Flitzer Sport Flying Association

Flitzer Z-21A G-FLIZ

Initial Flight Test Report

The subject of this flight test was the second prototype Staaken Flitzer, being the first model 'A ', 'wide-body' variant, fitted with the now standard larger tailplane. The aeroplane was flown at the invitation of the owner, the evaluating pilot having 50+ hours on type. Venue was Spanhoe aerodrome in Leicestershire. Conditions, VMC, nil wind, +14C, using an approx.. 250 yd. grass strip. Take off weight was approx.. 710 lbs.

Pre-flight examination of the machine revealed that the flying and landing wires were all 1/8" dia. stranded stainless cable, having a breaking strain of 1760 lbs. Maximum load in the rear flying wire at +4.4g is 2226 lbs. at a laden weight below the new calculated MAUW of 750 lbs. The drawings called for all but the rear landing wires to be 3/16" dia. 7x1 9 lay stainless, with a breaking strain of 3700 lbs., or 3116" galvanised breaking strain 4200 lbs., or, since the machine is presently non-aerobatic, 5132" dia. 7x1 9 lay galvanised, breaking strain 2800 lbs. The 1/8" rear landing wire diameter was correct. The fitting of these under size flying wires was not considered to present a problem at this stage, since the flight was intended simply to evaluate the aircraft within a narrow flight regime, at under 2g.

Elevator horn cut-outs lacked fabric patches, so that the localised elevator structure was exposed, and these should be fabric covered in future.

It was accepted that the present propeller installation was not 'ideal', and that both cruise and climb performance would be reduced, by comparison with the 1st. prototype.

The engine cowling, although featuring good sized intake scoops for the cylinders, was deficient in that efflux air was limited to the exhaust pipe cut-out in the lower cowling. The small upper cowling louvres designed to evacuate hot air from above the engine, were compromised by the intake for the oil-cooler, which was mounted against the firewall face, in what was likely to be the hottest part of the cowling, and not in a free airstream. Engine side-cowling panels were sealed against the fuselage sides, and in combination with the cooling intakes for the magnetos it would appear that there would be a higher volume of air entering the cowling than could escape. There appeared to be no sump cooling, and the part-internally ducted exhaust system was not lagged by thermal tape which might have prevented excessive heat build-up within the cowling. Due to the 2" wider fuselage of the Z-21 A (24") more of the engine was enclosed than is the case with the Z-1 & Z-21 model.

The cockpit of G-FLIZ had been arranged to accommodate very tall pilots, and the evaluating pilot required additional cushions to provide what was considered to be adequate rudder travel together with full aft stick provision.

The throttle assembly was of flimsy construction, and a continuous push force, either against a 'spring' or the bending tension of the outer sleeves of the Bowden cable, caused the throttle lever to return to the nearly 'closed' position when released. Even with the 'friction nut' tightened to maximum, uncommanded closure of the throttle occurred to some extent, and conflict with the 'choke' lever could also occur. The hot air control could not be set at 'hot', the handle automatically returning to 'cold' within 11h seconds.

Starting was accomplished without difficulty, and initial ground running indicated a rather slow tickover. One thousand RPM was selected to warm the engine and the machine was taxied to the grass strip for power checks. No chocks were available, and an unsuccessful attempt was made to run up to max. power with the aeroplane held back by manpower, the aircraft escaping and veering. Sharp closure of the throttle resulted in the engine stopping.

Immediate hot-starting, (attempted at various throttle settings) met with no success. With the onset of evening, based on previous difficulty with hot-starting of that unit, the opinion was voiced that it would prove impossible to re-start that day. The suggestion by the pilot, based on experience with the prototype, that 'throttle-wide, blowing-out' might be worth a try, resulted in a re-start after three swings. Acceleration on take-off was slower than that of the prototype, as was expected. During the take off, at 3200 rpm. tail up, it was found that, probably due to the push-force necessary on the throttle, and the relative softness of the rear supporting cushion, full left-rudder control was no longer obtainable, resulting in inexorable progress toward the ploughed field bordering the right hand side of the grass runway. The aircraft was pulled off early and gently rolled left, stick then pushed forward to accelerate in ground-effect, before continuing the climb.

Handling in the air was normal, and identical to that of the prototype, being easy and responsive to fly. The aircraft was levelled at about 700', and throttled down to stabilise the CHT after the initial full-power climb, which was estimated at around 400 fpm. Turns were made in both directions, and the aeroplane proved to be correctly rigged. A small amount of back pressure was needed to fly level, this being expected, due to the low cruising speed of between 60 & 65 mph.

A further climb to 1.500' was made, full power providing 3200 rpm in the climb. Cylinder head temp. rose to just on 400°F, so the engine was throttled back until CHT returned to 'normal' at 200°F. A smell of hot oil was becoming more obvious in the cockpit, although both oil temperature and pressure were indicating 'normal'. Since no slipstream 'helical flow deflector', as is fitted to the 1 st prototype Flitzer (in the form of a 'blade', alongside the exhaust pipe tails), had been fitted to G-FLIZ, some fumes were anticipated, and the flight was continued.

It was noted that, when attempting a power-on stall, full throttle provided only 2800 rpm, and the result was inconclusive, the machine failing to reach a sufficiently high pitch attitude at a deceleration of approx.. 1 mph./sec. A power-off stall nearly resulted in the engine stopping, with individual blades visible until power was added, IAS reading about 44 mph., with plenty of pre-stall warning in the form of short-period wing-rock and buffet, the nose just beginning to drop, as power was applied to catch the engine.

At this time, some 16 mins. into the flight, oil pressure began dropping, while the temperature needle started to climb. CHT remained constant at 200°, and the machine was positioned high downwind, maintaining a trickle of power throughout the descent, with a gentle slip into a short field landing on the grass strip. Speed was held at between 56-60 during the final approach, with ample control available. The engine stopped as the aircraft alighted.

The machine was pulled off the active runway, and with switches 'off the engine was pulled through several compression's and the end-float checked, all seeming normal. Oil vapour however, was evident as a mist above the engine cowling, hot oil was running down the firewall face, and the engine was 'sizzling'. Checking the dipstick, the pilot received a bum, and the indicated oil level was around 1/4 of its capacity.

Evidently a major oil leak and overheating had occurred, although in what order it was not possible to determine.

In conclusion, the aeroplane appears to be as viceless in its handling, at this stage in the test flying programme, as the No.1 prototype. Changes to the cooling and ventilation of the engine bay, based on drawings provided and outlined on page one, together with an improved throttle/ choke and hot air controls, ideally with the former replaced by straight rods and bellcranks, and a much improved propeller, should provide better cooling and enhanced performance.

Heat is enemy No.1 with semi-enclosed VW-Aero engine installations, such that no opportunity should be lost to ensure a significant airmass moves uninterruptedly through the baffles. This is assisted by arranging a 'pressure drop' cowling, ie. providing increased 'outflow', ideally some 50% greater outflow than 'in. The finned engine sump needs to have its own cooling airstream, and undercowl heat radiated from the exhaust system can be greatly reduced by binding the internal pipes with 'thermal tape', as used on racing cars.

The oil cooler is, in my opinion, best located as shown on the drawings, attached under the firewall, utilising the port-undercarriage leg lower attachment bracket as one of the attachment fittings, locating just ahead of the undercarriage bracing wires. The oil temperature on the prototype has never given cause for concern.

Lastly, the orienting of the rod for the fuel shut-off valve, directed at the pilot's chest, could result in obvious injury in the event of an accident. This should be re-directed to starboard, and the lever modified to accommodate the new angle, as shown on the Z-21 plans.

Overheating apart, the aeroplane was a pleasure to fly, and I look forward to hearing of your plans for resuming the certification process.

Yours sincerely,

Lynn Williams

Additional Comments From Lynn:

This is no doubt quite a useful piece of data, in that it describes the handling of the aeroplane as being thoroughly in line with that of the 1st. prototype. However, it is very critical of the way the engine had been installed and baffled, amongst other things, and I would not wish it to reflect the current state of the refurbished G-FLIZ, which has been thoroughly overhauled by its new owner, Mike Wood. Mike is presently enjoying the fruits of his considerable labours, with a now very tractable and safe machine, also currently equipped with brakes and a tailwheel, incidentally.

For more information on Mike Wood's Flitzer G-FLIZ, see "Brakes and Tailwheel"