Hi Al, 

 

Well, as I said I was a bit surprised to have the that attributed to you.  Relating the comments to sole  use of Av Fuel, it provides a more comprehensive context.  I find the use of Marvel Mystery oil in the context of unfouling plugs certainly interesting.  I happen to have purchased a couple of pints to mix with my 2 stroke oil for a different reason, but will be great if it extended my spark plug replacement interval.

 

No question use of 100LL in the rotary does lead to plug fouling after 20-30 hours - at least that is my experience over 300+ hours of rotary flying.  I tried a different plug but could tell no significant difference.  

 

The drop in rpm due to fouling appears have a tendency to occur in any high power situation - such as during take off - but even during cruise if running at a high power level.  My theory is with WOT the combustion chamber pressure is higher (due to the denser air/mixture ingested) and higher pressure makes it tougher for the spark to jump the gap.  So if lead fouling has started to occur, its easier for the electrical energy to follow the lead deposit than jump the gap.  Back off on throttle thereby reducing manifold pressure resulting in less combustion chamber pressure makes the job of jumping the gap a bit easier and the spark plug starts to function normally resulting in power recovery.

 

Normally you do not have both rotors (at least my experience) encounter this situation simultaneously - unless  you have ignored the problem for a considerable amount of time.  Normally its one or the other.  However, I did have both rotors go into SAG mode (once before I fully understood what was happening)  taking off fully loaded.  Performance WAS adversely affected  and the pucker factor was there until I realized that even with both rotors SAGGING, I still had over 500 fpm rate of climb -  what I could only  have hoped for flying a Cessna 150.  So I just climbed up to altitude over the airport I had taken off from, pulled back on the throttle and in approx 3 minutes the SAG situation had cleared up.

 

When SAG occurs I first notice a  change in the drone of the engine, then I find EGT of the afflicted rotor drops about 300F. Rpm will tend to drop a bit as well - although not as much as in cruise as during take off.   I presume the lower temps are  because the unburnt fuel is causing a cooler exhaust condition in that exhaust port's header.

 

So, anyhow,  thanks for setting the matter straight, Al. 

 

Ed

 

----- Original Message -----

From: al p wick

To: Rotary motors in aircraft

Sent: Monday, May 22, 2006 10:43 AM

Subject: [FlyRotary] Re: Questions from a potential rotaryphile

I'm here Ed. Appreciate your consideration given you were inadvertently set up. The original post is below. You will note the paragraph above the section you read talks about negative effect of EXCLUSIVE use of av fuel. Also described with "this happens every 20 hours".

 

Original post fwiw:

 

<<Al- just let me in on the system for the auto engine logistics- do all the FBO's serve up auto fuel?

 

Auto fuel relatively difficult to find at airports. You can do web search for all the ones within flying distance. I planned my flight from west coast to Osh last year. Two different routes. With the cruise range of the Cozy it was no big deal to buy auto all the way. I recall one location I'd have to buy a few gallons of aviation fuel.

 

In the past, auto engines would notice slight rpm drop during cruise if they exclusively burned aviation fuel. Week after week it would increase. If they ran one tank of auto fuel, it would fix itself until around 10 avgas tanks later. They now use Marvel Mystery oil of all things, and it reportedly eliminates all negative effects. Marvel better than 2 other lead scavengers.

 

<<Do the rotory fliers carry chain saw oil mix with them when going cross country to pour in their tanks after a fill up?

 

Rotary is different issue. Their unusual combustion chamber requires them to mix 2 cycle oil with each tank. If they don't their compression seals die prematurely. Just like your boat motor mix, I don't see it as a big deal. In addition, if they use aviation fuel, they develop power drop on departure and have to replace all their plugs before next flight. This happens every 20 hours. They don't have solution for this.

 

<<somebody said they were using jerry cans of auto gas and bringing them to their hanger to fill up their tanks- is this right?

 

I find almost all my flying is from home base, returning later that day. So I fill (3) 5 gallon cans at gas station 1 mile away from airport. While I'm doing preflight, these drain into my mobile 30 gallon tank. I then wheel it over to the plane and it takes 20 seconds to fill tank. (compressed air transfers it very rapidly). Neat trick I learned from motorcycle buddy. No more inconvenient than taxiing over to HBO to get fuel, way less expensive.

 

If I don't value auto fuel savings, just add some Marvel each av tank, off I go.

 

-al wick

 

 

On Mon, 22 May 2006 08:06:13 -0400 "Ed Anderson" <eanderson@carolina.rr.com> writes:

I'm a bit surprised hearing it came from Al Wick as he was on this list for a while.  I thought he had a better understanding of what was going on with the rotary.  But, you're right a little knowledge means incomplete knowledge which can be dangerous.

 

Ed