AutoPRSUs engine discussion

Discussion in 'General Auto Conversion Discussion' started by pfarber, Aug 29, 2019.

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  1. Jan 13, 2020 at 5:02 PM #161

    PMD

    PMD

    PMD

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    Anyone Can build a gear. VERY few can build a good one. A lot fewer still can meet the demands of gears in a redrive, especially on engines that have torsional resonance issues (i.e. two cycle singles and twins and four cycle up to 4 cylinders). Did a bunch of gearbox testing for one of the very best gear makers on Earth, and still had failures (in medium duty trucks).

    BTW: had lunch with a friend who used to build RR turbines. What he/they went through in machining parts was far beyond what your wildest dreams/nightmares could imagine.
     
  2. Jan 13, 2020 at 10:52 PM #162

    Lendo

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    Mulla- anyone can make gears anyone can pick a ratio,what their made from, how good is the tooth profile designed for what RPM and how long will it last, is entirely a different story . Then there's the housing and it's needed strength to cope with prop loads and Power loads, not to mention the bearings considering Thrust loads, then there's the cooling/ oiling considerations. Then there's the Torsional Vibrations issues, that must be handled with a damper - of a type suitable.
    Get that all sorted, then your right to go - get it wrong and you might imagine the result.
    George
     
  3. Jan 13, 2020 at 11:22 PM #163

    pfarber

    pfarber

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    Wow I mis-remember that big time. I was sure it was a certified. The procedure they go through doens't seem to bad, but I don't think the FAA would do this for a 172.
     
  4. Jan 14, 2020 at 3:47 AM #164

    mcrae0104

    mcrae0104

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    Better not tell the FAA about this one then...

     
  5. Jan 14, 2020 at 4:20 AM #165

    pfarber

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    Category: Exhibition

    So its not really something useful.

    Experimental Purpose of Exhibition (§§ 21.191(d))

    "This purpose includes exhibiting the aircraft’s flight capabilities, performance, or unusual characteristics at air shows, fly-ins, and similar events; for motion picture, television, and similar productions; and for the maintenance of exhibition flight proficiency, including (for persons exhibiting aircraft) flying to and from such events and productions."

    I think this is a significant difference from what E/AB which allows passengers and 'free flight' not linked to an exhibition.

    Here is the 'Certified structural parts are not allowed' rule of 21.191(g)

    f.Type-Certificated Aircraft. Altering, repairing, or rebuilding type-certificated aircraft constitutes maintenance of a type-certificated aircraft under part 43, not fabrication and assembly of amateur-built aircraft. This policy has been in effect since 1952 under section 1.74-3 of the Civil Aeronautics Manual (CAM) 1, which specifically states, “structural components of other aircraft may be used [for amateur-built aircraft]; however, it is not intended that this provision be used to avoid obtaining approval of major alterations to aircraft previously certificated in another category.”

    Without knowing the hoops they had to jump through, its a little disingenuous to say 'you can do it too!' because you really don't have a useful aircraft.
     
  6. Jan 14, 2020 at 3:05 PM #166

    Air Trikes

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    Almost nothing to add.
    SPG systems are in production from 2003, about 1500 units have been made, we tried this and that, we were making mistakes and improved these systems, we know this is not easy thing to make a good reliable gearbox for an aviation conversion. I'm glad most of you understand this.
     
  7. Jan 14, 2020 at 7:55 PM #167

    pfarber

    pfarber

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    I don't believe that gears for AC are especially exotic. Take a crankshaft gear from a Lycoming. This one gear is several thousand dollars. Sure its' NDTd and higher tolerance, but its not made of super exotic material or some spaced based manufacturing process. They really are not. Can you use 'off the shelf' gears? I'm sure you could if you inspected it first.

    If any of the PSRU manufacturers are here, post your gear specs and lets see.

    I hate to do the 'car analogy' but how many differentials/transfer cases/trannys go 100,000+ miles without even an oil change.

    I'd happily change gears every 500 hours (10 years for the average pilot) to get the cost of the PSRU to a sane level.
     
    mullacharjak likes this.
  8. Jan 15, 2020 at 7:01 PM #168

    rv7charlie

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    Exhibition Category is actually quite useful; virtually all the foreign-built (and many USA-built) warbirds are flying in EE category, as are many foreign and USA built acro aircraft. At one time, 'proficiency' flying was limited to a 300 nm radius around the home airport, with no landings anywhere else, and notice had to be given for each time the a/c was 'exhibited' at an event. But the rules changed many years ago. Many EE owners these days just fax to their FSDO, at the beginning of the year, a list of all the airshows/events that are scheduled for the year. Any non-event flying they do is for 'proficiency', and the 300 nm/home airport only has been removed. The effect is that EE category *operates* in virtually identical fashion to Homebuilt category.

    The Robinson V8 site has a page that details the EE process pretty well. You basically need to be doing something new/different with the plane that is worth demonstrating or 'exhibiting', to get it into the category. I've explored the idea with my airpark neighbor who is an FAA FSDO employee, and it really isn't very complicated to do. Just remember that the old 172 will never again be on the rental line, or carry freight ( ;-) ) again.

    Charlie

    edit: I think that you'll find that the quoted paragraph 'f' was written to prevent moving a type-cert a/c into *homebuilt* category, by 'assembling' a stock set of type-cert wings, tail, fuselage, etc into the same a/c, but calling it 'homebuilt'. Note that it does allow the use of cert components. I believe that the context for that paragraph is the '51%' rule for homebuiilt category; if you use a type-cert set of wings, for example, you get zero credit for wing building tasks. If you gather up all the various bits, then you get zero credit, though homebuilt certs have been issued in the past for just such things; I know of a Taylorcraft that was rebuilt with clipped wings & flown as a single seat a/c, and the FSDO issued a homebuilt cert for it. Wasn't supposed to, but did.

    Charlie
     
    Last edited: Jan 15, 2020 at 9:18 PM
  9. Jan 15, 2020 at 9:32 PM #169

    Lendo

    Lendo

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    pfarber,
    I'm not a Gear, Transmission or Harmonics expert, but I listen to people who are. In layman's language what's required is, good gear steel, right tooth profile with tip relief, right tooth count for the RPM, right hardening and tempering process, FEA of the Housing under load with right bearings and tuned for the harmonics with the right damper.

    Anything else is a risk taking process and I would hazard a guess every PSRU manufacturer, has had more than one prototype and the costs associated. To use one without prior extensive testing is compounding the risk.

    Do yourself a favor and study Gear Design and Transmission theory, then ask more advanced questions.
    George
     
  10. Jan 16, 2020 at 2:56 PM #170

    Neal Scherm

    Neal Scherm

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    The devil is not in the gear...
    It's ALL about harmonics. If you don't harness the power pulses adequately, it doesn't matter if the gears are made out of Vibranium. Yes, the material and hardness matters. Yes, the cut and relief matters. Yes, the ratio matters. However, the power pulses of a high reving 4 stroke or just about ANY 2 stroke will destroy a PSRU faster than you can say MAYDAY. Usually under full load on climb out. ASK ME HOW I KNOW!!!
    I can understand a persons misguided notion that "it's just a transmission". Nothing could be further from reality. A propeller is a HUGE flywheel. It doesn't stop and start again well. The engine is doing that. a LOT. SOMETHING has to be installed between the two. EVEN the lowly 'ol Rotax "B" box has a ratchet mechanism in it that requires ROUTINE service.
    If you can overcome the harmonics, the gearing is a much less high mountain.
    I have helped design several different PRSU's. Some that were successful and others were painfully not. After seeing first hand the totality of the project, I am letting the experts provide mine.
    A rotax "E" box for my Briggs and an Aeromomentum box for SOLO.
    If anyone decides to "roll your own" design on something as functionary as a PRSU, I wish them success and feel for their heirs... Better minds have tried and died.

    Fly safe,
    N
     
  11. Jan 16, 2020 at 9:14 PM #171

    Lendo

    Lendo

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    Neal-S, Agreed!
    That's what I like about Bill's new design of the the Internal Spur Gear type PSRU. Powersport spent hundreds, even thousands of hours designing testing before they were happy with reliability and longevity with their design, they had their failures and broken gear teeth, but not just through Torsional Vibrations. Expansion and contraction are issues on the mating of teeth and their alignment, with the Spur Gear type and are also major considerations, as is cooling. Don't forget the heat issues considering metal expansion :).

    The Planetary type PSRU do have additional clearances to cater for self centering the Planet carrier and caters for expansion, but this allows for additional Lash, which it would seem exacerbates the Torque fluctuations.

    This is just the tip of the issues regarding geared PSRU's, but their the best for high powered aircraft say over 100 hp to 300 maybe even 400 hp, then there's another step up to more sophisticated designs.
    George
     
  12. Jan 16, 2020 at 11:22 PM #172

    Neal Scherm

    Neal Scherm

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    I used a RWS unit on a rotary engine. Wouldn't try it on a 4 stroke... The rotary seemed to be less abusive to it for a couple of reasons. One was the differences in the harmonics. BIG difference. The other was the high gear ratio. More tooth engagement to spread the load. Bearings were the weak link. Ford never designed that planetary to spin 8500 :)
     

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