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Thread: Reduction drives

  1. #1
    Super Moderator orion's Avatar
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    Reduction drives

    As many of your have concluded, auto conversions are a realistic substitute for our airplanes. Given the continuous and generally trouble free service in automotive applications, there is no reason to assume that an airplane application woud result in failure. As long as the user understands that the airplane application will operate the engine at a higher power level than the engine sees in a car, then all other factors should be pretty much equal.

    The problem therefore is not so much the engine but more so the reduction drive we place between the engine and the prop. In our research we have of course found many potential suppliers of redrives however, when we analyzed them for their published performance, we determined most to be lacking. To compound the problem, we have also discovered that many of these drives were generally "eyeballed" with no real engineering behind them. We also found that those who developed these critical components had no real knowlege of drive design requirements, nor of the potential loads that a flight environment will impose on the drive's components.

    For those interested, I've posted a couple of engine/reduction articles at our web site. If you go to www.oriontechnologies.net and go the the Papers and Articles page, there are a couple of articles that talk about several of the issues to consider in this arena.

    One interesting aspect of this is the real attitude of many of us who are considering an engine option for our airplane. We udertook a survey of the industry back in the mid eighties, and a supplementary one on the mid nineties. What we found is that there is tremendous interest in alternative engines. Virtually all responses (over ninety percent) respoded with a strong interest in automotive applications, reduction drives and all associated technologies.

    However, when asked what engine all these people were most likely to put in their own airplane project, virtually all said Lycoming and Continental.

    Thus far, we have therefore concluded that if an engine/redrive package is to be successful in the market, it first must have a professional level of technical backing behind it, it must appear professionally developed, machined and built, and it must be flight-tested to the level that a certified engine would be. This does not mean that folks want these engines to be certified, it just means that a substantial amount of testing needs to be behind it before the customer base takes it seriously.

    Also, the customer must get past the company glitz, in order to do a real evaluation as to the suitability of the package. There are several companies out there providing redrives or drive/engine packages that look slick and professional - they are very well machined, anodized in pretty colors, and supported with slick sales brochures. But unfortunately they have virtually no real engineering, nor history, behind them.

    There are a few good ones out there but discerning between the good and the bad is difficult. In essence, what this does is force the customer into the position of being a test pilot, something I'm sure most of us don't want to be. And so, most still consider the overpriced tractor-level technology standard to be the only choice for our airplane.

    I think most of us would like this to change, but it will require a responsible approach to the development, and of course, a few dollars to make it work.
    Last edited by orion; March 3rd, 2003 at 11:26 AM.

  2. #2
    mel
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    Lightbulb redrives

    Hi This is Mel in Orange Park Fl. You are prob right. I have no engineer training. Still I putting on my engine a redrive using quick change gears from cars. They are strong and tuff. The only grief is that I don`t know how to hook up a Constant speed prop to it but will figure it out. All of this goes on a 300ci six Ford that is inverted.

    The other thing is I couldn`t access your website. All I got was "can`t find server". Will keep trying though.

    TKS
    Mel

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    Site Developer Jman's Avatar
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    The other thing is I couldn`t access your website. All I got was "can`t find server". Will keep trying though.
    Try it now mel.

    Jake

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    Heard about Honda and Lycoming ?

    I think the best thing that could happen for us lighter homebuilt builders would be a merging of engineering talent from the auto engine industy with the aircraft engine industry. I read an article about Honda working with Lycoming possibly on a new series of aircraft engines. It is hard to believe Honda is interested in spending their time on something like this, maybe they think the small general aviation market will really take off when the Sport Pilot thing finally happens.

    And its also hard to believe that Lycoming would want to have new competiion for its own "stone knife and bear skin" technology line of engines. Of course they may be seeing how many engines Rotax is selling and have decided that they want a piece of the under 110 HP uncertified engine action. Actually I am surprised they haven't started an uncertified engine subsidiary disting off the old blueprints and making their old 65 horse engines again.

    I have owned several Hondas and would love to see Honda create a line of small aircraft engines. Especially knowing that they have partnered with a knowledgable (although hopelessly 20th century) aircraft engine company on the project. I am currently looking at the Geo/Suzuki engine and the Raven Reduction drive. I know the Lycoming/Continentals are reliable but I can't justify spending year 2020 cash for year 1930 technology even though it would be the easiest path to take.

  5. #5
    Super Moderator orion's Avatar
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    I agree with you. My wife and I both drive Hondas and personally, I think the engines would be wonderful in an airplane application. As far as the company being interested in aviation, I wonder if it's just a reaction to the Toyota program. That was introduced several years ago and an aviation version of the engine did finally come out. I do not know the status currently but given the significant lack of information out there about it, I wonder if it didn't just fade away.

    I know some time back the Toyota group actually developed a new airplane to act as a test bed and to be produced as a certified product however performance wise, it turned out to be a dog, delivering performance far below the advertised hype. (Actually knowing the design team, I'm not too surprised.)

    One other thing I wanted to address regarding an earlier thread: several reduction drives out there are being based on the automotive gears found in automatic transmissions. These are planetary type and come all self contained in their own housing, with matching ring gear and sun gear. They are relatively easy to develop into a drive and have been tried by several suppliers of planetary systems.

    However, I would caution how they are used. The environment these gears see in an autoamtic transmission is very benign - this is not necessarily the case in an aviation product. Given limits on torque and rpm, the sun and ring gears should be OK however the planets should cause a bit of concern.

    The planetary gears are made from powdered metal, then sintered into shape. This is a process of taking the powder and subjecting it to high pressure and temperature, thus causing the powder to turn into a semi-liquid state, forming the part. The process is well known and although the quality controls are good, I wonder if they are dependable enough for our application.

    I remember back in school we were shown a number of examples of part failure that were caused by incomplete formation of the powder to solid metal and/or part failure due to internal voids. I'm pretty confident the gears are OK for the automatic transmission application but for aircraft? I am not so sure.

    About three years ago one company evaluated the gears for their engine configuration. The parts they were considering were either a four gear clusters or a six gear cluster from a Ford C-6 heavy duty transmission. In service the gears saw torques and rpms such as are put out by large trucks and other heavy duty applications. However, when analyzed by the engine company's transmission designers, they determined that the gears in an aviation application would be sutiable for engines producing no more than about 120 hp at 5,200 rpm. This was quite an eye opener not only for me but for several other similar projects.

    If you're going to use this setup, my recommendation is to use the other components, but make your own planet gears from billet - throw the sintered gears away.

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    Simplest reduction drive tech

    The simplest solution that does the job is always the best. In the under 110 HP range that I am interested in two pulleys with multiple V-belts sure seems like the best way to go. I am sure this would be inadequate for 500 HP V-8s.

  7. #7
    Super Moderator orion's Avatar
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    "V" belts are a good way to develop a simple reduction drive but keep in mind several things: the "V" belt system is one of the lowest efficiency power transmission methods there is. While gears loose about one to two percent in efficiency per mesh, "V" belts can loose more than 15%. This loss is in the form of friction, which in turn is heat that has to be dissapaited. It also means that 15% less power is available for the propeller.

    Also, as the system ages and the belts "break in", they can become loose, requiring periodic adjustments or a good idler/tensioner pulley. This deteriorating condition also causes further loss of efficiency.

    Yes, "V" belts are simpler but keep in mind they do introduce significant drawbacks also. If this is the way you want to proceed, look at cog belts (such as teh HTD type) or other, more efficient systems.

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    Good point, how efficient is a cog belt drive and would you want to use multiple belts for redundency like with v-belts?

  9. #9
    Super Moderator orion's Avatar
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    A well designed cog belt looses less than five percent per mesh. I have seen the manufacturer's data indicate that the losses can be as low as for gears (two to three percent).

    The main thing to pay attention to in cog systems is the alignment of the two pulleys. Early attempts at cog reduction drives were of poor design and resulted in failure in a very short amount of time. I've seen several slapped together drives with lives of less than 15 hours. Well designed drives however can last over a thousand.

    Multiple belts can of course add redundancy but will require the high level of alignment between all the cogs. Standard practice seems to be to just go with a single, wider belt instead.

  10. #10
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    Better go back and check those belt vs gear #s. Planatary is the worst, gear to gear is next. . The best is poly v drive.
    I like the quick change idea. i have a stack of gears and the noise is cool. ( Noise means loss of power.tho)
    MM

  11. #11
    Super Moderator orion's Avatar
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    Hi;

    Actually I don't have to check the numbers as I deal with them quite often on my own and in my business.

    I don't know where you get your numbers but "V" belts consistently are the worst in power transfer. This doesn't require a whole lot of thought since if you consider that a "V" belt functions as a result of friction between the V's sides and the "notch" in the pulley, you will realize that in its work, the "V" belt continually loses energy and generates heat as a result of the surface contact.

    Simple mechanical contact of gears or even cog belts is dramatically better through most functional realms.

    Gear tooth-to-tooth contact results in only 1.5 to 3% loss per mesh. "V" belt loss can range from about 6% to more than 15%, depending on pulley configuration and type of contact. Yes, planetary gears can add up to a higher number but that is a function of how many planets you have in play. Many planets can reduce the load per contact, but the higher number of contacts does result in higher energy losses.

    As a ballpark, some chains (silent type) and cog belts have about the same energy loss per drive. Chain must eliminate the heat through oiling while the belt requires a good air flow.

  12. #12
    Registered User Johnny luvs Biplanes's Avatar
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    What about the good old hot rodded GMC type blower belt (on dragsters). Would have though that they would use the easiest and most efficient system! Easy to design, manafacture, alter ratio's and can be fairly light. John
    Do ya thing in a 2 wing

  13. #13
    Super Moderator orion's Avatar
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    The belt system used in the blower setup also depends on contact friction and has some limits on torque and rpm. Long term effects such as those encountered in aviation (or any other permanent setup) would have detrimental effects on belt life.

    The reason they are used in the automotive industry is the same as you listed - they are simple, easy to install, easy to modify for the application, and relatively cheap.

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    Excellent Notes, Will take a note of it.

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    belted redrive

    Several helicopters are using V belts and poly-V belts in their primary drive reduction and in most cases the belt drive functions as the power clutch. The ones that come to mind are: Enstrom, Robinson, Hughes. If those belts were absorbing 15% of the power I would think they would melt. Those choppers are in the 160 to 225hp range and 15% is 30hp converted to heat or about 80,000 BTUs. My information shows Vbelts losing about 5%. What do the helicopter guys say?
    Bob Young

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