B011

B011.html

DESIGN: SynchroLite ~ Power Train - Secondary Reduction (planetary drive)

See: OTHER: Mechanical - Gear - Planetary

Gear Calculation Note re Outside Helicopters and SynchroLite:

Hamilton's spiral bevel gear calculations have been compared to Arrow's spiral bevel gear calculation, using a 3:1 ratio, 6 DP. gear set. Both Hamilton and Arrow are based on a Service Factor of 1. The results are;

	Arrow HP	Hamilton Durability HP	Hamilton Strength HP
	83.3	98.4	80.0

The following settings were use for the Hamilton calculations;

	Allowable Contact Stress:	Rockwell C 60 min.
	Allowable Bending Stress	Rockwell C55 min.
	Elastic Coefficient	Pinion and Gear - Steel
	Load Distribution Factor	One member straddle mounted

Since the 2 are very close the Hamilton calculations used to design with should be correct.

Outside Helicopters

Revolution

OTHER: Helicopter - Outside - Single (1seat) - Revolution - Mini-500 ~ Transmission

K-MAX

There are 5 planetary gears in their planetary gearbox. The pitch is 6 and the ratio is 4.138:1. The teeth are: 29 tooth sun; 31 tooth planets and 91 tooth internal ring. 29 + 91 = 120teeth / 5planets = 24 i.e. whole number

UltraSport 254/331

Transmission comes from Arrow Gear, Chicago.

	OD.	= 6-1/2"
	Height	= 7"
	Input shaft	= 5/8" dia.
	Output shaft	= 1-5/8" dia. w/ 3/4" bore.
	Weight	= 25 lb. +/-.

See sketch in UltraSport file folder.

American Gear Manufacturer Association Class 11 Ground standards from 9310 carborized steel.

1^st and 2^nd reductions have the same pitch diameter. It is probably a diametral pitch of 12 since a 60 tooth ring gear (as noted below) will have a pitch diameter of 5.000" whereas a diametral pitch of 10 gives a pitch diameter of 6.000".

Face width of 1^st is half of face width of 2^nd.

Tooth counts below are from viewing video.

1^st reduction Ring = 48 teeth, Sun = 18 teeth, Planet = 15 teeth (calculated) Note this means 3 planetary gears.

gives 3.67 : 1 primary reduction.

2nd reduction Ring = 60 teeth, Sun = 30 teeth, Planet = 15 teeth Note this means 3 planetary gears.

gives 3 : 1 secondary reduction.

FORM: Gear - Spur - Horsepower (Hamilton)

The specifications on the Sportscopter 254 transmission are correct or very close to it. The form on the left uses the same criteria as is use to determine the correct gears for the Synchropter therefor comparisons can be made.

Sportscopter literature says that their transmission is rated at 60 horsepower continuous operation.

Looks like 4 planetary gears in both stages.

Durability 4 * 10.3 = 41.2 hp. 41.2 / 60 = 0.6866 Service factor

Strength 4 * 16.0 = 64.0 hp. 64 / 60 = 1.066 Service factor

October 9, 2001 ~ After re-viewing the video, the face widths of the planet gears in the secondary reduction appear to be the same width as their pitch diameter. The face widths of the planetary gears in the primary reduction are definitely less than their pitch diameter. This means that the above calculations give too high a horsepower rating and the safety factors will be less.

With a face width of 1.25";

The Durability will be 8.6 hp * 4 = 34.4 hp. 34.4 / 60 = 0.57 Service factor.

The Strength will be 13.3 hp * 4 = 53.2 hp. 53.2 / 60 = 0.89 Service factor.

Gives 11.01 : 1 total reduction.

Literature says 12:1 ratio for the 254 and 331. The 496 has a 11:1 overall ratio.

The gearbox pictures show a ratio of 11:1

Video says rotors turn at 500 fpm. 500 * 11 = 5500rpm, 500 * 12 = 6000rpm

Planetary gears are straight tooth not helical.

Ultrasport pilots operating manual says:

	Minimum	Mean	Maximum
Engine RPM	5600	5895	6720 (114%)
Rotor RPM	475 (95%)	500	560 (112%)

Note: minimum and maximum are power on.

This gives a reduction ratio of 11.79:1. I have seen 11:1 & 12:1 mentioned.

Bell 206

Exact count of teeth on gears in planetary (secondary) reduction:- Ring = 99, Sun = 27,=, Planets = 35.

Access FORM: PT - Secondary shows the ring with 99 teeth, the sun with 27 and the planets with 36 teeth. This discrepancy in the number of teeth in the planet gear seems to confirm the comments of the person in Seattle and the article.

There are 4 planetary gears in their planetary gearbox.

The Seattle gear designer and the UTS gear software program say "The sum of the teeth in the ring gear plus the sun gear must be divisible by the number of planet gears". In the above 99 + 27 = 126 which is not divisible by 4. Maybe changing the planets to 35 teeth had something to do with making it work?

The pitch diameter of the ring gear is very close to 10-7/8". This would give a Diametral Pitch of 9 or maybe a Module Pitch of 3. The width of the ring gear is around 1" to 1-1/8".

Secondary gear widths;

The ring gear on the 206 is not quite as wide as the planetary gears and the planetary gears are not quite as wide as the sun gear. (Helicopter Maintenance; p.215). This sounds reasonable because of the different amounts of wear on the teeth of the different gears. It will also reduce the weight of the ring gear.

Bell 47

There are 6 planetary gears in both reductions in their planetary gearbox.

Housings:

See: OTHER: Mechanical - Casting [B275]

Calvert is the University of Maryland's entry in 1999 AHS student design competition

There are 6 planetary gears in their planetary gearbox. The pitch is 7.5 and the ratio is 6.706:1. The teeth are: 41 tooth sun; 22 tooth planets and 85 tooth internal ring. 41 + 85 = 126teeth / 6planets = 21 i.e. whole number

For sample of UTS Gear Software Program see http://uts.com/1161ex.html http://www.uts.com/

Synchropter

Possible Tooth Combinations:

Number of pinions	4	3 or 4	3 or 4	4	3	3 or 4
Teeth in Pinion	24	25	24	25	25	25
Teeth in Planets	16	17	18	19	25	24
Teeth in Ring	56	59	60	63	65	72
Ratio pinion to planet carrier	3.33	3.36	3.5	3.52	3.6	4

Note:- It looks like with the Bell 206 and in the UTS example program that the planet gear is then reduces by 1 tooth so that the operating pressure angle is increased to more than 20 degrees in the Sun/Planet mesh and to less than 20 degrees in the Ring/Planet mesh.

Back to top | SynchroLite Home Page

Last Revised: August 17, 2004