3.0L Corvair/Zenith 601HDS Robert Audsley


I spoke with builder Robert Audsley on the phone yesterday for nearly an hour. He was motivated to call because he has recently started flying his 120hp/3,000cc Corvair powered Zenith 601HDS.


Robert had seen some of my recent stories and wanted to call in with his personal path to a very solid Corvair and a good flying plane. The journey wasn’t all perfectly smooth sailing, but as I have said many times before “In homebuilding, Persistence Pays.” The guy who gets his project to the flight line is the person who when challenged responds with my tough day shop mantra “I can always quit tomorrow” 


Below are some pictures and a video link, and a short brief in Robert’s own words. I encourage other flyers out there to text me pictures and their own story to share with builders working on a similar goal.








Above, a view of Roberts cockpit. High end panel with a lot of capability including an auto pilot. If you don’t know Zenith models, let me point out that Rob included many of the later XL upgrades like the forward hinged canopy and spring gear to his HDS.


From Robert:

“Here is the story in a nut shell. I bought the airframe of N305BM about 3 years ago. It was a flying airplane in 2003. Some time after owners passing and the aircraft being passed from owner to owner it became a basket case. So i bought it. I stripped it down, removed the empty instrumet panel, removed the landing gear struts, top of fuselage and removed a bunch more. Then I started fabricating parts. Dual controls, rudder pedals, forward tilting canopy, bigger baggage area, autopilot, new cabbles, nose strut, spring gear from a 601xl, wing tanks and of course the 120 hp corvair engine , baffle and cowling.

I started assembling the engine at corvair college #33 in april 2015. I was able to finish the lower end. Once I got the heads back I assembled the rest of the engine at home in July of 2016. I ran the engine for the first time in april 2017. I damaged the heads because I didnt keep a close eye on CHT and did not use an airscoop, instead had the engine cowled. NOT ENOUGH AIR FLOW. The first flight was February 25th 2018. Not one burp. I was not nervous, the engine had about 2 hours of ground run time, including the two minute test. I had a couple cylinders that were 70/80 with a plan to recheck after 5 hours. They came up to 74/80. I also checked the timing and set it to 28 deg. I now have 8.9 hours and CHT is down around 370 under the heads in the stock location. Its good for 100 knots at 3000 rpm, I have an airplane.”

The youtube video is:




Above, a very sharp looking bird, built and flown by a man who decided to see how much he could learn about both the airframe and edge, not how little. Every homebuilder makes this decision for himself. The people who aim higher and learn more are the ones who get the most out of homebuilding. Don’t seem yourself short, you can have any level of experience in homebuilding you select.


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.

4 Responses to 3.0L Corvair/Zenith 601HDS Robert Audsley

  1. Robert Audsley says:

    Thanks for the great conversation yesterday William, You made my day. I would like to thank you for your life long dedication, it allows the worker bee type of people like myself, who don’t have the time to design and test everything, to fly safely bihind a tested and proven design.

  2. Dave Carpenter says:

    Just so happens that I have a HDS kit to put together any words of wisdom would be appreciated.

    • robsley says:

      Words of Wisdom….Keep it light and simple, do not overbuild. Words of reflection. No matter what, its not a Lancair and will never be. It is very stable, easy to fly. The HDS drops like a rock when power is off so keep your airspeed up. I fly the pattern at 80 knots and keep a little power for landing. I used pushrod tubes for ailerons instead of cables. You can get wing tanks from Zenith, just call them. I’m not a fan of a big tank of gas in the cockpit. I followed Williams instructions and everything worked well. Open the engine inlets as big as you can. Oh yeah, Watch your CHT! The temps will come down after a few hours on the engine. For W&B I installed my battery in the AFT section of the fuselage just below the LE of the horizontal stab with a removable panel on the right side. I also made the top panel forward of the instrument panel removable. This allows easy access behind the instrument panel. I believe this to be a nessecity. I have had to get behind the panel several times after assembly. Just once makes the installation of several nut plates worth the time.

  3. jaksno says:

    Yeah! Very encouraging. Best flights, Mr. Audsley.

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