Tuesday 20 September 2011

Dummy Rotary Engine Kit - Part 2 - The DB 1/4 Scale Bleriot

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.


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.


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...

Solvent Glue

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.

Monday 12 September 2011

Dummy Rotary Engine Kit - Part 1 - The DB 1/4 Scale Bleriot

The process of selling our house is occupying more of my time than I had anticipated and other more enjoyable pastimes have had to go onto a back-burner. But... things are now returning to some form of normality and blogging will commence once again :)

So on that note here is how the dummy radial engine progressed for the DB 1/4 Scale Bleriot.

The pending move to the US has meant the reduction of model related items, leaving only an absolute minimum of paraphernalia to ship, so...alas the Bleriot is just one of many aircraft that I have reluctantly parted with :(( But on the up side it is going to a good home and will spend its foreseeable future on display, hanging from a ceiling somewhere.

The engine in this particular Bleriot was the 7 cylinder 50HP Gnome Rotary, hence the side cheeks to allow  the engine to rotate freely within the fuselage.


 DB Bleriot with RCV120 up front prior to installing the
dummy engine and propeller. One of the side cheeks is clearly visible.

The new owner of the Bleriot wants a dummy engine and propeller fitting so this work was duly undertaken. 

I thought I'd show you some of the dummy engine kits that I have in stock. There are many others available and mine are just a selection of whats out there.

 I have 2 supplied by Arizona Model Aircrafters of the USA. One is the 7 Cylinder Rotary Gnome and the other a 9 Cylinder Rotary Le Rhone or Gnome.These kits are OK but you have to supply your own nuts, washers, bolts, screws, wire and tubing. Sourcing these additional items can slow up the built time whilst you find appropriate fixings etc. But with  their inclusion of laser-cut acrylic components you can add extra detail to areas such as the cylinder heads and manifold pipes. Some of the cylinders, heads and push-rods supplied with the Arizona kits are manufactured by Williams Bros. and some cylinders they have machined to profile from plastic tubing and the heads are from laser-cut acrylic and the builder supplies the metal push-rods etc.


 Arizona 7 cylinder Gnome - 1/4 Scale.


Arizona 9 cylinder Le Rhone or Gnome - 1/4 Scale.



Then there are the Williams Bros. Rotary Engine Kits. These kits are excellent and really do look the part when completed. However, the Bleriot is 1/4 scale and Williams don't do a 'full' rotary engine kit at this size but they do supply the cylinder heads. So that just leaves the model maker to make up a crankcase and fit the 'off the shelf' cylinder heads and 'job done'


 William Bros. 9 Cylinder Le Rhone Rotary Engine Kit - 1/6 Scale.



The other rotary engine kits I have in stock and have often used are made by Mick Reeves Models from the UK. They represent good value for money and they are 'very' complete leaving nothing for the builder to source. So all you have to do is follow his instruction sheet and you'll soon have a very convincing dummy engine to install into your latest model.


 Mick Reeves 9 Cylinder Le Rhone Rotary Engine Kit - 1/4 Scale
can be converted to the Gnome Rotary Engine.


 Mick Reeves 9 Cylinder Clerget Rotary Engine Kit - 1/3 Scale
This one will be going into the Nieuport 17bis.


Here is a completed Mick Reeves Clerget Engine Kit that I made for a 1/4 scale Sopwith Pup. As you can see it looks quite convincing when complete. I will include details on painting and detailing the Bleriot finished engine kit later.

Close-up of engine and aluminium cowl.


Complete engine showing push-rods and spark plug detail.
Close-up of crankcase, cylinder and push-rods.
Reverse of engine showing construction.


Finished engine behind  the aluminium cowl.
The rivet detail and 'engine turning' was also added to the cowl.


The chosen engine will be the Arizona 1/4 scale kit of the 7 cylinder Gnome rotary. I will show the build in the next post.


To be continued...