Corvair - General Info

[kmacht]

Mike,

It is not a 25% increase over designed weight. That 60 lbs is compared to the aerovee which is already well under the design weight to start with. The actual number is closer to a 10% increase over the factory firewall design weight. Some of us are engineers who have done the modeling, stress and load calculations and are comfortable exceeding the 200lb limit. No engine is perfect and there are downsides to the corvair. The extra weight decreases useful load, has a higher gas consumption, and obviously does not come with any factory support. John did ask some valid questions about aircraft empty weight with a corvair installed. I am willing to be open about mine but doubt others with corvair will because of the way it was asked and what he was trying to imply. Nobody is forcing anyone to install a corvair. You have to make your own risk decisions and go with what you feel most comfortable with.

Keith
#554

[lpaaruule]

Mike,

You make a valid point about turbulance. However, to my knowledge there has only been one Sonex that has had an in-flight structural failure, and was a Waiex tail section that had nothing to do with gross weight.

I have a Jab 3300, and haven't flown above the designed gross weight; though I registered it at 1200lbs. The subject of engine reliability, and builder rational for their engine decisions interests me.

[pfhoeycfi]

ANY engine that adds that much weight to my B makes it a single place non aerobatic airplane. Given that I will adhere to the Sonex design specifications and limitations, I cannot use any such engine. There are plenty of options that will allow me to build this thing without busting the limits.

peter

[John Monnett]

the corvair engine was designed by GM to handle 140HP, so it's not being stressed at 100HP in the Sonex. The VW engines seem appear to be the reverse of this argument, with HP greater than they were ever originally designed.

It is statements like this that show lack of knowledge, misinform, and perpetuate myths related to modern "VW based" aircraft engines. I am sure that Revmaster, Great Planes, Scott Castler(Hummel),as well as, AeroConversions (me) will be quick to point out that the engines they produce bare little resemblance or share critical parts with the original VW. New stout counterweighted crankshafts, heavy duty heads, valves, camshafts, cylinders, pistons, etc., etc, that are race proven in literally thousands of engines to survive 7,000 rpm and several hundred HP elevate these engines to a new "standard". Poking that old saw "not designed for" is just ingenuous.

[Jgibson]

As I was posting my last post, John posted this last message which I have to respond to.
There is no such thing as a 'modern' VW, other than new parts most of which come from overseas with questionable lineage. Many of the parts in ANY VW conversion come from places where there is no quality control, and the record clearly shows that Chinese valves and other offshore parts just aren't good enough for OUR application. Comparing OUR application to auto racing applications simply isn't comparing apples to oranges. I have no problem blowing up an engine in my race car, however that same occurance in my plane elicits completely different outcomes. As I said: trust me, I know.
And yes, they may rev to 7,000 in racing situations however their longevity at that speed is severely diminished. Simply put: the cases were NEVER designed for sustained high rpm's. And NEVER designed to carry propellor loads that we're asking them to do, as the Corvairs weren't either. But the 5th bearing implementation has changed all of that.
But as I stated in my last post, I'm throwing my 2 cents into the discussion ONLY in the hope that you, as the designer of a fine aircraft, would embrace the engine and actually help those who want another solution to power the plane.
I completely understand personal 'brand loyalty' which I believe you are (as are many) 'guilty' of (and there's nothing wrong with that). And this is certainly not a personal attack, and if you perceive it as such I apologize in advance.
I'm simply asking for your expertise is moving the installations forward in a positive and safe manner.
Help us make the Corvair work safely. Period. And let's ALL check our attitudes at the door and work together.

[Jgibson]

For some reason, my FIRST post immediately before John's has disappeared or never appeared.
I THOUGHT it contained rational, reasonable information and counter point to the Corvair discussion. Because it isn't showing up, it sort of makes my reply to John incomplete.
Bottom line: as the designer of the plane, John is the one who can help us improve the safety and viability of the Corvair installation.

[John Monnett]

For some reason, my FIRST post immediately before John's has disappeared or never appeared.
I THOUGHT it contained rational, reasonable information and counter point to the Corvair discussion. Because it isn't showing up, it sort of makes my reply to John incomplete.
Bottom line: as the designer of the plane, John is the one who can help us improve the safety and viability of the Corvair installation.

There you go again...
The only way I could help is to design a completely different aircraft to accommodate heavier engines and violate the intent of what the Sonex is about... that is not going to happen. I'll leave adapting Corvairs to an inappropriate airframe to others.

[lpaaruule]

Hi John,

I'm was aware of the anacdote about tremedous horsepower being produced by VW engines. However, since I was ignorant of whether or not the engines had any longevity past running the 1/4 mile, or other short races, I rejected it as useful info, and stored it as interesting trivia. I would, however, find running a controlled over-stress test very interesting. Perhaps 500 hours at 110Hp on a dyno, though I don't know what the Hp could be without producing a foolish premature failure.

From your recent post I thought that you had genuine curiosity about builders rational for using the corvair, and their surpassing the design gross weight.

From your experience, do you not find any merit from a durability standpoint in running an engine at less than its rated horsepower?

[kmacht]

Lets be fair here. The aerovees are operating at a horsepower about double the original design but other than the recent connecting rod failure there are very few reports of internal "Chinese" components failing on the motor. Corvairs were not designed as an aircraft engine and they require modifications (i.e. 5th bearing) to make them withstand the rigors of flight just like the aerovee requires many modifications to a stock 36hp engine to make them able to handle 80hp. Neither is a clean sheet engine designed for what it is being used for and there are compromises that have to be made for both to work.

The aerovee can be a reliable engine. I have never denied that. Proof of that are the many sonexes (sonexi?) flying with them installed. Some of those installations have hundreds of trouble free hours. The problem I have is that it isn't understood what is allowing some engines to run trouble free while others are having sudden failures during takeoff. For many years I was of the opinion that it was probably the builder not paying attention to some detail when assembling the motor or failing to perform necessary maintenance. I really wanted to believe that the time and money I had invested in my aerovee was well spent and told myself that those must be the reason why their installation didn't work but mine would. That was until the factory had the same issue on two of their aerovee powered aircraft. The factory should be the pinnacle of correct assembly and proper maintenance and if they can't get it right how do I know I can. You can read John's explanation in an earlier post and decide for yourself if that is sufficient for you to feel comfortable behind your aerovee.

I am choosing the corvair because for me (and just for me) the risk/reward balance is better than the aerovee. I don't expect John or Sonex to ever embrace the corvair conversions as a factory supported engine and don't think it is productive to even ask. They have both business and technical reasons why they choose not to. He did bring up some valid questions regarding empty weight vs useful load but unfortunately I don't think many corvair Sonex owners will bother to respond because of the way it was asked and what he was insinuating about them.

There are risks with any motor you fly behind. You should make sure you fully research all options before making a decision. Your life could depend on it one day. Don't let what you read on an internet forum posted by a random person or what a business with a vested interest in selling their product says be the only thing that you use to decide. Do your own research and make an independent and informed decision

Keith
#554

[Jgibson]

Anyone know the difference between a weight of a full-up Corvair with new crank vs the weight of a fully installed Rotax (including radiators, etc.) AND the full up installed weight of the Jabiru 3300?
Just curious because I distinctly remember the same factory resistance to the Rotax motor until the B model came out using the same tail, same wings, and same tailcone.
Is the Rotax installation heavier, lighter, close?
I'm no engineer, however I'm certain the extra 50 pounds or so of the Corvair could be offset by lighter (glass) panel installations, lighter battery, minimal interior, no paint, etc.
No one, including me, is knocking the VW engine in slower turning power requirements. However it was just never designed to be running at 80 hp CONTINUIOUS in our applications. Show me VW aero conversions that run a minimum of 500 hours without head work, or conversions that don't require continuous re-torquing of heads, continuous valve adjustments, etc. They may be out there, but they are a rarity. The Corvair needs none of these maintenance issues and the ignition setup is bullet proof and redundant IF the William Wynn modified distributor is used. Standard aircraft carb.
The Corvair running in the aero mode is running at a much lower rpm than originally designed in the auto configuration. My turbo made it's 150 hp at 5500 rpm and as I noted in previous posts, I TRIED blowing it up and couldn't. Same with my Fitch prepared 110 hp. So I'm pretty comfortable running it all day long at 3100 rpm WITH a new 5th bearing setup.
Again: my opinions are just that. Mine. However they are based on facts and my own experience with the Corvair powerplants. I respect Mr. Monnet's experience and knowledge and believe he has designed a great airplane and done a lot for light aviation. Nobody is asking or expecting you/him to design a completely different airframe to accommodate the Corvair. Explaining the pitfalls of the Corvair installation, and/or possible structural upgrades serves everyone's best interest.
But dismissive remarks, like those that USED to come with the mention of a Rotax does nothing to advance either safety or promotion of either lite aviation or the Sonex product itself.
JMHO