🚀 go-pugleaf

On Date: Fri,  1 Jan 93 17:02:56 PST, Brian Stuart Thorn <BrianT@cup.
portal.com> writes:
>   Much has been said recently about aerospike engines, specifically
>   in regard to potential use on the DC-1. I've never heard of them
>   before, can someone give me (and anyone else in the dark) a brief
>   description of what an Aerospike Engine is?
 
Briefly, an aerospike engine uses an exhaust nozzle that can be thought
of as a conventional bell shaped nozzle turned inside-out.  The aerospike 
nozzle is a truncated version of an ideal spike;

       Bell           Ideal Spike           Aerospike

       ||||         |------------|       |------------|
      /    \         \          /         \          /
    /        \        \        /           \        /
  /            \       \      /             \______/
                        \    /
                         \  /
                          \/         

                               (| indicates the combustion location).

In a bell nozzle combustion gas flow expands outward from the centerline 
along the diverging walls.  This is a point design with optimum 
performance at one specific ambient pressure (altitude).  Careful design 
is needed to achieve desired high altitude performance while avoiding 
flow separation at low altitudes which can result in structural damage.  
Movable nozzle extentions can provide altitude compensation (larger 
exit/throat area ratio at higher altitudes) to overcome some of the 
compromise in design.

In an spike nozzle the opposite takes place and the gas flow is directed 
inward from an annulus at some diameter away from the centerline.  This 
flow is directly exposed to ambient pressure and its expansion is thus 
directly coupled to the external environment (continuous altitude 
compensation with no moving parts).  Truncating the ideal spike to save 
weight results in a bubble of flow at the base which has some performance 
loss.  This can be offset by pumping secondary flow (about 1% of primary) 
into the base region to elongate the bubble which then forms an 
aerodynamic countour similar to the truncated structure (hence the name 
"aerospike").

In an earlier post I discussed Rocketdyne's testing of aerospike engines 
and compared its efficiency with bell nozzles.

Disclaimer: Opinions stated are solely my own (unless I change my mind).
Ben Muniz, Rocketdyne, SSF Dynamics | "Man will not fly for fifty years"
munizb@rocket.rdyne.rockwell.com    |     Wilbur to Orville Wright, 1901