Corvair Engines - The Justification Series

[radfordc]

The Jabiru 3300 weighs 180 but the installed weight is 215 lbs. which is 35 lbs higher.

What do you think needs to be added to a 3300 Jab that weighs 35 pounds? The engine weight is quoted with everything except oil which is probably about 7 pounds. I'm pretty sure my oil cooler doesn't weigh 28 pounds. I remember when I did the original weight and balance thinking "Phew, that was close". My Sonex is all painted, but if the engine had been any lighter I would have had to hang weights on the nose. The initial weight was just 666 pounds (bit of help from the devil there).

Peter

I'm sure he is talking about FWF weight. Engine mount, baffles, wiring, battery, etc.

[Gordon]

The Weight Debate............?

That one post mentioned an O-200 Continental weighing in at 200 lbs for his Zenith. Apparently Lycoming has an 0-233 (a light weight 0-235) that scales in at 199 lbs.

I would love to have either one of those engines in my Onex if somebody made an engine mount for it. There are a few 3300 Jabiru's in Onex's but there lies the same problem.........no readily available engine mount.

I think that would be a much more reliable setup than the Turbo AeroVee in a Onex...........just saying.

Gordon......Onex......Hummel 2400

[daleandee]

Can a Cleanex (Model C = Corvair/Sonex) be flown by a pilot with a Light Sport Certificate? Let’s look at the regulations for Light Sport compliance and see how it fits.

* Maximum take-off weight less than 1320 lbs. Yes Gross @ 1250 lbs (8.7 % increase from standard).

* Maximum airspeed in level flight with maximum continuous power (Vh) of not more than 120 kts (138.1 mph) CAS under standard
atmospheric conditions at sea level. Yes 138 @ 2950.

More clarification on this point - Keep in mind that as the engine builder you are allowed to limit RPM (as the factory did with the Jabiru 3300-L engines) and use a climb prop instead of a cruise prop to limit cruise speed.

* Maximum stalling speed or minimum steady-flight speed without the use of lift-enhancing devices (VS1) of not more than 45 kts (51.8 mph)
CAS at the aircraft's maximum certificated takeoff weight and most critical center of gravity. Yes Clean Stall @ 48 mph – Full Flaps 42 mph.

Because stall speed is critical for LSA compliance we need to take a closer look. Everyone agrees that the factory numbers are correct for the stall speed of the air frame. Mark has already posted the formula for computing this:
Vs new = Vs old weight x √(new weight / old weight). Using this we arrive at the higher stall speed number with a known increase in gross weight and see that a clean stall of 46 mph/CAS at 1150 lbs. will be < 48 (47.9) mph/CAS at 1250 lbs. and well under the 51.8 mph/CAS allowed for light sport compliant aircraft.

There is another rule of thumb that can be used: “If weight is reduced by 10% from MTOW then Vs will be reduced by 5%, and conversely, if weight is 10% over MTOW then Vs will be 5% higher —“
So if the weight is increased by 8.7% then Vs will increase by 4.35%. That would give us 46 X 4.35% = 2.001 + 46 for a new Vs of 48.001 and still well below the light sport limit. Both of these methods confirm Mr. Lee’s flight test numbers of stall at 1320 lbs gross being 50 mph (math gives 49.3 mph). I’m not suggesting that this is a good idea at all … just sharing some math.

* Maximum seating capacity of no more than two persons, including pilot. Yes

* A single, reciprocating engine, if powered. Yes

* A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider. Yes

* A nonpressurized cabin, if equipped with a cabin. Yes

* Fixed landing gear, except for an aircraft intended for operation on water or a glider. Yes

Note: It has been suggested that the higher wing loading might take a Cleanex out of Light Sport compliance. There is no FAA mandated wing loading number given for compliance of any Light Sport Aircraft. Still, if there were such a requirement, the FAA has already certified a higher wing loading LSA than found on a Cleanex at 1250 lbs.

There’s always more number crunching that can be done. What I’ve presented here is for my aircraft only with its gross weight, Corvair engine output, & climb prop installed. Your gross weight, engine choice, & prop selection will be different so your mileage may vary. My expectation is that this gives clarity to the fact that by the factory data given on their web site and flight testing, my Cleanex remains within the LSA margins.

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

[daleandee]

Now that we’ve been through the data using hard numbers from the factory information we will turn to more of the empirical evidence (information by observation and documentation of patterns and behavior through experimentation).

For the basis of my own decision I sought out and continue to seek out other aircraft builders, designers, fabricators, and even engineers, to gather further information as to how well the structure can sustain the additional FWF and gross weight and maintain a high margin of safety. I am not at liberty to share any private data or other evidence that has been gathered nor will I give any names, methods, or results beyond those that are not already known and public.

Keep in mind the factory warning and heed it! If you decide to go beyond what they have set as the limits of their air frame you do that by your own choice knowing that the decision is yours and so are the consequences. The information presented now is easily found by web searching and gives evidence to support the safety of my Cleanex.

Cleanex airframe history! Dan Weseman’s Cleanex first flew on 9-11-2005 and he flew it for five years before selling it. Watch him fly his Panther through an aerobatic routine and realize he flew his Cleanex the same way. His Cleanex is with its third owner and still flying. Chris Smith built a Cleanex and flew it in 2006. It is now on its second owner and he doesn’t fly it straight and level either. Many Cleanex flying videos are available by doing a simple internet search.

Consider that for nearly 15 years there have been a number of Cleanex aircraft flying with passengers, performing aerobatics, and in some cases, passengers and aerobatics together (not recommended!). At last count there were nearly 30 (I don’t have accurate information for an exact number) of these aircraft flying. In all that time, with all these different Corvair configurations, there have been no (none, zero, zip, zilch, nada) reports of any structural failures of any kind. This includes other alternative engines that have been mounted that were above the factory recommended FWF weight limit.

The only reported structural failure of any Sonex aircraft was a Waiex with a 1st version tail that separated in flight. That particular Waiex had the factory VW conversion and the engine quit. The NTSB report noted that the fuel tank was not breached and it had no fuel in it. The engine type had no bearing on the cause of that crash. There has been one reported non-fatal crash of a Cleanex where the NTSB preliminary report concludes the cause to be carb ice because conditions were conducive for carb ice and the pilot admitted he did not use the installed carb heat until after the engine had quit.

Even before Dan designed and built the Cleanex there were a few builders using Corvair power on these air frames. I examined one in great detail at an early American Sonex Association gathering in Crossville Tennessee built by Danny Cash. He did quite a great job of it. Even earlier … it is believed that Del Magsam was the first to fly a Corvair on this air frame. Over all this time and the much different iterations of engine mounts and power outputs there have to date been no reported concerns with the structure of this air frame or engine mount when used with a Corvair conversion. None! Today’s conversions are lighter than early engines because of advances made and the newer, lighter, engines make more power! William’s new starter setup and Dan’s new billet cranks reduce the weight of the engine even further.

In desiring to bring more safety to my personal flying it was my conclusion that my focus must be where the real safety issue is found i.e. engine failure and loss of control in flight. Loss of control occurs many times after making bad decisions when the engine quit. So as we focus on safety let’s be honest; it is not structural failure that is killing most pilots.

So increasing engine reliability at the cost of narrowing the wide safety margin built into the air frame was a wise decision for me considering that the thing that is killing more pilots is not structural failures but power plant failures. If in doubt go and read the NTSB report (from the NTSB news release 5/22/2012) and note two of the clear conclusions they give:

• Accident analyses indicate that power plant failures and loss of control in flight are the most common E-AB aircraft accident occurrences by a large margin and that accident occurrences are similar for both new and used aircraft.

• Structural failures have not been a common occurrence among E-AB aircraft.

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

[samiam]

In desiring to bring more safety to my personal flying it was my conclusion that my focus must be where the real safety issue is found i.e. engine failure and loss of control in flight. Loss of control occurs many times after making bad decisions when the engine quit. So as we focus on safety let’s be honest; it is not structural failure that is killing most pilots.

This is the crux of it for me as well, Dale. Thanks for continuing the series.

[Jgibson]

Great information Dale, and much appreciated by me and many others I'm sure.
As I said in a previous post: the designer's reluctance to endorse the use of the Corvair is completely understandable as the airframe design now stands. However I didn't then and don't now understand the reluctance to help mitigate those vulnerable areas of the plane that installation of the Corvair supposedly exposes to failure.
IMHO the Corvair simply makes a good airplane a great airplane and if airframe changes and/or modifying the airframe safely can be achieved, then why not help the present and future builders of that airframe? What's wrong with another option for a different powerplant?
As I said: JMHO.

[LarryEWaiex121]

Dale,

You very eloquently put on paper what I've tried to say a number of times. Planes are falling out of the sky, not for using the wrong bolt, or wrong rivet. They have been coming down primarily do to power failure and loss of control due to power failure and loss of control in general.
Excellent write up.

Larry

[MichaelFarley56]

• Accident analyses indicate that power plant failures and loss of control in flight are the most common E-AB aircraft accident occurrences by a large margin and that accident occurrences are similar for both new and used aircraft.

This is the same for both E-AB aircraft in general, as well as the Sonex specifically. In the past, the Foundation has done a lot of research as to why Sonexes have crashed, and Dale just hit the nail on the head! Aside from just a few specific cases (several have ran out of fuel for example), nearly every single Sonex accident falls into one of those categories. Engine failure which can happen any time, or loss of control which seems to happen more often as new pilots are getting used to the handling characteristics of the airplane.

[dcstrng]

My 3.0 with billet crank is sitting in the coffee table in the middle of the living room waiting for the rest of the project to catch up. If i had some way to weigh i would. I’ll think about that one.

Am rather in the same boat -- my garden variety 100hp with no attempt at weight savings, came in at 229# wet (no exhaust other than the shorties), so 255# is pretty well within the upper limit I'd think (hope)

[daleandee]

The Cleanex FWF platform was developed by an aircraft designer! The FWF package used on my particular Cleanex is a well thought out design by Dan Weseman. While some builders in the early years made alterations to existing VW mounts, and adopted the original cowling to make the bed mounted Corvair work on this airframe, it was Dan that took a different approach. He worked with the developer of the Corvair aircraft conversion, William Wynne, to incorporate all of the latest ground and flight tested products available in his FWF design. Dan’s mount fits the airframe perfectly and the geometry of the main landing gear and the thrust line for the engine is right on the factory specs. Information from the SPA site reads; “The tail dragger mount is well tested and designed to take the rigors of grass field operation aerobatic flight.” Dan completed his FWF Cleanex package in 2005. William has been working with Corvair engines since 1989.

As the designer, builder, and test pilot of his own aerobatic aircraft, I trust the design work of Dan Weseman. Dan would never put his reputation or business at risk selling products that were not safe, tested, & fully developed. To my knowledge there has never been any concern such as cracks, or alignment issues, with Dan’s Corvair engine mount. William Wynne was there when this package was put together and he has endorsed Dan’s FWF design. Both of these men have an abundance of understanding, education, and real experience with designing, building, and flight testing their products thoroughly before offering them to experimental aircraft builders. Dan has brought many offerings to the Corvair conversion process since then. Most notably are his 5th bearing units and new stock & stroker billet crankshafts.

Dan’s cowling is also quite unique along with the large 13” prop spinner that greatly assists with the flow of cooling air into his fence baffle design under the easy to fabricate cowling that begins with his fiberglass nose bowl assembly. Doors on the cowling open easily for routine pre-flight inspections and light maintenance. Besides the functionality of the cowling and nose bowl combination, it greatly enhances the look of the airplane and gives it quite a unique appearance!

Neither Dan nor William has any desire to cause animosity with the kit manufacturer. However, they will quietly support the efforts of builders working with this air frame and engine combination. The reason I chose to use these companies (Fly Corvair & Sport Performance Aviation) came from watching and following the developments that were painstakingly taken over many years and the honest approach these men brought to the process. I first started examining Corvair power in 2004 as I considered upgrading to a faster aircraft. At that time William Wynne had been working with Corvairs for nearly 15 years, and having built a Corvair powered Zenith 601XL as a test bed, was well ahead of anyone else in knowledge & flight testing conversion ideas. Soon afterwards I discovered Dan Weseman and the skilled work he was doing. Still it would be another 8 years before my Cleanex (Myunn) would take to the skies.

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