William Wynne

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


Open E-Mail

December 26, 2004

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Subj: Valve Adjustment on Stored Engine
Date: 12/23/04

It was suggested that I do not adjust the valves on my Corvair until I am closer to having it run (probably a couple of years until I get the bird done). The thought is that the valve springs will retain memory of being left in a compressed position too long. I have old cars out of fields that have been abandoned for 20 years, dumped some Marvel Mystery Oil in the cylinders, broken the crank loose with a breaker bar and fired them up and have run great! What is your opinion on adjusting the valves and letting the motor sit for awhile?

John Monday, KR2S, Laguna Beach, CA

Reply from WW:
In the Conversion Manual, when I discuss valve springs, there is a nod given to this same thought. However, my fundamental feeling about the nature of springs is that a quality spring would not care if it were compressed for any length of time as long as it is not forced past its yield point. This said, certain types of metals under stress are more prone to corrosive attack; in the case of a valve spring, rust. In a nutshell, for these reasons we always replace the valve springs when we rebuild an engine. With new valve springs, in a noncorrosive environment, I do not think the springs being compressed is an issue. I have stored engines, with the valves adjusted, for two years without turning the crankshaft and experienced no problems. If you do wish to adjust your valves and store your engine for a lengthy period of time, you must take the effort to seal your intake and exhaust ports to prevent air from entering the cylinders through open valves.

Subj: Prop Clearance
Date: 12/24/04

I think this new idea, the Open Email, is a great way to cut through all the other “noise” on the Internet and get straight to answers I can use! Thanks for doing this. Please keep up the good work.

I just installed my 66 inch Warp Drive prop on my 601XL Tri-gear and I noticed that I have about 7" of ground clearance. That doesn't seem like much to me. What are you guys flying with for ground clearance? The engine mount is your stock William Wynne model.

Thanks, Phil Maxson, 601XL/Tricyle/Corvair, N.J.
Reply from WW:
Seven inches is more than you're thinking for a number of reasons. First of all, certified airplanes are primarily required only to maintain positive ground clearance with a flat nose tire and a collapsed strut. If you look at a Cessna 150, 152 or 172, they will not touch the prop to the ramp with a flat tire and a flat strut. But I doubt they have much over 7" of clearance under normal circumstances. The 601's nosegear does not have a ton of travel, nor does its small sidewall nose tire lower the nose much if it's flat.
Keep in mind the major issue here is that your aircraft is not yet in its flight configuration. Airplanes without wings or passengers are nose heavy. Adding the wings or the crew will tend to load the main gear and not the nosewheel. Under these circumstances, you'll have more than 7" ground clearance at rest. Over the years, we've operated a number of aircraft with far less propeller clearance. Props have to be very close to the ground to pick up trash, pebbles or gravel. The major reason experimentals occassionally have a prop strike is taxiing over very uneven ground with 4 or 5" of clearance. As a final note, consider that the standard 601 propeller for the factory Jabiru 3300 installation is a 68" diameter Sensenich. The thrust line of the Motor Mounts that we build are at the same level as the factory 3300 Jabiru. Thus, you have even an inch more clearance than the factory recommends.

Subj: Front-mount alternator brackets
Date: 12/23/04

Do you still intend to offer the front-mounting JD alternator brackets for sale, and if so, when?

Thanks, and Best regards, Don Lawrence, California
Reply from WW:
We're getting the first ones back from the CNC hydrocutter shop this coming week. I anticipate that it will be a very popular product. We have about 50 flight hours on ours, and it has worked flawlessly. The finished product will be nearly identical in dimensions to the handmade prototype pictured on Our September 2004 601 Web page. We'll post a notice on www.FlyCorvair.com as soon as they're ready for shipment.

Subj: Corvair Powered Piet
Date: 12/22/04

I'm still slowly working on my Corvair engine and on building a Pietenpol. This current series of questions has more to do with those two playing together and your recommendations. Basically, looking over Bernard Pietenpol's plans, the Corvair engine mount seems to have a significant downward pitch. This still the right way to do it?

Any suggestions on maximum diameter prop that would work?

And, any experience with the biplane varient of the Piet known as the Aerial (from St. Croix). I am trying to learn more to see if it might be viable.

Thank you, Jon Apfelbaum, Pietenpol, Utah
Reply from WW:
My Pietenpol is perhaps the only airframe to be flown both ways, with both Bernard Pietenpol's low slung motor mount down thrust in it, and later with the motor mount raised 4" so that the thrust line was level with the top longeron and built with no down thrust. It provides a dramatic difference in the appearance of the airplane. Any photo you see of my airplane when it's painted orange is the original Bernie mount, and all pictures of it when it's navy blue are with my mount. There was not a tremendous difference in the way that the airplane flew. It certainly flew no worse with the later motor mount. I largely think that Bernie maintaining the low thrust line was mostly influenced by his retaining the stock blower fan and keeping the thrust line in common with Ford Model A powered Piets. With our more compact electric start installation, I was free to move the engine up in the airframe. A lot of down thrust is common on airplanes which may be climbing at very slow air speeds. We used 60-65mph as a climb speed on our version of the Pietenpol and never felt the need for down thrust.

Most stock Bernie mounts utilize 66-68" diameter props. There are many different variables in landing gear design on Piets. Some people build their planes with very short legs, which cuts down on prop clearance. With the motor mount raised 4", we could have swung any prop we liked, but chose 68" for performance reasons.

There have not been a lot of Pietenpol Aerials built. The Piet does not have a gigantic tail. I strongly suspect that adding a second wing, without changing the size of the tail or length of the fuselage, would effect the stability in an unfavorable manner. In my humble opinion, there are many other better light biplanes which could be Corvair powered, like a Hatz.

Subj: Oil System info
Date: 12/26/04

What do you expect the new oil top cover to cost? I think that for my application with the turbo it would free up a lot of space and allows greater flexibility in the turbo placement. Please let me know how much so I can budget some funds for this component.

Hopefully you had a good Christmas and I hope you have a happy new year.

Best regards, John & Jean Kearney, 601XL, Nevada

Reply from WW:
The machined Oil Top Cover Plate with installation hardware is available for $69, which includes Priority Mail shipping inside the U.S. This part goes a long way toward cleaning up the engine compartment and providing more space to lay out a clean installation, whether it's turbo or naturally aspirated. You can see the whole story on the part at www.FlyCorvair.com Oil System Page. There's also several photos of the prototype now flying on the 601 Web Page, and you can also see several of these installations on customers' engines at the Corvair College #8 Pages.

Subj: Tachometer Coil Pickup
Date: 12/23/04

I listen and read stories about Tachometers optical and off the wire. What is wrong with a coil or distributor tachometer pick up? So simple so dependable. Yes they can short a coil but not with a low amp fuse.

Wayne B., Pegzair, Canada
Reply from WW:
I discourage people from using regular automotive aftermarket tachs for just the reason you point out, the potential of shorting out the coil. However, your point is good, that if it has a fuse, it is unlikely that a faulty tach could take out the ignition system also. Although I have not flown a Corvair engine in this configuration, Dave Blanton's V-6 Ford conversion manual recommended a 1/2 amp fast blow fuse for the tachometer circuit if a regular automotive tach was to be used. Personally, I like the Stewart Warner tach we have in the airplane because it has very smooth operation, and is completely independent of the ignition system. The full sweep nature of the tach and its 0-3500rpm scale make it appropriate for our application. Most auto tachs go to 6,000 or 8,000rpm, and we'd therefore only utilize a very small part of the scale, thus making it more difficult to watch for ignition and carb heat rpm drops during the pre-flight run up, let alone slight rpm drops during flight, which is the indication of the onset of carburetor ice.

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