1/3 Scale Harbinger 2

[Peter Balcombe]

As ribs 1A, 2, 3 & 4 are slotted to take the wide upper spar doubler, this cannot be slid in from the root end as there are no corresponding slots in the Root rib R1 or it’s doubler. As a result, I temporarily removed the slot “ears” on R3 & 4, then slid the doubler into R1A & R2 from the outer end. The top spar can now be put in position & remaining sub spars, webs etc. fitted. Don’t forget to fit the 9/32” brass rear incidence tube & ply end stop.

I’ve now started the airbrakes & have so far assembled the 4 brake vanes using the CNC ply parts, 3D printed parts and a bit of stripwood, plus brass pivot axle tubes.

LH brake vanes

Note that the brake vanes are “handed”, so the RH ones will be the mirror image of these.
Also note that as per the Brake drawing, the vane paddles are each different depths (approx 1mm) to cater for the reducing wing depth as you move outboard. Thus, when assembling the vane arms to the ply paddles, make sure you put the arm so that the crank horn is always on the outboard side.

[Peter Balcombe]

With the 4 brake vanes assembled, they can be each temporarily put in place with a 3mm rod & the brake box axle hole positions tweaked as necessary to get the blades parallel to the brake box sides & also centrally positioned in the box height. I found that the 2 inboard vanes needed tweaking whereas the outer 2 were about right.
The brake vane pivot doublers can now be fixed to the insides of the box webs, ensuring that each axle/vane is correctly positioned.
Once happy that the brake vanes pivots are all correct, the vane joiner link strip can be attached using 4 servo screws & then the linked vanes inserted into the box & axles slid in place. A pushrod between the vane link strip & servo arm completes the installation.

Brake vanes from top

LH brake open

[Peter Balcombe]

Today’s job was to fettle a wing strut core from a length of 3mm thick aluminium strip, 1/2” wide 1/32” brass strip & 3/16” brass tube.
The aluminium strip forms the strut core whilst the strip & tube make the end fittings for attachment to wing & fuselage. The core + additional ply strips fore & aft, will be sheathed in balsa & shaped to profile later.
The end fittings will be bolted to each end of the strut core once the fit has been checked on the rigged wing & fixing holes marked. With the parts ready, a check assembly can now be done as soon as the weather is favourable.

Strut core & end fittings

End fitting in position

Doubled brass strip at bolting area

[Peter Balcombe]

The wing has now been rigged onto the fuselage to fit the rear incidence tubes in both wing & fuselage, plus assemble the strut Aluminium core/end fittings & fix the end fittings in place with epoxy & M2.5 bolts.
Note that everything is inverted to avoid resting the wing etc on the rib building tabs which need to remain until the upper D box has been skinned.

Strut core attached

Overall view

Wing attachment point

Fuselage attachment point

[Peter Balcombe]

Top D box skin now applied & ready to start preparing for fixing the lower D box skin.
The inner skins are 0.6mm ply whilst the outer section (from aileron root) is 0.4mm ply.

The TE sections & rib caps will be done later.

[Peter Balcombe]

Jilles has recently had a similarly constructed strut bend during what appeared to be a ‘normal’ landing on a hard landing area with his Kirby Kite. He therefore recommends fitting 10x3mm carbon or aluminium strip doublers each side of the central core to stiffen this up.

Having now fitted the ply cores front & rear of the aluminium core, I have epoxied a 10x3mm aluminium strip centrally each side of the main core & fitted 1/8” balsa sheet front & rear. I have also pinned the 2 doubler strips together using 5off M3x10 Csk screws positioned so that they pass through the inner core lightening holes - thus not compromising its strength whilst ensuring that the internal structure is securely bonded & shouldn’t delaminate.
A final 3mm thick Balsa sheet layer will complete the intended 15mm strut fairing thickness before profiling.
Now for the shaping to an airfoil profile

[Peter Balcombe]

Well on the way with the 2nd (RH) wing now & starting to skin the lower ‘D’ box area.
Thought it worth sharing my simple method of getting the brake vane slots in the right place.

I made up 4 simple card templates with identical rectangular brake vane slots cut in them & then taped these to a long straight edge positioned at the rear of the skin sheet. With the straight edge clamped in position, the skin section can be slid under the templates & the holes marked.
Once the holes have been cut, you just need to ensure that the skin is correctly positioned when fixed. I use the white glue iron-on technique for skin attachment, so the skin can easily be accurately positioned & held in place during the ironing process.

Card templates positioned

Marking skin