The case of the Murphy Rebel, “eyeball vs. testing”


A Murphy Rebel builder forwarded the comment below in brown from the Murphy builders list. He was interested to know how I would respond to the writers comments. Rather than send back a private email, I thought it was worth putting up here, as we have about 10 builders putting the Corvair on the front of a Rebel, and I wanted them to understand why we know the combination will work, and why the guy below is not correct in all the assumptions he wrote into a single paragraph…..

“I seriously looked at the Corvair engines – but decided that with the wide front end of a Rebel – that the faster turning and therefore smaller diameter prop’ ( which you HAVE to use – in order to let the engine get up IN to it’s power band RPM range ) would be “inefficient” on the nose of such a meaty plane ( big front end ) …….
So I was forced by common sense to revert to a Lycosaurus ( Lycoming – dinosaur ) engine – with it’s slower turning / bigger diameter / more efficient propeller !”

Where do I start? OK, I’m not fond of the term Lycosaurus, even when it is used by people planning on buying a Lycoming. Moving on to more technical points, the biggest single argument, and the easiest thing for new builders to understand, is that we have long been successfully flying a plane that is bigger than a Rebel, has more frontal area, more drag, and a greater payload. Our Wagabond, flying since 2005, works great and actually flew with more payload than it’s empty weight……On a 100HP Corvair. So maybe the comments that the writer made don’t count. Simply put, his evaluation was based on his eyeball look and a handful of old wives tales, on the other side we have my testing and a plane that has been flying for 8 years.

Above, a Murphy Rebel. The cabin on the plane is 44″ wide, and it has a comparatively blunt windshield. A guy commented that the recommended prop size is 74” by 56 or 58, but this is only the prop for a 160hp Lycoming. For our comparison, let’s have a reasonable comparison looking at a 3,000 cc Corvair vs an O-235 and a 2,700 cc Corvair vs a Rotax. Below is a Chart off the Murphy site. Like almost every other airframe factory chart on the planet, lets just call the numbers ‘optimistic.’ (We have an O-320 Rebel here at our airport and it doesn’t match the chart, but this is typical in our industry.)

Engine Lyc O-320 Lyc O-235 Rotax 912 Rotax 912 Rotax 912
Horsepower 160 116 80 80 80
Power Loading (lb./hp) 10.3 14.2 18.1 15.4 16.88
Gross Weight (lb.) 1650 1650 1450 1232 1320
Empty Weight (lb.) 950 900 700 625 700
Useful Load (lb.) 700 750 750 607 650
Wing Area (sq. ft) 150 150 150 150 150
Wing Loading (lb./sq. ft) 11.0 11.0 9.7 7.0 9
Rate of Climb @ Gross (ft/min) 1200 800 500 800 550
Climb Speed (mph) 65 65 60 60 60
Take Off Run (ft) 300 400 450 300 450
Landing Roll (ft) 400 400 300 200 300
50′ Obstacle Clearance (ft) 533 754 976 626 976
Stall (No Flap) Power Off (mph) 44 44 40 38 40
Stall (FULL FLAP) Power On (mph) 40 40 36 35 36
Cruise (65% POWER) (mph) 120 105 100 85 100
Vne (mph) 151 151 143 143 143
Top Speed (mph) 140 125 100 105 100
Fuel Burn (gal/hr) 7 6 4 4 4
Fuel Capacity (US gal) 44 44 44 22 44
Range (hrs) 6.1 7.6 11.0 5.5 11
Range (statute miles) 733 797 880 468 880
G Limit (Ultimate) +5.7 -3.8 +5.7 -3.8 +5.7 -3.8 +5.7 -3.8 +5.7 -3.8

O-235 vs 3,000 cc. The 235 listed above makes 116hp.  If I asked the writer what exactly he ment by with it’s slower turning / bigger diameter / more efficient propeller !” He probably wouldn’t have an exact number in mind for rpm. Does 2,800 rpm sound real slow? Well that’s the rpm required to get 116 hp. Think I have been an A&P for 20 years and don’t know what I am talking about? Read the last model on the Wikipedia page: Also note that just about every 235 has to hit 2,800 to make rated power. Second, a fully dressed 235 weighs 280 pounds, at least 40 pounds heavier than a Corvair. A 235 is wide, within 1/4″ of the width of a 320. You can’t put a sleek cowl over it.

Now lets look at prop size: Think more diameter is always better for low speed thrust? Think again. Last week I changed props on Grace’s 85 HP Taylorcraft. I am setting it up to tow our glider. It had a 72 x 48 wood prop on it, and I got a 74 x 46 metal to replace it. But before I mounted it, I took it to American Props and paid $865 to have it overhauled, the pitch reduced, and to have its diamerter reduced to 70″. I am not a fool, The diameter reduction allowed higher rpm, and improved the climb rate by 500’/min. Props with diameters of 74″ are only efficient on engines like the Continental 65 with a low red line of 2300 rpm. Low rpm isn’t efficient in itself. A 65 Continental becomes a 75 continental with respect to power output by just a jet change and an RPM increase to 2600.  If turning the prop 300 rpm faster and using one with less diameter actually made less low speed thrust, than no one would have ever converted a 65 to a 75. Almost everything repeated in hangar flying stories or on discussion groups about rpm and efficiency is an old wives tale or pure BS that directly contradicts experience from certified engines and certified prop shops, but that never seems to stop people from repeating it as if it was told to them by Wilbur Wright and Kelly Johnson.

A 3,000 cc Corvair on a big plane can use either a 68 or 70″ in diameter prop. If the guy puts a 74″ prop on his 235, it is going to static near 2250 or 2300 rpm, 500 rpm below the engines rated power. He may tell people he has a 116 hp engine, but he isn’t going to get to use the last 12-16 horses unless he takes the diameter down to 70″ or so. Lets see…where is that big prop diameter difference the guy was speaking of? Yeah, it’s 2″, but don’t forget the Lycoming is 6″ wider, so which prop is operating with more blade area working in the clear?

We intentionally set up the Corvair to turn more rpm static, because more rpm is more power, and the Corvair builds hp much faster than prop efficiency decays, thus more rpm is a net increase in thrust.  A flatter pitch prop on a 3,000cc Corvair will static near 2,800 rpm. The tips will be well below sonic, and the power output will be near 100 hp. The 235 with a high-pitched prop will not only make slightly less power at 2350 rpm, the critical difference is looking at the blade angle of attack: much of the high-pitched blade will be stalled, far more of the low-pitched Corvair prop will be working. The Corvair will accelerate much better. You may have to read that twice to follow it, but real learning and understanding takes a bit more time than memorizing and parroting BS phrases like “Keep your prop as long as possible as long as possible!”

 Above, the wagabond outside our old hangar in Edgewater in 2006. It is built on a PA-22 airframe, which as a four place certified plane. It is bigger than a Rebel. It has taller gear, it has four lift struts, and at 147.5′ of wing area, it has just 2.5 feet less than a Rebel. In short, there is no rational reason to say that a Rebel would not fly as well or better on the same engine. In the photo, the plane is equipped with a basic 2,700 cc Corvair. Look at the prop, it is a 64″ diameter wood Sensenich. It worked great, it is using the same prop in the video link at the end of this story.

The picture above is just after Gus did the first flight in the plane in 2005, he is shaking hands with Dave. You can’t tell these things in pictures, but both Gus and Dave are about 6’3″ and they are both built like NFL defensive linemen. The empty weight of the plane was 804 with a 2700cc Corvair. We arbitrarily set the gross weight on the paperwork at 1320# to make it light sport compliant. We did a test flight at 1625 pounds during phase one. I was not worried structurally because we used a PA-22-108 colt airframe as the basis of the plane  which has a gross weight of 1650 pounds. The lift struts are off a 160 hp tripacer with a 2,000 pound gross.

The plane is not a speed demon. its fair to say that it will do 100 mph on 5 gallons per hour. It 100 hp climb rate at 1320 pounds is about 700 fpm on a standard day. Note that this is about the same as the 235 powered Rebel on the chart above. We are currently redoing the plane with some detail work intended to clean it up and repower it with a 3000cc Corvair. I am shooting to bring down the empty to 780 pounds or so. I have a 68″ Warp Drive for it. We are planning on bringing it to Oshkosh this year. I will gladly fly it against any 235 Rebel from standing start to 1,000′ agl. A smart guy with a light Rebel and a cut down prop would show very well against the Wagabond. But if the Rebel builder was the kind of guy who spent his time listening to old wives takes and bought a real expensive, big slow turning prop for his Rebel, It won’t be a contest at all.

A small number of people who read this will “get it.” The majority will not question the old wives tales they have been spoon fed over the years. They will not even stop to consider that none of the people who told them the tales had done any testing, had any education on the subject, or had put any real effort into learning. I have been sharing this type of information for 20 years, and still people say  “I seriously looked at the Corvair engines”  but evidently they don’t look close enough to really understand how engines and props work.

I used to wonder if I was doing a really poor job of sharing the things I had learned, because a lot of people still said things like the writer. I was operating under the false assumption that everyone in homebuilding wanted to really know how things worked, wanted to see the real tests, was willing to change their point of view if the facts indicated something different that their previous assumption.

I now understand that these conditions apply to just 5 or maybe 10% of the people in home building. I am OK with that, Corvairs are not for everyone, and they don’t need to have a giant following for our work to be successful. Having a few hundred traditional homebuilders, people who really want to learn, build and fly, to be the master of their creation, not its mere owner or operator, is all we need to flourish.  For those that get it, welcome. for those that don’t want to, I genuinely wish them good luck. They will need it, aviation isn’t terribly kind to people unwilling to learn.-ww 

If you would like to see a video of the plane in flight, look at this link to you-tube, it has 7,000 hits:-ww


Getting Started in 2013, Part #14, 2,850 cc piston/rod/cyl. Kits


The next piston option we are going to look at is one we developed in-house, as a purpose-built, clean sheet of paper concept, to bring advanced combustion characteristics to Corvair flight engines.

Most people who work with engines understand that the shape of the chamber in the head has a great effect on how an engine runs, particularly in challenging circumstances like aircraft. What a lot of these people miss it that at top dead center on the compression stroke, the head chamber is only half of the shape of the remaining space, the top of the piston is the other side of the equation. While a flat top piston works in many cases, it isn’t the optimal design to compliment the combustion chamber in flight engines. Flat top pistons are less expensive to make, but if you are willing to go a bit further, there are significant advantages to be had.

If you’re talking about putting the piston in a plane, the single most significant advantage is detonation resistance. If you think that you would like to run auto fuel extensively, using a piston like the designs we have in 2,850s and 3,000cc Corvairs is a very significant advantage. Regular flat top Corvair pistons can be run on auto fuel, people do it every day. Smart people doing this reduce the timing of the engine and enrichen the fuel mixture slightly, and resist the temptation to aggressively lean the engine. These things provide the margin of safety. On a 2,850 or 3,000 with our pistons, the margin of safety is provided by the shape of the piston head, and there is no reduction in performance required to have a very wide margin on decent auto fuel.

The 2,850 design predates the 3,000 piston by a year, so it is correct to see the 3,000 piston as a ‘big’ 2,850 instead of the other way around. The bore on a 2,850 is 90mm, which works out to .105″ over the stock 3.437″ (The 3,000cc bore is 92mm).  The cylinder we use for the 2,850 is the full fin, thick-walled Clarks cylinder they have had for a number of years. These are new, not rebored. We have sold the 2,850 piston/rod cylinder package as a kit for a number of years. Using our numbering system, lets look at how this fits in:


Piston and rod group (1300)


1300- Piston set with wrist pins

 The set comes with their own pins in the kit. Pistons are set to use either standard Corvair rods or ones bushed for floating wrist pins.

1301- Ring set

The rings that come with the kit are made by Total Seal, and they are specified by the Piston maker as the optimal ones for the piston design.

1302- Connecting rods -6-

The rods that come in the kit are standard rebuilt ones with ARP bolts. Most of the kits we have sent out have had the pistons mounted on Clarks 9203ww rods, some of the kits were delivered with upgraded rods with 12 point ARP nuts. We mount the pistons on the rods for the builder.


Cylinder group (1400)


1400- Cylinders -6-

The Cylinders in the kit are the Clark’s HD, full fin, brand new ones. Clarks has these cylinders in many sizes from STD to .060″. The 2,850 is bored .105 over and requires the boring bar to make several passes to get it his big, thus they cost more than the same cylinder with a smaller bore. A replacement 2,850 cylinder is an on the shelf item at Clarks, and has it’s own part number, C-11628ww. The Cost is $84.  The six cylinders are part of the kit price.

1401- Base gaskets -6-

The base gasket that I prefer for all Corvair engines is the all copper Clark’s part number C-1180. As a part number for an individual gasket, you will need to order six of them for a complete engine. We install them in the engines dry, with nothing on them. We built engines for many years with the stock steel gaskets, but they are less forgiving than copper base gaskets. A set of six is about $42.

1402- Head gasket set

For all 2,850s the standard head gasket that we recommend is a .032” solid copper gasket. These are available from Clark’s, part number C-3946  The head gasket set is about $30.

We sell the 2,850 kit for $1,750. The gaskets to complete Groups 1300 and 1400 bring the total to $1,822. Notice that this is $827 more than a 2,700 builder will spend. What is the attraction? First the combustion chamber shape, second the pistons are even stronger than the sealed power ones, third, up to 9 more cubic inches, and fourth, that the cylinders are new. If a builder had 3 or 4 core cylinders that have chipped fins, paying the core charge from Clarks gets part of the way into the price difference. If a builder is considering leaving the option open for turbocharging later, this is a much better combination to work with than a 2,700.  Below, some photos and commentary about the builders who are using 2,850 engines now.

In the next instalment we will look at an imaginary piston.-ww

 Above, a drop forged, made in the USA piston for the Corvair. The  displacement of this piston is 2,850 cc. Look at the dish in the head of the piston. Notice that it still has a quench area to match the one in the Corvair head. This piston is designed to allow the head gasket step in the head to be completely cut out, have a quench height of only the thickness of a .032″ head gasket, but still have less than a 9:1 compression ratio with a 110 head. With a 95 head and the quench clearance equally tight, the compression ratio is below 8.4:1. The former should be an ideal engine to run on unleaded gas or 100LL. The latter is specifically set for being run with a turbo, or with standard auto fuel.  I like the concept for a number of reasons. It is the largest bore that can be used without modifying the case and heads, the way you must with a 3,000. the ready availability of Clark’s new full-fin cylinders that can take this kind of overbore eliminates any special machining to the cylinders, other than boring them .105″ over.

Above, the 601XL of our west coast man, Woody Harris. It has flown all over the country on a 2,850. Note that Woody is from northern California and the photo above is at Kitty Hawk NC. Read woody’s story at: Zenith 601XL-2,850cc, Woody Harris

Pink Ticket

Above, Jeff Cochran (on the left) the day he passed his airworthyness inspection. Jeffs 750 is powered with a 2,850. Read Jeff’s story at: New “Zenvair-750″, Jeff Cochran, 2,850cc engine, N750ZV

Above,  Ron Lendon of Michigan flew in to Brodhead 2012 in his scratch built 601XL. It was originally powered with a 2,700 but he later upgraded to a 2,850.

Above, Roger Grable and his grandson Graham, with their running 2,850 at Corvair College #23. Read their story at:Corvair College #23 – 2850cc Engine, Roger Grable, CH-750 Builder

Above, Blaine Schwartz’s 2,850 engine a few minutes into its test run at Corvair College #22. Blaine is in the blue hat, his 750 is almost done. Read his story at: Schwartz Engine Runs at CC #22


Above, Clarence Dunkerley at Corvair College #21, beside his 2,850 which we later ran. The engine is now installed on his completed Cleanex.

Roy and Dave Glassmeyer, run Dave’s 2,850cc engine at Corvair College #20. It will power Dave’s Kitfox Model 5

Getting Started in 2013, Part #13, Basic piston/rod/cylinder combo.


If a basic builder wanted to go shopping a Clarks Corvairs for base line 2700cc Corvair pisron/rod/cyl. components, here is a break down of what the parts look like. I have rounded off some of the numbers slightly, but the cost is + or – only a few dollars.

I have seen a lot of very poor work come from local machine shops, so even on a basic engine it makes a lot of sense to get all the parts and machine work done at the same place. Make your life easier, don’t be the 100 th guy that found out this is the wrong place for a ‘local expert,’


Piston and rod group (1300)


1300- Piston set with wrist pins

The basic set of Sealed power forged pistons with rings from Clarks is just under $60 per piston, this includes the wrist pins.  $360 for the set. These are the pistons flying in  80-85% of Corvairs today. These pistons are available in several over sizes, most of the engines I have built over the years have been .030″ over and .060″ over. The price is the same. The .060″ engine will be about 2 pounds lighter and have slightly more displacement. 

1301- Ring set

The rings that we recommend for the above pistons are Hastings Chrome. These sell from Clarks for $120. Consult the catalog to get the correct number for your overbore size.

1302- Connecting rods -6-

The most common Rebuilt connecting rod in flight engines is the Clarks C-9203ww set. Clarks has several different options, and I had Mark their General Mgr. set up this suffix years ago so builders calling in an order always got the correct choice. I want to assure every one that I don’t make any money or kick backs on your shopping, the number is just to make communication easier. 

Years ago, a West Coast Corvair car parts supplier named Lon Wall saw these numbers and went on an internet rampage for 3 or 4 years, telling everyone that there was some secret connection between Clarks and myself; Confession time…There is a connection; I want to have people build Corvairs, Clarks offers normal service, and no one from their organization spends all day on the internet telling people how evil I am. Thats the connection, no money, no deals, just normal sane people. 

I use Lon’s name here because all the things he wrote all still exist in internet archives, and I want people who stumble over them to understand who the axe grinder was. Lon is still around, and 10 years later he still has rotten things to say, but not like his really good years 2003-2007 where he would post gems like “WW tells people things that will get them killed in planes, I know it, but I can’t say what it is..” notably, I am pretty sure that he has never flown in a plane in his life. Do you think I have a negative attitude about the un-restricted things that are said on internet? Google Lon’s name and ‘Corvaircraft’ and you can read 100 joyous posts. It wasn’t the kind of thing I imagined  I would be confronting when I got started developing an affordable flight engine in 1989.  The man didn’t deter many people, but it was a waste of time. In the end Clarks normalcy got all the business, we taught hundreds of people to build engines, and Lon went bust.

The 9203ww rod set is $411, but you get $150 bucks back/off for sending in your core rods, so the net price is $261.


Cylinder group (1400)

1400- Cylinders -6-

On a base engine, you just send your cylinders in to Clarks as a core, and get bored cylinders that match your piston oversize. Basically after the exchange of your cores, the bored and honed set of cylinders costs $150. The finish for the chrome rings is #220.

1401- Base gaskets -6-

The base gasket that I prefer for all Corvair engines is the all copper Clark’s part number C-1180. As a part number for an individual gasket, you will need to order six of them for a complete engine. We install them in the engines dry, with nothing on them. We built engines for many years with the stock steel gaskets, but they are less forgiving than copper base gaskets. A set of six is about $42.

1402- Head gasket set

For all 2700 the standard head gasket that we recommend is a .032” solid copper gasket. These are available from Clark’s, part number C-3946 for 1965-69 2700s. Engines with 1964 heads need part number C-3945.  We install copper head gaskets on engines dry with nothing on them. Ignore anyone who suggests coating the gaskets in any type of sealer or anti-seize. The head gasket set is about $30.

Totalling up the above numbers comes to $963. If you add $32 to this you can send your old rods in with the pistons still on them, and Clarks will return your rebuilt rods with your pistons already mounted on them, moving the total to $995. The assembly of these parts are all covered in our engine assembly DVD #2. In the next instalment we will get a comparison on the cost to upgrade to a 2,850 cc engine.-ww

Calling All “Zenvair” Flyers……601 / 650 / 750


I just spoke with Sebastien Heintz, President of Zenith, and we would like to have a Corvair powered Zenith in the Zenith aircraft display area at Sun n Fun. We have a long tradition of doing this going back to 2004.  Sebastien always likes to see affordable examples of his families designs prominently displayed. In the last nine years, between Sun in Fun and Oshkosh we have had about a dozen of our builders planes in their booths. We are not looking for show winning aircraft only, regular examples of traditional builder craftsmanship are actually prefered.

My Commercial display comes with a number of full week passes. Anyone with a plane in the Zenith booth will be an informal rep for Corvair power, so I will cover the pilots of the display aircraft with complementary commercial acess passes. Even if you are able to stay just part of the week, we are looking to cycle 2 or 3 Corvair powered Zeniths through the booth. The Zenith display is in the middle of the broad taxiway, so there is no difficulty moving aircraft midweek , after hours. We do not need a guarantee of being on hand, I just need to hear from Zenith pilots who are planning on attending Sun n Fun so we can do a little coordination and planning.

Below are som photos of  “Zenvairs” in the Zenith booth in past Sun n Fun’s:


Above, Phil Maxson (Left) stands by his 601XL in the Zenith Booth at Sun n Fun 2006. Read Phil’s story at this link:  Guest writer: Phil Maxson, flying a 3100cc Corvair in his 601XL


Above, Rick Lindstrom’s 601XL in the Zenith Booth at Sun n Fun 2007.


Grace, Chris Heintz, and myself with our Zenith 601XL  at Sun Fun 2005.


Our  701/Corvair test bed aircraft in the Zenith booth at Sun n Fun 2010

To read about many more examples of Corvair powered Zeniths, get a look at this link:

List of Corvair Powered Zeniths

Fly Corvair at Sun n Fun 2013, Starts April 9th. (Booth N-66)


Grace and I have decided to return to Sun n Fun again this year. This will be my 25th consecutive year at the event. We will have a full commercial display, in booth N-66, which is on the row in front of building “C”, the third of the four main display buildings. This is one row over from where we were last year. Sun n Fun is the second largest air show in the US, and it has been held every spring in Lakeland Florida for many decades. It is a big event, and it draws thousands of planes.

Dan and Rachel Weseman are bringing the Corvair powered Panther prototype to the event, and they have an adjoining commercial display space, so we will have a place for all the Corvair builders to congregate. Just as we did at Sun n Fun and Oshkosh last year, we are going to work together to have a Corvair Cookout for all builders and fans of the Tonawanda master piece.

There will be a one day gap between Corvair College #25, held April 5-7th in Leesburg Florida (more info later this week) and the start of Sun n Fun. We expect to see many builders at both events. We are tentatively planning on having the Cookout on the first night of the show. We will keep every one posted as we get a little closer.

We will do all the regular stuff, parking lot tours to look at builders cores, have every catalog part on display, have short blocks for sale, etc. If you are going to attend the event and have a specific question or would like to pick up something special, just drop us an email or call.

Above, Sun n Fun 2012. old friends left, Roy Shannon, and center, Steve Bacom Jr., both VariEze builders. On the right is Arnold Holmes, long time Corvair pilot and host of Corvair College #17. Arnold is president of EAA  chapter 534, the local hosts of Corvair College #25. If you would like to see some of the events from last years sun n fun, get a look at this link:  Sun N Fun 2012 

For more info on Sn n Fun :

New Panther Cowling, shown in pictures.


Below is a picture of Dan’s new Panther Cowl roughed in on the front of his prototype. He and Rachel did this work over a 7 hour stretch on Sunday. I stopped by their hangar and saw it at this stage. It looks even better in person. The interesting side of this story is the method that Dan selected to produce this cowl. In short, he started with a RV-3 cowl and a Cleanex nose bowl and a very good imagination because very few people could picture how he was going to bring those together on the front of a single place aircraft. If you follow the link at the bottom, you can see the actual step by step process. There is still a lot of work to go, but this part will have been vastly faster to make than a traditional cowl made of carved foam blocks or plaster.

Dan borrowed my mock up/ demo engine and put it on his mount with the intake and exhaust in place. It rests inside the cowl in the photos. For all the people who have some question as to how sleek a cowl can be made, note that this cowl houses our regular front starter set up. The spinner is the same Van’s 13″ unit we have used since 2003 and promote for use with our nosebowl. At a glance, this cowl may look something like an RV-3 or 4 cowl, but as you go through the photos you can see that Dan has narrowed it more than 6.” Keeping the formula that served him well in his highly successful Cleanex development, Dan is utilizing as much of proven Corvair as he can and keeping changes to an absolute minimum. The panther has it own mount, intake and exhaust, but these are just adaptations of  our systems long proven and flying on other aircraft. Obviously it will have its own cowl, but all other Corvair parts on the Panther installation are components right out of our existing catalogs of Parts. -ww


To see the whole sequence of photos, get a look at Dan and Rachel’s Panther blog: 

Expert Witnesses in civil Aviation trials.


Let me expose you to a side of aviation that you are not likely to read about in our industry publications. I have worked in this industry for more than 20 years. I have done a number of different jobs and have a broad group of friends who also work inside our industry. I have access to more information that most people in homebuilding. One facet of homebuilding that is very rarely spoken of, but known to people working in the industry is the case of the “Expert Witness.”

Below, I am going to cover three different examples of this. The first two of the men are deceased, the third is not. I have extensively read the works of all three men, and I met two of them in person. The comments I make here are not hearsay nor are they hangar stories. This is valid information, not internet comments from a mystery email name.

I am not questioning that all three of these men made contributions to homebuilding. The only point I am making here is that each of these men have been part of a much less attractive side of aviation, one that it rarely spoken of. Each of these men have their fans. However, very few of these fans are aware that their heroes engaged in behaviour that many rank and file homebuilders would consider to range from unproductive to unethical. Speaking for myself, I think that the damage done to our industry by the actions of these men acting for their own financial profit far outweighed any good they ever did.

The important point that I would like traditional homebuilders to understand and take away is simple. All three of these men wrote books that are often cited in homebuilding circles. Each of these books has sections that purport to be grave warnings about terrible flaws in aircraft designs in aviation. Riblett wrote large diatribes about ‘dangerious airfoils.” Hollmann attacked the structural design and flutter characteristics of numerous aircraft. Finch wrote extensively on aircraft fires and how poor planes were. I cannot comment on how strongly any of these men felt about these topics, but I will tell you that each of these men aggressively pursued legal positions on these subjects so they could hire themselves out as industry experts in some very expensive and damaging lawsuits, including the highest one ever paid out.

Many people new to homebuilding are concerned about potentially dangerous things. This is normal. However, each of the above men implied that they were impartial servants of aviation safety sharing the truth with fellow homebuilders for the good of aviation. Read all the links, google each man’s name and the words ‘aviation lawsuit,’ and make up your own mind. After you do this you may very well decide that things you previously assumed were truth, said for good reasons, may be little more than a profiteer’s ploy to abuse the legal system. I went through this very transformation myself. I never looked at the work of these men the same way again. Give some thought to the fact that most aviation editors who have been around for 10 years could have written this story, but evidently none of them did.

Homebuilders need real information to make good decisions on. It is ok for people with a particular issue to be passionate about it. My point is that if they guy is hiding the fact that his passionate tone is largely driven by the potential for an incredibly high payday, than the process is inherently deceitful. People should speak the truth about mistakes, and they should do it in the court room if it comes to that. But I have zero respect for anyone whose opinion on safety is for sale to a high bidder, and I hold a very special contempt for people who engage in any practice that has the byproduct of making Americans more fearful. To the extent that the comments of these three men made aviators afraid to fly aircraft that had long been proven to be within acceptable risk levels, and they made a profit at this, they were acting in the same capacity as terrorists. Think that over, review how the work of these men may have made you personally afraid of an airfoil, a design, or a Cessna fuel system,  before just disagreeing with it.

Harry Riblett passed away recently. He wrote on airfoils, and a number of experimental aircraft use his airfoils. He sold a book for 20 years that proposed a series of computer generated airfoils. I own and have read his book in its entirety many times. I also got my aerodynamics training at Embry-Riddle from some very well-respected professors. Let me throw in that I have built and flown an aircraft that used one of Riblett airfoils. The man made some good points, and most people in aerodynamics generally follow the things he said. Here is the disconnect: Riblett was very prone to stating things very dramatically, throwing around terms like ‘dangerious’ and ‘killer’ throughout his writing. He was a guy who always liked a good conspiracy theory, and he had a claim that much of the work of NACA was flawed, and their wind tunnel work was inaccurate. He did this while never using more than a basic computer to model the performance of his own airfoils. He wrote a lot of press releases to national media blaming the FAA for certifying aircraft with particular airfoils. I doubt he made a ton of money selling is book, and I know of no designer that paid him a significant royalty for his airfoil. I believe that the book sales were aimed at providing a flow of small money while establishing his position as an “industry expert.”  In this capacity he was available to law firms specializing in aircraft accidents. (Yes, these exist, they will show up when you google search the terms.) Just for starters, in your own personal search for more information, start at this link:,-FAA-and-NTSB-of-icing-problems_27.asp

While Riblett had some points on leading edge radius, it is nothing that is revolutionary or new. I am not a particularly talented pilot, but I have a lot of time flying an airfoil he classified as a ‘killer.’ Today, I think that Riblet may have started out well intended, but he became willing to grossly overstate things to put himself in the position of being a very well paid expert witness.  In my opinion, the good he accomplished lives under the shadow of this, and his work can not be considered objective because of it.

Martin Hollmann has also recently died. He was an accomplished aeronautical engineer. For all of his good talents, he worked the legal system to his own personal profit more than any single person I have met in aviation. He was very famous for offering to hire out his ‘expertise’ to either side of a debate. He would often offer to defend a manufacturers design that was facing trouble. Many of the designers who took him up on this did so because they correctly understood that Hollmann was fully willing to represent the people who may have a suit saying the design was flawed. By hiring him, he could no longer be on the potential plaintiff’s witness list. The manufacturers knew this and would pay this form of blackmail. If you search the internet you will find that Hollmann didn’t wait for people to come look for him. He wrote countless posts to internet groups that were thinly veiled proposals for suits. He often was hired by wealthy builders to find a fix for the “flaw” that Hollmann “discovered” in their kit’s design.  Consider the single quote of Hollmann’s below. The only designer he was afraid to cross paths with was Rutan. I really doubt it was out of respect, I have a strong feeling that it was because he knew that Rutan was a fighter, and would not fold up like a lawn chair in a contest of lawsuits.

 “I consider Mr. Rutan an ambitious and prolific aircraft designer willing to take risks to explore new designs. Such people must be encouraged and supported if we are going to advance the state of the art. If I did not feel that way, I would not have turned down an offer from attorneys to work on behalf of the plaintiffs in a lawsuit against Mr. Rutan in the canard Microlight aircraft accident in which the owner and test pilot of this aircraft were killed.”

If you do your own reading, you will find countless cases of Hollman being involved in legal action or selling his services or testimony to people involved in legal action. Again. I am not suggesting that the man didn’t know the topic, I am saying that he was willing to sell this to a high bidder, even if he had to fan the flames of conflict or doubt to drive up the value of his expertise.

Some one is going to write me and say “he couldn’t say it if it wasn’t true.”  This very pleasant elementary school ideal does not apply to expert witness testimony. Read on and you will find that under US law, “absolute immunity extends to acts or statements of experts which arise in the course of or preliminary to judicial proceedings.” and “Under California law, no lawsuit alleging negligence against a licensed engineer may proceed without the expert opinion of an independent engineer.” There are some valid reasons for both of the above, but they have long since been lost by the system that pays tremendous amounts of money to expert witnesses.

Many people were given a favorable opinion of Hollmann by reading his books, but most of his positive exposure came from Kitplanes magazine under the 18 year editorship of Dave Martin. There was nothing Hollmann ever did that got less than a glowing review by Martin. Hollann’s design “The Stallion” was hailed as the greatest of kits in the era of the high-end kit. In spite of this, only a small handful of the planes were ever finished. Martin’s infatuation with Hollmann was not deterred by Hollman’s legal activities, nor his personality. At times Hollmann was polite, even patient with anyone who he suspected was an emerging member of his fan club. On the other hand, many people found him to be incredibly arrogant, without the slightest trace of humility. As you read his work, factor this in: Hollmann was a German, he certainly believed that some people were superior to others, and he was very fond of pointing out that his father was a Nazi scientist. He was the kind of German who never understood why many Americans didn’t find that something to be proud of.

Richard Finch is well-known in Experimental aircraft circles for writing a book called “Auto engines for experimental aircraft” This was one of the very first books I read on experimental aviation, and I found it very motivational. Finch was also very well-known in Corvair car circles for writing a guide on “keeping your Corvair alive.” He also wrote a number of articles on auto engines experimental aircraft magazines. Ten years after reading Finch’s books, I had done a tremendous amount of work on alternative engines of all types. Not just Corvairs, but with V-8 Lancairs also. I had actively researched lots of conversions, including flying with Steve Wittman in his Olds V-8 Tailwind. I came to understand that almost none of the aircraft it Finch’s book had flown, and that he had not personally ever flown behind a Corvair, nor many of the other engines in the books he wrote. Seen through experienced eyes, his relentless claims that car engines were always lighter and more reliable than certified ones seemed dangerously unrealistic, if not outright wrong. I met Finch in person the first time in 1999 at a Corvair car convention. I quietly asked him if he had flow a Corvair. In a speech reminiscent of Waldo Pepper saying “Quiet, Let’s not disconcert the masses” he confirmed that he had never flown a Corvair despite his books offering the reverse impression.

One of the constant themes in Finch’s books is that aircraft fuel systems as we know them are all poorly made and are the root cause of post crash fires. His books compare them to the ones in race cars, conveniently ignoring the differences in application. It seemed something of a mystery what he expected homebuilders to do with his criticisms. He showed pictures of car fuel cells but didn’t address how they would be put in the shapes of planes. A little known book of Finches on fire safety in planes, hardly more than a glorified pamphlet on the topic, was specifically written on the fire topic. I saw it once in the Embry Riddle library. It had never been checked out. The purpose of the book was made plain later.

In 2002 I had barely recovered from my crash a year earlier, and I was still covered in fresh skin grafts. At Oshkosh, Finch approached me and said that I was obviously barely able to work and he had a way for me to make a good paycheck in aviation. I listened incredulously as he said he had been well paid to be an expert about fires in this lawsuit where Cessna lost $480 million dollars:

Finch explained that I could get a years pay in a few hours of testimony. The fact I was an aircraft mechanic and had been burned over half my body made me valuable, and I could get real good money. The comments in his books about how poorly designed certified fuel systems are were now in a different light; The book on fire safety was just there as a qualification, it was never intended to be useful. Looking at Finch’s books, the introductions tout his qualifications, including a highly suspicious claim that he was an engineer on the space shuttle. (Finch is the only person I have ever met that claimed to be an engineer who didn’t know what vector addition is.) I could now picture this being read off by a personal injury attorney as an impressed jury listened.

I told Finch that I thought the whole concept of  testifying for money was immoral. I told him that if I thought Cessna made bad planes I would say so for free, but not for money. I was not a prostitute. I had 6 lawyers contact me about trying to sue the pilot who crashed my plane. They all pointed out that the man was an investment banker. I had told every one of them to “drop dead” because it had been an honest mistake, and he man was genuinely sorry about it. This perspective was as perplexing to Finch as his expert witness job was to me.

In 2006 Finch bought a 601XL and decided he was going to put a Corvair on it. On the internet few people knew who he was, and the often politely steered him to our webpage. This was hard for him to take. He purchased a motor mount and a number of other parts from us. While waiting for a backordered $59 part, Finch used this as a premise to write 3 different five-page emails to the management of the EAA suggesting that I be fired from EAA publications and that I be banned from commercial displays at Oshkosh. I had a very good look at what he did in aviation for real money, and he was concerned that I might “disconcert the masses.” It was a long cycle from picking up Finch’s book in the library 16 years earlier.


The point of these three stories is to get real home builders to stop and consider some of the things they have been told. Many (but not all) aviation writers who had a strong axe to grind were actually doing so to develop their position as a paid witness. Be careful who you are willing to elevate to the level ‘expert’, not all of these people have the advancement of aviation and the pursuit of the facts as sole motivation. -ww

Getting Started in 2013, Part #12, Piston Choices


Here is a look at some notes on the 1300 group. I left out the 1302 section on rods because I am revising it now. For right now this is a good overview on piston choices.

Engine kit notes:

Builders purchasing a 2,850 or 3,000 cc large bore kit from us receive the new forged pistons, the wrist pins, Total Seal piston rings, new cylinders, head gaskets (2,850s get base gaskets also, 3,000 cc engines don’t use them), and professionally rebuilt connecting rods with ARP rod bolts with 12 point nuts. The price of the 3,000 cc kit includes the machine work to the case and heads to accept the larger bores. Builders selecting either of these options will be fulfilling the contents of both the Piston and rod group (1300) and the Cylinder group (1400).


Piston and rod group (1300)

1300- Piston set with wrist pins

1301- Ring set

1302- Connecting rods  -6-



In January of 2011, when I still was a part of online discussion groups, I sat down over four nights and wrote the history of pistons and cylinders on Corvair flight engines. It included the who, what, where, when and why of the whole spectrum of possibilities. It was a four-part story that covered nearly 18,000 words. I looked at it before writing this section of the Manual. Reading it now makes me reconsider things. The life of a great person is worthy of such documentation, but is the history of pistons and cylinders on Corvairs a valid subject at this length? Who was I writing it for? Was it to convince skeptics that I really am “The Corvair Authority”? The people who are focused on the Internet discussion liked it, but I doubt it needed that length for people focused on building. I am writing this for people who want to know how to build an engine today, to use it to fly, and a much shorter piece is afforded by this focus. I am just going to cover the pistons we use today, have a short section on what not to use. Please realize that there is no combination that you are likely to hear of that we don’t know about. We probably test ran it, and may have flown it. If it isn’t in here, there is a reason. If you ignore that reason, the odds of your plane ever getting finished just got smaller.

1300- Piston set with wrist pins

There are three displacements of Corvairs that we build today. They are the 2,700 cc series, the 2,850 cc and the 3,000 cc engines. There are two good piston options for the 2700 and they both come in 3.437” standard bore, .020”, .030”, .040” and .060”. The pistons for the 2,850 and 3,000 cc are available from us; they come as part of Piston/ring /cylinder kits, but we will discuss them as a separate part here.

First, a quick mention of all the pistons you should never use in a flight motor: Never use a cast piston of any kind. This includes old GM pistons, the ones sold by Clark’s as “high-tech,” any piston that is labeled as Hypereutectic, and the vast majority of pistons intended for VW applications. All of these cast pistons have flown in Corvairs before, but we have been telling people for 20 years never to fly any kind of cast piston because they are not tolerant of any kind of mistake in engine assembly, tuning nor operation. Their life span in an engine that is detonating hard is about 15 seconds. This will also hurt forged pistons, but they will not break or get holes in the piston tops. The second type of piston never to fly is a forged one made by a company focused on making light weight, high rpm pistons with thin tops. Pistons designed to make the most power at 7,500 RPM are different from ones designed to be ultra-reliable in 4,000 RPM engines.

Traditionally, the most popular Corvair flight piston for a 2,700 cc engine was referred to as the “TRW” piston.  In the past 10 years, a corporate name change on the box led most people to call these “Sealed Power” pistons. Until 2009, these were made in the United States and the quality was very good. About eight years ago, the pistons began coming with a greenish gray anti-scuff coating on the skirts. Approximately 90% of the Corvairs now flying have these pistons in their bores. They were available in standard, .020, .030, .040, and .060. Over the years, I have built more than 100 engines using these pistons, almost all of them .030 and .060. They work very well in flight engines and have an excellent reputation for staying together even in engines that are being detonated heavily. I have never seen a hole punched in the top of one of them.

In 2009 the wonderful world of outsourcing had the manufacturing of these pistons moved to India. The corporate ownership was so proud of this change that they announced it by keeping the box exactly like it was with the sole exception of printing the words “Made in India” on the end of the box in a print size usually reserved for credit card contracts. The pistons manufactured in India look exactly like their U.S. counterparts. There is nothing wrong with them; however there is clear, irrefutable documentation that the manufacturing tolerances of the Indian built pistons are significantly looser than their U.S. built predecessors. I would not seriously worry about this, but it is a reality. These pistons are available from many different sources, including Clark’s.  

1301- Ring set

The kits we sell for the 2,850 and 3,000 cc engines include Total Seal rings. These rings are carefully matched to the bore finish of the cylinders that come with the kits. These rings feature the highest quality chrome steel, from a company known for a quality product. The brand it Total seal, which people thing is ‘gapless’ which is not so. Total seal bakes both gapped and gapless rings, we use the former.

For builders working on a 2,700 cc engine, there are numerous choices when it comes to rings. Over the years we have tried them all. I feel that the best combination for a Corvair flight engine is the Hastings chrome ring mated to a 220 wall finish on the cylinder. There are also moly rings available for the Corvair, and the appropriate finish for these rings is 280. We have built a number of motors around moly rings but I don’t see any particular advantage in our application.  With proper break-in, regular oil changes, and breathing filtered air, the lifespan of chrome rings should easily be 1,500 hours. Moly rings would theoretically last longer, but they are far more difficult to break in and they are less forgiving of the wall finish. We have also flown a number of engines on regular cast iron rings. These break-in literally in minutes and they are surprisingly tough. Their Achilles’ heel is any kind of detonation. Even a few moments of knocking will often crack a top ring if it is only made of cast iron. Although their low price makes them tempting, stick with chrome rings.

The rings that go in your engine must be the same size as the pistons. For example, .030” over bore pistons require a .030” over ring set. Corvair piston rings are expensive by automotive standards. If you shop around you can often save a significant amount of money.


Calling Central FL builders, Meeting 9am Sat. 26th


Just a quick reminder that I am going to be the guest speaker at the Leesburg EAA chapter at 9am. The meeting is held at the airport in the hangar on the west end. I am headed down to meet the members of #535 and answer any remaining questions they may have about the up coming College #25 at Leesburg. If any builders are in the area, feel free to stop by. I will be there until 12 noon.-ww

Mail Sack, 1/25/13. Terry Hand Editorial, Numbering System


Here is a sample of the mail on Terry Hand’s Editorial:

Zenith 601XL builder and flyer Phil Maxson writes:

“This is an excellent article. Each of these points resonated with me, but I’m particularly struck by number 5. I am beginning my 24th year with Mars, Inc, a mult-national food company. We are very big on the Freedom principle, and in our case, it is called “Freedom within a framework.” In a company of 70,000 associates it is not possible for everyone to have their own “do whatever you like” form of freedom, but each one of us is obligated to exercise our own talents and skills within our purview. We have a framework that includes five principles: Quality, Responsibility, Mutuality, Efficiency and the one I’m emphasizing here: Freedom.”

Builder Matt Lockwood writes:

“Terry- Thanks for this. Especially point #1. There is a certain discipline that comes with making yourself slow down and consider the ramifications of your decisions…i.e fish tank tubing for fuel lines and/or routing it through the cockpit. Some of the information that is out there on the internet doesn’t consider the ramifications, nor do these anonymous advisors out there have to suffer the consequences of you taking their advice. Everyone, please be careful. Thanks again to you and to WW. P.S. I thought ‘NATOPS’ stood for ‘Navy’s Attempt To Operate Planes Safely’Matt Lockwood, VT-3 1997-1998”

Builder Jerry Mcferron writes:

“Footnotes and warnings are often written in blood. Don’t add yours.”

“In the early 60s my Dad was a Navy flight instructor at Pensacola teaching in T-34s. Earlier, in 1958, Dad was the co-pilot in a helicopter that crashed and he was severely burned. He was the only survivor of the four crew members. A few years ago I received an e-mail from a lady looking for my Dad. Her Dad was the pilot of the helicopter. She had not yet been born at the time of the crash, so she had never known her Dad. If the fates of our fathers had been reversed, I would not be here. The investigation into the crash resulted in changes to the procedures for flying helicopters. Dad is now 76 and passed his physical a few weeks ago. He is still teaching people how to fly. When Dad calls me and says “I got to go flying today”, it makes my day.-Jerry”

Builder Dan Branstrom:

“Amen, and Semper Fi.”

On the topic of the numbering system, Builder Harold Bickford writes:

“Hi William, It is quite clear that as long as a supply of heads and crankcases are available the Corvair conversion will continue unabated at an advantageous price. Even new cast heads and crankcases would not be impossible if the need arose. Given that aftermarket new cast Chevy 409s are available at around $5,000 suggests cost-effective supply would not be an issue.The key is to build it here.-Harold”

On the topic of the numbering system, 750 Builder Blaine Schwartz

“William, This is a great explanation of how the Gold parts assemble and the reason why there are the way they are. Sometimes, we builders read instructions and then either forget them or hear some BS regarding a better way. I have all your Gold parts and have most of them either installed (engine components) or am in the middle of installing them and this reminder you posted is invaluable to help keep me on track. Those small comment like the bushing for the PM generator will save me a lot of time! I continue to be amazed why a builder would literally put their life in the hands of an unknown “internet voice” rather than following proven methods. Keep ‘em coming! Thanks, Blaine”