Answer: The VMAR Power Module system uses a fixed firewall "ring" permanently attached to the fuselage and a removable forward firewall "plate" to which the engine mounts are installed. Four stud bolts protrude from the fixed firewall ring and are used to set the offset spacing and hence the angle between the fixed firewall ring and the removable firewall plate.

 

This system provides a great deal of control over the offset spacing ("gap") between the firewalls to accommodate a wide range of different engine depths and spinner types. By varying the placement of the retaining bolts and washers on the four stud bolts, modelers can also control both the horizontal and vertical engine thrust angles.

 

We recommend a default setting for the horizontal and vertical engine thrust angles of 0, 0 respectively by having a consistent (equal valued) offset between the fixed firewall ring and forward firewall plate. The most common departure for this default configuration is 1-3 degrees of right thrust to assist with take offs. The vertical thrust angle can be adjusted as well if for example a particular engine power and weight combination results in "ballooning" of the model when additional power is applied above a cruise setting sufficient to maintain level flight. Such ballooning is often an indication of the need to adjust vertical thrust angles.