Thermalist (oz11429)

About this Plan

Thermalist. Towline glider model. High performance sailplane.

Quote: "FAI maximum eleven feet five inches sailplane contest giant. Thermalist, by R Minney.

THE imposing contest record of this huge model culminates in the magnificent aggregate of 2093 secs, for two flights that gave Bob Minney first place in the International Sailplane Contest at Eaton Bray against such opposition as Fillon, last two years' winner, and Cheurlot, who also had an over 30 minutes aggregate.

Fuselage: Two sides of the fuselage are built in the normal way out of 1/4 inch square medium balsa. Then the main fuselage former is positioned and the rear of the fuselage brought together, the cross struts are put in and the nose former fitted.

The items such as weight box, wheel cover, detherrnaliser box, sheeting, etc, are positioned next. At this point the fuselage is laid aside and construction commenced on the wing.

The 3/4 inch square LE is shaped and laid down flat on a plan, also the TE. As the wing is so large it is necessary to build it up in 4 pieces. The small number of ribs are cut en-bloc out of 3/32 inch sheet and cemented in position. The main T spar is then constructed and slotted into the rib tops. At this juncture the wing structure is removed from the plan, and the rear spar of 1/4 inch square cemented in position. Rib members 1-6 inclusive should have holes drilled for paper tubes rolled to take a 5/8 inch diameter aluminium tube and a 3/16 inch diameter dural tube. The tubes are the next part of the construction. These are rolled and cemented in position. Next, before the outboard panels are fixed to their respective centre sections, the wing fixing is built.

Two more paper tubes are rolled for the fuselage and two airfoil sections cut out of inch sheet - one for each side of the fuselage. These are pinned roughly in position, the dowels fitted, and the centre sections fitted. These are then lined up, with correct incidence, etc, and the paper tubes and airfoil section cemented permanently into position.

The cabin windows are then glazed and the wing fixing strengthened with struts across the fuselage. The whole fuselage is covered with 1/16 balsa sheet, hard at the nose, soft at the tail, with the grain running crossways. The nose block is shaped and fitted, and the 4-1/2 inch airwheel fitted.

The fin is built up flat on plan and the 'thickness' added later. This fin is best made a fixture to the fuselage and the under fin is then covered with 1/32 sheet, A wire support from the front of the fin to the fuselage completes the fuselage construction.

Wings: These are continued by building the outboard sections, the T spar continuing to the tip. The outboard sections are then fastened to the centre sections at the correct dihedral and two 1/8 ply dihedral braces fitted to each wing. The leading edges are sheeted with 1/32 hard balsa, and the inside top of the TE sheeted with 1/16 sheet.

Tailplane: The construction of this is very simple, with its flat underside and large rib spacings.

Covering: The fuselage was sanded and covered with one layer of rag tissue. The fin was treated in the same manner. The wings and tail were covered with rag tissue and given one coat of thin dope.

The second layer of tissue on the wings and tail was orange English tissue. This could only be applied with tissue cement as paste would not stick to the dope underneath. This second covering was steam shrunk and doped with one coat of thick dope, and one of banana oil or varnish.

The fuselage was given two coats of clear dope and two coats of Catesby's brushing cellulose, black. The fin was similarly treated.

Flying. The model balances under the rear main spar, and should require about 1 lb of lead in the nose. The all-up weight should be about 4 lbs - well above FAI weight.

The initial tests provide no great difficulties, the glide being slow and flat. When towing up remember that the model is fully strong with plenty of area so that a strong pull may be applied to the towline - of string - without fear of the wings breaking. The only hook so far used has been the front, the rear one being kept for dead calm days."

Scan from DBHL, cleanup by rchopper56.

ref DBHL-5318.

Direct submission to Outerzone.

Note for a more manageable 60 inch half-size version of this design, see Thermalist (oz3484) by Bill Dennis, from Aeromodeller 1985.

Update 11/08/2019: Added article, thanks to RFJ.

Supplementary file notes

Article.

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