Corvair Engines - The Justification Series

[daleandee]

I would like to reiterate that this series on justification is to answer the question of why I followed the path I did by installing a Corvair engine on this air frame. Remember that the views in this series are mine. Should anyone decide to follow a similar path they must understand that the choice and consequences are theirs. What has been successful for me isn’t a guarantee for anyone else. Having said that; I did follow a well-trodden path in my journey to find and build the best experimental, light sport compliant, airplane I could afford. My airplane is a very close clone to previous Cleanex models. I tried to duplicate all the things that had been shown to be highly successful on previous builds. Not only what parts to use, but the placement and coordination of the parts and how they worked together. My engine choices were limited by my budget. This caused me to work to find the best fit, the greatest reliability, and the highest performance my budget would allow. Enter the 3.0 Corvair conversion built by Dan Weseman.

We talk about safety and that must be the number one factor in our approach to building. The key factor in safety is reliability. Regardless of money savings, visual appeal, ease of operation, no maintenance required, latest & greatest, or any other attraction … if it’s not reliable it’s not worth flying behind. One of my favorite safety reminders is a William Wynne quote; “There is no characteristic more important than reliability. Anything you could get in trade for reliability isn’t worth it.” Very close to this is consistency. A great trait for humans as well as flying machines is that they will continually do their work on a reliable, dependable, and consistent basis. Working within those parameters means that changes are a warning that something is wrong and requires an investigation. That’s why it’s important to me that my engine never stumbles on the take-off roll. If it does, something is wrong and we go back to the hangar and investigate.

Real performance! As we approach safety from a different view another ‘justification” is realized by the performance data of the Cleanex showing improved capability with the greater horsepower available from a 3.0 Corvair conversion. My earlier VW version of this air frame would climb solo at a rate of ~750 fpm, and at gross of 1100 lbs. at 350-400 fpm on warm Carolina days. A Cleanex with a 3.0, 120 HP Corvair at 1250 lbs. gross will out climb a solo piloted VW powered version quite strikingly with well over a 750 fpm climb out rate. Excess power to climb is an excellent safety feature to have on an airplane. High density altitude, hot summer days, short strips, grass fields, climbing to get over mountains, etc., all become easier with more power that doesn’t over tax the engine, isn’t limited to a couple of minutes at WOT, or overheats the engine quickly requiring “step climbing.” Whenever recovering from a balked landing or a go around needs to be executed in a hurry it is easier with extra power on the nose of the airplane.

In 2009 two Corvair powered aircraft flew alongside a Jabiru 3300 powered one from Florida to Tennessee for the ASA gathering. Comparing notes upon arrival it was discovered that the fuel burn and speeds for the two different engines installed on these air frames were remarkably close to the same.

It has been suggested that a heavier Cleanex would suffer in take-off & climb performance. Take a moment to consider power loading numbers at gross for a few engines (realizing that the lower the number the better):

80 HP VW @ 1100 lbs. – 13.75
85 HP Jabiru 2200 @ 1100 lbs – 12.94
100 HP O-200 Continental @ 1250 – 12.5
100 HP VW Turbo @ 1150 – 11.5
120 HP Jabiru 3300 @ 1150 lbs. – 9.58
120 HP Corvair 3.0 @ 1250 lbs. – 10.41
110 HP Viking 110 @ 1250 – 11.36

Better numbers are available for some if using a lower gross. A 700 lbs empty weight, polished, Cleanex with a 3.0 and using 1150 lbs for gross would give a 450 lbs. useful load and the exact same numbers as the Jabiru 3300 for power loading. So when considering performance note that the 80 HP engine with the lower gross actually has the poorest power loading number while the 120 HP Corvair @ 1250 lbs. gross falls only behind the 120 HP Jabiru 3300 at 1150. That’s performance!

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

[DCASonex]

Dale, One minor clarification. The Jabiru and CAMit 3300s maximum continuous RPM is 3300. With the L series Jabiru limited by name plate change to 2,850 so that Sonex can still qualify for light sport.

David A.

[daleandee]

Dale, One minor clarification. The Jabiru and CAMit 3300s maximum continuous RPM is 3300. With the L series Jabiru limited by name plate change to 2,850 so that Sonex can still qualify for light sport.

Hi David,

Thanks for the catch! I went back and deleted that line. I did find the 3300-L limitations in their install manual i.e. "The 3300L engine has a maximum continuous RPM rating of 2850RPM. The engine may be operated at engine speeds above 2850RPM for up to 10 minutes."

As you pointed out & is seen in the manual, there is no difference at all in the engines so the RPM limit is strictly for light sport compliance. For any wanting a reference, that information is here, under section 3.1.1 - http://jabiru.net.au/Manuals/Engine/JEM3304-9_IM.pdf

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

[daleandee]

Safest engine available in my price range! Scanning the NTSB site gives accident data for various engines that were available to me for this air frame in the price range I could afford. There are various ways to slice and dice the numbers so absolutes as far as true reliability are hard to measure. At the end of the day the Corvair came out ahead of any of the competitors in the price range that I was working with. From 2001-2017 the NTSB site list 14 accidents when the word “Corvair” is used in the word string box with all others blank (one was for a certified aircraft using a Corvair fuel pump). Remember that Corvair engines are used on many different types of air frames including Zenith 601, 650, 701, 750, KR’s, Peitenpols, Dragonfly, Panthers, Cleanex, and countless other aircraft since 1960 when a Corvair first flew on a Pietenpol.

As there have been many versions of flying VW, Subaru & Honda engines so there have been variations of the Corvair conversion process. Nevertheless my goal was to find out the reliability and failure rate of the particular conversion I was interested in as opposed to all other choices I could afford at the time. One of the biggest advantages I had was my previous experience with a factory VW conversion on this air frame for a number of years. It isn’t my purpose to criticize the factory offering so I’ll focus on what makes this particular Corvair conversion and its reliability so attractive for me:

• Simplicity! No need for a radiator, water hoses, water pump, cooling fan, gearbox, turbo, fuel pump, or oil cooler lines.

• It doesn’t overheat. CHTs are less than 300ºF in cruise. Oil Temps (using the stock GM cooler) are 180-220ºF.

• The Marvel Schebler aircraft carb is excellent in operation. It doesn’t hesitate, stumble, bumble, or burp.

• It does not use or leak oil. Viton seals on the pushrod tubes seal tightly and are very resistant to heat.

• It has an oil fed front bearing (5th bearing) attached to the case for prop loads.

• The hydraulic valves stay adjusted after the initial setting during the engine build.

• No head retorquing required.

• Dual ignition based on the original GM designed distributor system that advances the timing as needed for flight.

• Ignition coils that are mounted away from the engine and don’t suffer from exposure to extreme heat.

• Ignition timing is set and checked at condition inspection with an automotive timing light using factory timing marks.

• Dual fuel piston design allows the use of 100LL or 93 octane auto fuel. Ethanol free is preferred but not required.

Modern Corvair engine conversions have proven themselves to be reliable, provide good smooth power, and are quite robust. The simplicity of this well-designed, air-cooled, direct drive, naturally aspired conversion is a major part of the reason that it is as dependable as it has proven to be. Another builder makes a valid point when he insists, “If it’s not there, it cost nothing, weighs nothing, and is 100% reliable.”

Like any engine it requires regular maintenance. But with hydraulic lifters, Viton pushrod seals (no oil leaks), iridium plugs, dual ignition, certified aircraft carb, and the use of K&N high quality oil & air filters, maintenance mostly consist of oil & filter changes at 25 hours and new spark plugs during the condition inspection if needed.

Corvair reliability is a safety factor that should not be dismissed. Many things make it reliable but one of the most notable is that it is not being strained to put out an amount of power it was never designed for. In its original role the later engines were rated up to 180 HP at 5600 RPM. To ask a modern updated & de-rated version of this engine to now give 90 HP at 2800 RPM falls well within the original design specifications and greatly enhances the reliability factor.

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

[daleandee]

As I close out the list of justifications I have for using the Corvair engine on my Cleanex one of the most important, yet often overlooked factors, is not only the quality of the build, but the availability of parts and service. Even were it possible for me to spend more money on a certified engine for my aircraft the ongoing maintenance cost could be substantial. Not only the cost of replacement parts but the ability to find them and receive them quickly was high on my priority list.

Respect for where my Corvair was designed (GM) and assembled (USA), the quality of the original build (SPA), access to high quality replacement parts, easily obtained service manuals, and knowledgeable personnel if needed was extremely important to me. Installing a certified aircraft engine could get quite expensive when the time came for serious replacement parts. Depending on where on earth an engine or engine kit is made can cause delays in obtaining parts.

If the builder/owner will be the mechanic in charge (the one responsible for engine repair/maintenance) they will need proper reference manuals and materials. Corvairs are well covered using the GM shop manual, Fly Corvair conversion manual, and the newest highly detailed and illustrated manual from SPA. The more complex the FWF package is the more knowledge the mechanic in charge must have available to him. Many other FWF offerings have quite complex systems that cannot be serviced in house so they would have to be shipped out for repair or replaced. Examples may include, Electronic Fuel Injection parts, Electronic control computers, turbo units, FADEC controllers, gearbox drives, and the list goes on. The beauty of the Corvair conversion is in it's simplicity! Gravity fed aircraft carb, simple electronic & point ignition.

Because of the massive amount of Corvair engines that GM produced, core parts are easily attainable. The engine is converted using high quality parts that are “made in USA” (with a few exceptions for ignition components) and are readily available. Parts that are design specific to my conversion have come from either William Wynne (Fly Corvair) or Dan Weseman (Sport Performance Aviation). These two companies are rock solid in the aviation business. William Wynne has been teaching, converting, upgrading, producing, and selling parts for nearly 30 years. For over 12 years Dan Weseman has been successfully designing Corvair upgrades, building engines, and now has sold quite a few kits for his own Panther design aerobatic aircraft that used the Corvair engine on the prototype.

As an example with parts; the recommended carburetor for these engines is a standard and reliable aircraft carb by Marvel Schebler or Stromberg. My particular Cleanex uses a Marvel Schebler carb that has been produced by the tens of thousands and used on O-200 Continental equipped Cessna 150 training aircraft for many years. Easily obtainable and they work! No changes in carb jetting or set-up are required.

Most all of the standard maintenance parts like spark plugs, wires, distributor cap, rotor, coils, oil, filters, gaskets, O-rings, etc., are readily available and found at most any nearby auto parts store. Other internal engine parts can be sourced through many online Corvair vendors as these vendors also support Corvair car clubs and racing teams.

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
172.6 hours / Status - Flying
Member # 109 - Florida Sonex Association
Latest video: https://www.youtube.com/watch?v=1VP7UYEqQ-g

[dbdevkc]

Just a personal note to add on here. I had been evaluating my potential use of a Corvair conversion engine long before this string of posts started. I looked into all the potential downsides of this choice (including potential dangers), and what I personally consider the upsides.

My current thought is to move ahead and go completely off the farm. I have a core motor that I am disassembling and cleaning up in the hopes to get some useful donor pieces.

I hope to be able to continue to participate in this forum and continue to get great info and tips. I guess I will just not be talking powerplants publicly.

[vigilant104]

Parts that are design specific to my conversion have come from either William Wynne (Fly Corvair) or Dan Weseman (Sport Performance Aviation). These two companies are rock solid in the aviation business. William Wynne has been teaching, converting, upgrading, producing, and selling parts for nearly 30 years. For over 12 years Dan Weseman has been successfully designing Corvair upgrades, building engines, and now has sold quite a few kits for his own Panther design aerobatic aircraft that used the Corvair engine on the prototype.

And, just for completeness, it should be mentioned that those interested in a Corvair-based aircraft engine can also look to the Spyder engine from Azalea Aviation http://www.azaleaaviation.com/products/Spyderengines.html. Bill Clapp has a reputation for quality work and good customer service.
The existence of several sources for Corvair-based aero engines, parts, and assistance is, IMO, a positive factor that anyone considering these engines should consider. Also, it has been my observation that opinions are strong in the Corvair community (VW community, too!), and that there are "tribes" which have some amazingly deep-seated animus towards each other in the Corvair world. That part is unfortunate.