New Powerplant

The August issue of AOPA PILOT reports a "tiny jet engine" is being
developed with 150 lbs of thrust. Its 15" long, 8.6" in diameter and
weighs 19 lbs. I wonder what it costs? This sounds like a great power
to weight ratio.

wrote in message
oups.com...
The August issue of AOPA PILOT reports a "tiny jet engine" is being
developed with 150 lbs of thrust. Its 15" long, 8.6" in diameter and
weighs 19 lbs. I wonder what it costs? This sounds like a great power
to weight ratio.


It is, but what you gain from the engine you loose from the amount of fuel
yoo have to carry. Take a look at www.microjeteng.com for what's available
now. I seem to recollect that a video was published on the internet of a
glass glider with a pop out pod with two jets on it.

Peter

On Thu, 25 Aug 2005 12:40:30 -0700, richard.kiray wrote:

The August issue of AOPA PILOT reports a "tiny jet engine" is being
developed with 150 lbs of thrust. Its 15" long, 8.6" in diameter and
weighs 19 lbs. I wonder what it costs? This sounds like a great power
to weight ratio.

I don't think power/weight is very significant for our use. Thrust/drag
ratio is a lot more use. Calculate that for your glider at typical
inter-thermal speeds, double it and that's probably all the thrust you'd
need. I did a rough calculation for an SZD Junior at 65 kts and got about
22kg of drag, Double it and you're looking at 40kg, 88 lbs thrust.

Fuel consumption is also important: a turbojet at sensible glider speeds
will be thirsty. Maybe you just carry jet fuel instead of water ballast to
bring you up to Mtow?

Finally, make sure the engine management system is as good as those on RC
models because this means that the engine will take care of its start
sequence all by itself: if you're low you don't want to be paying
attention to a manual start sequence.

Its all been done anyway: a German University project flew a Ventus on a
single 35 lb st. engine (climb rate .001 m/sec IIRC) and there is/was a
glider on the US display circuit with a pair of 35 lb st. engines: the
implication was that it was self launching from a sealed run.

--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Snip

Its all been done anyway: a German University project flew a Ventus on a
single 35 lb st. engine (climb rate .001 m/sec IIRC) and there is/was a
glider on the US display circuit with a pair of 35 lb st. engines: the
implication was that it was self launching from a sealed run.

It's a not-so-silent Silent sailplane, based in Albuquerque:

http://www.silentwingsairshows.com/jet.html

Yes, it really does self-launch and is no worse than some motor gliders
I've seen. Personally, I'd like a bit more thrust if I were going to
self-launch.

Mike

"Pete S" wrote in message
...

wrote in message
oups.com...
The August issue of AOPA PILOT reports a "tiny jet engine" is being
developed with 150 lbs of thrust. Its 15" long, 8.6" in diameter and
weighs 19 lbs. I wonder what it costs? This sounds like a great power
to weight ratio.


It is, but what you gain from the engine you loose from the amount of fuel
yoo have to carry. Take a look at www.microjeteng.com for what's available
now. I seem to recollect that a video was published on the internet of a
glass glider with a pop out pod with two jets on it.

Peter



Originally, I thought the horrible specific fuel consumption would make
these 'dog whistles' unsuitable for glider use.

On second thought, the residual weight after all the fuel is burned is much
less than a piston engine and propeller. The extend/stow mechanism is much
simpler as well. If they were used only for self launch and the entire fuel
supply were to be consumed in that launch, the idea has merit.

One worrisome issue is the temperatures of the tail surfaces that are in
contact with the jet exhaust. Bob Carlson told me that the fin on his jet
"Silent" reached 140F during the engine run even with two small turbojets
canted slightly outward to spare the fin. I suppose it's possible to choose
resins and curing processes that would make those fin temperatures
tolerable.

I have to admit that I like Bob Carlson's idea that if the ballast tanks
were to be filled with Jet A instead of water and then when in trouble just
start the jet and fly home instead of dumping ballast. My Nimbus would hold
75 gallons of Jet A which is several hours of engine run.

Bill Daniels

140 degrees? Hell, sounds like Uvalde in August. Or Phoenix. I
wouldn't worry too much about it.



Larry




"Bill Daniels" wrote in message
:

"Pete S" wrote in message
...

wrote in message
oups.com...
The August issue of AOPA PILOT reports a "tiny jet engine" is being
developed with 150 lbs of thrust. Its 15" long, 8.6" in diameter and
weighs 19 lbs. I wonder what it costs? This sounds like a great power
to weight ratio.


It is, but what you gain from the engine you loose from the amount of fuel
yoo have to carry. Take a look at www.microjeteng.com for what's available
now. I seem to recollect that a video was published on the internet of a
glass glider with a pop out pod with two jets on it.

Peter



Originally, I thought the horrible specific fuel consumption would make
these 'dog whistles' unsuitable for glider use.

On second thought, the residual weight after all the fuel is burned is much
less than a piston engine and propeller. The extend/stow mechanism is much
simpler as well. If they were used only for self launch and the entire fuel
supply were to be consumed in that launch, the idea has merit.

One worrisome issue is the temperatures of the tail surfaces that are in
contact with the jet exhaust. Bob Carlson told me that the fin on his jet
"Silent" reached 140F during the engine run even with two small turbojets
canted slightly outward to spare the fin. I suppose it's possible to choose
resins and curing processes that would make those fin temperatures
tolerable.

I have to admit that I like Bob Carlson's idea that if the ballast tanks
were to be filled with Jet A instead of water and then when in trouble just
start the jet and fly home instead of dumping ballast. My Nimbus would hold
75 gallons of Jet A which is several hours of engine run.

Bill Daniels

I had a look at the microjet engine. With 65 Lb of thrust, and with 36
cm long, 16 cm diameter, a 400 Kg plane should be able to climb at 1,3
m/s sustained (25 Lb for the aero drag, rest for climbing). Going to
1000 m would take just 12 mins and 11 Kg of fuel. I ignore the cost of
fuel, but at 1 $ /kg, that makes for cheap tows to offset the cost of
the engine.

Next, could the exhaust temperature be solved by embedding the tiny
engine behind the pilot and letting the exhaust out throug some
openning in the aft taper of the fuselage, and well below the tail
planes. This would however need some adjustable intake port in the
fuselage. But in all cases it should all be much simpler that folding
out a propeller with or without a piston engine.... .

I've seen the video of the not so silent wings. Now how long do you
think it would last until your neighbours would shut down the
gliderport? At mine, I guess about two weeks maximum.

Stefan

The biggest issue against these engines is the TBO.
The AMT 45lbs engines are 25-50 hours for TBO.
Not bad in 20 minute spurts, but 160 launches
for $4000 just in engine costs ain't chicken feed.
$25 per launch? Good, but not fantastic. And for
2 of them
maybe a bit more... Still, glider self-launch seems

like a much better GA application than many other
options...

At 21:48 29 August 2005, Titoa wrote:
I had a look at the microjet engine. With 65 Lb of
thrust, and with 36
cm long, 16 cm diameter, a 400 Kg plane should be able
to climb at 1,3
m/s sustained (25 Lb for the aero drag, rest for climbing).
Going to
1000 m would take just 12 mins and 11 Kg of fuel. I
ignore the cost of
fuel, but at 1 $ /kg, that makes for cheap tows to
offset the cost of
the engine.

Next, could the exhaust temperature be solved by embedding
the tiny
engine behind the pilot and letting the exhaust out
throug some
openning in the aft taper of the fuselage, and well
below the tail
planes. This would however need some adjustable intake
port in the
fuselage. But in all cases it should all be much simpler
that folding
out a propeller with or without a piston engine....
.


Mark J. Boyd

It strikes me that these units are much more suitable for use as
sustainers rathe than self launchers. You may only use them a few times
in a season saving on engine rebuild costs, their drag profile is
significantly better than a prop and two stroke engine assembly,
the'yre lighter than an IC engine. Lots of good reasons.