Front and Rear alternators, their part in numbering system


I am going to jump ahead in the numbering system to alternator choices. As you will see, The standard charging system, the front alternator system we have used for 9 years is Standard charging system group (2900).  This is the system that we sell on our website at the link below. It is the working system on about 150 aircraft.

Above, the Hangar Gang Wagabond in it original configuration that it had from 2005-2012. This is made of early parts and has a black hub and a modified alternator pulley. This system evolved to a much cleaner configuration when the Gold hub came in 2006. The photo also shows an early FRA-235 ring gear that has been superseded by a solid model. The Alternator is used with its stock pulley on a Gold hub system. The photo is a good representation of how the current systems evolved over time and have long been flight proven.


In the last year I worked with Dan Weseman to develop a direct drive rear alternator set up for the engine. Dan was looking for a system that he could use as a very compact arrangement for his new Panther aircraft. After much development, Dan took the lead on the project and worked out the details and manufacturing on it. I wrote it into the numbering system as Rear charging system group (2950). Although it is ground tested, Dan wants to hold off sending any out until we have it on an in-house test bed aircraft, either the Wagabond or his Panther. The target date for having them available pending flight tests is Sun n Fun. Dan and Rachel have had some notes on the rear system on their website, linked below. When the system is up and tested, it will be available from them as an alternative to our front system. More updates will be on their site as it develops.

Above is a high thrust line Pietenpol mount bolted on a Corvair with our standard intake an MA3 carb and the prototype rear alternator. All of our components are integrated to work together on this. The rear alternator makes its amperage output at a higher engine rpm because it doesn’t have the ratio advantage of the pulley. In ground tests, the rear set made good output, plenty for most simple aircraft. For single seat or tandem seated aircraft, a sleeker cowl may be possible. On side by side aircraft like the Zeniths and the Cleanexes, the front system fits inside the cowl nicely.


One of the first questions builders ask about the rear system is if we think it will allow more cooling air into the cowling. This is to be determined, but I don’t think that the front system is a choke point like some people eyeball it to be. Further down the road we can have some type of before and after test on the same airframe, but for now I would like to have people interested in cooling to review the four articles I wrote on the topic here last year. The links are below:

Corvair Cooling, Three 2007 examples from our hangar.

Corvair Cooling, something of a human issue…..

Corvair Cooling

Engine Cooling Factory Sheet Metal


Getting back to the numbering system, Below are how the two groups are laid out in my system. After both outlines, I give an example of my full notebook entry on the 2900 group, not just its outline form. It is lengthy, too long for the overview we are working on here, but I wanted to show builders the full depth of the information on this one topic. After this I am going to go back to the Rod and Piston group (1300) and the Cylinder group (1400). The full set of notes on those two groups is about 7,000 words. A lot of detail, but too long for keeping people focused on the big picture. I want builders to see enough to picture which engine they want to build in 2013. After that decision, we can go back and look at any component in the kind of detail seen below.


Standard charging system group (2900)

2900- Front alternator bracket

2901- Mounting hardware

2902- Permanent magnet alternator

2903- Altermator mounting hardware

2904- Drive belt

NOTE: If you opt for group 2900, then delete group 2950.


Rear charging system group (2950)

2950- Rear alternator bracket

2951- Mounting hardware

2952- Permanent magnet alternator

2953- Alternator mounting hardware

2954- Drive coupling

NOTE: If you opt for group 2950, then delete group 2900.


Below is a sample of the full write up on the 2900 group from the build note book, -ww


Standard charging system group (2900)



The standard charging system that we utilize on Corvair flight engines mounts a 20 amp belt drive alternator on the front of the engine. The system has a perfect reliability record while meeting the needs of Corvair builders in an economical manner that does not compromise any other system on the engine.

Over the years I have used many different charging systems on flight engines we have built. These include the stock Corvair alternators on blower fan engines on Pietenpols, one wire alternators, 60 amp teacup ND alternators, and several different models of the current AC dynamo mounted in several different places on the engine. The designs we recommend are based on this experience. Many people jump to the incorrect conclusion that we recommend 20 amp alternators because I have not tried more powerful ones or explored other ideas. A quick look at our Web page will show several Zeniths we built engines for in 2009 with 60 amp alternators.

The first question that most builders have is whether or not 20 amps is enough output for their aircraft. The most common mistake builders make when adding up the electrical power usage of their aircraft is assuming that they are going to be utilizing all systems at once. This would make the assumption that all of the loads would be full-time rather than intermittent. Looking at the most basic version of this concept, cranking the starter pulls about 250 amps. Does this mean that you need a 250 amp charging system? Of course not because cranking the starter is an intermittent load, and the reserve energy for it is stored in the battery. On a smaller scale, transmitting on the radio is the same concept. To an extent, operating a landing light is the same idea. Any time the electrical system demands are briefly higher than the output of the charging system, the battery is there to make up for the excess demand.

We frequently have builders tell us that they’re going to put a glass cockpit in their airplane, and they erroneously feel that they would need a much larger alternator to run this. In reality, glass cockpits use almost no energy as they are modern electronics and they run with significantly lower power consumption requirements than other types of instrumentation. The same goes for modern LED strobes and lighting, which consume a tiny fraction of the power required by traditional systems. Even modern radios transmit much more efficiently. Any realistic analysis of the power requirements of 99% of Corvair powered airplanes will show that they can run on 20 amps or less. To have a larger charging system is to be carrying excess weight on every flight. New builders are often attracted to unproven or unreliable modifications to the engine in order to reduce its weight. The same green builders will often be interested in charging systems that weigh more than double the 20 amp system that we use. In time, these builders will learn by studying successful installations to prize proven reliability above all else and learn why aircraft have charging systems sized as they are.

There is a second temptation among new builders to want to see the alternator moved to the rear of the engine because they imagine that it somehow interferes with cooling. The best proof that it does not are the dozens of airplanes flying with it up front. The Wicked Cleanex flew hard aerobatics at wide open throttle on a 120 hp Corvair, as you can see on our Corvair Flyer #1 DVD. It never overheated, and of course, its alternator is up front. There’s a serious liability to having a belt driven alternator on the back of the engine. The Corvair’s ignition system is on the back of the engine and is vulnerable to the belt being thrown off. This is not an imaginary scenario. My friend John Blackburn was killed in a Ford V-6 powered Mustang II from this exact scenario. On the handful of engines that I put a belt driven rear alternator on, I always had a belt guard that would prevent a frayed or thrown belt from getting to the ignition wires, and I always mounted the alternator on the opposite side of the distributor.

The only airframe that has a layout for a belt driven rear alternator that makes sense is a Pro-Composites Corvair Personal Cruiser. I built the engine and the rear alternator prototype, which is tucked in the place where the oil cooler normally is. It is well away from the ignition on the opposite side of the engine.  Over the years, we have sold several hundred front alternator brackets to builders who were choosing to make their installation a duplicate of the flight proven ones we promote.


2900- Front alternator bracket

Our front alternator bracket is a two-piece assembly that is CNC machined out of quarter-inch aluminum plate and then gold anodized. The two-piece nature of the bracket allows the inboard piece to be mounted on two of the 3/8” bolts going to the front of the case. The outboard section is bolted to the inboard with three AN-3 bolts. These two plates can be shimmed in relation to each other to allow perfect alignment of the belt groove with the alternator pulley. The outboard section forms a complete ring around the alternator to support it. It has a single mounting hole for bolting the outboard bracket to the cylinder head to stabilize it. The bracket set comes complete with full instructions.


2901- Mounting hardware

The inside of the alternator mounting bracket has holes for three AN-3 bolts to mount the two halves of the bracket together. We do not send these with the bracket because the length varies with the installation, depending on how the bracket is shimmed for alignment. These bolts should be finished with aircraft grade all metal lock nuts.

The outboard side of the bracket is stabilized by one bolt to the head. Depending on what year the head is, this bolt is either ¼”-20 or 5/6”-18. The length of this bolt varies depending on whether the engine has a 5th bearing or not. It is held off the head with a simple tubular spacer. The alternator bracket comes with detailed instruction on how to mount and align it.


2902- Permanent magnet alternator

The alternator we use is technically a permanent magnet AC generator. It has no brushes, has sealed bearings, can take over 10,000 rpm, weighs a shade over 3 pounds, is totally reliable, and costs under $150.  The only other thing I could ask for is that it be made in America, but it isn’t. It is made by Kokosan Denki in Japan. It is one of the few imported parts we use in the conversion.

You can’t buy direct from KD, they only sell to giant manufacturers. For a long time, we got these from John Deere dealers because they came on Deere tractors as original equipment. In the past 10 years, Deere has capitalized on the good name of their industrial equipment and moved into the homeowner lawn care market. Their dealers look like Harley Davidson showrooms. Over the years, they have been marking up their parts prices ever higher. The list price of the alternator is now well over $400, and retailers, with their green and yellow polo shirt clad sales staff, expect to get this kind of money from their upscale clientele who are their major customers.

Here is reality: John Deer tractors below 100hp all have had Yanmar tractor engines for decades. Once prices got high enough, I went over and found out that the part cost 1/3 as much if you buy it in a Yanmar box. The part number is 124190-77201. When we announced this on our website, an engineer for Deere got on the Web and stated that Yanmar parts are poor, and that the 300% mark up was justified by Deere’s quality program to make sure that they had a superior product. A very nice story for the members of the green tractor cult, but made of pure marketing B.S. I have bought dozens of both brands, and they are identical other than the box. Several years ago I met one of the chief engineers for Deere at Oshkosh, and he shared the entire history of Deere and Yanmar and confirmed that the parts are identical.

The best place to buy the unit is from Mike Schwab, a Yanmar marine parts distributor in Largo, Florida. He is building his own Corvair powered plane, so it is good to shop with friends. You can contact him through his website or by calling (727) 595-8813.

If you have a builder’s page online, avoid directly spelling out the exact source of your airplane alternator, as the legal team from the manufacturer might have something to say to their dealer about entering the airplane market.

As a back up source you can call or order from or (940) 592-0181. They have a website you can order from. If you call them make sure you do not mention that it is going on an aircraft, they have a note on their page about not selling aircraft parts. To my perspective, they are selling a part, your money is good, end of transaction, they are in charge of their business, you are in charge of your life.


2903- Alternator mounting hardware

The alternator is mounted to the bracket with a pivot bolt and a pinch bolt in the top slot.  The pivot bolt is set up as a AN6 (3/8″), the pinch bolt in the slot is an AN-5 (5/16″). Because there is a number of variables on type of front cover, Gold or Black hub, which 5th bearing, etc, it is best if each builder supply his own bolt length. The AN6 bolt does not fit the alternator housing exactly. The hole in the alternator housing varies depending on date of manufacture. If a builder would like a snug fit, a thin wall bushing can be used to bush the size down to the 3/8″ size of the pivot bolt. Both of these bolts should be finished with aircraft grade all metal lock nuts. The alternator brackets include detailed instruction on how to mount and align it.


 2904- Drive belt

For engines using a gold hub and a standard 20 amp alternator the correct belt is a Continental Conti-tech SF- AVX10 x 710. This particular belt provides several times the service life of more common belts. It is well worth getting one. For older arrangements with black hubs and previous alternators, we advise builders to measure each installation individually, as there are a lot of variables. Taking an old belt that is too long and cutting it into a form-fitting measuring tape is the best approach.

We have had a number of builders ask about using garden equipment belts, because they heard that one of the most common applications for the alternator is a John Deere tractor. This is true, but it isn’t the kind of tractor that homeowners or lawn service people use. Our airport has two of them for mowers; they have 5-foot-tall rear tires and they cut an 80” pass. The original equipment belts for the alternators are automotive style, not lawn service cross sections.

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