Small jets for sustainer engines on gliders
Steve
thrust) jet engines for use on gliders and how it would probably take
more than 100Lb of thrust to self launch with jet engines. There are
several companies which make 45 and 150 Lb thrust turbine engines. The
fuel consumption seems too high for these sized engines to work well on
a glider, however. Another alternative use for jet engines on a glider
could be as sustainer engines only. It seems to me that a greater than
40L/D glider could easily gain altitude with two small 28Lb thrust
engines and the installation would be much simpler and cheaper than an
engine/propeller system. The engines are small enough that they could
be permanently mounted outside the fuselage or pop in and out without
a great amount of drag. Also, existing non-powered gliders and
homebuilts could be more easily modified to accept the little jet
engines. The 28Lb thrust engines would burn much more fuel per minute
than a two-stroke, self launching engine, probably three times the
consumption but jet fuel is much safer than high-octane fuel and
gliders have the extra carrying capacity so that they could probably
safely carry three or more times the fuel, if needed. I would think
that two small jet engines, if they could be started in the air, could
work in conjunction with a winch launch system or an auto tow. You
wouldn't need the extra thrust to overcome the rolling friction needed
for takeoff but there might be enough thrust available to climb during
marginal soaring conditions. Flying gliders, especially in the midwest
and northern areas could become much more fun. The biggest issue in my
mind, is how reliable are the small turbine engines and how safe are
they. And, how would you get the proper airworthy paperwork through the
FAA.
Sent via Deja.com http://www.deja.com/
Before you buy.
Lower Faster
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Steve
anything over that would let you climb somewhat. The question then
becomes what climb rate can you get with two 28Lb thrust jet engines.
(I would think that one 40Lb engine would scorch the tail, so I would
rather have two smaller ones.) Last September, someone did the math for
an 1100 Lb glider and figured it needed a 150Lb thrust engine for
takeoff and climbing at 450fpm. That seems reasonable for self
launching, but there are other big issues with converting a
conventional glider to a self launch. Ability to taxi and directional
control at the start of the take-off roll come to mind. Using jets as
sustainers seems much easier and cheaper to do. Since I am math
dininclined, I would be interested in hearing what kind of climb rate
could be achieved, and at what speeds, with two small jets attached to
a 900Lb glider with a 40/1 glide ratio. Since jet engines are more
efficient at higher air speeds would it climb more efficiently at 100Kt
than at 60Kt? Could I bolt two jets on an old 2-33 and soar all day? I
would think that 10 to 15 gallons of jet fuel would be easy to carry in
the back seat. Yes, I know they don't have a 40/1 glide ratio but it
would be another way to extend the life of those old birds. Please
advise.
> > At 10:40 07 December 2000, Steve wrote:
> >>could be as sustainer engines only. It seems to me that a greater
than
> >>40L/D glider could easily gain altitude with two small 28Lb thrust
> Well,
>
> Roughly you can get the thrust needed to remain aloft by calculating
l/d
> versus weight... i think [weight / (l/d)] If i recall correctly...
>
> So, for example, a Schreder HP-14... approx 700 LB wet, 38:1 l/d ratio
> 700/(38/1)=18.42 LB thrust to sustain. So to climb, maybe even a 40
lb
> thrust engine would do it... work the math, a lighter glider is your
> friend. If one goes to http://www.amtjets.com, their 40 lb thrust
engine
> consumes 19 oz/min, 128 oz in a gallon so 6.75 minutes/gallon...
>
> Jet a weighs approx 7 lb/gal, and the engine itself weighs 5.3 LBS...
so
> 10 gal of fuel= 70 lbs, engine 20lbs (with all acessories/mountings
etc.)
>
> So less than 100 LB for 60 minutes, and if you want only 30 minutes,
then
> cut it almost in half etc.
>
> >>mind, is how reliable are the small turbine engines and how safe are
> >>they. And, how would you get the proper airworthy paperwork through
the
> >>FAA.
>
> As for safety, that is hard to say, i'm not sure i'd use one of the
model
> types that uses the fuel to lubricate the bearings... As for the FAA,
cant
> you put whatever engine you want on experimental craft? If you have a
> certificated airplane you would have a long road to hoe on that one...
>
> take care,
>
> Steve
> --
>
************************************************************************
***
> You move like a pregnant yak
> http://zarf.org/~jester
>
************************************************************************
***
Christopher Nicholas
about that for endurance/range!
Chris N.
Michael McNulty
you use 60 kts as a reasonable guess, then the 40 lbs thrust jet engine
is equivalent to about 7.3 useful hp. Even allowing for propeller
losses this would only be equal to something like an 8 HP sustainer
engine. Current sustainer sailplanes are using engines of about 21 HP,
and self-launchers are close to 50 HP. So, the 40 lbs thrust jet
engine would yield much lower performance than current motorgliders. (I
suspect it might be just enough power to be quite dangerous.)
Lower Faster
nothing new: look at
http://home.wxs.nl/~doormaal/calif.html
and
http://members.aol.com/_ht_a/piskorzgi/Index.htm
At 19:30 07 December 2000, Steve wrote:
>OK, so if you only need 18.42Lb of thrust to sustain flight then
>anything over that would let you climb somewhat. The question then
>becomes what climb rate can you get with two 28Lb thrust jet engines.
>(I would think that one 40Lb engine would scorch the tail, so I would
>rather have two smaller ones.) Last September, someone did the math for
>an 1100 Lb glider and figured it needed a 150Lb thrust engine for
>takeoff and climbing at 450fpm. That seems reasonable for self
>launching, but there are other big issues with converting a
>conventional glider to a self launch. Ability to taxi and directional
>control at the start of the take-off roll come to mind. Using jets as
>sustainers seems much easier and cheaper to do. Since I am math
>dininclined, I would be interested in hearing what kind of climb rate
>could be achieved, and at what speeds, with two small jets attached to
>a 900Lb glider with a 40/1 glide ratio. Since jet engines are more
>efficient at higher air speeds would it climb more efficiently at 100Kt
>than at 60Kt? Could I bolt two jets on an old 2-33 and soar all day? I
>would think that 10 to 15 gallons of jet fuel would be easy to carry in
>the back seat. Yes, I know they don't have a 40/1 glide ratio but it
>would be another way to extend the life of those old birds. Please
>advise.
>
>> > At 10:40 07 December 2000, Steve wrote:
>> >>could be as sustainer engines only. It seems to me that a greater
>than
>> >>40L/D glider could easily gain altitude with two small 28Lb thrust
>> Well,
>>
>> Roughly you can get the thrust needed to remain aloft by calculating
>l/d
>> versus weight... i think [weight / (l/d)] If i recall correctly...
>>
>> So, for example, a Schreder HP-14... approx 700 LB wet, 38:1 l/d ratio
>> 700/(38/1)=18.42 LB thrust to sustain. So to climb, maybe even a 40
>lb
>> thrust engine would do it... work the math, a lighter glider is your
>> friend. If one goes to http://www.amtjets.com, their 40 lb thrust
==============================================================
Lower Faster
>#
sorry that should read
http://members.aol.com/_ht_a/piskorzgj/Index.htm
Robert Ehrlich
>
> I would be interested in hearing what kind of climb rate
> could be achieved, and at what speeds, with two small jets attached to
> a 900Lb glider with a 40/1 glide ratio.
A 900Lb glider with a 40/1 glide ratio has 900/40 = 22.5 lb of drag and
would then need 22.5 lb of thrust in order to sustain flight. With 2 jet
engines of 28 Lb thrust, i.e 54 lb, 54-22.5 = 31.5 lb remain available for
climbing. i.e. you could climb on such a slope that the component of the
weight opposite to the thrust is 31.5 lb. For a small slope you can assume
that this component is the weight multiplied by the slope, i.e. ths slope
would be 31.5/900 = 0.035. Assuming a best L/D speed of 60 kt, your climb speed
would be 60*0.035 = 2.1 kt
> Since jet engines are more
> efficient at higher air speeds would it climb more efficiently at 100Kt
> than at 60Kt?
No, as far as best climbing slope is concerned. As jet engines are almost
constant thrust engines their power (i.e. thrust * speed) increase with speed,
but this doesn't help here, because drag also increase with speed. The best
climbing slope will be obtained at minimum drag, i.e. best L/D speed. For
the best climbing speed, you have to increase the speed, by decreasing the
slope from best climbing slope. How many will depend on other characteristics
of the glider (its complete glide polar), but what is sure is that if you
push the stick from best climbing slope, the speed will increase and the
slope decrease, but for a sufficiently small change, the effect of the increased
speed on the climbing speed will over-compensate the effect of the decreased
slope, because near its maximum value, the change in slope is of second order
compared to the change in speed (note that here only we need real mathematics :-).
> Could I bolt two jets on an old 2-33 and soar all day? I
> would think that 10 to 15 gallons of jet fuel would be easy to carry in
> the back seat. Yes, I know they don't have a 40/1 glide ratio but it
> would be another way to extend the life of those old birds. Please
> advise.
According to http://www.geocities.com/CapeCanaveral/Hangar/1850/schweiz.htm#2-33
for a 2-33, gross weight is 1,040 lb, best L/D is 23 at 39 kt. So the same
computation as above gives: drag = sustained flight thrust = 1,040/23 = 45.2 lb.
Available thrust for climbing = 54 - 45.2 = 8.8 lb. Best climbing slope = 8.8/1,040
= .0085. Climb speed at this slope = 39*.0085 = 0.33 kt. Yes, heavy and draggy
gliders need thrust for climbing !
Maybe you prefer the climbing slopes as horizontal/vertical distance rather
than the inverse I used, this yields 28.6 for the 40/1 glider and 117.6 for
the 2-33.
Last but not least : how does such a miniature jet engine start ? As far as
I know, when used in model aircrafts a high pressure blower is used to
blow in the air intake for that, but for a sustainer, you need to start it
in flight. Would the relative airflow be sufficient for that ?
Lower Faster
>> I would be interested in hearing what kind of climb rate
>> could be achieved, and at what speeds, with two small jets attached to
>> a 900Lb glider with a 40/1 glide ratio.
Climbing speed is 89kts
Jet engines are more efficient at high speed, but develop less thrust.
>> Could I bolt two jets on an old 2-33 and soar all day? I
>> would think that 10 to 15 gallons of jet fuel would be easy to carry in
>> the back seat. Yes, I know they don't have a 40/1 glide ratio but it
>> would be another way to extend the life of those old birds. Please
>> advise.
>
Sounds like a bad plan to me, as 2-33s are made of wood.
Bad coz it might kill someone, but good if it destroyed a 2-33! (he he he)
Al
cans and steel girders.
Al
Lower Faster
>Wrong they come from the schweizer iron works and are made of recycled coke
>cans and steel girders.
>
covered in ceconite fabric no-doubt.......
>Al
>
>
>> Sounds like a bad plan to me, as 2-33s are made of wood.
>> Bad coz it might kill someone, but good if it destroyed a 2-33! (he he he)
>
>
>
>
==============================================================
re...@in-newsgroup.com
Bruce Hoult
> Roughly you can get the thrust needed to remain aloft by calculating l/d
> versus weight... i think [weight / (l/d)] If i recall correctly...
Right.
> So, for example, a Schreder HP-14... approx 700 LB wet, 38:1 l/d ratio
> 700/(38/1)=18.42 LB thrust to sustain. So to climb, maybe even a 40 lb
> thrust engine would do it...
That would let you climb (in still air) at about your normal glide angle
and sink rate -- just up instead of down. So ... what? ... about 150
fpm.
Doesn't sound like a lot. What climb rate do current "turbo" models
manage?
-- Bruce
Steve
Robert Ehrlich <Robert....@inria.fr> wrote:
> Steve wrote:
> >
> > I would be interested in hearing what kind of climb rate
> > could be achieved, and at what speeds, with two small jets attached
to
> > a 900Lb glider with a 40/1 glide ratio.
>
> > would think that 10 to 15 gallons of jet fuel would be easy to
carry in
> > the back seat. Yes, I know they don't have a 40/1 glide ratio but
it
> > would be another way to extend the life of those old birds. Please
> > advise.
>
http://www.geocities.com/CapeCanaveral/Hangar/1850/schweiz.htm#2-33
> for a 2-33, gross weight is 1,040 lb, best L/D is 23 at 39 kt. So the
same
> computation as above gives: drag = sustained flight thrust = 1,040/23
= 45.2 lb.
> Available thrust for climbing = 54 - 45.2 = 8.8 lb. Best climbing
slope = 8.8/1,040
> = .0085. Climb speed at this slope = 39*.0085 = 0.33 kt. Yes, heavy
and draggy
> gliders need thrust for climbing !
>
> Maybe you prefer the climbing slopes as horizontal/vertical distance
rather
> than the inverse I used, this yields 28.6 for the 40/1 glider and
117.6 for
> the 2-33.
>
> Last but not least : how does such a miniature jet engine start ? As
far as
> I know, when used in model aircrafts a high pressure blower is used to
> blow in the air intake for that, but for a sustainer, you need to
start it
> in flight. Would the relative airflow be sufficient for that ?
>
starter, telemetry software so the engine temps, speed etc can be
monitored and, they claim, a 1/2" containment ring around the
compressor in case it blows up.
sfda...@my-deja.com
Microturbo TR-18 puts out more than 300 Lbs. of thrust, which seems
like an awful lot of power for a sailplane, even a two seater. There
are several American companies which make small turbojet engines for
the model market. RAM and AMT engines lubricate the bearings from the
fuel so I would question the life expectancy of their products.
Bearing failure at 1ooK rpm wouldn't be fun. Both also make larger 40
to 150 Lbs. thrust engines, RAM has a Lotus line of larger turbojets
and they also make a turboprop engine. I have no info on how they
are 'lubed. There is also a company in Wisconsin which makes a 40 Lbs.
thrust turbojet engine for use by University engineering departments.
That engine has a separate lubrication supply for the bearings so I
think it would be much more reliable. They don't sell it to the model
market, though. The Wisconsin company is called Turbine Technology
Ltd. and they are also developing a 200 Lbs. thrust engine and a small
turbofan engine. Their web site shows a small jet airplane with two 40
Lbs. ducted fans mounted on the tail.
www.turbinetechnologies.com
In article <90p279$1rgee$1...@ID-49798.news.dfncis.de>,
Marv
Steve <studeba...@my-deja.com> wrote in message
news:90nohg$2e2$1...@nnrp1.deja.com...
> Back in September there were several discussions about small (28Lb
> thrust) jet engines for use on gliders and how it would probably take
> more than 100Lb of thrust to self launch with jet engines. There are
> several companies which make 45 and 150 Lb thrust turbine engines. The
> fuel consumption seems too high for these sized engines to work well on
> a glider, however. Another alternative use for jet engines on a glider
> could be as sustainer engines only. It seems to me that a greater than
> 40L/D glider could easily gain altitude with two small 28Lb thrust
> engines and the installation would be much simpler and cheaper than an
> engine/propeller system. The engines are small enough that they could
> be permanently mounted outside the fuselage or pop in and out without
> a great amount of drag. Also, existing non-powered gliders and
> homebuilts could be more easily modified to accept the little jet
> engines. The 28Lb thrust engines would burn much more fuel per minute
> than a two-stroke, self launching engine, probably three times the
> consumption but jet fuel is much safer than high-octane fuel and
> gliders have the extra carrying capacity so that they could probably
> safely carry three or more times the fuel, if needed. I would think
> that two small jet engines, if they could be started in the air, could
> work in conjunction with a winch launch system or an auto tow. You
> wouldn't need the extra thrust to overcome the rolling friction needed
> for takeoff but there might be enough thrust available to climb during
> marginal soaring conditions. Flying gliders, especially in the midwest
> and northern areas could become much more fun. The biggest issue in my
> mind, is how reliable are the small turbine engines and how safe are
> they. And, how would you get the proper airworthy paperwork through the
> FAA.
>
>
Lower Faster
>U2?
is actually a very poor glider
Grob Egrett on the other hand (I know its a turbo prop)
==============================================================
Lester Hawksby
> is actually a very poor glider
I suppose it must weigh quite a lot...
- Lester Hawksby
Steve Bralla
> they claim, a 1/2" containment ring around the
>compressor in case it blows up.
That makes me feel a lot better!
Steve