Volare-Gypsy J-8 SU
Indoor Joined.-Wing Experimental Glider
by Alex Morillo

This is about an experimental balsa model built to test fly it for a maximum glide performance.

Precise Building  is the first process to undertake, because general geometry lines have to be very accurate, symmetric, and with the least wood and glue, to keep weight down. ( 9 grams )

The planform is type J-8 (front wing straight and-or with less than 5 deg sweep).
The joint point is at or near the 60% span. Outer panels are with plenty of dihedral.
Aft wings are with negative sweep and with anhedral.

Because of the joined-wing concept, the wings self-support each other in a strong
enough structure at low enough weight for this specific type of indoor glider.

Special care is taken with Incidence angles between wings to minimize drag.
Decalage is used for double duty: to generate lift with the rear-upper wings
and to impart pitch-up stability (aft portion of the aft wings).

High performance aerodynamics is possible because of several careful details:

Flat Airfoils, with very little frontal area (the aft wing is only 1 mm thick )
and fly at very little AoA.

The rear wings act as lift-wings (fore portion) and also because they are
set at low negative AoA, as a horizontal-stab tail, to provide pitch-up stability

A very small trim tab is glued on top of the rudder for trimming.

High aspect ratio wings are use as well as high spans  for minimizing Induced drag.
Winglets are also used to minimize tip vortexes.

Very low wing loadings of near 1,125 grams per sq dm.
Could be lighter , with more detail craftsmanship.

Flat Surfaces with selective boundary layer control (BLC) meaning that all
surfaces are partially covered with glossy, low-drag, clear plastic tape.

The initial laminar airflows tends to become turbulent at some point over the
chord of wings; therefore , clear tape is only adhered to the point where it is
believed to be the transition area from laminar-to-turbulent flow.

The airflows over raw balsa are tripped and reinvigorates the boundary layer
(about 1 mm thick?) so flow re-attaches to the wing as a stable-turbulent airflow with minimal drag consequences.

Another added benefit with this selective tape is that as the airflows get wider (higher) over certain areas, in such a way, that the flat airfoils gain some induced camber which improves the performance of the wings.

If this BLC is used on lower surfaces, it,s effect helps deflect airflows downward
near the under-surface of the Trailing edge, perhaps as split flaps would do.

Airflows on this glider, are at very low Reynolds Number, so viscous forces are
dominant,
therefor, clear tape to let air slip-slide effortless at front and to BLC farther aft
on any surface, like wings and rudder.

The glider is more, or less designed to fly at one speed , after the initial hand
launched acceleration. That speed has to be found, and/or calibrated for maximum
glide (L/D) at its highest speed possible, mostly due to very low drag from the glider itself.

The low wing loading was only possible by placing a thin steel rod WAY forward
on the keel, so that by its long arm (leverage) the right CG location can be attained; notice that the CG is around 55% chord.

Careful selection of wing planform shapes were used, like tapered wing tip portions.

The joint is a non-overlapping type for optimizing drag reduction of drag due to possible
Venturi effects. On this glider structural issues are secondary.

Self-leveling and efficient straight glides are possible with the robust-dihedral wings.

Great glides confirm that this system works; but I need to test it more.

Amorillo61@yahoo.com


I only take credit for the three pics of the glider; the other images belong to others for reference only during this study.