William Wynne

"The Corvair Authority"
5000-18 HWY 17 #247
Orange Park, FL 32003 USA

The Corvair Powered Zenair 601XL

September 23, 2004: Fuel and Oil Systems


The above photo shows a view of the top of the engine installation in our 601. What is different in this photo is the location of the oil filter. Normally, a Corvair oil filter is on the back of the motor, behind the harmonic balancer. The oil filter housing is bolted onto the accesory case. This housing is also the mount for the mechanical fuel pump.

We have revised the fuel system to delete the mechanical pump. Our new fuel system has an electric primary and an electric backup mounted in series on the firewall. With the mechanical pump removed, the stock oil filter mount could be modified or replaced. Our choice was to change the location of the oil filter to gain more room at the back of the motor. We made a block-off plate to replace the stock oil filter housing, and relocated a new, smaller filter piggyback on the engine behind the starter. The oil travels to and from it in AN-6 lines. The filter housing also features good locations to sample oil temperature and pressure. After flight testing this arrangement, it will likely become the recommended method to dress out the motor, and part of our firewall forward package. When coming up with ideas like this, I am integrating a complex series of requirements like reliability, cost, and ease of installation and maintenance. I am considering the type of instruments our customers will want and integrating all these ideas into an installation which average amateur builders can successfully complete and operate. It's a complex equation, and challenging to solve. No successful installation can ignore these issues. We have a lot of installation experience which makes resolving these installation details a fun challenge instead of a daunting task.

Above, the oil filter sitting on the Top Cover, inside the baffling. Before anybody wonders about it, let me say that this filter is designed so that it will not leak oil when it's unscrewed. Without knowing this, you might assume that an oil change would be rather messy. The filter is a K&N 1004, readily available from most auto parts stores. It has an internal bypass, and has a nut with a safety wire hole just like an aircraft filter. When we change the oil, I'll just slip a plastic bag over the filter and unscrew it. The housing is made by Permacool, and its four 1/2" NPT holes can easily be fitted with AN fittings and instrumentation. In this position on top of the engine, the filter may gain some slight cooling effect from the air. The oil fittings shown are full sweep, XRP, AN-6 90 degree fittings. It is very important to use full sweep fittings instead of sharp 90 degree bends in the oil system. The sparkplug wires here are Moroso Blue Max Spiral Core Wires. They're as good as automotive wire gets, and they have a reputation for not causing radio noise. We still need to make a little grommet for the spot where the hoses pass through the aluminum baffle.

Here is a view from above and behind the engine. The two oil lines lead to the block-off plate, which is taking the place of the stock oil filter housing. This plate is held down by five 5/16" bolts. It has two AN-6 fittings threaded into it. It is made of 3/8" thick aluminum. To install this, the fuel pump guide must be removed from the accessory case. The underside of the block-off plate must have a groove machined into it if the oil cooler bypass in the accesory case is to function correctly. This end of the oil lines also features 90 degree full flow hose ends. The ones on this end are made by Earl's, and have their unique swiveling feature. This allows the fitting to be rotated on the end of the hose after assembly. This prevents the hose from twisting upon installation. These are only needed on one end of a hose which has two curved ends, like these. The extra room gained by this modification is apparent in the photo above. This is not a requirement to fit the engine into the 601, but I intend to later install a turbocharger which will rest above and behind the engine, and I'll need the space where the stock oil filter went.

Above is the right hand side of the oil filter and housing. The top outlet is plugged right now, but we will later take the oil pressure line from here. The bottom outlet has an electric oil temperature probe. This is an AutoMeter unit. We still have the extremely accurate AutoMeter mechanical installation on the plane at the oil cooler. Flying with both of them hooked up will allow us to compare the efficiency of the coolers, as well as calibrate the accuracy of the electric gauge. This is a good example of the value of our rigorous flight testing to hone the Corvair installation in the 601. Without this testing, our comments on the installation would merely be speculation. With the testing, our comments become valid recommendation.

Fuel System

Here are a few quick pictures of the electric/electric fuel system going together. In the photo above, the fuel comes out of the firewall, goes through the Andair GAS375-M gascolator, makes a 90 degree turn to vertical, goes through two Facet pumps in series, then through a fitting which contains the electric fuel pressure gauge sender, and then through an AN-6 line to the carburetor. The wiring shown is from the previous installation, which was heavily instrumented in our test phase. This installation is a lot cleaner and simpler, and involves no handmade parts. When the installation is done and flight tested, we'll share a part number by part number breakdown with all of our 601 builders.

Above is the same view from a little farther back. We've ensured that none of the components will interfere with the tricycle gear installation parts. Our MA3-SPA carburetor can be seen in this photo. On production intake manifolds for tricycle geared aircraft, the carburetor will be moved 1" down and 2" forward.

This view is from above looking down behind the right hand side of the engine. The pressure sending unit and fuel line to the carburetor are clearly visible. The fuel line uses a full flow, 150 degree end on the firewall side, and a straight end at the carburetor. When we get both these systems tested, we'll share the results with Corvair engine builders.

Thank you.

William Wynne

The Corvair Powered Zenair 601XL

September 15, 2004


This update on the 601 will be mostly of a technical nature. We'll show a lot more details of the installation, and discuss installation and operation of the Corvair.

Pictured above is Corvair/KR-2S builder Joe Horton of Pennsylvania, left, with our test pilot, Gus Warren. Joe visited our hangar between Hurricanes Charley and Frances. We were prepping for Frances by storing all the valuable stuff in the hangar (it's brand new construction and rated for 120mph winds). During the lull, Gus took Joe up for an orientation flight. Joe is the first customer of ours to be flown in the plane. Over the years, we've taken time to fly as many engine builders as possible in our aircraft because I think there's some serious technical merit to engine builders having a seat of the pants experience on how smooth the engine is in normal operation, and allowing them to gather a lot of sensory experience with a perfect running installation. All Corvair engine builders should know they're welcome at our hangar, and conditions permitting, we'll provide the same experience for you.

The aircraft now has 75 hours on it. During this time, we've had the aircraft configured to gather a lot of information and data. Additionally, we've tried a number of different systems and approaches to installation issues. Using this experience, and all of our cumulative years with flying Corvairs, we distilled our optimal firewall forward configuration. We're taking 10 days in the hangar to change the configuration of the engine installation to reflect this. In a nutshell, we're going to remove some of the test instrumentation, simplify and clean up some of the systems, and turn the installation into one that would be typical of a 601 package installed by one of our customers.

The changes primarily will be altering the fuel delivery system, changing to a front alternator, and revising the oil system. If you're already working on one of our 601 conversions, no need to panic; we're not altering anything to do with products we've already shipped. Mounts, cowls, starters, exhausts, pulleys, props and spinners are all unaffected by the changes we're making. With this configuration change in mind from the beginning, all of our products were aimed at allowing builders to have a clone of our final configuration, not our test phase installation. So, our aircraft now accurately reflects the type of installation we have taught our Corvair builders to do.

Front Alternator

The above photo shows our new front alternator configuration. All of our builders know that I advocate a front starter/alternator combination for virtually every Corvair powered aircraft. The primary consideration is one of simplicity. Keep in mind that I have flight tested all types of starters in various locations on the engine, and my recommendations come after years of experience and countless engine builds.

In the test phase, our aircraft had the alternator at the back of the engine. This allowed the installation of a number of pieces of test equipment on the motor. Its final configuration will be with this front alternator setup. While the alternator is the same 18 amp John Deere unit we've recommended for years, the bracketry here is all new. I sketched out the design on a cardboard box, and gave it to Gus. After some careful measurement and one practice run, he made these brackets from 1/4" aluminum plate. They're light, incredibly rigid and do not impede airflow into the motor. The primary advantage of this configuration is that both the pivot and swing bolt are on the same plate. Although we've had no problems with our previous designs, this one is technically better because the alternator does not feel the thermal expansion and contraction of the engine. Builders with sharp eyes will notice that our alternator features an enlarged pulley. We do this modification for engines which will be operated at sustained high rpm. With the alternator mounted in the rear, it turns faster because of the larger pulley diameter. A rear mounted alternator on an engine turning 3,300rpm will need this. On a front alternator, it's just a nice option to slow the rotation. It produces plenty of power either way.

Above is a view of the bracket without the alternator. Although it may look large in the photo, it is neatly tucked into the engine and easily fits inside our nosebowl. We did not even have to modify our existing baffling to install it. People new to installations may ask if the alternator in this position impedes airflow to the engine. I have years of flight experience with alternators nearly in the same configuration that clearly shows it does not impede airflow. The restriction to airflow is by design the air inlet. The alternator is at an area of much larger cross section inside the nosebowl. Keep in mind that our style of baffling allows the air pressure to be balanced over all the engine. If slightly more air flowed into the left inlet, it would not matter because there's nothing stopping air from flowing to both sides of the engine no matter which inlet it comes through. Besides, the engine runs very cool even in the hottest of weather.

The inboard mounting of the brackets is pictured above. "A" is the main plate, and "B" is a 1/4" thick sub-plate which picks up the two front cover bolts. A & B are held together with three AN-3 screws. Between them is a 60/1000" shim. This shim and the ability to drill the three holes in the field provides complete adjustability to properly align and set the bracket, even if a builder introduces a variable like tall cylinders. We put a lot of thought into the brackets to make them useful not just to us, but to all builders.

These brackets are an excellent example of how we develop parts. The process always follows this route:

  • 1. Use our years of experience to configure the part to meet the need.
  • 2. Hand craft the prototype in our shop, tailoring the design to make it mass producable.
  • 3. Flight test under adverse conditions with the goal of finding out how it might not work. Note: This is very different than a flight test run to prove you can fly a part under certain circumstances.
  • 4. After successful flight tests, set up the part for CNC production if possible in order to lower costs.

    When this alternator bracket stands the test of time, it will join the ranks of our other flight tested products available for sale.

  • Fuel System

    Hundreds of people at Oshkosh studied our innovative fuel system for the 601/Corvair combination. The system primarily runs on the Corvair's mechanical pump. The backup is an electric pump on continuous automatic standby. Gus and I spent a tremendous amount of time to develop and test this setup, and I consider it fully proven. We worked it out all the way down to the pre-flight checklist. Although at first glance it has a number of components, its crucial characteristic is that it adds very little to the pilot's workload and does not require the pilot to do anything should the primary pump malfunction. Additionally, it features a system to automatically stop the electric pump in the event of an accident.

    Although the system works quite well, and it would serve anyone who would choose to duplicate it, I'm currently in pursuit of another system, one which would have an electric primary pump with a second electric as a backup. Always in the forefront of my mind is the fact that our work is to serve amateur builders and non-professional pilots. Our mechanical/electric system serves the recreational pilot well with its low workload, but I was concerned that it requires some talent to construct, and the mechanical pump itself has initial maintenance issues which cannot be ignored. With this in mind, we're pursuing the electric/electric combination. Remember, only low wing airplanes without header tanks, like the 601XL, need fuel pumps. The vast majority of Corvair powered airplanes are gravity feed.

    Presented here is a technical discussion of the mechanical/electric system. I present it here to further the greater understanding and learning of builders. We may yet use this configuration in another airframe, so it's a good case to study. The picture above shows modifications we made to operate the stock mechanical pump. The AN lines feature Earl's swivel ends, and XRP fittings. Also visible is the catch can, which would run a gas leak overboard instead of allowing it to drip onto the engine.

    Above is a view of the mechanical pump from behind. The pump we used in all of our flight testing is a Carter M-3988 made by Federal Mogul. It is brand new and costs less than $45. You can also see that we've replaced the screws with safety wired stainless Allens. The catch can and its white overflow tube is also visible here. The full flow hose ends are 180 and 150 degree bends. The hose size is AN-6, and the thread on the pump is 1/8" pipe. The only operating difficulty we had with the entire system in 75 flight hours was the need to retorque the pump screws at two hours and again at 10 hours. We checked them at several other intervals. The new pump crushed the gaskets slightly in operation, and needed the screws retightened to restore a good seal. If the screws were allowed to get loose, the pump would drip into the catch can. After these two intervals, the screws never again needed retorquing.

    Testing aircraft fuel systems is very serious business. To give you an idea of the detail, we used a micrometer to measure the length of the screws to ensure that screw stretching was not the cause of the loss of the preload on the gaskets. In my years of testing, I have learned to be very cautious about attributing cause to the first smoking gun you find. You have to be vigilant and seek out the real cause and effect, not just the first likely one you stumble upon.

    The firewall components of the mechanincal/electric fuel system are pictured above. Fuel comes through the firewall at the lower left, goes throught the Andair GAS375-M gascolator (an excellent piece of equipment), and goes into a Facet fuel pump. From there it goes up to the mechanical pump and returns under pressure to the right hand side of the upper tier. The three fittings are, from right to left, sender for the Autometer fuel pressure gauge, a Nason part number SM-2C-4F 4psi pressure switch, and an electric primer selonoid. In normal flight operation, the engine runs on the mechanical pump alone. If pressure drops below 4psi, the switch automatically turns on the electric pump. There is a manual override of this so the engine can be primed with the electric pump, and there is a Nason 15psi switch in the oil system to prevent the pump from turning on without the presence of 15 pounds of oil pressure. We have it set this way to preclude the electric pump coming on should the engine and mechanical pump stop in the event of an accident. The system is clever and relatively foolproof in operation. It has a warning light in the instrument panel to tell you the electric pump is on. I like everything about the system with the exception of the vigilance required on the initial installation of the mechanical pump.

    Above is a view of the lower right hand side of the back of the engine. The white tube is the translucent drain line from the catch can around the fuel pump. During the preflight, the electric pump can be turned on in the override position. If there is a leak in the mechanical pump, you could either smell it or see it in the overflow line. The coiled copper line is the primer. Our aircraft has an MA3-SPA carburetor with an acclerator pump. It does not truly need a primer, however an electric primer is easy to install if you have an electric backup pump. The line is coiled in this fashion, where it goes from the stationary motor mount to the moving engine. Careful attention to detail like this makes for reliable operating engines. All instrumentation and primer lines need to be carefully addressed to prevent any type of fatigue where they transfer from airframe to engine.

    Oil System

    Pictured above are components of the oil system which we will flight test in the coming weeks. When we go to an electric/electric fuel pump system, the stock oil filter housing of the accesory case will then only hold the oil filter and bypass. We have built a blockoff plate to replace the stock oil filter housing, and have two AN-6 lines feeding a Permacool remote oil filter housing. The oil filter is a high flow K&N 1004, which has an internal bypass and features a nut and safety wire hole like a standard aircraft oil filter. It has an internal baffle that keeps it from leaking oil when it's unscrewed. This will allow it to be mounted on top of the engine, without creating a mess at oil change time. My plan is to relocate the filter to the top of the engine, behind the starter. Relocating the filter and removing the mechanical pump will free up a tremendous amount of space on the back of the motor. We currently have plenty of room, but I'm organizing the installation to eventually allow the addition of a turbocharger. The 601 currently has a remote oil cooler and extensive oil temperature instrumentation. The intention is to convert it to a block mounted, stock, 12-plate oil cooler. Simplicity is the goal, even with turbocharging.

    When the changes on the engine configuration are complete, we'll present complete installation photographs on this site. If you have any questions, please feel free to call or write.

    Thank you.

    William Wynne

    November 2004 601 Page at www.FlyCorvair.com

    August 2004 601 Page at www.FlyCorvair.com

    May 2004 601 Page at www.FlyCorvair.com

    March 2004 601 Page at www.FlyCorvair.com

    February 2004 601 Page at www.FlyCorvair.com

    January 2004 601 Page at www.FlyCorvair.com

    November 2003 601 Page at www.FlyCorvair.com

    October 2003 601 Page at www.FlyCorvair.com

      Home  Turbocharging  Thrust Testing  Engine 4 Sale  Corvair College #8  Corvair College #7  Corvair College #6  Sun 'N Fun 2004  Corvair College #5  Daily Q&A  Flying Corvair Planes!  News  Who Is William Wynne  Conversion Manual  Online Catalog  Maximum Horsepower  All About Corvairs  Corvair History  Engine Specs  Sonex Installation  RV Application  Why Fly Corvair?  FAQs  Technical Support  Links  Liability Statement  Carb Ice  E-mail William 

    Copyright 2004 William Wynne Web Design by Aviatrix