TESTFLIGHT REPORT 2000-10-13
WINDEX 1200 C, SE-XSP.
Pekka Havbrandt

This report summarizes the results of my test flights in the new Windex 1200 C, SE-XSP, built and owned by Jarek Bator. I have written this report to give feedback to the designers, give background for future certification and with the next pilot to fly the Windex in mind.

Please be aware that this report is no substitute to the flight manual. I have simply summarized my personal experiences of test flying the Windex. I am a heavy guy (105 Kg) and the majority of the flights has been performed with the center of gravity at the forward limit. Test flights and spins with the center of gravity at the aft limit has been performed by my good friend Rune Ingman who is a little bit lighter (66 kg).

The characteristics of the aircraft may vary with the build of the pilot. Further I am very familiar with aerobatic aircraft. Other pilots may find some characteristics different, just because their style of flying is different from mine. All flights including aerobatics are dangerous and must be performed on a safe altitude and with a well trained pilot. You may find some of the speeds given in the various chapters to be too precise. The figures has been derived as an average from several flights and I do admit that I have deleted a couple of values noted on my knee pad in the air, which I by logic can determine to be unrealistic.

1. GENERAL CHARACTERISTICS

The first thing you will notice is that this is a small airplane. When lying down, you are not sitting, the visibility forwards is restricted by the instrument panel, you have only one inch between your head and the canopy and no inches outside your elbows.

When strapped up I can not reach the release knob, the radio and the transponder and I have only my fingertips on the stick when it is in full forward position. This must be adjusted to future aircraft, this prototype had no proper back and head rest during the test flights. One good solution for increased space in the cockpit is to modify the panel around the stick to enable the pilot to move 3-5 cm forwards. To be able to do the inverted flight testing a special backwards bent stick was manufactured. It is very difficult for heavy guys to maneuver the flaps to +30 deg position because of the restricted elbow room. I have deferred from using +30 deg flaps on some busy landings because of this difficulty.

Once in the air you will find the controls very quick and precise. The propeller pitch control will require your constant supervision in order to maintain the correct prop speed and the sensitive controls requires your undivided attention during the take off. The climb rate is at best, moderate, with this könig engine hence you will need to plan your take off and obstacle free climb carefully. The aircraft is very stable and the controls are light with increasing control forces with increasing speed.

The aerobatics characteristics are the best I have encountered in any glider. Windex is probably the best aerobatic competition aircraft available. How about a roll rate of 6 seconds, a spin rate of one turn in 4 seconds and permission to pull +9 and -7 g after a 350 km/h dive.

The landing is straight forward using 8 or 30 deg flaps and the Spoilers are extremely efficient.

Although the aircraft is not difficult to fly it is very different from larger low performance aircraft. Therefore I personally would recommend potential pilots to fly modern high performance gliders for 100 h and do some spins and other aerobatics maneuvers together with a good teacher before flying the Windex 1200C.

1.1 JAR 22.143 AND JAR 22.155 CONTROL AND MANEUVERABILITY

General characteristics

Windex has excellent stability and very good handling qualities in the air. The stick forces are very low around the neutral point of the stick, but increases with increased stick input. This gives you a very good feel of the aircraft. Actually the Windex controls feels like if you were flying a significantly larger aircraft. This prototype has no trim installed and the stability with hands off the stick can only be tested at low speeds. If I let the stick free at 110 km/h the aircraft will continue a stable flight. The altitude will vary 10-15 m and the speed will vary within +-10 km/h with a frequency of 17 seconds. If I let the stick go at higher speeds the aircraft will continue stable flight but slowly increase the speed.

At high speeds the stick forces will increase in a very pleasant and natural way. Even at very high speeds the aircraft feels very stable and presents no difficulties with the pitch control, which one could have expected looking at the short fuselage. At stall the nose will drop with no tendency to dip a wing.

The operation of flaps and Spoilers will not effect the stability nor will they give significant trim or stick force changes. The glide path will naturally be steeper with flaps and Spoilers extended.

On production aircraft I recommend installation of a trim. The aircraft is very sensitive and it is easy to loose altitude, resulting in increased speed and rpm, just by looking at the map during normal cruise conditions.

1.2 ROLL AND SIDE SLIP STABILITY

The stability in the roll plane is excellent and the aircraft is not sensitive to side slip. I have tested 15 deg side slip and brutal rudder movements at low speeds ( stall + 10 km/h ) in climb, descend and cruise with no tendencies for stall or a wing dip.

Intentional flight with rudder and stick at opposite sides at airspeeds between 120-220 km/h has been demonstrated. This control combination will produce a well controlled side slip with very conventional characteristics.

1.3 JAR 22.46 STALL SPEED

30 deg flaps, no brakes, max. weight, max. forward center of gravity, engine idle, cooling covers closed = 75 km/h.

Windex 1200 C will not stall easily. With the center of gravity in front of the center it will continue to fly even with the stick all the way back. To enter a stall you need to either do it dynamically or with a slight climbing attitude. The nose will drop down straight with no tendency to dip a wing. A small 5 deg side slip will not affect the stall characteristics. You will have aileron control throughout the stall. The altitude loss is 25 m for a normal stall with no Spoilers and 40 m with Spoilers extended.

1.4 JAR 22.201 STALL SPEEDS

Stall speeds normal upright flight, no engine, center of gravity in the middle.

The aircraft is not at all sensitive for small or moderate side slip. I have not found the stall speed to be different enough to distinguish this difference from the small differences between different center of gravity positions and plainly different days.

Stall speeds with engine on idle rpm, normal upright flight, center of gravity in the middle.

Stall speeds with engine on 90% Power, normal upright flight, center of gravity in the middle.

1.5 JAR 22.203 STALL SPEEDS IN 45 DEG TURN

With the center of gravity forward from the center the aircraft will stall very gently in a turn. You will notice a buffeting and the stall goes into the turn.

Stall speeds in a 45 deg turn, no engine , center of gravity in the middle.

Stall speeds in a 45 deg turn, engine at idle power, center of gravity in the middle.

1.6 JAR 22.181 STABILITY AND JAR 22.251 VIBRATIONS AND BUFFETING

Flutter tests has been performed with hand held stick and hands off the stick, with and without Spoilers. An introduction of flutter has been performed by hitting the stick with hands off the stick at all speeds up to 330 km/h. No flutter tendency has been noticed. The aircraft will respond with a damped, maximum 2 oscillations, approximately 0.5 seconds oscillation. No flutter is felt in the controls, the oscillation is caused by torsion of aft fuselage and the tail.

I encountered continuous vibration at speeds over 180 km/h on one flight. After landing it was found that, a non standard experimental extra glass fiber fairing, specially built and designed by Jarek, around the wheel was cracked. It probably happened during the start on the grass strip. This vibration vas visible on the wings. After removal of this extra aerodynamic fairing the vibration has not reoccurred.

Windex performs well at high speeds. It is stable, the control forces increases with speed and the aircraft is not overly sensitive even at the top speed. In fact the Windex do not feel particularly different to fly at maximum speed compared with cruise speed.

1.7 JAR 22.145 FLAPS

Maneuvering flaps do not cause any trim or other changes in the characteristics other then a steeper glide path. The control forces are low. It is very difficult to maneuver the flaps into +30 deg position because of limited elbow room. I have successfully maneuvered the flaps at low ( 88-110 km/h ) speeds in climb, decent and in aerotow, with no immediate change in altitude or attitude.

1.8 JAR 22.71 RATE OF DESCEND and JAR 22.75 LANDING GLIDE PATH

Max. Weight, max. forward center of gravity, no engine. 

The flaps has been maneuvered successfully with no unexpected or spectacular effect in aerotow, at 1.1 x Vso, at max. cruise power and 1.1 x Vs1.

1.9 JAR 22.145 SPOILERS

The Spoilers are extremely efficient. The Spoilers can be extended at any speed and have been tested at all flight conditions with and without power. No trim change or immediate altitude loss will occur at extension of the brakes and the control forces are low. The glide path will naturally become steeper with extended Spoilers.

These spoilers are the most efficient I have come across so far, and I have flown aircraft with hefty brakes like Puchaes and Pik 20. You will normally need only half or quarter brakes for a normal final. The control forces are low and there is no noise with extended brakes. On most aircraft you can hear and feel when the brakes are extended, not so in a Windex.

1.10 JAR 22.73 HIGH SPEED SPOILERS

Stable end speed with 45 deg diving angle and fully applied Spoilers =260 km/h.

1.11 JAR 22.143 WET AIRCRAFT

Wet aircraft presents no surprises. The gliding performance is slightly reduced but the aircraft has not shown any spectacular characteristics when maneuvered in wet condition. The normal precautions should naturally be applied, for example 10-15 km/h extra speed on final.

2. JAR 22.51 START

2.1 JAR 22.65 CLIMB

With 105 kg pilot.

Time from take off to 300 m = 3 minutes and 15 seconds.
Altitude 4 minutes after take off = 410 m.
See also pos 5. Cruise and Climb below.

With 66 kg pilot.

Time from take off to 300 m = 2 minutes and 16 seconds.
Altitude 4 minutes after take off = 450 m.

2.3 GRASS STRIP

The ground roll is very bumpy and it is not possible to do anything about the direction of the ground roll until you have speed enough to lift the tail wheel. Start from wet grass strips can not be recommended and you need a long strip or obstacle free climb path. It can also be recommended to decide a point where you will abandon the start if not airborne at that point. A good headwind is also one of the prerequisites for successful grass strip starts.

Runway: Dry grass, no wind, climb speed 1.3 x Vs1=104 km/h.
Start can be performed with flaps at 0 or +4 deg. The later will give the best and shortest start.

2.2 CONCRETE RUNWAY

On concrete runway the aircraft is not steerable at low speeds. When you reach 40-50 km/h the tail can be lifted and the aircraft balances well on the main wheel. Heavy crosswind may cause the fin to move in the downwind direction at the point when the tail is lifted. This needs to be compensated with the rudder. The aircraft will lift at about 80 km/h. The climb rate is only 1,5 m/s and the ground roll is around 240 m until the aircraft gets airborne. The altitude is about 30 m at the end of a 1000 m runway. Thus a long runway or an obstacle free climb path is required.

It presents no problems to start with one wing on the ground. At the start of the ground roll the two wheels gives good directional stability and the wing can be lifted with the ailerons after a short ground roll well before it is time to lift the tail. It is however important to be careful with the line up of the aircraft before start. The direction the aircraft is lined up at will be the direction of your first 50 m of ground roll.

2.4 JAR 22.145 TOW IN CROSSWIND

I have successfully demonstrated power start and start after a tow plane in crosswind components up to 30 km/h. Higher crosswind components may well be possible, but have just not been tested.

At tow starts in heavy crosswinds, it is easy to get a few bounces since the aircraft gets airborne before the tow plane and compensation for the wind with the rudder will cause a loss of lift resulting in a bounce back to the earth. This is however not a problem, just a fact of life with every light airplane towed for start.

The directional stability in the beginning of the start is very good. In fact you can not steer the airplane the first 50 meters of the ground roll. This is an advantage in crosswinds since the wind do not effect you at all at low speeds. A dip of the wing into the ground do not make the aircraft change direction. After reaching 40-50 km/h you can lift the tail and the aircraft is very easy to control.

2.4 TOWING

I have made tow starts with and without somebody holding the wing. Both ways are easy. The ground roll is however very bumpy on grass strips. It may scare you if you do not expect this. I recommend tight straps. The aircraft has a very good performance and will be airborne well before any tow aircraft gets in the air. It is easy to control the aircraft during the tow, bearing in mind that the controls are very precise but sensitive. During the tow you will not see the tow aircraft. The visible part is two wings sticking out on both sides of the compass if you do not prefer the low tow concept.

2.4.1 JAR 22.151 TOWING

The aircraft can be towed at relatively high speeds due to its excellent stability and good maneuverability. I have tested towing between 100 - 180 km/h encountering no problems. This is not a maximum speed, just the highest speed I so far have tested. The recommended tow speed is 110-120 km/h.

Low tow, recovery from + 15 deg over the tow aircraft and up to 30 deg turns in tow has been successfully demonstrated.

2.5 JAR 22.233 DIRECTIONAL STABILITY AND CONTROL ON THE GROUND

The directional stability in the beginning of the start is very good. In fact you can not steer the airplane the first 50 meters of the ground roll at start and at the end of the landing roll. This is an advantage in crosswinds since the wind do not effect you at all at low speeds. A dip of the wing into the ground do not make the aircraft change direction. After reaching 40-50 km/h you can lift the tail and the aircraft is very easy to control. You can lift the wing and control the aircraft with the ailerons at about 20 km/h.

Taxing is not easy. At low speeds Windex is not steerable because of the fixed tail wheel. You can change direction by using the brake, giving a power burst and a rudder input at the same time. This causes the aircraft to balance on the wheel for a short moment and the direction can be changed blowing on the rudder with the engine slipstream. The other option is high speed taxing ( 40 km/h ). Any taxing on grass is extremely bumpy. You need to be well strapped.

3. JAR 22.153 LANDING

Landings has been demonstrated with 30 km/h side wind component, this is probably not an absolute limit just what we so far has demonstrated. Landing characteristics are excellent and no tendencies for ground loop has occurred during side wind landings. When the tail wheel is in contact with the ground it provides good directional stability. Landing can be performed with flaps in + 8 or + 30 deg position. The + 8 deg position is recommended at high side wind conditions. Landing can be made without engine and with engine at idle speed.

Using the wheel brakes is a little noisy but effective. Watch out for keeping full brakes on at the end of the ground roll. The aircraft can tip to its nose when the aerodynamic forces are reduced at low speed and the braking force will take over.

4. ENGINE AND PROPELLER HANDLING

When the engine is cold it will start easily. Full choke, ignition on and turn the key. After ignition reduce choke immediately and control the rpm with the throttle.

If the engine is hot it will give you a lot of trouble to get it started. Even if you may succeed I would recommend a coffee brake before attempting a restart of a hot engine on the ground.

I have also noticed that the power of the engine is reduced when it is hot. On one occasion I only reached 3550 static rpm with full power after a long taxi session. Do not taxi on the runway for five minutes and attempt a start from a short grass strip directly after this. It is smarter to tow the aircraft or roll it by hand to the starting point. I have performed several starts directly after long taxi and hold from full length concrete runways without problems, but you better be aware of the power reduction. I have also encountered engine stops when increasing the power from idle after the landing ground roll leaving me with a hot engine in the middle of the runway. This seems to happen when the engine has been running on idle for an extended period of time during the landing pattern. To prevent this, it is wise to give the engine a couple of power bursts during the landing pattern.

Restart of the engine in the air is very easy. At normal cruise speed you turn on the ignition and slowly unfether the propeller and the engine starts. I have even started the engine during aerotowing. I have tested restart of the engine between 140 and 260 km/h. I have lost approximately 30-50 m altitude during the engine start. I have also tested restart with the propeller adjusted to fine (normal cruise ) pitch. The engine will restart but you will loose

150 m and you will need 180 km/h for this.

4.1 JAR 22.1041 and JAR22.1047 ENGINE COOLING

The engine cylinder head temperature is 115-125 Degrees C in stable cruise conditions and remains in the range of 130-140 Degrees C in stable climb conditions. The current slightly larger fuel nozzle seems to have solved all the early temperature problems with this engine installation.

The cooling is increased by the opening of the engine cover when the propeller is in its working position. The cover is closed when the engine is shut off and the propeller is in fethered glider configuration. This system works well.

5. CRUISE AND CLIMB

Windex will cruise at 200 km/h at 4200 rpm. The engine rpm is controlled by a variable propeller pitch. The control mounted into this prototype is too heavy to maneuver and has a big clearance at the change of the direction of rotation, making the rpm control cumbersome and unprecise. The dead movement when changing direction of the control is 1,5 turns. I have to constantly monitor the rpm and it is very easy to overev the engine when increasing the speed or immediately after take off when the speed builds up and you are occupied with looking out for obstacles and emergency landing spots.

This control must be changed on future aircraft.

This table has been performed with the 105 kg pilot. Climb performance is better with a lighter pilot. Rune Ingman has reported an indicated 2 m/s climb speed compared to my 1.5 m/s.

6. GLIDING

After engine shut down and feathering of the propeller the aircraft becomes an excellent glider with characteristics well known to anyone accustomed to modern glass fiber gliders. I have tested thermals with flaps at 0, +4 and +8 deg. It is easiest to fly in thermals with + 8 deg flaps and speeds around 90-100 km/h in narrow thermals, The best performance is achieved with 90 km/h using +4 deg flaps, if the thermal is large enough. 0 deg flaps do not give the best performance but is feasible to do.

7. JAR 22.255 AEROBATICS

I have flown the aircraft in approximately 250 aerobatic maneuvers, stressing the aircraft between +6 and -3 g. I have also participated in the Swedish national championships. With only 5 h of aerobatics experience in the Windex I ended up second. This is a very promising competition aircraft. Everybody were very impressed by the performance of this aircraft in competition flight. In my opinion this is the very best existing competition aircraft with performance well in excess of the today popular Fox and Swift aircraft.

The stick forces increases in a very pleasant way with increasing g forces giving the pilot an excellent feel for the aircraft in aerobatics maneuvers.

7.1 ROLLS

Good rolling characteristics. Windex makes one slow roll in 6 seconds. Recommended entry speed is 180 km/h.

7.2 JAR 22.147

The time for change between right and left 45 deg turns with 0 flaps and 1.4 x Vs1 is 3 seconds. At higher speeds it can be lower then 2 seconds.

7.3 LOOPS

Loops has been performed with entry speeds ranging from 180 km/h to 280 km/h and with 4g to 6 g entry. The loop has conventional characteristics. Recommended entry speed is 180-200 km/h, 4 g and 0 flaps. I have tested loops with negative flap positions. With negative flaps the aircraft becomes more sensitive to g-stall. I recommend 0 deg flaps when flying aerobatics. A skilled pilot may find some benefits using the flaps in the low speed portions of some of the maneuvers. However for me and most pilots the benefits are probably not worth the complication.

7.4 SPINS JAR 22.221

Spins with the center of gravity fully forward, full rudder, stick fully straight back, no engine, no brakes, flaps 0 deg and a 105 kg pilot.

Spins with the center of gravity fully forward, full rudder, stick fully straight back, no engine, no brakes, flaps 0 deg and a 105 kg pilot. 

Spins have stopped by itself after two turns, still with full spin rudders applied, when the center of gravity has been at the forward extreme. It is very difficult to make the aircraft to spin with the center of gravity in front of the center position. The way to do this is as follows. Ease the stick back gently, with neutral airlerons, until you feel the beginning stall not letting the aircraft start to sink before the stall. At this point, apply full rudder into the desired direction. Hold the stick fully back and give airlerons inwards the spin together with full rudder. The aircraft has also recovered when the stick is moved against the spin with the center of gravity at the forward extreme. ( Ex. left rudder and right airleron). Remember that this is not a recommended recovery procedure, the normal recovery procedure of neutral airlerons and opposite rudder followed by forward stick, shall always be applied.

The aircraft will spin better with the stick inwards into the spin. ( Ex. Left rudder and left stick, for an upright spin )

Left spins with the center of gravity at max. aft pos, full left rudder and a 66 kg pilot.

The aircraft do not spin with opposite airlerons ie. Left rudder and right airlerons.

The rotational speed is 3 seconds per turn and the aircraft generally speaking “Spins better” with the center of gravity aft of center.

7.4 HAMMERHEADS AND HUMPTY BUMPS

The hammerhead is very conventional with the exception that with an entry speed exceeding 180 km/h the vertical line becomes much longer then you are accustomed to in gliders. With 250 km/h the vertical line is more similar to a Pitts special rather then to a glider. The vertical is easy to find and hold. I have given rudder at indicated airspeed of 70 km/h. It still remains to be tested which speed is the best. The humpty bump is equally easy to perform.

Recommended entry speed is 200 km/h. I have tested entry speeds up to 280 km/h. Vertical rolls on the down line is very pleasant since you do a good marginal to the maximum speed.

7.5 TAIL SLIDES

Tail slides has very conventional characteristics.

7.6 EIGHTS AND 45 DEG LINES

The low drag and good speed performance gives you an excellent opportunity to impress your glider aerobatic friends with long and consistent lines on half cubans and other combinations of lines and loops. Recommended entry speed for a half cuban 8 is 200 km/h and for an reversed half cuban 8 230 km/h.. If you prefer, it is feasible to increase these speeds to 250 km/h for longer lines.

7.7 INVERTED FLIGHT

I have demonstrated inverted straight flight and 30 deg turns inverted so far. It handles very well so far.

Comments by Windexair AB

Pekka Havbrandt wrote this flight-report. Windexair has not cut, added nor changed the contents of the report but we would make some comments.

• Regarding the problem Pekka Havbrandt had to reach the control knob: The Windex SE-XSP that Pekka Havbrandt was flying was built by Jarek Bator that has a completely different body constitution than Pekka Havbrandt and one solution is to put in a back and head rest which Pekka did propose in the report.
• Regarding the take-off and climb performance: Both the engine and engine-installation are redesigned to enhance the engine performance.
• Regarding the roll rate (slow roll): Pekka Havbrandt had no complains about the roll rate but it is possible to increase the roll rate quite a bit for pure aerobatic competition pilots but you will get more adverse yaw and higher stick forces. This has been done on two Windex 1200C with good results.