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Dynamometer Developments




Associated with aerospace performance testing from its early beginning, Kahn has always placed

strong emphasis on new product development.  This continuing development effort has resulted in

a wide range of new dynamometer products and applications and has reinforced Kahnís position

as the world leader in dynamometer technology.  Some of our more recent accomplishments and

new dynamometer applications are highlighted below.

Dynamometer Designs for Attitude Test Applications     



In attitude test applications, the engine and dynamometer are installed on a variable attitude

test stand where they are operated in all attitude positions from horizontal to vertical (nose up

and nose down) and at large roll angles. This test capability permits the engine manufacturer

to simulate actual flight conditions in the test cell.  In the late 1980s, Kahn provided the

dynamometer for attitude testing of the Rolls-Royce AE1107C turboshaft engine which powers

the V22 tilt rotor aircraft. Based on the experience gained with this and other attitude test

applications, Kahn recently developed the Model 405-025 hydraulic dynamometer specifically

for attitude and roll testing of high speed turboshaft engines. The initial application was for the

Pratt & Whitney PT6C -67 turboshaft engine used on the BA609 tilt rotor aircraft.

Like other Kahn high speed dynamometers, the 405-025 is equipped with circumferential

carbon seals which provide positive sealing between the water compartment and the bearings

in all attitude positions and under all operating conditions, including zero speed.  Additionally,

to prevent flooding of the oil jet lubricated aircraft bearings in extreme attitude and roll

positions, the dynamometer is equipped with a complex internal oil scavenging arrangement.

The same design features are also incorporated in the high speed inertia flywheel associated

with the dynamometer. The flywheel is used to simulate the propeller rotor inertia during

transient test procedures performed in the test cell. Kahn has provided a number of different

dynamometer models for attitude test applications and has more experience in this area than

any other dynamometer manufacturer worldwide.


Advanced Bearing Support Technology

In the past, the speed range of high speed dynamometers was limited by rigid body critical

speeds which can cause high vibration if they occur within the operating speed range of the

engine. Kahn resolved this problem by incorporating state-of-the-art bearing support technology

used in modern turboshaft engines, in its dynamometer designs.  A number of Kahn high speed
dynamometers are now equipped with proprietary squeeze film damper bearing supports which

significantly reduce vibration amplitudes in the rigid body critical speed range and thereby

extend the usable operating speed of the dynamometer. For example, on the Model 405-025

dynamometer for attitude testing described above, this technology made it possible to increase

the maximum operating speed from 30,000 rpm to 35,000 rpm. Kahn is the only dynamometer

manufacturer worldwide which has integrated this advanced technology in its dynamometer designs.


TP400 Engine Testing for the Airbus A400M Military Transport Aircraft


                                       Europrop International TP400-D6 Turboprop

The breadth of Kahn's dynamometer product line was evidenced by recent testing of the

TP400 engine. The TP400 is the turboprop engine currently under development by a European

Consortium to power the A400M military transport aircraft. Kahn is supporting this project

by testing the entire engine including the propeller gearbox and the accessory gearbox. 


Kahn's Series 305 hydraulic dynamometers are designed to test large turboprop engines as well

as marine diesel engines. Kahn's Series 101 hydraulic dynamometers are designed to test

auxiliary power units (APUs) as well as gearboxes. 



Innovative Engine Test Stand Designs


Kahn has extensive experience in test stand designs for turboshaft and turboprop engines. 

Computer-aided finite element analysis techniques are used to assure that the test stand natural

frequencies are safely above or below the operating speed ranges of the engines.  As shown in

the pictures above and below, this design method results in highly rigid test stand structures which

promote smooth operation at low vibration levels. While most test stand designs are configured

for testing a single family of engines, Kahn has also designed a number of universal test stands

which can be used for testing a variety of different engines.


One recent design configured for testing two different turboshaft engines is shown above during

the engine trial installation at Kahn.  This engine test stand is configured for testing either General

Electric T700/CT7 turboshaft engines (on the left) or General Electric T58 turboshaft engines

(on the right). The test stand is equipped with a Model 404-025 high speed hydraulic dynamometer

rated at 2500 hp (1860 kW), 30,000 rpm.  Located in the center of the test stand, the dynamometer

can be used for testing either engine.





Another recent universal test stand design (shown above), features a Model 406-040 hydraulic dynamometer rated at 10,000 hp (7460 kW), 16,000 rpm. This dynamometer is capable of testing both General Electric T64 turboshaft engines used on the CH-52 Sea Stallion helicopter and Rolls-Royce AE1107C turboshaft engines for the V22 tilt rotor aircraft. Shown on the left is an engine test stand which can be configured for either the T64 or T700 engine as shown below. The dynamometer, shown on the right, is mounted on a rigid subframe equipped with retractable casters. This feature permits moving the dynamometer from the engine test stand to a storage location.  The T700 dynamometer can then be moved into the test cell.  Quick and accurate positioning of the dynamometer relative to the engine is accomplished with a hydraulic docking system installed on the engine stand.






High Speed Dynamometer Development



The recent emergence of micro gas turbines and other prime movers operating at rotational speeds significantly above the 20,000 to 30,000 rpm speed range of current turboshaft engines has accelerated the development of a new generation of high speed dynamometers at Kahn. One example is the flange mounted Model 404-012 smooth disc hydraulic dynamometer which is currently being manufactured for an overseas customer.  With a power rating of 700 hp (520 kW), this unit is capable of operating at rotational speeds up to 60,000 rpm. Equipped with latest technology high speed ceramic ball bearings, the dynamometer features a proprietary multi stage shaft seal design.  Given the demand for even higher speeds, development work continues on dynamometers capable of operating at rotational speeds up to 100,000 rpm.


Illustrated above, the smooth disc type dynamometer rotor is manufactured from a high strength stainless steel forging.  In contrast to conventional hydraulic high speed dynamometers, the smooth disc type absorbs power by viscous shear rather than by turbulent action. This process inherently discourages cavitation erosion and thereby eliminates the need for frequent replacement of the power elements.  Like all Kahn smooth disc high speed dynamometers, the 404-012 carries a 5000 hour/5 year special warranty against cavitation erosion of its power elements.

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