Flitzer Sport Flying Association
Cockpit Size
Comments by Lynn Williams
April 18, 2003
Tony's aeroplane is a good example, built quickly without
embellishment, but then equipped with such things as streamline leg fairings and wheel covers over
time. Aesthetically perhaps more attention could have been directed towards the cheat (break) line
of the cowling and its continuation throughout the fuselage, where, together with the stiffening ply overlap, this should have created a feature, flowing from propeller boss to tailplane leading edge. This is part of the Flitzer 'look', as well as having a structural role.
The problem of ingress with Tony's Flitzer (Z-21A) is that he hasn't built the door into the cockpit side, so that you have to lift your leg a further 6" to enter, and you do not have the advantage of being able to support your body weight on the port longeron. Also he has put pressure on the 1.0 mm rear decking to the cockpit by sitting back on that area when climbing out, and has rippled the ply, which was never stressed for such weight.
I recognised the need for such a door (all Flitzers except the tiny Goblin, which is equipped
with a foot step at thrustline height are so furnished) even before drafting the first prototype,
since I wanted the decking to be high enough to protect the upper body from the slipstream, for
speed and comfort. I also wanted to convey the impression of a much bigger aeroplane, in which
you sit well down inside the fuselage, which is why a small element of the control system is
actually external, ie. under the fuselage, maximising the available space. The apparently small
windscreen is also part of the illusion, but is very effective and should not be enlarged.
The aeroplane is really quite small, at 18' wingspan, but the physical impression is of a 'normal' sized aeroplane, standing high as it does on the long undercarriage. The leg length and large wheel size enable the machine to adopt the correct angle of attack for perfect three-point landings and smooth out the roughest strip due to the relatively large rolling-radius of the wheels and excellent bungee suspension system.
The cockpit is very comfortable (Z-1/Z-21 at 22" width) and view is particularly good for a biplane. The wider fuselage (Z-21A at 24") is frankly too wide for my needs, and is best suited to heavier pilots. Taller pilots may also find the Z-21A better, as they can take advantage of the width to abduct their knees slightly, although there is plenty of room for a 6'6" pilot when the rudder pedals are located at their most forward position. The only situation where this may be constrained is if the shorter fuselage option is built (-2") to cater for the longer installed length of some of the professionally manufactured VW motors, with their starter and alternator cases grouped on the rear crankcase, using the Diehl backplate, etc.
There would be slightly more drag and weight associated with the wider fuselage, and view downwards each side is slightly more limited, for shorter pilots. The actual measurement of such differences though is very subjective, since in the absence of exactly comparable engine power ratings on the three existing Flitzers that have flown, major propeller differences, instrument calibration, ambient pressure, and other factors, one can only form impressions.
As the only pilot in the world to date to have flown more than one Flitzer, I can say that in terms of handling there was no difference, both being rigged identically. However, G-FLIZ (a Z-21A) had at that time a lethally bad 'engine management' system and a pressure drop cowling system that worked more like a pressure cooker. In addition the propeller was about the worst I had flown behind. Eighteen months previously I had borrowed it in an emergency, and fitted it to the prototype, D692, and it cut my cruising speed by 27 mph at the same RPM., and my climb dropped from about 800 fpm to 400!
The engine virtually seized while I was approaching to land after aborting the one test flight that I performed on G-FLIZ with that propeller/engine set up. The back seal had blown off the rear of the crankshaft, amongst other things, and 75% of the oil had sprayed out or boiled off. Basically the engine installer had totally ignored comprehensive detail and instruction on engine cooling for the VW which are clearly indicated on the plans.
The constructors, Bell Aeromarine, had made a good job of the aeroplane, however, and apart from the undersized flying wires (which had originally been installed for static exhibition) the aeroplane felt taught and stable, with only a slight 'pull force' required for straight and level flight - due to the very low cruising speed (60-65 mph) with that propeller. No trimming system is employed on the Flitzer, since with the CP travel of the USA 35B wing section, the aeroplane is naturally (hands-off)trimmed at Vc with 3/4 fuel and average pilot weight, and the stick forces outside those parameters are light and acceptable.
The bigger tailplane fitted to the 'series' (plans-built) aeroplanes provides a lower 'natural trimming speed' for the approach and landing, ie. a comfortable stick position allowing a good view attitude for the recommended curving approach, throttled back to about 1000 rpm (the lowest rpm attainable in the air, apart from when experiencing engine failure!). This speed is 60 mph. on the Z-1 prototype, and 55 mph. on the Z-21 & Z-21A, and having flown the prototype with a facsimile 'Z-21' tailplane I was able to confirm this, and used the lower speed for the approach and successful emergency landing in G-FLIZ onto a very small patch of grass.
...Note that the 22" cockpit width is common to Flitzers Z-1 M, Meteor, Z-1K Goblin, the Z-1 S Stummelflitzers, Types S & R, and the Maksimov SK26 'fighter biplane'. However the Z-2 Schwalbe fuselage is 24" wide, for maximum comfort in what is a very small two seat aeroplane. (Actually, the part-built prototype Meteor fuselage was built at 23", a compromise wrought by the builder who has since parted with the project.)...
Best wishes,
Lynn Williams