Starting procedures on Corvairs, 2,000 words of experience.
I recently had some conversations with out neighbor Bob Woolley. He is building a Panther, and he is the second pilot who is working with Dan to fly the test program on the Panther prototype. You can read this link about Bob on the Panther website:
Above, three aircraft with carbs below the engine parked in our front yard. L to R, Louis’s 601XL – MA3-spa, Grace’s Taylorcraft – Stromberg, and Dan Weseman’s Cleanex-MA3-spa. The 601/650 is one of the few Corvair powered airframes that uses fuel pumps, almost all others are gravity feed. You might not guess this at first glance, but the Cleanex has no fuel pumps, it is only gravity feed, but it worked great, even during aerobatics. Do not accept complexity without good reason. The 601/650 have the fuel in the wings, which is a good trade-off for complexity. High wing planes can also have the fuel in the wings, but they don’t need pumps.
Bob is a outstanding pilot with a lot of experience both in building and flying, his professional approach rooted in his years in the USAF. Although his homebuilt experience runs from Pitts Specials to Glassair IIIs, almost all of the time is behind Lycomings. The panther was the first Corvair powered aircraft that he flew, and I wanted to catch his first impressions the same day he flew it. Came down to three points: It was the smoothest engine he could remember, It had more power than he expected, and it started easily.
Anyone who has been to a college and seen a Corvair that has never run before fire right up after 3 or 4 seconds of cranking will attest to Bob’s last point. When I put up the video of the test run on the 2,850 a few days ago, I intentionally showed how well the engine will repeatedly hot start. Between videos like this, colleges and flying planes, there are countless examples of how well the engine starts.
A second thing that came out of the conversations with Bob was that part of his Lycoming experience was different from Corvair procedure. With Lycomings, the major concern in starting operation is not flooding the engine, because if you do, it can be very hard to restart. For this reason, Lycoming pilots shut their engines off by pulling the mixture to idle cut off and starving the engine for fuel. When starting, they are very cautious not to get too much fuel in the engine by priming. The biggest factor on why Lycomings flood is their magneto ignition producing a low voltage, low energy spark, a plug gap of only .016″ and fairly low compression. If you get too much fuel in a Lycoming cylinder, the ignition can’t burn it off the plugs, and the lower compression will not vaporize the fuel just from the heat of compressing the air in the cylinder. It is a big issue, and if you are at an airport and you hear someone grinding away on a Lycoming starter, they probably flooded the engine.
The Corvair is a contrast to this. The 40,000 volt high energy ignition and .035″ plug gap is comparatively immune to flooding. The ignitions that we build have enough energy to fire plugs that are dripping with fuel, and when they do start, they will generally burn the carbon off the electrodes. The Corvair’s compression being one point higher doesn’t sound like much, but it gets it over the threshold of vaporizing fuel. If a corvair is cranked, it will vaporize excessive fuel and blow it out the exhaust, where a Lycoming will often leave wet drops of fuel in the cylinder even when it is cranked repeatedly.
When a piston comes to top dead center on the power stroke the air and fuel in the cylinder gets instantaneously hot. This is called adiabatic heating. The higher the compression, the hotter it gets. Our thermodynamics teachers loved pure textbook examples, where there was no heat transfer to the container, but those scenarios only exist in textbook land and unicorn world. Professors actually love things like “Carnot cycle engines” which we paid money to learn was perfect, albeit with the small flaw of just being theoretical and not possible to build. Thermo is the only branch of science that devotes time to studying and being fascinated with perpetual motion machines. Ah, but I digress…….
Above, an overhaulled NAS-3 that went on the Pietenpol of Dave Minsink. Read the story at: Stromberg Carbs
What you can take away from this is if you ever have a hard time cranking a Corvair, it is far more likely to be under primed than flooded. Dan provided Bob with a detailed procedure checklist to adapt his Lycoming experience to Corvairs. This included stopping the engine with the ignition switch rather than the mixture, priming the engine with the MA3’s accelerator pump one second before cranking, and starting the engine with the throttle cracked open slightly opposed to on the idle stop.
With these differences, the Corvair will start instantaneously. These procedures apply to MA3-SPA planes, but a variation on them also works well for Corvairs with other carbs. Our test stand has an old MA3-SPA on it, and it has done the first run on more than 150 engines. It has no primer, other than the accelerator pump in the carb, but I can generally get a brand new Corvair to fire off in 3 seconds at a College. Builders at these events in cold weather have seen me use the accelerator pump with as many a four shots before starting. This will make fuel drip out of the corers of the airbox. This leads people to think of the engine as potentially ‘flooded’, but in reality, excess fuel in the airbox doesn’t mean it got to the cylinder head.
With a warm engine or in warm weather, as seen in the video, the engine will start without any priming at all, unless the last operator shut it down by pulling the mixture. Again, other carbs will have slightly different procedures on a Corvair, but the concepts are the same, and I can think of many flying examples of Corvair powered planes for all of the popular carb choices that are capable of starting instantly. There is no reason to accept less than this on your own aircraft.
An entirely separate issue is engines that don’t crank well. Over the years I have had a handful of builders report to me that their Corvair powered plane had difficulty starting. One of the common things that these people said was that it could start easier on the points side of the ignition than it can on the electronic. More than one builder went to putting a very small second battery just to power the ignition during cranking or as some sort of back up. The fact this ‘worked’ seemed to validate their conclusion. In reality something else was likely at work. Read on;
First, let me say that several hundred running Corvairs use our E/P ignition. It completely dominates the flying Corvair community. Aircraft as diverse as Mark Langfords KR2S and Bernard Pietenpol’s “Last Original” have used our system. It is on the vast majority of all the Corvair powered planes you have ever heard of or seen pictures of flying. It works period. One of the things that any operator can tell you is that going from E to P, the ignition is on the other side instantly. Going from P to E, there is an audible delay of perhaps 1/4 of a second. Most people would not notice it without the comparison. From this, people with a starting issue often conclude that the two different sides should have different starting behavior. If they are just looking at one plane, this looks like reality. However, I have seen countless planes start easily on the Electronic side. Since we know that the modules, coils, and effectively the engines on these planes are the same, why are some people having an ‘issue’?
The most common answer is not the ignition, but the cranking end of the equation. Several things I have seen on planes have caused enough voltage drop on particular planes that the Electronic side had difficulty getting the voltage to start instantly.
Before we get to specifics, a quick test: If a plane is hard to start on the electronic side, hook a second, fully charged, 12 volt battery just to the E-coil with little jumper wires. If this ‘cures’ the problem, you almost certainly have one of the following going on:
-Low Main battery, or a dead cell in it.
-Missing or barely connected ground wire or strap causing high resistance and a system voltage drop.
-Starter shimmed too tight and binding, causing excessive current draw/voltage drop.
-undersized or poorly connected positive power cables.
-a separate ‘starter solenoid’ on the firewall (your starter has one, and if you put a second in, a-la the aeroconnection work book, you will cause yourself issues.)
radically advanced timing, incorrectly set.
Putting a second battery in is not the ideal way to correct the problem, the right way to do it is to fix the direct issue that is making the hard starting plane different from the others that function correctly.
The battery on the test stand is just a cheap one I borrowed from a garden tractor 9 years ago. It has less than 40% of the cranking power of a Oddessy 680. Yet it will go for a College and many months without being charged, happily starting Corvairs instantly. If an engine does this on my stand for its first fire up at a College, but is a hard starter when later installed in a plane, chances are, it has something to do with the airframe installation.
You might scoff at this, but last year, Dan and I had a series of phone calls with a Corvair pilot, a second owner who didn’t build his plane, who was having an ‘issue’ with a ‘bad’ starter. Dan specifically told him to get a set of jumper cables, and jump the starter off a car directly as a test. Pilot claimed to have done this, but didn’t actually try it. Instead he replaced the battery; borrowed a car and drove 100 miles and paid a guy to rebuild the starter in spite of the fact the rebuilder said there was nothing wrong with it; called me and asked if we could send him an entirely new starter: went on the internet and asked local experts for help; nothing worked. The issue? Of course his ground wire to the engine had fallen off. If he had followed the test of the jumpers, he could have saved several frustrating days and about $1,000. Experimental aviation is a very expensive hobby if you have trouble with following good advice.
Here are things that are not likely to be an issue:
-“stuck weights” in the distributor. I have had people claim this as a possibility on a hard start, but I can show anyone that the starter we use on the Corvair can crank the engine with 30 degrees of static advance.
-a variation in parts i.e. “My Crane E unit must have a different character than all the others” Mass produced electronic devices are not like this. There is far more variation in the quality of ground straps and battery connections made by homebuilders.
If any builder experiences anything other than quick starting, I encourage them to write me or call. There is no reason to tolerate sub-standard operation, and there is really no reason to follow sub-standard advice. ww.