A prototype of a new, internal combustion (IC) engine concept has been completed. The Nutating Engine features an internal disk nutating (wobbling) on a Z-shaped power shaft. The engine is exceedingly compact, and several times more power dense than any conventional (reciprocating or rotary) IC engine. This paper discusses lessons learned during the prototype engine's development and provides details of its construction. In addition, results of the initial performance tests of the various components, as well as the complete engine, are summarized

Boruta, Mike

Meitner, Peter L.

NASA Technical Reports Server

Peter L. Meitner
U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio
Mike Boruta and Jack Jerovsek
KINETIC/BEI LLC, South Elgin, Illinois
The Nutating Engine—Prototype Engine Progress
Report and Test Results
NASA/TM—2006-214342
October 2006
ARL–MR–0641
U.S.  ARMY
RESEARCH LABORATORY
https://ntrs.nasa.gov/search.jsp?R=20060056193 2019-08-30T00:14:07+00:00Z
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The Nutating Engine—Prototype Engine Progress
Report and Test Results
NASA/TM—2006-214342
October 2006
National Aeronautics and
Space Administration
Glenn Research Center
Cleveland, Ohio 44135
Prepared for
Forum 62
sponsored by the AHS International
Phoenix, Arizona, May 9–11, 2006
ARL–MR–0641
Peter L. Meitner
U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio
Mike Boruta and Jack Jerovsek
KINETIC/BEI LLC, South Elgin, Illinois
U.S.  ARMY
RESEARCH LABORATORY
Acknowledgments
The authors dedicate this paper to the memory of Mr. Len Meyer, the inventor of the Nutating Engine. Regrettably, his
untimely death prevented him from seeing his lifelong dream of developing his engine concept come to fruition.
Available from
NASA Center for Aerospace Information
7121 Standard Drive
Hanover, MD 21076–1320
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Available electronically at http://gltrs.grc.nasa.gov
Level of Review: This material has been technically reviewed by technical management.
NASA/TM—2006-214342 1
The Nutating Engine—Prototype Engine Progress Report and Test Results 
 
Peter L. Meitner 
U.S. Army Research Laboratory 
Glenn Research Center 
Cleveland, Ohio 44135 
 
Mike Boruta and Jack Jerovsek 
KINETIC/BEI LLC. 
South Elgin, Illinois 60177 
 
Abstract 
A prototype of a new, internal combustion (IC) engine 
concept has been constructed and initial performance tests 
have been completed. The Nutating Engine features an 
internal disk nutating (wobbling) on a Z-shaped power shaft. 
The engine is exceedingly compact, and several times more 
power dense than any conventional (reciprocating or rotary) 
IC engine. This paper discusses lessons learned during the 
prototype engine’s development and provides details of its 
construction. In addition, results of the initial performance 
tests of the various components, as well as the complete 
engine, are summarized. 
Introduction 
Unmanned Air Vehicles (UAV’s), either fixed wing, or 
VTOL (Vertical Take Off and Landing) have a promising 
future and figure prominently into the Army’s future tactics 
and operations. However, for small UAV’s (arbitrarily defined 
here as requiring less than approximately 75 kW, or 100 hp), 
there are no engines available with the following desirable 
attributes: The ideal engine would simultaneously be fuel 
efficient, powerful, compact, smooth running (low vibration) 
and be able to readily burn heavy fuels. The U.S. Army 
(through a Phase I and Phase II SBIR (Small Business 
Innovative Research) contract) has sponsored the 
demonstration of a unique and innovative new engine concept 
called the Nutating Engine which possesses all these qualities. 
This paper describes the prototype engine and presents the 
initial test results.  
Engine Concept Description 
References 1 through 4 describe various versions of the 
Nutating Engine and discuss its advantages compared to 
conventional IC engines (size, power density, and the ability 
to readily burn heavy fuels). Figure 1 shows the simplest 
version of the Nutating Engine, which uses a single, two-lobed 
disk nutating (wobbling) on a Z-shaped power shaft. The 
unique motion of the disk is achieved by mounting the center 
of the disk in the middle of the Z-shaft, at an angle to the 
power shaft. As the power shaft rotates, the disk nutates, but 
does not rotate with the shaft. This is achieved via an anti-
rotation pin, shown in figure 2. Power is transmitted directly 
to the output shaft, doing away with the complicated linkages 
needed in a piston engine to change the linear piston motion to 
rotating output motion. Since the disk does not rotate, the seal 
velocities are lower than in an equivalent IC piston engine. 
The disk wobbles inside a housing and, in its simplest version, 
half of the single disk (one lobe) performs the 
intake/compression function, while the other lobe performs the 
power/exhaust function. Note that the disk lobes can be 
configured to have equal compression and expansion volumes, 
or to have the compression volume greater than or less than 
the expansion volume. This means that the engine can be self-
supercharged, or operate as a Miller/Adkinson cycle. Self-
supercharging gives better efficiency for high altitude 
missions, while operating as a Miller cycle gives increased 
efficiency at low altitude. 
The nutating motion of the disk results in each of the 
displaced volumes being generated twice per engine 
revolution (via overlapping processes, each over 270° of crank 
angle), producing two intake/compression and two 
power/exhaust events per crankshaft revolution. This produces 
very high power density (2 and 4 times higher than a 
conventional 2-stroke cycle and 4-stroke cycle engine, 
respectively) and a smooth torque curve. 
The Nutating Engine operates as a four stroke cycle – 
intake, compression, power (burning) and exhaust. The 
intake/compression side of the disk feeds the compressed air 
into an accumulator. From there it is metered to a combustion 
pre-chamber (at the power/exhaust side of the disk), via 
valves, which open at the appropriate time (the pre-chamber is 
that volume into which the fuel and air charge is introduced 
and contained when the nutating disk is at the position of 
minimum chamber volume). Fuel is injected, and a spark plug 
is fired (for a non-compression ignition cycle). The burning 
gas then expands through the power/exhaust side of the disk. 
The burning (power producing) process continues over 270° 
of crank angle (versus 180° for a conventional IC engine). 
This means that, for heavy fuel, the Nutating Engine can run at 
higher speeds than a conventional IC engine before the 
limiting speed (set by the fuel burning rate) is reached. This 
further increases power density. Also, the geometric shape of 
the combustion volume always has a three-dimensional 
character, which aids the combustion process. 
NASA/TM—2006-214342 2
 
 
 
Prototype Engine Description 
To simplify the prototype engine construction and to help in 
the understanding of the individual processes, the prototype 
Nutating Engine was constructed using two disks, one disk 
dedicated solely to the intake/compression function, and the 
other to the power/exhaust function (fig. 3). In addition, the 
significant time and money constraints inherent in a Phase II 
SBIR contract dictated a spark ignited (versus compression 
ignited), relatively low compression ratio (10:1) configuration, 
with initial testing performed with gasoline instead of heavy 
fuel. For the prototype engine, the most important contribution 
was felt to be the successful demonstration of the basic cycle, 
which could most readily be demonstrated with gasoline. The 
more challenging issue of operating on heavy fuel (and at 
pressure ratios allowing compression ignition) will be 
addressed in future efforts. 
 
 
 
 
The development of the Nutating Engine necessitated a 
multi-pronged approach. A modeling and simulation effort 
developed computer programs to better understand the 
complex geometric, kinematic, combustion, and 
thermodynamic aspects of this unique engine configuration. 
Additional, difficult factors which had to be addressed 
included the development of seals, a combustion pre-chamber, 
oil circuits, cooling circuits, controls, and a fuel injection 
system. Paper length limitations preclude a discussion of all 
these items, but the final prototype engine seal configurations 
are shown in figure 4. The radial seals shown in figure 4 are 
located on the insides of the housing side walls, placed every 
10° along the path of the disk. During its motion, the disk 
moves over and depresses the seals in an almost pure rolling 
motion (there is some sliding). Note that the outer surfaces of 
the disks never come in contact with the housing inner walls. 
NASA/TM—2006-214342 3
 
 
This gives the Nutating Engine a distinct advantage over all 
other IC engines, since it allows the majority of the housing 
inner wall surfaces and the power/exhaust disk outer surfaces 
(except for the areas holding or making contact with the seals) 
to be thermal barrier coated. This, in turn, greatly reduces the 
heat soaking into the engine, allowing a much smaller cooling 
system, as well as increasing engine performance. This feature 
was not incorporated into the prototype engine. 
Figure 5 shows the completed Prototype Nutating Engine, 
along with geometric characteristics and predicted 
performance parameters. Note that over 100 hp are expected 
to be produced at 3000 rpm from 2 disks only 8 in. (20.32 cm) 
in diameter. The prototype engine was constructed from steel, 
without regard to low weight, and a fully developed engine 
would be far lighter than the prototype’s 148 lb (67.3 kg). For 
comparison, figure 6 shows projections for a fully developed 
UAV engine using two 5 in. (12.7 cm) diameter disks. This 
engine measures a very compact 16 in (41 cm) long, 9 in. 
(23 cm) high, and 7.5 in. (19 cm) wide, and is conservatively 
predicted to produce 50 hp at 5000 rpm and to weigh only 
32.5 lb (14.77 kg). No other IC engine available today can 
approach these numbers. 
 
Test Results 
Intake/Compression Module 
As already stated, for cost and risk reduction purposes, the 
intake/compression disk was designed for a compression ratio 
of only 10:1 (necessitating spark ignition). During testing, the 
disk was driven by an electric motor and the resulting flows, 
temperatures, and pressures were measured. Tests were first 
NASA/TM—2006-214342 4
conducted with open outlet ports and then with the outlet ports 
plumbed into an accumulator which was manually throttled to 
maintain a desired accumulator pressure. The 
intake/compression module (disk) performed as intended, 
achieving the design pressure ratio “out of the box.” With the 
accumulator outlet valve closed (dead headed flow), the disk 
provided pressures well above the design pressure ratio. 
Compression efficiency was very good and increased with 
time, presumably caused by “seating” of the seals. Maximum 
test speed was 2600 rpm. These excellent results strongly 
suggest that future designs will readily achieve the higher 
pressure ratios needed for compression ignition.  
Power/Exhaust Module 
To reduce wear and tear on the intake/compression disk, the 
power/exhaust disk was first tested as a stand-alone unit by 
connecting it to a high pressure air tank. This caused the disk to 
rotate and to produce measurable power (with no combustion 
taking place). Once a steady rpm was established, fuel was 
briefly injected and the spark plugs were fired, resulting in 
increased rpm and exhaust temperature. These tests began to 
establish an understanding of the important and complex 
relationships between air flow, pre-chamber geometry, and 
fuel injection and spark timing. High speed samples of 
chamber pressure were taken for every degree of module 
crank angle. 
Complete Engine 
Once the basic operation of the Power/Exhaust module had 
been verified by the described stand-alone tests, the 
Intake/Compression and Power/Exhaust modules were 
connected and briefly tested as a complete engine. 
Unfortunately, by this time, the allocated resources of the 
Phase II SBIR contract had been depleted. Limited testing 
verified that the engine self-sustained, but no performance 
data were taken. 
Conclusions 
1) The primary goal of the Army’s Phase II SBIR contract 
has been met successfully. The Nutating Engine concept’s 
mechanical integrity has been demonstrated and its 
thermodynamic cycle has been validated. 
2) Compressor performance exceeded expectations, with the 
critical components showing little or no wear. 
 
3) The Expander worked well, and also exhibited low 
friction. 
4) As with any new engine, the major challenge is the 
combustion system and its optimization. The complex 
relationships between air flow, combustion pre-chamber 
geometry, fuel injection and spark timing are, as yet, not 
sufficiently understood.  
5) While harsh programmatic time and cost constraints have 
limited the scope of the prototype engine testing, the 
authors are confident that further development of this 
unique engine cycle will produce a heavy fuel engine that 
is unrivaled in regards to compactness and high power 
density for a multitude of applications. 
References 
1. Meitner, P., and Boruta, M., “The Nutating Engine –The 
Ideal, Heavy-Fuel Powerplant for Small UAV’s,” 
American Helicopter Society 59th Forum Proceedings, 
Phoenix, AZ, May 2003. 
2. Korakianitis, T., Meyer, L., Boruta, M., and McCormick, 
H., “Introduction and Performance Prediction of a 
Nutating-Disk Engine,” ASME 99–GT–279, International 
Gas Turbine & Aeroengine Congress & Exhibition, 
Indianapolis, IN, June 1999. 
3. Korakianitis, T., Meyer, L., Boruta, M., and McCormick, 
H., “One-Disk Nutating-Engine Performance for 
Unmanned Aerial Vehicles,” ASME 2001–GT–466, 
International Gas Turbine & Aeroengine Congress & 
Exhibition, New Orleans, LA, June 2001. 
4. Korakianitis, T., Meyer, L., Boruta, M., and McCormick, 
H., “Alternative Multi-Nutating-Disk Engine 
Configurations for Diverse Applications,” ASME 2001–
GT–572, International Gas Turbine & Aeroengine 
Congress & Exhibition, New Orleans, LA, June 2001.  
 
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NASA TM—2006-214342
ARL–MR–0641
E–15562
10
The Nutating Engine—Prototype Engine Progress Report and Test Results
Peter L. Meitner, Mike Boruta, and Jack Jerovsek
Internal combustion engines; Compression ratio; Efficiency
Unclassified -Unlimited
Subject Category: 07
WBS
22R–714–30–0359–02
A prototype of a new, internal combustion (IC) engine concept has been completed. The Nutating Engine features an
internal disk nutating (wobbling) on a Z-shaped power shaft. The engine is exceedingly compact, and several times more
power dense than any conventional (reciprocating or rotary) IC engine. This paper discusses lessons learned during the
prototype engine's development and provides details of its construction. In addition, results of the initial performance tests
of the various components, as well as the complete engine, are summarized.
Prepared for Forum 62 sponsored by AHS International, Phoenix, Arizona, May 9–11, 2006. Peter L. Meitner,
e-mail: p.l.meitner@nasa.gov, U.S. Army Research Laboratory, NASA Glenn Research Center; Mike Boruta,
e-mail: kineticresearch@sbcglobal.net, and Jack Jerovsek, e-mail: bakereng@pathwaynet.com, KINETIC/BEI LLC,
2197 Brookwood Dr., South Elgin, Illinois, 60177. Responsible person, Peter L. Meitner, organization code Z,
216–433–3715.




The Nutating Engine-Prototype Engine Progress Report and Test Results

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