Page 30 - MFW March 2024

impossible to get incidences wrong as the spine is traced 1/2inch which equates to 1.5 to 2.5 degrees with the CoG
directly off it. The frames are pure semi-circles drawn with at 55% of the wing. Barrie advised that these are realistic
a compass. Mini servos are fitted directly in the stabilizer; and Dan in the US confirmed it, so this is what I have built
not my preferred practice as even their tiny weight would to.
have an impact on balance, but I couldn’t see an
alternative, based on the shape of the stab, so leads were I took the plane, nearly completed to the Nats just for
installed at this point. display, where it got a lot of comments, mostly in the range
of “what on earth is that?”
The second side was done exactly the same as a mirror
image and the two glued together. It came out straight and After the Nats, I focused on getting the final setup done
remarkably stiff and strong. The undercarriage is a single and recently took it to the field for its first test, the results
wheel faired with blocks. The stab has small sub-fins were much as expected and there will be a process of me
which steady the model on its wheel. learning while I find out its parameters. Initial glide was ok
but ended in a stall causing only minor damage. I have
The wing is undercambered so it was built on jigs. The analysed the flight in my head over and over, especially in
plan shows ten different rib profiles, but based on the middle of the night. As can be seen in the photo, the
dimensions and spar locations, I could find use for only model attitude looks ok, at least initially. I made the
seven of them; this is what I mean when I say I have my mistake of launching slightly up, rather than downward
concerns over the plan. Though nicely draughted, I doubt which probably caused the stall. And if that wasn’t enough,
the draughtsman has built a model. I probably interfered with the elevators rather than let it do
its own thing. The repairs weren’t major and were quickly
The plan had a central main spar which means threading completed. I have had much help from Barrie Russel and
all the ribs on to the spar, placing it on the jigs and then others overseas with information and hints so I
spacing them out and gluing them. Yeah Nah! I wonder if understand the flight better, so it has promise.
Petrolia had actually designed it this way, but anyway I Subsequent test flights have continued the challenges
redesigned things with all lower surface spars to not alter and the repairs. Suffice to say it is on-going, one of the
the upper shape. It was sheeted as shown for rigidity, and challenges each time, with this very different model, is to
my other pet hate job, it is fully cap stripped, top and work out what happened, why and how to remedy it.
bottom. All five panels are true and the wing has come out
fine and nicely rigid. The upper fuselage shape is I am aware of a very small number of Cobras having been
continued over the top of the wing giving a “shoulder” built; there may be more. Ted Petrolia built two, one in
design, which is planked like the rest of the fuselage. I 1948-50 and a second, judging from the photos, very
should have weighed the bare frame, but omitted to do slightly different, in the 1990s. There are photos of another
that. one, I think in the States, it has a different colour scheme to
Petrolia’s second one. My post on FB elicited a response
The frame picture clearly shows the locations for the which indicates another one nearly complete in South
rudders/elevators which is why the servos are mounted in Africa. Many people seemed to be aware of the design,
the outer panels of the stabilizer. The stab is a lifting but modellers mostly seem to have avoided it. While
section with flat bottom so because of its size, essentially Barrie’s initial reaction was that it is “ugly” he came back
the plane is a tandem wing which makes the trimming and said it grows on you, yes it does. What it is; is different!
unusual, at least it is to me. Incidence is given as 3/8 to

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