Contributed by: Paul Marsh | Published: September 2003 | Views: 164039 |  Email this Article
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Review by: Paul D. Marsh
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Photo: Library of Congress
The
beginning of the first flight of a manned, powered aircraft--the
1903 Flyer with Orville Wright at the controls, December
17, 1903. |
2003
is a year of aviation anniversaries. December of this
year marks the 100th anniversary of the first-ever
flight of a manned, powered, heavier-than-air aircraft.
On the 17th of that month in 1903, Orville
Wright piloted the 1903 Flyer on its 120 foot, 12 second
flight. That momentous event is being celebrated here
in the United States throughout the year in a number of
ways, including many recreations of the flight itself
with hand-built replicas of the 1903 Flyer. Also, for
the first time since 1948, when the Smithsonian Institution
in Washington, D.C. acquired it, the original 1903 Flyer
will be displayed at eye level for close inspection by
museum visitors. Prior to this, it had always hung high
near a ceiling. In addition to this signal event, 2003
also marks the 50th anniversary of the formation
of the United States Air Force Thunderbirds flight demonstration
team. |
| For
those of us in the model aviation community, and
particularly those in the model jet world, 2003 marks
our own notable event--the 20th anniversary
of the first-ever flight of a micro-turbojet powered model
aircraft. While this achievement may not rise to the level
of distinction of that of the Wright brothers, I think
we can agree that it ushered in the birth of an industry
that, in two short decades, has seen remarkable technological
developments, the launch of many new businesses, and has
brought countless hours of enjoyment and fascination to
thousands of individuals. |
| If
my personal fascination with micro-turbojet engines seems
a bit excessive to family and friends, it may be due to
the fact that it was only relatively recently that I learned
of their existence. Im still in the "I-cant-believe-these-are-real"
stage. I recall reading the article in 1983 that announced
the success of the UK team, led by Jerry Jackman, in making
that first micro-turbojet flight. At the time, Mr. Jackman
felt it unlikely that such engines would be available
anytime soon on a commercial basis--they would be far
too expensive. For a time, he was right. Even then I was
fascinated and hung on to that magazine for years until,
somewhere along the way, it was lost. The timing of that
article also happened to coincide with my leaving the
R/C hobby. Little things like marriage, home ownership,
children, business travel and night school distracted
me a bit. Then, about two years ago I heard of a "jet
meet" in my home state of Florida. Yes, I was told,
they will be flying true micro-turbojet engines.
I had no idea that Mr. Jackmans engine, or one like it,
had been commercialized. Of course, I had to check this
out, and upon seeing and hearing the genuine article,
my fascination was instantly renewed. To this Rip Van
Winkle, it seemed as though these marvels of miniature
engineering had appeared overnight. |
Photo:
Paul Marsh
Beautiful
F/A-18 turbojet powered model aircraft spotted at
2003 Florida Jets.
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Drawing:
Radio Modeler Magazine
Early
design of Jerry Jackman's micro-turbojet engine.
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Photo: Radio Modeler
Magazine Barjay,
the first radio controlled model aircraft powered
by a home-built micro-tubojet engine.
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The
reality, of course, is somewhat different. In
1975, Jerry Jackman built a prototype engine that
could run in self-sustaining mode, but could not
accelerate. It would take another eight years,
and the addition of four people to the effort,
to achieve success. Each team member contributed
to the project in their area of expertise. Chris
White, a machinery engineer, refined the design
of the compressor and turbine blades. David Stitch
improved the overall rotor design. Ray Carter
worked on the overall mechanical design of the
engine, and Barry Belcher designed and built the
model aircraft, named "Barjay," that
was to be the test bed for the worlds first flying
micro-turbojet engine. Finally, on March 20, 1983
the team made model aviation history when, during
what were to be taxi trials only, Jackman allowed
the aircraft to accelerate to takeoff speed and
made the three minute first flight.
Jackman's engine measured 4¾" in diameter, 13½"
long and weighed 3¾ pounds. At 85,000 rpm it produced
over 9 pounds of thrust and had a top speed of
97,000 rpm. Twenty years later, commercial engines
of roughly similar dimensions and weight are in
the 30 pound thrust class when running at 120,000
rpm. The airframe, with its twin-boom high-tail
configuration, is remarkably, perhaps inevitably,
similar to many of today's trainer aircraft.
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Photo: Radio Modeler
Magazine Jackman's
engine itself mounted on "Barjay," the aircraft
test bed.
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Photo:
Radio Modeler Magazine
Jerry
Jackman, leaning over Barjay, starts up his micro-turbojet
for a test run.
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| It
is somewhat fitting that a British team was first
in the air with a working micro-turbojet. Forty-six
years earlier it was another British team, led by
Frank Whittle, that developed and ran the first
full-sized turbojet engine. However, it should be
noted that the first operational turbojet engine
was developed in Germany by Hans von Ohain. His
engine powered the Heinkel He 178 in the world's
first jet aircraft flight on August 27, 1939. According
to additional historical accounts, the American
powers-that-be weren't all that excited about jet
power at the time and, as a result, lagged significantly
behind in development. Not so with micro-turbines.
An American team, led by Bryan Seegers, was hot
on the heels of Jerry Jackman. In fact, this team
had their micro-turbojet running reliably in 1981.
Had Seegers found a suitable airframe, he may have
had his engine in the air in 1982. Still, first
is first, and it wasn't until 1988, five years after
Jackman's flight, that Seegers' engine took to the
air in a radio controlled model aircraft. |
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| When
it comes to tenacity, you have to admire Bryan Seegers.
He tried to build his first turbojet engine when
he was in the fourth grade. It consisted of two
cat food cans, tin lids cut and twisted to form
a three-stage axial flow compressor and two-stage
axial flow turbine, a threaded-rod shaft and jam
nuts to hold it all together. In his own words,
"It didn't run." Today, Seegers runs M-Dot Aerospace,
a company he started to commercialize his (working)
S-100 micro-turbojet and which continues to specialize
in micro-turbine machinery. At the time, he had
a great deal of difficulty getting the hobby world
interested, primarily due to his projected price
of $2,200, so he changed focus to other areas of
micro-turbine technology, taking on a number of
government and university projects. |
Photo:
Bryan Seegers
Bryan
Seegers' S-100 micro-turbojet. Three S-100's were
built. This is the third, which powered the first
flight a turbojet powered R/C aircraft in the
US.
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Photo: Courtesy
of Bryan Seegers
Bryan
Seegers works on his engine and aircraft prior
to first flight.
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In
1978, Seegers laid out his concept for that first
micro-turbojet engine. The one that finally flew
in 1988 was little changed from that design. In
the interim period, he took three years off from
his micro-turbojet project to build a full-size
composite aircraft called the "Dragonfly." He then
attempted a redesign of his turbojet engine, only
to return to his original concept. Like Jerry Jackman,
Seegers' ultimate success was the result of a team
effort. Bob Wahl, an expert in his field, developed
the electronic engine control system. Jack Erwin,
at one time a NASA aerodynamicist, worked on the
diffuser design and Bill Caan, a combustion engineer,
designed the burner hole pattern. Jim Allen Jr.
designed the aircraft test bed, which was built
by Seegers himself. Allen was the only person to
ever actually fly the turbine powered model aircraft.
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Photo:
Courtesy of Bryan Seegers
A
jubilant team returns with a slightly damaged
aircraft after its first flight. The pilot and
designer of the aircraft, Jim Allen Jr. in yellow,
walks alongside as Bryan Seegers holds the tail
of the plane.
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| The
challenges facing such a complex project were many, but
a few stand out. Seegers had designed and built a number
of engines before settling on a final design for the flight
article. He wanted the flight version to burn gasoline
in lieu of propane. Redesigning the burner to accomplish
this proved to be one of the toughest challenges. Another
significant challenge was working out the shaft dynamics
on the bearing system. In terms of integrating the engine
and airframe, the biggest hurdle was the fuel system.
Nearly everything from the stainless steel fuel tanks
to electronic controls had be designed and built from
scratch. He even designed and built a drum brake for the
nose wheel. I can only assume that Jerry Jackman and his
team faced similar challenges leading up to their success
in 1983. |
On
July 30, 1988 Bryan Seegers and his team made their
own contribution to model aviation history when
they became the first in the US to successfully
fly a radio controlled model aircraft powered by
a micro-turbojet engine. That first flight, however,
nearly ended in disaster. Although Seegers was not
going to fly the aircraft, he maintained tight control
over all aspects of the project. Without his knowledge,
someone dialed-in significant down trim on the elevator
control. After takeoff, when Allen relaxed up-pressure
on the elevator, the aircraft dove into the pavement
breaking the landing gear. However, the engine kept
running and Allen was able to get the plane back
in the air.
Along the way, Seegers experienced another significant
event--Hans von Ohain himself visited Bryan's Arizona
home, enjoyed tea in his kitchen and watched his
engine run. That visit remains a high point in Bryan's
life. |
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| Considering
the enormous effort involved in this undertaking,
and the time span from concept to flight (8 years
or more for Jackman, 10 years for Seegers), I wanted
to know what inspired them to keep going. For Seegers
the answer was simple and straightforward--he just
wanted to hear the incredible sound of a turbojet
engine in flight. I think a lot of people can relate
to that sentiment. Even now, after years of micro-turbojet
powered models being flown at fields around the
world, the sound alone turns heads and causes onlookers
to drop what they are doing to watch and listen.
Today, Bryan Seegers' engine, and the aircraft it
powered, are on display at the Champlin Fighter
Museum in Mesa, Arizona. I do not know the disposition
of Jerry Jackman's engine or the test bed, Barjay,
but I hope both are still in one piece and might
find their own way into a similar display. |
Photo:
Paul Knapp
Bryan
Seegers' engine and aircraft on display in the
Champlin Fighter Museum, Mesa, Arizona.
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Photo:
Scale R/C Modeler
A
representative of the engine manufacturer inspects
the installation in Continental RPV's target drone.
|
When
it comes to claiming "firsts," the waters can get
a bit murky. We all take for granted the fact that
the Wright Brothers were the first in the world
to fly a manned, powered aircraft 100 years ago.
Yet, until relatively recently, that claim was still
being disputed by some. Those disputes do, however,
seem to finally be laid to rest. To muddy these
waters a bit, just before Seegers' team made their
first flight in the US, there was another project
underway utilizing turbojet power in a radio controlled
model aircraft. Continental RPV of Barstow, California
was attempting to meet a goal of 200 mph with their
radio controlled target drones in order to qualify
for a military contract. They tried various piston
engines and pulse jets, but none were up to the
task. They got a break when the military de-classified,
under certain restrictions, small turbojet engines
then being made to power missiles. Continental RPV
was granted permission to use one of these engines
in their drones. On
the day that Continental broke the 200 mph target
with a turbojet-powered target drone, Norm Goyer,
then editor of Scale R/C Modeler magazine,
was offered the opportunity to fly the beast. With
sweating palms and knees knocking, he was handed
the transmitter once the 1/5th scale
MiG 27 was in the air. He flew the model aircraft
through the speed gates at a nerve-wracking 226
mph! Now, to put this accomplishment in perspective
so as not to diminish the achievement of Bryan Seegers
a few months later, the engine that Continental
RPV used, a Sunstrand TJ-70, was only on loan from
the military. Continental couldn't even buy one,
let alone a hobbyist. It was about 6½ inches in
diameter and weighed 14 pounds. The drone with engine
weighed 95 pounds. There were no provisions for
throttle control--the entire flight, from it's launch
off the bed of a pickup traveling at 60 mph to flame-out,
was made at full thrust. The drone had no landing
gear. Reflecting a familiar sentiment, Goyer wrote
of this event, "How do these miniature jets sound?
Real Real Real." |
Photo:
Scale R/C Modeler
Norm
Goyer with the turbojet powered Continental RPV
he flew at 226 mph.
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| For
a time, it was fair to say that the micro-turbojets
that power model airplanes were not scaled-down
versions of the high bypass ratio, multi-spooled
turbofan engines that power today's commercial and
military aircraft. Indeed, long before micro-turbojets
became available to modelers, there were real-world
reasons to develop scaled-down versions of very
sophisticated full-size turbojet engines. In the
mid-1950's, Williams International, for example,
was started to develop small turbojet engines leading
to multi-spooled turbofans intended for use in cruise
missiles and other military applications. Unfortunately,
such engines were still far too complex, too expensive
and, at 150 pounds, too large and heavy for use
in model aircraft. If modelers were to have true
turbojet engines, they would have to be designed
from the bottom up instead of top down. |
Photo:
Hill Aerospace Museum
Williams
International F107-WR-101 advanced two-shaft
turbofan engine built to power the AGM-86B
Air-launched Cruise Missile (ALCM). Weight:
146 pounds. Thrust: 600 pounds.
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Even
after the successes of Jackman and Seegers, the
average modeler did not have access to micro-turbojets
for many years. In the interim period, though,
we have gentlemen like Thomas Kamps and Kurt Schreckling
to thank for their efforts in developing engines
and publishing plans that would allow anyone with
access to a relatively well-equipped machine shop
to build and fly their own engines. The availability
of off-the-shelf centrifugal compressors made
the job of building one's own engine easier, but
it was still a demanding exercise. Before complete
engines became available, there was one other
development that aided the home-builder. With
the growing interest in micro-turbojets, at least
one company went into production of axial turbine
wheels, these being perhaps the most difficult
part for the home-builder to fabricate. While
these developments opened up the world of micro-turbojets
to such fortunate individuals, commercialization
and mass production were yet to bring these engines
to the general model aviation community.
Today,
of course, we have a wonderful mix of not only
commercially produced engines, but a continuation
of home-built, one-of-a-kind examples that push
the envelope of this miniature technology. Indeed,
while the commercial manufacturers are doing a
great deal to refine and improve micro-turbojet
engines, much of the innovation continues to be
among home-builders. Recent examples include multi-stage
axial compressor designs and twin-spooled turbofan
engines.
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|
Photo:
Ewald Schuster
Ewald
Schuster's remarkable Pegasus-style turbofan
intended to power his VTOL Harrier.
|
One
of these innovators is Ewald Schuster. He is self-taught
in the art and science of turbojet design and fabrication,
yet has achieved remarkable results in miniaturization
(more on that later) and turbofan fabrication. He
is currently working on a Pegasus-style turbofan
engine with movable ducting for a scale Harrier.
We are rapidly getting to the point where this bottom-up
development, as opposed to scaled-down engineering,
is leading to engines that do indeed emulate their
larger cousins in function and sophistication. The
sophistication of these engines, and that of the
model aircraft they power, has blurred the lines
of distinction between hobby aircraft and military/commercial
unmanned aerial vehicles, or UAV's. |
|
| One
example of where these worlds collided ("merged"
may be a better choice of word) was the "F18 Project"
conducted by North Carolina State University in
conjunction with the US Navy and Bihrle Applied
Research. The micro-turbojet powered aircraft that
came out of this program would make any jet modeler's
eyes tear with envy. In the mid-1990's, this team
was tasked with the development and flight test
of a 17.5% scale F/A-18E/F Super Hornet. The model
itself was 10 feet long with a wingspan of 7.5 feet.
It was powered by two micro-turbojets, each producing
40 pounds of thrust. It weighed 140 pounds. |
|
| The
purpose of the F18 Project was to support the flight
test program of the full-size aircraft and associated
flight simulators. The advantages of a test program
of this nature are many. First, the total cost of
the model effort equaled only a few hours of flying
time of the full-sized, manned test aircraft. Second,
a flying scale model allows data to be collected
on a new airframe without endangering the life of
a test pilot. In addition, aerial maneuvers can
be performed that are not easily simulated in a
wind tunnel with non-flying scale models.
During
the test program, the model F/A-18 would be flown
by a radio control pilot standing next to the runway.
After reaching altitude, control would be turned
over to a remote cockpit elsewhere on the ground.
An on-board video camera relayed images from the
model to the remote cockpit. As the remote pilot
took the aircraft through a series of preplanned
maneuvers, on-board sensors would collect and store
data for later analysis. If a flight emergency arose,
the radio control pilot could take over flight at
any time and, in any case, was handed back control
for landing after the test flight was complete.
|
Photo:
North Carolina State University
NCSU
team prepares 17.5% scale F/A-18E/F Super Hornet
for test flight.
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Photo:
North Carolina State University
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Photo: Ewald Schuster
Ewald
Schuster's 2¼" diameter engine produces 4 pounds
of thrust.
|
While
some have been working to make micro-turbojets more
complex, others have been working to make them smaller.
In addition to the turbofan mentioned above, Ewald
Schuster has built a tiny turbojet engine that measures
a mere 5" long and 2¼" in diameter. It weighs only
6.5 ounces, yet develops 4 pounds of thrust. This
engine has had four successful flights to date.
Schuster is currently working on an even smaller
engine that will measure 1¼" in diameter, run at
500,000 rpm and produce 1½ pounds of thrust. Smaller
still is a mini-micro-turbojet developed by Bryan
Seegers' M-Dot Aerospace under a project funded
by the Defense Advanced Research Projects Agency,
or DARPA. This little gas turbine can fit inside
an egg and develops 1.4 pounds of thrust. |
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| Developing
ever smaller turbojets poses significant hurdles
that must be overcome if one is to produce a viable
engine. Among the most significant are the reduced
efficiency that results from downsizing and the
increased demands on bearings. The clearance between
turbine blade tips and housing must get tighter
in order to maintain operating efficiency. In the
case of Schuster's 2¼" diameter engine, the clearance
is only 0.0025", which is less than the thickness
of a human hair. Smaller engines run at higher rpm's,
placing huge demands on bearings. Still, these hurdles
are being overcome and both Schuster's and M-Dot's
tiny turbojets have run successfully, with even
smaller engines to come. |
Photo: M-Dot
Aerospace
M-Dot's
turbine-in-an-egg has produced 1.4 pounds of thrust
in bench tests.
|
|
Photo:
Sandia National Laboratories, SUMMiT Technologies
The
legs of a spider mite dwarf the gears of this
MEMS device.
|
Just
how small will turbojet engines get? Imagine, if
you can, a machine so small that you need a microscope
to see its parts; so tiny that the legs of a spider
mite can bring its gears to a grinding halt. Borrowing
from the techniques used to manufacture semiconductor
computer chips, students and engineers at the Gas
Turbine Laboratory of the Massachusetts Institute
of Technology have developed what amounts to a turbine-on-a-chip.
These engines, and other tiny machines made by the
same process, are referred to as micro-electromechanical
systems, or MEMS. Built-up and etched one layer
at a time, just like semiconductors, these MEMS
engines have all of the essential components for
true turbojet operation. The entire package, including
the compressor and turbine rotor assembly, diffusion
vanes, turbine nozzle vanes, fuel injectors and
combustion chamber is no larger in diameter than
a dime. It weighs about 1 gram and is expected to
have a thrust to weight ratio of 100 to 1. The best
modern jet engine has a thrust to weight ratio of
10 to 1.
To date, each of the components that make up the
entire MEMS turbojet has been individually tested,
but the package has not yet run as a complete turbojet.
The turbine with nozzle guide vanes, measuring 6mm
in diameter, has been run at 1.4 million revolutions
per minute. The compressor with inlet guide vanes,
measuring 8mm in diameter, has been run at 480,000
rpm and has achieved a compression ratio of 4:1.
The method of manufacturing these engines is essentially
a two dimensional process, limiting the compressor
to centrifugal flow and turbine to radial flow.
Emerging technologies, however, may lead to three
dimensional manufacturing processes which would
allow for the design of axial flow components.
While the primary application of the MEMS turbojet
is electric power generation, these mini-micro-turbojet
engines could be used to power micro air vehicles,
or MAV's, which are defined as being no larger than
6 inches in any dimension. MAV's are being developed
to carry out a number of military and some civilian
missions including real-time reconnaissance utilizing
tiny on-board video cameras, laser marking of targets
and even analyzing the air for potential chemical
or biological warfare agents. Personally, I can
clearly envision one of these ultra-small turbojet
engines powering my park flyer. |
Gra phic:
Gas Turbine Laboratory, Massachusetts Institute
of Technology All
of the essential components for true turbojet
operation are present in this "turbine-on-a-chip."
|
Photo:
Gas Turbine Laboratory, Massachusetts Institute
of Technology Measuring
just 4mm in diameter, this MEMS turbine has been
spun up to 1.4 million rpm.
|
Photo:
Gas Turbine Laboratory, Massachusetts Institute
of Technology
Cutaway
of entire MEMS turbojet showing flow channels
and compressor disc.
|
|
| It
has been a fascinating 20 years in the world of
micro-turbojets since Jerry Jackman made his first
flight in 1983. The pace of development seems to
only be accelerating. The next 20 years promise
to bring even more excitement to the radio control
jet modeler. |
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Sources:
Barrie,
Darwin N. "Turbo Jet." Radio Control Modeler December
1988: 222-226, 230.
Batt, Gordon. "Jet Flight Triumph." Radio Control Modeler
September 1983: 148-150.
Epstein, Dr. Alan H. (Director, Gas Turbine Laboratory,
Massachusetts Institute of Technology.) "Millimeter-scale,
MEMS Gas Turbine Engines." Paper presented to ASME Turbo
Expo 2003. 16-19 June 2003.
Goyer, Norm. "True Turbines are Here to Stay - Flying
High and Fast." Scale R/C Modeler March 1988: 34-39,
74-76.
Goyer, Norm. "True Turbines are Flying in America." Scale
R/C Modeler November 1988: 32-39.
Jacobson, Dr. Stuart. (Deputy Director, MIT Microengine
Project, Massachusetts Institute of Technology.) Personal
Interview. 14 August 2003.
Schuster, Ewald. Personal Interview. 5 August 2003.
Seegers, Bryan. Personal Interview. 19 March 2003.
Williams, Bob. "NCSU-built model to save Navy big bucks."
The News & Observer January 28, 1997.
Links
of interest in order as they appeared in article:
U.S.
Centennial of Flight Commission
U.S.
Air Force Thunderbirds
M-Dot Aerospace
Champlin
Fighter Aircraft Museum
Williams
International
North
Carolina State University "F18 Project"
Sandia
National Laboratories, Microsystems
Massachusetts
Institute of Technology, Gas Turbine Laboratory
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