Production/Civil Rocket Glider: Any Such Animal ?
Chris Purvis
Is there such a thing as a production, civilian-use rocket glider ?
I would design a rocket glider that used two small rockets to climb
rapidly to
altitude (up to say 13,500 ft, exact altitude depends on loaded fuel).
At the target
altitude, the rockets would be shut down (having expended all fuel) and
sailplane
operations would begin.
Rockets would be designed so the glider could climb steadily at a safe
indicated air
speed and at approx. a 60 degree flight path angle.
Each could be positioned just behind the wing, pointed through the CG,
designed to
be throttled, and preferably retracted through a small door once all
fuel has been
safely expended.
If one rocket fails on the way up, no problem: you just climb half as
high. In flight
failure of one of two rockets should produce no serious yawing moment if
pointed
roughly through the CG.
For launch, restraints would prevent the (thrilling) launch off a short
ramp until both
rockets are confirmed live and in steady burn. Since only low power is
required, the
rocket fuel used might be safer than gasoline (sorry can't offer a fuel
type here).
*** Is there any such aviation animal ?
Imagine eliminating tow planes, tow pilots, tow gasoline, tow time, and
tow costs.
Might be cheaper -- and certainly would be more thrilling and faster
from start to glide. -- Chris
t_b...@my-deja.com
Well, as a guy with some soaring experience, a lot of high power
rocketry experience and a lot of radio controlled boost glider and
rocket glider experience, let me just say it it isn't practical.
The Germans, circa 1940, had a system of metal cased reloadable solid
fuel rockets that could boost a glider to about pattern altitude, or
less. Twin motors, much as you describe. A novelty at best.
If you run the numbers on cost, you will find out that it is
prohibitive. If you were considering solid propellant: One of the larger
reusable rocket motors available today is the Aerotech M1939, which
gives you an average thrust of about 400lbs for about 4 seconds or so.
This would not even get the average sailplane to pattern altitude and
the cost is about $600.00 for the motor case and $475.00 for the solid
composite fuel elements. $475 still buys a lot of tows, even today.
You "might" be able to design a hybrid motor system as they have done in
hobbyist high power rocketry that uses nitrous oxide as the oxidizer and
some type of solid plastic or enhanced paper as the solid fuel. Would it
ever be practical and cost effective and safe? I don't think so.
High power model rocketry operations seem to have an observed motor
failure rate of at least 1-2% or so (case failures, nozzle failures,
etc.) and these failures tend to be rather spectacular and not something
you would care to have your sailplane close to.
And then there is the effect of rocket exhaust on the grass field as you
take off....<G>
A fun idea, best left as a fun idea....
Sent via Deja.com http://www.deja.com/
Before you buy.
MilesB
comes in is that anyone that flies it would have to have PPL, IR, Twin, AND
jet - totalling one hell of a lot of hours just to get the lazy way up to
13000
Miles
Chris Purvis <dyn...@ispchannel.com> wrote in message
news:38B21694...@ispchannel.com...
Bert Willing
MilesB wrote:
> There was one - the Swiss Prometheus 2 motor(!!) Glider. Where the problem
> comes in is that anyone that flies it would have to have PPL, IR, Twin, AND
> jet - totalling one hell of a lot of hours just to get the lazy way up to
> 13000
>
The Prometheus is actually a jet-powered motorglider, not a rocket-powered
one.
--
Bert Willing
-----------
Caproni Calif A21S D-6600
Come fly at La Motte du Caire in the French Alps:
http://www.decollage.org/la_motte/
Michael Zaharis
ME163
Komet. This airplane, which reportedly attained a top speed of 600 MPH,
took off
on the power of a rocket engine which burned for 4 minutes, propelling
the
aircraft above Allied bomber formations, at which time it switched to
glider
(dive glider) mode, and dove through the bomber formations, guns/cannon
a-blazing, then gliding to a landing. I do believe that they did in
fact shoot
down a few bombers, but they were generally more hazardous to their own
pilots.
In fact, the rocket fuel was so corrosive that one pilot literally
dissolved when
the rocket fuel leaked into the cockpit.
It is difficult to build a solid rocket (liquid rockets are WAYYY too
complex for
operation by a private operator who isn't a "Rocket scientist") with a
relatively
long duration, low impulse performance. Where rockets have been used
for
aircraft assist (JATO/RATO), they are used to help a heavily laden
aircraft up to
speed, by supplying a short burst of power during the takeoff run. An
alternative would be a series of small rockets which fire sequentially,
but this
would probably fall apart in the engineering analysis - too much weight
for too
little impulse. Remember that rockets need to carry their own oxidizer,
which
makes them rather inefficient for that type of use from a weight
standpoint.
Plus, the reliability issue raised earlier. All in all, it would more
efficient
to use one of the lightweight low-thrust jet engines produced by
Williams
International or another manufacturer if someone was determined to build
a non-
propellor motorglider.
WBY0NDER
non-powered ME-163 replica glider. Saw photos on some website ( I could dig up
the URL if pressed) The text says that the builder-pilot was a 136 pilot
during the war and currently flys with a gliding club. The craft is said to
handle nicely and does aerobatics well.
MM
Vorsanger1
weeks, and would love to be able to see it if it is anywhere near where I will
be. thanks.
Cheers, Charles
Sarah
http://www.kolibri.lr.tudelft.nl/people/students/fun/rob/163repl.htm
Lets us know if you find it, it looks like quite a ride..
Sarah
tom_systek
JaKo
> Have you ever considered a motor glider?
... or even better yet -- a jet powered
motor glider :)
You know, a pulse jet powered one. No prop
to fold, 9V battery starting ... just a
"little bit" more noise ...
A 100# thrust (2 x 50# pulse jets) should be
plenty for a 1,000# glider of L/D of 20 or
better ...
Are there any regulations about propane
containers in an airplane?
JaKo.
dynocrp
I recall from my engineering days that accelerating a large volume of air
through a small velocity increment is far more efficient than vice-versa.
Examples of the former are too complex and expensive for gliders: very
large propellor, high-bypass turbofan, or Unducted fan turboprop (remember
they tested those in the 80's?). An example of the latter is a simple jet,
which can be very inefficient, noisy, dangerous.
I guess motor gliders with propellors exist for a reason.
*** Maybe the best solution is to hook a micro-turbine to a propeller. Why
? You get the propulsive efficiency of a prop. Very small turbines can put
out high power and don't require much space (and often can burn a variety of
fuel). Turbines often run 1000s of hours between overhauls, and a glider
would only use a turbine for a very short percentage of its flight cp. to
conventional airplanes. You'd carry enough fuel to get to altitude, not
much more. Why not consume it all at max power in order to get to altitude
quickly ?
-- Chris P.
Michael Zaharis
Thanks for the feedback.
Yes, you are correct. Thrust is equal to (Mass Flow Rate) * (delta velocity).
So, the 2 ways you can increase thrust are to increase mass flow rate or change
in velocity. However, it is much more efficient to increase mass flow rate than
change in velocity. Rocket engines use a relatively small mass flow rate with a
high increase in velocity, and are therefore inefficient in producing a large
amount of thrust per amount of energy. The way I made the concept intuitive in
my Aerospace Engineering classes was to recognize that when you have to impart
energy to the airflow to accelerate it. Remember that the kinetic energy of an
object, including air particles, is 1/2 * mass * velocity squared, which makes
it more expensive energy-wise to increase velocity than mass, at a given thrust
level (if you have to choose to increase velocity or mass flow rate, which is
analogous to mass for a continuous flow). There are even more mathematically
rigorous ways of proving this, but my Aero E 101 books are packed away in a back
corner of the basement.
Actually, the high-bypass turbofan might not be too expensive for the
(well-heeled) glider enthusiast. Thanks to the cruise missile industry,
companies like Williams international have developed smaller and smaller jet
engines, most of which have a relatively high bypass (I don't know how this
works out in the peace dividend vs. danger to the planet ratio, but this is
rec.aviation.soaring, not gov.military.nuclear, or whatever). Smaller and
smaller engines are now being developed for the civil aviation industry. I
don't know if there is yet an engine which is in the appropriate weight and
thrust range for sailplanes, but the industry trend is in a positive direction
from a private aviation/glider viewpoint.
Your idea for a turbine hooked up to a prop is a good one. Turbine engines can
be very light, and since they don't reciprocate, there is less
vibrational/cyclical stress on components. The only concern would be
manufacturing a reliable, light gearbox to reduce the shaft speed (maybe 40,000
rpm or faster) to an appropriate propellor speed (maybe 2,000 rpm). One
possible solution, which is what the Navy is trying to do with their destroyers,
is to use a turbine to drive an electric generator, which can then turn an
electric motor. This has several advantages - the turbine can be located
anywhere in the aircraft, to optimize cooling, airflow, or CG, the propellor can
run at a rotational rate independent of the turbine, allowing the turbine to be
optimized to run at a constant rotational rate, and power transmission is done
via wires, as opposed to shafts or belts. It might also simplify the propellor
retraction mechanism. This idea could also be used with a conventional
reciprocating engine, with many of the same benefits.
osborne
electric motor is an interesting concept. Perhaps an extension of this would
be to use a hydrogen/oxygen fuel cell to provide the electrical power
directly. Current technology fuel cells are able to use standard motor fuels
(gas, diesel or jet fuel) as a source of hydrogen.
The use of some of the small gas turbines is somewhat troublesome from the
standpoint of safety. Most of the "cruise missile" or "drone" engines are
not qualified for manned vehicles. One of the more challenging aspects of
this is the case of the rotor burst. When you fail a small turbine - turning
50000 to 75000 rpm, the amount of structural damage that can be done to the
aircraft is pretty impressive. In the case of a glider, it would take a
significant effort to ensure that the pilot did not suffer some of the same
sorts of structural damage.
"Michael Zaharis" <mzah...@us.oracle.com> wrote in message
news:38B99E12...@us.oracle.com...
Sean
click the gallery and select "Cri Cri"
It is a page of a french pilot who mounted two micro turbines (designed for
model jets) on a tiny, one-man plane and flew it.
""Noted French pilot Nicolas Charmont has installed 2 AMT Olympus
turbines in his Cri Cri together with AMT on-board automatic
start-up units and individual EDT's.
The Cri Cri weighs 170 Kg, and should have enhanced
performance withover 36 Kg of thrust available.
The Cri Cri has made his maiden flight in the weekend of 7-8 March.
Top speed at this flight was 240 km/hour (150 mph). Flying with
only one engine the speed is still 160 km/hour (100mph).""
I have no idea what the specifications are of the Cri Cri beyond it's
weight. This test may, or may not, be applicable to gliders but it does
raise some interesting questions.
Sean
--
se...@direct.ca
Michael Zaharis <mzah...@us.oracle.com> wrote in article
<38B99E12...@us.oracle.com>...
tom_systek
minutes to get to 2000 ft AGL. 400 lbs for 4 sec is TOTALLY UNUSABLE!!!
Tom Seim, 2G DG-400
Richland, WA
Jeff Greason <jgre...@hughes.net> wrote in message
news:FhCx4.24$1i5....@news2.randori.com...
> <t_b...@my-deja.com> wrote in message news:88uf4b$66m$1...@nnrp1.deja.com...
> > In article <38B21694...@ispchannel.com>,
> > Chris Purvis <dyn...@ispchannel.com> wrote:
> > > Production/Civil Rocket Glider: Any Such Animal ?
> > >
> > > Is there such a thing as a production, civilian-use rocket glider ?
> > >
> > > I would design a rocket glider that used two small rockets to climb
> > > rapidly to altitude (up to say 13,500 ft, exact altitude depends
> > > on loaded fuel). At the target altitude, the rockets would be shut
> > > down (having expended all fuel) and sailplane operations would
> > > begin.
> > >
> ...
> > > Imagine eliminating tow planes, tow pilots, tow gasoline, tow time,
> > > and tow costs. Might be cheaper -- and certainly would be
> > > more thrilling and faster from start to glide. -- Chris
> > >
> > >
>
> My company, XCOR Aerospace (www.xcor-aerospace.com), is
> designing liquid fuel rocket engines specifically for manned aircraft
> use. We have considered the sailplane market as one potential
> market for small engines.
>
> >
> > Well, as a guy with some soaring experience, a lot of high power
> > rocketry experience and a lot of radio controlled boost glider and
> > rocket glider experience, let me just say it it isn't practical.
> >
>
> Our preliminary analysis suggests it's quite practical -- with liquid
> propellant engines. With solids, neither safety, reliability, or cost
> look promising.
>
> >
> > If you run the numbers on cost, you will find out that it is
> > prohibitive. If you were considering solid propellant:
>
> It depends on what you consider "prohibitive" of course; but
> while the initial cost to purchase the engine system might be
> high, the cost per flight can be low. 400 lbf thrust for 4seconds
> (to use your example) using liquid propellants consumes less than
> $8 in propellant, even when confining ourselves to the more
> expensive propellants which are widely available and
> safe enough for use by the general aviation community. With
> liquids, the cost is in the engine, not the propellant.
>
> >
> > And then there is the effect of rocket exhaust on the grass field as you
> > take off....<G>
>
> Even this can be dealt with, but (as always) the tradeoffs depend on
> the demands of the customer.
>
> If anyone is interested in a rocket powerplant retrofit to a
> sailplane and you could afford to work with us as a "launch
> customer" for the capability, please contact us -- we'd be
> interested in talking to you. You can reach me at the
> e-mail below or at (805) 508-4437.
>
> ----------------------------------------------------------------
> "Limited funds are a blessing, not Jeff Greason
> a curse. Nothing encourages creative President & Eng. Mgr.
> thinking in quite the same way." --L. Yau XCOR Aerospace
> <www.xcor-aerospace.com> <jgre...@hughes.net>
>
>
Jeff Greason
Jeff Greason
news:38B755A1...@hotspam.com...
While it isn't on our web site yet, we are also seeking customers looking
for a
fully rocket-powered replica of the Me 163, with modern, safe propellants, a
new engine, and retractable gear (all of which should make it safe enough
to fly). As a side effect, performance would be improved over the original
Me-163. However, it's an expensive project -- more in line with the top end
of the warbird market than with the costs usually associated with
sailplanes.
But if you're interested, we'd love to hear from you (the Me-163 isn't on
our
web site yet).
Bruce Hoult
<jgre...@hughes.net> wrote:
> > If you run the numbers on cost, you will find out that it is
> > prohibitive. If you were considering solid propellant:
>
> It depends on what you consider "prohibitive" of course; but
> while the initial cost to purchase the engine system might be
> high, the cost per flight can be low. 400 lbf thrust for 4seconds
> (to use your example) using liquid propellants consumes less than
> $8 in propellant, even when confining ourselves to the more
> expensive propellants which are widely available and
> safe enough for use by the general aviation community. With
> liquids, the cost is in the engine, not the propellant.
I agree, but 400 lbf thrust for four seconds isn't enough! That thrust
would take about two seconds to accelerate the smallest lihtest glider
with a small pilot (I'm trying to hit 400 lb total weight here :-) to
flying speed. The best thing to do would be to stay level and accelerate
until the engine stopped (40 m/s, 78 knots) and then pull up and you'd get
to maybe 60m altitude at stall speed. That's just not enough! A minimum
at that thrust level would be about 15 seconds total, which might get you
to 1500' or so.
If that's going to cost $30 in propellant then you're better off taking an
aero-tow, and much better off taking a winch launch for $5.
Given that amount of fuel, it'd be better to have 200 lbf of thrust for 30
seconds. Or even 100 lbf of thrust for a minute and make good use of
those huge wings you've got out there -- a typical glider will only have
maybe 30 lbf of drag at a good climbout speed.
-- Bruce
Bruce Hoult
<tom_s...@email.msn.com> wrote:
> My DG-400 generates about 200 lbs of thrust. A launch takes AT LEAST 5
> minutes to get to 2000 ft AGL. 400 lbs for 4 sec is TOTALLY UNUSABLE!!!
That's *static* thrust, and will decrease drastically as you gain speed.
A rocket has (almost) exactly constant thrust at any speed. 200 lbf of
thrust from a rocket would give you the same initial acceleration but
would quickly leave your DG200 in the dust. Because the thrust stays the
same with speed, the greatest "horsepower" is at higher speeds, so the way
to fly it would be to accelerate to something higher than best L/D speed
and then climb at constant speed (which with 200 lbf thrust would be like
a winch launch).
You're quite right that 400 lbf for 4 seconds is nowhere near enough.
Four times that would be in the ballpark, but you'd really want a lot less
thrust for longer -- same amount of fuel, easier to control, smaller &
lighter engine.
-- Bruce
Jeff Greason
tom_systek <tom_s...@email.msn.com> wrote in message
news:#8UDWYYi$GA.236@cpmsnbbsa02...
> My DG-400 generates about 200 lbs of thrust. A launch takes AT LEAST 5
> minutes to get to 2000 ft AGL. 400 lbs for 4 sec is TOTALLY UNUSABLE!!!
>
Oh, obviously! The previous poster computed solid propellant cost for 4
second
burn, so I compared the cost for the same length burn with liquid propellant
just
to show the dramatic difference in cost from solid to liquid propellant.
Liquid rocket engines can burn as long as you want (Me-163 carried about
three minutes worth at full throttle). I suspect that any sailplane launch
application
would burn at least 30-60 seconds, with thrust depending on the application.
If you're interested, contact us, and we'll run the numbers on the mission
you
have in mind.
tom_systek
Tom
Bruce Hoult <bruce...@pobox.com> wrote in message
news:brucehoult-09...@bruce.bgh...
> In article <#8UDWYYi$GA.236@cpmsnbbsa02>, "tom_systek"
> <tom_s...@email.msn.com> wrote:
>
> > My DG-400 generates about 200 lbs of thrust. A launch takes AT LEAST 5
> > minutes to get to 2000 ft AGL. 400 lbs for 4 sec is TOTALLY UNUSABLE!!!
>
Ian Johnston
: How do you compute horsepower from thrust & speed?
Horsepower = thrust (in N) times speed (in m/s) / 741
Ian
Mark Lenox
tom_systek wrote:
> How do you compute horsepower from thrust & speed?
>
> Tom
>
Y'all correct me if I'm wrong here...
Power is Energy per unit time. (1 Watt = 1 Joule per second, 1 horsepower = 746
Watts)
Energy is Force over a (times) distance. (1 Joule = 1 Newton-Meter)
Speed is distance per (divided by) unit time. (Meters per Second)
Therefore,
Force * Speed = Power
Rockets provide the same force at higher speeds because their reaction mass is
traveling with them, whereas jet and prop powerplants must accelerate their
reaction mass (air), and there is a limit to their ability to do this.
Therefore, the horsepower that the rocket is developing goes up as the speed of
the craft goes up. Pretty cool. Plus, since their mass is continually
decreasing(linearly) due to the loss of fuel and:
Force = mass * acceleration
Acceleration increases linearly as well, neglecting air resistance.
Of course, the final altitude and speed being limited to the amount of energy
imparted from the rocket fuel being burned. All energy being conserved...
Mark Lenox
tom_systek
> the effective exhaust velocity is 1960 m/s (6400 ft/sec) -- you're
> throwing the reaction products backwards at nearly 2000 m/s.
Well, I guess there goes the ol noise suppression initiative.
>
> If you hold the aircraft stationary then *all* the energy is going into
> the exhaust. If the aircraft is travelling at, say, 50 m/s (98 knots) 95%
> of the energy is going into the exhaust and only 5% into the aircraft.
Let's see; to get a respectable 25% efficiency you will only have to fly at
500 m/s or 980 kts! Sounds like an exciting launch to me.
Bruce Hoult
<tom_s...@email.msn.com> wrote:
> How do you compute horsepower from thrust & speed?
From high school physics:
work = force * distance
power = work / time
speed = distance / time
Putting it all together:
power = (force * (speed*time)) / time
= force * speed
We're talking about the vicinity of 200 lbf thrust at say 80 knots climb
speed. Let's call that 90 kgf (880 N) of thrust at 40 m/s, giving 35.2 kW
or about 47 HP.
Unlike a propellor, slowing to, say, 40 knots, will halve the power (to 23
HP) of a rocket. OTOH, if you can happily fly at 120 knots then the
rocket would produce 50% more power, or about 70 HP. Note that this is at
*exactly* the same fuel flow rate, so as long as your drag at 120 knots
isn't drastically more than at 80 knots it would be a big win to fly
faster. This effect is most pronounced in rockets (which don't
beneficially interact with the air at all), a little less in military
jets, and much less in high bypass ratio airliners.
I don't know what sort of Isp Jeff's rockets would get (depends on fuel,
chamber pressure, size of nozzle etc), but I'd imagine 200 - 250 would be
about right for, say, a 85% peroxide and kerosine rocket. That would give
a mass flow rate of about 0.8 - 1 pound per second, or about 30 pounds for
a launch to 1500 ft.
-- Bruce
Bruce Hoult
wrote:
> Of course, the final altitude and speed being limited to the amount of energy
> imparted from the rocket fuel being burned. All energy being conserved...
Right. And unfortunately at the low speeds we're talking about most of
the energy is wasted. To use my assumptions from a previous post, that a
rocket that might be cheap and suitable and use cheap and safe fuels might
have an Isp of 200. What this means is that a lb of fuel will produce a
lbf of thrust for 200 seconds. Or 200 lbf of thrust for one second...
Simple conservation of momentum tells you that in a 1G field that means
the effective exhaust velocity is 1960 m/s (6400 ft/sec) -- you're
throwing the reaction products backwards at nearly 2000 m/s.
If you hold the aircraft stationary then *all* the energy is going into
the exhaust. If the aircraft is travelling at, say, 50 m/s (98 knots) 95%
of the energy is going into the exhaust and only 5% into the aircraft.
-- Bruce
Bruce Hoult
<jgre...@hughes.net> wrote:
> If you're interested, contact us, and we'll run the numbers on the mission
> you have in mind.
Have you done anything before of approximately suitable size? The XLR-11
would be far too powerful -- even a single chamber would be eight to ten
times too much.
Maybe the ROTON tip thruster would be close? 350 lbf and throttlable. I
don't know what the Isp for it is, but it's peroxide monopropellant so I'd
guess maybe 150?
OK, so silly person that I am, I just knocked together a spreadsheet to
see how the numbers worked out.
I assumed a 300 kg glider (which is not bad for a typical single-seater
with pilot and no ballast), a takeoff speed of 20 m/s (40 knots), and a
desired launch height of 500m at 30 m/s (60 knots) straight&level. I
assumed a four-part flight profile:
1) ground run with 20 kg of drag until liftoff speed
2) accelerate in ground effect at 1.5x L/D max until max speed attained
3) climb at the angle required to maintain the desired max speed
4) after engine cutout pull up/push over to obtain desired cruise speed.
I assumed this phase was 100% efficient.
The optimum profile in all cases is to accelerate at low level until you
have enough speed to cut the engine and do a gigantic pull-up.
Unfortunately, this requires about 190 knots, which most gliders won't
like. So I've decided to adopt a fixed maximum speed of 50 m/s (98 knots)
and I've assumed that we have an L/D of 30 at that speed. (In fact the
exact L/D desn't matter much at all while in powered mode)
For the purposes of calculating propellant mass used, I assume an Isp of
150. As the mass fraction (proportion of takeoff weigth that is
propellant) is very low, Isp has essentially no effect on performance
(assuming a given thrust level), so propellant mass is simply inversely
related to Isp. i.e. if the real Isp is 100 then multiply my calculated
propellant mass by 150/100.
It turns out that rocket takeoff looks quite practical at a thrust level
anywhere from about 100 kg of thrust to 250 kg of thrust. Below 100 kg it
takes too long to get off the ground and then accelerate, and above 250 kg
you have very little time to control the aircraft, have to climb too
steeply to limit the speed, and need a very violent pushover when the
engine cuts.
The total fuel usage actually varies very little: by only 8% in the range
100 kg to 250 kg thrust, and by about 25% in the range 50 kg to 300 kg
thrust. In all cases, more thrust leads to less fuel used, but it's right
around 28 - 30 kg for everything except the 50 kgf case (which is nearly
35 kg).
A ROTON tip thruster of 160 kgf (350 lbf) thrust turns out to look *very* nice:
- 4.4 seconds and 44m to liftoff
- 6 seconds and 210m accelerating in ground effect
- 30.3 degree climb at 50 m/s (98 knots), giving 16.6 seconds of 5000 fpm
rate of climb
- 6.5 seconds in a 0.4G push-over to level out at 500m and 30 m/s (58 knots).
Total: 33.5 seconds for the launch, 27 seconds of it powered.
This is all -- other than the high speed -- no more dramatic than, say, a
launch on a typical winch. More thrust, OTOH, could get quite sporty...
thrust 50 kg 100 kg 160 kg 250 kg 300 kg
Ground run 204 m 76 m 44 m 26 m 22 m
Dist at low level 945 m 420 m 210 m 160 m 130 m
climb angle 8 deg 17 deg 30 deg 55 deg 86 deg
powered time 104 s 45 s 27 s 17 s 14 s
If you (Jeff) violently disagree with any of my assumptions or results,
please let me know!
-- Bruce
Bruce Hoult
<tom_s...@email.msn.com> wrote:
> > Simple conservation of momentum tells you that in a 1G field that means
> > the effective exhaust velocity is 1960 m/s (6400 ft/sec) -- you're
> > throwing the reaction products backwards at nearly 2000 m/s.
>
> Well, I guess there goes the ol noise suppression initiative.
Yep :-)
> > If you hold the aircraft stationary then *all* the energy is going into
> > the exhaust. If the aircraft is travelling at, say, 50 m/s (98 knots) 95%
> > of the energy is going into the exhaust and only 5% into the aircraft.
>
> Let's see; to get a respectable 25% efficiency you will only have to fly at
> 500 m/s or 980 kts! Sounds like an exciting launch to me.
Actually, only at 268 m/s (520 knots), but still pretty sporty...
It might be hard for the rocket brigade to bring themselves to do, but
making a rocket with a lower Isp (and exhaust velocity) would help. If
you got the Isp down to 100, then the exhaust velocity would be 1000 m/s,
the noise would be a quarter as much at the same mass flow rate, or half
at the same thrust. And 25% efficiency would come at 134 m/s (260
knots). Still a big ask for a glider.
On the other hand, have you figured out the efficiency of a gasoline
engine driving a prop? It's probably 20% - 25% thermal efficiency for the
engine, and the prop must lose a good bit more.
And don't forget that a towplane is lifting itself as well as the glider,
so the total mass going to launch altitude is probably three times the
weight of the rocket-powered glider. Which gives the rocket a factor of
three advantage right there.
Put all that together, and 5% efficiency isn't all that bad, actually...
-- Bruce
Jeremy Harris - Network Service Providers Division
bruce...@pobox.com (Bruce Hoult) writes:
> ... rockets (which don't
> beneficially interact with the air at all),
Tell that to a missile designer and you'll get laughed at.
Just because the aspect ratio isn't quite up to Stemme numbers
doesn't mean that no lift is induced by motion through the air.
Cheers,
Jeremy
tom_systek
>
> On the other hand, have you figured out the efficiency of a gasoline
> engine driving a prop? It's probably 20% - 25% thermal efficiency for the
> engine, and the prop must lose a good bit more.
>
> And don't forget that a towplane is lifting itself as well as the glider,
> so the total mass going to launch altitude is probably three times the
> weight of the rocket-powered glider. Which gives the rocket a factor of
> three advantage right there.
>
A 2000 ft launch (near sea level) for my DG-400, which weighs about 1000
lbs, takes about 2 liters of gas. The same launch behind a Super Cub might
use 2 gallons (7.5 l) of gas and you're lifting around 3000 - 3500 lbs.
Somebody out their must know the BTU content of gas and can calculate the
efficiency.
Tom
Jeff Greason
> In article <K9Rx4.5750$1i5....@news2.randori.com>, "Jeff Greason"
> <jgre...@hughes.net> wrote:
>
> > If you're interested, contact us, and we'll run the numbers on the
mission
> > you have in mind.
>
> Have you done anything before of approximately suitable size? The XLR-11
> would be far too powerful -- even a single chamber would be eight to ten
> times too much.
Over the careers of the people involved, we've covered a range of thrust
from a few pounds to 250,000 lbf. Right now, we have a small demonstration
engine on the stand which we're using to prototype the safety improvements
needed for general aviation use. It burns nitrous oxide and a variety of
fuels at the 15 lbf level -- and the same basic design can be scaled between
15 lbf per chamber and 2000 lbf per chamber.
>
> Maybe the ROTON tip thruster would be close? 350 lbf and throttlable. I
> don't know what the Isp for it is, but it's peroxide monopropellant so I'd
> guess maybe 150?
For a variety of technical reasons, you wouldn't want to use that thruster;
and high-strength hydrogen peroxide is neither readily available to the
potential sailplane user, or something I would recommend for handling
without some training.
For the sailplane application, we would propose nitrous oxide as the
oxidizer -- you buy a bottle and screw it into the system to "load the
oxidizer". This uses similar skills to those involved in attaching a
propane
bottle to your barbeque.
> For the purposes of calculating propellant mass used, I assume an Isp of
> 150. As the mass fraction (proportion of takeoff weigth that is
> propellant) is very low, Isp has essentially no effect on performance
> (assuming a given thrust level), so propellant mass is simply inversely
> related to Isp. i.e. if the real Isp is 100 then multiply my calculated
> propellant mass by 150/100.
Without specifiying exactly what performance we are obtaining right
now, I think you can safely do your performance estimates on the
basis of 200 second Isp.
> If you (Jeff) violently disagree with any of my assumptions or results,
> please let me know!
With the exception that your Isp is a bit low, you're seeing similar
results to what we've seen. Rocket launch isn't a way to pinch
pennies on tow costs, by any means -- but it can do some pretty
interesting things for "specialized" niches where pilots might want
those capabilities. Since the rocket adds negligible drag and (when
propellant is exhausted) negligible weight, it is feasible to retrofit
to an existing sailplane without changing the performance characteristics.
If anyone out there is interested, please contact us -- we're looking for
a "launch customer" to pioneer this application.
Bruce Hoult
pat...@DONTSPAMME.worldnet.att.net wrote:
> j...@uk.sun.com (Jeremy Harris - Network Service Providers
> Division) wrote:
>
> >In article <brucehoult-10...@bruce.bgh>,
> > bruce...@pobox.com (Bruce Hoult) writes:
> >> ... rockets (which don't
> >> beneficially interact with the air at all),
> >
> >Tell that to a missile designer and you'll get laughed at.
>
> No he wouldn't.
Good :-)
> >Just because the aspect ratio isn't quite up to Stemme numbers
> >doesn't mean that no lift is induced by motion through the air.
>
> He wasn't talking about aerodynamic lift/drag due to the
> rocket fins/body, etc. He was talking about interaction
> between the rocket exhaust/means of propulsion and the air.
> Unlike a propellor driven plane, the thrust from the rocket
> doesn't depend (much) on whether the rocket is in the
> atmosphere, or out in space.
In fact the rocket thrust is *worse* in the atmosphere.
-- Bruce
Bruce Hoult
<jgre...@hughes.net> wrote:
> Bruce Hoult <bruce...@pobox.com> wrote in message
> news:brucehoult-10...@bruce.bgh...
> > In article <K9Rx4.5750$1i5....@news2.randori.com>, "Jeff Greason"
> > <jgre...@hughes.net> wrote:
> >
> > > If you're interested, contact us, and we'll run the numbers on the
> > > mission you have in mind.
> >
> > Have you done anything before of approximately suitable size? The XLR-11
> > would be far too powerful -- even a single chamber would be eight to ten
> > times too much.
>
> Over the careers of the people involved, we've covered a range of thrust
> from a few pounds to 250,000 lbf. Right now, we have a small demonstration
> engine on the stand which we're using to prototype the safety improvements
> needed for general aviation use. It burns nitrous oxide and a variety of
> fuels at the 15 lbf level -- and the same basic design can be scaled between
> 15 lbf per chamber and 2000 lbf per chamber.
Actually, 15 lbf might be suitable as a tip thruster on a prop. Put one
of those on each blade of a 2-bladed prop with a tip speed of 300 m/s and
you've got the equivalent of a 40 kW (54 HP) engine right there, which is
about what single-seat self-launchng gliders have. But I don't know how
much fuel they normally use.
Hmm. A Stemme S-10 VT puts 115 HP into the prop, takes off in 180 m, and
climbs at 800 ft/min. So let's make that 30 lbf per thruster, which with
an Isp of 200 will give a flow rate of 140 g/sec, or 8 kg/min, and you're
going to need about 2.5 minutes to takeoff and climb to 500m, or about 20
kg of fuel/oxidiser.
That doesn't seem much better than the pure rocket solution, except that
the Stemme weighs 650 kg empty, so will be more like 900 with a couple of
pilots etc, so we're taking three times the weight of the 300 kg glider I
was basing calculations on before, which makes the efficiency about 3.5
times better using the prop than using the pure rocket.
> For the sailplane application, we would propose nitrous oxide as the
> oxidizer -- you buy a bottle and screw it into the system to "load the
> oxidizer". This uses similar skills to those involved in attaching a
> propane bottle to your barbeque.
.. and you can get it from your local go-faster car accessory supplier.
What's the density like?
-- Bruce
JaKo
> [snip]
> thrust 50 kg 100 kg 160 kg 250 kg 300 kg
> Ground run 204 m 76 m 44 m 26 m 22 m
> Dist at low level 945 m 420 m 210 m 160 m 130 m
> climb angle 8 deg 17 deg 30 deg 55 deg 86 deg
> powered time 104 s 45 s 27 s 17 s 14 s
>
>
> -- Bruce
Great "work-out"!!!
Some of the numbers look quite like a winch launch at about 1 to 1.5 kN except for
the ground run where winch has better performance (much faster accelleration).
Wouldn't be possible to combine the rocket (or perhaps a pulse-jet engine)
propulsion with an old good bungee (elastic cord) start-up, to get off the ground
faster?
JaKo
P.S.
Poor Americans :(
kg is a unit of mass not force! "kgf" may be understood as kp -- an old unit of
force (app. 9.81N) or weight of one kg in "std." Earth's gravity.
lb (pound) is unit of force! "lbf" is an oxymoron :)
In the "imperial system" unit of mass is a SLUG (go figure :)
BUT:
My favorite is the salt over ice (as zero) to asshole of a healty horse (as 100)
temperature == Farnheit ~}8-O