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Old Apr 12, 2010, 05:43 PM
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In order to see where I should place the main components I need an estimate of the CG as early as possible ...

I looked at various CG options, and with a CG of 18% MAC (which is appropriate for a delta wing planform) I end up with a CG at around 40% of wing root chord. That puts the CG around 27.3 cm from the wing LE at the fuse side. For the maiden I would move that forward of 1cm, to say 26.3cm.

I'd say that 39% to 40% wing root chord is a good starting point, in any case better be conservative than too far back.

When I get a chance I will recalculate the CG taking the front fuse and tail lift into account, but I think the above should be pretty close.

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Old Apr 13, 2010, 01:55 PM
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I used three independent methods to estimate the CG, method 1 is using the simple trapezoidal graphic method with 18% mac as appropriate for delta planforms, method 2 is using a more sophisticated method that takes the fuse and tail lift into account, and method 3 is to compare with the published FeiBao CG for their MiG-21 - which should be close and represents a good check.

Method 1 : 27.3 cm from wing tip at root (40% of root chord)

Method 2: 26.5 cm from wing tip at root (39% of root chord)

Method 3: 26.3 cm from wing tip at root (39% of root chord)

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Old Apr 17, 2010, 02:26 PM
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After more sanding, adjusting, locating components, reinforcing retract mounts etc. I started on the fuse planking.

I precut a bunch of strips, and then glued them one by one with ca. Later I added pu on the inside where they meet the formers, so they stick real nice.

I also added some ultra-lightweight spackle and did some preliminary sanding. That way the planks stay nice and tight.

For now I will only partially plank the fuse, so that I still retain some access to the inside with the electronics & the wiring.

Also, part of the front bottom will stay open until the nose retract & steering is done.

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Old Apr 17, 2010, 02:30 PM
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I might use one of these (the bigger mains) for the front strut, or a c21 strut. I also have some struts for the mains.

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Old Apr 20, 2010, 02:23 PM
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Still in the planking stage ... I secured the planks with CA, and glued them with the same to the formers.

Between the formers I use Aero-Elmers with a special BVM applicator tip to put a thin bead of glue, spread with a finger, between each plank and the next.

The CA holds the planks in place while the glue dries. The white aliphatic holds them in place against each other, is very lightweight, enviromentally friendly (damp sponge cleanup) and later very easy to sand.

On the fuse inside, they planks are secured with a tiny bit of PU. Finally lightweight spackle is added on the outside, and then sanded when dry.

The final finishing coat will be .5 oz fg, z-poxy finishing resin and automotive primer, so that's four types of glue for one job .

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Old Apr 20, 2010, 02:30 PM
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The canopy seems like major work ... I have found a couple that are very close in shape, once trimmed to size.

The one shown in the pic above is a thin gws j-10 canopy. The larger and thicker one on the table is a sapac composite t-45 (hawk) canopy, of which I have an extra. The latter can be ordered as an inexpensive replacement from sapac america.
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Old Apr 22, 2010, 01:55 PM
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Box of 18g and 58g per m2 glass cloth arrived from hc (less than 1/2 price of my usual source, and better quality) so I finally started glassing the fin, horiz. stabilizers and wing bottoms.

I used Z-poxy laminating (finishing) resin, diluted with isopropyl alcohol and with some glass microbaloons added to fill the weave.

A large disposable brush is the only tool that works for me in applying resin.

Later I added one coat of rattle can polycrylic I had around to fill the weave some more.

Automotive primer is used to fill the weave, although I prefer now to fill it with a mixture of diluted resin and microballons.

If you need to fill the cloth weave, you might as well do it with something that adds rigidity & ding-resistance...

I had some slight warp in the horiz. stabilizers, so after applying the resin and glass cloth, I pressed both of them against a thick flat ply board ... should give me a nice straight flat bottom airfoil .

Next they will be partially primed so that they can be installed half-prefabricated. The Springair retracts should be here today, took only 10 days to get them.

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Old Apr 27, 2010, 02:37 PM
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The Springair retracts arrived in a bit more than a week ... I pressure tested them and they work fine .

I have now five sets of Springairs and they hold pressure for weeks if not months.

Not like some of that other leaky junk out there . Best quality in its class as far as I know.

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Old Apr 27, 2010, 02:40 PM
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The nosegear installation was a challenge due to the limited space.

I found it more convenient to have all setup before planking the fuse bottom. It is so much easier to get in there.

My mounts are not and object of beauty, but I do know that nose gear can take a real beating on some landings.

Gregg tells me I build edf jets like lightweight tanks made to last for ten years

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Old Apr 27, 2010, 02:48 PM
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All the servo cables need to be routed before the fuse planking is finalized.

I also did some carving on various balsa parts.

The rudder, elevators, ailerons and flaps still need to be cut out and hinged/

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Old Apr 27, 2010, 02:53 PM
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For outline I used a number of excellent 3-d views of the MiG-21 MF (Fishbed J) I found online, including sections.

These were essentual in finding for ex. the proper length of the LG and the correct wheel size.

Also, I am tryng to avoid that bass-mouth shaped intake so typical of many poorly designed edf jets ...

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Old Apr 27, 2010, 03:00 PM
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As far as the scheme is concerned, I am leaning towards the russian aerobatic one.

The top is bright red, and the bottom will be bare metal (dull aluminum) finish.

Bare aluminum metal will be applied to the fuse bottom, but the wing bottom will be just tamiya acrlylics to save weight.

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Old Apr 27, 2010, 03:11 PM
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For cockpit details I again rely on internet pictures of various origin,
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Old Apr 28, 2010, 08:11 PM
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Last weekend I was able to finish up the wing innards (retract mounts, aileron servos, flap servos), so the time had come to finish up the wing by skinning the top.

I also sanded and primed the elevators and fin, ready to cut out the moving surfaces.

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Old Apr 28, 2010, 08:13 PM
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New look at this stage,

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