My obvious choice of dummy engine kit for the DB Bleriot would be the one supplied by Arizona Model Aircrafters. it was their version of a Gnome engine kit and it had the correct number of cylinders. Had I used one of the other kits in stock it would have been necessary to remake the crankcase and change the number of cylinders.
The kit included a 'detail' set laser cut from clear acrylic sheet. The intention with this set was to 'super' detail the cylinder heads. There was, however, some discrepancies with the laser cutting, insufficient holes and some in the wrong place. Also some of the laser cut acrylic discs were way too large a diameter and would not fit into the tops of the supplied Williams cylinders. So the decision was made to run with the injection moulded cylinders and cylinder heads from Williams and discard the acrylic sheet. I say 'discard' but like every true model maker you keep it safe as it will almost certainly get used for something at a later stage.
The objective with this exercise was to make a convincing dummy engine quickly and not get too bogged down with making things fit and sourcing additional items when the Williams moulded parts were more than adequate.
The kit included a 'detail' set laser cut from clear acrylic sheet. The intention with this set was to 'super' detail the cylinder heads. There was, however, some discrepancies with the laser cutting, insufficient holes and some in the wrong place. Also some of the laser cut acrylic discs were way too large a diameter and would not fit into the tops of the supplied Williams cylinders. So the decision was made to run with the injection moulded cylinders and cylinder heads from Williams and discard the acrylic sheet. I say 'discard' but like every true model maker you keep it safe as it will almost certainly get used for something at a later stage.
The objective with this exercise was to make a convincing dummy engine quickly and not get too bogged down with making things fit and sourcing additional items when the Williams moulded parts were more than adequate.
Discarded laser cut acrylic sheet.
The first job was to make sure all the moulded components were present and correct.
Components ready for assembly.
Satisfied that all the parts were present, the 2 halves of each cylinder were sanded flat, 14 in total. This was done using the plate glass sheet with abrasive paper stuck to it. Then any 'flashing' on the moulded parts was removed.
Sanding the parts to achieve a 'good' fit
Next the 2 halves of each cylinder were glued together and spark plugs fitted. These parts are 'handed' and each cylinder when glued together should have only 'one' area for fixing the spark plug to.
Cylinders glued together and spark plugs fitted.
The cylinders required opening up to allow the cylinder heads to fit correctly. Again these parts are 'handed' when assembled. When looking at the engine from the front the push rods should also be facing towards the front and the spark plug should be on the left.
Cylinders with heads fitted.
Workshop Tip No. 10
There are many kinds of glue available for sticking together 'polystyrene' or 'ASB' plastic commonly found in injection moulded kits. The traditional 'polystyrene cement', 'liquid polystyrene cement' and 'model cement pens' are OK, but they all leave 'glue' between the two surfaces being fixed together to a greater or lesser extent. These glues should be applied sparingly so as not to look unsightly.
My preference are 'solvent' glues such as 'plastic weld'. This product actually welds together the two surfaces and doesn't leave a 'glue' build-up as any excesses solvent quickly evaporates. Also capillary action 'wicks' the solvent around the joint distributing the solvent producing a continuous weld. Make sure you follow the manufactures guidelines when using solvent or polystyrene glues.
A selection of 'plastic' glue, cement, solvent.
You can also use solvent glue to stick vacuum formed parts to different kinds of wood. Simply 'wet' the area of the vacuum formed part with solvent that comes into contact with the wood and apply solvent to the wood also, this prevents the wood from absorbing the solvent applied to the plastic before it has time to do its job. Then before the solvent evaporate press the vacuumed formed part firmly onto the surface of the wood. The solvent melts the surface of the vacuum formed part and this melted plastic is transferred to the surface of the wood. This can produce a very good bond when done correctly. Practice first on a scrap piece of vacuum formed material and make sure your solvent has melted the surface of the plastic sufficiently.
All the wooden parts are laser cut and require removing from the waste. Once this has been done it will be apparent that there are many duplicate parts. These additional parts are included to allow the builder to adapt the crankcase depth to hide the working engine or electric motor.
All the wooden parts are laser cut and require removing from the waste. Once this has been done it will be apparent that there are many duplicate parts. These additional parts are included to allow the builder to adapt the crankcase depth to hide the working engine or electric motor.
Laser-cut parts removed from the waste.
I had to make a small modification to the crankcase sides as the 'cut-outs' were too shallow. This was easily undertake by cutting down the thickness of the lugs on the crankcase side pieces.
2 of the crankcase side pieces, modified lug shown on the bottom.
This is how a typical crankcase side part fit before and after the simple modification.
Before, part is standing proud of the crankcase ring.
After, part is flush with the crankcase ring.
Next each side part had a chamfer sanded to both of the long edges, this allows them to fit tightly together. The angle of the chamfer is not critical and any gaps left on the reverse will be filled with glue later. I glued 3 side parts to the crankcase ring with cyanoacrylate first to hold the shape, the remainder were glued in with wood glue, I'm not a great fan of cyano!
The initial side parts glued to the crankcase ring.
Chamfered parts can be clearly seen in this shot.
Part finished crankcase with all side pieces fitted.
The Gnome engine drawing seen under the part finished crankcase is for reference. This drawing has been enlarged to the correct size for the 1/4 scale DB Bleriot . The square outline drawn around the engine indicates the available space within the fuselage and any part of the dummy engine that crosses this outline with have to be removed. This indicated that 3 cylinders would have to be cut down slightly.
After the part finished crankcase had dried the cylinder surround pieces were glued in place, one to the front and one to the back for each cylinder. To ensure a tight fit around each cylinder all the cylinder surround pieces were glued in place to the front first. Then each cylinder in turn was placed up against the front surround piece and the rear piece added.
The last cylinder surround piece being glued in place.
Having got this far most of the build is finished. Remember the construction will be tailored to your individual requirements, engine chosen etc. In my case this dummy engine was to replace the original power-plant altogether.
These were the finished components that made up my dummy engine. Additional parts were added to the rear to enable the whole engine to utilize the same bolt holes that the RCV 120 engine used and to take up the same distance fore and aft. A bulkhead 'packer' with be added to achieve this fore and aft requirement. This 'packer' is not shown in the picture below but will be included later.
The finished engine components.
The nut and bolt are to retain the scale propeller.
The next post will see the engine components assembled, painted and installed it to the Bleriot. A scale propeller will then be made in a future post.
To be continued...
