Ben Shereshaw's "Cumulus"

Every year our club - Arvada Associated Modelers (AAM) holds a vintage fun-fly event. I've always had a love for the older designs so this year I wanted to add a real classic old-timer to my hanger. The rules state that the design had to be published or kited before 1942 so I started looking for something that would win the LMR (limited motor run) "climb and glide" event but was also a real looker. After months of searching on line, I cam across a photo of an airplane called the "Cumulus" that was built by Alan Knox from New Zealand. He did a beautiful with a slightly smaller version and was getting very good contest results. I was hooked! The Cumulus was first published in October, 1938 in Flying Aces magazine (see a copy of the original article here: Oct 1938 Flying Aces Article PDF) so I started looking for a short kit or at least a set of full sized plans. I was able to find a "cutting" of the flat wood (ribs, fuselage formers and such) from Klarich Kits for the original size of 96" (8') wing span. I had a few other projects to finish up, but I was able to start on it in May for a contest date on Aug 12th.

 

The construction is a little "old-school" as you might imagine with lots of stick wood and rounded wing top sheeting. Since the original was designed for free-flight, I had to make several modifications for RC-assist (rudder, elevator, and throttle) and also for the electric power plant replacing the gas engine. I defined and built in hinge lines for the elevator and rudder and blocked in the nose a bit. All control surfaces are pull-pull for weight and great looks. I did try to stay as close to the original build style and materials and I actually used less than more in several places. The plans that shipped with the cutting were not very accurate and contained several mistakes and omissions. Those sorts of things can really slow you down, but I plugged through and I believe it turned out quite well. It is covered in SolarTex which is a pre-painted iron fabric from England. It is great stuff to work with and not as heavy as folks think. It also takes paint well and I decided to paint the trim with my newfangled airbrush. That was a really fun process and a million times better and easier than spray cans - what control! I even found a set of authentic "Trexler" pneumatic wheels! They were brand new in 1938...

 

So, how does it fly? Like it is filled with helium! Ben said "you'll have to shoot that thing down with that airfoil!" and he is right. It is quite majestic and graceful in the air with plenty of control. The power is good, but I will be increasing from 400W to 500W with a new lighter battery to get even better performance. The glide is very slow and it reacts to the slightest lift like a big sailplane. And, about the contest... The Cumulus took first place in the LMR climb and glide and took first place in the Concours contest for the model that best embodies the Old-Timer look and feel. She "maxed out" (more than five minutes in the air) after a 30sec climb three times in four flights. Her first flight was only four minutes and eight seconds due to her pilot flubbing up the last bit of the climb. She made up for that with room to spare!

 

If you are interested in an old timer with that classic 30' racer styling then consider building a Cumulus. It is beautiful, strong and a fantastic flyer!

 

There is a build log here: Build Log on RCGroups

 

Check out a cool video of the Cumulus doin' her thing here: Cumulus at AAM 2009 Vintage Event

 

Specs are as follows:

Below are some photos: