Sunday Papers Volume I - Ignition Systems
This is the first in a series of technical papers giving an in depth look at a particular aspect of a Corvair flight engine.
A lot of the information on this part of our Web site is news and events oriented. The Sunday Papers are intended to be educational
and timeless, something you'd print and keep with your Conversion Manual. If you're one of the people new to the Corvair
movement considering attending an event like Corvair College #11, the Papers will serve as a perspective on the scope and
depth of my knowledge on Corvairs, which is free to anyone, and the place to come to learn.
When I was 18 years old and getting started in drag racing in New Jersey, I was working at a drag racing house called
Speed World in Union. Our home track was Englishtown, site of the NHRA Summer Nationals. Even the sportsman racing was
fiercely competitive. We were fortunate enough to have one of the East Coast champions, Bill Houska, as one of the shop's
sponsored racers. In drag racing's single eliminations, defeating your competitor is referred to as "trailering" him. Frequently,
in 8 rounds of eliminations, Bill would trailer everyone he came up against. Initially it seemed like magic or voodoo. Only in
time did I learn that it was meticulous preparation, checklists and concentration that were the key elements of his success.
As a starting point to emulate his success, I copied all his style and techniques, down to wearing the same kind of sneakers.
In our youth, he seemed as old, wise and powerful as Obi-Wan Kenobi. He was about 30 years old.
As you're looking at ignition systems for your own Corvair powered airplane, take the lesson to heart and start by emulating
what works. Virtually every flying Corvair powered airplane built in the past 10 years has one of my ignitions on it.
The two or three other airplanes that flew without it are yet to log 100 hours between them. No aircraft has ever had any type
of a forced or precautionary landing made on our ignition system. It works. Period.
Above is a wiring diagram that shows the basic layout of my ignition system. This page is taken from our 601 Installation
Manual, so it includes some of the wiring associated with fuel pumps. The key elements of the design are redundancy, low
power consumption and low voltage tolerance. It's also immune to voltage spikes and high temperatures. No other ignition
system that builders have proposed or theorized has these qualities, far less thousands of hours in the air to prove it.
I've tried many different versions of the ignition system. Beyond flight testing, having the distributor machine and
dynomometer are force multipliers that allow me to examine a bigger picture than is available to
anyone who has a favorite theory about ignitions.
With our system, notice that you can fail one of the coils or one set of points and still have 100% power available through
the backup system. Once every few months, a builder will propose a system that has three pickups and a wasted spark system using
three coils and two plug leads from each coil. I know these systems well, and they're not safe to use in Corvair engines
because with three coils and three pickups, you're statistically more likely to have a failure and when you do, you'll be
immediately down to 66% power. However, the dyno shows that dragging two dead cylinders means you're really down to 50% power
and most Corvair powered airplanes will not climb on half power.
Our August Update contains a photo of Mark at Falcon's EFI engine. Note that it actually has
six LS1 coils which have built in modules. This is acceptable because a single coil failure will bring you down to 83%
theoretical power; about 75% power on the dyno dragging one dead cylinder. This illustrates the point of why it's acceptable to
have single plug ignition on a six cylinder engine. The performance loss of one cylinder on a six is not catastrophic like losing
one cylinder on a four cylinder engine. Corvair powered airplanes have taken off and flown on five cylinders on three occasions
that I know of without incident. This was due to a missing plug, blown head gasket and missing rocker stud, respectively.
The shot of the workbench above shows 85 Distributor bodies neatly stacked. Over the years, I've reworked several hundred
Distributors. I've had the opportunity to examine many of them after they've put in a year or two of flight service. We've
continuously had running Corvair vehicles to test all types of ignitions in the ground environment. Many of the theories I was
taught and believed 15 years ago proved inaccurate or inapplicable to our situation.
One of the most important aspects of the ignition system is that it's low voltage tolerant and a low power consumer. There's
a lot of theoretically great electronic systems that work fantastically as long as there's more than 11.5 volts available and
a steady flow of 10 amps to power it. In the world of flying, where you could have an alternator or voltage regulator failure,
and be reduced to the amount of electrical power stored in your battery, these electronic systems are not acceptable. A Corvair
engine running one of my ignition systems will run for hours on the battery that started it. The points system will work all
the way down to the 9 volt range. Electronic ignitions with computers on other alternative engines have demonstrated as
little as 20 minutes flight time with very serious consequences after a charging system failure.
My new Electronic/Points
system utlizing the Crane module is a very low power consumer and additionally has the unheard of quality of producing stable
sparks well below 9 volts. No other electronic ignition that we tested demonstrated this. Corvair cars frequently use a
system made by Pertronix. While not a giant power consumer, the Pertronix system is very voltage dependent. I searched for a long
time to find an electronic system that could complement the points. I had looked at the Crane system, but it was our friend
Steve Makish, an electronics expert, who first tested his own version of it. Based on his review of
the Crane unit, I evolved our own Dual Points Distributor to Electronic/Points. This system is now flying on the aircraft of
Mark Langford, Mark Jones, Rick Lindstrom, Dan Weseman and others. It's my intention for this to be our new standard
ignition system. As logic would dictate, we have tried to supply the people with flying airplanes first, before making it a
regular part of our Catalog.
I continuously buy piles of core distributors and disassemble them so we only use parts that are in excellent condition. The
distributors above were provided by Bob Bentz, an excellent source of core motors for builders who want to pick them up near
Lakeland, Florida. Contact him at (813) 716-1633.
In the above photo, the Crane unit replaces one set of points. This uses the same coils and systems as our Dual Points
Distributor with the exception of eliminating the condenser on the electronic ignition's coil.
The above photo shows the firewall mounted electrical box from Gary Coppen's Skycoupe. We put this
together seven years ago to house all the electrical components and flow cool air over them. The only difference in today's
method is the use of Bosch Blue Coils, readily avaiable from Great Plains Aircraft. The Accel coils shown above must have external
ballast resistors, which are internal on the Bosch Blue Coils. The top shelf houses the MSD 8210 coil switch. There's some
discussion about the use of the Mallory equivalent of this part. The system will work with either; it does not care.
Above is a sectioned Corvair distributor body showing the location of the dual bushings. Corvair factory distributors only
had the top bushing. For many decades, it's been a popular high performance modification to install the second bushing in
the bottom of the Corvair's housing. The primary requirement for this is to support the distributor shaft under a load.
The ignition system is not the load on the distributor. The work it does driving the oil pump requires at least 25 times the
effort from the distributor shaft.
I occasionally read Internet discussions where an armchair theorist describes eliminating
the Corvair's distributor. This illustrates how little some people inspect the engine before speaking. Even with an
ignition system that has no distributor cap, such as the EFI system, you still must have a distributor assembly to drive the
oil pump. I have long told people to use standard Corvair oil pumps and thin multigrade oil, and never to use oil coolers
without bypasses. These oil system issues will affect your ignition system by overstressing the distributor shaft. Conversely,
my thoughts on the distributor shaft are now leaning toward a single bearing design. Many companies made dual bushing housings.
Clearly the absolute best ones were made by Dale Manufacturing. I've heard the term "Dale Housing" used to
describe any dual bushing housing of any quality level. Dale no longer regularly makes these housings because no one is
willing to pay what it takes to do them correctly.
We've long modified the housings ourselves. It takes a long time to do this
correctly. There are quick and dirty ways of doing it, but unless the bushings are perfectly aligned, you're better off
having only one. Even slightly misaligned bushings will show as housings that run hot in the distributor machine. Additionally,
any variation in the hardness of the bushings will produce rapid wear on one of them. Worn bushings show up as dwell variations
in points systems. One of the advantages of our E/P Distributor is that the Crane unit is immune to timing changes caused by
bushing wear. While the end goal is to come up with a bushing system that will not wear, it is still currently an advantage.
I've long been in pursuit of an economical replacement distributor body which can incorporate a bearing instead of a bushing.
Above, the sectioned stock housing sits next to an idea I'm pursuing. The small end of the housing on the right is a machined
billet. It's inexpensive because it's a pure body of rotation and it comes out of a piece of 2" stock. The large end is the
stock Corvair end severed on a lathe. The two pieces grafted together are much more affordable than a whole CNC body, which would
increase the cost of the distributor several hundred dollars. The two bearings in the photo are a straight roller and a double
angular contact ball bearing. Both of these require sleeving the shaft size up. I have one other design that uses a single
row ball bearing in a remachined stock housing. This is done and currently in testing, but the stock housing restricts it to
being a fairly small ball bearing.
Having a perfect and affordable bearing/bushing system that is mass producable is the long term goal. For now, orders are
filled with dual bushing housings that are individually tested on the distributor machine to ensure they have proper alignment.
The above photo shows a Dual Point Distributor in the machine. I recently disassembled the distributor machine and overhauled
it. It was made in 1950 and has a single vacuum tube inside that I handled very carefully. The items piggybacked on the top row
allow the simultaneous operation of the electronic side of the Distributor while superimposing the EI picture on the scope.
When running a Distributor on the machine, I can vary the rpm it's turning and observe its advance directly. When your
Corvair engine is idling, the advance weights in the Distributor are held shut by springs. The advance at this point is referred
to as the static timing. I set the Distributors so they have no advance below 900 rpm. As the engine comes off idle, the
mechanical advance inside the Distributor's body makes the spark occur earlier. This is the mechanical advance at work.
All the mechanical advance needs to be in by 2,400 rpm or so. This way, you can tie the tail of your airplane down, run it to
full power and check what the total advance is at the propeller's full static rpm. Total advance for engines running on 93 octane
fuel should not exceed 32 degrees. For engines on 100 low lead, 34 is the limit. Beyond these numbers, the engine could be
aggravated to detonate.
Each of our Distributors is marked on the underside with its mechanical advance and the beginning and ending rpm of its curve.
Thus, if you have an engine you're going to run on 93 octane fuel, and your Distributor says "18-1,000-2,400," use a timing light to
set the static timing to 14 degrees below 1,000 rpm. With the plane tied down, raise the rpm above 2,400 and verify
that the total advance does not exceed 32 degrees. A dire warning: Never touch the ignition wires while the plane is running
and turning a propeller. There is a remote possibility you'd get a high voltage shock and inadvertently flinch into the propeller.
It's a very remote possibility, but a builder in Australia did it and was lucky to keep his fingers.
The only distributor caps we use are made by Echlin. The tan cap is the heavy duty unit that's intermittently available from
NAPA. Both have copper contacts inside. They were made in Mexico for the past five years but have recently been shipped to
us with "Made in the U.S.A." stickers and slightly different mold marks. Although the 1830 part is considered heavier duty
than the 183, it is Bakelite, not thermoplastic, and therefore more brittle. A VariEZ builder recently returned to us a Dual
Points Distributor with the 1830 cap for the Electronic modification. He carelessly packed it in a small box, and it showed up
here with the cap smashed. The 1830 caps should be handled with more care. Let's keep in mind they're aircraft parts.
In the above photo, the screwdriver points to one of the two 8/32" screws that hold down the Points Plate. Shown here is
the stock GM slotted screw. For years, I've replaced these with stainless Allen screws that are slightly taller. Builders
need to be aware that some aftermarket distributor caps will not clear the Allen screws. This is easily detected because the
cap will rock back and forth on the screws instead of sitting flush. Merely tightening the screws is not the solution. I have
reverted to using slotted screws to prevent unobservant builders from replacing their cap with an incompatible one. The slotted
screws will clear any cap I've seen.
The above photo shows four point cams. Occasionally people ask if they can recurve distributors at home. It would be a very
difficult process, and while you might achieve some results, a lot of the fine tuning we do to distributors is very difficult
to see. Off the end of the screwdriver is the part of the point cam that the counterweight touches. Notice the four different
profiles shown here. There are six different common Corvair profiles. The upper two are ground to match templates we've
developed to produce ignition curves that suit aircraft use. The upper two point cams appear shinier because they're nickel plated,
an ongoing test we're doing.
A long time ago, I'd recommended Moroso Blue Max ignition wires. They're very good, but in recent years, I've come to prefer Accel
5041 sets. They have a tougher silicone jacket that holds crimps better. They're available in a variety of colors from
www.SummitRacing.com. The set has enough wires to do the coils and 8210 also. Also in the photo is an MSD sparkplug crimper
from Summit. These ratcheting crimpers cost about $60. But they're the absolute minimum standard for making ignition wires. $10
auto parts store crimpers are completely unacceptable for flight applications.
We have a number of customers who have patiently waited for these developments with ignition systems so that they can have
the most up to date pieces we produce. There are also a number of builders whose airplanes are closer to flying who've requested
their orders be filled with Dual Points Distributors. We're equally happy to comply with either request.
Now At The Hangar
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December 2006 At The Hangar Part 1
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At The Hangar In April 2006
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At The Hangar In February 2006
At The Hangar In January 2006
At The Hangar In December 2005
At The Hangar In November 2005
At The Hangar In October 2005
At The Hangar In September 2005
At The Hangar In July 2005
OSH, Illinois and SAA June 13, 2005
At The Hangar June 13, 2005 Part II
At The Hangar In May 2005
At The Hangar In April 2005