VSKYLABS Scheibe SF-25 Falke Manual

The VSKYLABS Scheibe SF-25 Falke

Flight Manual

Flight manual for use with X-Plane 11 flight simulator

This manual is containing information which was translated from the original Flight Manual and Maintenance Manual/May/June 1990 Edition.

Although major parts of the information in this page is based/translated from the actual flight manual, the following information, data and procedures are not to be used for real-world training.

The VSKYLABS SF-25C Falke was designed to follow the actual flight operations of the real Falke, and it is highly recommended to use the The original Flight Manual as a reference. Slight changes in aircraft configuration may occur.

A recommended copy of the Flight Manual and Maintenance 1990 (June) Edition is available for download in the following link:
(It is not a VSKYLABS link nor materials and the credit goes to

To make things easier, this page is containing a brief summary along with practical instructions of how to operate and fly the VSKYLABS SF-25C Falke in X-Plane.


Getting started - Cockpit layout and instrumentation

The VSKYLABS SF-25C Falke is featuring a VFR cockpit layout, along with a GNS-530 (including two radios both for COMM and NAV). Although having a GNS, the aircraft is intended to use in VFR day conditions only. 

General VR manipulators optimization:
The VSKYLABS SF-25C Falke was designed to be fully compatible and usable with X-Plane 11.20 native VR capabilities. Operating the aircraft using VR controllers should be straight forward, although some functions may not feel comfortable or optimized for some users, depending on personal preferences and manipulators limitations. This project, like all of the VSKYLABS projects is under constant development, and such issues will be addressed on a regular basis through the active update system.

Note: Although optimized for VR, thr VSKYLABS SF-25C Falke is perfectly tuned and usable for standard 2D experience.

Cockpit Walk-Around

The VSKYLABS SF-25C Falke is featuring a basic, VFR cockpit. In the default version, cockpit placards are written in German language. The following illustrations and information is explained in English. However, once jumping into the seat, cockpit operations are very intuitive and straight forward.

Note: Airspeed Indicator, Vertical Velocity Indicator and Variometer instruments are all scaled with the Metric system. Aircraft airspeed measured in Kilometer per Hour (KM/h), and sink/descent rate is measured in Meters per Second (M/s).

Cockpit Handles and Levers
Handles and levers are shown in the following screenshots (from left to right):

  • Canopy Center-Line and Locking-Handle:
    • To be used to open/close the canopy.
    • Located behind the pilot, up in the attachment point of the canopy rail and the fuselage center line. 
    • It is a toggle mechanism.
  • Wing Spoilers:
    • For use during landing or rapid descent. Grab and twist forward/backwards this handle to control the wing spoilers extension ratio.
    • Glide path may be controlled with the spoilers, and approach at about 90 km/h with extended spoilers will increase the sink rate to approximately 3.7 m/s (12 feet per second).
    • There is a secondary spoilers handle in between the seats, for right seat pilot operations.
    • NOTE: In the real Falke, pulling the spoilers handle beyond it aft limit will activate the wheel brake. In the VSKYLABS Falke, the wheel brake is being operated with the use of the Parking Brake handle, which can be gradually pulled during the landing run.
  • Elevator Trim:
    • Mechanical Elevator trim, connected directly to the trim tab which is located on the elevator.
    • Elevator trim can be operated by grabbing and twisting the handle.
  • Fuel Shutoff Valve:
    • Main fuel line valve.
    • This is a toggle switch, meaning that it is being operated with a "on" / "off" mechanism.
  • Parking Brakes:
    • As described in the 'Wing Spoilers' information above,  In the real Falke, pulling the spoilers handle beyond it aft limit will activate the wheel brake. In the VSKYLABS Falke, the wheel brake is being operated with the use of the Parking Brake handle, which can be gradually pulled during the landing run.
    • Make sure that you are not landing with this handle pulled, or the aircraft may nose-over upon touch down.
  • Cowl Flap:
    • Operates the engine's cooling vent.
    • Grab and push/pull this handle.
    • The aircraft is equipped with a cylinder head thermometer. The supply of cooling air to the engine can be accurately regulated by controlling the cowling flap. The cylinder head temperature must be monitored carefully: under no circumstances must the temperature be allowed to exceed the maximum of 250 °C.
  • Cockpit Heating:
    • Cockpit heating handle.
  • Throttle:
    • Throttle control.
  • Carburetor Heat:
    • Use this handle to control Carburetor Heating.
    • RPM should reduce by approximately 150 rpm when carburetor heating is applied.
    • Do not start with carburetor heating pulled.

Cockpit Switches and Knobs:
Switches and knobs are shown in the following screenshots (from left to right):

  • Power Switch:
    • Main Battery power switch.
    • This switch will cut off electrical power. Systems that are connected directly to the Hot Bus will not be affected.
  • Starter Switch:
    • Activates the electrical starter for Engine start.
  • Circuit Breakers panel:
    • The Circuit Breakers panel in featuring push-pull breakers. These are practically working with a toggle mechanism.
    • On each breakers "neck" there is a painted color to be visible when a breaker is in its pulled-out position.
    • All breakers are painted in White, except the Electrical Fuel Pump and the Electrical Fuel Priming breakers which are painted in Red.
    • Aileron Trim:
      • The aircraft is equipped with an electrical aileron trim control, which is being operated manually by pressing the aileron trim switches (located on the main front panel along with a trim indicator).
      • This CB will disconnect the aileron electrical trim.
      • It is also to be used to disconnect the Electrical trim in a trim-runaway failure.
      • This CB is usually positioned "IN" in most of the time during flight.
    • Battery Bus:
      • Battery Bus CB.
    • Fuel Pump:
      • Electrical fuel pump operation.
      • To be used primary in conditions that require extra Engine reliability (before take off, rough weather etc...).
      • This breaker "shoulder" is painted in Red color. it is usually positioned "OUT" in most of the time during flight.
    • COM2:
      • Radio CB (COM2).
    • Avionics:
      • Disconnect all electrical avionics systems from the electric bus.
    • Cockpit Lights:
      • This breaker controls cockpit interior lights.
      • Note: The VSKYLABS SF-25C Falke is not equipped with instrumentation for night flying/IFR.
    • Fuel Priming:
      • The priming system draws fuel from the fuel tank directly into the cylinders prior to starting the engine.
      • During cold weather, when engine is difficult to start, fuel priming helps the engine to start as there is not enough heat available to vaporize the fuel in the carburetor.
      • This breaker "shoulder" is painted in Red color. it is usually positioned "OUT" in most of the time during flight.
  • Beacon Lights:
    • Activates the aircraft Beacon Light.
  • Nav Lights:
    • Activates the aircraft Navigation lights.
  • Ignition:
    • Ignition switch to drive the spark plugs (Magneto).

Cockpit Systems and Avionics:
Avionics/systems are shown in the following screenshots (from left to right):

  • Slip & Turn Coordinator:
    • The Slip & Turn Coordinator display the rate of turn and roll information, as well as quality and coordination of the turn.
    • The Falke should be flown with attention to turn coordination (how much the nose of the aircraft and the actual turn path are aligned).
  • Magnetic Compass:
    • The magnetic compass is a reliable, self-contained unit requiring no external power source, therefore it is extremely useful as a standby or emergency instrument.
    • Note that because if its internal mechanism, it is mostly accurate "around the horizon", so readings should be taken while the aircraft pitch attitude is less than ~18 Degrees.
  • Variometer:
    • The Energy Variometer gives information regarding the change in total energy of the aircraft. This is expressed in vertical speed (Meter per Seconds).
    • In powered flight, the Vertical Speed Indicator is being used for monitoring flight level trend changes and to ensure that level flight is being maintained. In up-powered flight ("Gliding"), the Variometer is being used almost continuously during normal flight, sometimes along with an audible output, to inform the pilot of rising or sinking air without the need to constantly monitoring the indicator inside the cockpit.
    • The VSKYLABS SF-25C Falke Variometer is featuring an Audio on/off switch and a dedicated volume control. 
  • Radio (com2).
  • Transponder.
  • Electric Aileron Trim:
    • Electrical aileron trim control.
  • GNS-530:
    • Fully operational GNS-530.
    • Consists Radio (COM1) and Nav.
    • GNS-530 can be hidden/shown (version v1.0a and above):

Cockpit Flying Instruments:
Flying Instruments are shown in the following screenshots (from left to right):

    • Vertical Speed Indicator.
      • Calibrated with the Metric system and shows Vertical speed in Meters per Seconds.
    • Airspeed Indicator:
      • Calibrated with the Metric system and shows airspeed in KM/h.
    • Yaw String:
      • A simple "device" for indicating a slip or a skid in the aircraft during flight.
      • It does not require the pilot to look down into the cockpit at the Turn & Slip indicators.
    • Altimeter.
    • Fuel Meter:
      • Fuel meter is located on the back wall of the cockpit, close to the fuel tank.
      • Fuel measurement should be taken in a straight and level flight, as this is a floating-ball system. Pitch attitude will affect accurate fuel measurement.

Flight Manual
LIMBACH L 2000 EA / EA 1
Although major parts of the information in this page is based/translated from the actual flight manual, the following information, data and procedures are not to be used for real-world training.

1.     Specifications and Limitations

1.1  Engine

       Limbach L 2000
       Max. rpm                                          3400
       Max. continuous rpm                     2700
       Minimum continuous rpm             2300
       Static rpm approx.                         2500 - 2700
       Max. cylinder head temperature
       at any of the four cylinders (2C)      250

1.2  Fuel

       AVGAS 100 Low-Lead or four star petrol (leaded auto 
       Fuel tank         litres         gallons (Imp)   gallons (US) 
                                  80              17.6                    21.1

1.4   Propeller

       Two blade wooden fixed-pitch propeller: 
        Hoffmann HO 11A-150B 90L or 
        MT-Propeller MT 150 L90-1A.

1.5  Engine instrumentation


        Starting range    0 - 700 rpm        (yellow sector) 
        Normal operating  700 - 2700 rpm     (green range sector) 
        Caution range     2700 - 3400 rpm    (yellow sector) 
        Max. revs         3400 rpm           (red line)
        Static revs.      ca. 2500 - 2700 rpm

       Oil Pressure Gauge

       Operating range          1-4 bar (15-59 psi) (green sector)
       Minimum oil pressure  1 bar (15 psi)   (red line)
       Maximum oil pressure 4 bar (59 psi)   (red line)

       Oil temperature gauge

       Operating range            50-120 °C      (green sector) 
       Minimum temperature   50 °C             (red line)
       Maximum temperature  120 °C           (red line)

1.11 Airspeeds

     Maximum airspeed                     190 km/h (102 knots 118 mph)
     Maximum maneouvring speed   150 km/h (81 knots 93 mph) 
     Maximum rough air speed          150 km/h (81 knots 93 mph) 
     Maximum airspeed
     with spoilers extended                190 km/h (102 knots 118 mph)

     Airspeed indicator markings

     Red line         190 km/h (102 knots 118 mph)
     Yellow sector    150-190 km/h (81-102 knots 93-118 mph)             
     Green sector     70-150 km/h (43-81 knots 50-93 mph)

1.12 Weights

       Empty weight                                        415 kg approx
       Max. permissible load including fuel     235 kg approx
       Max. permissible AUW (all up weight)  650 kg (1344 pounds)

1.15 Aerobatic maneouvres, cloud flying

    Aerobatics and cloud flying are not permitted.

2.  Operating Instructions

2.1 General

The 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 the operations of the engine. He must become thoroughly acquainted with the Flight Manual and the Operating Handbook and master the essential details of the airframe and engine.

2.3 Pre take-off checks

It is essential to check the following points before each flight.

    • Folding wings secured (if applicable)
    • Canopy closed and locked
    • Safety harnesses secure
    • Trimmer set
    • Spoilers closed and locked
    • Full and free movement of controls
    • Fuel on
    • Fuel in tank
    • Cowling flap open

2.4 Starting the Motor Glider

Starting procedure:

   • Apply parking brake
   • Open engine cooling vent
   • Open fuel cock
   • Push in for 5 seconds the Fuel Primer electrical pump if engine is cold.
   • Throttle to Idle
   • Master switch on
   • Switch off any sensitive electrical equipment 
     (radio etc.)
   • Ignition on
   • Is the propeller clear?
   • Press starter button

As soon as the engine starts release the starter button,and set the throttle so that the engine ticks over at about 1,000 rpm. The oil pressure should increase within 10 seconds.

2.4.3 Warming up, static rpm check

Full engine warm-up is not needed when using the VSKYLABS SF-25C Falke in X-Plane. However, the following procedure may be used to replicate real-life operations:
Warm up the engine by first running it at 1,000 rpm for about two minutes then at 1,500 rpm for five to 10 minutes (depending upon the ambient temperature) until the oil temperature reaches its operating point of 50 °C. The temperature gauge is relatively slow to respond so that at an indicated 50 °C the engine is already sufficiently hot. If the take-off point is some distance away, the engine may be warmed up whilst taxiing.

As soon as the operating temperature is reached,apply the brake, hold the control column fully backand run up the engine. Gradually open the throttle,check oil pressure and temperature and run for about 20 - 30 seconds, then check the carburettor heating. The revs should reduce by approximately 150 rpm when carburettor heating is applied. (Do not start with carburettor heating pulled). Then turn off carburettor heating and return to tickover.

2.4.4 Taxiing

The Falke can taxi unaided and is steered on the ground with the tail wheel, with a turning circle of 12 - 15 m. The main wheel brakes will stop the motor glider effectively. 
2.5   Take-off and climb

(Caution: See also 2.12 Wet wings - warning).
Pre-flight check list (see 2.3 or the placard in the cockpit).

  • Trim neutral, spoilers closed and locked, control column central (do not push the column forwards).
  • Apply full throttle.
  • For normal take-off run see section 3.1.
  • Check engine revs, allow ground speed to increase to 85-90 km/h (46-49 knots 53-56 mph) then climb with the airspeed not less than 85 km/h (46 knots 53 mph), with rpm at 2600 - 2700 rpm. Continue climbing to about 650-1000 ft such that the airfield is within reach in case of engine failure. After reaching about 150 - 250 feet the engine revs may be reduced.
  • Check that the oil pressure and oil temperature are in the green sector. The limits must not be exceeded.
  • Ensure that the airspeed when climbing is sufficient to cool the engine, so preferably keep the airspeed a little higher, 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. i.e. accept a shallower climb on reduced power.

2.6 Level Flight

The minimum airspeed for level flight is 80 km/h (43 knots 50 mph). Best cruising speed is about 130 km/h (70 knots 81 mph) at 2,500 rpm. Maximum cruising speed 150 km/h (81 knots 93 mph) at 2,700 rpm.

2.7 Landing

The aircraft can be landed with the engine either running or stopped. Approach at about 90 km/h (49 knots 56 mph), flying a normal gliding type circuit. Control the glide path with the spoilers. As the spoilers are effective it is not usually necessary to slip the aircraft. With spoilers extended the rate of sink at 90 km/h (49 knots 56 mph) is approximately 3.7 m/s(12 feet per second). At minimum touch down speed (80 km/h 38 knots / 44 mph) the Falke touches down with the tailwheel then with the mainwheel. The landing run of about 300 feet can be reduced effectively using the mainwheel brakes. The brake is operated by the spoiler control on the last part of its travel when it is pulled fully back so never touch down with the spoiler lever pulled fully back by the parking brake handle which is to be pulled out gradually during the landing run, if braking is needed.

2.8 Stopping and starting the engine in flight

Before switching off allow the engine to cool down by gliding on tick-over or flying level with the engine throttle back for a minute or two then return the throttle to tick-over, switch off all sensitive electronic equipment and finally switch off the ignition. Reduce airspeed to no more than 80-85 km/h (43-46 knots 50-53 mph) to reduce windmilling so that the propeller brake may be applied if desired in the final stages. If the engine has not been allowed to cool there may be a tendency for it to continue firing spasmodically. If this occurs, apply full throttle, during the last stage of the engine turning. 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, switch off all sensitive electronic equipment, switch on the ignition, fly at about 80-90 km/h (43-49 knots 50-56 mph). Set Priming and throttle settings for hot or cold engine as on the ground. The engine is very easy to start if the pilot is familiar with its operation.

If the engine is cold do not use full throttle until the oil temperature reading has returned to the green sector. At airspeeds of about 130-150 km/h (70-80 knots 81- 93 mph) a quick blip on the starter will start the propeller turning and the engine will start immediately (depending on engine temperature). Prime on, about one third throttle, ignition on. Height loss is in the order of 500 - 600 feet.

2.9 Flying with the engine stopped

The aircraft handles very well at 80-95 km/h (43-51 knots 50- 59 mph) with a sink rate of about 1.2 m/s (3.94 ft/s) in straight flight.

Close the cowling flap to reduce drag when the engine is off. Open the cowling flap again before restarting the engine. The Falke, being a low wing monoplane, has to be flown cleanly. When skidding or flying at less than 80 km/h (43 knots 50 mph)the airflow breaks away from the wing/fuselage filletarea and performance is lost. When gliding and especially when turning, fly the aircraft as cleanly as possible and avoid skidding in turns. The traditional solution of a length of string mounted on a 10 cm (4") piano wire mast, about 20 cm (8") ahead of the canopy in front of each seat (the VSKYLABS SF-25C is equipped with a single string mounted ahead on to the center of the canopy). It is still a highly cost-effective aid to accurate flying. With a little practice the pilot will be flying accurately and climbing well in thermals even when compared with pure gliders.

2.10 Slow flying and stall characteristics

At maximum flying weight the stalling speed is about 65-70 km/h (35 knots 40 mph) with the engine running or stationary. At this speed the airflow over the wing roots begins to break away; ailerons and rudder are still fully effective. With a forward CG position the Falke simply lowers it's nose if the control column is pulled right back. With rearward CG positions it is possible to fly on, fully stalled in still air conditions with the control column right back whilst retaining full aileron and rudder effectiveness. In both CG positions immediate recovery is effected by easing the control column gently forward. Needless to say, in rough air conditions stalling will cause a wing to drop. When the aircraft is stalled with high engine revs the propeller slipstream tends to produce false ASI readings from the tail mounted pitot. If this occurs a stalled condition is still recognisable by the fact that the ASI needle flicks vigorously between 50 km/h (27 knots 31 mph) and 100 km/h (54 knots 62 mph). (needle flicking is not yet featured in the VSKYLABS SF-25C Falke, but it will be in future versions). If stalled in a 30° turn, the Falke gradually drops the outer wing such that normal flying speed may be regained when both wings are level. Stalling characteristics are the same engine on or engine off.

2.11 Spinning

Except with rearward CG positions it is very difficult, if not impossible, to make the Falke spin. If no corrective action, such as releasing the backward control column 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 rearward CG positions a continuous spin is impossible. A spin may be induced by gradually easing back the control column and crossing the controls but it will come out of the spin within five turns of its own accord even if controls are held crossed: the spin becomes a slipping manoeuvre from which normal flight is easily resumed. Pro spin aileron will cause spin to become a spiral dive from which the pilot should pull out gradually but without delay to avoid overstressing the aircraft (see above).

A spin can of course be corrected in the normal manner, this taking about half a turn. When rotation stops pull out of the resulting dive gently and do not hesitate to use the spoilers to prevent the speed building up excessively. The Falke is not approved for aerobatics.

2.12 Wet wings warning

The following change in handling of the Falke due to wet wings is not being simulated in the current version of the VSKYLABS SF-25C Falke:

The Falke wing has a glider airfoil which is sensitive to rain. Drops of rain on the wings disturb the air flow and reduce the lift. Whereas minimum airspeed with dry wings is about 70 km/h (38 knots 44 mph) with wet wings it is 80-85 km/h (43-46 knots 50-53 mph). Wet wings change the stalling characteristics. Whereas the Falke is positively docile with dry wings it will drop a wing when wet. When flying in rain keep the airspeed above 85 km/h (46 knots 53 mph). Do not attempt to take-off at less than 85 km/h (46 knots 53 mph). Fly at about 105 km/h (57 knots 65 mph) when climbing and on the approach. Avoid steep turns and other maneuvers involving high G-forces. If there is snow or ice on the wing it must be cleaned off completely before take-off. Do not forget the tail-plane.

2.13 Cold weather flying and risk of carburettor icing

Especially when flying in the winter it is important to check that the oil temperature does not drop below 70 °C whilst the engine is running. The carburettor and intake are warmed by the hot recirculating 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 must be monitored carefully: under no circumstances must the temperature be allowed to exceed the maximum of 250 °C.

Carburettor icing can occur when humidity is high (especially near clouds) and where the air temperature is between -10 °C & +18 °C. The pilot will recognise the rough engine note and reduced rpm. Carburettor heating control should be pulled immediately.

Carburetor icing can also occur when the engine is idling for long periods whilst gliding. Pull carburetor heat from the start but remember to cancel carburettor heat when you require full engine performance again.

Operation of the carburettor heater (when there is no icing in the carburettor) results in a drop in revs of approximately 150 rpm. in warm dry air carburetor heat should be fully off (pushed fully home).

2.15 Safety factors and engine reliability

It should always be borne in mind that the motor glider engine is not designed to such stringent specifications as that of a light aircraft (e.g. single ignition system instead of dual); it is simpler and cheaper. This must be taken into account when flying, by observing safety heights and flying in such a way that suitable fields are always at hand should it be necessary to land out.

2.19 Crosswind

The Falke has been flight-tested for take-offs and landings in crosswinds up to 13 knots (15 mph).

2.20 Field landings

Flight-testing of the tricycle undercarriage SF 25 C Falke included field landings on unprepared soft earth (a potato field) along the rows. Other factors to take into account include wind strength and direction, length of landing area, obstruction free approach, gradient etc.

3.  Performance Data

3.1   Take-off performance

Note: More than 100 flying hours were made only during the Flight dynamics evaluation in the development process of the VSKYLABS SF-25C Falke Project. The Flight dynamics model was tested thoroughly and tuned to deliver the most realistic aircraft performance and handling qualities. However, due to certain limitations in a PC based flight simulators, some of the performance figures may result with reasonably margins when comparing to the read-world Aircraft.

These performance figures have been obtained from type test results and can be reproduced provided that the motor glider and engine are in good condition and that the pilot is of average ability and skill.

Maximum all up weight (AM): 650 kg (1433 lbs) Level airfield with short well kept grass. Wings dry, wing surface clean. No wind. Air pressure standard for height of airfield above sea level.

Lift-off speed: approx. 70 km/h (38 knots 44 mph).

                   Airfield                       Air temperature C
                                         -15°              0°               +15°          +30°
                  m        ft         m  ft           m    ft          m      ft       m       ft
Take-off     0         0        90   295     101  331      112  367    124   407
 run           250     820     95   312     107  351      119  390    131   430
                 500     1640   101  331     113  371      126  413    139   456
                 750     2460   107  351     120  394      134  440    148   486
                 1000   3280   114  374     128  420      142  466    158   518

                                        -15°              0°               +15°          +30°
                  m        ft         m  ft           m    ft          m      ft       m       ft
Distance     0         0        233   764   261  856      291  955     322   1056
req. to        250     820     247   810   277  909      308  1010   341   1119
clear           500     1640   263  863   294  965      327  1073    362   1188
15 metre    750     2460   279  915    312  1024    348  1142    385   1263
(49ft)          1000   3280   296  971    332  1089    369  1211    409   1342

3.2 Rate of climb

Maximum all up weight at sea level 
Rate of climb: 2.9 m/s
Climb speed: approx. 85 km/h (46 knots 53 mph)

3.3 Airspeeds

Level flight from 75 km/h (40 knots 47 mph), throttled back

Cruising speed:
ca 130 km/h (70 knots 80 mph) at 2500 rpm

Maximum cruise speed:
150 km/h (81 knots 93 mph) at 2700 rpm

Speed on approach: 
90 km/h (49 knots 56 mph)

Touchdown speed: 
70 km/h (38 knots 44 mph)

3.5 Gliding performance

Engine off, cowling flap closed:

Min sink: 1.09 m/s (3.58 ft/s) at 75 km/h (40 knots 47 mph) 
(single wheel undercarriage)
1.15m/s (3.77 ft/s) at 75 km/h (40 knots 47 mph)
(two wheel undercarriage)

Glide ratio: ca 1:22 at 90 km/h (49 knots 56 mph)