Barnet Rotorcraft
Barnett Rotorcraft
4307 Olivehurst Avenue
Olivehurst, California 95961

Phone (530) 742-7416
Fax (530) 743-6866


The Barnett gear reduction unit is unique in the fact that . it is so small and compact. Yet, it can handle as much as 600 HP, or more!

Many years have gone into the development of this truly practical unit. The geometry is remarkable because the total of the two sets of identical gears will allow such a large final ratio. Each set of gears, for example, are a little over 1.4 to 1. The input starts out with the small gear on the input shaft, from the engine, which meshes with the larger gear. This gear is mated with an idler, or common shaft, that has ball bearings mounted on each end to carry the imposed loads. Next to the large gear, is another small gear, that is driven by the same shaft. This gear meshes with the large output gear, that is mounted to the output shaft and out to the propeller flange. The final ratio 1.999 to 1.

This arrangement generates the centerline input and output. By virtue of the way the gears are arranged, it now becomes a three gear type system. This means that the first gear turns left, (for example) the next gear turns to the right and the third gear will bring the direction back to the same direction that the first gear started with. A three gear system will not allow a centerline input or output. By adding one more gear (on the common shaft) to this unit, the friction has been reduced as well as the size AND the input and output are on the same centerline while turning in the same direction as the engine.

This may not seem like a big thing, but if you really think about it, a basic 2 : 1 two gear reduction unit turns backwards in ratio to the engine. To have a 2:1 ratio with a two gear system, the larger gear must be twice the size of the small gear. If an engine is fit up with a two gear system, the prop turns the opposite way the engine turns. If you have a standard left hand prop (as viewed in front of the prop), you will have to get another prop. Quite expensive. Also, the gears on the small engines, like Rotax, are too small to carry large horsepower of 100 to 600 HP!.

The only other way to obtain the same direction rotation as the engine, is to do the belt thing. Belts always break at the wrong time. Belts require 6 to 10 inches of offset and require large plates to maintain the correct alignment of the pulleys to the belt. This means weight, and the more that is added for bearing stabilization, the more it weighs. If the belt(s) are too tight without bearing stabilization, then the engine will suffer premature main bearing failure. Bearing stabilization requires a bearing to be utilized so that tightening the belt(s) will not affect the main bearing and brings the weight up some more. Weight in aircraft is an unwanted medium. The Barnett 'Le' Drive' belt reduction unit is OK for smaller engines up to 80-90 HP. This unit has an idler pulley to keep the belt at the proper tension, but IF the tension is too tight, the engine will suffer, and it will lose horse power!

If the belts are too loose, then the pulleys and belt(s) suffer from premature wear and will have to be replaced sooner than expected

The Barnett 'Shoe Box' gear reduction does not suffer from any of the problems associated with the belt drive systems!

The early gear boxes were made of 6061-T6 aircraft aluminum plate, as they are now. Both the front (with the fins) and the rear plates were done on a programmed milling machine. The center section was fabricated by using 1/4" plate and welding half pieces of 1/4" wall tubing together, to form the inside of the gear box cavity. Then the first of the rims were welded in place, followed by the addition of each of the 3 fins welded in. After the second rim was welded in place, the unit was placed on a fixture and machined to the final dimensions. It was a time consuming, long and arduous task, to say the least. It took much too long to produce a finished assembly, but it was better than cast, so CNC.

CNC means that a computer controls a large milling machine. The spindle, like on a drill press, only goes up and down. The table that the part is mounted to, is controlled and is moved to the proper position by the computer. The accuracy is phenomenal, less than one tenth of a thousandths of an inch.

All of the data on each of the pieces that comprise the entire unit, of the gear box, was entered into the computer. The center section, for example, is made from a solid block of aircraft aluminum. A cutter about 3/4" in diameter is used to cut the material for the roughing . It moves down and is turning at a high rate of speed. Cooling liquid is ever present, spraying from all angles, at the cutter bit. Down into the solid block of aluminum. Slowly moving, contouring the inside and outside shape of the gearbox. With a cutter change, the 4 fins are cut around the outside, which give the unit nearly 50% better cooling than the welded sections. Chips are being thrown in all directions, but fall harmlessly to the base of the unit, which is enclosed with a wrap-around see-through window that is between the machining and the operator.

The word 'shoe box' comes from the compact size of this assembly. It is 6.5" wide, slightly under 10' high, 5.25" thick and 8" from the 1/2" mounting plate to the prop flange. It will literally fit into a box for shoes!

Race car drivers have used quick-change gears for years, without a failure when installed correctly.

The patent application was for a "QUICK CHANGE GEAR REDUCTION UNIT FOR AIRCRAFT". The gear box for race cars are bigger and bulkier, which makes them heavier and they are cast. The front and back covers have gaskets. Gaskets cause problems. They can be tightened unevenly and cause the alignment to be off on the bearings. This can cause gear, bearing and seal damage. Then as the cover is subsequently re-tightened many times, the clearance from front-to-back is less and less, which causes heat and drag (friction) and causes loss of power to the output. Not to mention the high whine it causes when the whole package is not together correctly.

The Barnett 'shoe box' gear reduction assembly does not use gaskets! No gaskets! The sealing is all done with 'O' rings. The front cover, or rear cover can be removed and re-installed without changing a thing.

The surface of each plate has a groove for the 'O' ring. As the plates are secured, the 'O' ring is the sealing agent between the two surfaces. This type of seal is designed to withstand 1500 pounds of pressure. The other outstanding feature of using this type of seal, is the fact that there is never an alignment problem. The plates are aligned with dowel pins and when the unit is assembled, the pressure of the six 3/8" heat treated through-bolts will maintain positive pressure and alignment to the engine mounting plate.

The input shaft is sealed on the rear with a standard lip seal. The idler shaft bearing is open when the gear box is not mounted to the plate, but has an 'O' ring , slightly larger than the bearing, resting in a groove on the rear plate of the unit. This causes a positive seal between the gear box and the mounting plate. The bearing for the front of the idler shaft is inside the front cover, so it doesn't have to be externally sealed. The output bearing is a special double row heat treated and double sealed unit. It is fastened to the front cover by (3) 1/2" special heat treated bolts. There is an 'O' ring between this unit and the front cover and spacer.

With all of the features this reduction unit has, it is easy to see why it has become so popular. The mounting system to the engine is very straight forward. Behind the 1/2" aluminum mounting plate is the drive plate. It is part of the flywheel, as a unit. No shock is transferred back to the crankshaft from the prop output, or the input shaft. The shock unit has heavy duty springs around the input spline drive, and supply the transfer of power from the engine to the input of the gear box.

The 10 pound flywheel is specially constructed to give a means of starting and at the same time having enough mass to run smooth at all engine speeds. The engine can run without a propeller bolted on.

This gear reduction can be attached to almost any engine. However, at the present time, our efforts are limited to the Subaru EJ 22. We purchased new engines from the factory and we sell the engines complete, with the Barnett gear reduction unit installed, as a package from the firewall forward for $7000.00! This includes the entire fuel injection system with computer control, wiring, fuel pump, exhaust pipes w/ BAM. muffler and the isolation engine mount. Connect the fuel, battery, radiator, wires and it is ready to run. Put your prop on and it is ready to fly. All engines we sell are run on a test stand and are ready to go. We do have new short-blocks, that do not include intake manifold or injection components, which may be purchased as is for $3500.00, in the event you want to experiment on your own.

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