At 11:17 PM 31/05/2010, you wrote:
Considering we are in a resource limited world, 2l sounds a bit
better to me than 5l+
Todd
From: Ron Sanders <[email protected]>
To: Discussion of issues relating to Soaring in Australia.
<[email protected]>
Sent: Mon, 31 May, 2010 10:02:17 PM
Subject: Re: [Aus-soaring] latest jet glider
Most IC powered SLGs can get up to 2000' for about 2 litres of fuel.
Most modern ones have a climd of 800 fpm or thereabouts at <50kts with
a steep climb angle. And although there are millions of moving parts
in the engine. they're all the type of part that a chap with a lathe
in the back room can turn up in an hour or so. You can't say that
about the jets, whatever their advantages.
Far out!!!
I ran the numbers for angle of climb. All numbers ISA sea level as
per standard practice.
For a 400 Kg flying mass modern 15/18m glider with 68 Kg jet thrust
static best Angle of Climb is at 50 knots or so at 7 knots climb rate.
At 500 Kg, 60 knots at 6.4 knots RoC.
In both cases CS22 motorglider takeoff performance is met.
You can go to 600Kg like the latest 18m gliders but you need full
thrust (80Kg) for the takeoff and it doesn't meet CS22 but still
isn't bad. You can throttle back after obstacle clearance and still
get a good rate of climb. Just like operating any powered aircraft
you take the aircraft weight and conditions of the day into account.
No problems here.
-----------
Obviously whoever made that comment about engine parts hasn't ever
manufactured anything. In principle it is correct. In the real world
you need to know the material specification, heat treatment pre and
post machining, if any and may need specially treated parts to
machine - good luck with getting the raw crankshaft forging, for
example or making a crankcase from a billet with a CNC machine. It
can be done but is about a difficult as making a set of nozzle guide
vanes and a turbine blisk and machining to final shape. That is the
only thing that's difficult in the small jets. The compressors are
automotive industry parts, the rest alloy steel and aluminium and
stainless steel. I think there are more moving parts in the carby of
a two stroke than in an entire small turbine engine.
------------
As for a resource limited world - it seems we may already have run
out of up and coming engineering talent.
When has the world NOT been resource limited in the sense that people
want more stuff than they have and it costs more than they are really
wanting to pay? Just offhand serious considerations of resource
constraint goes back to Thomas Malthus or more recently the Club of
Rome around 1970. Their predictions for the end of the 20th Century
were way off.
I can remember a prediction about how photography was doomed because
we were going to run out of silver due to its use in photography.
Efforts were made to find a substitute but no satisfactory ones were
forthcoming. Look what happened.
Sure we can *make* ourselves resource limited by refusing to allow
mining or drilling, or refusing to use nuclear power or spending our
societal wealth on useless energy sinks like windmills and solar
panels but if this goes on .... "eat your Greens" may take on a
different meaning.
When it gets to whether 2 litres or 5 litres of fuel is required for
a glider self launch or 8 litres for an aerotow and it is a serious
issue it won't matter. Something as frivolous and trivial and useless
as gliding will have been banned, taxed or otherwise driven out of
existence and the organisations running it will happily aquiesce as
they have done and are doing with all the restrictions placed on the
activity up to now.
Mike
Borgelt Instruments - manufacturers of quality soaring instruments since 1978
phone Int'l + 61 746 355784
fax Int'l + 61 746 358796
cellphone Int'l + 61 428 355784
email: [email protected]
website: www.borgeltinstruments.com
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