Comet II (oz9465)
About this Plan
Comet II. Free flight cabin model for CO2 power.
Quote: "Noel Crane's miniature for CO2, based on his Brown Junior petrol powered 72in span original Comet II built in 1937. Researched, re-drawn and traced by Phil Smith."
Scan from DBHL, cleanup by theshadow.
Direct submission to Outerzone.
Update 10/08/2020: Added article (from scan by Algy2) thanks to RogerC.
Quote: "Mini replica of a popular design of the 30's. Designed for CO2 power by Noel Crane, described by Phil Smith. Comet II.
TO THOSE WHO were at the Aeromodeller Vintage Days at Old Warden, many and various were the fascinating Vintage replicas of pre-war 'Gas-powered' pioneering planes of the late 30's - but one particular Gas propelled little beauty the Telco Cot powered mini-replica of the 'Comet II' built by Noel Crane of Poole in Dorset was particularly attractive.
Noel is lucky enough to have all the references for a perfect miniature, for he still has his original Veron Comet II, built in 1937! This model flown in pre-war days with a Brown 'Junior' petrol engine, was in fact built by Capt ST (Tommy) Grant, DFC, RFC and his son Derek Grant. Tommy was for many years a member of staff at Veron at their original address at Hankinson Road in Bournmouth. In those days, the firm sold 'ready-builts' as well as their kits all neatly packed in plywood boxes!
The original design of the Comet II must of course be credited to AE Brooks, the General Manager of Veron, though the plans and kit artwork were created by Bill Forster, the active modelling Secretary of the company, who incidental) was responsible for the drawings of other Veron designs, notably the 'Sky-Rocket', featured in the Model Aeroplane Constructor - precursor of the Aeromodeller - back in the year 1937!
It is interesting to note that Tommy Grant chose to build Noel's Comet II utilizing 1/32 ply for farmers and sheeting, with Red Deal (Oregon Pine) for all structural members, except that the wing mainspars were full depth hard balsa (that new-fangled building material), also sheeting the tailplane and fin with balsa - earlier versions were not sheeted, being usually just silk covered.
So Noels' model is a compromise, having top and bottom spars, but in balsa - and a fully sheeted fin. Derek Grant, now retired, has confirmed much of the detailed data by which the author has built an accurate full size replica. Seen with Noel Cranes miniature in the accompanying photograph.
The building of this 23in span 'Mini' relies much upon accurate and precise cutting out, shaping and assembly. Noel's model is powered by the Telco Turbotank 3000 which makes installation a 'doddle', though the standard Telco 1000 with separate tank and charging nozzle can easily be adapted. The Telco instruction data gives detail installation details, though it must be stressed that with this motor, the tank must ALWAYS be installed upright. There is ample room for this to be packed in front of former 'B'. With balsa longerons and members, the only deviation from the original construction is the use of plywood formers. Select your balsa very carefully.
Construction: The most accurate method of reproducing plywood formers, balsa outline members and rib sections is to pin-prick outlines through the plan, pin-pricks at least ten to the inch. Straight edges on ribs and formers are best cut along a steel straight-edge. If fitting the 'Turbotank', the front ply former 'A' has the centre circle cut out to 11/16 in (17mm) diameter to accommodate the tank, or, if fitting the standard Telco 1000, leave intact.
Cover the plan with waxed or greaseproof paper, not only to protect it from building adhesive but to ensure the building of successors to this fascinating little model!
Steam the lower longerons to form the only curve, all other joints and changes of angle are scarf-joints, Use PVA glues. Build two accurate identical sides using the same pin locations either side of members (never through). Join fuselage sides with
Formers 'A', 'B' and 'C' to which top edge and bottom edge crosspieces have been accurately cut to match the corner cut-outs. Use rubber bands to 'clamp' whilst drying, checking for squareness with set-square and alignment end-to-end over the plan. A 'whiff in kettle steam will permit the scarfed top longerons just aft of Former 'C' to be pulled in for the even taper to the rear. Cut all crosspieces in matching pairs for top and bottom. Do not omit the two gussets in the nose structure for the undercarriage tubing.
If fitting the Telco 1000, mark and drill two holes for attaching the motor. Secure the nuts to the rear of the ply bulkhead with epoxy-glue to permit the 10 BA bolts to be screwed and un-screwed for thrust adjustment. The tank is best secured by inserting into a close fitting hole in a block of polyurethane foam, itself neatly fitted into the space before former 'B'. The tubing to the motor can be coiled to reduce length as required and lead out to the motor cylinder via the 'windshield'. Attach the charging nozzle to a small 1/16 ply mounting plate set just aft of the nose former on the port fuselage side. Fix the nozzle with the two bolts (or screws) provided in the Telco kit.
The fuselage front may now be sheeted with medium quality 1/32 balsa sheet, as detailed on plan. Noel's model had very neat windows cut out with curves reamed out with sand paper wrapped around dowel. Cellophane was stuck behind each cut-out including the front windshield. Non-purists may ease the detailing by painting on after covering and doping!
Neatly drill holes either side of fuselage to permit insertion of two lengths of 20 swg aluminium tubing for undercarriage wire location. Push through and fix with epoxy glue, the gussets in these areas strengthening the undercarriage attachment. Also use epoxy to fix the wire tail skid.
Cut out 20 ribs for mainplanes from light quarter grained stock, using a ply template pin-pricked out from section on plan. Cut slots in trailing edges - these are unusually deep, but are very efficient! Pin trailing edges in place, also lower spar. Fit all ribs, canting the two base ribs to allow for dihedral. Add top spar (both spars have centre-section extensions) then slot in the leading edge. Join two diagonally-grained tip pieces together on the flat - but set off the board between the trailing edge and the raised leading edge - see dotted aspect on rib section drawing! Top and bottom spars may now be 'cranked' and 'scarfed' to brace the tips.
Plate-gussets for the mainspars are detailed on the plan as well as scarfed gussets for the level centre-section. Glue in place offcuts of leading and trailing edges, all this whilst supporting each wing tip 3in above the board. Enormous dihedral was also a feature of early 'Comets' too! Enclose the leading edges from spar to spar by wrapping completely around the nose with very soft 1/32 balsa sheet. Damp with a cloth on the outer surface before wrapping, glueing and temporarily pinning whilst setting. Obstinate balsa sheet can be encouraged by brushing with ammonia - but keep your nose and eyes out of the way! Finally, sheet the centre-section top and bottom. Note that like Noel's original model, the ribs are not stepped or recessed to give flush fitting of the leading edge sheeting! When dry and set, smooth to streamline all the edges of the tip pieces. Continue with separate sheeting top and bottom at the tips.
The cambered tailplane is a 'must' and cannot be replaced with a flat structure. The 1/32 sheet ribs are a bit fiddly but the effort is rewarding. Pin-prick the complete tailplane outline onto very light balsa sheet joined edge-to-edge (3 in sheet is not quite wide enough). Outline pieces are cut from light 3/32 sheet and are glued in place for leading edges, but cut slots for ribs in trailing edges before laminating down in place. Ribs are fitted, stepping onto leading edge, slotting into trailing edge. Top spar is slotted into place, butt-jointed at centre with scarfed strengthening gusset. Top sheeting of is laid between leading edge and spar, damping on outer surface to aid temporary curvature. Also sheet over centre-section. Allow to set completely hard before lifting and sanding all edges.
The fin is straightforward, 1/16 x 1/8 strips laid flat and neatly jointed, then covered both sides with 1/32 soft light balsa, bringing total thickness to 1/8 in. Sketch shows how 1/16 dowel pegs are fitted for rubber-band retention with small washers epoxied to ends. Note small reinforcing discs of 1/32 ply both sides of fin. Smooth leading-edges to 'round' and trailing-edges to 'streamline'.
Undercarriage wires are all 20 swg, shown full length on plan. Join the front and rear wires by wrapping with fuse-wire and touching with solder. Noel used miniature coil spring tensioners with open looped ends engaged around small washers soldered to the legs and brace struts - just like his original! But we non-purists will probably use rubber-bands!
Cover all surfaces with lightweight tissue. Noel used coloured lightweight Modelspan, red for the fuselage, yellow for all flying surfaces. Use tissue-paste adhesive (not dope or PVA), water-shrink, and when dry apply two thin coats of clear shrinking dope on fuselage, one on wings, tail and fin. Fin is glued centrally above tailplane, then wide securing pegs permit alignment of the fin to create trim for gentle turns during flight. Wet-and-dry abrasive paper is glued both to top of tail-bay and the underside of tailplane to prevent movement, once a setting has been made.
The Telco Turbotank 3000 is secured by four bolts screwed in from the front with rear nuts anchored with epoxy glue. A small amount of downthrust is shown on the plan, and a minute amount of right side-thrust ',against torque) would be advantageous, though the fin is very dominant.The model should balance very slightly nose down in normal gliding attitude, when supported under the wings on the balance line shown. One might expect the high lift tailplane to require a rearward CG, but Noel assures us that this is not so - probably because of the large longitudinal dihedral (angle between wing and tail) which gives the model a steep and somewhat stepped climbing angle just like the original petrol-powered Comets. There is no incidence under the mainplane, the large camber produces enough, but 1/16 in under the leading edge of the tailplane as seen on the plan.
Flying: Glide test only in very quiet conditions over reasonable terrain. A small quick partial charge is suggested for first trim flights. A compromise torque and rudder setting to give a wide circular flight to the right on both power and glide. Adjustments may be made by loosening the motor securing bolts and packing with slivers of post-card or 1/64 ply. A model should never fly one way under power and the opposite on the glide!
With full charges, when trimmed, ensure that you are fit and in good breath - for you are certain to find yourself enjoying quite a few long runs after this endearing little model, just as we of the older generation enjoyed hareing off after our pioneering free-flight 'Gas-powered' originals in the good old thirties. But Happy Landings!"
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