The preview versions are provided in a simple ZIP archive for the time being. Simply unzip the archive in a folder of your choice and run the executable SkyDolly.exe.

You may want to create a "desktop shortcut": simply right-click on SkyDolly.exe and choose "Create shortcut". Move the shortcut onto your desktop and/or to the Windows start menu.

Load the Flight

Sky Dolly automatically stores all recorded flights in the logbook (an SQLite database):

* Select a flight by left-clicking on a row in the logbook table

* Click the "Load" button

* Alternatively double-click on a row (except on the Title column which starts editing the Title of the flight)

The flight is now loaded into memory and is ready for replay.

Replay

In order for Sky Dolly to be able to send ("replay") the recorded "simulation variables" to Flight Simulator 2020 a flight must be already present.

In Flight Simulator 2020

In order to create a new flight in Flight Simulator 2020 follow the usual steps to start a new flight:

* Choose any location on the world map as either departure or arrival (*)

* Choose an aircraft, preferrably the same as with which the original flight has been recorded (**)

* Click the FLY button

* Optional: choose the desired time of day and wheather

(*) The selected location does not matter: the aircraft will be "teleported" to the proper location upon replay

(**) It is technically possibly to replay the flight with any aircraft. Note though that the exact same flight path will be taken (and wheels may seem to be "stuck" in or "float" above the runway, depending on the original aircraft height). So if you record a flight with a Cessna and replay it with an A320neo the flight will be... interesting ;)

The original aircraft with which the flight was recorded is shown in the logbook table as well in the "Flight" (press key F) dialog, under "Aircraft". That "Flight" dialog also shows the initial weather conditions, for information purposes (only).

In Sky Dolly

Now the previously loaded flight can be replayed with Sky Dolly:

* By clicking the "Play" button in Sky Dolly

* Alternatively hit the spacebar or P key

* Hitting the same key again stops the replay

* The key ESC also stops the replay (just as it also stops the recording)

If you want to load another flight simply follow the inital steps above. No need to restart the existing flight in Flight Simulator 2020. Note though that when changing location it may take a while for Flight Simulator to download / update the new terrain data. Graphical glitches are to be expected in this case.

Most aircraft do not like it when they suddenly drop from 20'000 feet altitude right onto the runway upon time slider changes ;)

So it is highly recommended to disable crash, stress & engine damage in Flight Simulator 2020 prior to replay. This is because forces acting on the aircraft are still simulated during replay - and especially also during replay position seeking with the time slider.

So disable the following options in Flight Simulator 2020:

• Assistance Options / Failure And Damage / Crash Damage -> Disabled
• Assistance Options / Failure And Damage / Aircraft Stress Damage -> Disabled
• Assistance Options / Failure And Damage / Engine Stress Damage -> Disabled

SimConnect

Sky Dolly - like most other third party applications - communicates with Flight Simulator via the official SimConnect application programming interface (API).

That API gives access to the aircraft state in the form of so-called "simulation variables". Examples of such variables are:

* Latitude / longitude / altitude

* Aircraft attitude (bank, pitch, heading)

* Gear / flaps up/down

A complete (long!) list of simulaton variables is available in the official developer documentation:

https://docs.flightsimulator.com/html/index.htm#t=Programming_Tools%2FSimVars%2FSimulation_Variables.htm

Supported Simulation Variables

In order to keep the required storage space at a minimum and improve performance by minimising the size of the request message sent to Flight Simulator during replay Sky Dolly primarily focuses on variables having the greatest "visual impact". So if a given lever or button activates a visible surface (flaps, ailerons, but also canopy or a landing hook) an attempt to record that variable is made.

Optimised Messages

During replay the previously recorded simulation variables are sent for each "simulated frame" event. In order to optimise performance (fewer messages = less CPU usage) and especially also storage requirements only those variables which have actually changed are recorded and requested during replay.

This is illustrated in the "Simulation Variables" dialog in Sky Dolly (press key V):

* The tabs represent the "simulation variable groups"

* "Inactive" variables - where the value did not change during a certain amount of time - are rendered as disabled text, indicating that they are currently not sent to Flight Simulator 2020 during replay

Note that Sky Dolly applies a clever "seek & search" algorithm which makes sure that all previously set variables are still applied, regardless of when their value has changed last and regardless of the new timeline position which has just been set. Clever :)

Known Limitations

Not all simulation variables are actually "writeable", that is, external applications such as Sky Dolly cannot modify them. Which is a precondition in order to "replay" a given variable.

In addition, not all aircraft honour those simulation variables. That is specifically true for third party aircraft. This is because some aircraft use their own set of (local) variables (for various reasons).

Other aircraft do react to simulation variable changes, but have their own local variable which "counter-acts" against the simulation variable. As Sky Dolly goes a step further - again in order to save on storage space and optimise performance - and only sends variables if their value actually changes such "counter-action" is a problem, as it "nullifies" the effect of the previously set value.

One such example is the "canopy" which either is always closed or opened again, depending on some switch in the cockpit of the given aircraft. In order to override that switch (in effect the corresponding local variable) Sky Dolly offers a "Repeat Values" setting (under File / Settings...), which - if enabled - always send the simulation variable, also if its value does not change.

A320neo (A32NX) by "FlyByWire" (FBW)

Unfortunately one notable example of a 3rd party aircraft which ignores (or "acts weird upon") the official simulation variables is the A320neo (now renamed to A32NX) by "FlyByWire" (FBW), specifically the development version (at the time of this writing). The current 0.6 stable version should still work fine, but the current development version is implementing more and more "custom systems" which do not react upon (or even properly report) the simulation variables, as own internal "local variables" are used to model the various aircraft systems.

Unfortunately that development is "out  of reach" for Sky Dolly, and one shall see whether support for the official "simulation variables" will be (re-)added in future "stable" versions of the A32NX.

Recording Frequency

Sky Dolly offers the possibility to select the desired recording frequency, or sample rate:

* File / Settings...

* Open the Recording tab

* Set the desired Record Frequency (default: "Auto")

The default setting "Auto" will automatically adjust the recording frequency to the "simulated frame" events, as reported by Flight Simulator 2020. Or in other words: the aircraft state (-> "simulation variables") is sampled every simulated frame.

So why offer the possibility of recording at rates as low as 1 Hz ("one sample per second")? Because the more samples are taken, the more work Flight Simulator 2020 needs to do (to gather the values and send the response messages via the SimConnect adapter to Sky Dolly) and the bigger the storage requirements get.

Interpolation

In any case Sky Dolly always interpolates between the recorded "sample points" with what is known as "cubic spline interpolation" (e.g. refer to https://en.wikipedia.org/wiki/Spline_interpolation as  a good starting point). "Interpolation" basically makes "educated guesses" about values between "known values" ("samples").

However it is intuitively clear that the less data we sample, the less "details" we can capture. When it comes to flying "less details" mostly affects the accuracy of the recorded flight maneuvres: if we only sample at 1 Hz a barrel roll with an (exagerated) roll rate of, say, 2 Hz (two rotations per second!) cannot possibly recorded in an accurate manner!

On the other and airlines which "mostly fly straight lines" and "slow roation movements" may be perfectly captured with a sample rate of 1 Hz only!

The following video illustrates the usage of three different recording rates and compares the results with the original captured video:

https://youtu.be/bfgkY0eXL4w

Recommendation

* When in doubt, use the "Auto" setting: this gives the best accuracy in any case (at the expense of required storage space - CPU usage is only marginally affected)

* When "long flights with airliners" are to be recorded lower the recording rate accordinly - even 1 Hz results in good results

* Note that you can dynamically change the recording rate while recording!

The "Formation" module in Sky Dolly allows you to manually take control of the aircraft and join the formation.

Since Sky Dolly v0.8 there are two "formation replay modes" available, namely:

• Take control of recorded user aircraft
• Fly with formation

Both replay modes essentially allow you to manually fly together with the recorded aircraft(s) - the formation. The difference: in the first mode you take control of an already recorded aircraft (the one currently selected as "user aircraft"), whereas in the second "Fly with formation" mode you fly along with your currently "active" (loaded) aircraft. This means that you can also join a "single aircraft" formation (the "Take control" mode on the other hand requires at least two recorded aircraft - otherwise you'll simply fly alone again).

This is how it works in detail:

Take Control of Recorded User Aircraft

• Load an existing flight (at least two aircraft)
• Switch to the Formation module (press F2)
• Select the "Take control of recorded user aircraft" replay mode (combobox bottom right)
• Select the desired aircraft, by marking it as "User Aircraft" (double-click on the table row, or select the row and press the "Set User Aircraft" button)
• Press "Play" (key P)

You are now in control of the previously recorded user aircraft.

Note that in this repaly mode you can switch the current "user aircraft" (the "active" aircraft being followed by the camera and being flown with the currently loaded aircraft) at any time, also during replay:

• Select the aircraft in the table
• Press the "Set user Aircraft" button
• Alternatively simply double-click on the aircraft row in the table

Fly with Formation

• Load an existing flight (at least two aircraft)
• Switch to the Formation module (press F2)
• Select the "Fly with formation" replay mode (combobox bottom right)
• Select the desired user aircraft you wish to fly next to, by marking it as "User Aircraft" (see above)
• Select the desired starting position, by clicking on one of the aircraft icons in the "Bearing" group box
• Choose the initial vertical / horizontal distance (which is measured in "multiples of wing spans" of the selected user aircraft
• Press "Play" (key P)

In both modes you can press the "Pause" button (or key P), which also pauses (technically: "freezes") your own manually flown aircraft. In the "Fly with formation" replay mode you can also re-position your aircraft again while paused, by simply clicking on one of the aircraft icons in the "Bearing" group box again.

Returning to Normal Replay

If you get lost you can simply select the "Formation (normal)" replay mode. This will hand back full control to Sky Dolly, over all recorded aircraft.

Yes, since Sky Dolly v0.8 the tail number of the recorded aircraft can be changed in the Formation module (double-click with the left mouse button on the corresponding table cell to enable edit mode).

However it is correct that this does not yet have a visible impact on the currently loaded flight in FS 2020, for two reasons:

* The tail number of the user aircraft (the one being followed by the camera in FS 2020) does not get updated (unless the flight is restarted in FS 2020)

* "AI aircraft" (in formation flights) show a white empty box instead of the tail number (that is a bug in FS 2020)

But I still decided to make the tail number editable in Sky Dolly, because it may actually work better with future releases of FS 2020.

Why does the engine shut down?

Sky Dolly v0.8 introduced improved "is the engine running" detection and better "autostart/shutdown" support based on a new "combustion" simulation variable which is now being recorded.

For existing flights recorded with Sky Dolly v0.7 and before this simulation variable is initialised ("migrated") on a "best effort guesstimate", as follows:

• If the thrust lever is > 0, then the combustion is initialised with 1 ("engine running")
• If the thrust lever is "fully pulled back" (= 0) then the combustion is initialised with 0 ("engine shutdown")

Of course that implies that the engine - again, for flights recorded with v0.7 and earlier only - is now shutdown whenever the thrust levers are fully pulled back. And started again when the thrust levers are pushed forward again.

For flights recorded with Sky Dolly v0.8 the actual "combustion" value as reported by the flight simulator is recorded.

Note that all engines are started at the same time - including for flights recorded with Sky Dolly v0.8 - as soon as one engine combusts: this is because an "engine autostart" event is sent to flight simulator, which is the equivalent to "CTRL + E".

So while this does not allow a faithful replay of the actual engine startup process (specifically when multiple engines are involved) it should more reliable detect when at least one engine is running. This also works when seeking back and forth in the timeline, so "flying aircraft with dead engines" should now be a thing of the past.

Can I re-enable my engines such that they run constantly during the entire flight?

Yes, but this requires some manual steps which involve "diving into the database" (logbook), using a database browser such as:

https://sqlitebrowser.org/

• In Sky Dolly it is recommended to first create a backup of your logbook
  • File | Logbook Settings..., choose "Next time, when exiting Sky Dolly"
• Close Sky Dolly
  • To execute the backup
  • Also in order such that no other transaction is running on the same database while we are modifying the data in the subsequent steps
• Launch DB Browser for SQLite
• Open the logbook
  • Set the file filter to "All files"
  • Logbook location, see Files | Logbook Settings... in Sky Dolly
  • Default location: "c:\Users\[Your Username]\Documents\Sky Dolly\Sky Dolly.sdlog"
    • Your backups will by default be in a "Backups" subfolder in that same location
• In the "Execute SQL" tab copy and paste the following update statement:
  • This will update the "combustion" value of all four engines to 1 ("combusted" = "running") ...
  • ... for the flight given by :id (this placeholder is to be replaced with an actual flight ID, see below)

update engine
set general_engine_combustion1 = 1,
    general_engine_combustion2 = 1,
    general_engine_combustion3 = 1,
    general_engine_combustion4 = 1
where aircraft_id in
(select a.id
 from aircraft a
 join flight f
 on a.flight_id = f.id
 where f.id = :id
);?

• IMPORTANT: Before you execute this update statement replace the :id (including the colon) with the actual flight ID, e.g. 73
  
  • The flight IDs are shown in Sky Dolly, in the column "Flight" of the logbook
• In order to persist the updated data click the "Write changes" button (top-most toolbar)
  • Or execute a commit;

That is it, the engines should now be constantly running for flight 73.