Looked at the web site, read the specs, still want to know a few things, and here seems to be a good place to get the info out:

First, what is the rated gyroscopic reaction moment for this system? The prop is a very large inertia being spun and then there are yaw and pitch rotation from the airframe. Even if the drive's propshaft and bearings were not sized with this in mind, some simple math will produce loads due to unaccelerated loadings and to yaw and pitch rates. A trip to the bearing catalog would then tell us how long the bearings can be expected to live. Another set of junior level ME calcs will tell you if the prop shaft can be expected to live long (or not) under the same loads.

Second, Do you have limits on inertia of engine side and prop side inertia with this system? These two inertia are important to keeping resonance out of the operating range, and I would expect that you might have set limits on one or both of these inertia.

Third, what are the main resonant modes and their frequencies? With hundreds delivered, shouldn't you have at least run a torsional vibration survey on some popular engine and prop combinations to see that resonance is out of range and damaging vibration does not exist in the operating range?

Billski

**Ace Aviation Redrive design calculations**:

To the customer (Or Wsimpso1) -------- You may one day be using the redrive on a permit aircraft and get a request for calculations from an approval body.

This means my initial rough numbers need updating to suit the revised structural design of the redrive. It assumes a 3” or 75mm deep propeller boss and 1620mm overall diameter.

To cover the liability issue I’ve gone over the top with the propeller out of balance at 10 grams, (.352 ounce) this will cover loss of a tip for instance from a stone, and a pilot would soon land his machine at the earliest opportunity with 56.61 kilos of force shaking his aircraft around, provided the engine mounting coped.

To recap:-

Up to 5 times 10 to the eighth power cycles, allowable stress in 6082 (T6) alloy at 280N/mm² is the yield times 0.38.

Yield is 280N/mm², so 280x0.38 is 106.4N/mm²; this is the ‘fatigue limit’ limit we should not pass.

http://www.roymech.co.uk/Useful_Tables/Fatigue/Fatigue.html
5 x 10 to the eighth is a life of 4,167 hours at 2,000rpm. At 100 hours a year this is 41.67 years.

Belt pull check:- use Rotax 503 power levels:-

50Nm torque on 100 dia pulley = 50N/0.05 radius = 1kN or 102kgf

Acts at 44.8mm away from C/L of plate; B.M = 1000x0.0448=

__44.8Nm__ or

__44,800Nmm__
Add centrifugal force; assume 10 grams out of balance propeller (damage to tip on departure)

http://www.calctool.org/CALC/phys/newtonian/centrifugal
*Radius:* 810

2500rpm

centrifugal force = 555.165N (kg.m/s²) or 56.61kgf

Acts at maximum 144.7m away from backplate

so added BM = 555.165x0.1447m or

__80.33Nm,__ or

__80,332Nmm__
Total BM = 80.33 + 44.8 = 125.13Nm = 125,130 Nmm

Taking moments about prop boss assembly and redrive backplate

1) Max BM at narrowest point of plate= 144.7/53x125.13=341.634 Nm

2) Max unsupported BM at base of prop boss = 144.7/43x125.13=421.07 Nm

1) Section Modulus Z = BD²/6 or 2x32 x 16²/6 = 2730mm³

Material stress = BM/Z. = 125,130/2730 =

__45.83N/mm²__
2) Section Modulus = 96 x 16²/6 = 4096mm³

Material Stress = 125,130/4096 =

__30.55N/mm²__
__Bearings __The way bearings are rated is full load for one million revolutions, or about 6-7 hours running at full 2,500 propeller revs, however…

The belt pull at full throttle is around 90 kilos, tension around 90kilos and centrifugal force 5.24kilos so under 200kilos total at worst full throttle, at half throttle cruise maybe half that figure.

Capacity of the bearing is 11.2kN or

__1,142 kilograms each__, as there are two bearings total capacity of redrive bearing assembly is 2,284 kilograms.

So bearings are

__eleven times__ stronger than they need to be, the 6005 -2RS (rubber shielded) are totally sealed and are sheltered inside the assembly so doubt contamination is an issue.

As you can see, stress imposed is under one half of the maximum the alloy can accept; however as deflection of the plate causes misalignment of the pulleys, this is a desirable situation.

Hope that this explains a few things.