Item 0584
MAKE: Control - Power Train - Soft Start Clutch - Assembly - Final
Drawing:
Using Poly-V belt
In the Robinson R22, where, once the rotor starts turning, the belt is moving past the slipping sheave and heat buildup is distributed over the whole V-belt. In this design the heated belt does not move on and allow a cooler portion of the belt to come in contact with the slipping sheave. Maybe use a wider belt and distribute the heat over a larger area.
2 independent Poly-V belts - L section
There are 2 separate Poly-V belts.
They are wrapped around the secondary drive's internal ring gear and attached housings.
The T-1 end of both belts is permanently (unless engine synchronization by mechanical belt movement is used) attached to the corner posts.
The T-2 ends of each belt are attached to the locking clamps that in turn are connected to the corner posts.
The belt should provide much greater friction than brake band (item #0438) method because
a) The material is rubber.
b) The surface area is greater per width of belt, because of groove (accordion) arraignment.
c/ The belting is designed to grip.
|
|
Torque into secondary reduction |
= 71.7 lb-ft |
|
|
Sun to Ring gear ratio |
x 2.5 |
|
|
Torque on the Ring |
179.25 lb-ft |
From Speed/Torque/HP calculator & Browning p. D-14 Table 1 it looks like the maximum torque for 'L' belts is;
|
|
50 hp |
1800 rpm |
< 147 lb-ft |
|
|
30 hp |
900 rpm |
< 175 lb-ft |
|
|
25 hp |
700 rpm |
< 187 lb-ft |
The slower the speed the higher the allowable torque.
The pitch diameter is 6.65" and at 200 rpm & 6.65" dia. the allowable torque will be 16 lb-ft / rib.
197.175 / 16 = 12.32 ribs required
At 0 rpm it will probably be over 20 lb-ft / rib, which means that 10 ribs will do. This does not take any shock loading into account.
Note: Static friction is greater than sliding friction and the sliding friction only takes place during partial load (when collective is 0 degrees and rpm is not at running RPM.
The minimum recommended diameter for An 'L' sheave is 3".
The sheave face width for a 10-groove 'L' is 2-7/16".
The belt width for a 10-rib 'L' is 1-7/8".
Could easily use a 12 rib belts if need be. Maybe not!
The belts would be anchored to the frame's vertical corner posts.
Only one belt has rotational adjustment; for synchronization.
YES; If electronic engine synchronization does not work or until electronic engine synchronization developed. Design a device that allows one of the above soft-start belt assemblies to be rotated up to 50 degrees around the mast. See: [DESIGN: Control - Power Train - Engine Synchronization - by Soft-Start Rotation] 0746. Note the "sheaves" may creep on the belts over the course of a flight and there may not be enough adjustment left to correct this after the initial timing adjustment has been made.Option - Using M section belt
The minimum sheave diameter for 'M' belts is 7". 6.65" is close enough, in fact the belt's stiffness may help keep the belt away from the sheave when brake is not activated.
@ 200 rpm & 7" dia. the allowable torque will be 36 lb-ft / rib
197.175 / 36 = 5.5 ribs required
@ 0 rpm it will probably be over 50 lb-ft / rib, which means that 4 ribs will do. This does not any take shock loading into account.
The belt width for a 4-rib 'M' is 1-1/2+".
If they made one. Consider slitting an 8-groove belt into 2 4-grooves.The belt width for a 6-rib 'M' is 2-1/4".
Method of Operation
Both of the band brakes have their own belts and actuation device. This actuation device will have operating characteristics similar to a De-Sta-Co clamp
[Item 0750].Optional Idea:
Could one ring gear have the brake band for starting the rotor rotation (w/ wide belt). The other ring gear could have a worm and wheel arraignment for timing its engine with the engine of the previously locked brake band's engine? The 2nd engine will be running faster since it ring gear is not locked. Its ring gear will have to take half of the other drive-trains load before the ring gear stops turning and the worm can be engaged with the wheel
Load on bearings:
The more degrees of belt wrap there is on the outer ring gear;
Back to top | Return to Home Page
Last Revised: May 16, 2000