Sperry Monoplane (oz10818)

About this Plan

Sperry Monoplane. Scale model for micro-RC using a PZ brick or similar setup.

See RCGroups build thread by BlazingStar at: https://www.rcgroups.com/forums/showthread.php?2097479-Peter-Rake-18-Sperry-Monoplane

Note this plan was released into the public domain by Peter Rake, posted online at rcgroups.com/forums/showp... in September 2014.

Update 22/10/2023: Added article, thanks to hlsat.

Quote: "Peter Rake presents his pint-size Sperry Monoplane, with fullsize pull-out centre spread plans.

Since the little Eastbourne Monoplane (oz10661) feature from a few months back proved so popular, I've decided to treat you all to a similar sort of column. Instead of my usual waffle, this month's column will just be a construction article to go with the first part of the full size plan that appears elsewhere in this issue. Good or what? Not only do you get to see me writing my own column, you get a free plan to boot.

The model: Once again this is a scaled down version of an already successful design. This one, however, is intended to use a Vapor receiver 'brick', brushed motor and single cell LiPo. The plan shows a Nine Eagles motor unit, which is pretty much like many of the Parkzone units. It also shows an alternative motor plate (MM) to suit the motor I actually used in the prototype model - an AEO 7 mm unit. This proved adequate for my model, so if you opt for the larger motor you'll have no problems with regards sufficient power.

One thing that you will notice in the photos is that I used some 1/32 ribs in my wings, but the plan shows all 1/16 ribs. Similarly, my model has balsa trailing edges, but the plan shows bass. The reason for these changes is that as the tissue shrunk, my original wings buckled quite badly. They didn't just warp; they almost destroyed themselves. Ribs buckled and trailing edges actually broke in places.

Because I can't specify very hard balsa for the laser cut parts, the publisher will doubtless offer, bass is a good option for trailing edges and the thicker ribs should make your life easier all round.

At just 18 inch wingspan, you are going to need to keep the model light. Even with the replacement trailing edges (from the hardest balsa I could lay my hands on) and heavily repaired ribs, my model came out at a respectable 35.5 grams ready to fly.

Let's get building: As you can see, there really is nothing particularly complicated about the build, so I won't bore you with a 'stick A to B' style article. I'll run briefly through how the model goes together, just explaining anything I feel needs more information.

There's nothing unusual about the basic assembly. It's the usual build-over-the-plan sort of affair. You make two fuselage side frames, mark former and receiver mount positions on them and join with formers, MM and cross braces. I built in the centre section (c/s) struts as I built the side frames, but they could just as well be fitted after the sides are joined.

Worth noting here is the need to use fairly soft 1/32 sheet for the rear decking. Not only is it lighter, it will also be easier to curve over the formers without distorting the rear fuselage.

The main undercarriage (u/c) is assembled as two-ply structures, which are assembled over the plan and glued into the slots in formers F2 and F3. Since the area between these two formers is filled with 1/32 balsa, you'll also need to trim slots in that to clear the u/c legs. l like to cover this area before gluing the u/c in place; s just so much easier that way. There's absolutely nothing at all funny about trying to tissue cover around an u/c firmly glued into your fuselage.

If, like me, you opt for the AEO motor (they're cheap, and I'm very fond of cheap), position MM (the alternative one) so your prop is in the right place and glue the motor into the former. Set up thrust lines to match those shown on the plan.

After a little sanding, you'll have a completed fuselage, so now I suppose we'd better build some bits to hang onto it.

The hardest part of the tail surfaces is laminating the outlines. I like to use depron forms, pinned to the board. Then the soaked and glued strips can be held in place around them using scraps of balsa to hold them snug against the forms. Some people like use a pin 'fence' to shape around, but I find that tends to crease the wood.

Once the outlines are completely set, pin them over the plan and stick in all the little bits of balsa that are supposed to fill the gap. I usually sand then as complete tailplane/elevator and fin/rudder units before separating them. Be careful just how much you sand them. It's surprising how quickly your 1/16 tail surfaces can become 1/32 tail surfaces.

Although you can just make out some experimental fishing line hinges in the photo, I decided that wasn't very practical. I ended up using narrow strips of scuffed up floppy disc material for the hinges. I just found it a lot easier to work with than fishing line I could barely see half the time.

Okay, I can see I've run out of space again - the hazard of including a plan in the column, but we will finish this off next time. Then we'll finish building the model and take a look at tissue covering..."

Update 30/10/2023: Added article (part 2) thanks to hlsat.

Supplementary file notes

Article (parts 1 and 2).

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