Shootout at the Stromberg corral

Builders,

Most Experimental Aviation companies don’t do any more testing than they have to, its pure overhead, and lots of the stuff you see is rigged or slanted to persuade not to actually discover anything.  However, I look at my work in aviation predominantly as a learning and teaching exercise, to share with builders what they need to know to be the master of their creation, not just its owner.

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The next major testing will take place this coming weekend. With the help of other Corvair builders Like Paul Salter, Terry Hand, Jeff Moore and Dan and Tracy Sheridan, I have gathered a 1/2 dozen Stromberg NAS-3 carbs in a number of slightly different configurations to test in a wide range of power setting on a 3,000cc Corvair on my run stand I ‘m shooting to do them all the same day to minimize atmospheric variables. As always, I will just present the data and some thoughts on it, and suggestions to builders.

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Above, five of the six carbs on my workbench. There are small subtile variables between models and configuration. My Pietenpol always flew a Stromberg, and our second test mule the Skycoupe flew one, even when we turbocharged it. in 2004 Gus Warren and myself ran a series of comparative jetting flight tests on the Wagabond at the old hangar in Edgewater, and developed the configuration that is referenced in my conversion manual. We are just looking to expand that knowledge base a bit further.

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Would you like an example of how testing is better than “Hangar tales from local experts”? Try this: its always said that the mixture control on Strombergs isn’t effective, and you should just wire it shut. Here is what testing says: if the carb is assembled with worn parts, the mixture is less effective, but if properly overhauled, the mixture control can run the motor from so rich its smoking (9.5:1 air/fuel) to lean misfire/detonation (16:1) at any rpm above 1500.  It is true the mixture will not function as an idle cut off like a MA3’s will, but the Stromberg’s mixture can be much more effective than 95% of the people in your EAA chapter think.

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Above, my engine stand, with Stromberg #6 mounted. In the foreground is an integral part of the testing, it is a very sophisticated O2 sensor in the exhaust wired to a digital Air Fuel instrument that cost several hundred dollars. It logs the A/F ratio to a tenth of a point. Many pilots like to talk about using cheap one wire O2 sensors and $50 agues, and I have used these myself, and I wasn’t impressed with their accuracy nor reliability, and they have the ugly habit of defaulting to reading “Green” when they are in default.  Although this is also an O2 sensor, this one has a heating circut, run by the instrument. Look at the bonding jumpers which are installed to make sure there are no errors from grounding variations. This is critical, but ofter ignored.

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In the big picture, if your carb is set right, you can fly the plane without an O2 sensor or even an EGT.  If you think about it, Cessna 150s don’t even have a CHT gauge. They just have a specific engine configuration, including the carb and the cowl, and the plane is operated within parameters known to work. Our testing here is to expand the known configurations of Stromberg to support the same concept for Corvairs. Results to follow.

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Wewjr.

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About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.

8 Responses to Shootout at the Stromberg corral

  1. Terry Hand says:

    Glad I could help in a very small way, but I can’t wait to see the results. Real testing with recordable data for analysis – not just hangar talk. Keep us posted.

  2. John Klemin says:

    Have y’all done the same testing with the MA3?

    • John, we have,. The other factor with MA3’s is we have dozens of them flying on very heavily instrumented planes that we can collect data from , like SPA’s Panther. The Strombergs tend to be on planes we don’t have that kind of feedback on.

  3. David says:

    Hey William I know this may be off subject but have you started planning this years colleges yet? I hope you will have one in the southeast? Thanks for all the good articles you write it is part of what keeps excited about my airplane build, cant wait to use my engine!

  4. Since you brought it up now, are there any sensors out there available from places like Summit, that do have good accuracy and better failure indications. I had those single wire type sensors slated for my engine installation based on Mark Langford’s good write-up on their usefulness but now you have given me reason to pause on that. I do like a well instrumented engine and it seems like a good parameter to monitor and use so now the question is just what do I need to make it work and not risk a false sense of proper operation.

    • Sarah, Good to hear form you, hope everything is going well. If you want to check out something pretty good that will fit in the same space, check out an Innovate 3918 from summit. Works great. Your friend, William

      • sarahafl says:

        Thanks for that bit of information William. I checked out the component that you recommended and added to my Wish List at Summit with other stuff I need for FWF. The only short coming I noticed was that it was intended for attachment to a single exhaust stack while in the Corvair we have two. That might not be too bad an issue for the carbureted aircraft since they should be the same on each side more or less but with my Airflow Performance Fuel Inj system I would prefer to watch both sides and see if any differences crop up. They do allude to the possibility of putting in something like a splice on long runs but seemed concerned in that regard that the user might not be sophisticated enough to properly insulate a joint. Maybe I just need to see the schematic from the sensor to the gauge to know what it would take to include a LT/RT switch. Can the standard exhaust manifolds that you offer through SPA have the bungs added to them for the sensor prior to delivery? When I get all my project dusted off I want to evaluate which standard system will fit using my FWF mock-up and get those parts on hand.

        In other changes and changes to come it looks like I am going to be relocating to Oklahoma City for a new job so I anticipate that I can get active again out there with a house of my own and a big garage. The past couple of years have been down time while fulfilled family commitments and the project had to move to a storage unit. While the build did not progress I did git in some serious design work and picked up an RV-8 canopy from AeroCanopy that I will use the back of, sort of P-51 style. It is little details like that which needed to be thought through so I did not build anything that required significant rework after the fact when I got to such details.

      • If you look at the brand on summit they have a two sensor model with one gauge face for $399. They come with very specific weld in bungs that keep the O2 sensor at the proper distance out of the direct stream. Glad to hear you will have more progress soon.

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