More Crank Info
Pictured above is the crank rack in my hangar. It has only half of the cranks in the hangar in it. Having this many
on hand helps us in pursuit of crank R&D. A builder wrote us assuming that our testing was based on seeing two or three
cranks. He proposed looking at two groups of five. I honestly told him that over the years we'd seen literally hundreds
of Corvair crankshafts, and if my comments were based on seeing only 10, I'd keep them to myself. Beyond direct experience,
the strength of our commentary is also based on my ability to corelate this with experts we've sought out.
In my book,
Steve Wittman was the greatest airplane builder/pilot of all time, and Smokey Yunick was the greatest internal combustion
R&D man. I got to fly with Steve Wittman and discuss engines with Smokey Yunick because I've never been shy about
seeking out experts, introducing myself and listening to the voice of experience. My knowledge of the Corvair engine
exists simply because of our testing, flight experience and the input of qualified people. This goes on continuously, and this is why
our knowledge isn't static, but always increasing in quality and quantity.
Crank Procedure
The following is the radiusing and nitriding procedure which I sincerely hope all Corvair engine builders will take. The
Corvair is an experimental engine and you are free to build it any way you wish. If it were a certified engine, an AD
would force you into compliance. In the case of experimental aircraft, I can only appeal to your common sense and hope that
you will avail yourself of what our testing has shown to be a significant reduction in risk for a very modest cost.
Nitriding the crank reminds me of five years ago, when I told everyone that flight engines really needed forged pistons.
A giant debate ensued, mostly on the Net. People who were not flying had plenty of arguments: "Cast pistons are good
enough," "I heard people flew them for years without a problem," "I don't want to spend the extra money," etc. In the
end, I convinced perhaps 95% of builders that forged pistons were the only way to go. My call for nitriding all flight
engines has been met with positive review and simple acceptance from most builders. A handful have brought up the
same type of arguments that we'd heard before against forged pistons. In the long term, our testing and logic will win over
the vast majority of people. Nitrided cranks will take their plance alongside forged pistons and ARP rod bolts as minimums.
It's all part of teaching you how to build the best engine at a reasonable cost. This is the focus of our work. No part
of my work is aimed at finding out what most people can get away with.
Ion Nitriding
Builders fall into three categories: core crank stage; reworked crank stage; and flying crank stage. The situation varies
a bit, but essentially I want everyone to have their crank ion nitrided.
Core Crank Builder
This is the point when your crank is in the same condition as removed from your core motor. Previously, builders had
sent their cranks to us. We threaded them, ground them, and equipped them with Hybrid Studs and
a Safety Shaft. If they were also gas nitrided, the turnaround time on the crank crept up toward
six weeks. We did not run an exchange; each builder got his own crank back. This has been an elaborate operation because
the grinder and the nitrider are 30 and 100 miles away from us, respectively, in opposite directions. Our nitrider is
also a gas nitrider, which is not as desirable as an ion nitrider. The nitrider we've selected as the best available
for Corvair engine builders is Nitron Inc., in Lowell, Mass. Since it would not make sense for us to mail your crank
back and forth to Massachusetts, we're now encouraging builders to have their cranks ground with proper radiuses at their
local machine shop, where they also can be threaded for the Safety Shaft. They can then be mailed directly to Nitron,
where your crank can be turned around in a week or two. We will still provide Safety Shafts and Hybrid Studs, and of
course, the Conversion Manual contains a drawing showing the threading of the crank. Unlike gas
nitriding, ion nitriding can reliably be done as the last procedure in preparing your crank. It is done at a significantly
lower temperature than gas nitriding, and there is comparatively no chance of crank warpage in the ion process. This is a
significant benefit and you should take advantage of it by having all your machine work done before sending the crank.
Reworked Crank
The reworked crank stage includes anyone between the core crank and an engine that has flown. You may have had your
crank prepped and just kept in a bag, you may have installed it in your engine already, or you may have even run the
engine extensively on the ground. In any of these cases, the crank can be prepped and shipped to Nitron directly. Again,
the turnaround time will normally be one to two weeks. Engines that have been run on the ground only have not put any significant
bending stress on the crankshaft. They are excellent candidates for nitriding. Again, this is another opportunity to
inspect the radiuses before shipment. We will shortly have an update with some good photos on this. Keep in mind that
the staff at Nitron are experts in their field, but they are not going to offer any commentary on magnafluxing, radiusing,
or machine work. They are taking the highly respectable position of keeping their comments within their field of expertise.
Flying Crank
The third category is flying engines. If you have a Corvair that's flown even just a few hours, you should call me at the
hangar 9 a.m. to 5 p.m. EST weekdays, (386) 478-0396, and discuss your position in detail. The reason why we're insisting on proper radiuses and nitriding
crankshafts is to reduce the chance of them cracking due to flight loads. Using the right people and the right equipment,
I can inspect a crank to see if any crack has started. But here is a much more reliable procedure than inspection:
retiring the crank. The types of cracks that we're concerned about do not happen in cars because they do not experience the
bending loads associated with flight. A crank removed from a car and given a careful ring test for cracks is a better
position to start with than using a non-nitrided crank that has experienced flight loads. The flight crank may have a
minute, undetected crack, and the nitriding will do no good. For this reason, I encourage people with flying engines to
directly contact me. We have a large number of cranks in reserve for this program. It is in the long term interest of
Corvair powered flight that we have a procedure available to retire previously flown non-nitrided crankshafts. Unlike other
aircraft engines, the cores are fairly cheap, and I'm willing to shoulder a lot of the burden to make this happen. Please
note that this is a trade-in program for people with flying engines only. I do not sell crankshafts outright to builders in
the first two stages because this would rapidly deplete our reserve that makes the stage three program possible. We're
here to help everybody, but reasonable builders will understand us prioritizing this.
Sending Your Crank to Nitron
Nitron Inc.'s address is: 26 Wellman St., Lowell, MA 01851. Nitron is run by an extremely friendly, aviation knowledgeable
gentleman whose first name is Pramod. I first met him several years ago at Oshkosh. His phone number is (978) 458-3030.
As we've mentioned with our other business sources, please be respectful of Pramod's time. We're providing detailed instructions
here so that builders can utilize his services with a minimum of hassle and delay. If every builder needed to call and
review the following procedure, or wanted to debate ion vs. gas nitriding, the process would have to be more expensive
and it would take longer. I encourage builders to follow the procedure and trust my judgement that Nitron is the correct
provider of what we're seeking.
Prepping
The crank needs to be as clean as possible. The fuel pump eccentric, washer and distributor gear should be removed with
a puller. If you have a stage two engine, a propane torch can be used to warm the end of the crank to 300F to soften the
Loctite on the Hybrid Studs and Safety Shaft. Do not subject the Studs to more than 30 pounds of torque in unscrewing them,
and be cautious not to overstress the crankshaft when removing the Safety Shaft. As an alternative to propane, the crank can
be left in a household oven to heat soak at 300F for an hour.
The crank should be degreased, dried off and wrapped in a plastic bag. It should then be wrapped in two turns of clean
carpeting, leaving excess to protect the ends of the crank. Take a little time to build a sturdy wood box held together
with sheetrock screws. Mark which screws to remove to open the box. Nitron normally deals with batch quantities of
industrial goods. We want to make handling our retail work as easy as possible for them.
The cost is $150 plus the return shipping. When you're ready to ship your crank (I recommend the U.S. Postal Service
for this), find out how much it costs, add this as the return cost to the $150 nitriding charge, make the check
out to Nitron Inc. and include it in the box with a Nitriding Liability Statement.
This Liability Statement is a simple, plain language form to help everyone understand that they are still in charge of
their own risk management. This is a reasonable request. Many of the nitriding outfits I contacted refused to touch
experimental aircraft parts. Others doubled their price. I believe that Nitron's process is the one we want, and it's
simply an additional plus that he's willing to provide it to experimental aircraft builders at a reasonable cost.
Upon the return of your crankshaft, you'll still have to carefully clean it before installing it in your engine. But
its ion nitriding will provide a significant reduction in the risk of crankshaft breakage in any Corvair flight engine.
A word about fillets: In our previous update, I wanted to convey to builders that properly radiused fillets were
not a substitute for nitriding. After speaking with a few builders, I realized I need to equally convey that first
class nitriding does not make bad radiuses acceptable. In extreme cases of tool marks or nonexistent radiuses, nitriding
can actually make the situation worse. This is a rare instance, as most crank grinders understand what a proper radius
looks like. We're working to have an update on radiuses, which will include highly magnified images to compare with
your crankshaft. We're actively investigating available radius gauges to put simple tools in the hands of every builder.
We're shooting to have this done next week. I want builders to understand that radiusing and nitriding are complementary
procedures, and I consider both a requirement. Reasonable builders will obviously want to stack everything in their
favor within the bounds of affordability to reduce their risk. We've all heard the saying "If the job of the captain
was to protect the safety of the ship, he'd never leave port." The only perfectly safe airplane is one that never flys.
But we're all in this to go flying. My goal is to help you do it without taking unnecessary risks. A properly radiused
ion nitrided crankshaft provides a large increase in strength and fatigue resistance to a direct drive Corvair's
crankshaft. Because there have been many examples that have been flown for a thousand hours without this, some builders will
take the perspective that they can get away without it. Conversely, my mindset on the issue is this: If the crank will usually
perform well without it, the ion process will move the engine one giant step closer toward being what homebuilders would
consider bulletproof. Industry people with an in depth knowledge of metals and processes recognize that a properly done
job will likely give the crankshaft an infinite fatigue life based on the loads we currently apply to it.
Ongoing Fifth Bearing Research
Keeping in mind that there are builders who would like to use the Corvair with propellers and flight loads that go well
beyond what is currently considered acceptable on direct drive automotive engines like the Corvair, VW and Jabbiru, we
continue work on fifth bearings and spline drives.
In the above photo are three crankshafts: The top one is from a Lycoming O-320, the middle is a Continental O-200, and the
bottom is a Corvair. To resist the bending loads brought on by a flying propeller, the top two cranks have extended length
front bearings. This can clearly be seen as the distance between the front throw and the raised thrust surface behind their
prop flanges. The Corvair, being an automotive crank, does not have this. It counts on its stiffness across the first two
throws. With light props, this has proven to work over the past 45 years. With proper radiusing and ion nitriding, I believe
that most all of the flying applications today, such as KR-2s, Pietenpols and 601s, with 8 pound props, can fly with an
acceptable level of risk. This is not unusual. VW engines and Jabbirus are both restricted to using props with an even
smaller moment of inertia than a Corvair. It's interesting to note that the Corvair's main bearing diameter is 2.1" and
the O-200's is only about 1.8". The O-320 is about 2.3".
My goal by putting a fifth bearing on a Corvair is to move the engine into a strength category falling somewhere between
the O-320 and O-200. The O-320 crank seen above is approved for continuous use with 75 pound constant speed props. I'm
reasonably sure you could pull a snap roll with the combination and not break the crank. The O-200 has been shown to
successfully fly aerobatics with a 25 pound metal prop. This is made possible by the length of the straight section of
the shaft supported by bearings behind the prop flange. We're getting closer to having a running example of just such a
system. By changing the style of the nosecone, and the crank extension, the system can actually test several different
types of bearings.
In the above photo are four plain bearing styles. The long one on the bottom is from an O-320. It has separate thrust
surfaces in the case. Keep in mind that this is essentially serving as the last two bearings in the engine, and the strength
of the system is based on the diameter of the shaft, but importantly, how far the two bearings are apart. From left to right
across the top are a Corvair thrust bearing, Pontiac 455, and small block Chevy.
Our primary focus is utilizing the small block bearing as the fifth bearing. I exchanged some e-mail with our friend
from Canada, Wayne Burtney, this week. Wayne is a very clever guy who is building a Pegzair. In Corvair circles, he is
best known for having built a 3,100cc engine with a fifth bearing housing that utilized a Corvair's thrust bearing.
He built this from a set of 1960s drawings that are currently sold by Falcon Air in Canada. The project drew attention
because it was featured in Contact! magazine. Wayne shared with me that he has not run the engine, and it is currently
in storage while he finishes the wings for his plane. In the past two weeks, I've received more than a hundred e-mails, varying
from polite to rude, about crankshafts and fifth bearings. All contained some type of suggestion of how to proceed. Many
of these clearly came from someone who'd never seen a Corvair engine in person. Buried in this comes an e-mail from Wayne
which I can honestly say is the standout suggestion received: He said that he would not build his current drive again; given
a fresh start, he'd base his efforts on a 460 Ford bearing and its 3.00" interior bore size. This would allow the use of a
lot of existing components, like Hybrid Studs and a Safety Shaft. In retrospect, it is not surprising that the most practical
suggestion came from a guy who already built an engine. Based on his thought, I studied the Clevite bearing catalog and
went down to the auto parts store to pick up the Pontiac bearing. It is 3.25" and slightly wider than the Ford bearing.
We're going to work on this in parallel with the small block, study both and see which yields more practical application.
A few words about research: 17 years ago, I had a Corvair engine sitting in front of me, and having read every issue
of Kit Planes I could get my hands on, I was determined to make it into a good airplane engine. I was long on
enthusiasm, but did not own a plane, have a pilot's license, nor enough money to overhaul the engine in one shot. I'd
overhauled countless land based powerplants, but had no real background in experimental aviation powerplants. At the time,
I did not realize that the articles I was reading came from people who were perhaps a single step ahead of me in the process.
Although I would not have wanted to hear it at the time, it would take many hard years before we could mount an effective
R&D program on any subject. Yes, it took spending money, and lots of it in some cases. But there was no substitute for the
practical experience that came only with time and day to day experience; learning from experts in the field like Al Jonic,
people who were making things fly, not writing magazine articles, was a real turning point. My five years at Embry Riddle
was the force multiplier that enhanced every aspect of my pursuit of the affordable airplane powerplant. I read all of the
suggestions that recently came in. Had there been an Internet, it's not difficult to imagine myself writing one of them
17 years ago. I've not forgotten the desire to create that drove me 17 years ago. It's more alive today in my hangar than it
was in my imagination then. The frustrations I experienced then are a large part of why I'm thankful to be able to work
in our hangar seven days a week in an effective manner today.
On a slightly less serious note, a handful of people asked whether it was statistically a good test to look at a small
number of engines and base my nitriding recommendation on it. My recommendation is really based on our overall experience
with hundreds of engines. The latest round of testing is really just a small part of this. I'm well aware of the statistical
limitations on small samples. While my mathematics skills in differential equations were nothing to write home about, I was
a stellar student in statistics at Embry Riddle. A lot of branches of aviation, from engineering analysis to accident
investigation, use statistics, and the school had a very rigorous program of statistics classes. I was later hired by
the school to teach statistics. Upon reviewing my record in calculus, the head of the program labeled me an idiot
savante in statistics.
Concurrently, we're working on the spline drive, which will be a field installable front bearing unit. The fifth bearing
and the spline drive share some parts in common, like the front plate. We received some mail about splines, mostly some
general questions. One or two e-mails did contain comments from people unfamiliar with splines. One of these people stated
that the power of a Corvair engine could not be transmitted through a spline.
The above photo shows a phantom view of the Corvair transmission and differential from the GM manual. Below it are two
halves of a Corvair input shaft. The input shaft connects the clutch disk to the input side of the transmission. It, of
course, is splined on each end. If you study the drawing in the shop manual, you'll see that the power from the engine
in the car goes through at least six sets of splines on its way to driving the wheels. Splines are very common in the
mechanical world. Virtually all cars have them in the driveline. The largest aircraft engine I've ever touched is a Curtiss
Wright turbo compound R-3350. This 3,700hp piston engine drove its propeller through a set of SAE-60 splines. With 59 days
till Sun 'N Fun, we're shooting to fly a fifth bearing engine there, and perhaps have a spline drive prototype on display.
Seventeen years after beginning my work with the Corvair, we're in a pretty good position to conduct such tests. Years ago,
I could come up with ideas, make drawings and discuss them, but today, through hard work and persistence, I've been able to
assemble the skills of the Hangar Gang, including an extraordinarily skilled test pilot, a
facility full of tools, instrumentation, three flying testbed airplanes, the years of experience, and
contacts with expertise in the supporting industries. This puts us in the unique position of actually being able to
design, build, test and perfect systems that we could only talk about years ago. My basic creativity drives the work, but
we're glad to conduct this work on behalf of Corvair engine builders everywhere, and make the information available to all.
It's going to be a creative and exciting year. We're glad to have you along.
Now At The Hangar
June 2011 At The Hangar
May 2011 At The Hangar
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January 2011 At The Hangar
December 2010 At The Hangar
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Christmas 2007 At The Hangar
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December 2006 At The Hangar Part 1
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December 2006 At The Hangar Part 3
December 2006 At The Hangar Part 4
November 2006 At The Hangar
October 2006 At The Hangar
September 2006 At The Hangar
August 2006 At The Hangar
At The Hangar In July 2006
June 2006 At The Hangar
At The Hangar In May 2006
At The Hangar In April 2006
At The Hangar In March 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
