Myths about propeller efficency

Builders,

On the Pietenpol discussion group, a well meaning guy reposted a story from the 1996 Pietenpol newsletter. The subject was on prop efficiency. It included the comment:

The Corvair engine is another compromise. They have a loss of efficiency due to the small diameter propeller and accelerate poorly (due to the tall gear effect) but produces good power. ” 

The guy who posted this probably didn’t know it, but I know that the comment is without merit, and no one who actually conducted a test, or understood propellers would make such a comment. Yet, here we are, 18 years later, in the information age, following the same myths that have been floating around for decades.

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The above comment has no educational value. Take it line by line: All engines, not just a Corvair are a compromise, period. Testing shows that a 100HP engine climbing at 60 mph with a 66″ prop may be close to 95% as efficient as one with a 72″ prop; Ask any tester you like, there is no such thing as an engine that produces good power but accelerates poorly. This only happens when it has a bad prop on it.

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OK, the whole point of having a dialog, reading thoughts or communicating about the building of planes is to learn something and use this knowledge to improve the plane you are building. The comment above serves none of these functions. It is only valuable to people who which to reinforce false realities they believe in. You can divide almost every story you read that allegedly shares information on airplane building into to camps: Valid testing that supports learning, and opinion or out of context stories that support myths. Only one of these will make your plane better.

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This division cleaves all discussion, any story can be put in one pile or the other.  What always gets me is this simple fact: Less than 20% of homebuilts are completed. I have been around Pietenpols a long time, and I would guess that their completion rate is far below 10%. What no industry magazine or salesman is going to tell you is that the completion rate, as a whole for our branch of aviation is actually dropping. Yes more planes get completed, but the sell many more these days. Given this fact, you would think that builders would all recognize that to personally beat the poor average, they have to make some smart choices, and a critical one is learn from valid tests, and don’t waste time listening to the same myths and old wives tales that lead 80% of previous builders to failure. But, for some reason, the myth mill still works every day, and people participate in it, directly sabotaging their own chances of learning and success

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It is somewhat frustrating to conduct a mountain of public tests, but they are cited less often than dubious sources from decades-old news letters. For people who wish to see real side by side thrust tests and dyno runs, get a look at this link to our testing page: Testing and Data Collection reference page. For Pietenpol builders who want to see that a 72″ prop doesn’t hold a candle to a 66″ one bolted to a powerful engine, look at: Pietenpol Power: 100 hp Corvair vs 65 hp Lycoming. If you would like to read about how most of the things said about “prop efficiency” are myths, get a look at this:The case of the Murphy Rebel, “eyeball vs. testing” I would hope that the next time the myth machine goes to work, someone will share a link to these pages, or even this story.

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Here is a simple example of testing and common sense from the last story link:

“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.”

Some pretty basic logic. I only ask people to believe what I can show them with tests and common sense like the point above. To counter this, the myth makers only have old newsletters and stories like “I heard a guy tried that once but it didn’t work.” Occasionally there will be input from a guy who touts a long dusty engineering degree as some credential as credibility for his favorite myth. If that is more valid than a specific test done in public, then I have a Unicorn to sell you.

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If you would like a simple example to destroy the myth that low speed aircraft have to have large slow turning props to have performance, let us take a look at some work from a man who only valued one thing in planes: Performance. This man was the greatest air racer who ever lived, and almost all of his work was done on planes that could be well powered by a Corvair. The Mans name was Steve Wittman.

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Let’s look at the plane below and the prop on it. It is Wittman’s “Big X”. It is a 4 seater powered by a 150HP Franklin. It was noted for having a very wide speed envelope.  Did Wittman use a big slow turning prop said to be efficient? No, he used a high rpm, smaller scimitar prop. This plane climbed at 70 mph, it had to have good low speed thrust, and it did. How long have people known that the only thing slow props have going for them is sound suppression? Well the photo here is from 1947.

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Below, the Buttercup. The photo is from the EAA museum where the plane was retired to after flying for 60 years. It is reported to have 3,000 hours on it. The prop is not the correct one, it is just for display. This plane will fly and climb at speeds well below the stall speed of a Pietenpol. it will also do 145 mph on the top end. How does it cover such a wide envelope with a C-85? Simple, it has a smaller diameter prop that it spins faster. For people who claim that high rpm props don’t make thrust, please explain what was making the thrust that drove the plane forward at 145 mph when the engine was turning 3,400 rpm. Again the ideas are not new, the buttercup was built in 1937.

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How about a slightly faster example? Below is a youtube link to Steve flying his Tailwind N-37SW, powered by a direct drive inverted Olds 215 V-8, bored and stroked to 262 cid. It has a 62″ diameter prop on it. It was cut down from a Cessna 150 aluminum prop. It climbed very strong and topped out at 3,600 rpm and 195 mph with out wheel pants. How do I know this? Because I flew in the airplane with him for a very vigorous flight in 1993. Notice that people who present myths always have a mysterious “guy who tried it”. I am essentially doing the same thing here, with the exception that I was there, my “guy” actually existed and was one of the greatest builders and pilots of all time, and, conversely, it worked for him. Other than those details, my story is just the same as any other internet myth.

http://www.youtube.com/watch?v=WsH-j4pF4fE

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Something I wrote about real aviators at the core of flight:

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“If you look at their lives close enough, all of the greats offer something to guide us in pursuit of the timeless truth of flying. Pietenpol teaches that we are more likely to find it in the simplest of planes; Lindbergh knew that you started your search inside yourself; Gann said that we will not see the truth directly, but you can watch it at work in the actions of airmen; and Wittman showed that if you flew fast enough, for long enough, you just might catch it. These men, and many others, spent the better part of their lives looking for this very illusive ghost. Some of them paid a high price, but you get the impression they all thought it was worth it.

While it is possible that someone who rents a 172 or even a person who reads Fate is the Hunter has some access, I honestly think that the homebuilder who dreams, plans, builds and eventually flys his own plane is infinitely more likely to experience the timeless truth of man’s quest for flight. All of the aviators who had some insight to guide you found it while they were in action, in the arena. If you inherently feel that you want to build a plane, you feel just like Pietenpol did. When you’re building it, you will find out how determined you are and what kind of perseverance you have. Lindbergh evaluated these qualities in himself every day. As you finish and prepare to fly, you will find others of enormous qualities and flaws, and you will learn to sort them and their counsel, as Gann always did. And when you fly your plane, and come to trust it because it is your creation, and you cut no corners, you will never want to stop, the way Wittman never did.” -ww-(2008)

Parts List, Pt. #3, 2,700 cc, basic engine

Builders:

Below is a look at the Conversion parts cost for a 2,700 engine with a standard oil cooling system based on a stock 12 plate cooler.  Below on the chart I have highlighted in blue the parts used.  This engine layout has been used on countless Corvair powered planes.  Although we have a lot of stories about 2,850 and 3,000 cc engines, there are still more 2,700 cc engine built than the other two displacements combined.  Some people call the 2,700 the ‘small’ Corvair, but describing it that way is misleading. It still has 25% more displacement than the largest commonly available type one VW the 2180cc.

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Above, Becky Shipman’s 2,700 cc engine on my test stand getting ready for its break in run. The engine is equipped with a Weseman bearing  and our Gold Conversion parts. This engine is intentionally built on the light combination of 1964 heads and 1960 full fin cylinders bored out to 3.437.” It is about 8 pounds lighter than a standard Corvair. Read the story at this link: Shipman Engine at CC#22.

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If a 25% difference doesn’t sound like a lot, let me share a story. Years ago, when new Corvair powered planes were just beginning to show up in numbers, KR-2S builder Mark Jones brought his to a KR gathering were they had a timed performance run. Most of the planes entered had a VW engine. Common talk at the time said that the Corvair’s 45 extra pounds of weight made it a ‘boat anchor.’ Some of the same people said Mark’s airplane wasn’t slick because he had a taller wider cabin and tri gear. They didn’t say it to his face because he is a very burly guy. Expectation was almost all of the VW planes would beat Mark over the long course.

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It didn’t work out that way. When the dust settled, Mark had a higher average speed than the VW powered planes there. There was some major ego correction in process. Two of the VW planes had listed “175 mph” as their cruise speed on their prop card. In the race they had logged 15 mph under this going flat out, losing handily to Mark’s ‘boat anchor.’  Because I am a smart ass at times, I offered to loan one of these guys a Sharpie pen so he could ‘correct’ his prop card.  He tried to save face by saying that his cruise speed was higher at altitude. That might have worked in another setting, but I know enough about aerodynamics and performance to explain to the people present that all naturally aspirated aircraft have their highest speed at sea level. Mark was gracious about his performance that afternoon, but later in a smaller group he said it felt pretty damn good to clean up in the air after reading a lot of talk on the internet.

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Other simple examples: There have been almost 100 Pietenpols built with a Corvair engine over the years. I have seen more than 45 of these in person. Overall I have personally seen maybe 250 different Piets of all types in the last 25 years. They had all kinds of power plants, but not a single one of them had a VW installation. This isn’t just a weight and balance issue, it is confirmation of the 2,700 cc power output. As I sit here and type this, I am pretty sure that every single Corvair powered Pietenpol flying is using a 2,700 cc displacement.

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For a single example of a power and performance difference between traditional 65hp engines and a 2,700 cc Corvair get a look at this link: Pietenpol Power: 100 hp Corvair vs 65 hp Lycoming it also had a good explanation of how a 50% increase in power can yield three times the rate of climb.

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Part description         Part Number              Pricing          Notes

Drive end

Hybrid Studs                2502                              $79

Safety Shaft                    2503                              $79

Short Gold Hub            2501(B)                       $579 

Front Starter kit          2400                             $566  

Ft Alter. Brackets         2901                              $99

Oil Systems

Gold Oil Filter housing   2601(S)                  $239 

Gold Sandwich                 2802                        $169

Hi-volume Oil case          2000HV                   $289

Billet Oil Pan                      2201(B)                    $289

Deep oil pick up kit         2202(A)                     $59

Ignition

E/P Distributor                  3301E/P                   $349 

External items

Valve Covers                       1900PC                    $149

Pushrod tubes                    1602PC                     $60

Piston, Rod, Cyl. Kits

2,850 cc Kit                           2850CC                 $1,800

3,000  cc kit                          3000CC                 $2,200

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The stock 12 plate oil system uses the parts listed. It is based on the ‘Group 2700′ in our numbering system. Many aircraft are flying on this arrangement. Our design is modular, and if a builder later wants to go to a HD ‘Group 2800′ Oil System as an upgrade, he can do so economically without a lot of back tracking. For more info look at this link: Heavy Duty Gold Oil Systems, new cooler model.

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The Welded oil pans are slightly lighter and $40 less expensive, but the Gold Billet Pans are more popular.

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Our standard ignition is the E/P  distributor. We will still make D/P distributors on request, but I would prefer than have people use the modern ones.  Almost all builders use our Valve Covers. They look good, but they have important mechanical features like being able to see TDC on the engine by removing the oil cap and looking at the #1 rocker arm instead of pulling a plug out. Zenith installations must also have the oil fill in the valve cover.( the stock filler neck hits the cowling.)

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Price totals:

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If you add up all the parts above, you are looking at $2,547.   Keep in mind that most builders buy the components slowly over time, but I have the total here because we have had a number of requests for a total price from people who wish to buy the parts at one time.

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Obviously this isn’t the total price for a 100 HP /2,700 cc engine. This number does reflect the Conversion parts cost, and a big part of the internal engine parts. The list above is the part of the budget that builders spend with us on their project. As I have pointed out many times, we try not to resell anything we can simply direct builders to acquire for themselves, such as the Weseman parts and Falcon heads.

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There are a lot of different options on building the rest of the engine, and if you would like to look at them, read this link,Getting Started Reference page. Specifically look at the links to parts #5 through #9 at the bottom, it gives every specific examples of the cost of different levels of bottom ends on the Corvair. -ww.

Parts List, Pt #2, Example: Zenith 750

Builders:

OK, lets look at an example. I am just calling this a 750, but in reality it is also a potential Panther, Waiex or Cleanex engine also. What I am getting at; this is a big bore engine (3,000 cc) with a Heavy Duty Group 2800 oil system. The Conversion parts going into the engine are highlighted in blue in the chart below.

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Above, Greg Crouchley and I stand with his 3,000 cc engine in my hangar, after it’s break in run. Note the reverse oil filter housing. We do not install the HD oil system for the test run because we want to have the oil temp come up early. The engine is now in Greg’s Waiex.

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We have written stories about engines like this. For 750s look at: 3,000cc Engine Running for a Panther look at:Panther Prototype Engine 3,000 cc/120 hp to OSH and for a Waiex look at:World’s Strongest 3,000cc Corvair, built by Greg Crouchley. Between the there engines above, the only difference in the Conversion parts sets is that the Waiex uses a 2601(R) Reverse Gold oil filter housing instead of a standard one.

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Note that the Conversion parts set doesn’t change with either a GM or a Weseman Billet Crank, or even if the engine has a Gen 1 or a Gen 2 bearing. Listed below are the conversion parts that a common to all 3,000 cc engine with Heavy Duty oil cooling systems. Each engine still has some custom choices in the rebuild parts that each builder can make. Below the part number we have some discussion and a look at budget totals. In part #3 of this series we will look at a 2,700 engine with a standard oil system.

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Part description         Part Number              Pricing          Notes

Drive end

Hybrid Studs                2502                              $79

Safety Shaft                    2503                              $79

Short Gold Hub            2501(B)                       $579 

Front Starter kit          2400                             $566  

Ft Alter. Brackets         2901                              $99

Oil Systems

Gold Oil Filter housing   2601(S)                  $239 

Gold Sandwich                 2802                        $169 

Hi-volume Oil case          2000HV                   $289 

Billet Oil Pan                      2201(B)                    $289 

Deep oil pick up kit         2202(A)                     $59

Ignition

E/P Distributor                  3301E/P                   $349 

External items

Valve Covers                       1900PC                    $149

Pushrod tubes                    1602PC                     $60

Piston, Rod, Cyl. Kits

2,850 cc Kit                           2850CC                 $1,800   

3,000  cc kit                          3000CC                 $2,200 

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In the front end category, I left out the 2901 front alternator brackets because many of these engines going in 750s and all of the ones going in Panthers use the Weseman’s rear alternator bracket, which is Group number 2950 in my numbering system ( but you get these direct from Dan and Rachel).

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In the oil systems, The Heavy Duty system uses all the parts listed. Additionally many people use a block off plate part number 2805 it is $20. The Welded pans are slightly lighter and $40 less expensive, but on 3,000 cc Corvairs the Gold Billet Pans out sell them 5 to 1.

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Every Flying 3,000 cc Corvair I can think of has an E/P style distributor. Only a few of them, like the Panther prototype are E/P-X models, a $40 upgrade. Almost all builders use our Valve Covers. They look good, but they have important mechanical features like being able to see TDC on the engine by removing the oil cap and looking at the #1 rocker arm instead of pulling a plug out. Zenith installations must also have the oil fill in the valve cover.( the stock filler neck hits the cowling.)

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The price of the 3,000 cc Kit includes the machine work to the case and heads to fit the larger cylinders. The 3,000 cc pistons are specifically designed and made for Corvair flight engines. They work with both 100LL and auto fuel.

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Price totals:

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If you add up all the parts above, except for the 3,000 cc kit, you are looking at $2,906. If you add the 3,000 cc kit, you are up to $5,106. Make the distributor an X model, add the block off plate and the total is $5,166. Keep in mind that most builders buy the components slowly over time, but I have the total here because we have lately had a number of requests for a total price from people who wish to buy the parts at one time.

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Obviously this isn’t the total price for a 120 HP /3,000 cc engine. This number does reflect the Conversion parts cost, and a big part of the internal engine parts. The list above is the part of the budget that builders spend with us on their project. As I have pointed out many times, we try not to resell anything we can simply direct builders to acquire for themselves, such as the Weseman parts and Falcon heads.

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There are a lot of different options on building the rest of the engine, and if you would like to look at them, read this link,Getting Started Reference page. Specifically look at the links to parts #5 through #9 at the bottom, it gives every specific examples of the cost of different levels of bottom ends on the Corvair. -ww.

Engine conversion parts list, Part #1

Builders,

Below is a table listing the most common parts we offer. They are easier to see at a glance in this format compared to studying our catalog in depth. In part two of this series, I will give several typical examples based on popular airframes.

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If you would like to get a very detail look at how each of these parts fits in our numbering system, click on this link: http://www.flycorvair.com/products.html.

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Note: The first two digits of the part numbers are the group number in which the full description of the part can be found. ie, Hybrid studs, 2502 are in The Hub Group (2500).

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At the very bottom are  numbered notes that address the right hand column.

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Part description         Part Number              Pricing          Notes

Drive end

Hybrid Studs                2502                              $79

Safety Shaft                    2503                              $79

Short Gold Hub            2501(B)                       $579               (1)

Front Starter kit          2400                             $566              (2)

Ft Alter. Brackets         2901                              $99

Oil Systems

Gold Oil Filter housing   2601(S)                  $239               (3)

Gold Sandwich                 2802                        $169              (4)

Hi-volume Oil case          2000HV                   $289            (5)

Billet Oil Pan                      2201(B)                    $289            (6)

Deep oil pick up kit         2202(A)                     $59

Ignition

E/P Distributor                  3301E/P                   $349            (7)

External items

Valve Covers                       1900PC                    $149              (8)

Pushrod tubes                    1602PC                     $60               (9)

Piston, Rod, Cyl. Kits

2,850 cc Kit                           2850CC                 $1,800          (10)

3,000  cc kit                          3000CC                 $2,200          (11)

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(1) This is the hub used with a 5th bearing. 2501(A) is for no 5th bearing

(2) Front starter kit includes the 2401 starter, the 2402 brackets, the 2403 tail bracket, 2405 top cover, 2406 gasket and the 2407  hardware. We are glad to sell it as a kit or by the part, the kit is slightly less expensive.

(3) this is the standard part. For a reverse model (Sonex-Waiex) the part number is 2601(R). The part can be seen at: http://www.flycorvair.com/goldoilsystem.html

(4) This is for HD oil cooling systems. See the above link for more info.

(5) This part number is for the remanufactured rear case with our CNC high volume pump already installed. Includes at parts in the 2000 group. Read more at this link: High Volume Oil Pump

(6) This is the Gold machined part. The welded pan is 2201(W) for $249. It uses the same 2202 pick up kit.

(7) For more info, and the E/P-X option read this link:                                      E/P and E/P-X Ignition systems, (3301E/P and E/P-X)

(8) These are modified with the filler and breather ports, they come in several colors. Read more here: E-mail
Now: Custom Valve Covers Available Through Monday

(9) These are stock GM steel tubes that have been cleaned and powder coated white.

(10) This kit has Remanufactured rods with ARP bolts, Forged dual fuel pistons and new Clark’s full fin cylinders. A look at the parts can be seen here: Complete Engines for Sale

(11) This kit has Remanufactured rods with ARP bolts, Forged dual fuel pistons and new Custom machined, full fin cylinders. Price includes machine work to case and heads. A look at the parts can be seen here: Complete Engines for Sale

E/P and E/P-X Ignition systems, (3301E/P and E/P-X)

Builders:

Below is the story on our standard and optional ignition systems. The E/P stands for “Electronic /Points” , as it utilizes both. The E/P-X model is internally identical, it just has a few external features to make a slightly nicer installation. We have been producing E/P distributors since 2006. In our numbering system Group 3300 is the engine ignition group. the specific part numbers are 3310 E/P and 3301 E/P-X.

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Above is a photo on an E/P-X distributor. The features that make it an -X model are the Weatherpack quick disconnect plug system, the studs holding the cap on (instead of screws) and the fiberglass jacket on the wires. Other than these items, both E/P models are identical.

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We looked for a long time before finding the Crane module that is the heart of the E/P ignition. There are many electronic ignitions on the market, but for flight use they have two critical Achilles’s heels: They use many amps of power and they do not work at reduced voltage. The made in the USA crane unit has neither of these issues.

 There’s  a lot of great automotive electronic systems that work fantastically as long as there’s more than 11.5 volts available and  a steady flow of 10 amps to power it. In the world of flying, where you could have an alternator or voltage regulator failure,  and be reduced to the amount of electrical power stored in your battery, these electronic systems are not acceptable. Electronic ignitions with computers on other alternative engines have demonstrated as  little as 20 minutes flight time after a charging system failure. Many alternative engines that are converted modern car engines have this defect. Most of the people who fly them have never run them at cruise power with the charging system disconnected to know just how short their window is.

A Corvair  engine running one of my ignition systems will run for hours on the battery that started it. The points system will work all  the way down to the 9 volt range. My Electronic/Points  system utilizing the Crane module is a very low power consumer and additionally has the unheard of quality of producing stable  sparks well below 9 volts. No other electronic ignition that we tested demonstrated this. The power wire to the crane unit is a tiny 22 gauge wire. When testing distributors on the machine you can run the Crane unit for an hour and it is still cool to the touch.

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In the above photo, an E/P ignition running on our machine. This uses the same coils and systems as our Dual Points  Distributor with the exception of eliminating the condenser on the electronic ignition’s coil. The photo is from 2006. We have since produced more than 200 E/P units and retrofitted more than 100 D/P distributors with E/P plates.

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 Success can sometimes come from pioneering work, but it always comes from emulating what has proven to work. Virtually every flying Corvair powered airplane built in the past 15 years has one of my ignitions on it.  No aircraft has ever had any type  of a forced or precautionary landing made on our ignition system. It works. Period. The only issue builders have has are reversing the red and yellow wires while installing it (this instantly burns out the Crane unit at a cost of $75; bad, but not like burning out a $1,600 Rotax 912 ignition) and we have had 3 people pinch a wire carelessly putting a distributor cap back on. This said, no one has had one of these units fail while flying, and they have been airborne for thousands of hours.

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Above is a wiring diagram that shows the basic layout of my ignition system. This page is taken from our 601 Installation  Manual, so it includes some of the wiring associated with fuel pumps. This drawing shows the D/P wiring, but the E/P only has two minor differences. The key elements of the design are redundancy, low  power consumption and low voltage tolerance.

With our system, notice that you can fail one of the coils or one set of points and still have 100% power available through  the backup system. Once every few months, a builder will propose a system that has three pickups and a wasted spark system using  three coils and two plug leads from each coil. I know these systems well, and they’re not safe to use in Corvair engines  because with three coils and three pickups, you’re statistically more likely to have a failure and when you do, you’ll be  immediately down to 66% power. However, the dyno shows that dragging two dead cylinders means you’re really down to 50% power  and most Corvair powered airplanes will not climb on half power.

Our EFI page contains a photo of Mark at Falcon’s EFI engine. Note that it actually has  six LS1 coils which have built in modules. This is acceptable because a single coil failure will bring you down to 83%  theoretical power; about 75% power on the dyno dragging one dead cylinder. This illustrates the point of why it’s acceptable to  have single plug ignition on a six cylinder engine. The performance loss of one cylinder on a six is not catastrophic like losing  one cylinder on a four cylinder engine. Corvair powered airplanes have taken off and flown on five cylinders on three occasions  that I know of without incident. This was due to a missing plug, blown head gasket and missing rocker stud, respectively. You would not get away with this on a four cylinder engine.

The shot of the workbench above shows 85 Distributor bodies neatly stacked. Over the years, I’ve reworked  hundreds of  Distributors. I’ve had the opportunity to examine many of them after they’ve put in years of flight service. We’ve  continuously had running Corvair vehicles to test all types of ignitions in the ground environment. Many of the theories I was  taught and believed 25 years ago proved inaccurate or inapplicable to our situation. All that counts in the aircraft arena is what you have proven. Theory is fine for ground debate, but people going flying need proven systems.

D/P Ignition Systems, (P/N-3301D/P)

Builders:

Here are some notes about our oldest ignition system, the Dual Points distributor. I made the first of these models nearly 20 years ago. We went on to produce several hundred of them. In the last seven years there have been superseded by our E/P and E/P-X distributors, which themselves are evolutions on this basic design.

Dual Points distributors served the Corvair flight community very well. Many thousands of hours have been flown on these ignitions, and there has never been a single forced landing nor accident attributable to the design. (we have had people fail one side because of pinching a wire putting the cap on, but they flew on the other side) The design uses two sets of points from a Corvair mounted 180 degrees apart. either one can run the whole engine smoothly.

We mount the condensers remotely on the coils. When I introduced this, there was a giant debate on the internet claiming the condensers being on the end of 20 inches of wire would case some sort of ‘delay’ in the ignition, even though I pointed out that electrons travel down wires pretty much at the speed of light, and 20 inches vs 186,000 miles per second is a very short interval, the debate lasted years. Meanwhile, many happy people went out and flew countless enjoyable hours without noticing.

In the 1960s, companies like Mallory made dual point distributors for racing Corvairs, but these had three lobes not six, the goal being much shallower ramps on the point cam that would allow 7,500 rpm operation. such a distributor can not provide redundant ignition.

Today, we sell only a handful of D/P distributors a year. They are a special order item, but the remain popular with some very old school builders and some builders Down Under. They work well, but I highly encourage all builders to use E/P series distributors instead, they run smoother and have comparatively little maintenance. (D/P points need cleaning or replacing every now and then, but on the E/P the points are a back up and pass no current normally and may go 1,000 hrs. of operation without adjustment.) All the engines we build and sell are equipped with E/P series ignitions. Read all the articles and decide which system you like, they are all well flight proven.-ww.

In the above 2006 photo, a Dual Points distributor P/N 3301(D/P). The screwdriver points to one of the two 8/32″ screws that hold down the Points Plate. Two things I tell builders relentlessly, but are sometimes not heeded: 1) Never adjust the points to make the gap .019″, the gap on all distributors come from us pre set to a specific dwell, not a gap, and if you let anyone talk you into jamming an old feeler gage in the points, you will upset the pre adjusted timing. I have had 40 or 50 people do this and then rationalize it by saying “the gap looked small.” If people want to do this, I will fix it, but it does tell me who reads directions and who wants to argue rather than learn and understand. 2) Never take the two plate screws loose for a look inside, it will have the same effect as doing #1. Builders can replace points on these in the field, but it is done by matching the existing preset gap on the original points, not by using some book value.

The above photo shows a Dual Point Distributor in the machine. If you look closely at the 11:00 o’clock position you can see the illuminated arrow pointing at the degree wheel. the distributor machine was made in 1950. The items piggybacked on the top row  allow the simultaneous operation of the electronic side of the Distributor while superimposing the EI picture on the scope. Every single distributor we ever send out the door is test run in this machine.

When running a Distributor on the machine, I can vary the rpm it’s turning and observe its advance directly. When your  Corvair engine is idling, the advance weights in the Distributor are held shut by springs. The advance at this point is referred  to as the static timing. I set the Distributors so they have little advance below 900 rpm. As the engine comes off idle, the  mechanical advance inside the Distributor’s body makes the spark occur earlier. This is the mechanical advance at work.  All the mechanical advance needs to be in by 2,400 rpm or so. This way, you can tie the tail of your airplane down, run it to  full power and check what the total advance is at the propeller’s full static rpm. Total advance for engines running on 93 octane  fuel should not exceed 30 degrees. For engines on 100 low lead, 32 is the limit. Beyond these numbers, the engine could be aggravated to detonate.

Each of our Distributors is marked on the underside with its mechanical advance and the beginning and ending rpm of its curve.  Thus, if you have an engine you’re going to run on 93 octane fuel, and your Distributor says “18-1,000-2,400,” use a timing light to  set the static timing to 14 degrees below 1,000 rpm. With the plane tied down, raise the rpm above 2,400 and verify  that the total advance does not exceed 30 degrees. A dire warning: Never touch the ignition wires while the plane is running  and turning a propeller. There is a remote possibility you’d get a high voltage shock and inadvertently flinch into the propeller.  It’s a very remote possibility, but a builder in Australia did it and was lucky to keep his fingers.

For a better understanding of ignition timing please click on this link:

Ignition Timimg on Corvairs.

We also have more information on this link:

Engine Operations reference page.

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The above photo shows four point cams. Occasionally people ask if they can recurve distributors at home. It would be a very  difficult process, and while you might achieve some results, a lot of the fine tuning we do to distributors is very difficult  to see. Off the end of the screwdriver is the part of the point cam that the counterweight touches. Notice the four different  profiles shown here. There are six different common Corvair profiles. The upper two are ground to match templates we’ve  developed to produce ignition curves that suit aircraft use. The upper two point cams appear shinier because they’re nickel plated. We later switched to chromed ones we use now on all models.

Above is a wiring diagram that shows the basic layout of my ignition system. This page is taken from our 601 Installation  Manual, so it includes some of the wiring associated with fuel pumps. The key elements of the design are redundancy, low  power consumption and low voltage tolerance. It’s also immune to voltage spikes and high temperatures.

With our system, notice that you can fail one of the coils or one set of points and still have 100% power available through  the backup system. Once every few months, a builder will propose a system that has three pickups and a wasted spark system using  three coils and two plug leads from each coil. I know these systems well, and they’re not safe to use in Corvair engines  because with three coils and three pickups, you’re statistically more likely to have a failure and when you do, you’ll be  immediately down to 66% power. However, the dyno shows that dragging two dead cylinders means you’re really down to 50% power  and some Corvair powered airplanes will not climb on half power.

The above 2001 photo shows the firewall mounted electrical box from our test mule at the time, The Skycoupe.  We put this together so all the electrical components and flow cool air over them. The Wagabond has something similar. This function is done on aircraft like Zeniths by having the coils and the MSD 8210 behind the firewall. The only difference in today’s  method is the use of Bosch Blue Coils, readily avaiable from Great Plains Aircraft. The Accel coils shown above must have external  ballast resistors, which are internal on the Bosch Blue Coils. The top shelf houses the MSD 8210 coil switch. There’s some  discussion about the use of the Mallory equivalent of this part. The system will work with either; it does not care. If you look at the wiring diagram above, you and identify most of the parts in the system.

Engine Operations reference page

Builders:

Here are links to a great number of stories on operations. Many companies have no such data on their website. Their goal may be just to simply sell engines, and that is easiest if the potential buyer is never brought into a mechanical discussion. On the other hand, we have data because we are in the business of teaching builders to be the master of their engine, and this involves some reading.

If your goals are those of the traditional home builder, to learn, build and fly, to be the master of your plane not just the guy that owns it, then read on. All of the stories below are written by myself, and reflect my 25 years of working with Corvairs. Contrast this experience with the fact that more than 50% of the engine sales people at Oshkosh have never put a wrench on the inside of an engine, not even the one they are selling.

In the 100-120HP range, just 3 engines have a 50+ year track record of flying: Lycoming O-235, Continental O-200 and the Corvair. I have worked with the Corvair since 1989, and slowly evolved it to the engine we have today.  Along the way, we learned a lot, both about the engine and the needs of builders. The stories below are a reflection of this knowledge that we stand ready to share with any builder who has set his goal on learning and mastery.

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 Above, a winter 2005 photo of our 601XL, N-1777W with hangar cat “Whobiscat” warming herself on the Cowl. We have been working with Corvairs a long time.  Gus Warren in the cockpit at the end of a long day of flying.

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Click on any color link to read the story:

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Shop perspective: Mastery or ?

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Operations:

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Thoughts on cold weather operation, minimum oil temps, etc.

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Starting procedures on Corvairs, 2,000 words of experience.

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Engine oils and oil systems:

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Notes on Corvair flight engine oils.

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Corvair Oil Change interval….. Lessons part #1

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Corvair Oil System, information on oil pressure gauges.

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High Volume Oil Pump

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Ignition and timing:

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 Aircraft wiring 101

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Ignition Timimg on Corvairs

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When to check your timing, Lessons learned Pt#2

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MGL vs Corvair ignition issue

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Cylinder Head Temperature:

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Cylinder Head Temperature measurement

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Corvair CHT, letters and notes.

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CHT part #3, Letters, notes, sources and inlets.

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CHT Part #4 more notes

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CHT part #5, flight data from Zenith 750

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Measuring Cylinder Head Temps on Corvairs.

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Cowling Inlet Area, marketing, accident stats, Darwin where are you?

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Spark Plugs:

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Spark Plug Installation

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A Tale of Two Spark Plugs……

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Spark Plug Issue resolved…..

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Cowlings:

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Cooling with J-3 style cowls. (Pietenpols, Cubs, Biplanes, etc)

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Corvair Cooling, Three 2007 examples from our hangar.

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Corvair Cooling, something of a human issue…..

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Corvair Cooling

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http://www.flycorvair.com/pietengineissue.html

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