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Bob's PSS Nimrod MRA4


Bob Jennings 1
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  • 3 weeks later...

Tail end halves coming together. Squaring up the formers and fixing in place.

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Checking it's all true, up and down. Fin core is polystyrene.

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Spruce stringer in place. I decided to cut the stringer notches after laying the stringer in place and marking before using a square file to create the notch inside the pen lines.

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The formers are thick enough to butt up adjacent panels. A bit of relieving is usually needed to get a nice tidy fit.

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Back end space for the tailplane assembly.

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Closing up the bottom section to add some stiffness.

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Now... I had an utter mare with the nose section and to make it right required some surgery to my beautiful planking. Lesson learnt and I need to re-draw the formers on my plan at some point.

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It was emotional taking a saw to it. But I'm glad I did. Meanwhile, the wings arrived! Happy day.

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Just need the centre section building now. All the flappy bits in the wing need making up plus the nacelles and tippy bits. The tailplane needs jigging and fairing into the back end. Lots still to do.

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Wings are a good size.

Getting down to business with the twin bowden cable outers for the elevator.

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I used some of the lightening holes to support the cable runs.

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Once they had been thinned down.

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The MAD boom sorted. Balsa formers and solid blue foam wrapped with brown paper and PVA. Incredibly light. I thought spiral wrapping the paper might add some structural integrity. As if it needed it!

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The tailplane needs to have a secure fixing so I'm fashioning these stress plate sandwiches to enclose the tubes to allow the tailplane halves to slide on. It will make sense later. The idea is to set the dihedral and incidence with these plates in the fuselage.

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A bit of tail fin detail.

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Fin skins, chamfered at the trailing edge to allow a shrouded rudder housing.

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Fin skins, chamfered at the trailing edge to allow a shrouded rudder housing.

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All glued up and clamped.

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Progress shot.

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And the rudder. Trying a balsa and 1/32' ply structure. It won't need glassing just primer and paint. Not sure if I'll save any weight, but you have to try these things. It will be stiff though.

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Making sure to take photos sometimes slips my mind, there's so much to do but I'll keep shooting the key bits.

Thats it for now.

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I do use sanding sealer made from celly dope and talc when I'm building a model I'm covering with tissue so I'm not totally against it, I just find it takes a few coats to really seal the grain and even on a close grained thin ply, I still think epoxy will do it all in one coat and smell less.

I don't find WBPU a very good grain filler. I've seen people use 6 or 7 coats just because it dries quickly but I am not a fan

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  • 1 month later...

Okay, where were we? Oh yes, finishing off the season on top of the Great Orme! What a brilliant day. Very busy!

The 'rod has cracked on apace.

I had the rather tricky task of how to fit the tailplanes in a fashion that was detachable... the principle is easy to imagine. Transferring the loads to the rest of the airframe caused some head sctatching.

The tail planes are at a 6 degree dihedral each side and at a negative incidence of 1 degree. This was set without the tailplane on the fuselage by angling some stress plates with some insert jigs at the correct dihedral and raising the aft jig by 1 degree to the datum. The design of the stress plates, mounted in the correct orientations allows the tailplanes to simply slide on!

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Measuring the torque rods for the elevators, driven by dual Bowden cables, will allow me to close up the rear fuselage ready for glass. Then it's a case of attaching the linkages and fairing over this rear section with the detachable tail boom.
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A bit out of sequence, this is how I glued the tailplane tips with gorilla glue...

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... with holes in a ply plate to let the glue flow through to the balsa. This was shaped to section once it cured

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Centre section next!

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With quite a few formers in the centre section and the alignment of the nose mounting tubes to consider, I did a dry fit of the central core structure that everything hangs off.

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Phenolic wing spar tube is 38mm diameter.

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Happy that everything was pretty darned square, the glue and angle section balsa tied it all together.

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Creative use of clamps squares and elastic bands kept everything straight at the front end.

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  • 2 years later...

Well, it's been a long time since the last post and there has been some development!
Here's a photo update.
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Wings were cut by Phil at Cloud Models. And a grand job he did too.

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Filling in the space for the wing root adjacent to the flaps

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Wings are taking shape here with the huge built up surfaces all with recessed Robart hinges

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Starboard side root


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Positioning the nacelles and exhaust pipes

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Intakes starting to take shape


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Using up some old packing foam

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Helping the shape and firming up the foam with some Polyfilla Onefill.

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Agricultural means of ensuring a good Gorilla glue bond!

 

Back to the main fus

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Making up the fuselage wing for fairing

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Overall fuselage taking up a lot of space in the shed!

 

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Large builds seem to require a lot of holding devices. This is about a quarter of my clampage stock!
 

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Edited by Bob Jennings 1
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