Item 1014

DESIGN: UniCopter ~ Power Train - Assembly - Engine Reversed, All Gear

For use with Rotax 912 and 914.

Drawing:

 Ideas:

Locate the axial clutch or rework the Rotax clutch at the aft end of the engine.

Drive cooling fan from the aft end of the new propeller shaft.

Reverse the air intake manifolds and carburetors so that the air cleaners are facing aft.

The lengthened propeller shaft may absorb the engines spikes.

Another Idea:

Replace the two engine gearbox's spur gears with roughly 10 degree miter gears, so that the longitudinal shaft heads forward and upward from the engine to the X-shaft. This will give room for bearings, seals, centrifugal clutch etc.

 Possible Disadvantages:

Can the extended propeller shaft pass over the top of the crankshaft.

 Advantages:

Total of 8 gears. Three gear sets between engine and each rotor.

 Arraignment of Components:

Engine:
  1. Primary Reduction: 2.43:1 ratio. Item 0945
  2. Torsional Shock Absorber: Could use the one in the Rotax gearbox or the twisting of the lengthened propeller shaft.
  3. Right angle transfer: Miter gearbox. Ratio 1:1 or dependent on reduction in engine gearbox and RRPM requirement.
  4. Soft-start: Consider Rotax's or SMC Axle Clutch, Item 0751 , or Zanzottera Item 0975
  5. Overrunning clutch: Located on crossover shaft, near mid location. Item 0524, if strong enough.
  6. Final Reductions & Rotor Synchronization: Two 81-degree, 3:1 ratio, spiral bevel gears.

Rotors:

Rotor Brake: Located on x-shaft.

 

 Notes:

This is designed for the Rotax 912 or 914 engine with modified propeller shaft.

The gearing may be 2.66:1 on the final, 1.06 on the secondary and 2.43:1 on the primary for a total of 6.85. 5000 / 6.85 = 725 RRPM. Is this is a little too fast? Consider making the mid-gearing with a ratio slightly greater than 1:1 or run the engine at a lower rpm. In other words, derate the engine.

The weight of the engine is 125 lbs and its CG is 13" behind the masts. This brings the craft's CG close to the center of the masts and increases the GW to around 735 lbs.

 Notes re Spiral Bevel Mid Gear Set:

Arrow Gear Calculations:

for diametral Pitch of 6 and 24/24 teeth. 4" pitch diameter

For 1.06:1 ratio, the other sprocket should have 25 or 26 teeth.

The following is too light for the Rotax engines. Consider using Pitch 05 Arrow 1:1 ratio

 

Horsepower:

85.4

hp

 

Pinion Speed:

2056

rpm

 

Pinion Working Torque:

2618

in-lb

 

Estimated Rated Pinion Torque:

5236

in-lb

 

Catalog Rated Pinion Torque:

2991

in-lb

 

Catalog Pinion Pitch Diameter:

4

in

 

Pitch Line Velocity:

2155

ft/min

 

Dynamic Factor:

0.792

 

 

Allowable Pinion Torque:

2368

in-lb

 

Service Factor:

0.905

:1

 

 Notes re Secondary Spiral Bevel Gear Sets:

Two 81-degree, custom spiral bevel gears. See B301. I think that these gears are applicable to Assemblies 0925, 0946 and 0999. Except the ratio has been changes to 2.66:1

 General Thoughts:

 Center of Gravity of Engine:

 

X = -13"

Z = 8.75"

Y =

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Last Revised: January 5, 2002