Subject: Re: Small model jet turbine engines

From: [email-masked] (Dr. Stefan P. Mueller)
Date: Tue, 25 Jun 1996 21:13:51 +0200

In article <[email-masked]>, [email-masked] (Dale Puch)
writes:
|>I am looking for plans and/or information on making a small model jet
|>turbine engine.  Say about 6-10 lbs. of thrust range...

This thread got me interested and I found the folowing URL on the web:

   http://www.worldway.com/mall/savoy.html

It looks like SAVOY SCIENTIFIC,  P.O. Box 1398, Dept. I,  SANTA MONICA, CA
90406 is selling plans for a jet engine for 15$

Stefan

-- 
Dr. Stefan P. Mueller, Nuklearmedizin, Universitaetsklinikum, Essen,
 e-mail: [email-masked], phone: <49> 201/ 723-4179, FAX: -5964

---

From: [email-masked] (Barry Workman)
Date: Fri, 28 Jun 1996 07:06:26 GMT

and they have been doing so since my high school days (in Santa
Monica, class of '63)

I have second hand information of one being built...
-- 
    - Barry Workman

---

From: [email-masked] (Bill Webster)
Date: Fri, 28 Jun 1996 07:45:47 -0400

> and they have been doing so since my high school days (in Santa

Yup.  And I bought those plans 25 years ago for $10.  It was advertised
back then just about the same way as now.  The ad said it could be built
for under $100.  Yeah, right!  The cost of the specified nuts and bolts
would cost over $100 at that time.  Not to mention the body tube!  I've
yet to find anybody who could build one and get it working properly.  As
the saying goes, "you get what you pay for".

regards.

-- 
Bill Webster   [email-masked]

---

From: [email-masked] (Craig Wall)
Date: 28 Jun 1996 14:47:45 GMT

In article <[email-masked]>, [email-masked] says...

>the saying goes, "you get what you pay for".

    I also have purchased the Savoy jet engine plans (a couple of times, 
    in fact- the first time was about 1965) and haven't moved on it- though
    I did hear about a kid that built a *1/3* sized version for a science
    fair project!  I think it required some additives to the kerosene to get
    it to run, but supposedly it did.

    I think the engine would be most attractive if it was used as a fanjet 
    core, since the engine apparently splits it's effective output between 
    exhaust thrust and spindle torque.  I believe the original engine was 
    actually flown as a turboprop; a good front fan and duct arrangement 
    might well get you a couple hundred pounds of static thrust.

    Is anybody interested in a consortium to build these?  I mean one group
    doing turbine nozzles and turbines; another doing casings and shells; 
    another doing impellors and spindles; etc....

    I think the engine has merit.  I'd love to build a jet homebuilt aircraft,
    but the only engines I see that are remotely suitable are the Gluhareff
    propane pressure jets (*DON"T* confuse these with ramjets or pulsejets),
    which have excellent performance but require a pressurized propane tank
    (and *NO*, they will not work with any other fuel).  The Savoy engine
    would let you fuel up at any airport that services jets, and it would be
    a true advance if these engines were made available in a decent form.

    Craig Wall

---

From: [email-masked] (Boris Beizer)
Date: Fri, 28 Jun 1996 11:48:08

In article <[email-masked]> Craig Wall wrote:
>Date:	28 Jun 1996 14:47:45 GMT
>From:	[email-masked] (Craig Wall)
>Newsgroups:	rec.crafts.metalworking
>Subject:	Re: Small model jet turbine engines

Have to put my two cents in, having in a former lifetime worked with real 
turbojet engines. 

>    might well get you a couple hundred pounds of static thrust.

I doubt that.  Not without breaking a few laws of thermodynamics.  It's 
very hard, on a small scale, to get a 1:1 or better thrust to weight ratio, no 
matter how you couple the engine's output to the air (e.g., direct, fan, 
turboprop).  Fans, direct, or turboprops are just alternate ways of coupling
the power to the medium.  A "couple of hundred pounds of static thrust" engine
will probably way 300+ pounds--hardly what I would call "small" or model scale.
    Efficiency goes down, sharply down, with smaller scale.  Internal drag,
blade loss, boundary layer effects (and associated losses) are all 
proportionately higher at smaller scales because such losses are related
to the linear dimensions or the square of linear dimensions while the thrust
is proportional to the cube of linear dimensions.  

>    another doing impellors and spindles; etc....

I would assume that both centrifugal compressors and turbines are in mind. I
can't see possibly building and balancing a bladed turbine or compressor. 
And frankly, considering the very high temperatures, thermal distortions,
thermal stress, coolant management (inside the buckets -- the blades are 
called "buckets" BTW), I don't think I'd want to be around when such a home
built was fired up.  Also, note that the buckets are often filled with 
liquid sodium or other nasties--has to be centrifugal/centrifugal to even 
have a possibility of being home built.

>    I think the engine has merit.  I'd love to build a jet homebuilt aircraft,

Model builders who want to build RC jet aircraft use an ordinary reciprocating
high-performance model aircraft engine with an attached fan.  Seems to work
real well.  Such engine/fan combinations are commercially available for a 
couple of hundred bucks.  I don't follow this, though. 

>*DON"T* confuse these with ramjets

Certainly not.  A ramjet engine won't work worth a damn unless you've got
the airspeed up to Mach 2+.  In a ramjet, all the compression is done by
the inlet instead of the bladed compressor.  Compression ratios have to about
5:1 or better to get any kind of positive thrust.  Furthermore, the inlet 
must be variable geometry, as well as the exhaust nozzle.  No blades or such
but really complicated as hell.  And again the inevitable scaling problems.
Note that every ramjet project (and there were hundreds of them all over the
world from 1935 on) eventually petered out without producing a viable engine.
Sorry to throw buckets of water on this one, but the ramjet has yet to make
it in the full-scale world.  And there's that little problem of getting up
to mach 2.

> or pulsejets), which have excellent performance but require a pressurized
> propane tank

Various brands of model pulsejets have been available for model aircraft
builders since about 1947.  They ran on various fuels, often kerosene,
gasolene, propane, what not.  Except for the air intake valve, which is built
out of something nasty like berrylium-copper (it is a flat, multi-lobed, leaf
spring) the rest is well within the scope of an avid home machinist who has
access to a stout concrete bunker for testing.

Boris
Boris Beizer

-----------------------------------------------------------------------------------------------------
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Huntingdon Valley, PA 19006 USA
TEL:     215-572-5580     FAX:  215-886-0144     Email:  [email-masked]

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-----------------------------------------------------------------------------------------------------

---

From: [email-masked] (Craig Wall)
Date: 28 Jun 1996 17:59:59 GMT

In article <[email-masked]>, [email-masked] says...
>Have to put my two cents in, having in a former lifetime worked with real 

   Sorry, Boris- I was predicating my remarks on using this engine for 
   a homebuilt aircraft, not a model airplane.  

   Apparently you are not familiar with the Savoy "Screamin' Demon" engine;
   this is not a model-sized engine, unless it is a very LARGE model. The
   prototype produced the equivalent of a 30hp motor when coupled to a 
   gearbox and propellor. 

>will probably way 300+ pounds--hardly what I would call "small" or model scale.

     See the above- this is NOT on a model scale.  I would expect the all-up
     weight with a suitable duct/nacelle combination to go about 60 lbs or
     so, and produce on the order of 100-200 lbs of thrust. Two should power
     a single seat airplane adequately, if not spectacularly.  I doubt very
     seriously this would break any physical laws, since engines with similar
     performance are currently being flown in ships like the Caproni and the 
     BD-5J.    

>is proportional to the cube of linear dimensions.  

     Yes, you are quite correct. The fuel consumption will be through the roof;
     but if I could have one I'd still use it- freely admiting that it was 
     *in no way* a "practical" engine.

>can't see possibly building and balancing a bladed turbine or compressor. 

      Quite right again; these are simple centrifugal flow engines with impulse
      turbines, which of course can be balanced by a *careful* amateur. The 
      plans describe knife edges and a 60hz vibrator setup; a bladed wheel with
      "christmas tree" assembly is far beyond an amateur.

>have a possibility of being home built.

     Well, these turbines (you haven't seen them, remember) are hacked out of
     a solid chunk of stainless and have a blade thickness of 1/8th" and a
     diameter of 4 or 5".  IOW's, they're pretty "meaty".  They are crude, I 
     admit- but I do believe they would work, as they have a 90 degree bucket
     and the nozzle feeding them is at a 45 degree angle.

>couple of hundred bucks.  I don't follow this, though. 

     Yeah; I think they sorta suck. Jets that sound like weedeaters just sort 
     of *annoy* me, but to each his own. Again, though, I'm talking about a 
     single seat full-sized airplane, NOT models.

>it in the full-scale world.  And there's that little problem of getting up

     You missed me with that bucket of water.  I'm way ahead of you here.

>access to a stout concrete bunker for testing.

    You missed again, Boris- and while your editing makes it look like I was
    saying pulsejets have excellent performance, it was *pressure* jets I was
    refering to.

    Pressure jets, as designed by Eugene M. Gluhareff, run *only* on propane,
    have no moving parts, and have both the best thrust to weight ratio and 
    the best specific fuel consumption of *any* jet engine short of a full-
    sized turbofanjet.

    Craig Wall

.

---

From: [email-masked] (Boris Beizer)
Date: Fri, 28 Jun 1996 15:58:06

>   a homebuilt aircraft, not a model airplane.  

I guess we all have different concepts of "small"

>   prototype produced the equivalent of a 30hp motor when coupled to a 

I was not familiar with it.  Hardly a model-size.   

>     performance are currently being flown in ships like the Caproni and the 

Again, scale issues.  At 60 lbs, 100 lbs thrust should be reasonable, and
200 not out of sight at all--at least theoretically.  

>      "christmas tree" assembly is far beyond an amateur.

I think that even a centrifugal flow engine at 60 pounds would be one
hell-of an amateur challenge. 

>     and the nozzle feeding them is at a 45 degree angle.

Probably not cruder than the prototype centrifugal jet engines built in the
30's and 40's, and probably better material. 

>     single seat full-sized airplane, NOT models.

Different worlds. I cam in late on the thread and falsely assumed that you guys
were talking about model-sized turbos, not light aircraft jets.   

>    the best specific fuel consumption of *any* jet engine short of a full-

What's a "pressure jet."  Educate us.  Never heard of that kind of engine. 
It's not a pulse jet, as you said.  And obviously not a ramjet.  If it has
no moving parts, what does the compression?  Or does this run at atmospheric
pressures?  I assume that when you say "runs only on propane" you mean as a 
fuel and presumably the oxygen comes from air.  So where's the compressor?
Without a compressor of some kind (moving parts or no) it will have to violate
some laws of physics to get decent thrust--or as Scotty say's "I can nae break
the Laws of Physics, Cap'n."

Boris

Boris Beizer

---

From: John G Wright <[email-masked]>
Date: Fri, 28 Jun 1996 21:46:00 +0100

In article <[email-masked]>, Craig Wall <[email-masked]>
writes
>    a true advance if these engines were made available in a decent form.
You are asking for help with info on making model jet turbines. They
can be made from published designs and will work. The hobby is in its
infancy and the designs are evolving. I hope others will find this info
helpful.

There are 2 books available both written by Germans and recently
translated into English the first is by Kurt Schrekling and called Gas
Tubine Engines for Model Aircraft. The second is Jet Engines by Thomas
Kamps.Both books are available from Traplet Publications and they have a
good web site at http://www.traplet.co.uk/traplet the books can be
ordered on the internet and there are pictures of both front covers.  

I have made Kurt's engine and have like all involved found it an
absorbing hobby. The actual making of the parts is reasonably
straigtforward but it is not easy to make changes because there are so
many variables. The engines all tend to run hot (red hot!) and the only
succesful one is the one that runs at about 500 centigrade. I have had
results similar to those Kurt claims for the design 4.5Lbs thrust at 600
centigrade and 72,000 rpm. I have seen an engine with a revised
combustion chamber run at 6.5Lbs thrust at higher revs and still be at
less than 500 centigrade, so I know that it is possible to get good
results.

When Thomas ran his engine he was getting about 8Lbs thrust at low
temperatures but the engine is heavier than Kurt's. I have not heard of
any that have made Thomas's design yet.

Several are flying with these engines. The power to weight ratio is 1:2
so they will power an 11-12 lb model. I have only seen the videos which
look really spectacular. The sound is really like a jet with a whistle
and a roar. The noise levels are apparently lower than piston engines ,
but I still wear ear defenders when running mine on the bench!

The materials are aluminium and 310 or 316 stainless for the parts that
get hot.The compressor on Kurts engine is made of plywood! and the one
on Thomas's is a car turbocharger compressor. The welding is TIG welding
which I had the local shop do for me.
John
-- 
John G Wright

---

From: Dave Ruigh <[email-masked]>
Date: Fri, 28 Jun 1996 19:34:51 GMT

> is proportional to the cube of linear dimensions.

Your points about effeciency and relative unimportance of the coupling
method are well taken. Small turbines for model aircraft, both
homebuilt and commercial, have existed though for several years. The Schreckling
and Kamps designs have been succesfully built and flown by amateur 
machinists. Schneider-Sanchez/GWM, JPX, AMT, SWB, Turbomin, and several 
other new manufacturers are selling model turbines in the 6-30lbf thrust range.
Kurt Schreckling has adapted one of his designs to shaft power, and has 
used it in a model helicopter. As you predict, fuel consumption is an order of
magnitude higher than full-sized turbines.

> have a possibility of being home built.

Most of the commercial units use axial (bladed) turbines coupled with
turbocharger style radial outflow (centifugal) compressors. These designs
are less optimised for thrust in the interest of keeping turbine
inlet temps in the 500-700C range. No internal blade cooling is
used in any of the commercial units I've heard about. Amateur 
built turbine wheels have been made from 300 series stainless 
steel, most commercial units use 713c or other high temperature
nickel alloys. Turbomin uses a radial compressor and turbine,
and most all employ a bladed diffuser. The Shreckling FD3 uses a 
radial compressor partly made of wood! (reinforced with carbon
fiber). With speeds in the 65,00-110,000 RPM range, and standard
radial ball-bearings, balance is critical, but presents no special 
problems.

> couple of hundred bucks.  I don't follow this, though.

Ducted fan systems are, of course the practical way to enjoy the model jet
"experience", though some are willing to invest the thousands of dollars
on "real" turbojets which have recently become available, and the home
builder with paitence can acheive nearly the same performance for very 
much less. Although full-sized homebuilt turbojets have been discussed
in the rec.aviation newsgroups, I haven't actually heard of one being
built, but the same scale effect applies, and larger engines should 
actually be easier to build than model-sized ones. I would expect
far more problems getting the FAA to sign off on any hombrew turbine
(perhaps with good reason).

Dave
<<<other interesting stuff about ram and pulsejets snipped>>>

---

From: Scott C Tudor <[email-masked]>
Date: Fri, 28 Jun 1996 12:48:26 -0700

Traplet publishing sells a couple of good books on building jet engines.

You can email them at:

     [email-masked]

The STB - Gas Turbine Engines for model aircraft book is $24
The MJE - Model Jet Engines book is $24

Goodluck!

---

From: Mark Marks <[email-masked]>
Date: 29 Jun 1996 16:35:13 GMT

>90406 is selling plans for a jet engine for 15$
-----
Save your money and do *not* order the plans from Savoy 
Scientific.  That ad has been running in Popular Science Magazine 
since the 1950s.  About six months ago I posted inquiries on 
several online services about Savoy and found that nobody had been 
able to construct an engine from their plans.

I've seen postings on this forum from someone who has completed 
the Schreckling turbine -- it's your best bet.  

Mark Marks, Florida
1950s.  About six months ago I posted inquiries on several online 
services about Savoy and found that nobody had been able to 
construct an engine from the plans.

I've seen postings on this forum from someone who has completed 
the Schreckling turbine -- it's your best bet.  

Mark Marks, Florida

---

From: [email-masked] (Bill and Cindy Funk)
Date: 30 Jun 1996 03:54:49 GMT

>    another doing impellors and spindles; etc....
I'm interested in a consortium to build a turbine engine. 
I am planning on using it in a hybrid electric vehicle.
I am currently leaning toward a Tesla turbine due to 
it's simplicity.

I have access to solid modeling and rapid prototype casting, but 
the cost for a conventional (Savoy) turbine would be at least $200
in 20 pc lots.  I've also got a couple of old turbochargers and 
someone told me that you can use them to make a gas turbine engine.

---

From: [email-masked] (Alan Shinn)
Date: Sun, 30 Jun 1996 00:36:58 -0800

> someone told me that you can use them to make a gas turbine engine.

Those are both interesting subjects! I thought that a tesla turbine was
steam driven. Do you have other ideas? What would you use for a combustion
chamber/ plenum for the turbocharger engine?

---

From: [email-masked] (PARSEK)
Date: 1 Jul 1996 15:36:42 GMT

In article <[email-masked]>, Craig Wall <[email-masked]> wrote:

>     a single seat airplane adequately, if not spectacularly.

At least some cruise missiles use small turbojets engineered from truck
engine superchargers.  Check rec.aviation.military & rec.flying.homebuilt.
Even if you managed to acquire such an engine, the FAA probably wouldn't
let you fly it.

---

From: [email-masked] (philip evans)
Date: Mon, 1 Jul 1996 16:44:27 GMT

>Even if you managed to acquire such an engine, the FAA probably wouldn't

What if you got a cruise missle that presumably already has FAA cert, strap on 
a saddle and your goggles, and stow a twofour where the nuke is supposed to go?

Um, just kidding.

---

From: Allen Majorovic <[email-masked]>
Date: Mon, 01 Jul 1996 17:25:00 -0700

Craig Wall wrote:
>   <snip>

What are the specific problems that make them so scarce? They sound pretty 
good.

Allen

---

From: [email-masked] (Edward Haas)
Date: 2 Jul 1996 08:07:34 -0700

> <[email-masked]>
Distribution: 

: What are the specific problems that make them so scarce? They sound pretty 
: good.
	--A buddy of mine has one. For starters, it has an unusual shape 
(no idea why) which is *not* aerodynamic: there is a large pipe that 
sticks far out sideways. Also, on a quiet day you can probably hear the 
thing in neighboring countries: that thing is LOUD!
-- 
	"Steamboat Ed" Haas	:	Yikes, I'm 50!!! 	
	COMING SOON		:	The second THIRD of Life...
	http://www.west.net/~steamer  	
		---Decks a-wash in a sea of words---

---

From: Allen Majorovic <[email-masked]>
Date: Tue, 02 Jul 1996 17:42:27 -0700

> thing in neighboring countries: that thing is LOUD!

About ten (fifteen? twenty?!!) years ago I spent a couple of hours on the 
phone with a fellow who was trying to adapt the Glufareff to an aircraft of 
his own design. The noise was one of the things he commented on. He told me 
that when he did taxi testing of the aircraft the local police department 
would get complaints. The reason this is remarkable was that the field he 
used was also used by corporate and commercial jet traffic. *They* didn't get 
as many complaints taking off as this little plane did during taxi tests. He 
told me that the jet is also very sensitive to intake restrictions. These 
lead to unpredicatable changes in the action of the engine causing it to go 
>from  thrust "mode" to burner "mode". He also told me that the big engine was 
merely a scale-up of the twenty-pound-thrust engine and that resulted in the 
engine self-destructing after about twenty minutes due to the greater strains 
generated by the large engine. This had caused him to do a considerable 
amount of redesign of the engine. 

A light, cheap, efficient, throtleable jet engine sounds great but I don't 
think that that is what the Gluharef is.

Allen

---

From: Richard Hager <[email-masked]>
Date: Wed, 03 Jul 1996 02:10:51 -0400

> along with some other comments towards a respondent to his original posting.
-- 

Hello fellow turbine crazies,

As a long-time aerospace nut, I just can't resist sticking my eleven cents in here. 
(I'm long winded, but mercifully infrequent, right guys?).

I'm lucky enough to have a scientist working for me who's a thermodynamics expert 
that worked for Rockwell for 15 years designing Space Shuttle main engines, among 
other projects.  In addition, he's written two textbooks on turbomachinery.

So I've asked him about all this on a number of occasions.  Frankly, it sounds like 
Craig is being a little optimistic and maybe shouldn't have jumped quite so hard on 
the kind respondent to his earlier post, who was actually correct in his comments.

It would be almost impossible to make the engine Craig describes within his weight 
target.  Theoretically sure, but not practically with any kind of materials 
workable in a home shop (or affordable by us!!).   

The power/weight ratio of a turbine (or any heat engine for that matter) is 
directly related to the combustion efficiency, which is highly dependent on the 
combustion temperature.  Temps in the working range of stainless steel (500-600 F) 
are way, way below efficient operation.  Stoichiometric burning (most efficient 
mixture) for jet fuel is around 3,000 - 4,000 degrees, I forget the exact number.

Military engines run upwards of 1,000 - 1,500 degrees, but are made of all kinds of 
exotics like Hastelloy, Inconel, exotic Titanium alloys, carbon-carbon, silicon 
nitride ball bearings, etc, etc.  Some of these materials cost over $1,000 -per 
pound- !!  Seriously!  These guys jump up and down when they squeeze another 50 
degrees out of their designs.

And that's just the materials problem.  Even -with- those materials, such engines 
-have- to use special film cooling techniques on internal rotating parts to keep 
the parts from literally evaporating ! (well, oxidizing and ablating away to be 
exact).

Notice I said 'rotating' parts.  The fluid distribution and sealing problems are 
truly incredible, and incredibly expensive to solve.  Even after all the above, 
you're looking at an MTBF (mean time between failures) of a few hours.  Between the 
engines and the electronics, most fighter aircraft must be serviced every 5 flight 
hours or so.  Not something I'd want -my- wife flying in.

As far as the comment someone made about the FAA not allowing a home-built jet, I 
don't have the FAR's in front of me, but I'm pretty sure the regs are quite loose 
on craft registered as 'experimental', although they may well keep you out of the 
TCA of major metro airports.  You probably also still have to meet noise and 
pollution specs.  It may not be tough to meet those specs, but it's going to be 
damn expensive to get all the measurements done by the required certified agencies.

Like Craig, I've dreamed about my own jet homebuilt for years, and in fact designed 
a 3,000 lb variable geometry wing supersonic two seat twin about ten years ago.  
However, building it would be a life-consuming project, literally, and I've got 
fish to catch, music to listen to, and newsgroups to participate in.  So I let it 
go.

I learned a hell of a lot from the exercise though, and boy did I have a lot to 
learn!  Many, many little hidden gotcha's, from the stress fracture temperature of 
materials, to the tribology of asymmetrically loaded bearings.  Great fun!

There -is- some incredible progress being made in 'tough' ceramics and even 
'engineered materials' (-designed- molecules, if you can believe it).  In another 
ten to twenty years, these materials may have become available enough to the small 
shop that such a high-temp but economical engine will be doable for us.  Not now 
though.

Crack a couple of books Craig and keep at it!  Even if you can't meet your current 
power/weight ratio target, if you learn enough about the inner workings and real 
engineering requirements of turbines, you are sure to be able to produce an engine 
with a completely usable ratio for a homebuilt.  Any pictures you post of your 
ongoing work would be greatly appreciated.

Good luck!

        Richard Hager

+ Ah-ha! Design Group, Inc.           -
+ Precision CNC Technology, since 1991 -
+ 612-641-1797, Fax: 612-641-8681       -
+ "I just like to build things" So...    -
+ for CNC info, don't email me, call      -
+ or email Ah-ha! directly.  Thanks!       -
+ www.gdic.com/ahha  email: [email-masked]   -

---

From: [email-masked] (Bill Webster)
Date: Wed, 03 Jul 1996 08:33:07 -0400

And, to add to this thread...

I realize the original message was not about model airplane jet engines,
but, the Taiwan company ThunderTiger, has in the 1996/97 catalog, a
turbine jet engine (along with several great pictures of it).  This is not
a ducted fan using a separate IC engine.  But, a real jet engine (if
you'll allow me to loosely use that term for lack of knowing the correct
term).  No price was listed, but it is to be available later this year.

regards.

---

From: [email-masked] (Jonathan M. Elson)
Date: 5 Jul 1996 19:28:07 GMT

philip evans ([email-masked]) wrote:
: In article <[email-masked]> [email-masked] (PARSEK) writes:

: >In article <[email-masked]>, Craig Wall <[email-masked]> wrote:

: >>     See the above- this is NOT on a model scale.  I would expect the all-up
: >>     weight with a suitable duct/nacelle combination to go about 60 lbs or
: >>     so, and produce on the order of 100-200 lbs of thrust. Two should power
: >>     a single seat airplane adequately, if not spectacularly.

: >At least some cruise missiles use small turbojets engineered from truck
: >engine superchargers.  Check rec.aviation.military & rec.flying.homebuilt.
: >Even if you managed to acquire such an engine, the FAA probably wouldn't
: >let you fly it.  

I've seen these engines.  They look in NO WAY like they have anything in
common with a turbocharger.  They are multistage axial-flow compressors,
combustion chambers and a turbine, which drives a fan out in front.
VERY similar to a high-bypass commercial jet engine in miniature.  The
damn things even have hydraulic constant-speed-drives for the 400 Hz
alternator that powers the electronics!  Since civilians are flying
jet-powered aircraft (some home-built) they CAN'T keep you from flying it
if it meets airworthiness rules and if you get the needed certification
and insurance.

: What if you got a cruise missle that presumably already has FAA cert, strap on 
: a saddle and your goggles, and stow a twofour where the nuke is supposed to go?

Cruise missles DON'T carry an FAA certification, since they are military
aircraft.  I wouldn't want to fly with goggles on anything that goes
250 MPH!

---

From: [email-masked](Morris Jones)
Date: 6 Jul 1996 15:03:53 GMT

<snip>

Small model turbine engines do not violate any laws of physics.  They
are flying all the time nowdays.  At least three versions are in
production and available for purchase.  They can be seen in any model
airplane magazine reviewing model jets.

Due to the small size, low renolds number operating range, and scale
effects, only single stage radial compressors work well.  You could not
power a large craft with these as the thrust is below 30lbs for most of
them.

Materials and the fact they are placed in a model with balsa wood and
fibre glass limit the operating temperatures at the exhaust to 650
degrees or so.

The people who have built them seem to say that getting the balance
right is no big problem, and that it takes a "LOT" of tinkering to get
one to run well.  Most often, the blades do not fail, but rub the case,
and stop the turbine when too hot.

I have both the books mentioned.  They explain not only the
construction, but in a find german tradition, are a complete treatment
of the physics and math involved in the design.  If you enjoyed
thermodynamics in college, you will really enjoy reading these
chapters.

It can be done, 

Morris