About this Plan
Xernes. Flying wing glider. Designed by L. C. Harris 77” span FF tailless glider from Aeromodeller November 1950.
Quote: "ORIGINALLY designed and built four years ago, after some measure of success with a friend's tailless glider, Xernes is a conventional model with excellent flying characteristics.
No fancy wing section, or excessive wash-out towards the tips, knock-off tip panels to avoid damage and simple construction make this an ideal first tailless for any keen modeller.
Construction. The airfoil used throughout the wing panels up to the detachable tip portion is Clark YH. Select hard balsa for the spars and cut the trailing edge from medium stock. Cut rib No.1 from 1/8 ply and numbers 2, 3, 15 from 1/8 medium balsa. The remainder are cut from 3/32 medium sheet. Whilst it is preferable to cut these ribs individually to the accurate templates provided, it is possible to make them by the sheet-cum-block system though this will give each rib a bevelled edge due to the sharp taper of the wing.
The boxes are built from 1/16 ply, glued and slotted into the root ribs which are set for the dihedral angle. The wing panels are then built up in the conventional manner incor-porating 3° negative incidence at rib 15. The space between the spars and the boxes is filled with hard 1/4 in sheet balsa.
It will be noted that rib No. 15 is slotted to incorporate a locating piece for the tips, which are detachable. On the original model the tips were built in one piece with the wing ; but this arrangement proved unsatisfactory. Although amply strong for flying stresses the tips were vulnerable in hard landings when the model tended to cartwheel. Cover the centre section between ribs 1 and 2 with 1/8 sheet and face the trimming weight box with 1/16 ply.
With the exception of No.15A, which is of 1/8 sheet, the wing tip ribs are cut from 3/32 medium balsa. A hard 1/4 in locating piece is cemented to 15A which must be adjusted to give the required anhedral angle. Fit the 20 swg piano wire hooks to the leading edges and trailing edges for rubber band attachment.
Centre Rib: The centre section rib is cut from 4 in. ply and incorporates a skid. Towhooks can be fashioned from a strip of 16 gauge dural and screwed to the centre rib. Cut the wing tongue from 1/4 in ply and crack and steam to give the required dihedral angle. This amounts to 2-1/2 in, at each side at the point rib 15. Then glue the wing tongue in the slot of the centre section rib, making lightening holes wherever considered necessary.
Covering: The prototype was covered with heaviest grade English tissue; but for a lasting job, the designer recommends silk or nylon. Four to six coats of glider dope can be used to give a good finish. Finally add the ailerons which are cut from sheet and covered with tissue.
Trimming: Check that the CG is in the region of 65-70% of the root chord. Then trim for the flattest glide by aileron adjustment and additional or less ballast. When you are satisfied with hand launch tests and one tow line flight, fix the ailerons by cementing firmly before making further towed flights."
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