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Post  batjac Sun Oct 15, 2023 9:59 pm

At the annual control line contest at Reeves field last month, a young boy and an elderly visitor showed up at the contest, but when there was a lull in the competition flying I realized that there was not a club trainer that we could have used to put the youngster or the retread up in in the circle.  I talked to a couple of other club members and they agreed we could use a club trainer.

I also realized that it’s been a few years since I built a Ringmaster for the annual Fly-A-Thon.  So I figured I’d kill two birds with one trainer.  The other two club members said that a C.G. L’il Wizard would be good, but it gets pretty windy around here.  I thought a .15 sized plane would make for a better trainer in the variable winds at the field.  I also thought that a slab wing would be better than a built up wing.  So, thinking on it for a little while, I decided on a Pat King Ringmaster Jr. Trainer.  Pat King sells kits for all his plans, but he also will sell a .pdf file of any of his planes for $5.  I contacted him and got a .pdf of the plane and looked them over.  Now, I am congenitally incapable of building anything exactly per the plans.  But, since this was to be a club plane and not my own, I resisted.  The only changes I made were to install a bass wood strip along the leading edge of the wing for prang protection, use a hardwood dowel insert in the wing for the bellcrank, and a wire skid at the back.  I also tapered the top and bottom rear of the wing rather than leaving it square.

I won’t do a build thread because this is basically just a Beginner’s Ringmaster, just .15 sized.  I built it for a Medallion .15 engine, being a Cox Fanboy.  I just used an aftermarket head that uses standard glow plugs, as I’m the only Cox fanatic in the club, and the only one likely to have a precious .15 glow head.  Everyone has a standard glow plug in their flight box if one burns out.

My new PDK RM Jr. Trainer 20231005-110943
My new PDK RM Jr. Trainer 20231015-152737

The only things I’ll talk about are a couple of things that I’ve found out over the years when building sheet wing planes.  When I used to cut out the wing slots for slab wing planes I’d invariably cut the slot with a slant.  So I’d end up doing a lot of sanding to get the slot right.  It never seemed to be right and the slot would always be too large for a tight fit.  One day I had an epiphany.   I realized that my tee sander would be perfect for the job, using the leg I’d normally hold in my fingers as a guide.  I just turn the sander 90 degrees and sanded the slot perfectly.

My new PDK RM Jr. Trainer 20231003-123312
My new PDK RM Jr. Trainer 20231003-123303

The other thing I learned the hard way is to cut out the wing slot and engine bearer slots before cutting out the rest of the fuselage shape.  If you cut the fuselage blank before you cut the slot and sand it to shape, you can put too much pressure while holding the top and bottom of the fuselage blank and crack the fuse below the wing cutout.

My new PDK RM Jr. Trainer 20231003-123122

The Instructor Mark
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Post  Mike1484 Mon Oct 16, 2023 6:16 am

Good ideas Mark, and the plane looks really sharp!
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Post  andrew Mon Oct 16, 2023 8:51 am

The plane looks really good, Mark. Super job.

I can think of all kinds of ways to use your sander idea -- getting a perfect 90° angle has a lot of applications. Thanks for sharing.
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