Bellanca’s Decathlon From The Cockpit

The Decathlon is a strut braced, high wing monoplane of steel, wood and fabric construction with a tandem seating arrangement for two. It is powered by the AEIO-320 Lycoming engine of 150hp; the Super Decathlon by the 180hp Lycoming AEIO-360. In the case of the Decathlon, power transmission can be to either a fixed pitch or constant speed (CS) prop; the Super has but a CS prop. The engine installations have full inverted fuel and oil systems. The inverted oil system consists of an inverted/upright shuttle valve, oil/air separator and interconnecting lines. Oil pressure can be momentarily lost in some flight attitudes or combinations of manoeuvres and, for this reason, knife edged flight for longer than 15 seconds should be avoided (I wonder if MiG-29s are similarly restricted!). The inverted fuel system includes a 5. 6 litre header tank with a standpipe in the forward cabin; one-half of the tank capacity is usable in inverted flight but it must be remembered through a sequence that upright time must be allowed between periods of inverted flight in order for the header tank to refill.

The fuel system has a total usable capacity of 151. 4 litres, stored equally between left and right wing tanks, which have interconnected vent and feed lines so that the total (or combined) fuel quantity can be read by a single gauge in the root end of the right tank. This simplicity and yet adequacy of approach is reflected throughout the aeroplane as embodying the design philosophy for the machine.

For the materials, construction of the Decathlon is standard: the fuselage consists of a welded tubular steel frame, with Dacron fabric covering. The cockpit has a light alloy floor, likewise for the rear baggage area behind the back seat. Wings consist of wooden spars and ribs, again covered by Dacron. The wings are braced to the fuselage with light alloy V struts, interplaned with small jury struts mid length. The wings have inspection hatches, circumferentially stiffened holes in the fabric covered by light alloy circular plates, secured with only pincer strips – a weaker design detail as the strips tend to loosen their grip with in-flight vibration, so that the tendency is to leave the loose plates off, not a good practice – exposing cavities to possibly resonant aerodynamic excitation. The flight control surfaces are also fabric covered. The wing struts are themselves attached to the fuselage adjacent to and aft of the main gear attachment points. The gear itself is fixed, with a tailwheel. Main gear consists of steel spring legs, with a step fastened to each in order for the pilot to view the overwings and access/check the fuel tank filler caps. Under the fibreglass cowl you will find either an AEIO-320 or -360; the extra 30 horses from the AEIO-360 in the case of the Super Decathlon, driving through the CSU-ed prop, makes all the difference to the aircraft’s capabilities, but that’s for later.

The 8KCAB – as it is designated – is a straightforward aeroplane, with the simplest of systems: minimal electrics (starter, fuel pump, turn co-ordinator, engine instruments and radios is about it), toe operated mainwheel brakes and very little else. Seating accommodation is tandem for two. Seats are comfortable; up front the pilot has a quite shallow panel lying above fuselage frame cross-members, with nevertheless adequate space to make a sensible VFR panel (and needless to say you will find the Decathlon enthusiast who has IFRed his machine, with much thanks to Mr King, Collins or Becker for that matter, without whose miniaturisation of avionic electronics such wouldn’t be possible in this machine). On the left of the panel are grouped the engine power and condition instruments with possibly the odd nav display instrument (VOR or ADF indicators), which may mean that the VSI is removed to the far right of the panel, to the right of the radio stack. Also on the left is a subpanel containing engine controls, including starter button and mixture and below them, the throttle and RPM controls. Mag switches are in the left overhead position – quite a good ‘eye-catching’ location for the pilot as he turns to get out. Dual flight controls are standard, but whereas the passenger has stick and rudder, he has an incomplete set of controls. This, coupled with the obscured vision from the rear, particularly on the ground for this nose high attitude aircraft makes instructing a somewhat difficult exercise.

Before we turn over the engine, a few words about the history of the Decathlon. Whilst that is what I have chosen to centre the article on, it is not at all where the ‘design’ first appeared. Before the Decathlon – the Citabria, (aerobatic spelt backwards) and before that – the Aeronca, the root of the design. The family tree starts with the USAAC and J A Roche in particular, whose configuration was developed and produced by Aeronca (the Aeronautical Corporation of Cincinnati of America) as the C-2. Then came the C-3, also an operi cockpit, high winged aircraft. The series then got a case of wing shiftiness, the L series getting a low wing and the K series taking a high wing. The direct lineage started after the war, with the introduction of the 7AC Champion, a sport plane with appealing handling. When in 1951, Aeronca ceased Champion production, 10,000 had been produced, a mammoth production rate.

Enthusiasm for the design meant good business sense and so it was that in 1954 the Champion Aeronautical Corporation was formed by Robert Brown to continue the type. Brown aimed to update the ‘old’ design by trying a few variations, including tricycle and multi engine configurations. It was an aerobatic model however, the 7ECA Citabria, that took off this time. Over the next two decades from the sixties, over 4,000 Citabrias were built by Champion and Bellanca, which acquired the design. As an aerobatter the Citabria had many shortfalls – underpowered, non-inverted systems, to mention a couple – but as a sports aerobatics machine it fitted the market, for which its two seat appeal was a vital factor. A string of product improvements, including invert systems, on the 7KCAB concluded with the introduction of the 8KCAB Decathlon in 1971 (taking on a new wing section and new aileron shapes) and the Super Decathlon in 1978.

Let’s strap in then – and the word here is securely, what with the five point aero harness and lap/shoulder belt over the top to provide for forward restraint crash protection. First and foremost the Decathlon makes for an excellent trainer for several endorsements upon the basic licence of a fresh or low time PPL (try to find a club or flying school with a Super Decathlon on the line) – viz CSU and tailwheel endorsements, of course an aerobatics endorsement should you want, and even an appreciation of tandem seating, which funny enough I think is worth a bit of time for the inevitably side by side trained PPL.

Not interested in aerobatics? Nevertheless the Decathlon is worth some time on for the other experiences alone. The up front seating position is such as to provide the driver with good over the nose vision during taxi; this means that on the takeoff roll, when the elevator comes alive, you have to consciously lower the nose well down in order to get the fuselage horizontal for maximum acceleration thereafter to liftoff speed. Airborne, the aeroplane is lively without being too sensitive. The ailerons could do with yet more improvement in effectiveness; the aeroplane must be flown with rudder, to counter significant adverse yaw on turning and to balance a noticeable slipstream effect. The rudder has a large horn for aerodynamic balancing.

Visibility from the front seat of the Decathlon is very good, equally helpful for stock spotting and for aerobatic reference. When it comes to doing aerobatics, the Super Decathlon in particular has enough power to hold its height through all the basic manoeuvres. It is a good trainer for them also: normal or inverted loop, enter at 120 knots, same for a barrel or slow roll, 80 for a snap roll, etc. Tailslides and lomcevaks are out unfortunately. Spin characteristics, at least in my experience, are well behaved: a fast rate of rotation, steep nose attitude, reasonably prompt recovery. Interestingly the flight manual spin recovery technique details positive stick movement to neutral and opposite rudder (as opposed to the standard recovery technique from spins of rudder-pause-stick). The positive stick movement is required because the elevator is over balanced (locked stick back by . aerodynamic forces) and requires a hefty push to centralise.

Whilst 180 is enough horses for the Super Decathlon to stay up there through a continuous basic/medium level sequence, it isn’t enough to give the machine much vertical performance – about one vertical roll is all she’ll handle.

In the circuit, normal and crosswind landings, flying the Decathlon will get the uninitiated up to a good standard of tailwheel handling. So if that’s the fun side to ‘KC’ flying what is the practical use of it? As mentioned the aircraft makes a good workhorse for glider tugging, spotting, mustering or general farm duty transportation. In general though, it has to be said that for an aircraft whose primary function is transportation of more than one, the Decathlon shouldn’t be considered. However to satisfy a yen for a mixture of sport and transportation, this is one aeroplane which will fit the bill nicely. Four hours endurance at about 95 knots gives a no reserves range of about 400 nautical miles. Maximum takeoff weight is 817kg (1,800Ib) so that for a typical empty weight of 576kg the maximum payload with full fuel is about 131kg, allowing for a luggage load with just the pilot of a bit over 50kg max. (45kg is the maximum allowable load in the baggage compartment. On the other hand with two persons on board the fuel load is limited by maximum takeoff weight considerations to about¾ full. )

The Decathlon performs . . . takes little ground to liftoff on takeoff, at a speed of no more than 55 indicated (knots); similarly landing distances are ‘short’. Rate of climb in the case of the Super Decathlon is particularly helpful. KC’s are popular aircraft on the used market, making for a good investment at buy in prices of between $24-30,000.