Scale Soaring UK

This is from the Mike Trew plan, a 1/5 scale 118" span model of the French 50's sailplane and, apart from an aborted similar scale Minimoa from many years ago, will be my first scale glider traditional build.

The plan has been acquired from Sarik and extensively studied in order to formulate a build method, materials needed and what changes to Mike Trew's original design may be desirable. First decision was to go with a different wing section and a PDF file was kindly supplied by Peter Balcombe with the HQ rib profiles, so I should end up with a more versatile model. The pushrod activating the ruddervators will be dropped in favour of mini/micro servos, the ailerons and brakes will be wing mounted servos.

Decisions still to be made:
Colour scheme: although this can wait until later it will have some bearing on how I cover/finish the model. At the moment I'm leaning towards glassing the fuselage and filming the wings/tail surfaces.

Wing joiner: the plan shows a traditional brass box/steel blade arrangement, I will probably go with this as I can get the parts and it's what I'm familiar with.

Brakes: I probably won't do the scale blades (scale police look away now), they look like a lot of work that could be easily wiped away on a slope side landing so will either go commercial or "barn door" type diy.

I intend to fit a tow release and instead of balsa I will manufacture the nose from car body filler, this will add a lot of ding resistance and weight where it's needed.

The back end is known to be vulnerable so needs beefing up, first thought on this would be to replace the 1/8" x 1/8" top spruce longeron with a 1/8" x 1/4". Any ideas on this would be welcome! The wood is on it's way from SLEC and today I made this: 2 metres long so should be future proof

All being well I can make a start on cutting out parts next week ...............

Good work Stephen.
You went for the Bridson jig after all then

Thank you Peter, yes it made sense - re-usable/adjustable and super accurate, what a clever idea and I'm looking forward to it's maiden build!

Stephen,
Hope I’m not teaching you how to suck eggs, but:
Mark a fuselage datum line on all formers once cut & use your jig to hold each former at correct height & station via uprights on your jig brackets - datum marks should all be a the same height on each side of the Fuz.
You will be able to check fuselage straightness by eyeing from front along top spine slot to check everything stays in line.
Probably a good idea to add longerons on each side in left/right pairs to even out bending/twisting forces (steam longerons if necessary).
Once top half of the fuselage is planked, it should be rigid enough to hold its shape once taken off the jig in order to do the lower half.
Peter

Thanks Peter, I'm eager and grateful for any advice I can get as this is my first "jig" build. What are your thoughts re. increasing the depth of the top longeron to strengthen the rear of the fus (I'm mindful of previous comments regarding the weakness in this area)?

Stephen,
I will have a look at the plan, but from what I remember, the main issue around the rear of the fuselage is that given that there are two largish holes in the fuselage planking where the tailplanes fit in, there isn’t much to prevent the fuselage failing at the point immediately in front of the tailplanes.
Given that you are not planning to need ruddervator pushrods going through this area - just two servo cables, I would suggest some internal strengthening (without adding much weight) from say the former in front of the one where the tailplane LE connects, to the rear former (where the rear of the tailplanes are secured).
(I made the rearmost former (or certainly reinforced it) with a former made from 1/16” thick epoxy board, particularly as it had the screw threads poking out of it to secure the tailplane halves)
I found that if the model went over onto its back for any reason, the fuselage broke off just in front of the tailplanes!

I am glad to see you have made a start Stephen. I am also glad to see you have made a "Robbie Jig". I made one many years ago and have used it to build at least 5 very straight gliders since then. I will watch your build with interest.
Brian.

A large stock of wood arrived from SLEC a few days ago leaving me little excuse not to get started. The jig is fully up and running with former supports now added:
First job was to christen the Dremel and make a start on the forward 3mm ply formers, I soon realised that this wasn't going to be a quick job with the fuselage being round, not to mention the constant in/out of the Dremel blade (which is a fiddle) to facilitate cutting inside:
After the 3mm formers are complete I then have to cut the rear formers from 1/16" ply and laminate to 1/16" balsa, at that point I should be able to start jigging up and getting the glue out.

Apologies for off topic - nice to see the Moulton in the workshop

paulj wrote: ↑31 Jan 2019, 18:30 Apologies for off topic - nice to see the Moulton in the workshop

Well spotted! There's also a TSR30 hanging just above the TSR27.