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Hangar Flying / Ellison
« on: January 11, 2006, 01:30:13 PM »
I don't have any performance numbers.
However, the Ellison should yield higher manifold pressure because it doesn't require much (any) venturi (restriction) to create a vacuum signal to deliver fuel. All of this may mean more horsepower is available, which might give better takeoff and climb performance.
The other benefit of the Ellison is that it may allow for an installation that has better mixture distribution. This may mean that your airplane will get slightly better fuel economy.
The downsides I have seen with the Ellison are that it seems to be more susceptible to fuel contamination, and may be more sensitive to turbulent airflow entering the unit (causing weird mixture issues). A friend has an Ellison on his LongEZ, and it seems like his might suffer from the last issue I mention. He can't seem to get it to have stable mixture over the full range of throttle movement. Transition from idle to part throttle seems problematic, along with overly rich full throttle mixture.
Also, the Ellison doesn't have an accelerator pump, and so (as has been mentioned) it will likely require some kind of primer system. Lacking an accelerator pump may also cause the engine to stumble if the throttle is racked open quickly. The pump on the carburetor acts as an enrichment device in such a situation.
One final disadvantage of the Ellison is that if you have a problem with it while on a trip, you may have trouble getting parts for it, or getting an A&P to work on/troubleshoot it. I would hazard a guess that every A&P has worked on a Schebler, but not nearly as many have played with an Ellison. Probably not a big deal, but something worth considering..
One final thing about the Ellison.. It isn't new. It's been around at least since the early '80s.. I think all of the issues with it are known and documented.
Matt-
However, the Ellison should yield higher manifold pressure because it doesn't require much (any) venturi (restriction) to create a vacuum signal to deliver fuel. All of this may mean more horsepower is available, which might give better takeoff and climb performance.
The other benefit of the Ellison is that it may allow for an installation that has better mixture distribution. This may mean that your airplane will get slightly better fuel economy.
The downsides I have seen with the Ellison are that it seems to be more susceptible to fuel contamination, and may be more sensitive to turbulent airflow entering the unit (causing weird mixture issues). A friend has an Ellison on his LongEZ, and it seems like his might suffer from the last issue I mention. He can't seem to get it to have stable mixture over the full range of throttle movement. Transition from idle to part throttle seems problematic, along with overly rich full throttle mixture.
Also, the Ellison doesn't have an accelerator pump, and so (as has been mentioned) it will likely require some kind of primer system. Lacking an accelerator pump may also cause the engine to stumble if the throttle is racked open quickly. The pump on the carburetor acts as an enrichment device in such a situation.
One final disadvantage of the Ellison is that if you have a problem with it while on a trip, you may have trouble getting parts for it, or getting an A&P to work on/troubleshoot it. I would hazard a guess that every A&P has worked on a Schebler, but not nearly as many have played with an Ellison. Probably not a big deal, but something worth considering..
One final thing about the Ellison.. It isn't new. It's been around at least since the early '80s.. I think all of the issues with it are known and documented.
Matt-