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Jet Glider Sparrowhawk



 
 
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  #11  
Old January 14th 04, 03:09 AM
Bill Daniels
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"Eric Greenwell" wrote in message
...
Mark James Boyd wrote:

Eric Greenwell wrote:

Mark James Boyd wrote:
At 500 lbs, a notional Sparrowhawk with two AMT-450s

would accelerate at .12 g's (2 knots/second), to 40 knots
in 20 seconds using 1200 feet of runway. Assuming wheel
friction and drag make this figure double, under 2400
feet of runway is still respectable.

Wouldn't that be (500/(45+45) = 0.18 g's ? Or 3.4 knots/second to 40
knots in 10.4 seconds, and about 330 feet? So doubling is only 600 feet.



I avoided the math and safe-sided the heck out of it and
got a way too big figure. Thanks for the extra work


Using one engine, 0.09 g's gives 1.7 knots/sec, 21 seconds to 40 knots,
and 640 feet, doubled to 1280. With all due respect to Mike B, I might
be happy with one engine.
Eric Greenwell



For self-launch, perhaps, but for 100 knot level flight,
or 500 fpm climb, 200 Newtons (45 lbf) may be not enough.
I haven't done the disciplined math for this, nor
do I know the actual drag in Newtons of the Sparrowhawk.
I suppose this can be calculated rather than SWAGed based
on weight and the shape of the polar, eh? Any takers?


That's an easy one. Basically, the weight/(L:d) at the speed of
interest. Sticking with the 500 pounds weight, the drag at best L (36)
is 500lb/36=14 pounds, leaving 30 pounds thrust to climb. 500/30=17 L
climbing; climb rate is [59 knots at best L]/17=3.5 knots 350 fpm. Not
great, but interesting. For 500 fpm climb, a 56 lbf unit would do it.

For a 2000 foot climb:

- 2000'/350fpm = 6 minutes
- 6 min x 460 grams/min = 1200 grams, or almost a gallon liquid.

So, carrying 5 gallons would give you one launch, a 4000 foot climb out
of a big holes, and some travel towards home at 100 knots.

The L at 100 knots ~ 12, so 500/12=41.5 lbf for level flight, so that
goal is met with one engine.

OK, these are a bit optimistic, because I assumed the engine added no
drag. It does show one engine is close to being good, but a 55-60 lbf
engine would be "ideal".

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA


Have you math whizzes figured out how far the wing runner will have to run
before this dog whistle is going fast enough to have aileron control?

Bill Daniels

  #12  
Old January 14th 04, 04:39 AM
Eric Greenwell
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Bill Daniels wrote:


OK, these are a bit optimistic, because I assumed the engine added no
drag. It does show one engine is close to being good, but a 55-60 lbf
engine would be "ideal".


Have you math whizzes figured out how far the wing runner will have to run
before this dog whistle is going fast enough to have aileron control?


Wing runner? On an 11 meter motorglider? We don't need no stinking wing
runners! This is _Self_ launching! Put wing tip wheels on it and let it
roll! Actually, letting it slide on it's plastic pads would work fine,
since there is so little weight on the tip. The wing will come up when
it's ready. In crosswinds, put the downwind wing down, to help keep it
straight. The ultimate answer is a tailwheel with just enough steering
ability to keep it straight, since it doesn't need to taxi.

--
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change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

  #13  
Old January 14th 04, 04:53 AM
TomnKeyLargo
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Current Jet Cat turbines require propane to start them. The RC Jet guys at our
field have a whole bunch of Jet RC planes and fly from our field several days a
week. Including a FAA safety Inspector. The Jet Cat turbines due to using
propane for start, cannot be started inflight. The wind with blow out the
flame. Also, our RC guys do have flameouts everyso often requiring them to have
a dead stick landing. Jet-RPM of Sweden is making a Jet turbine, I have spoken
with him. His Jet Turbines will have a electric start, he hopefully will be
ready soon to start selling them. He said the price would be around 3450 euros,
this was several months ago. To prep a current Jet Cat for engine start does
take alittle time. I believe in March, in Lakeland, Florida the Jet RC people
are going to have a big meet. You might want to check it out. Jet RPM said
several sailplane manufactures have spoken to him already. It appears the small
turbine with a electric start could become a substainer with inflight start
very soon. Tom
  #14  
Old January 14th 04, 04:59 AM
Eric Greenwell
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Bob Kibby wrote:

My D-2T does not self launch. After an aero tow the D-2T handbook says 216
nm range based on sawtooth method at 882lbs gross weight, 3.43 gal of usable
fuel. I don't think that any current small jet engine approach can even
approach this. I think it will take a high bypass fan to compete with my
current and existing performance.


Two stroke engines are much more economical, for sure, but the turbine
_seems_ to promise a simpler, more reliable, more easily started system
and much less drag while the engine is out, especially interesting in an
engine failure situation. And there is the ability to cruise
significantly faster.

Any one need a copy of the Flight Manual
pages documenting this performance?


Nah, my ASH 26 E manual says I can go 290 nm on that much fuel, so I
believe you (I'm not sure I believe the manual, though!)

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

  #15  
Old January 14th 04, 07:19 AM
Mark James Boyd
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Bill Daniels wrote:

Have you math whizzes figured out how far the wing runner will have to run
before this dog whistle is going fast enough to have aileron control?


Well, we've got a name for the project!

Project Dog Whistle. LOL

And Bill rightly points out that if the thrust
is behind the CG, any yaw at low speeds means
a ground loop on takeoff unless the tailwheel is
firmly tracking.

One more reason why the twin Cri-cri version had it
right, with the two engines well ahead of the
CG, and with exhaust away from anything that might burn.

  #16  
Old January 14th 04, 07:27 AM
Mark James Boyd
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Mike Borgelt wrote:

When you do the performance calculation correctly you are in for a
surprise.

Jet engines have more power available the faster you go.


The downside of this is if the specs are for thrust in Newtons
available at a certain airspeed (not 0). At 0 airspeed, it
may be that the AMT-400 puts out significantly less power.
This would extend the takeoff roll some, and decrease efficiency
at any airspeed lower than "spec."

Or maybe the spec is for thrust on a test stand, who knows?

  #17  
Old January 14th 04, 07:30 AM
Steve Davis
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A Genesis owner in Sweden is planning to install one
or two jet engines which will pop out of the BRS hatch.
He's planning to use the electric start version which
is being developed. His progress can be monitored
on www.genesisflyers.com He has also done some wing
root fillet modifications and testing to improve low
speed air flow. Good pictures and descriptions.


At 05:06 14 January 2004, Tomnkeylargo wrote:
Current Jet Cat turbines require propane to start them.
The RC Jet guys at our
field have a whole bunch of Jet RC planes and fly from
our field several days a
week. Including a FAA safety Inspector. The Jet Cat
turbines due to using
propane for start, cannot be started inflight. The
wind with blow out the
flame. Also, our RC guys do have flameouts everyso
often requiring them to have
a dead stick landing. Jet-RPM of Sweden is making a
Jet turbine, I have spoken
with him. His Jet Turbines will have a electric start,
he hopefully will be
ready soon to start selling them. He said the price
would be around 3450 euros,
this was several months ago. To prep a current Jet
Cat for engine start does
take alittle time. I believe in March, in Lakeland,
Florida the Jet RC people
are going to have a big meet. You might want to check
it out. Jet RPM said
several sailplane manufactures have spoken to him already.
It appears the small
turbine with a electric start could become a substainer
with inflight start
very soon. Tom



  #18  
Old January 14th 04, 07:36 AM
Mark James Boyd
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Bob Kibby wrote:
My D-2T does not self launch. After an aero tow the D-2T handbook says 216
nm range based on sawtooth method at 882lbs gross weight, 3.43 gal of usable
fuel. I don't think that any current small jet engine approach can even
approach this. I think it will take a high bypass fan to compete with my
current and existing performance. Any one need a copy of the Flight Manual
pages documenting this performance?

Bob Kibby "2BK"


This turbine approach absolutely will not compare to the fuel
efficiency of a piston engine. Our point was simply that
fuel efficiency issues are dwarfed by the other advantages of
a turbine. Four times a small number is a small number.
If the turbine uses four times as much fuel (14 gallons in this
case) we are really talking about an additional 70 pounds/$20
of fuel, which we believe is a minor additional cost
compared to the other advantages a turbine provides.

This is clearly not true for ALL applications (if the 70# extra
means you are over gross and can't fly, then this kills the
whole idea). But on balance, for many cases, it looks like the
turbine idea, with it's fuel inefficiency, is interesting...
  #20  
Old January 14th 04, 11:31 AM
Vaughn
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"Mark James Boyd" wrote in message
news:4004fb99$1@darkstar...
Bill Daniels wrote:

One more reason why the twin Cri-cri version had it
right, with the two engines well ahead of the
CG, and with exhaust away from anything that might burn.


But introduces the possibility (certainty?) of asymmetric thrust! I
saw a Cri-cri (piston) lose power on TO one year at Oshkosh, it crashed
almost at the crowd line.

Vaughn





 




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