Staaken Flitzer

Williams supplies plans for several sub-types of the basic design. The original Z-1 Flitzer was his bright red prototype, powered by an 1835cc VW. Next came the stronger Z-21, incorporating a longer span horizontal stabilizer and other small refinements, but still using a 56cm wide fuselage. Larger pilots can build the later Z-21A featured in this article, with its enlarged, 61cm wide cockpit.

The slightly more compact StummelFlitzer has a shorter fuselage with raked cabane, a larger tank bay and rounded flying surfaces.

This model is available in two versions, the

“ A smaller version is designed to use a less powerful 1835cc VW engine bolted directly to the firewall, and has no vertical stabiliser for added excitement.

” Types S and R, optimised for intermediate level aerobatics, using more powerful engines in the 60 to 110hp (45 to 82kW) range (including that Australian Rotec radial featured in Australian Aviation June 2006). The StummelFlitzer’s structure is strengthened to cope with +6. 0 /-3. 0 G loading, and balanced slaved ailerons have been added to its upper wings to improve roll performance.

A smaller version, the Kobold (or Goblin) Flitzer also under development is designed to use a less powerful 1835cc VW engine bolted directly to the firewall, and has no vertical stabiliser for added excitement. A two-seat Z-2 Schwalbe (Swallow) version is in the pipeline, plus the bigger, longer range Z-3 Falke.

Being a compulsive doodler, Lynn is forever inventing imaginary new subversions, like the Walter powered F. 2 Tiger ‘Fighter Trainer’, Rotec powered Maksimov SK26 ‘Russian Fighter’, and ‘racing’ Meteor Speedwing. For the current status of these and his other brain children, you should visit the FSV website (see specs box).

Over 200 sets of Flitzer plans have been sold. They come as 33, comprehensively illustrated, 90cm by 60cm sheets, with muchtext and many perspective, exploded views of individual components. All metal fittings are drawn to full size, and the original plans have been updated to reduce fabrication time.

Those sub versions are all derivatives, and so come as modifications to the basic plans. The fuselage is its longest component and being less than 3. 6 metres long means it can be built in a small workspace, like a single-car garage or even a spare bedroom.

I have sampled two of the half-dozen or more flying Flitzers. Englishman Rupert Wasey’s award winning example (the natural wood coloured one in these photos) has an 80hp (60kW) Aerovee (Monnet) 2180cc VW conversion with a single magneto and electronic ignition with dual Hall effect coils, each firing two spark plugs. It also has a starter and an alternator charging an on-board battery, and drives a 1. 53 metre diameter, 86cm pitch Alan Newton (British) beech wood propeller.

Rupert’s significantly out-performs an 1800cc VW powered Flitzer kept in the same hangar.

The second Flitzer I flew was Australian design and technology teacher Mark Crawford’s.

His has a four-cylinder Jabiru 2200cc motor, also developing 80hp (60kW) at 3300rpm, but driving an Australian Heliptera propeller. His blue fuselage mimics that of WW1 Lt Jansen’s of Jasta 6.

Flitzers use conventional construction with plank spars and built-up ribs forming the USA 35B wing sections, squared off with laminated wood wing-tip bows. All ribs are identical for ease of building, although the lower wing’s structure is a little more complex, and the upper wing has a slightly wider chord due to its thicker spar. The interplane struts are complex works of art, utilising spruce blocks, plywood cheeks and spruce fairings, making them look like authentic single-piece wooden components.

All flying surfaces are wire-braced, the empennage with single-strand piano wire, and the wings using beefy multi-strand wound cable. This is not flexible aircraft control cable, but proper 3/16-inch and 1/8-inch structural cable, fastened over thimbles with Nicopress swages and adjusted by turnbuckles in the time-honoured way.

The short cabane struts are of welded steel tube, and the landing gear is also a steel tube structure: a pair of triangular frames supporting two fixed cross-axles. These support a third, floating axle, held in place with tightly wound half-inch elastic bungee. The legs are wire-braced and faired with balsa wood, then fabric wrapped for streamlining. Like other components, there can be some variation in the wheels. The plans call for re-spoked Honda C-90 moped wheels with new hubs and no brakes, but both the examples I flew had cable-operated heel brakes and fat motorcycle tyres.

The Flitzer’s fuselage is the usual built-up wooden box with scarfed ply exterior skins and fabric covering, and beautifully scarfed pressings of 1. 0mm and 0. 8mm ply for the rear decking and cable fairleads. The tail and control surfaces have similar construction to the wings but with either built-up or solid spruce or fir ribs, drilled out for lightness. A baggage locker behind the cockpit has enough room for a tent, sleeping bag, mattress and a change of clothes or two.

Both examples are beautifully built, with exquisite cockpit finishes. There is a small black rectangle of non-slip walkway on the left wing root, from which you lift your right leg over the Tiger Moth-style fold-down hatch and step on to the seat and down into the cockpit. This is perhaps a little snug despite the widened fuselage, with a fairly upright seat and fixed four-point harnesses. In both cases, my shoulders touched the cutout sides, but there was enough room for comfort, although my head did stick well out into the breeze because I am 1. 86m tall. Lynn tells me there is now a modification to lower the basic Z-21 seat by 5cm, while the Z-21B has a deeper decking and later sub-variants have bigger, deeper fuselages.

The small instrument panels each hold eight miniature instruments plus a radio. Rupert’s is a Micro-Air, which fits into a standard 2. 5 inch instrument hole, while Mark uses a hand-held Pilot (Vertex). Rupert’s has a throttle and mixture quadrant on the left sidewall, fuel on/off selector on the right and a sprung carburettor heat knob in the centre. Mark’s layout is slightly different, with a single sidewall throttle

Believe me, this aeroplane has classically harmonised controls, with light ailerons, slightly heavier elevators, and a rudder that is just slightly heavier or firmer in feel – perfect!

(the Jabiru’s Bing carburettor is selfcompensating and so needs no mixture control), beside which is the choke. The carb heat plunger is under the left of the panel, with the fuel cock directly below the tank, a long stretch under the panel’s centre. Both use cork-and-wire fuel gauges and are otherwise similar.

Rupert’s Flitzer’s empty weight includes 2kg of lead ballast to compensate for its heavy engine, while Mark’s is built from denser fir, so they both tip the scales at around 245kg. Adding 27kg of fuel and 82kg of Bob took our total to 354kg – somewhat more than the 340kg official maximum. The temperature was around 22°C for all my flights, and generally with a 10kt breeze slightly across the runway.

The Flitzer is small and short-coupled, with a tall, narrow-track landing gear, so building it with the original fixed tailskid would only be a good idea if all your flying was to be off grass (most unlikely nowadays). Because of this, both Rupert and Mark have fitted theirs with differential footbrakes and a lockable swivelling tailwheel to improve ground handling on hard surfaces.

Your eyes look straight along the forward fuselage past a small windshield and through a low triangular tunnel of cabane struts. The nose sticks up high ahead and pretty much in the way of a direct forward view, but it is quite narrow, so your weaves need only be 15 to 20 degrees either side of track. The main gear is nicely sprung, and both aeroplanes’ brakes were exactly right, with no play, and enough effect to turn precisely.

For a tighter turn, you can ease the stick forward a little and give a blast of power without any tendency to lift the tail and stand the ironmongery on its nose.

When I opened Rupert’s throttle, that big VW emitted a most un-Volkswagenlike snarl and the little aeroplane surged forward with steady acceleration. Only a tiny bit of left rudder pressure was needed until I lifted the tail at around 25kt. Then it gave a wayward dart to the right, easily and immediately caught by a prompt dab of increased left rudder.

At 40kt in the tail-high attitude, she flew off cleanly with a gentle backpressure on the stick. I accelerated to 55kt in ground effect in the time-honoured manner, after which we were soon climbing like an interceptor at an eager 700ft/min.

By then you can no longer hear the enthusiastically blattering engine over the torrential roar of slipstream in the wires.

Having a muffler as standard, Mark’s Jabiru engine is much quieter, and it rotates the other way (like a Continental or Lycoming) so right rudder is required, but otherwise its handling was much the same. Its performance was perhaps a little less sprightly, but that was probably a propeller issue rather than an engine one.

Maximum level speed at full throttle for both aeroplanes was around 83kt IAS, but setting 3000rpm on the VW gave a comfortable 74kt cruise, burning perhaps 15 litres per hour, giving an effective safe endurance of two hours.

Rupert usually cruises his at 65kt at about 2750rpm.

Being a biplane, visibility in flight is inevitably less than brilliant forward past all those wings and wires, but it is generally more than adequate, and especially behind the trailing edges. Both windshields were a little small for me; I could feel the wind biting between my goggles and the helmet’s rim. Nevertheless, it was great to wheel and turn over the countryside, framing golden villages and green fields between those silver wings.

Turns each way need just a little squeeze of rudder to coordinate; over-do it with a bigger, Tiger Moth-sized push and the nose will slew across the sky.

As expected, Flitzers have low aileron forces, with instant response and a high roll rate. The ailerons are very powerful and the elevator is light, but with plenty of feel. Indeed, all the controls are light, and yes, actually very nicely harmonised, something writers often claim without it really being true. Believe me, this aeroplane has classically harmonised controls, with light ailerons, slightly heavier elevators, and a rudder that is just slightly heavier or firmer in feel – perfect! I made tight turns left and right with the cabane struts parallel to and just above the horizon. This gave a neat and easily judged 60 or so degrees of bank, and I was satisfyingly able to hit my own slipstream after just two rotations.

A properly coordinated wing-waggle was a bit harder, because at first I used too much rudder. For this little lovely, just a squeeze is all you need. I know the Flitzer’s supposed to be a mythical inter-war sportplane, but this thing’s an eagle in dove’s plumage – a Great War dogfighter in civilian colours. Although, while it’s a pussycat in the air, it can be rather more of a tiger on the ground! Nevertheless, the slow handling is fine. Throttled back, speed reduces more gradually than the low inertia and apparent high drag had led me to expect – even despite the fine-pitched propellers and all those unstreamlined wires. However hard you raise the nose, a Flitzer won’t really stall, but just mushesdownwards at between 36 and 39kt (depending on aeroplane, weight and configuration) despite pulling back quite hard on the stick. With no elevator trim, eight to ten pounds of stick backpressure are needed to achieve a stall, which is good.

Even with some power on, these aeroplanes just nod their noses, with no warning buffet, but no wing-drop either.

But they do sink power-off. Doing just a couple of stalls lost me a full 500ft! Lynn told me that the Z-21 is significantly stronger than the prototype Z-1, which was calculated to a strength of +8. 5G ultimate at top weight. That was designed to the old British Semi- Aerobatic category of +3. 8G with a reserve and +4. 4G Ultimate.

All reserve factors on the Z-21 were subsequently increased for those components with less than a 1. 5 reserve (so the Z-21 tailplane forward spar is 87 per cent stronger than that of the Z-1 – which was already adequate). This makes Z-21 Flitzers fully aerobatic, with a manoeuvring speed (Va, the speed at which full control travel may be used) of 87kt. Nevertheless, Lynn recommends against flying snap manoeuvres, sustained inverted flight or outside manoeuvres.

Rupert said he manages Immelmanns with about a +3G pull-up, and everything else you might want to do can be accomplished at or below that figure.

Entry speed for a loop is typically 95kt, although during testing Lynn has dived to 109kt IAS. ‘Design diving speed’ is 139kt, with Vne set at 104kt.

First I tried a few wingovers each way in both aeroplanes. These were very easy and tremendous fun, so I went further, flying gentle aerobatics from 3000 to 2000ft with a maximum of 2. 5 g. Rupert had warned me that his could flick if you pulled too hard over the top of a loop, which surprised me, considering the Flitzer’s light weight and low wing-loading, but I didn’t encounter this problem with either aeroplane. Perhaps he doesn’t have the safecracker’s fingertips needed to ease her over the top of gentle aerobatics at below the 1g indicated stall speed.

You need some rudder each way in the loop (right as you dive, left as you slow with the VW motor, and the opposite for the Jabiru) but not much. I started my first at 95kt and saw 35kt on the dial over the top. All my loops probably weren’t properly circular, but they were quite tight, and it was very satisfying to look up over the centre-section to admire the inverted world above while floating across the top.

Barrel rolling to the left at 90kt was a bit difficult because of interference between the stick, my knee and the throttle.

It was easier rolling to the right, but either way you do have to raise the nose very high before applying aileron, or else it falls a long way during the manoeuvre, even if you roll with full aileron. Rupert said he got a face-full of fuel when he tried a slow roll. Neither aeroplane’s fuel cap had been modified for aerobatics, so I decided not to bother with those.

Hammerheads took increasing rudder on the way up (left with the VW, right with the Jabiru motor). Holding each aeroplane in the vertical for just a moment (as anticipated, they slow quickly), I hit the appropriate rudder at 35kt and round they both went, pirouetting right on the spot, sweet as a chocolate-coated nut, and with very little need for either forward elevator or opposite aileron.

Throttling back halfway around kept the radius tight and gave me plenty of time to accelerate in the downward vertical before pulling out.

This aeroplane is just instinctive to fly, a marvellous dog-fighting aircraft – a biplane Turbulent or Corby Starlet, but much stronger.

Back in the pattern, I flew downwind with 2500rpm and around 60kt, and then throttled back to 2000rpm for the approach at 55kt. Rupert said “don’t fully close the throttle”, because she sinks rather rapidly in this configurationalthough later, when I was more used to the type, I did try several glide approaches. Some stick backpressure is needed at this speed, but there is still plenty of control authority for countering gusts.

Aeroplanes of that period would normally have flown glide approaches because of their engines’ unreliability, and that is still not a bad idea when using a converted automotive powerplant today. But with their throttles closed, Flitzers glide like a Chubb safe. Add full rudder with aileron for a side-slip and they come down like a safe with the door open! Helicopter pilots would be familiar with the forced landing glide angle; sailplane pilots need not apply.

A curving approach is best for decent forward visibility, and to keep the threshold in sight. With the nose well down to hold 60kt, I found I actually got the best view of the runway by stretching my neck to look over the top wing. There is plenty of elevator effectiveness, with or without power, and on one occasion when the Jabiru engine stopped on final, I found there was still enough elevator control for a proper flare. Despite a fairly prolonged hold-off, these little aeroplanes don’t float far, thanks to that vast amount of drag, especially with the nose raised and the undersurfaces of all four wings presented to the airflow.

Staaken Flitzer

Z.21A
(Technical specs)
Powerplant
One Aerovee 2180cc
VW normally aspirated,
four-cylinder, horizontally
opposed engine,
producing 80hp (60kW)
at 3300rpm, or one
normally-aspirated,
air-cooled, horizontallyopposed,
four-cylinder
Jabiru 2200, producing
80hp (60kW) at
3300rpm.
Performance
(Manufacturer’s stated)
Sea level Vne 104kt
Max speed (SL) 86kt
Max cruise 75kt
Economy cruise 65kt
Stall 35kt
SL takeoff dist 900ft
SL takeoff run 400ft
SL landing dist 400ft
SL climb rate 720ft/min
Service ceiling 12,000ft
Max endurance (45 min
reserve) 2 hours
Weights
Equipped empty
242/246kg
Max takeoff 340kg
Standard fuel 40 lit
Load factors +6/-3g
Dimensions
Wing span 5.49m
Wing area 9.01m2
Length 4.5m
Height 1.93m
Cockpit width 56/61cm
Plans from
Lynn Williams at:
[email protected]
www.flitzerbiplane.com
Builder support and information
network (FSV):
av8rblake.flitzerbiplane.
com

You have to rotate the nose through a very big angle to get it up to the correct three-point attitude, and this takes time. However, if you are not patient, and your stick is not fully against the backstop by the time the wheels brush the turf, the aeroplane will bounce on its stiff main gear legs. Trying to correct thisby pumping the stick back and forth merely causes pilot-induced oscillations and divergent bounces. The only solution is to open the throttle and go around.

Mark’s Jabiru Flitzer was better in this regard; its slightly softer bungees have a little more ‘give’ and generally allowed a softer, bounce-free landing, despite my repeated inability to get his stick all the way back to its rear stop.

When you do get the flare right, and everything comes together nicely, it can be truly satisfying. For a proper three-pointer you hold the stick right back into your gut as she touches down, and then ride out the little bounces and waddles as she gradually loses momentum, dancing your feet lightly on those rudder pedals (and, just occasionally, the brakes) to keep straight.

Nearly every time both aeroplanes slowed, and despite their engines rotating in opposite directions, they both showed a distinct attraction towards the trees along the right runway margin. Sometimes an early rudder input would stop this before it got started, but on other occasions a good jab of left brake was needed to rein them in. I did not fly either of them off a bitumen or concrete runway, but I suspect that would be a little more challenging.

Nevertheless, and partly because of their ground manners, Flitzers are the kind of aeroplane you would never tire of – endlessly challenging to fly accurately, but immensely satisfying when you get things just right.

Nimble, manoeuvrable and sprightly, their handling is perfect for the connoisseur. Above all, they’re just so much fun!