September 18, 2005

Last week, I got a phone call from Mattituck explaining to me that they managed to fail a couple of the Superior Ryton sumps. Turns out that it cannot withstand a backfire under certain circumstances. Those circumstances are if you’re running an electronic ignition system that uses a waste spark (fires two cylinders at the same time). Most electronic ignitions do this, including the one on your car, my car and my FADEC system. Hmmm.

What happens is that when the plane has been sitting, fuel and therefore vapours collect in the intake tracts. When you go to crank the engine, as the spark fires (two of the cylinders) it just so happens that the valve overlap on the cylinder that doesn’t need the spark means that the cylinder is open to the intake tracts. Then, the air in the intake gets compresses a little, and the spark goes off and boom! You have yourself a little combustion chamber right where you don’t want it.

Well, if you run an electronic ignition, the way around it is to fire it up on the mag, then switch in the electronic ignition once the engine is running. This will clear out the intake tracts. If you run FADEC, you should crank your engine a couple of turns to suck all the vapours through before switching on the FADEC units.

There have been a few failures of the sumps out in the field that we have all heard about. Mostly on tail draggers. It seemed to be associated to sniffle valves being mounted at the front of the sumps instead of the rear. Now that Mahlon Russel at Mattituck has gotten to the bottom of it (pardon the pun) and figured out what the real issue is, we can take steps to avoid such an event.

Now, my question is, does this really affect me? The reason I ask that is because I don’t have a throttle body injection system, so in theory there should be no fuel at all in my intake tracts as it’s injected directly before the intake valve at the cylinder head. I’m going to call Mahlon tomorrow and run this by him. It may well be fine for me to stick with my Ryton sump.

Right now, Superior are feverishly working on upgrading the sump to withstand this type of event.

Watch this space.