Cumuless (oz8390)

 

Cumuless (oz8390) by Eric Marsden 1997 - plan thumbnail

About this Plan

Cumuless. Presented by Eric Marsden. A half-size version of Ben Shereshaw's free flight Cumulus. 48in span for .5cc - 1cc engines.

Note for the original 96 ich span Ben Shereshaw 1937 Cumulus design, see: Cumulus (oz5363).

Direct submission to Outerzone.

Update 3/6/2022: Added article, thanks to RFJ.

Quote: "A half size version of Ben Shereshaw's Cumulus free-flighter. Cumuless, by Eric Marsden.

Cumulus was one of the series of models designed by Ben Shereshaw and published in Flying Aces between 1934-39 (there may have been others after 1939 but many of us were too busy to notice - and there was some interference in cargo shipping from the US so the magazines which we found on market stalls at fourpence each tended to be in short supply!).

Cumuless is 48 inch wingspan and could be powered with any engine from .5 cc - 1 cc although I would not recommend the latter size since my model, with a DC Merlin - second hand - climbs in a very steep spiral, making a lot of height from half a cc of fuel in the hypo-barrel tank.

The fuselage is straightforward - the turtledeck sections are all circular and are decked with soft 1/16 balsa which will usually set into place dry to be held with drafting tape for gluing. My model weighs around twelve ounces and has a glide which can be disconcertingly good so that ultimate lightness may not be the most desirable thing, allowing less than contest type balsa to be used comfortably.

To make engine thrust adjustment a little easier, I mount engines on either light alloy or Paxolin plates about 1/8 - 5/32 thick, drilled and tapped for the engine fixing screws which can be trimmed flush to the underside of the plate. The plate is then fixed to the bearers with 1/2 x 4 pan-head screws, through slotted holes arranged to allow sufficient movement for side thrust adjustment.

I find large gussets placed at the handling position for launching well worthwhile as they reduce the tendency to develop saggy places caused by inadvertent thumb and finger pressure on the covering. Do fit gussets wherever you think a load path might require them - for this kind of fun-fly model, their extra weight is negligible but their improvement of longevity is valuable. Make your gussets with the grain running parallel to the hippopotamus - any load path will be diagonal to the adjacent structure and the gusset must therefore be able to cope with this - a short-grained gusset has no value at all.

For rib cutting, a 1/16 ply template fitted with spikes made by epoxying two pins into place with about 1/16 of the point protruding..."

Supplementary file notes

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Cumuless (oz8390) by Eric Marsden 1997 - model pic

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User comments

I built this one and tissue covered it with yellow tissue and dope. I had three channel in it with a small PAW diesel. I can not remember which size but the smallest in the range I recall.
All the Big boys were there at our Northern Burrows flying field in North Devon.
Not much room for a bad mistake else you are in the sea!!
The model flew sohhh well. Really docile just like me.
I loved it. But somebody loved it more.
One of our top aerobatic flyers called John came up to me one day and said" Pete I love your little plane so much...would you sell it to me complete?".
Wow!!!!!... I was bowled over that a top man would have ever been interested in such trivia built by myself.
He even congratulated me in my build standard and how light I kept it.
I was so pleased he liked it I sold it to him.
Oh yes....It had a Micron Rx in it.
The little white cube shaped Micron Rxs came in kit form.
I enjoyed electronic projects so bought six of them
Of course by todays standards they were actually huge!!!
So if you want a really good flyer. I can promise you that this little thing is a dream. It actually thermalled a bit too under quite windy conditions by the sea .
Okay Pete. You have convinced yourself... I am going to make another. Thus time even lighter with a non throttled cox 049 and smaller lighter servos for rudder and elevator.
Why are you waiting?
Peter Cane - 03/06/2022
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