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G-JIMG08/04/2020 12:48:22
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145 forum posts
108 photos

Managed to fit the first set of undercarriage doors. I have no idea how to upload videos, or even if it can be done, so you'll have to make do with a few sequence photos smiley.

The doors are mounted using a length of piano hinge. The spring between the two doors is reasonably weak. It serves two purposes; it keeps the doors apart and aligned when they are open and pulls the doors closed when the retracted oleo leg pushes down on it.

uc doors closed.jpg

uc start travel.jpg

uc half travel.jpg

uc nearly extended.jpg

uc extended.jpg

Jim.

G-JIMG09/04/2020 15:44:53
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145 forum posts
108 photos

I tend to apply the fibre glass covering quite early in the build, I find it prevents all but the very worst "hangar rash".

There are countless ways of applying the covering; here's what works for me:

For small parts I use Z-Poxy resin as it's easy to mix small quantities. For larger areas, such as wings and fuselage, I use West Systems resin. In both cases I mix the resin according to the manufacturer's instructions and then I add slightly less (~75%) than an equal amount of Meths.

resin.jpg

The West System pumps are a worthwhile investment as they dispense the correct amount every time. The wooden stirrer is courtesy of McDonalds (their sauce cups are excellent for mixing small quantities of glue, etc.) and the plastic card is a hotel key card (I always keep them, they have so many uses in the modelling world). The brush is a cheap amazon throwaway.

When mixing the resin I find the Meths initially makes the mixture go a light purple colour, slowly changing to a milky white, before finally returning to the original resin colour. At this point you know it's fully mixed.

I place the pre-cut cloth over the area to be covered and brush on the resin. Being 'watered down' by the Meths it is very easy to apply. Once the cloth is fully applied I VERY gently draw the plastic card over it. The idea is to remove the surplus resin without disturbing, or dragging the threads of, the cloth. This also removes any small air bubbles under the cloth.

Once fully dry (overnight) I remove any excess cloth by running a very fine glass paper along the edge. You could use a very sharp blade but I find the glass paper works best for me.

covered wing.jpg

Jim.

G-JIMG10/04/2020 12:36:40
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145 forum posts
108 photos

The real aircraft has winglets, so I have reproduced them by gluing two pieces of balsa together with araldite and with three toothpicks inserted vertically for additional strength.

Once the glue had set I shaped the winglet and hollowed out the wing tip as much as possible, leaving enough balsa to support the Nav Light bulbs.

wing tip side.jpg

wing tip rear.jpg

Jim.

cymaz10/04/2020 14:43:20
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9197 forum posts
1186 photos

Can you stretch the cloth over compound curves or is that the wrong technique

G-JIMG10/04/2020 16:03:41
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145 forum posts
108 photos
Posted by cymaz on 10/04/2020 14:43:20:

Can you stretch the cloth over compound curves or is that the wrong technique

The cloth is extremely light, a square yard weighs less than 1/2oz, so it follows most curves without the need to cut it. In the event a ridge forms that will not smooth out with a little pressure it's simply a matter of cutting along the centre of the ridge and smoothing both edges down with the brush. The fact they overlap is not an issue, as the cloth is so fine the layers blend in to each other without leaving a ridge.

Jim.

G-JIMG11/04/2020 12:49:20
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145 forum posts
108 photos

Made a start on the empennage today.

The horizontal stabiliser is aerodynamically shaped, much like the wing, so is built in the same way. The ribs were cut on the CNC machine and assembled over the plan in the traditional way.

50 horizontal stab.jpg

I also used the CNC machine to produce the Radome parts. The max cutting depth of the CNC machine meant the Radome had to be made in 4 sections, glued together to give the basic shape, and finally sanded to match the drawings. Building it in sections had the advantage that I could cut internal ducts for the Strobe and Tail Light wiring.

53b tail radome.jpg

Jim.

G-JIMG12/04/2020 12:28:16
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145 forum posts
108 photos

Managed a bit more on the horizontal tail assembly.

Applied the balsa skin and manufactured the elevators.

54 horizontal stabiliser.jpg

Lightly clamped the assembly in a vice so I could test if the snake operated the elevator as planned. Again, I can't upload a video so pictures will have to do.

Elevator at Neutral:

elevator normal.jpg

Elevator fully Down:

elevator down.jpg

Elevator fully UP:

elevator up.jpg

Jim.

G-JIMG12/04/2020 12:41:49
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145 forum posts
108 photos

Apologies, I forgot I had taken a picture of the elevator linkage.

The central curved part is double sided PCB board, securely attached to the elevator rod. The other end has a standard clevis attached that connects to the snake.

52 tail elevator linkage.jpg

Jim.

cymaz12/04/2020 12:52:10
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9197 forum posts
1186 photos

Will you  be putting a cap head screw and a captive bolt so you can access the linkage at any time?

Edited By cymaz on 12/04/2020 12:52:26

G-JIMG12/04/2020 13:10:13
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145 forum posts
108 photos
Posted by cymaz on 12/04/2020 12:52:10:

Will you be putting a cap head screw and a captive bolt so you can access the linkage at any time?

Edited By cymaz on 12/04/2020 12:52:26

Personally, I can't see why I would need to access the linkage in the future. I have used this sort of torque tube control on a number of models and never had an issue with it. have others had problems?

If the linkage were to fail on the ground I would have to rebuild the tail. If it fails in the air I wouldn't have enough left to repair indecision.

cymaz12/04/2020 13:11:54
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9197 forum posts
1186 photos

Fair enough...just thinking aloud smiley

G-JIMG13/04/2020 15:25:06
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145 forum posts
108 photos

Not much to report, the wing build has reached the tedious stage of filling and sanding before priming.

In preparation for painting with primer I use 3M Putty on the surface:

3m putty.jpg

It's very easy to apply (the hotel key card again), dries extremely fast, is very easy to sand down and fills the fibre glass weave, and any surface irregularities, perfectly.

ailerons 3m.jpg

It looks a lot worse than it is, the putty is not as thick as the picture makes it appear.

After sanding with fine glass paper the surface is very smooth, flat and ready for paint.

aileron pre-paint.jpg

Jim.

G-JIMG15/04/2020 17:51:08
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145 forum posts
108 photos

Still doing the tedious filling and sanding but took time out to make some cooling slots.

The real aircraft has cooling slots either side of the nose and a scoop on the starboard side.

aircraft side scoop.jpg

I figured it would be easier to make panels that I can let in to the fuselage, rather than try and cut them into the skin itself. The panels are LitePly cut on the CNC machine. The starboard one has the scoop attached so I can let the entire assembly into the fuselage.

cimg2043.jpg

The observant ones will have noticed the real aircraft has 6 slots whereas mine have 7. I tried it with 6 but it just didn't look right. Using a 1mm Bit and 6 slots leaves too much material between the slots. Using a 1.5mm Bit (my only other option) means you can only get 5 slots and not enough material between them.

Anyway, as Platt's 4th law states, "How right it looks matters more than how right it is". smiley

Jim.

Denis Watkins15/04/2020 18:08:24
4335 forum posts
104 photos

In brightness and "brain deception" terms Jim

The Original has 6 black curves stripes ( maybe an optical illusion)

But your build has 7 whites stripes or 8 wood stripes, which appear straight and narrow.

The Romans played with lines on pillars and builds and appearance can alter perception.

Flipping heck, I never meant to go on so much

But car makers too know that curved black lines tell a different story than straight lines.

Am watching keenly

G-JIMG19/04/2020 13:56:30
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145 forum posts
108 photos

Still fibre glassing, filling, sanding and basically prepping the flying surfaces for paint. frown

The aircraft elevators have a reinforced leading edge.

tail metalwork.jpg

I have simulated this by affixing metal tape to the model's LE.

elevator rivets (2).jpg

I have also affixed acrylic 'dots' to simulate the rivet heads. Once spray painted the overall effect should be more realistic.

elevator rivets (1).jpg

The black line is 1/64" Chart Tape. I will eventually spray some primer over the tape, gently rub it down until the tape is just visible before removing it. The resultant indentation will simulate the Elevator Trim Tab once the model is finally spray painted.

Jim.

G-JIMG21/04/2020 17:01:50
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145 forum posts
108 photos

Been working on the vertical tail assembly.

It looks pretty horrible at the moment but will hopefully look good when it's sprayed with a top coat.

The photo isn't very good so I've added some lines for clarification. As you can see, the Elevator Snake exits the tail outside the fuselage skin. I did this to keep the bend as shallow as possible and it isn't an issue because the King Air has a Dorsal Fin that will conveniently hide the snake. There is also a smaller diameter tube installed that will carry the lighting wires.

Like the Elevators the Rudder also has a reinforced leading edge, but flush riveted. Again I've simulated this with metal tape. I have also simulated the 3 inspection panels with a thinner metal tape.

The orange lines represent the Rudder torque tube. The snake from the rudder servo will run in a straight line to the bottom and, as the inner snake moves forward and aft, it moves the Rudder left and right. (the same servo arm will also connect to the nose wheel steering).

v tail.jpg

Jim.

G-JIMG22/04/2020 16:37:37
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145 forum posts
108 photos

This fibre glassing, filling, and sanding is never ending. Have to keep telling myself it's worth it in the end.

Unfortunately I broke one of the flaps today angry. The hinge point is near the narrowest, and thinnest, part of the flap and the balsa gave out when I was reinserting the hinge. The flap on the other side is fine so I'm hoping it was just a weak spot in the balsa. Really annoying though, especially as it was pretty much ready for paint.

Decided to do something other than work on the flying surfaces for a while so I've made a mould for the under fuselage pod.

plinth model.jpg

Next step will be to make a silicon mould so I can make a fibre glass part for the model. It will be the perfect size to take two LiPos side by side, an ideal battery pack. However, I still haven't settled on a method of securing it to the model. Ideally I want to be able to easily install and remove it without using screws (not very scale like) but I'm conscious that two LiPos are not the lightest of things.

Any ideas would be more than welcome.

Jim.

 

 

Edited By G-JIMG on 22/04/2020 17:03:34

G-JIMG23/04/2020 09:31:32
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145 forum posts
108 photos

The mould came out very well.

plinth mould.jpg

Jim.

Nigel R23/04/2020 10:23:08
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3756 forum posts
587 photos

Build is looking fabulous Jim.

Have to ask - probably a silly question - if the flap has broken from hinge insertion, will it be strong enough for flight?

Also, I can't quite get my head around the geometry of the elevator torque rods, is there two separate rods and clevis, or are they joined in the middle and you rely on the wire flexing as the elevator moves?

Edited By Nigel R on 23/04/2020 10:24:52

Martian23/04/2020 10:25:47
2485 forum posts
1163 photos

Loving your build Jim and following with admiration

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