In article ,
Mike Borgelt wrote:
On 11 Jan 2004 14:39:20 -0700, (Mark James Boyd)
wrote:

In article ,
Mike Borgelt wrote:

I've come to much the same conclusion as Mike. I'd use a single
more powerful turbine (maybe the 1500) instead of 2, but
the numbers seem to work for even fairly short fields.

The heat on the tail scares me though. Hmmm...how do we
get rid of the glider tail?


The guys with the Silent don't seem to have a problem with the heat on
the tail - the two AMT 450 turbines seem to be mounted parallel to the
centerline. If this still worries you a V tail as on HP gliders or the
Salto is the easy answer.

I've never seen a turbine airplane design that allows the hot exhaust
to reach a control surface of the aircraft. The fact that the Silent
flew a few times in this configuration is not convincing to me.
If the owner would put it on a stand in a hangar and
run it for an hour with his face right in front of the rudder/stab,
I'd change my tune. I don't have any hard facts or figures,
but my intuition sets off some warning flags here...

I first thought of using the AMT1500 but when you do the numbers two
AMT450s (and soon the XP versions with about 10% more thrust) are
quite adequate for a 400kg glider.

The larger engine isn't for more thrust than two engines, but
just for the lower complexity of using one engine. Two engines are
best used in aircraft with high wing loading that carry
passengers through turbulence. Two engines in a light-wing
loaded aircraft is just unneccesary, IMHO. Engine failure is
a non-issue due to the glide ratio, and the reliability of turbines.
The added weight, wiring, two starters, fuel lines, etc. seem
silly if a single turbine can be used instead.

Great for motorising motorless gliders as the weight in the fuselage
is minimal. Convert part of the water tanks/bags for jet
fuel.60Kg(75liters) will give you one hour.

Figuring out how to manage fuel from two tanks is a minor
complexity, and being able to dump fuel should ensure
one doesn't fly "chinese style" (won weeng lo).
It does seem using the fuel as ballast is an excellent feature,
but I'd want to really think hard about fire dangers.
Perhaps use less flammable fuel? I guess there is quite a
variety of fuel choices available...

Now look at a Sparrowhawk
One AMT 450 will self launch this adequately.
Two smaller engines may still be optimum for slightly increased thrust
and engine out capability.

More power than adequate = better. One can always throttle
back for fuel savings. I suspect the designers used two
engines instead of one because the 1500 may not be readily tested/
available rather than due to the need for redundancy. Again,
I've flown some twins and they have their uses; a powered glider
isn't a good match for two turbine powerplants
(just overkill/expense)...

Hope the Windward Performance guys have a plan to increase production
because if this works they might be swamped by customers.

The Sparrowhawk may be ideal for this application, but other
light gliders also have comparable potential. And I personally
would want to see a competitor which could taxi well.
A self-launch glider which has trouble taxiing is less
interesting to me personally than something more flexible.
Besides, the noise may get one banned from the gliderport and forced
to use a gasp towered airport... ;P