Rotax Avid/KF Mounting

[flattie45 17]

Just a question that I have wondered about for some time: It seems that the two stroke Rotax's are mounted inverted on Avid Flyers. Is it true that they are mounted cylinder head up in Kitfoxes? Does it make a difference? Is inverted better than right side up, or vice versa? Or, maybe KFs are inverted as well (I can't remember where I read that KFs had the cylinder head on top, maybe I made it up?). Not that it matters to me, I am just curious.

-Nate

[akflyer 1427]

Just a question that I have wondered about for some time: It seems that the two stroke Rotax's are mounted inverted on Avid Flyers. Is it true that they are mounted cylinder head up in Kitfoxes? Does it make a difference? Is inverted better than right side up, or vice versa? Or, maybe KFs are inverted as well (I can't remember where I read that KFs had the cylinder head on top, maybe I made it up?). Not that it matters to me, I am just curious.

-Nate

Kitfox do have the engines mounted upright. Most seem to like it better. I know with the inverted engine sometimes the plugs will fill with oil if you let is set for too long. I think Dean was trying to make it easier to stuff under the cowling

[Av8r3400 1179]

Kitfox 2-strokes are mounted upright.

Some have said to me that head up is better, but I've never heard a compelling reason why...

[flattie45 17]

Kitfox do have the engines mounted upright. Most seem to like it better. I know with the inverted engine sometimes the plugs will fill with oil if you let is set for too long. I think Dean was trying to make it easier to stuff under the cowling

Am I correct in assuming that this would be an engine with oil injection? If so, what about one w/o the injection?

It's just that I have been curious about this for awhile, so I thought I'd ask. It seems that with all the hours on the Avid/Rotax fleet, it must not be that big of a deal.

-Nate

[SuberAvid 617]

I started out running my rotax (inverted in the Avid) with the injection. Then one day discovered while preflighting that the cable had broken. It must have just happened and it was amazingly fortunate that I happened to notice that because obviously I would have been toast on that flight. Since then I have premixed my fuel for the last few years. The engine doesn't care; once it passes through the carbs itis all the same.

I do know that the inverted engine pools oil on the spark plugs. I have pulled my plugs after the engine has sat for a week or more and the plugs are pooled in oil. I started out running the standard NGK's and I could tell at between 25 and 50 hours I would get a subtle miss when throttled back in slow cruise. I started running the platinum NGK's EVX and they worked great but I still changed them after 50 hours. The last couple of plug sets I have been using the NGK's EIX Iridium plugs. They are spendy but the seem to fire no matter what and I never detected a miss. I finally changed the original ones out when I had my engine rebuilt 2 years ago and then just put in a new set this winter when I was having trouble starting. It turned out that my starter was the problem and would just not crank the engine over fast enough after it had set for a week or so. It took me a while to determine this (when the starter finaly died) but my plane got a new set of iridium plugs in the meantime. I am always amazed at the way the engine pops off knowing he plugs are sitting in a pool of oil.

Here is another question for the group. The Avids (and I think the KF's) have a problem with the alcohol fuel disolving the resin in the tanks. I have never detected any deterioration in my tanks based on the only indicator I really know of, and that is looking for strands of fiberglass on the finger strainers in the tank outlet. I pull mine every year at annual to check. I have checked the gas in the past for alcohol and have not been able to detect any appreciable amount, but it has been a couple of years since I have checked it. From what I understand of the gas situation in AK, it all pretty much comes from the same refinery. Do you guys have any knowledge about what gas brands may have or not have alcohol added?

Another theory that I have heard is that adding the oil to the gas by premixing helps protect the tanks from the alcohol. Any validity to that theory?

[akflyer 1427]

I started out running my rotax (inverted in the Avid) with the injection. Then one day discovered while preflighting that the cable had broken. It must have just happened and it was amazingly fortunate that I happened to notice that because obviously I would have been toast on that flight. Since then I have premixed my fuel for the last few years. The engine doesn't care; once it passes through the carbs itis all the same.

I do know that the inverted engine pools oil on the spark plugs. I have pulled my plugs after the engine has sat for a week or more and the plugs are pooled in oil. I started out running the standard NGK's and I could tell at between 25 and 50 hours I would get a subtle miss when throttled back in slow cruise. I started running the platinum NGK's EVX and they worked great but I still changed them after 50 hours. The last couple of plug sets I have been using the NGK's EIX Iridium plugs. They are spendy but the seem to fire no matter what and I never detected a miss. I finally changed the original ones out when I had my engine rebuilt 2 years ago and then just put in a new set this winter when I was having trouble starting. It turned out that my starter was the problem and would just not crank the engine over fast enough after it had set for a week or so. It took me a while to determine this (when the starter finaly died) but my plane got a new set of iridium plugs in the meantime. I am always amazed at the way the engine pops off knowing he plugs are sitting in a pool of oil.

Here is another question for the group. The Avids (and I think the KF's) have a problem with the alcohol fuel disolving the resin in the tanks. I have never detected any deterioration in my tanks based on the only indicator I really know of, and that is looking for strands of fiberglass on the finger strainers in the tank outlet. I pull mine every year at annual to check. I have checked the gas in the past for alcohol and have not been able to detect any appreciable amount, but it has been a couple of years since I have checked it. From what I understand of the gas situation in AK, it all pretty much comes from the same refinery. Do you guys have any knowledge about what gas brands may have or not have alcohol added?

Another theory that I have heard is that adding the oil to the gas by premixing helps protect the tanks from the alcohol. Any validity to that theory?

AS far as I know here in AK we are still not using substances meant for drinking in our gas. They have however, started using various crap to boost the octane rating, and even in a sealed container, if the gas is n=more than a week or two old, it is not up to the full octane rating. I normally just put in enough fuel for my flight and the 45 minute reserve, so each flight I put in fresh gas so I know I have good stuff in there.

I also have heard that the oil mix in the fuel helps to keep the tanks from getting eaten up. It is also possible that your being a MK IV probably has vinylester resin in the tanks and therefore should not be effected by the moonshine fuel.

[Av8r3400 1179]

Has anyone ever figured out a way of testing what resin exists in your tanks?

[akflyer 1427]

Has anyone ever figured out a way of testing what resin exists in your tanks?

Sure,

1) empty gas tanks

2) fill with moonshine

3) wait a couple days, if the tanks are empty and your plane smells like booze, you have the old tanks

Dont know of any way other than that to tell. I am not sure if Avid / Airdale has records of what tanks went out with what serial number plane

[C5Engineer 1170]

I also have heard that the oil mix in the fuel helps to keep the tanks from getting eaten up. It is also possible that your being a MK IV probably has vinylester resin in the tanks and therefore should not be effected by the moonshine fuel.

I thought of this a while back. I mix in my tanks..granted it's 100:1 so not a lot of oil but you would think the oil would coat the inside of the tanks over time. You may have started in interesting discussion here Leni.

To keep this thread from turning into an Ethanol discussion the biggest difference I notice between the KF straight up and Avid inverted is the over the nose visibility. I like the vis a lot better in an Avid. I have flooded my inverted engine by over priming it once or twice but that was my own fault. They have a little different procedure for priming the Rotary Valve and priming the engine for start but not enough to be an issue.