A new version of the HKS four-stroke engine used in Light aircraft, PPC’s and Trikes is now being delivered in the U.S.  In development and testing for nearly two years,  the new 700E has improved cooling performance and has been further optimized for pusher applications.    

Over 20 airframe manufacturers worldwide now offer the HKS-700E for their aircraft. 

The HKS 700E is a 60HP, horizontally opposed, two cylinder, four-stroke engine.  The 700E uses a combination of high technology and simplicity to achieve the twin goals of high power output and reliability. The 700E is a very high quality product.  Every major component was designed for light aircraft use and is made from the best materials and techniques available.  

In power to weight ratio, the 700E matches conventional two-strokes.  The real difference, however, is in the high peak torque (50.6ft.lbs@ 5000 RPM) of the engine and the very flat torque curve.  This allows the 700E to pull better in a climb or hold a higher prop load (pitch) than the 60 horsepower rating would suggest. 

 The integral gearbox on the 700E uses straight cut gears with a spring-washer type torsional coupling ahead of the large flywheel.  The gearbox is attached to the flywheel case; the gears are lubricated by the main engine oil system, the same as a Rotax 912 four-stroke.  The gearbox can be run up or down and is changed by rotating the flywheel case around.  The large flywheel mass and attention to the internal balance of the engine are the keys to the smooth running and low vibration of the 700E.  At a lower RPM you can hear the gears singing, not clattering.  The standard gear ratio is 2.58 to one. As the Max permissible RPM is 6200, the RPM at the prop is 2400.  With the optional 3.47 to one gearbox, the prop speed and noise is even lower. 

 The prop hub bolt pattern is the popular 75MM pattern; the direction of rotation is the same as a Rotax two-stroke.  HPower has conducted baseline tests of several popular propellers, including the Ivo-prop, Power-fin and Sport props.  In tests, the 700E can swing a 74” two blade and a three blade 68” was typical. The engine was just as smooth with a two blade prop as three. This also allows the use of a light, wood two-blade for certain applications.         

7 kgm at 5000rpm

Weights:

Q?  Why does the 700E have such a high operating RPM? Is this normal for a  four-stroke engine?   

A.      The 700E was designed to get two-stroke like power output from a four-stroke engine.  The way to get more power from a given size engine is to make it do more work, meaning more RPM.  The operating RPM range of the 700E is normal for an engine using modern motorcycle technology.  The Rotax 912 four-stroke has a similar operating range.     

 Q?  Why does the HKS have a gearbox, isn’t direct drive lighter and simpler?  

A.     The larger the propeller, the more thrust it will produce, particularly at the relatively slow climb speeds of light aircraft.  More low speed thrust means more climb.  As well, there is the great benefit of much lower propeller noise than direct drive.  The 700E gearbox has two ratios available 2.58 and 3.47 to 1.   top

Q? Can the gearbox be positioned up or down? Is it a big deal to swap the position? Can the engine be run inverted?

A.  The gearbox can be positioned up or down. To change the position the front cover is removed and rotated. The HKS 700E cannot be run inverted. top

Q?  Why does the HKS have separate oil tank? And what is a “dry sump” engine?

A.          The 700E has a separate oil tank to reduce the package size of the engine.  Most conventional aircraft engines are dry sump for the same reason. A “wet sump” engine has it’s oil supply in the oil pan at the bottom of the engine. A “dry sump” engine has a separate scavenge pump to take the oil from the bottom of the mini-sump at the bottom and a supply pump to send oil under pressure through the engine.     top

Q? Can the HKS engine be used in pusher installations?

A.          Yes. As a matter of fact the 700E has been designed to work specifically in both the pusher and tractor configurations. A majority of the hundreds of engines sold are operating in the pusher configuration.  top

Q?    What type of fuel does the HKS require? Can it use 100LL?

A.               Automotive Unleaded-high test is best.  92 octane Unleaded is typical.  100LL  Avgas can be used during cross countries without worry.  Constant use of leaded fuels requires different lubricating oils to be used to avoid lead deposits. top

Q?   What is the fuel consumption of the HKS? 

A.             The fuel consumption in typical operation is between 2 gallons and 3 gallons an hour.  In our testing, the fuel consumption we have noted is 2.5 gallons an hour  @ 75%.  The Dyno testing according to the JIS (Japanese Industry Standard) requires the engine to be tested in a manner that does not reflect propeller loading.  This makes HKS’s consumption numbers very conservative.   top 

Q?     What type of exhaust is required?  Can you run straight pipes?

A.               The 700E was designed as a complete system. There are requirements for back pressure and length of the exhaust manifold as a part of the system. Both the intake and exhaust manifolds are optimized for a flat torque curve.   top 

Q?    Are the carburetors used on the HKS altitude compensating?  Why don’t they  use  Fuel   injection?

A.             The Bing C.V. (Constant Velocity) carburetors are capable of 50% mixture compensation to approximately 10,000 Ft. due to the CV design which uses a diaphragm-slider to vary the mid range mixture. The Rotax 912 four-stroke uses the same carburetors.    top

Q?   How much does a complete engine package cost?

A.              HPower sells the 700E as a complete system. We have chosen the best accessory components we could find to match the quality of the engine itself. top

Q?   What is the warranty on the HKS 700E?

A.     The Warranty is one year or 100 hours of engine time.