Kwik-Fli Mk III – Plans for P Kraft’s Classic pattern model – 60” Span
Here is a reprinted plan made available from the archive of a collective of fellow aero-modelling enthusiasts. The non-profit making archive contains older and hard to find RC and free flight model plans as well as rare, or out of production, kit plans.
A service by aero-modellers for aero-modellers
The plan offered is a high quality print and does not fade in strong sunlight like the traditional dye-line prints used by the majority on plan suppliers in the past
THIS LISTING IS FOR A PLAN ONLY – YOU ARE NOT BIDDING FOR A KIT OR AN AIRFRAME
On offer is an unused reprint of a restored original “Mk III Kwik-Fli” plan showing the 60” span competition winning aerobatic model for this classic mid 1960’s ‘pattern-ship’ that was designed by the renowned American model enthusiast Phil Kraft. The model was successful at National and International level, with Phil Kraft becoming the Aerobatics World Champion in 1967 with this design. The model was so highly regarded in its time that it was kitted by at least three manufacturers (Top-Flite, Graupner and Jensen), but such kits are now a long time out of production and have become collectable in their own right.
Indeed it is interesting to note that Graupner have recently reintroduced the ‘Kwik-Fly Mk3’ into their range as an ARTF offering, with optional retracts. their suggested engine range makes use of slightly smaller sized ‘modern’ motors (Which would be the equivalent in power to an old .60cu in motor originating from the mid to late ‘60s – A point discussed below, in the notes on power unit choice). The Graupner ARTF version of the ‘Kwik-Fly Mk3’ costs over £100 (Without the optional retracts etc.) – If you can find one. Building from the plan enables you to replicate the Mk III Kwik-Fli at a much lower price (The actual wood required should cost you around £25 – with some residual stock left over) and gives you ‘full control’ of the build.
This 60” wingspan aerobatic low wing airframe is a typical example of a top-class “full house” aerobatic design of that era and was a proven competition machine in it’s heyday, when true ‘proportional’ radio control first became commercially available. This model truly helped to open up the performance envelope of aerobatic models to a new level. Clearly, this model is dated by the standard of today’s 2.0m x 2.0m machines, but it still offers highly satisfying aerobatic performance that would make a great sport model for the average club flier, or even a practice model for the pattern enthusiast. The model is of course eligible for ‘classic pattern’ competition flying.
If built and set up accurately the model is neutrally stable, has crisp control responses and is capable of a full range of aerobatics. This model is not difficult to fly, and could even be used as a first low winger if you had a competent instructor and used a ‘buddy-box’ set up. The model has a comparatively thick wing section and does not rely on brute force, or speed, to fly through manoeuvres. It is a comparatively slow flier when judged against modern competition machines.
The model was originally powered by a .60cu in 2-stroke IC engine (With an Enya 60 used in the original). The design flying weight for the Kwik-Fli is 6.0 lbs, with the recommendation not to exceed 6.6 lbs. A modern .46 to .52cu in engine will probably have similar power to such an early .60cu in engine, so you may be able to use a smaller motor and save some weight (never a bad thing). Of course, today you could use an equivalent 4-stroke IC engine or even an electric motor conversion. Examples have been flown using the AXI 4120/14 brushless motor on 5s Li-Po batteries using a 12” x 8” propeller
(I believe the average current draw for pattern flying to be around 35 amp on this set up). Alternatively the slimmer geared Hacker C50-13S (or 14S) with a 6.77:1 ‘Acro’ gearbox on 5s Li-Po batteries and a 13” – 15” propeller (for similar average current loading around 35 amp) would also get the job done if you don’t mind spending a bit more on the power-train. The capacity & weight of the battery remain your choice, but a pack around 6000mah should give around 10 minutes of ‘pattern’ flying. Duration is roughly ‘pro-rata’ for smaller capacity packs. So a 3700mah pack should give just over 6 minutes duration of ‘pattern’ flying. I often prefer the lighter packs and shorter duration as the performance can be better due to the weight saving. It also leads to a more disciplined flying style, which is not a bad thing when ‘pattern’ flying !
This plan has been restored and reformatted by ‘Yesterday’s Aero Modelling Plans Service’ from an original 1968 plan as published by Model Airplane News of America. The plan is a single very large sheet (33” x 70” approx) with crisp black print on white paper. The fuselage is shown complete in plan and elevation, with full details of all wing ribs and fuselage formers etc.
The entire model is of traditional built up construction and was intended for 4-channel “full house” proportional RC. Nowadays, the performance envelope could be enhanced by using a servo for each aileron, so that flap mixing (or even other mixing) could be incorporated. The model would only require very subtle flap movements, as too much flap movement creates excessive drag & spoils the performance. This is an easy conversion as the original design uses bell-cranks in the wing panels to operate the ailerons (Rather than the more traditional torque rods). Therefore, it is simply a matter of fully sheeting the bell-crank bay and mounting a servo there to drive the ailerons. (Making sure you incorporate an appropriate wiring harness in the wing for the servos !). There is a wide choice of options for mounting the wing servos. You could make something up in timber, or use commercially available mounting plates (Such as the ‘Radio-Active’ units) which have integral shrouds for the control output arms.
The plan shows the wing as being attached with rubber bands, which helps with minor “crash resistance” if you have to land in rough areas. It is straightforward to alter this to a bolt on wing if you prefer the improved accuracy of the wing fixing afforded by that method.
This is a traditional balsa & plywood build that provides an “old school” aerobatic ‘pattern-model’. It offers a satisfying build with some of carving and sanding on the fuselage to provide a nice rounded shape.
With the exception of the canopy, the design does not require any special, or custom made, parts, so all necessary items should be readily available from your local model shop. That said, the canopy is a simple large ‘teardrop’ type, so it would not be difficult to find a suitable unit. Alternatively, you could build an ‘open-cockpit’ look, with a simple ‘wrap-around’ windshield & headrest structure if you wanted something different on this ‘retro’ machine. (Don’t forget to add a pilot ! … or even one of ‘Biggles Buddies’ – see my pilot listings !). Parts for the undercarriage could be commercial units, or fabricated yourself ! The model has tri-cycle undercarriage with a steerable nose leg and wing mounted fixed undercarriage.
The fuselage has a simple box section, formed from sheet and strip balsa wood with plywood doublers. The formers are also cut from sheet wood. Full details for these parts are shown on the plan. The fixed horizontal stabiliser has a built up 3/16” thick frame, skinned both side in 1/16” sheet, with elevators shaped from ¼” solid sheet. The fin/dorsal and rudder are also shaped from ¼” solid sheet
The wings are built in two panels, then joined with hardwood dihedral braces. The plan also shows the full planform of one wing panel. The wing is straightforward with parallel chord planform. The ribs, and ‘sub-ribs’ are formed from one basic section. Full size details are given for the ribs, with notes and sketches to cover the variations (notches for various sub-components etc). The wing tips are shaped from block balsa (hollowed to taste – though the tips could be laminated if you choose). This aerobatic wing is fully symmetrical, so both panels are built over the same part of the plan – you just have to remember to make a ‘top & bottom’ (or left & right) panel – depending on how you choose to view it !
The wing features ‘inset ailerons’, which are cut out of the completed wing panel. This involves a little more work than conventional strip ailerons, but they are of wider chord and deemed to be more aerodynamically efficient.
This is a comparatively simple build, with some interesting features. The build is straightforward and would not present any problems to an experienced kit builder. It would even suit a novice plan builder if the information on the plan were followed diligently (Asking for help from an experienced modeller if necessary). The model is not suitable as an initial trainer, but is fine for anyone with good intermediate flying skills. It makes a good ‘improver’ model for the ‘club/sport’ flier.
Treat yourself to a building project that beats the “credit crunch”. Building from the plan will give you a great “retro” model at the fraction of the cost of a kit. It provides satisfying flight performance for intermediate to expert fliers. This has to be the ‘real deal’ for true ‘retro’ aerobatic flying as enjoyed by ‘classic pattern’ enthusiasts. Even at today’s prices, I guesstimate there will only be around £25 of wood required to build a MkIII Kwik-Fli, and you can control the selection of the wood ! (Much cheaper than sourcing a ‘collectable’ kit).
Bidding for this plan starts at £9.99
UK postage & packing will be £2.00 First Class, with plan folded in large envelope.
Can post overseas - £4.00 for Europe, or £5.25 for the rest of the world
Postage discounton multiple-purchases