Bob Jennings 1 Posted July 28, 2019 Share Posted July 28, 2019 I've been talking about building my own Nimrod for a while now. About 2 years and its taken 12 to finally get a plan together. So now it's drawn up, here we go! It's very much a prototype test, so bear with me as I work stuff out and tweak the plan as I go. The model is designed to break down so I can get it in my car without too much hassle. The nose and tail section are separate, locking into the centre section. The wings, plus nacelles, are a slide fit and it should all come in around 14-16 pounds at 2.66m span. First job... cut some formers. Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted July 28, 2019 Share Posted July 28, 2019 Subscribed Bob! Great to see you on here showing us how its done - your Nimrod will be a winner off the slope! Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted July 28, 2019 Author Share Posted July 28, 2019 I decided to build the nose section first to get to grips with a working method. I'm mixing planking and foam sculpting to bet some of the curves right. It all starts with a keel and split formers as shown here. Making sure they are vertical. Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted July 29, 2019 Author Share Posted July 29, 2019 It all goes together pretty easily and it starts to take shape really quickly. Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted July 29, 2019 Author Share Posted July 29, 2019 Added a plate to take equipment and support the formers which accept the tubes that hold the nose to the centre section. Somewhere along the line I missed with the stringer placement! The planking will add a lot of strength to the structure Quote Link to comment Share on other sites More sharing options...
Alan Gorham_ Posted July 29, 2019 Share Posted July 29, 2019 Go Bob! Beautiful aircraft, will enjoy watching this come together. Phil likes it so much he had to say it three times! Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted July 29, 2019 Share Posted July 29, 2019 Great shape Bob, and a good size too. Ready for October then? Quote Link to comment Share on other sites More sharing options...
Martin Gay Posted July 29, 2019 Share Posted July 29, 2019 That would be finished just in time to take part in the 2020 Mass Build! Quote Link to comment Share on other sites More sharing options...
Harry Twist Posted July 29, 2019 Share Posted July 29, 2019 Looking good Bob! Looking forwards to seeing this one come to life! Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted July 30, 2019 Author Share Posted July 30, 2019 Martin, I'll probably use the Mass build as a 'breather' to assess the complex centre section of the Nimrod once I have the wings ready. Quote Link to comment Share on other sites More sharing options...
Martin Gay Posted July 30, 2019 Share Posted July 30, 2019 If you need any parts CNC cut, closer to the end of the year, I may be able to help you out! We can chat about it over the weekend, if you are going to the Orme. Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted July 30, 2019 Author Share Posted July 30, 2019 Planking continues apace as you'll see I need to invest in some more modelling pins! I'm always amazed the extent ammonia will allow me to torture balsa wood into shape. The skin in this section is 1/8" Planking 'best practice' is to chamfer the edges. Later you'll see how this can be really useful in tight spots. Here, the juncture between curves needs tackling first with some tailored, chamfered balsa strips. Those spruce stringers tie the formers in nicely resisting any twist. There's a lot of pressure on some of those clamps. My entire stash of pins was employed to tackle this! Work stopped... Once dry, I could tackle some of the lovely curved panels on the roof. See how the grain points across the formers at an angle, not straight down the spine. This allows the balsa to follow the curve nicely. The overlapping edge can then be trimmed to accept the next panel. This is the opposite side. Edited By Bob Jennings 1 on 30/07/2019 11:42:32 Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted July 30, 2019 Author Share Posted July 30, 2019 Getting there with the underside This is one of those tight spaces I was talking about. Chamfered edges and a tailored piece that bends the correct way needs to fit here. Here, the edge is chamfered under the next panel Presenting a rough piece, marking it up (measuring twice) and cutting slivers off at near enough the correct chamfer angle. Applying pressure across a spare piece of balsa uses fewer pins in this case And its really starting to look like a Nimrod. Edited By Bob Jennings 1 on 30/07/2019 11:59:48 Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted July 30, 2019 Author Share Posted July 30, 2019 A better shot of the chamfer holding the edge in place, no glue. Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted August 7, 2019 Author Share Posted August 7, 2019 It's been a while since the last post. More glueing and pinning to get the Nose section to a near enough state prior to starting the tail section. I want to get all the big bits done together and then glass the whole lot once i'm sure the fuselage will fit together. I'm leaving the structure open here so I have access to the formers when I install the bracing tubes across the holes you can see inside. Just got to ammonia some more balsa to fit the upper cockpit area. It may need a sub-former the support the curve. Another addition to the plan! Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted August 7, 2019 Share Posted August 7, 2019 She's taking shape Bob Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted August 7, 2019 Share Posted August 7, 2019 Very nice Bob - capturing the complex curves very nicely there! Quote Link to comment Share on other sites More sharing options...
chris Ibbotson Posted August 7, 2019 Share Posted August 7, 2019 Bob, I'm following your build with interest. I have never heard of using ammonia to assist in bending balsa. Can you explain how you use it please. Thanks' Chris Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted August 7, 2019 Author Share Posted August 7, 2019 Hi Chris, it’s really simple. I’d wear a mask and gloves... brush ammonia onto the balsa, leave it for 10 minutes and you’ll see how pliable the wood fibres become. The bending can be enhanced by carefully assessing the best grain direction. Hold the piece in place until the balsa dries and it will have ‘set’ in shape. An additional coat of ammonia will allow further distortion. It is amazing how the balsa returns to its original rigidity once the ammonia has evaporated off. Try it, it saves hours of planking. Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted August 8, 2019 Author Share Posted August 8, 2019 I should also add that both sides of the balsa need a good wetting, especially if it’s thicker than 1/8”. I did manage to make a rolled tube from 1/8 balsa, so it’s a versatile method for creating complex shapes. Edited By Bob Jennings 1 on 08/08/2019 00:04:37 Quote Link to comment Share on other sites More sharing options...
Martin Gay Posted August 8, 2019 Share Posted August 8, 2019 Chris, I used a 10% ammonia/warm water mix and totally immersed the balsa in the fluid for about 15 minutes. The balsa was then strapped/banded/taped to a shaped foam block. After 24 hours of drying the balsa has adopted the required shape. The photo below is a 1/8" balsa shell for a Hind helicopter that I did many years ago: Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted August 13, 2019 Author Share Posted August 13, 2019 Nice one Martin. That's truly amazing! Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted August 13, 2019 Author Share Posted August 13, 2019 I hit a profile snag on the nose, so I'm leaving it to germinate! The tail section is next and the formers essentially create a cone that needs reinforcement for the tailplane. There also needs to be access for the elevator linkages as the tail is a slide fit in two sections with the strakes added as flexible plasticard. That MAD* boom needs to be as light as humanly possible, way out at the back! (*Magnetic Anomaly Detector) Quote Link to comment Share on other sites More sharing options...
Bob Jennings 1 Posted August 13, 2019 Author Share Posted August 13, 2019 I seemed to get carried away and Here the topcracked on attaching the tail end formers to the balsa spine without taking any photos! Here the upper skin has been attached with the stringers in place. I reduced the skin thickness to 3/32 in the hope that it will keep the weight down... It certainly bends better. No ammonia used here. The back end is open so I can install some reinforcement for the tailplane seat and rods. Used most of my pins and found my stash of binder clips! This is by no means an easy build. The structure is a beautiful shape, but there's so much to think of that I hadn't considered on my very 'general arrangement' plan. The tail section may well be the first section completed with servos, wiring and flying surfaces attached. More later. Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted August 13, 2019 Share Posted August 13, 2019 3/32" is my favourite size for planking and sheeting Getting her done mate, great to see! Quote Link to comment Share on other sites More sharing options...
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