Warning - For use with flight simulation only:
This Manual is based on the actual, real-world Tandem-Falke manual/technical references. However, it is presented here as the instruction manual of the virtual simulation model and it should NEVER be used as a real-world flying manual.
VSKYLABS Scheibe SF-28A Tandem Falke
MANUAL / POH
Edition rev.001 (issued February-2024)
Motor-Glider / X-Plane 12
Advanced simulation of the Scheibe SF-28A Tandem Falke TMG
The VSKYLABS development of the Scheibe SF-28A Tandem Falke project for X-Plane flight simulator was approved by ‘Scheibe Aircraft GmbH’. However, it is an independent VSKYLABS project which is not affiliated with ‘Scheibe Aircraft GmbH’.
TRAINING - GLIDE - TRAVEL - PERFORMANCE
TRAINING - SOARING CRUISING PERFORMANCE
The Tandem Falke, with seats one behind the other, offers a new alternative amongst two seat motor gliders. The front pilot sits ahead of the wing, and the rear pilot over the main spar of the wing. In conjunction with the one-piece perspex canopy this results in exceptional visibility. The seats are close together which ensures excellent communication in flight.
High performance in its operating range, easy handling, robust construction, reliability of airframe and engine and exceptional low operating costs are the main features of the Tandem Falke.
The Tandem Falke has a very good gliding performance due to the increased wing span, special wing section, the door which may be closed to reduce engine cooling drag, and the use of a feathering propeller. This results in a gliding angle of about 26/27 to 1.
The Tandem Falke is easy and pleasant to fly. Take off and landing is straightforward. It is docile when taken to extremes. The outrigger wheels on the wings are supported on nylon legs, and the tail wheel is linked to the rudder making it equally maneuverable on the ground. In flight the Tandem Falke is very quiet. This is important in localities where the inhabitants are sensitive to noise.
The Tandem Falke is a high performance yet robust aircraft, based on considerable experience with the Bergfalke two seat sailplane, and the Falke. It is suitable for club operation for training and practice flying, as well as for performance flying.
The 60 hp Limbach SL 1700 EA engine develops its maximum at 3,400 rpm, and is based on well proven Volkswagen components. A 12 volt electric starter and alternator are fitted as standard.
The Tandem Falke can be easily rigged or de-rigged by 3-4 people in 10 minutes, and can be loaded on a normal glider trailer with minor modifications.
INTRODUCTION
The project introduces the Scheibe SF-28A Tandem-Falke.
The real SF-28A vs the VSKYLABS SF-28A:
The VSKYLABS SF-28A simulation was developed to follow the real SF-28A handling and performance characteristics. It is a highly engineered, robust motor-glider simulation model which make use of X-Plane 12 sophisticated flight dynamics and physics simulation, extracting it to its limits.
Simulated systems:
The VSKYLABS SF-28A features X-Plane 12 latest native features, systems and physics. This assures a 'high airworthiness' in X-Plane, throughout its update process. Some systems may be restricted to X-Plane’s default systems algorithms.
General cockpit configuration:
VSKYLABS chose to design the SF-28A cockpit with a touch of a modern conversion. A simplified NESIS digital avionics package is included with an emulation of the NESIS engine-monitoring screen. Built in AviTab compatibility is included, and the main NESIS display can be used for displaying the AviTab, in a toggle mechanism.
The aircraft is fully functional from the back-seat (with some limitation which are derived from the real-world SF-28A backseat operations).
TECHNICAL DATA
ENGINE:
Limbach SL 1700 EA...........................................60 hp at 3400 rpm
DIMENSIONS AND WEIGHTS:
Wing span..............................................................53.4 ft
Length.................................................................26.8 ft
Wing area...............................................................199 ft²
Aspect ratio..............................................................14.5
.Wing loading......................................................6.35 lbs/ft²
Empty weight...................................................approx. 860 lbs
T.O. weight max. .....................................................1300 lbs
PERFORMANCE:
With engine operating:
Max. level speed.....................................112 mph 180 km/h 97 knots
Cruising speed.......................................100 mph 160 km/h 87 knots
Stalling speed.........................................40 mph 64 km/h 35 knots
Climbing speed......................................................7.5 ft/sec
Maneuvering speed Va..................................97 mph 156 km/h 84 knots
Never exceed speed Vne..............................118 mph 190 km/h 103 knots
Maximum permitted speed in rough air..................97 mph 156 km/h 84 knots
Take-off run........................................................500-650 ft.
Operating range..............................................approx. 280 miles
Economic endurance...............................................approx. 4 hrs.
Fuel storage...............................................102 Gall. US / 40 L.
Fuel consumption in cruise.........................................3.1 Gall/hr.
With engine stopped:
Min. sinking speed..................................2.95 ft/s at 43 mph (37 KT)
Glide ratio........................................1 in 26/27 at 53 mph (47 KT)
FLIGHT MANUAL SF 28 A - Operating instructions:
General
The Tandem-Falke is a self launching motor glider. It may be flown with an MGPPL (Motor Glider Private Pilot's Licence). It is of course necessary for the pilot to have a thorough understanding of motor gliders and operating the engine.
It is obligatory to study the documentation and to gain a thorough knowledge of the motor glider and its engine.
Starting the Motor-glider:
- Move the throttle to full power, check for freedom of movement and full travel and return to idle position.
- Wheel brake on (spoilers out).
- Engine cowl flap: Open
- Fuel cock: Open
- Electrical fuel pump: On for 2 seconds, then Off.
- Choke: Pull (no choke if engine already warm).
- Carburetor heat: Off.
- Propeller setting: Fine Pitch (push in).
- Throttle: Idle (if engine cold).
- Master power switch: On.
- Sensitive electrical equipment (radio etc.): Off
- Ignition switch: On.
- Propeller clear? Shout: "Clear prop!"
- Starter button: Press.
Caution:
Do not press the starter button for more than ten seconds. Before trying again allow 2 minutes for cooling off.
As soon as the engine starts release the starter button and set the throttle so that the engine runs at about 2,000 rpm. Check that the oil pressure rises within 10 seconds of starting and continue to monitor it. Do not increase engine revs until the oil pressure has settled down above 2 bar. Push the choke in fully.
Warming up, static rpm check:
- Parking brake: set (spoilers out).
- Elevator: up.
- During warming up: Monitor the engine instruments, let the engine run at 2,000 rpm for about 2 minutes, then continue warming up at 2,500 rpm until the oil temperature reaches 50°C. The time required will vary according to the air temperature.
- Check fuel supply: brief running at maximum rpm.
Caution:
After running at maximum rpm the engine should be allowed to cool off somewhat to avoid vapor formation in the cylinder head. The engine can also be warmed up whilst taxiing to the take-off point.
Taxiing:
The Tandem-Falke can taxi unaided and is steered on the ground with the tail-wheel which is linked to the rudder. Minimum turning circle about 15m with tail-wheel.
The wheel-brake on the main-wheel is effective and will always stop the motor glider quickly.
During ground handling it is helpful for an assistant to go to the rudder and turn it to control the tail-wheel.
Pre-Takeoff:
Caution: see also Wet wings - warning.
- Folding wings secured (if applicable).
- Canopy closed and locked.
- Safety harness secure.
- Trimmer set for take off.
- Spoilers closed.
- Check for full and free movement of the controls.
- Fuel shut-off valve open.
- Sufficient fuel in tank.
- Cowl flap open.
- Propeller set to take-off pitch (push in).
Take off and climb:
Trim neutral, spoilers closed, control column central (do not push the column forward). Apply full throttle.
Takeoff run normally about 240 meters (800 ft).
Whilst monitoring the revs, ease off the ground at 36-41 knots (41-47 mph, ~67 km/h) and hold level, letting the speed to build up to 46-49 knots (53-56 mph, ~89 km/h) and then climb at 49-54 knots (56-62 mph, ~96 km/h) with the engine revs at about 2600-2800 rpm.
Plan the climb to about 1000 ft. so that it necessary the airfield is within reach in case of engine failure.
After reaching 150-250 feet the engine revs may be reduced. Check that the oil pressure and temperature readings are in the green sector.
To maintain adequate cooling of the engine whilst climbing, keep the airspeed high, especially in hot weather.
During a prolonged climb in hot weather monitor the oil temperature carefully: if it approaches the upper limit then fly faster and reduce engine revs. Accept a shallower climb on reduced power.
Level flight:
Best cruising speed about 75-80 knots (87-93 mph, 145 km/h), at 2700-2800 rpm. Maximum continuous cruising speed is 81 knots (93 mph, 150 km/h) at 2800 rpm.
Landing:
The aircraft can be landed with the engine either running or stopped. Approach at about 49 knots (56 mph, 90 km/h) maintaining the glide path with the spoilers. As the spoilers are effective, it is not usually necessary to slip the aircraft. The rate of sink at 46 knots (53 mph, 85 km/h) is approx. 3.5 meters/second (11.5 ft/sec). At minimum touch-down speed of 38 knots (44 mph, 70 km/h) the Tandem-Falke touches down first with the tail-wheel then with the main-wheel. The landing run of about 300 ft. can be effectively reduced with the air of the main-wheel brake. The wheel-brake is operated by the spoiler control on the last part of its travel, when it is pulled fully back, so do not attempt to touch down with the spoiler lever pulled fully back.
*The VSKYLABS Tandem-Falke spoilers/brake system is set with dynamic/adaptive braking power which changes with ground speed, which reduces the actual braking power in touchdown speed and above, when the spoilers are fully out.
Stopping & starting the engine in flight:
Before switching off - Allow the engine to cool Before switching-off down by flying with the throttle closed or slightly open for 1 - 2 minutes. Reduce the airspeed to about 43 - 46 knots (50-53 mph, 94 km/h), throttle back, switch off all sensitive electronic equipment and then switch off the ignition. Whilst the propeller is still turning slow down the aircraft to reduce windmilling and set the propeller to feathered mode. Should it be necessary, the propeller can be aligned horizontally with quick blips on the starter.
Before restarting in the air - Open the cowling flap & set the propeller blade pitch for power (push in). Switch off all sensitive electronic equipment. Fly at about 43-49 knots (50-56 mph, 85 km/h), switch on ignition, set choke & throttle settings for hot or cold engine as on the ground. The engine is very easy to start if the pilot is thoroughly familiar with its operation. If the engine is cold, do not use full throttle until the oil temperature is again in the green sector. At airspeed of about 70-81 knots (80-93 mph, 140 km/h) a quick blip on the starter will start the propeller turning & the engine will start immediately (depending on engine temperature). Choke in, about 1/3 throttle, ignition on. Height loss is in the order of 500 - 600 ft.
Flying with the engine stopped:
The aircraft handles very well at 38-49 knots (43-55 mph, 70-90 km/h) with a rate of sink of about 0.9m/s (2.9ft/s) in straight flight. When the engine is off, close the cowling flap to reduce drag, but remember to open it again before restarting the engine. The Tandem-Falke, being a low wing monoplane, has to be flown cleanly. When skidding or flying at less than 41 knots (47 mph) the airflow breaks away from the wing/fuselage fillet area and performance is lost. When gliding & especially when turning, fly the aircraft as cleanly as possible & avoid skidding in turns. The old trick of fixing a length of string on or in front of the canopy is still an effective aid to accurate flying, and with a little practice the pilot will be flying accurately & climbing well in thermals compared with pure gliders.
Feathering the propeller:
The Tandem-Falke is equipped with a feathering propeller. The blades are feathered for soaring by pulling the propeller pitch control handle which is self locking. Only feather the propeller when it is not turning. Set the propeller pitch for power at an airspeed less than 54 knots (62 mph, 100 km/h) before re-starting the engine. Set the pitch by turning the handle about 30° to left or
right against the spring & then push it fully forward to the stop.
Slow flying & stall characteristics:
At maximum flying weight the stalling speed is about 34 knots (39 mph, 63 km/h) and 32 knots (37 mph, 60 km/h) when flown solo. At this speed the airflow over the wing roots begins to break away; ailerons & rudder are still fully effective & with a forward C.G. position, the Tandem-Falke simply lowers its nose if the control stick is pulled right back. With rearward C.G. positions it is possible to fly on, fully stalled, in still air conditions, with the stick right back whilst retaining full aileron & rudder effectiveness. In both C.G. positions immediate recovery is effected by easing the stick gently forwards. Needless to say in rough air conditions stalling can cause a wing to drop. Power stalls: When the aircraft is stalled with high revs the propeller slipstream tends to produce false ASI readings via the tail mounted pitot. When this happens the stalled condition is still recognizable by the fact that the ASI needle flicks vigorously around the stall speed. If stalled in a 30° turn, the Tandem-Falke gradually drops the outer wing, such that when both wings are level, normal flying speed may be regained. Stall characteristics are the same, engine on or engine off.
Spinning:
Except with aft C.G. positions it is very difficult, if not impossible, to make the Tandem-Falke spin. If no correcting action such as releasing the backward stick pressure is taken, the incipient spin becomes a spiral dive from which a transition to normal flight is easy. Use of spoilers is recommended in the spiral dive.
Even with aft C.G. positions a continuous spin is impossible. A spin may be induced by gradually easing back the stick & crossing the controls, but it will come out of the spin within 5 turns of its own accord even if the controls are held crossed: it becomes a slipping maneuver from which normal flight is easily resumed. Pro- spin aileron will cause the spin to become a spiral dive, from which the pilot should pull out gradually but without delay to avoid over-stressing the aircraft.
A spin can of course be corrected in the normal manner after 1/2 turns. When rotation stops, pull out of the resulting dive gently; do not hesitate to use the spoilers to prevent the speed building up excessively.
Aerobatic maneuvers are not permitted in the Tandem-Falke
Wet wings - warning:
The Tandem-Falke wing has a glider airfoil which is sensitive to rain. Drops of rain on the wings disturb the airflow & reduce the lift which means that the stalling speed is increased by about 8 knots (10 mph, 15 km/h), and the stalling characteristics are changed. Whereas with dry wings the Tandem-Falke is positively docile, it will drop a wing when wet. When flying in rain keep the airspeed above 46 knots (53 mph, 85 km/h), don't leave the ground at less than 43 knots (49 mph, 79 km/h), fly at about 55 knots (63 mph, 102 km/h) when climbing and on the approach. Avoid steep turns and other maneuvers involving loads. If there is snow or ice on the wings it must be cleaned off to a smooth surface before take-off, not forgetting the tail-plane.
The VSKYLABS SF-28A is simulating the effect of wet wings. In X-Plane 12, if you see rain-drops on the canopy, assume that the wings are wet. The amount of rain on the wings is dynamic and changes with the amount of the rain in the flying area (therefore - over the canopy).
Cold weather flying and risk of carburetor icing:
Especially when flying in the winter it is important to check that the oil temperature does not fall below 70°c (158°F) whilst the engine is running. The carburetor & intake are warmed to some extent by the circulating engine oil.
By installing a cylinder head thermometer (optional extra) the supply of cooling air to the engine can be accurately regulated by controlling the cowling flap. The cylinder head temperature is to be carefully monitored: under no circumstances must it exceed the maximum of 250° C (480°F).
Carburetor icing can occur when humidity is high (especially near clouds and when the air temperature is between -10°C & +18°C (14°F - 65°F). The pilot will recognize the rough engine note & reduced engine rpm. The carburetor heat control should be pulled immediately.
Carburetor icing can also occur when the engine is idling for long periods whilst flying. Pull "carburetor heat" therefore from the start, but remember that the engine cannot develop full power with carburetor heat applied.
Operation of the carburetor heater - results in an almost imperceptible decrease in rpm, unless the carburetor is already iced up. In warm, dry air, carburetor heat should be fully off.
Cross-wind:
Approved cross wind component at flight tests for take offs and landings is 14 knots, 25 km/h.
SF-28A PERFORMANCE DATA:
These performance figures were obtained from the results obtained during the type testing with propellor HO-V62/ L160 T-10 and HO-V62R/L160 T-10 in take off position and can be reproduced provided that the motor glider & engine are in good condition and that the pilot is of average ability and skill.
Maximum all up weight (AUW):
1300 lbs.
Level airfield:
with short well kept grass. Dry wing with clean surface.
Zero wind:
air pressure standard for height of airfield above sea-level.
Lift-off speed:
approx. 36 knots (42 mph, 67 km/h).
Climb speed:
approx. 46 knots (53 mph, 85 km/h).
Rate of climb:
Max weight, 2.3 m/s (450 ft/min).
Absolute ceilling: approx. 4000m asl (13000 ft asl) at rate of climb of 0.5 m/s (approx. 90 ft/min).
VSKYLABS SF-28A COCKPIT AND INTERACTION:
VR Interaction zones:
The green zones shown in the screenshot below represents the interaction areas for mouse and/or VR touch controllers.
