1. VMAR - Engine Power Module - Information & Tips
1.1. Power Module - Alignment - What angle to use?

Question: My VMAR ARF uses the VMAR Power Module system. What angle should I align the Power Module at?

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.  
 
The default 0.0 settings are the best place to start remembering that the VMAR Power Module system makes it easy to make incremental adjustments to the horizontal and vertical thrust angles as fliers become more familiar with their model and engine power settings. No setting is irreversible. The thrust angles can be changed at any time.
1.2. Power Module - Distance from fixed Firewall - How Much?

Question: My VMAR ARF uses the VMAR Power Module system. How much space should I allow between the fixed (aft) firewall attached the fuselage and the power module (adjustable) firewall?

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.
1.3. Power Module - Wood - Quality of Plywood

Question: A friend of mine has a VMAR model from a couple of years back. It has a power module with removeable firewall. He mentioned to me that the plywood used was strong but was not attractive to look at. Is this still the case?

Answer: We have been upgrading our plywood and sourcing new supplies since early 2004. Except for older production that may still be in the distribution chain, all firewalls now have a better and cleaner appearance. That said, please note that we were dealing with a cosmetic issue here. All firewalls have been more than strong enough to work well with the model they were supplied with.

1.4. Power Module - Wood - Laminations - Visible

Question: When I look at the edge of my power module firewall, I can see small gaps between some of the laminations. Is this normal? Is it OK? Is it coming apart?

Answer: Yes this is normal. Yes it is OK. No it will not come apart.

Expanded Answer: The power module wood firewall is made from 2 or 3 plywood layers that have then been laminated together with epoxy to produce a firewall that is approximately 1/4" (6mm) thick. There will be a wider gap between the plywood pieces than between the individual plys within a plywood piece. This is normal. The power module firewalls are extremely strong and are held together in operational use not only by Epoxy but by four engine mounting bolts and four power module to fuselage stud and nut sets. This represents 8 mechanical fasteners in addition to the epoxy between layers... all acting over an area less than the size of a dinner plate.

Short of a very violent crash the power module firewall is not going to come apart. Small gaps or voids in the plys or in the bonding layer between plywood pieces are not going to impact on the performance of the power module firewall in our application.

If you are wondering about sealing the power module firewall, please see below:

Power Module - Wood - How to Seal?

Question: Should I seal the wood power module firewall that came with my VMAR ARF?

Answer: It's not really necessary but it probably can't hurt aside from adding a bit of weight. If you have an hour or so and the right materials, you can improve the cosmetic appearance of the power module firewall by sealing it.

For those who wish to seal the edges and faces of the power module firewall, we recommend Pacer ZAP-A-GAP CA+ for filling edge voids or edge gaps between layers and then after the CA+ has cured, apply Pacer Finishing Resin to the edges and the front and rear faces of the firewall.

1.5. Power Module - Wood - How to Seal?

Question: Should I seal the wood power module firewall that came with my VMAR ARF?

Answer: It's not really necessary but it probably can't hurt aside from adding a bit of weight. If you have an hour or so and the right materials, you can improve the cosmetic appearance of the power module firewall by sealing it.

For those who wish to seal the edges and faces of the power module firewall, we recommend Pacer ZAP-A-GAP CA+ for filling edge voids or edge gaps between layers and then after the CA+ has cured, apply Pacer Finishing Resin to the edges and the front and rear faces of the firewall.

1.6. Power Module - Retaining Nuts - Self Locking & Plated

Question: What type of retaining nuts are used with the Power Module?

Answer: Prior to mid 2004, we used a lightly plated metric nut. These worked but occasionally rusted and required thread locker to ensure they stayed tight.

Since mid 2004 we have used a plated (chrome look) metric self locking hex nut like you would find on high end machinery. These look better, work better and do not require thread locker.