VIA Technologies EPIA SN-Series Specifications download pdf (Page 101)

FASTER Engineering Model

6.5.5 Tunnel in The Sky Management Block

The guidance tunnel is a critical tool for repeating the same planned trajectory during

flight and constitutes one of the peculiarities of the FASTER EM. A complete description

of the system is given in the next Chapter and here is presented only the Simulink block

used for transmit all the state variables needed for attitude representation and the

trajectory drawing.

The tunnel in the sky management block (Figure 74) is connected to both GPS and

I.M.U blocks; these two blocks have different update rates: 100 Hz the I.M.U and 5 Hz

the GPS one. The block itself must guarantee an adequate refresh rate to avoid “choppy”

animations during tunnel representation, and it is actually set to 10 Hz. This value is the

result of some trades off that involved also the graphical software running on the EPIA

board, which has limited graphical performances, and it is not able to reach an higher

video refresh rate.

Simulink is able to manage different block rate using Rate Transition Blocks. The

block behavior is automatically selected and depends on the sample times of the ports to

which the block connects, the priorities of the tasks for the source and destination sample

times and wether the model specifies a fixed or variable-step solver [Ref. (51)].

Being periodic the sample times of the GPS and I.M.U blocks the following behavior

are applied:

 GPS block outputs: inTS > ouTs (5 to 10 Hz), the block acts as unit delay with

data integrity and deterministic. The input is delayed and held by one

sampling interval.

 I.M.U block outputs: inTs < outs (100 to 10 Hz), the block acts as a Zero

Order Hold with data integrity and deterministic. It samples and holds its

input for the specified sample period.

Subsystem 1 & 4 operate a selection of the necessary variables while the small block

on the right bottom substitutes the yaw angle measured by the I.M.U (magnetic course)

with the yaw angle determined by the GPS receiver (true course). This “trick” solves a

visualization problem that arise when flying with high sideslip angles that could make the

tunnel impossible to be seen by the pilot. The virtual tunnel block is the processing block

that prepares data before transmission and manages tunnel waypoints.

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VIA Technologies EPIA SN-Series Specifications Page 101