chotia 460

Discussion in '2-Stroke Aircaft Engines' started by travis1990, Nov 7, 2009.

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  1. Nov 7, 2009 #1

    travis1990

    travis1990

    travis1990

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    What ever happened to the chotia 460. It powered the originial weedhopper. It was a direct drive two stroke. It had a reputation for being unreliable but I think that was a good concept and they should have worked out those problems.
     
  2. Nov 8, 2009 #2

    Dana

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    Direct drive 2-strokes are quite inefficient, which is why nearly all 2-strokes are run with redrives nowadays.

    -Dana

    When Marriage is Outlawed, Only Outlaws will have Inlaws.
     
  3. Jan 30, 2010 #3

    travis1990

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    Why do two stokes have to rev so high in order to be efficient?
     
  4. Jan 31, 2010 #4

    Dana

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    The way to get more power out of a small, light engine is to turn it faster. Even the Rotax 4-strokes turn fast and have reduction drives.

    -Dana

    Grow your own dope! Plant a politician!
     
  5. Jan 31, 2010 #5

    travis1990

    travis1990

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    But why don't 2-strokes have any torque? Theoretically they should have double the torque of a 4 stroke of the same displacement because they fire every other revolution.

    The only explanation I can think of is the exhaust port opening early.
     
  6. Jan 31, 2010 #6

    litespeed

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    Yep- the overlap of the ports allows a lot of pressure past and reduces torque and thus power. The use of a tuned pipe helps gain some of the power back.
    Additionally the compression ratio is low and this also reduces the torque.
     
  7. Feb 1, 2010 #7

    BBerson

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    Model airplanes have 2-stroke engines that have long stroke optimized for direct drive. I have not seen any gear drive on a model 2-stroke in 20 years at the field.
    No need for a reduction on smaller engines that operate at high rpm but still have low prop tip speed. The size of the engine has bearing on the usable rpm allowed for direct drive.

    I think a long stroke engine would be useful and it would sound better and probably be more reliable. Or two small direct drive engines like they used on the Lazair, for example.
     
  8. Feb 3, 2010 #8

    cpd

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    BBerson

    What is the biggest rc 2 stroke you have run? I used to have a Mr. Mulligan with a Super Tigre G3250. That thing vibrated like an out of balance washing machine at midrange (and lower) rpms. Dont remember the exact rpm but I think I was turning a 20X8 prop somewhere near 8500 rpm at wot.

    Chris
     
  9. Feb 3, 2010 #9

    travis1990

    travis1990

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    The biggest RC 2-stroke I've seen was a 600cc 3W 4-cylinder. It made about 60 HP.
     
  10. Feb 3, 2010 #10

    BBerson

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    My biggest RC engine is just a normal .60 size.
    My main point was that an engine purposely designed for a prop might work better than adapting another existing engine from a snowmobile or whatever. RC engines are designed for flight with direct drive.
     
  11. Feb 4, 2010 #11

    travis1990

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    With the power to weight ratio of these thing you could use a 60hp engine in place of 40 hp engine to get the thrust and you'd still have a ton of weight left over. But reliability would be an issue. I've heard 3W 4-cylinders have a tendency to snap cranks.
     
  12. Feb 5, 2010 #12

    mstull

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    A mechanic will tell you that power = torque x RPM. To get more power out of a given displacement, takes more RPM. In one way, 2-strokes are less efficient: When the ports open, the power stroke ends, losing some power and fuel efficiency.

    But in another way, 2-strokes are more efficient at making torque. The torque from an engine is measured as average. Since a 2-stroke fires every revolution, there's twice as many power strokes as a 4-stroke. So a 2-stroke will usually make more power and torque than the same displacement 4-stroke (turning the same RPM). That's one thing that gives 2-strokes such a power to weight advantage.

    So 2-strokes actually make excellent torque (for their displacement). The main reason to run a reduction drive is to improve propeller efficiency. The reduction drive multiplies the torque (while dividing the RPM), which allows you to turn a much larger prop that will produce much more thrust. Larger diameter props are much more efficient at making thrust (on low speed aircraft).

    I experimented (successfully) with running a 2-stroke direct drive on an U/L. If you run a small enough prop to let the engine rev up to where the engine puts out full power (or anything above 4,000 RPM), it sounds like a very loud, mad, screaming bumblebee. I got constant complaints about the noise (from the prop). So noise is another reason to run a reduction drive.

    So I was forced to use a larger prop, which brought the RPM down to where the engine makes much less power, de-rating the direct drive engine significantly. To my surprise, it made just as much thrust. Even with the engine making much less power at the lower RPM, the larger diameter prop's improved efficiency made up for it.

    I learned a lot about what it takes to make an efficient prop. There's pretty big differences in prop efficiency with seemingly minor differences in prop size and shape.
     
  13. Jan 29, 2012 #13

    corbenpilot

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    I have had many hours of flying behing, er, under a Chotia 460 when I way-back-when owned a Weedobber B model with a Square head Chotia. This engine did not produce it's claimed 20 HP but was unique in that it was a direct drive engine manufactured by the company the produced the Weedopper Ultralight.

    I was interviewed to work at Weedhopper back in the 80's just after John Chotia died in the crash of the Rocket. Weedhopper factory in Ogden Utah had a full machine shop producing engines. It was amazing to see as they sand cast all blocks and cylinders there on-site. The propellers too were made there on a duplicating machine imported from Holland that originally produced wooden shoes for the tourist industry...No Kidding!

    The Chotia engine was originally a round cylinder and No Kidding again was ignighted by a glow plug like a model airplane engine! This is real stuff! Later the engine was powered by a dual points ignition that ran off of battery power. This is no-**** stuff when I say it was powered by 6 "D" size flashlight batteries! I flew with that battery pack overhead! You knew it was time to get new batteries when the engine started to misfire and lose RPM....again No Kidding!

    Lest anyone think this was a failure think back to the low power, screaming 2-strokes that existed back in the day. The Kolb, Lazair, and Volmer macxhines were powered by not one, but two screaming little 2-stroke engines that barely kept them aloft. The long stroke Chotia, though crudely built required a less complicated exhaust system (able to scavange without the need of a complicated exhaust) and was direct drive.

    As the Chotia was crudely made, I opted to modify mine with a points ignition that got it started and a magneto ignition once it got going. This mod worked very well and was really dependable.

    Don't fault the Chotia by today's standards. Instead look upon it as a major advance (IN IT'S DAY) to a robust, simple and reliable power plant as against the THEN available engines for ultralights.

    I remember those days and what a remarkable advance the Chotia was. So was the Weedhopper design!

    I knew John Chotia to be an excentric type and he had an enormous "LACK" of engineering expertise. But that aside, he was a revolutionary figure in the progressive journey to the modern ultralight and converted the image of the hang glider with a crudely mounted chain saw emgine to a viable and respected aerial vehicle.

    John Chotia and his Weedhopper and it's purposely designed engine have earned a place in aviation history.

    As an aside, John donated one of his early "B" model Weedhoppers to a Fed aviation test facility and it was tested to destruction. It withstood "8" G's of stress before failure. A true wonder in the early days of ultralighting and design for sure!

    Don corbenpilot@yahoo.com
     
    Last edited: Jan 29, 2012
    choppergirl and captarmour like this.

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