ALMA MATER STUDIORUMUNIVERSITA’ DI BOLOGNAFACOLTA DI INGEGNERIA

DEGREE IN MECHANICAL ENGINEERING

Graduation thesis by:

Simone Paolizzi

Supervisor:

Chiar.mo Prof. Ing. Luca Piancastelli

Academic year 2010-2011

Session I

STUDY OF AN AERONAUTIC PLANETARY GEARBOX FOR A COUNTER-ROTATING PROPELLERS PROPULSION SYSTEM

GOALS

STUDY OF A PLANETARY GEARBOX

- Variable step counter-rotating propellers

- Reduction from 6000 rpm to 1000 rpm

- Engine 1300 JTD 150 cv

RELIABILITY

SIMPLICITY

LIGHTNESS

Gears sizing

Components studying

It has been used the Solid Edge v.18utility ‘Spur gearing Component’

All the components have been sized andverified thanks to SolidWorks simulation

DESIGN DEVELOPMENT

Sun gear Planets

Ring gear Carrier

By vincolating or moving the elements in different waysit has been possible to obtain several working typologies

TWO DOFs

1 crankshaft:6000 rpm

2 propellerhubs:

1000 rpm

-1000 rpm

Only the carter is bolted to the engine basement

PUSHING PROPELLERS

CONTRACTING PROPELLERS

1250 rpm 1000 rpm

The speed of the propellers may be chosen between1250 rpm and 1000 rpm

due to a better gears proportions: 1000 rpmhas been chosen

Ring gearNumber of teeth : 77

Pitch diameter : 115.5 mmFacewidth : 26 mm

Sun gearNumber of teeth: 31

Pitch diameter: 46.5 mmFacewidth: 24 mm

PlanetNumber of teeth : 18

Pitch diameter : 27 mmFacewidth : 24 mm

GEARSModule = 1.5 Pressure angle = 20°

PLANET

Straight-sided splinesconnect to the driveshaft

Thrust bearing lock

CARRIER’S CLUSTER

Solution with pivot and internal bearings

Solution without pivotwith external bearings

The external bearings solution reduces the number of elements and consequentlyIt also increases the SF. In addition it has removed the wearproblems.

PLANETARY CLUSTER

Planet

Angular contact ballbearings SKF 7205

Seeger ring A25

Seeger ring J52

INTERNAL SHAFT HANDLING SYSTEM

Carrier

Thrust bearingSKF 51201

Combined needle rollerbearing SKF NKX-40

Roller bearingNK 28/20

Propeller’s flange

Lock nut KMFE6

EXTERNAL SHAFT HANDLING SYSTEM

Ring gear

Screw M5 x 15

Combined needle roller bearing SKF NKX-70

Roller bearing NK 75/25

Propeller’s flange

Lock nut KMFE11

CARTER

The carter is the only elementbolted to the crankcase and it isthe less stressed; since thepropellers are counter-rotating ,the gyroscopic moment is inequilibrium.For this reason only axial forces

act on the carter.

USED MATERIALS

Gears: steel 15NiCr13

Carrier, propeller’s flange, external shaft: titanium alloy Ti6Al4V

Carter: aluminum alloy 2024

FEM ANALYSIS

PlanetDeformation Scale Factor : 350 S.F.= 5.8

Sun gearDeformation Scale Factor: 492S.F.= 8.7

All the components are verified thanks to Solidworks simulation, which is a FEM software

CarrierDeformation Scale Factor : 28S.F.= 2.6

Ring gearDeformation Scale Factor : 2768S.F.= 6.7

External shaftDeformation Scale Factor : 651S.F.= 5.9

CarterDeformation Scale Factor : 199S.F.= 10

CONCLUSION

RELIABILITY The lowest safety factor is 2.6

LIGHTNESS

SIMPLICITY

ALL THE GOALS HAVE BEEN REACHED:

Due to a new planetary gears constructivesolution it has been possible to decrease theelement’s number in favor to a better simplicity

The whole gearing mass is 7.667 kg

FUTURE DEVELOPMENTS

Whereas the minimal safety factor is near to the straight-sided splines it is possibleto increase the reliability by substituting involute splines in place of straight-sidedsplines; in this way there is a larger range of gearing lightening.

The FEM check has been executed thanks to Solidworks simulation. In order toobtain Simulations closer to reality I suggest to use more flexible FEA softwares.

It might be interesting to have a second look to the project considering also theeconomical aspects, that in this work have not been considerated.