Posted Friday, November 13, 2009 @ 07:59 AM  

The Zenith 28 RXZ (completely standard) works fine in the vertical until you run our of airspeed.

I regularly fly a quarter vertical roll with a hammerhead at the top as the second figure in my display routine. I believe that, all the way up the vertical, the engine is running on the fuel in the float bowl, because with only aerobatic fuel aboard (15 litres, three U.S. gallons) the tank outlet is uncovered the moment you get past about 45 degrees nose-up. The engine usually keeps running throughout this figure, but it does stop after around ten seconds, so you have to be quick to kick at the top or the motor stops just as you need it for the yaw. That's because my 1400cc motor burns 15 litres per hour at full throttle, and the float bowl only holds (20ccs? 50ccs? I've forgotten) but I remeber that I calculated it as 13 seconds worth of full-throttle power. That's theoretical of course, so the ten seconds is about it.

If all you want to do is a vertical climb from 120 moph or so to a hammerhead at 40 or a canopy-down humpty-bump, or a tail-slide, there is more than enough fuel in the float bowl to keep the motor running throughout.

That's the problem with slide carburetors. They have no float bowl, and so, no fuel reservoir, which is why a simple bubble in the line will make your engine quit. This most ususally happens immediately after take-off on a warm day.

That's why I would junk your slide carb and fit a proper Zenith. sorry.

Posted Friday, November 13, 2009 @ 04:40 PM  

The Ellison works great in the RV and there are hunderds being used sucessfully in all sorts of experimental aircraft.

I'm taking a good look at the new Rotec carb. It would require a pump, but it looks like a clone of the Ellison for small engines.

I'm not sure how the Aerocarb would handle a fuel pump. It does not seem to have a "demand flow" type fuel regulator on it like the Ellison or the Rotec. I'll look at what they do in the Sonex.

Of course I can always but the carb back on it.

Posted Monday, November 23, 2009 @ 11:51 AM  

It is a pumper carb that presumably needs a pressure pulse to make the pumping happen and it does not have a float bowl, so probably is not much better than the Aero carb.

I did try some 20 degree up lines and down lines yesterday to see how the Aerocarb was behaving and with a 1/2 full tank it did not skip a beat.

I was looking at the Zenith 28 RXZ and cant help but wonder about the narrow looking intake.

Is there a way to determine the correct size of carb throat opening for a specific HP engine?

My thought is that the faster the air has to move through the carb the greater the atomization of fuel, which is good, but isn't carb icing potential increased with a narrow throat?

How do we know that the engine is even getting enough air mixed with the fuel? Runs rich if not?

I also think that having the engine driven or electric pump on a float carb would be an added safety measure.

Is anyone running a pump with the Zenith 28?

Just some thoughts for comment.