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Apr 19, 2019, 02:32 PM
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AntiArf's Avatar
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Thanks all.
Pleased with the weight at this point, with the airframe weighing 18.5oz and 24oz with a 5.5oz 3s-1800. Shouldn't gain more than a few oz at this point. The exhaust bulges fabricated from 1/32" balsa sheet worked out well. Paper templates were made to cut the exhaust bulges from, trimmed to fit. The rear of the templates were made a few mm wider than necessary, so that the sheets could be trimmed to fit flush against the wing trailing edge stock, when wrapped around and glued to the clear plastic exhaust exit rings. Note that there is no framing required for the sides of the exhaust bulges, as the adjacent sheeting sections on the wing butt up against the sides of the exhaust bulges. Once glued together the seam is strong. Just a small amount of filler will be needed to create the fillets on the sides of the exhaust bulges. Now to finish sheeting the wing center section and cut open/sculpt the inlets.
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Apr 20, 2019, 11:27 AM
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Nice work Bill. That is a lot of scale detail for a small jet
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Apr 23, 2019, 06:05 AM
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Thanks Turbo
Finished sheeting the wing panels. The sheeting at the wingtips has about 2 inches length of inset sheeting below the outer sheeting layer, which allows for sanding the outer sheeting down to zero thickness to taper and blend into the wingtips. The sheets all require precision fitting, which takes time to gradually trim to fit where they fit around the retract bay door perimeters. Second pic shows curved backing strips glued to the under side of the wing sheeting panels, to keep them from flattening out where there are large open areas without wing ribs underneath. Pretty much have to shape these to perfection matching the airfoil shape, of there will be warps in the sheeting. The pencil points to a small area where I thinned the sheeting with sandpaper to provide maximum tire clearance. The wheel doesn't need to go up that high to fit into the wing, but it needs full available travel to close the door without the tires interfering with the door when in motion. The door closing ratio could be changed, but then the door with opening springs add more load on the servo and I only needed that last 1/64" of travel for the door to fully close. In Pic 4 note the stringer running at an angle from the bottom stringer to the top stringer, between the first 2 wing ribs not yet sheeted, at the leading edge. While it acts as a stiffener for the wing, on the other side a hard balsa stringer was installed with a slight interference fit under pressure, which was fitted to correct a slight mismatch in the wing incidences. Always good to have dead straight wing panels.
Apr 23, 2019, 03:52 PM
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balticS2's Avatar
The shape is just popping out now Bill. Looking forward to seeing you tackle the intakes.

Alec
Apr 23, 2019, 05:13 PM
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Thanks there's a lot of wood to mill through there. The openings are marked off at a point that should get them close. Thinking of using a small drum router to cut into the area.
Apr 23, 2019, 08:48 PM
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St. Martin's Avatar
Very impressive, Bill.
Apr 30, 2019, 12:10 AM
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Thanks Fuzz
Started routing open the intakes and quit until tomorrow since it makes a good deal of racket in the house late at night. The photo showing the router bit is a bit flashed, where the other photo shows a series of pencil lines drawn for referencing, to help keep both intakes symmetrical. With 9/32" thickness of laminated balsa at the intake openings, there should be ample thickness of wood to sculpt the inlet rounds. The 1/32" sheet balsa intake ducting is already installed inside the wing panels.
Apr 30, 2019, 09:23 PM
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stacker's Avatar
Looks super Bill!
May 01, 2019, 01:13 PM
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Looks pretty incredible actually - getting that Tail working is quite a feat. I'm surprised that 30mm fans have the thrust to make it fly, but I have no experience with fans smaller than 70mm, and I just watched a video of the real one flying and I guess anything bigger would make scale flight difficult if not impossible in a jet that size. Are scale inlets going to be sufficient or will you have to use cheater holes in an unobtrusive location? Great job - good inspiration!
May 01, 2019, 05:37 PM
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Thanks Dave and Joe.
The QX 7000kv 32mm fans are an entirely different fan than 30mm fans like the Eflite and GP. They're more like an EDF40 with a motor in the mid to high 5k kv range on 3s. Should easily have 50% T/W at a light wing loading for the size. The TU104 airliner built with these fans flies at well under full throttle. Actually this build could be a bit larger, given the weight and available thrust. No need for cheaters, the inlets at scale sizing are plenty large enough. Sizing was determined with an intake template made when the wing was designed. Over time I've learned to build smaller EDFs at about 1/2 the weight of the average builder. 1/16" framing, 1/32" sheeting, Microlite covering, IPS BL type fans, and no servoless retract bricks. In this case servoless retracts wouldn't be close to scale in the wings, let alone they wouldn't fit properly. Actually just weighed a servoless unit collecting dust with the strut and dual nose wheel at 75 grams. The combined weight of all the retract components used here including wheels and even harness extensions into the fuselage are no more than that weight.
May 01, 2019, 07:50 PM
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St. Martin's Avatar
Glad your able to keep working on this, Bill. I like shaping intakes. Esp., dual or bifurcated. A good lesson in symmetry.

Fuzz
May 01, 2019, 09:33 PM
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turbonut's Avatar
I always like the look of buried(is that a word) intakes..so classic jet looking
Latest blog entry: In flight
May 01, 2019, 10:09 PM
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Thanks Fuzz and Turbo. Yep you have to work to keep everything symmetric. There is a seam in the sheeting not too far back from the intakes, which is a good reference to take measurements from. Of course there's about 1mm of difference that needs to be taken into account when measuring from the seams, since the stringers that the sheets are seamed on were located after the wing was built. I wasn't sure where I would want them all initially and they would have been in the way of installing the intake ducting. Got the intakes routed open to about where they should be. A bit of tweaking and then time to round the intake lips which will provide more area, and some finessing at the sides of the intakes.

Shaping the intakes it becomes quickly apparent that the bottom edge of the opening is more rearward than the top edge, to get the correct shape. In the first photo below the top and bottom edges of the openings are vertically aligned, which does not produce the correct shape. The intake bottoms will need to be shaved rearward a bit. The camo stripes on a full scale that is currently being restored are useful, in getting a good idea of how much rearward the bottom edge is from the top edge. The camo stripes are close to vertically aligned from a front view, where from a side view it can be seen how much rearward the bottom edge of the intake opening is located.
Last edited by AntiArf; May 02, 2019 at 09:12 PM. Reason: add full scale reference photo
May 06, 2019, 08:58 PM
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Time to cover and finish this model. The intakes lips have been sanded again, after a heavy coat of fill primer in the photo below. The scheme worked well with the 1/32" sheet balsa ducting already installed and joined to the double laminated 1/8" balsa LE with a final layer of 1/32" sheet on the outer wing surfaces. Just a bit of filler was required to blend the intakes into the fuse, and into the 1/32" balsa sheet ducting lap joined against the inner surface of the intake laminates. Worth the added effort of pre-fabricating the intake ducting and installing the thick laminates at the LE required for sculpting the intake lips.
May 06, 2019, 09:46 PM
Registered User
Oddly shaped inlets on the real one. they look almost as asymetrical organic shapes. Even looks like a divergent duct inlet design ?
Regardless... It clearly worked well..
Your work is a good representation.. well done.

.Good progress too... It'll soon be finished at this rate .


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