On Dec 8, 4:15*pm, wrote:
On Dec 8, 2:30*pm, "Tim Mara" wrote: keep in mind Jet engines move a LOT of air....a LOT of air and only a very
small amount of the air being moved is actually used in combustion so what
you have is a lot of air....and a small % of (fire) combustion...
tim

Tim already knows this, but just to clarify -- the above description
is true for turbofans, but not for turbojets, the difference being
that a turbofan has (ready for this?) a big fan on the front that
bypasses the compressor, combustor and turbine sections. It is
normally driven by an additional turbine section at the very end of
the engine. The higher the "bypass ratio" the more air goes around the
hot section of the engine. Generally the higher the bypass, the more
static thrust and better specific fuel consumption (lbs of fuel per lb
of thrust per hour) you get, particularly at low speeds and lower
altitudes. *Most of these smaller engines are simple turbojets because
you can get away with a single stage compressor and a single turbine.
Lots cheaper to build. I don't have the specs for what Hph is using,
but from Tim's comment perhaps they are already using a turbofan - the
self-launch capable engine certainly is fan with a high(er) bypass.
In any event the simple fact that they have something flying is proof
that you don't need a titanium vertical fin for this to work.

9B

According to the spec sheet from Turbinenbau Schuberth for the
TBS-400, the engine uses a single compressor and a single-stage
turbine with no fan. The maximum EGT is 720 degrees C. I'm sure things
cool down sufficiently by the time you get to the fin, but I wouldn't
put my hand behind directly behind the engine to see if it's running.

I think in the end jets will replace props for sailplane self-launch,
the greater simplicity and lower weight, plus more favorable
operational considerations count in their favor and the efficiency
tradeoff isn't much of a concern unless you want to go significant
distances.

9B