Page 9 - July 2019

The Arrow II construction project

In the early part of the coming year the project will be aiming to install a temporary undercarriage in the aircraft,
thus enabling the unfinished airframe to be put on display during the Wings over Springbank Airshow in July 2019.

More details here: http://wingsoverspringbank.com/
To this end, the short term objectives for this quarter were as follows – accurately level the fuselage and wing
structure before permanent epoxy/fibreglass bonding between the wing spars and the fuselage walls; issue
tenders for the undercarriage boxes and undercarriage components and commence installation; commence
assembly of the tail fin components and assemble the tail fin; purchase fuel tank fittings to allow continuation of
the four fuel tank’s assembly work in the second quarter.
Wing Structure
We were still on target for the wings to be attached to the fuselage by early 2019. Although we use the term
“bonding the wing to the fuselage”, this is not a simple task. This connection must be able to withstand 10 G
forces, not from flight which will be restricted to a maximum of 5 Gs but from the potential effects of extremely
heavy turbulence or a very heavy landing.
Prior to any bonding work, the fuselage and wings were mated together and supported on various wooden
platforms. Then a laser transit was used to level both fuselage (side to side and lengthwise) and the wing on the
fuselage within fractions of an inch. After more than one week, the levelling was checked to ensure no
movement had taken place. The leading edge of the wing was required to be 1/16” below the top of the fuselage
to allow for the future mating of the upper wing skins to the wing, giving a smooth transition. The final levels
were confirmed to be well within “5/1,000” of the exact requirement.

This picture shows the external wing to fuselage bonding joints

There are eight attachment points between the fuselage and the wing. Four of these, where the two main spars
connect with the fuselage, are the key strong points. First, 0.4” thick (40 layers of carbon fibre) carbon fibre plates
were bonded in between the carbon fibre rod caps on the spar webs and spread 6” each side of the fuselage wall.
Then 8” by 6”, six layer, fibreglass pads were bonded onto the fuselage walls, extending the walls up alongside
the carbon fibre plates. At this point, the bonding proceeded with an epoxy/cotton flox filet being shaped in each
of the four segments of each joint followed by multiple double layers of unidirectional fibreglass epoxied in place
diagonally between the carbon fibre plates and the fuselage wall interspersed with vertical single layers of the
same unidirectional fibreglass. This provides exceptional strength of approximately 44,000 lbs. shear strength per
joint or 176,000 lbs. strength in total between the four main connection points of the spars and the fuselage. This
provides a 10 G connection with the fuselage.

Beyond these four joints on the two main spars, there are four more connection points that add to the
wing/fuselage connection strength - the forward spar and the leading edge connection point to the fuselage wall.
The forward spar was treated similarly to the main spars but only on the rear side of the spar – a carbon fibre
plate and the fibreglass pads on both sides of the fuselage wall. The leading edge connection relies upon