the inlet guide vanes, compressor blades,
contrarotating compressor blades, and interior stator should
be in the 1.8 or so range.

Without burning, the partially
compressed air is directed out through the turbine blades
in two 135 degree arcs directly opposite each other, leaving
two 45 degree arcs for the turbines to operate in. The
air regeneratively cools the turbine blades and picks up
a minor amount of compression before being directed
into the higher compression blades. The regenerative cooling
helps define the mach limitations of this particular cycle,
along with the material capabilities of the blades. If the
blade material can operate reliably at 1,600 degrees
farenheit, the this compression ratio can operate to
mach 5 without any other cooling measures of the turbine
section.

After cooling the turbine, the heated air is directed through
the compressor blades between 10 and 25 degrees latitude.
The blades are faster than in the first stage area, but not
supersonic due to the higher mach number of the heated air.
Total compression after this set of stages should be in the
3.5 to 4 range, including all previous compression by the
first compressor set and the minor compression through the
turbine area.

A stochiometric, or equivilence ratio of 1 burn is used inside
the lens before being directed through the turbine sections
to power the whole arraingement. The pressure after the turbine
is expected to be about 2.5 times the inlet pressure at about
4,000 degrees. This will be barely supersonic through the
nozzles at sea level. With a 16:1 air/fuel mix, net fuel Isp under
static conditions should be in the 1,200-1,400 range. With
a compression ratio this low, considerable improvement can
be expected at higher airspeeds.

A 3 foot diameter lens would process about 280 pounds of
air per second, with a net thrust in the neighborhood of 21k.
Fuel burn of 17 pounds per second. Primary mass of this
layout can be approximated by 4 spheres 3 foot in diameter.
With the complexity of shape, and symplicity of stress lines,
each of the spheres would have the mass of a pressure tank
at 4 times the maximum 60 psi seen by the active system.
Using a mix of materials with an average density of 2.5, and
average stress of 100 ksi, primary structure seems to be in
the 130 pound range. This is for the 4 shells representing the
inlet guide/ flow control as one, the contrarotating lenses as
two more, and the fixed stator/burner can as the last.

The axle, bearings, fuel pump, nozzles, intakes, and other
systems will mass considerably more than the bladed lenses
here. To hit the 120/M target suggested, these systems need
to be held to less than 745 pounds. This would yield a 24/1
T/W ratio. It is not likely that conventional systems, especially
the intake, can hit this target. To make it posible, the lensjet
must make better use of the delivered air to reduce intake
size requirements. It also needs to deliver a higher
pressure after the turbine to reduce nozzle size and variability
requirements.

The intake in particular needs to be redesigned for higher
performance, lower mass, and lower complexity and cost
than what is currently available.

John Hare