Steel tube Pietenpol fuselage with landing gear and 12 x 4.8″ tires.

Builders,

Here is a look at Terry Hand’s Steel tube Piet project. The fuselage is an original short length, taken directly from the plans in the Flying and Glider manual.  We added several tubes to the right side to allow for a front door on that side.

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The gear is significantly lengthened from the plans, allowing the top longerons to sit at 12 degrees in the three point position. This is patterned after the gear we built for my Pietenpol in 1999, Which our demo pilot Gus Warren confirmed to allow the plane to be three pointed about 8 mph slower. This significantly shortens both the take off and the landing roll. The axle location is set for 1.5″ behind the leading edge, a location optimized for planes with brakes, suggested by Bernard Pietenpols work and writings in the 1960s. I have written extensively on our testing of Pietenpol CG’s, which covers the thinking behind this work: Pietenpol Weight and Balance project. You can get copies of the reports here:Pietenpol Weight and Balance article source

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The die spring gear is the same style we have put on a number of planes. You can read more here: New die spring landing gear on a Pietenpol, 10 a.m.-4 p.m.  The gear, axles, and the die spring struts weighed 27 pounds for the pair. Because the gear is longer (which produces higher loads in the tubing), and we were planning on very robust construction, I opted to use the same size tubing as a late model Super Cub, and one size thicker wall. This is the same as my plane in 1999. I studied the charts on column bending limits in the back of Bruhn’s Analysis of Flight Vehicle Structures for a long time to make these choices. It is a minor weight penalty, for the gain in strength. Most Piet gear doesn’t have good enough welding on the end fittings, they are the week point, even on the standard gear. If you look at the ends we made in my shop, you will understand why I know we will get full strength potential of the increased strength tubing.

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The tires are 12 x 4.80″ trailer wheels. This is a project I have had in the back of my head for a long time. 13 years ago we had a Stits SA-7D Skycoupe as a test mule. It very successfully used 8 x 4.80″ tires. Look at these photos: 2,700cc-Skycoupe-2002 Photos. The 12″ wheels and tires are no where near as heavy as people suspect; the pair is 29.5 pounds. There is no question they are strong enough; the pair cost about $110; they have the same frontal area as a 6×6, but far less rolling resistance on rough ground. They will likely never wear out, but if they did, any town in America would have the replacement. Would you like to tow the plane home from the airport? There is no question on if the tires and wheel bearings are up for it. We are working on a lighter hub that incorporates a mechanical drum brake. Terry found a company that sells full moon hubcaps specifically for the 12″ trailer wheel. On the inside a 12″ pizza pan from the dollar store fit perfectly, and weighed only a few ounces. The concept is to offer an alternative to traditional spoked wheels, at a tiny fraction of the cost, with a very small weight penalty.

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Above, Terry hand stands with his fuselage at Corvair College #33. You can clearly see the pizza pan on the far wheel. We are sizing the drum brakes to fit entirely inside the pan. For height comparisons, Terry is about 6’2″.  He is the moderator of our new Piet / Vair internet builders group, started 4/24/15. The motor mount is one of the ‘high thrust line’ mounts we make for Pietenpols. Read more here:Pietenpol Motor Mounts, P/N 4201(C)

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Above, the fuselage on the ramp in front of our hangar the day before. The added side tubes for the door are painted white. To see more about the structure, you can study the shadow on the concrete.

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Above, another angle, showing the die spring installation. It has spherical rod ends that thread in and out for perfect camber adjustments.

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Above, we added a pad for a modern 1.25″ tail wheel spring and modern tailwheel. I found them in the sun n fun flymart for $100. This will have far greater control than older designs, and it is full swiveling. This style installation gets the tailwheel horn in a position to be connected to the rudder horn, eliminating things like spliced cables. This also has a longer wheelbase. Note the little brace tubes to pick up the loads the front of the spring would otherwise introduce into the lower longerons.

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Above, the die spring cans. The oldest aircraft I have seen this layout on is a Plane built by Bernard Pietenpol in the 1960s. It is vastly better than any arrangement with the springs on the outside and slots milled into the tubes. Bungee cords hate heat and oil, and are subjected to this all the time in the traditional location. conversely dies springs are impervious to heat and actually like oil.

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Above, get a look at how the ends of the tubing have reinforcements and sockets made for them. I carefully made these on our milling machine, and then we TiG welded them on very carefully. I am 52, and have been welding continuously since I was 17; Vern is 62 and has been welding for a living since he was16. Between us, we have welded parts that have flown on several hundred planes from ultralights to F-14s.  I take every opportunity I can to share what we know about welding with those who want to learn. The same week we made this gear, a  person on the matronics Pietenpol internet list, with a mystery email name and no cited experience claimed that because it was Tig welded (like 99% of all aerospace structures today) it was absolutely “going to crack.”  If you are a new builder, learn this: That kind of person is the enemy of your success in building and flying, and that is why we have both the Zenvair and Pietvair private groups which are free of that kind of person. 26 years in experimental aviation has taught me that I can’t win arguing with people like that, and the solution is to have colleges and groups that are free of them, just made of people who want to understand, build and fly.

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Above, the 1 and 1/16″ axle. I bored it out on the lathe to lighten it. Axle cost: $10.50. The front plate is 1/8″ 4130. The long bolt is where the mounting/ pivot bolt for the spring strut goes. If there is anyone who thinks that this weld isn’t strong, or is somehow ‘brittle’, or could have been done to a higher quality with a gas welder, they are a victim of poor information.  If they convince you of this, you are allowing them to sabotage your dreams. Take your pick.

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Above, Terry’s project at Corvair College #33, with Bob Lester’s Pietenpol in the background.

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-ww.

Steel tube fuselages part #2

Builders,

A while back I wrote a story on the subject of design considerations for risk management in experimental aircraft. It was one of the most popular essays I put together in the 20 months we have been on this site.  If you missed it, you can get a look at it by clicking on this link:

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Steel tube fuselages, “Safe” planes and 250mph accidents

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Part of the above story is examining the structure of fuel dragsters in accidents, as they are something of an extreme example of steel tube aircraft fuselages. I was searching for something else on You Tube and came across this link,

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http://www.youtube.com/watch?v=zHfcC6EHnbc

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which is a 500km/hr (300mph) accident in an Australian top fuel dragster. Total damage to the driver was a burned thumb. You may not be planning on having that kind of an accident, but it is visual proof of the value of simple concepts like steel tube fuselages and perhaps the idea of flying in a surplus Nomex jumpsuit or at least not flying in shorts and sandels.

On the way back from CC#26, Grace and I stopped by the giant Summit Racing warehouse in Georgia, exit 216 on I-75, (They are open 7 days a week 9am to 9pm). As I walked in I was surprised to see a restored version of Don Garlits’s “Swamp Rat 13” (the car blown in half in our original story) on display hanging from the ceiling. Hundreds of people a day go through that store, but I doubt that many of them know the significant history of the car or the role it played in the evolution of motor sports.  People drift through racing, aviation, and many other serious human pursuits with little appreciation of the depth of experience precedes, and is still available to them. I find everything a far richer experience when I have some understanding of those who pioneered their arena at a very high level of intensity.

Above, Don Garlits in command of Swap Rat 13. A very different era; Open face helmets and a 2,500 hp hemi in your lap.

Steel tube fuselages, “Safe” planes and 250mph accidents

Friends,

I recently saw parts of a discussion of the merits of different types of fuselage construction from a crash worthiness stand point. These discussions go on in homebuilt circles endlessly, and they are mostly harmless banter. People tend to have seen the results of a single accident, or have some type of favorite construction that they would like to promote as ‘crash worthy,’ mostly to reassure themselves that they have made a good choice.

In professional circles, there is little question that steel tube structures are the most crash worthy of the readily available methods of construction for light aircraft. People are entitled to disagree with this, but they would have a hard time statistically supporting their position. My degree from Embry-Riddle is in Professional Aeronautics, which was the accreditation term that covers the discipline of accident investigation. Even back then my focus was on light aircraft and we have 5 feet of shelf space on the sun porch devoted to books on the subject. If your thinking about a basic book on the subject, start with Thurston’s “Design for Safety.” All of the material and data on the porch supports the use of steel tubing.

One of the best ways to look at an issue is study an extreme example, like Ag planes. Almost every successful Ag plane design has a steel tube structure. These aircraft have a very high survival rate in accidents for a lot of reasons like the pilots being very skilled and the fact they almost all wear helmets, but the basic structure of the planes has a lot to do with it. The actual example I use below is just a little outside aviation, but it does a very good job of illustrating the protective nature of steel tubing in accidents.

There are a lot of other factors that go into aircraft safety. Some are often covered, others that are very important get little consideration. Example: Many people, especially people just learning how to fly, are fixated on STOL aircraft because they believe the quoted low stall speeds make a plane easier to fly and thus ‘safer.’ These same people never think about something I would gladly trade low stall speed for: Glide Ratio. Power off, many popular STOL planes have glide ratios of 4:1. The may have stall speeds of 30 mph power on, but they can not flair to land without power from such a speed. Arrive at the ground power off at this speed, pull the stick back and the plane will fly right into the ground. They commonly need to use 65 or 70 mph as a power off glide to have enough energy to flair and check the rate of decent. timing on this maneuver requires some skill, real training and a fair amount of practice. These planes do not “fly like a Cub.”

 If the engine stops in a STOL plane at 1,000′ AGL, you are going to be on the ground in 60 seconds or less, and you are barely going to get a 1/2 mile of ground distance covered in this glide. When you get to the ground you will round out at speed substantially higher than a Cub flairs at, and you will need to time the flair carefully because the energy will bleed off very quickly when you begin the flair. With practice, the actual ground roll can be very short.  A STOL airplane pilot who always flies power on approaches is probably not going to be able to self teach the above technique in a 60 second window the first time he has a power loss. To benefit from the airplanes capability, this must be practiced.

Contrast this with the 56-year-old 1-26 glider in our front yard. With no power or lift and 1,000′ AGL, it will have more than 9 minutes before it gets to the ground. It’s ground track will be more than 4 1/2 miles long. It has a 24:1 glide ratio clean, and 3:1 with the spoilers open and in a slip. the flair is the definition of forgiving. Our glider has 6,000 landings on it, it has never had the luxury of a single go around, and it has never had a single dent put in it in a landing. That’s 6,000 consecutive forced landings with a great outcome every time.  Yet listening to internet chatter about characteristics of ‘safe’ planes, glide ratio rarely comes up.

Food for thought: Here are some of the risk characteristics I think of in light planes, followed by the ratings from most desirable to least (None of this touches on the single most important factor, a skilled alert pilot.)

FUSELAGE CONSTRUCTION:

Steel tube–Composite—-sheet metal—-wood.

FUEL TANK MATERIAL:

rotationally molded—-bladder—-aluminum—-fiberglass

FUEL TANK LOCATION:

none (glider)—-tips—-wings—-leading edges——cockpit

STALL SPEED:

Low—— medium—-High

POWER OFF GLIDE RATIO:

24:1————-10:1—————4:1

TURN OVER STRUCTURE, ABILITY TO ESCAPE INVERTED AIRCRAFT: High—-low.

I think of the factors as a matrix. Consider the 1-26: It has a steel tube fuselage, no fuel tank, a low stall speed, a great glide ratio, and a steel tube roll over structure and the ability to discard the canopy in seconds by pulling two pins on the inside. Experience says this aircraft is pretty low risk in a forced landing. Conversely, you wouldn’t choose to be in a wood plane with a fiberglass fuel tank in the cockpit, a high landing speed a 5:1 glide ratio and no turn over structure. Chances are your airplane is in between these extremes, but you still have choices. I like the wing tanks instead of header tanks in Zenith HD and HDS models. If a plane had a fuselage tank, I would make it from aluminum rather than fiberglass. It a plane as an optional long wing, choose that. There are combinations I like and those I don’t. Example: I don’t mind flying planes with fuselage tanks, as long as the plane has a steel tube fuselage and the tank is not fiberglass. There are vetos, like no planes that are wood fuselages and pushers, no planes with stall speed much over 65 mph. There are particular designs I would fly, some I wouldn’t fly if you were willing to pay me a cubic foot of $20 bills, and some I wouldn’t fly with a pistol at my head. These are my opinions, the point is to develop your own.

A single factor isn’t king: Two Pietenpols, one steel tube the other wood, which is ‘safer?’ If the wood one has no header tank, strong cabanes and is in CG, I would fly it before I would fly a steel tube plane with a fiberglass header tank, dinky cabanes and an aft CG.

Dan Weseman has a personal rule I find interesting. He will not fly a plane that can not out climb it’s glide slope. If he takes off and climbs out at full rate, he has to know that the plane can turn around and glide back to the airport. For a plane that climbs at 60 mph and has a 10:1 glide ratio, it needs to climb at better than 528 fpm. Ultralights make the grade even though the have poor glide ratios because their rate and angle are both very good.

Keep factor #1 in mind: Who is flying? I would rather land a fast wooden plane at night with a zip lock bag of 100LL in my lap, a lit Cuban cigar in my teeth and my feet chained to the rudder pedals than take a trip around the pattern on a sunny day in a Stearman with some of the pilots I have met. I am serious. Avoid these people like your life depends on it, because it does. Make it your goal in aviation not to be one of these pilots.

Back to looking at a single factor, the steel tube fuselage.  Here is the best example of their strength: Top fuel dragsters. Their frames are steel tube structures, made very much in the same way as aircraft fuselages. A fuel rail weighs about 2,000 pounds. take everything off but the steel tube chassis, and it weighs about 400 pounds. The tubing is bigger than light planes, but most planes don’t go 325 miles per hour and none have 7,000 hp. Below is a link to a phenomenon of the 1980s called a “Blowover” I was present at the 1986 summer nationals at Englishtown and saw the very first one from the 800′ mark on Garlits’s side. It was stunning in person. He flew by backwards going 225 mph.  Watch the video to know that Garlits is the greatest show man on earth because he drove back down the track to the middle of the grand stands, got out on his own, stood up and took a bow. 75,000 fans went wild, we had just seen the greatest moment ever in Drag racing, the purest of American motor sports.

The link:  http://www.youtube.com/watch?v=C0KmGfBCJtQ

(Above) The 1990 photo of Don Prudhomme’s wreckage in Montreal. It is outside the rail, and went over backwards at 250 mph. The lightly built front end is gone, but the drivers section is intact. This was one of two wrecks like this for him in one season. He was protected enough to not only live, but come back a week later and compete.
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 There is no wood structure that could be built as a chassis for a fuel rail that would protect a driver in a blow over. Steel tubing works. Notice the drivers get right out of the dragsters even after the most violent of blow overs. Prudhome, Hill and Collins were all doing more than 250 mph. When you watch the details, notice that dragsters don’t have diagonals in the frames. They do this to be flexible in ways that are not desirable in fuselages. People often talk about energy absorbing structures, but they must deform without exposing the occupants. Steel tubing passes this test. Wood often does not.

 Don’t know much about drag racing? Your missing the drama of dueling and the sound of pure thermo-mechanical violence. Ask any person who has felt (it goes way beyond hearing) the launch of two 7,000 hp dragsters and they will tell you nothing compares with it.  If you are a Corvair builder who thinks our favorite engine sounds sweet, you will love it. If a person likes the sound of a Rotax 912, I am sorry, they can’t be helped.

 The two photos below tell an interesting tale. All of the dragsters in the blow overs are rear engine models. These came into being in the 1970s. If you think that the blow overs required people of a particular courage to keep racing, you are correct. But if you asked any of them, they would all gladly testify that the required courage was less than what it took to drive Front engined fuel rails, arguably the most demanding and dangerous motor vehicle.

 These emerged in the 1960s. Advances in engines made thousands of hp available before chassis design caught up, and when safety was drivers in open-faced helmets, sitting on the ring and pinion, with the clutch between their legs, and a raging blown Chrysler in front of their face. These were very special humans with the courage to do this.

The 1960s were a period of time when we generated a number of people willing to take risks to achieve something. To me, Don Garlits and Neil Armstrong had more in common than most people noticed. Advanced education gave Armstrong a different path than a young man from Ocala FL in the 1940s could hope for, but in their own arenas, their personal courage and their willingness to engage calculated risk made them legends. Today our society is obsessed with celebrity culture, people famous for going to rehab, actors with little talent, talk show people with nothing to say, and all day to say it. It is a distorted reality, and I choose to ignore it and focus on a time when we thought more clearly and knew what made individuals worth admiring.

Aviation, particularly Experimental Aviation is one of the very few pure arenas left where you as an individual can personally challenge yourself and develop your skills and hone your craft. Even in experimental aviation, ever more people are looking for a short cut where they don’t have to learn, where they can get done instead of mastering the task. People who think that way have been poisoned by consumer-celebrity society, and their path doesn’t go far. I have been in aviation for a quarter of powered flight and half the history of experimental aviation, and I will absolutely state that the people who get the rewards of learning, building and flying are only the people who are willing to devote themselves to mastering each of these steps. If you are building your own engine to master it, if you are willing to really understand flight, they you will have your place among people of real values and courage.

 Above, Don Garlits in a front engine blown fuel rail at the moment of the drive line detonating under 2,500 hp. He has just lost most of his right foot. It would be easy to understand if he never got back in a dragster again, but Don Garlits was the kind of American that we respected because quitting wasn’t part of his DNA. He came back from this and competed for 20 more seasons. This event is 16 years before the first blow over. I choose to spend as much of my life in Aviation as possible, because aviation still respects commitment, persistence and courage.

Your fellow Corvair builder, Myron Pickard, above left, (with Archie Frangoudis at Corvair College #14). Myron is a member of the Motorsports Hall of Fame, and one of the owners of the New England Dragway. Myron was a nationally known competitor running front engine top fuel rails with blown Chryslers. Running 6.6’s at over 200 mph with a 2,500 hp Hemi sitting right in your lap is not for the timid. This era predated national sponsorships, and Myron, like most of his competitors, wrenched on the car and drove it. Today he’s working toward a more subtle experience, flying behind a Corvair.-ww

Aluminum push rod tube issue resolution.

Builders;

This commentary ONLY applies to aftermarket aluminum push rod tubes, which are  in maybe 3% – 5% of Corvair flight engines. If you have stock steel push rod tubes like the powder coated ones we sell, it does not apply.  However, the notes still make good reading and give some appreciation for detail design considerations GM put in the engine, and unforeseen potential consequences in modifications, particularly in combinations with other work.

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The original design of the aluminum tubes goes back more than 15 years. They were the work of Charlie Johnson, aka “One Sky Dog”. I’m pretty tight with Charlie, you can see pictures of the two of us hanging out at my place in Florida, building engines and shooting AR’s in this 2017 story: Last Engine of CC #39

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Part of the awareness of this issue with the aluminum tubes surfaced when we were building and testing Charlie’s personal 3.0L for an upgrade in his flying Dragonfly, read: Corvair powered Dragonfly, Charlie Johnson, aka ‘One Sky Dog’ .  The basic issue is this: When the aluminum push rod tubes are used in an engine with heads milled for a tight quench area, they restrict the oil flow back to the pan, and oil builds up in the valve covers.

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This isn’t a small consideration, I have seen a motor with 4 quarts of oil in it suck air into the pick up because it had filled each valve cover with 2 quarts, and it was in the process of ejecting a lot of it out the breather tube.  This wasn’t an easy issue to spot, because it is dynamic, and if you stop the engine and wait a few minutes, all the oil shows back up in the pan. Sight tubes on the valve covers confirmed the issue and the relatively simple solution.

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Above, is my own personal 3,000cc Corvair, (3,000cc Corvair (lower compression) engine), and you are looking at the #1 cylinder with the intake rocker removed. Notice there is  no space between the guide plate and the push rod tube. that is the normal path oil used to flow back to the pan. In operation, a lot of oil is pumped through the lifters, up the hollow pushrods, and sprayed out sprinkler style onto the rocker and the valve spring to cool them. It drains back by gravity through the push rod tubes, but it can’t be restricted. The stock steel tubes have never had an issue with this, but the following pictures will show why it is an issue with aluminum pushrod tubes.

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Above, same part of the engine from a slightly different angle.  The tube leaning on the head is a stock GM steel push rod tube which has been powder coated. Notice the wall thickness at the top is only .035″. This allows plenty of room for oil to flow between the guide plate and the tube. Now look at the Aluminum push rod tube in the engine. It’s wall thickness is more than 3/16″, .187″ This can block the return oil flow. The hole in the guide plate is where the pushrod goes, and in operation the pushrod is moving several thousand strokes a minute, oil doesn’t return through the space around the pushrod.

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PS: The photo shows a roller rocker, but I just removed these from the engine. I have a few hundred hours on them since 2004, but I opted to replace them with new, standard Elgin made in USA rockers as a pure reliability issue.

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Above, Why some Corvairs have used aluminum pushrod tubes without this being an issue, and why it is a problem in others: This is a very Common 3.0L Corvair set up. The “step” in the head, an upraised area where the head gasket sits, has been intentionally milled down to get a better “Quench clearance”. This in combination with any of our 2,775, 2,850, 3.0L and 3.3L engine kits with special designed dished pistons produces a very detonation resistant engine with a very desirable tight quench / moderate static compression ratio combination. We have built motors this way for almost a decade, but never encouraged the use of anything but GM steel pushrod tubes in them. Thus it was a long time before I saw the rare example of the dysfunctional combination. As luck would have it, my own personal engine had the combination, so I got to test and address the issue for other builders. My own engine has tested a lot of stuff, and in its details isn’t typical of engines we teach role to build for themselves.  BTW, we did nearly the same modification to Charlie’s personal engine which has aluminum tubes also.

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Above, on the left is the stock aluminum tube as they are made. I had these powder coated, like we do to steel GM ones.  On the right, the same type of tube which I just fed through my lathe. I shortened the tube .125″ and spend the end of the tube to give a generous oil return clearance around the guide plate when installed.

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Above, I was trying two different end treatments, but either one will work to resolve the issue.

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Above, proof of anything requires testing. Above is the engine with the modified aluminum push rod tubes running on my stand in front of my house.  Its green in the picture, but it wasn’t real warm. This issue shows up mostly on warm ups in cooler conditions, but if your engine has aluminum push rod tubes in it, this really needs to be checked and addressed.  Again, this doesn’t apply to steel GM pushrod tubes.

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15 or so years ago, when Charlie made the first set for himself, these rapidly because a hot discussion topic on the internet, particularly on the Corvaircraft list. People who had never held one, far less put one in a running engine, spent a lot of time talking about how great they would be because the set weighs 15 ounces less than the stock ones, and they must cool the oil.  I spent some time debunking the myth of cooling, as the oil in the head is at least 150F cooler than the top of the tube in operation. It meant little, as the discussion was dominated by people without a running engine who were sure their opinions were more valid than any measurement I took.

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For the record, Charle has not made any tubes in many years. He was never the guy driving the internet claims about them. Soon after he made a few sets, a west coast Corvair Car company made copies of them, and he drifted away from the project. In the end, this isn’t a tough issue to fix, but it is a lot more work than meets the eye because the heads have to be un-torqued to remove them, and without a lathe, it would be hard to fix. In the end it is a bit of a precautionary tale of how a small combination of alterations can produce things like the oil pump sucking air in an engine with plenty of oil in it. In the end, the great majority of builders are best served by very specific combinations of parts that we use every week to build very proven engines.

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Wewjr.

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PS; Something to laugh about: In the story: 2018 Zenith Open House -The long run., I pointed out the presence of a salesman, who was promoting an engine which had never flown on a Zenith, which he didn’t own, nor had ever even seen one run. For a moment, contrast that with the type of detail and testing above, and consider the 29 years I have been doing this and the 1,100+ stories on this site alone, and all the builds and engine runs, and colleges, and ask yourself what kind of person would listen to a salesman who has never even heard his Chinese engine run.

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Mail Sack, 11-18-12, Steel tubing, exhausts, advice….

Friends.

On the subject of Steel tubing and risk management;

601XL Builder and Flyer Ron Lendon writes:

“WW, I really enjoyed this article and was in the drag racing game in the 1970′s as a mechanic. Some of those experiences have prepared me to expect the unexpected and like the Boy Scout motto “Be Prepared”. The learning experiences of building and flying the Corvair powered CH601 have been one of the most enjoyable and exciting endeavors I have undertaken to date. Now that I’m getting older and wiser, I will be paying much more attention to the details of the proven path. Thanks for persisting my friend.”

Pietenpol builder, CC#24 grad, ATP/USMC, Terry Hand writes:

“William, You are correct that safety is not a “one trick pony”. Safety is a combination of choices, not just a single choice of steel tube over wood, for example. Safety is also a recognition of the human factor. The pilot who practices his/her emergency procedures, particularly his or her engine failure procedures, knows and flies the glide ratio of the airplane and keeps their skills up is far better, in my eye, than the pilot who kicks the tire, lights the fire, takes off, and then thinks nothing will happen when they fly 10 hours per year. But, as you have said many times, it is not safety. It is risk management.”

DC-3 owner, International aviator of adventure Tom Graziano writes:

“William, Spot on about the crash worthiness of steel tube fuselages. I’ve been around more than a few crashes. Steel tube holds up/protects the best IMHO. One AT802 crash in particular pretty much had only the cockpit remaining intact – the CSAR guys couldn’t believe the pilot survived, let alone got out and staggered down to a river to wait for rescue. (Pilot did sustain a fairly serious concussion from the ordeal.) My latest project is definitely steel tube. There are some good threads about crash worthiness over on http://www.homebuiltairplanes.com

“I will be changing my fuel tanks from a straight aluminum tank to a polypropylene tank inside an aluminum outer tank/box. Adds a little weight, but its a price I’m willing to pay for the extra margin. Self-sealing bladders are probably the best way to go, but their weight, maintenance, life limit, cost, and availability makes them not so feasible to me. I’ve decided to install self-sealing breakaway fittings at the tanks and one or two other key places. I saw a Super Cub crash once where the fuel lines pulled away from the tanks and drenched the occupants with fuel which self-sealing breakaway fittings would definitely have prevented. Fortunately, there was no post crash fire. I believe homebuilders give too little thought or serious consideration to flammability and fire. Toxic fumes from foam, upholstery and other things can kill just as fast as fire….”

Builder Tom Griesemer Sr. Writes:

“The 1960s were — individuals worth admiring.
This paragraph is so true…-Tom G”

Tom, I can think of no better example of the poisonous effects of celebrity culture and how degrading ‘entertainment mentailty’ is than Bruce Jenner. Once a genuine American Champion in the 1970s, today portrayed as a buffoon for the benefit of ratings and consumerism. I know a number of people who work in the national media. The only bias they share is an obsession to find a flaw in any effort, the gap in a personality, the small error in any advancement. This quest to degrade or critique betrays their very ugly view of human nature, a grotesque view that does not acknowledge, and can not permit, the recognition of a Champion or a Hero. They will never focus on how Jenner trained 8 hours a day for 6 years, living near poverty, to defeat the Soviet state trained athletes in the 1976 decathlon. Yet they gleefully show you his fall where he is brought to the pettiness of dealing with a vapid family without a single redeeming quality. They do not believe that an individual, even through intense effort, should be allowed admiration of  society.-ww

Builder, CC#5 grad. and linguist Dan Branstrom writes:

“Both my parents spoke Swedish first. My dad, because he was born in Sweden, and my mom, because she lived in a farming community composed of Swedish Immigrants.For her, it was easy, because her mother had been a school teacher. My dad learned English after he immigrated to the U. S. at 17. He put himself through an academy (high School), two years of college, then seminary, and left for China at 26 and learned to speak Chinese. I asked him what the hardest language for him to learn, and he answered, “English.”

I wrote all that because I understand how difficult it can be, particularly with all the homonyms we have and our hodgepodge of spelling rules we have because our language comes from so many disparate sources William, you do things with a flair, but you flare a tubing or an airplane.Knowing you, you probably flare an airplane with a flair.To get even more ridiculous, a very dramatic person at the scene of an accident would light a flare with a flair. Thanks for the essay on construction modes. The only thing I’d add would be that a good system of restraint is mandatory. At least a 4 point seat belt should be used.-Dan”

I include this note from Dan to show that he functions as my editor when Grace is out-of-town. The corrections often come in stylish sentences like above. Dan lives in CA and has been part of the Corvair movement for a long time and has a very interesting family history.-ww

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On the subject of Zenith Exhausts and Advice, Zenith 750, 3,000 cc Builder and Flyer Doug Stevenson (First person to fly a 750 on Corvair power) writes:

“William, I certainly agree with you….these discussion groups can lead you far astray. Much better to go straight to the “horses mouth.” Regarding this topic, my pipes fit perfectly 1/2″ below my 750 firewall, but I do not have any exhaust gaskets between my exhaust pipes and the pipes coming out of the heads. Should I have used gaskets? My engine seems to run and sound fine without any gaskets, and I cannot detect any signs of leakage. (Doug, I would put gaskets in, it’s a good idea-ww)

On another subject, some time back, I complained to you that my coil splitter was defective and would not allow the engine to run properly. I finally discovered the solution to the problem, but not until spending many hours searching for a solution and having four very experienced mechanics try in vain for several hours to fix the problem. I even sent the new splitter back to the factory for replacement without solving the problem. What was so confusing was that when bypassing the splitter and wiring directly from either coil to the distributor, the engine ran perfectly. I even flew the plane on one coil without the splitter for a short period until I discovered what was wrong. The answer was that the coils were wired with reverse polarity. I had learned many years ago from my hot-rodding days in the 1950′s that it didn’t matter whether the coil was wired from the power source to the + or – side of the coil, the engine ran the same. However, not so with a coil splitter, because the diodes in the splitter won’t allow the current to flow in the opposite direction. I’m bringing this to you now in hopes this information disseminated by you will save some other poor builder the problems I endured. Thanks, Doug Stevenson ps: My engine runs like a dream. I’m really happy with it.”

Doug, Thanks for the note. KR builder/flyer Dan Heath reversed the polarity on his coils before flying last year, and it took a bit of head scratching then also. I have had builders suspect the coil splitter, but I have never seen one fail. You are correct, sharing this type of detail advances the movement. I define success in aircraft building as the comparison between what a guy knows going in and how much he knows when the plane flies. Learning isn’t a common goal in all experimental aviation, but it is in the land of Corvairs.-ww

2,850cc Zenith 750 builder CC#22 grad Blaine Schwartz writes:

“William, I appreciate your comments regarding internet builders. I reread some of these posts and it is very clear the author has never seen the business side of a wrench. People just don’t get it: Carl Sandburg once wrote “experience is the best teacher” and there are no words that are more true that. sometimes the truth just hurts. I would much rather seek out the truth based on proven techniques than risk my life on some phony internet expert. Please keep pursuing the pure unadulterated truth for us who use logic in our aviation decision making.-Blaine”

2,850 cc powered Zenith 750 builder/flyer Jeff Cochran (3rd Corvair powered 750) writes:

“William, Every once in a while the photos do not show up on the post. When I click on the icon, it opens a new window that says I am no longer logged on to AOL, and ask me to log in. Would like to see the exhaust photos because I have the same situation. The pilot side has melted some of the fuse skin. I will use your dowel method to bend it down slightly. Meant to ask you about this, so glad it came up.- Jeff”

Jeff, The issue with some photos is that I have taken them out of emails, Grace has a way of correcting this later, but you have to hit F5 on the computer if I sent it out wrong in the first place, sorry about that, I am a troglodyte. Inspect the skin and make sure it’s only paint damage.-ww

Builder Jackson Ordean writes:

” It is the very ‘attitude’ that you exhibit that some folks apparently don’t like is the main reason I tend to believe every word. Don’t change it. I don’t know what to tell ya’ about these guys ‘A’ and ‘B’, except they’re giving the alphabet a bad name.-unabashed fan and future college attendee.”

Jackson, Both A&B are good guys in general, but that doesn’t mean that their advice nor judgment are good to follow. Its OK to be a Fan of the corvair and/or the movement, but I like friends not fans. At Oshkosh a guy told me that I come across as a “know it all” in my writing. I said I was some thing of a “know most of it” on Corvairs. I asked he if he would prefer getting his building information from some one who knew less about the engine or was unsure about their data? I also pointed out that I always tell people I am a caveman, a Luddite, and I can’t paint, fly complex aircraft, sing, dance, do differential equations, be civil with annoying people, or (as Dan Branstrom points out) spell. I am still mystified on how this could be read as being a “know it all.”-ww

On  crash worthiness, Sprint builder Joe Goldman writes:

“How about stress skin construction over aluminum .040 2024T3 oval bulkheads. The Sprint is the same size as the zenith 601 planes, 27ft wingspan, 19′ fuselage. and according to the designer uses 18′x4′ less AL sheets, then the HD601. If I am lucky stall at 38mph@1150lb with 9:1 glide. Off course I have to finish it to prove it.-Joe”

Joe, Sounds like a Sprint should fly a lot like a Zenith 601/650, which I think has a very good combination of factors. The 601s glide ratio was probably higher than 9:1 and is had a low min. sink rate. The Zenith 601/650 are a fairly good STOL planes, even if they are not perceived as such. Woody Harris just told be about landing his at a 1,400′ strip is a very remote part of CA and using less than 1/2 the runway.-ww 

Stainless Steel Exhaust Systems – Follow up

Jeff Cochran, CH-750 builder from Alabama with a running 2,850 cc engine, writes:

Welcome back to the world wide web. You have been missed. Questions about the installation of your SS exhaust pipes. First, if ceramic coating of mild steel is bad, what about wraps on the SS system (except for the heat muff section)? Next, do the Heat Muff Box Ends need to be attached to the pipe and if so what is the best and worst method? And last, you say the pipes do not require tail pipe brackets, but the 601 Installation Manual calls for a steel tubing brace across the ends?
The new site is great, keep blogging.

Jeff,

Good to hear from you. The photo above is the first run of your engine at Corvair College #19.

Wrapping the pipes is bad for mild steel for the same reason why ceramic coating the outside of mild steel is bad: It keeps heat trapped in the steel, and mild steel can’t take this. If you look at the pictures of our Pietenpol in the late 90s at our http://www.flycorvair.com/carbice.html page, it had wrapped exhaust. I learned my lesson then. As a concept, it is worse than ceramic coating steel because when it cracks or disintegrates, you can’t see it. The only Corvair builder who I can think of who found this out the hard way was 601 builder and pilot Scott Laughlin. His wrapped mild steel exhaust gave in in about 100 hours, but he initially didn’t see it because it was wrapped. Wrapping the exhaust had its heyday in drag racing 25 years ago before coatings were available. Today they are a fashion statement on custom motorcycles. I can attest that it doesn’t work all that great either. My motorcycle, a Buell XB12X Ulysses came secondhand with a wrapped exhaust right where it passes my right thigh. It still radiates enough heat to be very uncomfortable. Sooner or later I am going to send the header pipes out to Jet Hott in Texas to have them ceramic coated inside and out. The best way to secure the heat muff ends it to get the box built and fitted right where you want it and then let a local welder put two tack welds on each end. The welds don’t have to be very big, two spots 1/4″ in diameter will do it. Other builders have used a hoseclamp above and below the box. Avoid anything that would puncture the main exhaust tube like a rivet or a screw. Your Zenith Installation Manual is an early one where we experimented with tying the ends of the pipes together aft of the nose gear. Subsequent experience has shown that this isn’t necessary.

Thank you,

William

This follow up came in from Gary Burdett, 750 builder from Illinois, also building up a 2,850 cc engine:

I take it that the short stubs are the place for the egt clamps.

Gary,

If you’re planning on 6 egts, the stacks are the place to go. However, a majority of Zenith builders are using just 2 egts, one in each pipe, allowing them to monitor each side of the engine. In this case, they mount it about 6″ past the last stack.

Thank you.

William

Stainless Steel Exhaust Systems

Friends,

One of the most popular products we sell are Stainless Steel Exhausts for Corvair powered planes. We have been continuously making them since 2005. In this post we will cover the different systems that we make, talk a little about the pros and cons of certain designs, and look at some applications.

Prior to stainless, we built systems out of mild steel and had them ceramic coated. They looked great, but actually had a shorter life than plain painted steel. This is a surprise to many people, but here is why: Ceramic coating really works. It is a great heat barrier. A normal mild steel exhaust lives for a while as long as it can run cool.  Ceramic coating the outside of it makes it look good, but it is actually hurting the system because it is trapping the heat in the metal. All affordable ceramic coating is done on the outside of parts. Very high end shops like Jet Hott charge several hundred dollars for a system because they use special tools to apply the coating on the inside of the pipes.

In 2003, I built an exhaust for our 601XL, N1777w. It was made from mild steel, but it was ceramic coated by the Moore Brothers, a very high end shop in Florida. The coating alone cost $300. It worked, and the best evidence of this was the fact that the heat muff for the carb didn’t work because the coating prevented any useful heat transfer. The system also racked up a lot of time on our plane, and it held up well. When other Zenith builders wanted to follow our success, I began to look at stainless as a better material for production exhaust systems.

Above, a pair of 304 stainless tubes before they are welded into the system. They are precision CNC machined; note the tapered surface to match the bevel on the Corvair exhaust gasket.

Stainless is inherently a better material for exhausts because it is stronger at elevated temperatures and it is very resistant to corroding. Both of these are a big deal in aircraft because you can’t tolerate any kind of an exhaust leak in a plane. Everyone first thinks about carbon monoxide getting in the cabin, but my real concern is the possibility of starting a fire in the engine compartment. It is remote, but it is something that experienced aviators actually consider more of an emergency than having an engine quit on you. The strength and rust resistance of stainless, combined with good materials and welding techniques, applied to a design that has been flight proven not to resonate or crack on your airframe is the answer to minimizing your risk.

The stainless we use is an alloy called 304.  It is the standard alloy of certified exhaust systems. The main tubes of our systems are bent for us by a shop in Florida that specializes in robotically bent tubing. They actually make the OEM systems for Lycoming and Continental, and make STC’d systems for companies like Powerflow.  The head pipes on our systems are CNC machined from solid  304 bar stock.  (They are made in the same shop in Florida that produces our Gold Prop hubs.)  We have a separate shop that produces the Heat Muff Box Ends and another company that makes the tight radius front pipes. All of the systems are TIG welded in our hangar with 308L rod while they are pressure back purged with argon gas.  Getting very expensive American made subcomponents from four different shops together in one jig and welded is something of a logistical challenge, but the end product is well worth the effort. In the past seven years we have produced about 250 Stainless Exhaust Systems for the fleet of Corvair powered planes. Chances are, most of the Corvair powered planes you have seen in person or seen in photos have a stainless Exhaust System that came out of our shop. Virtually every Corvair powered Zenith has an Exhaust System of ours on it.

To get a look at one of our Stainless Exhausts in action, watch this video of Jeff Moore’s Corvair powered Merlin on floats:

Jeff is from Newfoundland, Canada. His aircraft previously flew with a Rotax, but he has opted to repower his plane with a Corvair that he built with our conversion parts, http://www.flycorvair.com/products.html. His engine is a 2,700 cc 100 hp engine with all of our Gold Systems and a Weseman bearing. Jeff built his own mount utilizing one of our pre-welded trays. The Exhaust seen in the video is one of our Universal #2 Systems.

Below are  three of the four production Stainless Exhausts we make.  Universal #1 is the Exhaust System that is used on KR-2s and Cleanex airframes. Chris Smith’s “Son of Cleanex” was the first aircraft to fly with this system.  The Universal #2 is the system that we make for aircraft like Jeff Moore’s Merlin.  It fits a broad variety of planes like John Pitkin’s Kitfox 5 and Russ Mintkenbaugh’s Wagabond. It combines good motor mount clearance with the ability to work with a high thrust line.  It is also a good match for a Pietenpol. Universal #3 is specifically bent for aircraft with a very low thrust line, like a Tailwind. Ordering information is on our Exhaust System page, http://www.flycorvair.com/uniexhaust.html  

If you have any questions about which model is correct for your plane, just send an e-mail or give me a call on the shop line, (904) 529-0006.

Universal Exhaust Systems

Our fourth production system is our Zenith 601-650-750 System.  This is specifically engineered to fit in the Zenith’s engine compartment, which has plenty of room, but the Exhaust has a sophisticated shape because it passes through the mount and clears the nose gear installation. This has proven to be the most popular system we sell. The Zenith has a particular motor mount geometry that requires this Exhaust to fit the engine correctly to the airframe. While some aircraft like Pietenpols utilize stock car exhaust manifolds, this is not an option on a Zenith because the car manifolds actually hit the upper tubes of the motor mount. Thus, a stainless system is an upgrade on a Piet, but a requirement on a Zenith.

Two of the six stainless steel Clamps that we send out with each Exhaust System. They hold the Exhaust on the engine in the same way a traditional distributor clamp works.

One of the first things people ask about the systems is if they would make more power if they looked like aftermarket headers for cars. The magic answer is no. I tell them that you don’t have to take my word for it, you can just ask our Dynomometer. Before we came to the design we use, we tested lots of prototypes and systems. The technical reason why these compact systems do not restrict performance has to do with the camshaft pattern and the rpm range we use. The OT-10 cam has very little overlap, which is one of the reasons why it makes good torque. Engines like this, especially ones with 3,500 rpm power peaks, don’t see the same benefit from a full tubular exhaust system that a 7,000 rpm V-8 car with a high duration cam does. There are three basic goals served by making the most compact stainless system: First, it is lighter than something elaborate. Second, it is structurally stiffer, and therefore it is not prone to vibration damage (our Exhausts are cantilever off the bottom of the engine, they do not require tail pipe brackets nor secondary mounts). And last, it has a lot less surface area to radiate heat into the engine compartment.  This last one is a bigger point than many people suspect. If you operate your aircraft in a very hot climate, this makes a difference on whether it is susceptible to vapor lock.  I saw an experimental that had terrible trouble with vapor lock, yet when the builder looked in the engine compartment he missed the concept that his flat black mild steel tubular exhaust pipes were radiating the vast majority of the heat that was bothering his carb and gascolator. A poor exhaust system choice can easily put as much heat into the engine compartment as the engine itself. You are far better off having this heat run out the exhaust pipe. Stainless is a poor conductor of heat, and it does not radiate heat well. Combine this with a compact design, and you have the making of a cooler engine compartment.

We send every Exhaust System with a pair of Heat Muff Box Ends. They make constructing the carb heat muff a piece of cake.

The second most common question is about how loud the system is without mufflers. You can watch a number of videos, but they don’t give you a good feeling about the level of the sound. In person, most people are very impressed with the sound of the engine; throaty, but it doesn’t have a harsh bark.  Some of the video shorts near hangars sound harsh because any aircraft turning a prop makes metal hangars resonate like steel drums, and microphones are very good at exaggerating this frequency. Out in the open, the engine is not loud. A subjective comparison; a Cessna C-172 in the pattern of your airport is a lot louder than a Corvair powered plane.  It is also an effect of the engine’s cam timing; the low overlap means the cylinder is done burning by the time the exhaust valve opens. This short duration also has a secondary effect: Only one of the exhaust valves in each head are open at the same time. Each side of the exhaust system only has to serve one cylinder at a time, contributing to low back pressure. If you would like to use a muffler, you will end up with an exceptionally quiet aircraft. We flew our Pietenpol with a muffler for many years, and many people thought it was one of the quietest aircraft they had heard. Although many people think of quiet engines as being down on power, this is only true on engines that have a long duration camshaft design. Taking the muffler on or off our Piet only reduced the static rpm by 20-30 rpm.

On the subject of custom exhausts, I have produced a number of one-off designs for builders. Most of these were for engines equipped with 140 hp heads (they have a different size exhaust stack), or for a one-of-a kind airframe. If you find yourself heading in this direction, give me a call, and we will talk it over. It is also worth mentioning that we can install oxygen sensor bushings in the exhausts for builders who want to use an air/fuel meter. This is a concept with some appeal, but 90% of our builders still opt to use EGT probes, which are placed into the exhaust system after it is installed by drilling a small hole in the tubing.

Need Help Contacting the Builder of this Aircraft ASAP.

Builders,

I was forwarded the image of the modified Pietenpol pictured below.  It is Corvair powered, and I have been told it was signed off by the FAA, but I don’t have a record of working with him.

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UPDATE: The builder of the plane has sent a request saying that he wanted the image removed from this story and from our FB ‘Corvair College’ page. He prefers to not discuss his plane in public. I offered to help, meant it. I’m leaving the rest here because first time builders need to understand having a 100 people tell you on FB your plane looks nice isn’t an endorsement of the details.  

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Above is the Plane in Question. I do not consider it airworthy, even though the FAA signed it off.  The first thing Piet builders will spot it the tiny weak diagonal cabanes, as I discuss here: Pietenpol Fuel lines and Cabanes and here: Fuel lines and Cabanes, part 2. But that isn’t the main point, it is the Vee shaped lift struts on a parasol with near vertical cabanes and a center section. It is not structurally sound.

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In 1989, a guy in my EAA chapter, #288, named Bob Spenk, built a steel tube Grega with a nearly identical lift strut arrangement. To my then-uneducated eye, it looked fine. The Embry-Riddle department chair of engineering was also a #288 member, and he sat down and explained that the new strut arrangement had almost no ability  to resist the wing rotating in relation to the fuselage, and any differential load, such as deflected ailerons, would impart this.  He explained that in a cabin airplane with the same lift struts, the upper longerons contacting the rear spar and the diagonals in the fuselage resist the twisting, and he showed us that one of the largest tubes in a J-3 fuselage does this.  He went on to show that a heath model V parasol has no center section, but it still requires diagonal brace wires from the rear spar lift strut attachment to the motor mount.  He pointed out that a it was superseded by the Heath N, and follow on airplanes like the Baby Ace, with parallel lift struts are required to have the diagonal brace wires between the lift struts, even though they have no center section.  Aircraft structures is a very complicated business, and it doesn’t care if all the local hangar fliers say “I will be alright” and it doesn’t care if all the people on the internet say “Its just a low and slow plane’.  neither of those statements will make the plane right. it doesn’t work that way.

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“Hey, William Wynne, you are a jerk, mind your own business, the guy is probably very nice and you are only pissing on his parade. He probably isn’t even a customer of yours. This is why many people think you are an ass.”

 …….In 2016, a lawsuit for $350,000 was tried against me. It came from a person who had a Corvair in their plane, but never bought a single thing from me. If you thought that couldn’t be done, I understand, I didn’t previously believe it was possible either, but yes, it can get to federal court.

  ……..If you work in aviation, or even spend time here, you will have to decide at what level you are Your brothers keeper?  I have long ago decided that I’m fine with many people thinking I’m a jerk for pointing out something like the plane above, but I am unwilling to go to bed at night and try to sleep with a pillow made of justifications and rationalizations.

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If you want to read the story of the exact day I learned this, 25 years ago, look here: Effective Risk Management – 2,903 words

“This was the first time I can clearly say I understood the cost of keeping your mouth shut. This was the first step to me becoming the kind of “Bastard” who publicly points out people doing dangerous things.”

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wewjr.

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The Sheradin Special, a Corvair Powered parasol.

Builders,

Below is a look at the “Sheradin Special” a Parasol being built by Dan and Tracy Sheradin. While the plane is inspired by the Pietenpol, it shares very few part in common. Dan has taken the time to design and build a unique plane to suit his taste. He has two years of part time work into the plane. They are visiting my place in Florida, and we took the photos below in front of my hangar yesterday.

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Above, a rear quarter look at the fuselage. While it may look very much like this plane: Steel tube Pietenpol fuselage with landing gear and 12 x 4.8″ tires., Terry Hand’s Pietenpol, in person the fuselages are different. Dan’s is a foot longer, and has  a lot more room in the cockpit.  The gear and tires on both planes are similar, but Dan’s has disc brakes and Terry’s has drums.

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Above, a frontal look at the plane. Dan made the gear following this story I wrote: New die spring landing gear on a Pietenpol, 10 a.m.-4 p.m.. The carb shown is a Stromberg we tested two months ago: Stromberg Shootout, Pt #2.

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Above, the plane has a generous passenger door. The pilot is about 4″ further back than a long fuselage Piet.  Dan was able to build with confidence because using this information: Pietenpol CG and gear welding, he could calculate the location of the wing, gear , motor mount and seating and have the CG turn out correctly, rather than  just guessing.

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We didn’t have the wing present, but it uses a Riblett 13.5% airfoil and aluminum spars. The plane has very little wood in it.

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The tail spring is a stainless rod and an ACS swiveling unit. This adds significantly to good ground handing by extending the wheelbase, getting the tailwheel horn geometry in correct orientation with the rudder horn, and having quality operation. You can admire thrifty Piet guys who are rebuilding shopping cart wheels for tailwheels, but you would really prefer the operation of a normal tailwheel.

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Ahead of the firewall, Dan’s installation is identical to our Pietenpol parts. The mount is on of our off the shelf units. His engine is a 2,700 with all our gold parts which ran at Corvair College #39 at Barnwell SC. Dan and Tracy attended four of the Corvair Colleges there.  For a look at some of the parts common to Corvair/Piets, look here: Pietenpol Products, Motor mounts, Gear and Instalation Components.

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Above, the tailwheel from a different angle. It is mounted in an .058 x 1.0″  tube. Many Piet builders switching from the plans tailwheel to a more traditional leaf spring or a rod type forget that the fuselage needs a reinforcement to the front of the spring, because it will be in tension when the spring is deflecting. On Dan’s plane this task is being accomplished by the two small 1/2″ tubes. For a look at a lot more Pietenpol and Parasol information look here: Corvair – Pietenpol Reference page

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Above, a nice overall view of the fuselage. The plane is tall, the center of the prop hub is 63″ off the ground. It will be a very impressive plane on the flight line.

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Hats off to Dan and Tracy Sheradin, to very fine people, traditional homebuilders, people we are very glad to have in the world of Corvairs.

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ww.

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Thoughts on gas tanks and a point.

Builders,

One of the most enduringly popular stories I have written is this one from 2012: Steel tube fuselages, “Safe” planes and 250mph accidents. The surface subject is a discussion of fuselage materials, but the bigger point behind it is getting builders to think about developing their own personal risk management assessments.

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Another one, focused more on todays topic was this one from 2016: Dated Sources of Information: Example – Fiberglass fuel tanks. Again, it has a deeper point, that what is popularly deemed “acceptable risk” changes over time, and todays builders should not blindly accept yesterday’s standards, particularly because some critical elements of building environment have changed.

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Today’s story is a bit more specific look at some example gas tanks, but it also has a bigger point drawn from it.

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Would you fly in a plane which had a plastic fuel tank in the fuselage with walls just the thickness of a spark plug gap? How about if that plane had no firewall between the motor and the gas tank? What if it had open vents also? What if I also told you these vents would pour gas on the engine if the plane was put on its back? Think I’m making this combination up? Guess again, this is the actual fuel tank from a Kolb mark III pusher aircraft, and it sat right behind the occupants, directly below the engine. This particular one was signed off by an FAA inspector, and flown for early 20 years. The fact it never burned the plane down is one of those things that leads me to repeat my personal mantra; “god has a sense of humor which I am yet to understand.”

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OK, some plastic tanks are very good. In the center of the picture above is the plastic tank from my 15′ Boston Whaler. It is indestructible. It was made by Jazz, a fuel cell manufacturer, and it came from Summit Racing. It was less than $200. In the field of experimental aircraft, the best known tank of this style is the custom made one that goes in a Sonex aircraft. These are excellent, and they have nothing to do with the glorified milk jug from the Kolb.

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On the other end of the picture, is the milk jugs replacement, an aluminum gas tank folded up, which I’m TiG welding up for my friend Alex to put back in the Kolb. There are two of them in the plane, they will be slightly over 5 gallons each. I am making them in such a way where they can be heavily distorted in an accident without bursting a seam. This is done with several subtle details, like having generous radiuses, having no butt welds, and having the ends be inserts with outward facing flanges. Of course the vents will be properly located, the plane will now actually have a sump to drain the tanks and check for water on pre-flights. Alex is a good guy. Friends with TiG welders don’t let other friends fly with milk jugs for fuel tanks.

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The Bigger Point: Every year, many people quit their project, because they hit a serious stumbling block they don’t like on the design. In about 90% of the cases, particularly with first time builders, they have picked the wrong system or detail to get bent out of shape about. They just need to talk to some other experienced builders and learn why a particular part is done the way it is. However, there are cases of things which builders may have a legitimate discomfort with. In that case, instead of fretting over it for months and letting it sap motivation, the solution is to enlist some help from AVIATION PEOPLE, NOT “RACE CAR” PEOPLE, and come up with a good workable solution, like I did with the tanks above, and get on with making it, and get back to finishing the plane. Don’t be one of the countless builders who allow a small issue to sap their motivation, let their project languish, and eventually never come back to it. Point: if you have an issue, go to the experienced builders with your specific plane, and only if you need to, align the detail design to better suit your own acceptable risk management standards.

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