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 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 adjust the gap and also control both the horizontal and vertical engine thrust angles.

 

We recommend first checking the assembly manual for your model and any specific Read Me First or Knowledge Base articles that may refer to this specific question as it pertains to your model.

 

In the absense of any specific documentation, we suggest the following:

 

a) Look over the cowl mounting tips provided in your assembly manual and in the article referenced below. Without installing the power module, mock up your cowl installation on the fuselage. No need to actually cut the cowl out at this point. Just align it and angle it etc per the articles and your assembly manual. Generally this leaves the back edge of the cowl overlapping the front of the fuselage by about .125-.25 in. (3-6mm). Mark the edge of the cowl with low tack masking tape for later reference.

 

b) Measure the distance between the front of the cowl crankshaft clearance hole and the forward face of the fixed firewall attached to the fuselage.

 

c) Now remove the cowl from the fuselage. Install your engine mounts to the power module firewall and your engine to the engine mounts.

 

d) Install the power module firewall with engine mounts and engine onto the four threaded studs using the nuts and washer arrangement outlined in your assembly manual.

 

e) Position the power module firewall so that the distance from the fixed firewall (fuselage front) to the forward face of the engine thrust washer (behind the prop) is about .125-.25 in. (3-6mm) longer than the distance measured in b) above. You can adjust the location of the power module firewall and the engine on the mounts to obtain this distance.

 

f) This can be a bit of an iterative process. You may have to try several different positions to get the optimum solution for your particular engine and model combination. Work slowly and patiently. Try to think ahead about eventually cutting out the cowl to clear your engine and muffer. Also the location of the fuel tank. type of spinner and prop etc. Also the thrust angles etc. We have referenced a thrust angle article below to keep in mind when adjusting the distance between the fixed firewall and the power module firewall.

 

g) Remember that the power module system gives you tremendous flexibility to accomodate a great number of different engines. If it does not work out on the first try, don't sweat it, we've given you a system that you can easily adjust many times until you get it the way you want it.