Direct drive SBC

Discussion in 'Chevy' started by Natty Bumpo, Oct 24, 2011.

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  1. Jul 2, 2014 #921

    akwrencher

    akwrencher

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    This is a great thread, and the debate drew out lots of great info for anyone looking to do any kind of V8 conversion. Best of luck on your projects. Keep us posted of course :)
     
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  2. Jul 2, 2014 #922

    Toobuilder

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    There have been a few V-8 RV-10's done. Most are SIGNIFICANTLY overweight. Make sure you do your homework.
     
  3. Jul 2, 2014 #923

    nerobro

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    I was under the impression that part throttle BFSC is greatly improved with higher compression ratios. Lycoming and Continentals already start off on the bad side of the compression ratio curve. This is why Saab was working on variable compression ratio engines before their latest blowup.

    Now i'm pondering the idea of an engine designed to run at 10k ASL...
     
  4. Jul 2, 2014 #924

    MARCVINI

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    Yup!!! I am pretty aware of that!!! The only way to solve the weight problem is by using a light PSRU (I am hooked to belt ones...) and a light (and good) FP propeller, à la CATTO. I count on having a 80 lbs weight loss over a typical Geared Drives (Bud Warren´s) instalation, wich could result in 20 to 30 pounds heavier an intalation in comparison to a 540 + FP propeller equiped RV 10. But I am still evaluating the possibilities. Money is an issue here...

    Marcvini
     
  5. Jul 2, 2014 #925

    crytes

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    from what I've seen a durable reduction drive capable of handling the same power will be about the same weight reguardless of weather it is a belt or gear. So it becomes a choice of preference. In my opinion the belt should be easier to fabricate so initial costs will be lower however belts are an expendable item so belt replacement over the life of the unit should be concidered. Also failure mode of a belt range to slipage to free wheeling prop. A gear drive requires accurate machiening so initial cost should be higher however with proper lubrication no new parts should be needed before TBO. Failure modes in gearboxes tend to progress from metal in oil through gear noise to free wheeling or locked up prop hopefully allowing some warning before catastrophy.
     
  6. Jul 3, 2014 #926

    MARCVINI

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    Aside from direct drive powerplants, wich are what I like most, here is what draws me to belt PSRUs: they are the only type that have lots and lots of FLYING examplaries, and doing it reliably and economically. Ben "Stol" Hass and the many Belted Airpower RV6s are the living (and flying...) proofs of that. Many Northwest Aero PSRU fitted aircraft too. Decades of good flying. The engineering behind them seems to be fully understood and belt quality is better than never, hence the Gates Poly Chain Carbon belts.

    As for geared PSRUs, most seem to have unsolved problems, regardless of the time they have been under test/experimentation: a. Ross from SDS seems to have been struggling with harmonics until very recently. I don´t know if he has already reached his desired goals in therms of taming those harmonics; b. the new Geared Drives owner seem to have changed the oil recomended for his units, from thick_mineral to thinner_sinthetic, under the argument that it is less foamy, and doing this after decades of Bud Warren´s preaching on mineral oil.

    That EPI ENG guy always preaches against belted and chained PSRUs, regardless of the fact that those are the only types of PSRUs that, at least in the alternate aircraft powerplant world, stood the test of time.

    I am not saying that the "concept" of geared PSRUs can´t work. The problem is that the engineering tasks that are necessary for them to "deliver" is, for the most part, out of reach of us, mere experimental aviation mortals.

    As for the main failure modes of belted PSRUs, I mean, belt and bearings longevity, the remedy is simple: instal new ones every two or three years. It is a simple, cheap and mind relieving task that anyone can do. Just as easy as changing a cam tooth belt of your daily driver.

    Ben "Stol" Hass´s "XXXX" signal is not in vain. IMHO

    Marcvini
     
  7. Jul 3, 2014 #927

    nerobro

    nerobro

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    Anyone else notice that geared factory engines all use gears, not belts? ;-) But that gets off topic. This is about direct drive.
     
  8. Jul 3, 2014 #928
    Gear reduction is just a mechanical exercise no matter what type of reduction someone prefers. If done correctly, all of the various methods will work. Some appear simplier than others, some heavier, some more rugged. Take your choice. To me, thing that one should first consider is whether an engine will produce "sufficient" or desired hp at a lower rpm and withOUT a reduction drive. If it does, then I see no reason for a reduction drive other than to alter the location of the thrust line when installed. If the particular engine in question does not fit that scenario, you must honestly consider whether to live with whats available or switch to another engine or add some type of turbo or supercharger.
    If someone does decide to go for the reduction drive unit, initially they will be running at higher rpms to create more power. That requires the reduction drive to be more beefy than power availbility in order to have a safety factor above the operating margin. Additional beef means more weight. At this point, you have added cost,complexity,and more weight than actually needed in order to have a margin of safety.You are operating the internals of the engine at exponentially larger stress levels. Engine life will be reduced and engine reliability may be reduced. With the selection of certain engines, you may have no choice but to run a reduction drive to have sufficient power. That usually applies to smaller engines. The thing is........one needs to decide what the overall engine package will weigh, and how much power it will produce per lb. Then look at the other factors for cost, reliability, and ease of construction. You also need to look at whether your desired airplane is capable of handling the power output of your engine. It does no good in an airplane to produce 300 hp is your airframe can only use 200. Just as the violent and sudden application of horsepower in a car or motorcycle my cause the front wheels to lift, a sudden over application of power in an airplane can cause uncontrollable results. Most of us "macho" A type personalities have grown up with the "more is better" mantra when it comes to horsepower. In an airplane, we need to temper our testosterone with some logical maturity.
     
  9. Jul 3, 2014 #929

    Toobuilder

    Toobuilder

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    Concerning the plan to run the RV-10:

    These are airplanes with a very wide operating speed range. They takeoff slow and cruise fast. This essentially requires a C/S prop. Sure you can throw a bunch of power at a very course prop, but that's hardly the most elegant solution. The other factor is the TAS limit on the -10. Even with a NA 260 HP Lycoming one has to be careful at high altitude not to bust the TAS redline. A belted LS-3 would be WAY too much power here. And do you really want to carry around the weight of a big engine, PRSU, and the cooling system to support, only to run around at part throttle?

    If anything, the RV-10 would benefit most from the direct drive V-8 discussed at length in this very thread. Still a bit heavy for the -10, but a better fit than one with a PSRU.
     
  10. Jul 3, 2014 #930

    MARCVINI

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    Good reasoning. It seems that we have a "short blanket" case here, Huh???

    I believe that a belt drive "reduced" V8 powerplant for the RV10, specially if the "crate" chevy LS3 were the engine of choice, would only make sense if one used moderate power settings, more specifically: a 1:1.43 reduction (à la Belted Airpower) and the engine spinning at 3800 max rpm, wich, by the way, is not so slow a reving but enough to make power without excessive heat to be cooled: that would put out about 580 ftlb torque at 2700 rpm, wich is enough torque to propel it decently with a FP propeller. Ben Hass´s beefed up Belted Airpower PSRU seems to be adequate for the aplication, and it is reasonably light, since it weighs in proximatelly 47 lbs, as per Bens scales. Let´s not forget that today we have those Gates Poly Chain GT Carbon belts, wich, altough expensive, are bullet proof.

    Given the "rumours" about the good performance of CATTO´s FP for the Lycoming 540 (505 ftlb torque at 2700 rpm), I believe that a similar propeller would be perfect for the aplication, and it weighs in at no more than 20 lbs.

    Such a not so "elegant" solution DOES make sense from a cost perspective, altough I agree that it keeps being "hardly the most elegant solution". Cost wise, I believe that it would be quite on par with a Glasair Sportsman with an inverted SBC/SBF engine, wich is my first airplane of choice.

    By the way: this discussion seems off topic at a first glance, but the subject is so wide that it is impossible to perfectly limit certain topics to their specific threads.

    Marcvini
     
    Last edited: Jul 3, 2014
  11. Jul 4, 2014 #931

    Autodidact

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    transmissability

    Sometimes I think we're all over thinking (or maybe under thinking?) this torsional vibration thing; it's still as important as we think it is, but we seem to put all the emphasis on merely avoiding resonance, when we should also reduce the amplitude of the input vibrations as much as possible. On the EPI website, as well as in books on torsional vibration, there is discussion of a principle called transmissibility. Transmissibility is a distinct mathematical connection between resonant frequency and the amplitude of the input vibrations. The farther away from the input vibration frequency that the resonant frequency can be put, the lower the amplitude of the input vibration (actually, the amount of force) that the driven system sees (propshaft/prop in DD, and that as well as the gear train in a PSRU).

    For example: If you have a 220hp v8, then the instantaneous torque is about 195% of the mean torque, or about 800 lb-ft. So you need a spring that can handle a maximum of 800 lb-ft torque. And, if this spring compresses angularly by, say, 15 degrees, to reach maximum capacity, then you have a spring constant of 800/15 = 53.33 lb-ft/deg. This is a low spring constant and will result in a very low resonant frequency. The connection between the low resonant frequency, and the low transmissibility of the input torque amplitude can be illustrated like this; at operating rpm, the angular displacement (acceleration/deceleration) of the crankshaft away from a constant velocity is about 1 degree or so, and the propeller is like a large flywheel with a large moment of inertia, and will try to keep spinning at a constant velocity. If the spring has a large travel, and a 53 lb-ft/deg spring constant (which means little or no preload), then the spring will unwind by about a degree as the crank decelerates slightly (minutely less if the prop decelerates a bit), which equates to a reduction in the torque that the prop shaft sees of only 53 lb-ft. In other words, the amplitude of the input vibration has been reduced from 100% of the total (total is 10% to 195% of the mean torque) to 7.4% of the total. From very rough to very smooth.

    In a PSRU system, this would mean the ability to use smaller, lighter gears, and therefore a slightly lighter gear box, since the force on the teeth would not vary greatly from the normal loading/unloading. In a DD set up, it would mean the ability to almost completely isolate the crankshaft vibrations from the propeller so that for lower "stock" hp engines, an ordinary (cheap, OEM) crankshaft - designed for that horsepower in an automotive application - could be used, like maybe a bone stock Ls1, or if you could use a heavier engine @ 175hp and 500lb or so, a stock, iron SBC or SBF, Mopar, etc...

    Watch this video (and among other things, look at the simple device for measuring the spring rate of the clutch disc center - there are thousands of different spring loaded discs available with long travel, short travel, variable rate, etc. Some viscously damped and some un-damped; although they're all generically called "dampers", only the viscously damped ones are truly damped, the others are erroneously labeled dampers, when they are actually attenuators, or "tuners". Drill the rivets holding the pads on, then bolt it to the flywheel, or use a marine spring disc that's already set up that way. Be sure and measure the spring constant and do the frequency calculations so to select the correct "damper"...) :



    and read this web page (why damping is a band-aid, which does help when applied properly, for less than optimum design, among other things):

    Transmissibility: The Magic Bullet, by EPI Inc.

    PS,
    Great, I misspelled "Transmisssibility" in the title...
     
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  12. Jul 4, 2014 #932

    stol

    stol

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    Re: transmissability

    The latest article on the "beast"...........

    You need good speakers to hear it run too....

    [video=vimeo;99409296]http://vimeo.com/99409296[/video]
     
    Last edited: Jul 4, 2014
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  13. Jul 4, 2014 #933

    MARCVINI

    MARCVINI

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    Re: transmissability

    You´ve just made my day, Pale!!!

    Now, all I wanted to see was that EPI ENG guy explaining why your airplane couldn´t have flown like that for all these years!!!

    Cheers, my friend. :ban:

    Marcvini
     
  14. Jul 4, 2014 #934

    Autodidact

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    Re: transmissability

    That's a strange thing to say, since the EPI ENG guy has never said anything about Stol's airplane good or bad, never said that belt drives won't work, and actually said that hy-vo chains could make a good PSRU. Why are you trying to make a straw man out of the EPI ENG guy? Especially since he only did things to further the "cause"; his web site was a fount of good (and free) information while it was up. And the GP-5 was not a successful aircraft, engine-wise, until the PSRU was replaced with an EPI ENG designed redrive - which doesn't exactly discredit the EPI ENG guy's ability and knowledge:

    [video=youtube;019Ro3E_mhA]http://www.youtube.com/watch?v=019Ro3E_mhA[/video]
     
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  15. Jul 4, 2014 #935

    MARCVINI

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    Re: transmissability

    I respectfully desagree with you: if people didn´t think independently and took to the letter what he says, you wouldn´t have people like the Belted Airpower guys, Ben Hass included, who have been flying belted PSRUs for decades with no harmonics related issues and correlated stuf.

    I think it is funny that that guy writes pages and pages on auto conversions, writes pages and pages praising his designs qualities in comparison to belted and chained PSRUs, but you can hardly find his units actually flying and doing so economically and reliably, just as Ben and others like him have been doing for so many years. Do you know how much one of his miraculous PSRUs cost? You can count on paying about 20K for one of them.

    As for the GP-5 aircraft, look again: you will see that the problem behind its original powerplant wasn´t the chained PSRU itself, but the engine. And if you look and search carefully, you will see that his geared PSRU weighs in more than the Geschwender PSRU it replaces (85 versus 78 lbs), altough he keeps saying that his units are lighter. By the way: the G PSRUs were used quite succesfully in front of Ford 460 engines, even in crop spraying operations, wich is quite harsh an environment, and that is something that contradicts completely his sayings about the reliability and practicability of those units.

    So, I wrote what I wrote because I think it is funny how all his theories and complex explanations have led to so few results in comparison to the many good and sucessful examples you can find among the crowd who, consciously or not, dared to do things diferently than what he preaches. The PSRU types that he capaingns against (belted and chained) are exactly among the ones that you can find more succesfull stories.

    To sum up things, I say that he is the typical kind of guy who wants people to think that things would have better been done the dificult and expensive way.

    Please, do not take my sayings personally, OK?

    Marcvini
     
  16. Jul 4, 2014 #936

    Autodidact

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    And I must respectfully disagree with you as well - about the content of the EPI website, anyway. The information was good and helpful to anyone who wanted to learn about reduction drives. He never said belt drives won't work, he said that they were usually trial and error designs which always have an element of luck, but of course they will work and if you could go and read the article on transmissibility you'd see why. He also said very clearly that chain PSRU's could work well if designed correctly. The purpose of his web site was less to sell PSRUs, which were admittedly gold plated, but to help other people design their own successful PSRUs. The PSRUs he designed and sold were more of a hobby, and as an engineer, he had a lot of irons in the fire other than just the gear boxes.

    And I believe that you're also wrong about the GP-5; the EPI guy redesigned the entire firewall forward installation, including the engine mount, the PSRU and the propeller; from the GP-5 Wiki page:

    Implying that the redrive contributed to the engine failure. EPI's objection to the Geschwender PSRU was not with the gear box itself, but with the crank coupling. Chain type PSRUs are not much more numerous than EPI gearboxes. It is the poly belt PSRU's that are most numerous and that is because they are less expensive and work well enough. The Robinson PSRU is a hy-vo chain drive and works fine, but it is heavy and expensive much like the EPI product: http://www.v8seabee.com/

    I do not take this personally, I just don't understand why anyone would harbor unfounded prejudice against technical knowledge that could be helpful - another facet of this technical problem to be used in help of the "cause", where all input is welcomed and potentially helpful.
     
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  17. Jul 4, 2014 #937

    stol

    stol

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    Geez.... I am NOT an engineer, and I have ALOT of irons in the fire too.....

    Your point is ?????
     
  18. Jul 4, 2014 #938

    crytes

    crytes

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    Weather or not you have the traditional education of an engineer once you start designing and calculating you've become an engineer.
     
  19. Jul 4, 2014 #939

    stol

    stol

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    I agree 100%......

    I just don't have a piece of paper hanging on my wall that shows a degree...

    I just have a successful auto engine conversion sitting in my hangar....... I will take that any day over a piece of sheepskin..
    :)
     
  20. Jul 4, 2014 #940

    MARCVINI

    MARCVINI

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    ... I appreciate that and praise the way you put things. BUT...

    This is the video of the very "engine failure" of GP-5, in Reno 2010, wich, subsequently, let to the EPI mods:

    Osprey GP-5 Reno 2010 - YouTube

    Well, everyone can see that the PSRU had nothing to do with the engine failure. No crank break, no PSRU break, it is evident that the problem was only with the engine internals. More specifically with the upper part of the engine, given the smoke that came from the exhaust. One interesting thing about it is that the airplane still "had engine" for taxing, right after the emergency landing. So, instead of confirming the "impliances" that the EPI ENG might lead to, this video shows that the information in that site is misleading.

    Now, read the information I quote below, wich comes from that very site:

    "Consider an example. Suppose a PSRU with a 2.50" wide, 1/2-inch pitch Hy-Vo chain and a 23-tooth driving sprocket is used on a 450-HP 8-cylinder, spark-ignition piston engine. The engine makes a takeoff-power value of 450 HP at 4600 RPM (515 lb-ft of torque) and makes 400 cruise HP at a 4000 RPM. (530 lb-ft of torque). Also suppose that the coupling between this PSRU and the engine crankshaft provides sufficient torsional absorption so that virtually no torsional excitation is applied to the PSRU's driving sprocket (not very likely, BTW, unless it is using an EPI coupler).In that scenario, at the takeoff power rating of 450 HP and 4600 RPM, the design life of a 2.50-wide chain (using Morse engineering data) is just under 13 hours. At the cruise rating of 400 HP at 4000 RPM, the design life is is less than 16 hours. The appropriate Hy-Vo chain for that engine, assuming good torsional attenuation, is a minimum chain width of 3.00 inches in order to have any reasonable life expectancy."


    Well, if that information was correct, even the V8 Legends and the many Geschwender equiped Ag Planes wouldn´t make history in the auto coversion arena, since their engines had aproximatelly the same rating as the one used as exemple by the EPI guy, but were their PSRUs were weaker, since they had 2 inch wide chain, instead of 2.50 inch as the example given by that guy. Another misleading information from the EPI site.

    And the list of misleading information goes on. It is just a matter of time and atention for finding them in the EPI site.

    Marcvini
     

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