In article 419af6e1$1@darkstar,
(Mark James Boyd) wrote:

In article ,
Bruce Hoult wrote:

A low stall speed isn't what you want. By far the most important thing
is a high Vne. The best way to climb in a jet is to accelerate in level
flight (in ground effect if you can) to Vne and then climb at Vne.

This may be the best way in terms of efficiency and power, but
I'm not sure it is as practical as the alternative.

I'm thinking of a situation where acceleration to a speed where
climbing out of ground effect is possible. If we assume a
glider weighing 400 lbs total, it takes a certain amount of thrust
to accelerate it to above stall speed, and then Vx and Vy. It then takes
a lot more thrust to get it to Vne.

Thrust is cheap. The amount of fuel used is to a first approximation
independent of the thrust of the engine (in fact to a certain point more
powerful engines result in less fuel used). But an engine that will
give you only 200 fpm of climb will take *forever* to get you to any
reasonable flying speed.


There are also rockets. Lighter, simpler, less fuel efficient, and
(probably) cheaper than jets.

It looks like $20 for 4lbs of thrust for 8 seconds. Each launch looks like
at least hundreds of dollars (worth of commercial rockets sold
by Public Missiles, Ltd and the like).

Perhaps these can be constructed as reusable and experimental,
for much less cost, but I'm just not familiar with this.

If you can give us some estimates on costs and thrust and burn time,
that would be great Perhaps the largest barrier to this
is unfamiliarity and not knowing how such a burn is controlled.
How does one perform an aborted takeoff?

You seem to be assuming solid rockets. That would be a *very* bad idea.
Liquid rockets are reusable and use cheap fuels. Have a look at the
videos etc on XCor's web site (http://www.xcor.com/). They've built
liquid/gas fuelled rocket engines with thrust levels ranging from 15 lb
to 1800 lb. One of their 400 lb thrust alcohol/oxygen engines would
launch a typical glider with performance similar to a winch launch using
about 45 lb of fuel.

I've done calculations on takeoff performance several times over the
years, and posted the results on this newsgroup.

http://groups.google.com/groups?selm...12003%40copper
..ipg.tsnz.net

http://groups.google.com/groups?selm=an_595515430

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Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------