More Thoughts on PSRUs

Discussion in 'General Auto Conversion Discussion' started by rv6ejguy, Jul 4, 2014.

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  1. Sep 16, 2015 #201

    rv6ejguy

    rv6ejguy

    rv6ejguy

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    Given the typical auto OEM validation testing for engines and transmissions, safe to assume these are made from heat treated and hardened alloy steel. I've never seen iron gears in any automotive transmissions in the last 40 years. I think the turbo four was around 145hp in these cars as was the V6 option.
     
  2. Sep 16, 2015 #202

    jac

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    Definitely Steel material for the final drive gearset. Strength does not concern me. Consider this. V6 2.5l has 156ft/lb torque @ 4800rpm.
    Gear ratios in manual trans run as follows- 3.3/1 first, 1.833/1 second,1.31/1 third & 1.03/1 fourth. Therefore if we multiply 2nd and 3rd by the torque figure we get ~286 ft lb in 2nd & 204 ft lb in 3rd., No point in using 1st in the calc as tires will seldom hold 100% traction in low gear.
    Remember the final drive in the car is a 3 gear set and if you split that the first smaller set is approx. ~2/1+ ratio so that 286 or 204 ft lb is what the smallest final drive gear has applied to it, therefore the middle gear will apply 572 ftlb in 2nd & 408 ft lb in 3rd to the large gear. The middle gear is approx. 4" dia, larger than the pinion on the Ballistic gearset above. That's back of a benchtop calc, but its enough for me to feel it should do the job. I would be happier though if the helix was handed the other way.
     
  3. Oct 18, 2015 #203

    TXFlyGuy

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    A bit late to jump in here, but wondering how the Autoflight / Titan PSRU's fit into the discussion? Never heard of any issues, and they are running 300 hp plus in the applications. What is the determining factor on power limits...is it horsepower, or torque?
     
  4. Oct 18, 2015 #204

    rv6ejguy

    rv6ejguy

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    Torque, propeller vibration characteristics and MMOI (propeller inertia) are the big deals. One Autoflight failure down under on a T51 was due to using an untested, high MMOI prop with apparently dangerous resonances. Two failed in short order. Stay within the torque rating, prop inertias and have a prop vibration study done before you use a new combination.
     
  5. Oct 19, 2015 #205

    quickcut

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    Good Day all

    Hope this is in the right place and not to much of a hi-jack . Attached (hopefully) is a thesis/report of an automotive conversion documented with it's PSRU. I found it on the net once , but have never been able to re-find it.
     

    Attached Files:

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  6. Sep 9, 2016 #206

    blane.c

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  7. Sep 10, 2016 #207

    wsimpso1

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    The author designed and built a substantial PSRU with some startling design omissions in this thesis:

    No review of the origin of loads on the PSRU:
    No listing of the loads on the various components;
    No review of loading of the support structure for the pulley's and shafts;
    No check of Eigen Modes and Frequencies.

    A review of the origin of loads would have produced a list of load circumstance, load types and relative magnitudes that would be applied to the PSRU during operation. This list would have to include events of cranking, firing, acceleration to idle speed, acceleration to taxi speed, acceleration to take-off, climb, cruise, descent, and landing speeds, and all expected maneuvers. It would then also produce an operational list of rpm, engine and propellor torques, bending moments on the shafts, mount reaction loads of the PSRU to the engine and the engine to the airframe mounts. Significant in it absence is estimates of the torques and bending moments applied to the system by P-factor and gyroscopic precession from the propellor.

    A listing of loads on the various components would have commenced with the external loads listed above and proceeded to find the defining load/rpm circumstances for the components. A more substantial review of loads on more of the components would result and could drive more targeted analysis. The loads developed in many of these parts will likely be much more substantial than those presented.

    A review of the support structures loads would have resulted in analysis of the various attaching loads and an independant review of component loads to backup other analysis of the system. Offset loads on bearings, shafts, bolted joints were not discussed, nor where there any life analysis of the bearings conducted.

    A check of Eigen Modes and Frequencies is essential in powertrain design, as encountering resonance within the flight power regime can be catastrophic to both the powertrain and the airplane.

    In particular, the report indicates to this engineer that this engine/PSRU/prop has not been designed to keep damaging resonance out of the operating range, nor have the components been designed to handle likely pitch and yaw rotations based upon anticipated flight envelope.

    Complete? Fractional at best, with some huge misses of important issues to a gadget that is flight critical.

    Billski
     
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