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Re: Nimbus 4D - 7 metre

Posted: 24 Jan 2020, 20:52
by Peter Balcombe
SP250 wrote:
24 Jan 2020, 20:31

How about leaving the nose release as is.
Fit the two 2600mAh batteries in the nose wired in series, put another 5200mAh (or 2 more 2600's) battery/s close behind them (it'll still be in front of the CG.
The TEC probe for the vario energy compensation 90% of the way up the fin, where the full size one is?
Bernie Jones does the small bore tubing for connecting to the vario or you could use compressed air U/C retract tubing.

John M
Do you mean two 2600mAh batteries in parallel?

Re: Nimbus 4D - 7 metre

Posted: 24 Jan 2020, 21:18
by SP250
Yes Peter I do - well spotted (its been a long week)!

Re: Nimbus 4D - 7 metre

Posted: 24 Jan 2020, 23:11
by RobbieB
No longer than last week John............................

Re: Nimbus 4D - 7 metre

Posted: 25 Jan 2020, 00:40
by SP250
Its all relative Robbie.................

Re: Nimbus 4D - 7 metre

Posted: 26 Jan 2020, 11:16
by harry curzon
You're a tough audience...... but you're right. I have left the original towhook and servo mount in place and am working on other ways to install the batteries and pitot. The batteries are more important to me than the pitot, as the 2600s will be in my K-18 and I want the 5200s in this Nimbus but for the moment I have gone ahead with installing the pitot in the fin. Options are very limited as near the top of the fin is a wall to wall thin glassfibre "floor" which acts as the elevator servo mount and the only access to the fin is the small space between that and the top of the fin. So, that's where the pitot has to fit and has to be pushed well out so that its two air tubes at the back do not collide with the elevator servo.

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The distance from the pitot to the receiver is 1.9metres, so do I put the pressure sensor beside the pitot with short air tubes and a long electrical data wire to the Rx, or fit the sensor near the Rx and extend the air tubes all that way? Advice I received is to extend the air tubes which I did with Robart 1/16" i.d. air tube. In order to avoid any sharp change of direction and possible kinking of the air tubes I have routed them past the servo and then down the fin through a hole in the servo mount plate. To avoid the thin gf plate from chafing and cutting the tube I drill the hole larger than required and glue on a piece of 1/8" wood with the correct size of hole cut in it and countersunk - this acts like a grommet, protecting the tube. To keep the tube well controlled and away from the servo I glued a tube tidy to the side of the fin, it is meant for 3mm air tube and this tube is slightly loose in it so I glued on a piece of balsa over the top to keep the tubes in.

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Then the real frustration started, as I could not get the pull through to turn from the fin into the fuselage and drop forward. it took me a long time to realise that there is another gf floor at the base of the fin. It has a tiny hole in it near the front for the elevator servo wire, how that was ever installed I do not know. The only access to this "floor" is from a small opening at the bottom rear of the fuselage underneath the fin post, so I had to drill a hole almost right at the back and again install a wooden "grommet". Then by taping the tubes to a length of thin piano wire I was able to route them from the top of the fin down into the fuz, and pull out the piano wire. At last I could attach a small weight and drop the tubes all the way down to the front of the fuselage to where the Rx will be. Plugging the tubes into the sensor and blowing gently on the pitot showed an airspeed registering on the transmitter so that system is now ready for final installation of the radio.

Re: Nimbus 4D - 7 metre

Posted: 27 Jan 2020, 13:41
by harry curzon
Back to the underside of the wings, iirc Paul had used poly-c varnish to attach the glass cloth which was fine when covered with vinyl but not good for painting. A trial with a thick coat of two-pack filler primer could not fill the weave of the cloth, but even the grain of the veneer was showing through the cloth into the primer! I put on a coat of finishing epoxy (from Fighteraces, best one of a few brands that I have tried using over many years) and after it was cured I wet sanded it down smooth. I spray on a dusting of cheap grey primer before sanding epoxy coats, then I can see what areas have and have not been sanded, and little spots of grey sitting down in the low points shows areas that still need sanding until all the grey has been removed.

After cleaning up the mess, I gave the wings a thorough wash with panel wipe (also known as pre-paint) and set them out for priming. I wipe over with a fresh tack cloth immediately before spraying. My first choice of paint is always Klass-Kote 2-pack epoxy, it is a paint that I get on well with and have been using since it was first imported into Britain about 15 years ago. My favourite primer is white with the "fast white" catalyst and I am applying it with a mini-HVLP gun with a 0.8mm needle and 2 bar pressure. A very thin coat so that it is minimum possible weight, not enough to be opaque but enough to even out the colour for the top coat.

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The mix ratio is 1:1 volume which I measure by syringes. Many years ago I had terrible trouble with fish-eye contamination on a paint job, which I had to strip off and clean several times, I degreased everything over and over but the fish-eye kept occurring. Eventually I realised that the rubber plunger in syringes has a tiny bit of lubricant on it which I cleaned off with soapy water and the problem was cured. To make life easier I now use special syringes with no rubber and no lubricant and these are also much in use for injecting Hysol or other epoxies around fillets, or with extra nozzles to get all sorts of glues into tight spots etc.

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One of the primed wing panels

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Re: Nimbus 4D - 7 metre

Posted: 28 Jan 2020, 09:22
by harry curzon
While the primer on the wing cures, back to the fuselage and I can start work on the cockpit and the radio installation.

This may be sacrilege to some of you, but I am just not into scale cockpits and dolls, especially when the dolls cost a 3 figure sum of money. My aim is that the model looks real if someone takes a photo of it in flight, so it needs someone in the cockpit, but going beyond that does not excite me enough to justify much work or cost. I appreciate the beautiful work and lots of details that some people add, it just doesn't fire me up enough for me to put the effort in.

The model came with a cockpit tub, two instrument binnacles, and two seat backs. To that I will add just one pilot, in the front seat, and I have got a head and body kit from "scale-me-down". Scale-me-down attend some of the model shows where they take a laser scan of your head and can then 3D print you at any scale required, I already have mini-me in my Pilatus B4 and ASK-18, so I have bought another mini-me for the Nimbus.

The cockpit tub is a single gf moulding, covering the entire length of the canopy opening. It has been painted with stone effect paint, I might try stripping that off. I cannot find any decent on-line photos of full-size Nimbus cockpits and am not sure that they would have a separate inner skin as implied by this tub - why add weight for cosmetic reasons? The fuselage has 4 mounting flanges, each with a nut on the underside, but the tub has no corresponding holes for bolts. Before I go chopping up the tub I thought it would be a good idea to get the locations for the bolt holes in the tub. I put a bolt through the nut in each flange but from the underneath, protruding a couple of mm above the flange, put a drop of white paint on the tip of the bolt, then put the tub down into position so the paint transferred to the tub and marked the required location for the holes, which I then drilled.

The tub blocks all possible access to the radio, switches etc., plus it leaves too thin a space between it and the fuselage to fit some of the radio and plugs. My plan therefore is to separate it into front and rear sections with a few inches of what is basically the back seater's foot well removed altogether. I will have to remove the pilot, front instrument binnacle and front tub to get the front battery in and out, but during a flying day I will have access to the switches in that gap in the middle and there is no depth limit for fitting some of the radio equipment in the gap.

The tub in place
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Bolts installed from underneath to mark the tub
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the underneath of the tub with the 4 white paint dots showing location for drilling the holes
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Re: Nimbus 4D - 7 metre

Posted: 29 Jan 2020, 12:28
by harry curzon
I cut out this section of the cockpit tub and then put a coat of a mild paint remover on the stone effect paint on the inside, but that only partly removed it so I applied another coat and left it overnight.
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I can get one of the 5200mAh batteries plus a little mount for it, sideways in the nose where the front seater's feet would be, immediately in front of the tub and the nosewheel cover. I made the mount from 1/8" ply with velcro straps epoxied to the underside and a piece of non-slip mat cyanoed on the top, then the assembly was glued to the fuz with Hysol.
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I 3D printed mounts for the satellite receivers, drawing obtained from thingiverse website.
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To locate the ends of aerials, I cyano a bit of plastic tube to a section of wooden coffee stirrer (free at your fav coffee shop!!) and that bit of wood is then easy to stick to any material, I find a dab of Zap-Goo is excellent for a quick stick to an uneven surface such as the inside of a glassfibre fuz
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Re: Nimbus 4D - 7 metre

Posted: 30 Jan 2020, 15:49
by harry curzon
I have now completed the fuselage radio installation and wiring, only the wiring in the wings remains which will be done after painting.
I need extension leads between the Jeti distribution box (a Central Box 200) and the two batteries. Jeti CBs use Mpx sockets. When I make leads with Mpx plugs I add on the plastic insulation grip, made with a hot melt glue gun and a Winkler mould (available for several plug types, from esoaringadgets and others).
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Each wing has 4 servos so I would like to connect them using a 12 pin Ashlok but the hole in the fuselage is a reinforced square not long enough for a 12 pin plug to pass through and I do not want to enlarge it so I am using 2 x 6 pin Ashloks on each side. I fit them as 1 male and 1 female so that when connecting the wing there is no doubt that the correct pairs are connected with no need to mark which is which.
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Re: Nimbus 4D - 7 metre

Posted: 31 Jan 2020, 11:58
by harry curzon
I have applied the colour coats to the underside of the wing and am not happy with the result, but will just learn to live with it.

I chose to put indigo blue on the inner panels and fluorescent orange on the outer panels. It will not win any awards for aesthetics but all I am concerned about is visibility of the relatively very narrow chord wing at the distances that I hope to be able to use this large model. I would not have predicted that fluoro orange would work on the unlit underside of the wing, but I tried it on my 2.6 metre Mpx Cularis and it does work, showing up at the model's max distance in any conditions.

Applying the colour coat shortly after the primer was not an option so I left it for a few days to thoroughly cure then scrubbed it with a 3M grey pad to break the skin and key the surface. Paints used are Klass Kote indigo blue with gloss catalyst applied as per the primer with mini-HVLP gun 0.8mm needle at 2 bar, and an aerosol can of fluoro orange.
The problem is a very large number of pinholes which are extremely visible due to the contrast of white primer and dark blue top coat. Had I used grey primer or white top coat they would be pretty invisible. The coat of epoxy that I applied just could not cope with the huge number of deep holes through the cloth into the pores of the veneer that the acrylic lacquer leaves. If I had used a grey primer I would have seen them and dealt with them before applying the colour coat, but they just don't show up against a thin translucent coat of white primer.

The ailerons and flaps which I glassed from bare wood have no pinholes as the epoxy resin fills everything first time round so they look perfect.

It would not be unusual to get 2 or 3 pinholes if I had glassed the wing from scratch, so in hindsight it would always have been a better decision to use a grey primer on the panels that I intended to paint dark blue, as the grey is much better at showing up problems to be dealt with before the colour coat, and any that are missed are not so glaringly obvious due to less colour contrast. Live and learn!