Hi all,

     I am looking to build a 650 in the future once time and finances allow, and I'm very much interested in the 120HP corvair engine as a powerplant for my future build.  I'm looking at Azalea's corvair and William Wynne's 3.0L corvair and I'm leaning at the moment towards Azalea's because of the 32 amp alternator.  While the aircraft would not be a hard IFR platform, I do want to have the availability to fly IFR in the aircraft in case I need it.  I have been unable to find the rated output of the front alternator and was wondering if anyone knew off the top of their heads the rated output.  My question for you folks, is it possible to have both an SPA rear alternator and a front alternator from WW?  Each alternator would have its individual rectifier and voltage regulator.  Would it be possible to wire the two alternators in parallel after the voltage regulators and have the two alternators function as one alternator with a combined amperage output?  ie 2x 20 amp alternators @14V wired in parallel to have an output of 40 amps at 14V.  If that could work to wire both the front alternator as well as the rear SPA alternator in parallel, I think I would almost certainly go with the WW corvair conversion. 

Thanks all for any help,

Scott Kubiak

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Yes, you can run both the SPA rear and WW front alternator. The front alternator will have higher output at low RPM, so it will likely be the primary. You cannot wire them in parallel without a proper controller: https://bandc.com/product/standby-alternator-controller-14v-homebuilt/ The easiest way is to simply have a separate relay/switch for the second alternator.

I highly recommend the book: The Aerolectric Connection by Bob Nuckolls: https://www.amazon.com/AeroElectric-Connection-Bob-Nuckolls/dp/B001... Bob covers wiring two permanent magnet alternators in the book along with other ways of ensuring reliability and redundancy without dual alternators. 


     Thanks for the reply, I'll definitely take a look at the book you recommend.  I was thinking of each alternator having its own rectifier to change from A/C to D/C and regulator and then wiring them in parallel after the regulators once they are at the same voltage.  Do you think that could work or would that be more pain than it is worth? You mention that you cannot wire them in parallel without a controller, are you thinking about wiring in parallel straight off the alternators while the output is still A/C? 

Even with their own AC to DC regulator, you cannot just wire the outputs in parallel. Each, regulator/rectifier "senses" the voltage on the output side and tries to keep it 14V, turning the rest of the energy generated into heat.

If you are planning to run dual batteries (for redundancy) you can simply wire each battery/alternator independently with an isolation relay that you would activate in the event of the primary alternator failure. 

That has been true, but a modern regulator will use MOSFETs and switch the generator off when the set point is reached.


That link does a better job of explaining it than I could.  If you really want to pursue this system, get two MOSFET based regulators with different set points.  Say 13.4 and 14V.  Starting the engine pulls the battery down to 13.0, so both kick in right after start-up.  After a few minutes of working together, the battery has hit 13.4, and that one shuts off the generator windings to the one it controls.  It is now essentially in hot standby, while the other tries to push the battery to 14V all by itself.

I am building a 650 and will be putting 3.0L WW Corvair in it.
The alternators that WW recommends is a 12V 20A permanent magnet alternator. This works for most of the builders out there.
But, if you want to set your plane up to possibly be IFR compliant at some point in the future a 20 A alternator probably won't produce enough current.
The alternator that I found and bought is rated at 12V 35A and is the exact same size as the 20A version.
You can find an example at the link below.


The one I bought was through Amazon but this is essentially the same.

You will also need a 35A Rectifier/Regulator.
The one I bought is at the link below.


I have the rear alternator bracket from SPA and plan on mounting it in the rear position initially.
This is, as you mention, where it is run 1:1 off the engine. If it does not produce enough current in this position it can always be moved to the front where its output will be higher.

Hope this helps,


      I agree that 20A is not sufficient for IFR which is why I was wondering about running the two alternators in parallel after the voltage regulators.  From the looks of the 35A alternator you mentioned, I'm guessing it would take the place of the front alternator?  This helps quite a bit, thanks Earnie.

I predict that you will be very unhappy with that configuration.

The 650 is already marginal with a Corvair up front due to the location of the weight.  Adding more out on the nose isn't going to help.

The issue is that the nose will drop, and drop hard, when the tail runs out of authority in the landing flare.  You have to keep your speed up much more than you'd like for touchdown.


     Thanks for the heads up.  I think I'll start looking at lighter engines FWF that might help to reduce the nose drop issue that you mention.  I've heard of people using partial flaps instead of full flaps to help increase the pitch authority on landing.  Thanks for the information, Scott

I have a 601 with the 2.7L Corvair and I have no problem holding the nose up during flare. I can land on the mains with full flaps down to stall. I'd be glad to take you flying. Where do you live?

I definitely agree with exploring all FWF engine options. Although, I would not reject any one without speaking to and/or watching some of the YouTube videos of people who have that particular engine.
As far as the Corvair engine is concerned, I have seen quite a few videos of, and talked with others flying the 650/Corvair combination. I don't remember any of them mentioning that this combination was a marginal combination nor that the nose dropped hard upon landing. There may be those out there that do think this but, I have not come across them.
I have found and watched a number of videos that have the 650/Corvair combination. You may want to watch them and see how this combination performs on takeoff, landing and the other portions of flight for yourself.
One person who flies a 601HDS/Corvair combination and posts videos is Larry Nelson on his "Zenvair Pilot" YouTube channel. He has quite a few of his flights in his plane. He likes the combination well enough that he is building another 601HDS/Corvair airplane for his father to fly.
Another I've watched is Ken Pavlou's videos of him flying his 650/Corvair airplane.

I have personally talked to both of these people and neither even hinted at any performance issues during our conversations.
I would also encourage to attend Zenith's Homecoming in September as there is usually a number of the engine dealers there and many who have those engines in their planes fly in also.
That way you can talk to those there and see what their opinion of their airplane/engine combination is. You may find that the 650/Corvair combination is what you're looking for or, you may find another combination that better suits your needs.

I just think it would be sad if the combination that may best suit you was rejected without you having all the information from a variety of sources.
Hope this helps with your search.


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