Here's this month's update. We've been very, very busy in the hangar, but still found the time to make
progress on the 601. We've received a lot of e-mail from people with questions focusing on the availability of
motor mounts and cowlings. This month, we'll direct the update to those two aspects of the Corvair installation.
Above is a photograph of my airframe with the completed tail in place. In the past month, we've buttoned up a lot
of the stuff in the seat and center console area, and made a lot more progress on the wings. As we progressed more
with the Zenair kit, I still have to say that this is one of the most straightforward and fastest to build kits
I've ever worked with. Coming from a traditional A&P background, I had some questions about things like Avex
rivets, but I've got to say that all my questions have been answered in the affirmative. The airplane really
is a completely worked through concept. From the plans to the methodology to the parts, the 601 works as an
entire concept, and the more we work with it, the more I appreciate this as one of the best packages in aviation.
Right now, we're working on our own highly optimized 601/Corvair cowling. Taking advantage of the Corvair's
smaller physical size, our cowling will be much sleeker than the 235 cowling. I have a lot of experience making
high end composite parts, and this does not represent a huge challenge.
The Corvair motor, at only 28" wide, will fit into a very tight cowling.
Since our cowl will be built in a female mold, we'll obviously be able to produce them for other Corvair/601
builders. They'll cost about the same as Zenair charges for the parts
they build for people who have chosen other engines. In a later installment, I'll show you exactly how the cowl
My 601 motor mounts are constructed of 4130 aircraft tubing. I weld them using a combination of Mig, Tig and
gas, where appropriate. As you can see from the photo above, they're built in a very sturdy jig. Owners of my
Corvair Conversion Manual know that many pages were devoted to an in-depth discussion of motor mount building.
The Manual contains drawings for a motor mount very similar in layout to the 601's. I'll be happy to provide any
Corvair/601 builder with the exact dimensions I used in this motor mount, provided you've purchased a
Conversion Manual from me, and returned your Manual Registration and Liability Statement for my files. Although
I'm sure most guys will want to buy a mount from us, I'm always willing to help out our customers who are real
This is a 38mm Firewall Spool for a 601.
Each motor mount contains eight spools. The spools are used where the bolts pass through the firewall, and where
the engine mounting bolts go through the tray. Each spool is made of a piece of 1/2" .058 4130 aircraft tubing
welded to an area washer. In the case of the 601, the tubes in the firewall spools are exactly 38mm long.
This allows the Zenith O-235 Dynafocal firewall mounts to be used as shown in their drawings.
The washer on the firewall spools is an extra thick, CNC hydrocut, 3/16" x 1 1/8" diameter custom job. While the
thickness may seem to be overkill, it ensures that the tube maintains its position perpendicular to the firewall
throughout the welding process. This in turn means your motor mount will be far easier to install on Zenith's
stud type mounts. The four spools that mount the motor to the tray have 1 1/8" tubes and 1 1/4" washers. I cut
the tubes to an exact length using a parting tool on my semi-automatic lathe. I weld the tubes to the washers on
a variable speed motorized turntable. The lathe-cut ends allow for accurate jigging. And the feed rate of the
motorized turntable is optimized for my 220 volt Mig welder. If you've heard that Mig welders are not used in
aircraft fabrication, you've only heard half the story. Mig welders can be used for specific parts as long as
the setup is proper, and adjustments are made to the methodology. My motor mount design takes these factors into
account, and utilizes Mig welding where appropriate. The techniques have proven themselves in static, destructive
and flight testing.
The Corvair motor is a bed mounted engine. This means that it is supported from the underside of the motor like
a six cylinder Continental or a Franklin motor. The beginning of any mount is the part that we refer to as "The
Tray." The tray is directly underneath the engine. Shown in the photo above is my tray jig. Although it's not
beautifully painted (because it's used too often), this very heavy-duty and accurate jig weighs about 50 pounds
and is immune to distortion during the welding process. The tray is about 90 percent welded in the jig to ensure
Drilling a hole in the tray while it's in the main jig.
All the separate tubes of the mount are interconnected with 5/32" drill holes. When the mount is welded, it is
air tight if it's done correctly. Without air, it will not corrode inside. Aircraft tubing is fairly oily on the
inside from the factory. The drill holes allow the tubes to be welded without "blowing out" as you try and close off
the last little bit of weld bead on a sealed tube. This effect of the expanding air in the tube bothers Tig
welders more than gas welders. If your friends haven't experienced this with a Tig welder, they're probably not
making airtight welds.
The main jig for the 601 weighs about 70 pounds. It may look a little funny, but it takes into account the
601's sloping firewall, which is why the tray appears to be angled when mounted in the jig.
No motor mount can be built more accurately than the jig from which it came. The white diagonal bracing seen on
the jig is put in place to counter stresses in the jig assembly process. My 23 years of welding experience allow me to
take a lot of subtle factors into account to produce very accurate parts.
Side view of the 601 Motor Mount.
This is a brief overview of the motor mount/cowling situation. We have a few more photos to insert here, so
check back in a week or so.