Henry J. Nicholls' Junior Monitor II

Up / terug

Not a rock spider but a missed EBAY opportunity, communicated to a fellow hoarder who identified it as a Mercury Monitor sitting on a British car bonnet.

Once the disappointment had settled, my fellow enthusiast came up with the suggestion to build two examples of this model and so the Outerzone plans were taken to hand. The kit plan assumes the presence of prefabricated parts neither presented in detail nor existent on my work bench. Oh well..

Mercury Models was a post-WWII British kit manufacturer owned by a well-known gentleman by the name of Henry J. Nicholls, whose obituary makes interesting reading. The Monitor is just one of many of his designs. In this case, he appears to have challenged W.O. Fisher's work regarding charismatic appearance.

The PDF-format plan was split up into A4-sized segments later taped together. I spent an evening on this task, only to discover that the Adobe Reader now has a “poster” printing function that performs the split automatically for you.

The plan does not include ribs but images of the printed balsa sheets that were included in the kit. Translating those images to accurately cut ribs is less straightforward than one would like it to be.

The original concept had a pre-shaped leading edge with a milled slot to accommodate the ribs. My L/E consists of a lamination of two 10 mm strips cut from sheet stock and the slots are short and vertical.

The hearts of the leading edge and the ribs are matched. Looks OK here but much sanding was later needed to improve alignment.

Another EBAY find was this small collection of old school “silk” covering material which suits this model well.

The first wing (remember, I have to construct a sister ship) begins to take shape.

Two bell cranks in the making..

In order to reduce the chance of play the bell crank is thickened at it's hinge point and the attachment holes for the lead outs receive brass bearings made from short pieces of tubing. The lower fork prongs run up through the brass tubes while the upper prongs are rolled around them. Upper and lower prongs are bound with copper wire and soldered together.

The original design shows the bell crank mounted on a single 1/8” ply shelf between the two root ribs. My models will have upper and lower ply mounting plates for greater rigidity.

Wingtips have been added, whereby the outer tip contains a 30 gram lead pellet and the inner tip receives brass tubes for the flying lines.

For added strength, and to facilitate attachment to the fuselage, the center section is planked with 1,5 mm balsa.

Brass tube inserts for the leadouts.

The original Mercury Models kit is known for the simplified fuselage construction named “hollow log”. Unfortunately I never succeeded in finding a picture of the kit box's factory-machined contents and so my imagination has to fill the gap. To make matters worse, the individual that persuaded me to do this project has a special request, namely an undercarriage. In order to arrive at a solution whereby a damaged undercart can be removed for repairs, I chose to mount the engine upright versus sideways as per original. The engine bearers now serve as a solid base for mounting the u/c legs.

Rotating the motor bearers 90° and placing them on a platform created an issue with the fuel tank, originally a standard wedge model. Shortening the bearers was not an option because the undercarriage mounting relies on them. Eventually a complex shape emerged that would retain some bearer strength yet give sufficient tank capacity and functional shape (the last drops of fuel must be slung out by centrifugal force and not remain on the bottom). A dummy tank was made from MDF and cardboard templates created around it. The card templates were then transferred to tin plate from a biscuit container.

Three pipes are soldered into the tank, the design of which aims at constant fuel pickup pressure no matter how much fuel is present. As fuel is consumed, fuel pressure reduction is balanced by incoming air pressure. The aim of the “uniflow” tank is to prevent fuel starvation before the tank load is entirely consumed, i.e. obtain a consistent motor run throughout.

After checking for leaks the uniflow tank was tested together with a 2,5 cc Webra diesel engine. The results were most satisfying: a 10 minute consistently fast run was achieved (capacity is approximately 40 cc ).

Before being buried within the hollow log fuselage, the outside of the tank receives a coat of epoxy. The internals will hopefully be preserved by castor oil!

Underneath the motor mount two beech crosspieces have been glued. These are drilled to accept 4 mm brass tubing into which the 3 mm piano wire undercarriage is inserted.

The entire unit (motor bearers and undercarriage mounting) is glued into the fuselage log.

The plywood nose ring is not shown on the Mercury plan but I like it. It's main purpose is to help in achieving the ultimate fuselage shape, but it also adds some strength.

Bottom hollow log fuselage half and the wing are joined up.

Beforehand, a tunnel is cut into the rear of the fuselage to allow the elevator push-pull rod to pass through.

Engine cowling and undercarriage take shape. Today, the feeling that this project might succeed finally came around..

The plan shows a rather permanent engine mounting method using U-bolts cemented to the motor bearers. Preferring exit options, I chose straight bolts that pass through paper tubes under the nose. The aluminium motor mount can be seen at the bottom of the tubes.

The Monitor is almost done.

Tailskids often take a hammering and this one is fixed to a 2mm plate using copper wire and epoxy. The skid has a loop at the end that plays a role in retaining the model when using solo release apparatus (starting without a helper).

I get by with a little help from my friends ….” here my friend Klaas shows me how to do a Oracover job. A particularly nice detail is hiding the elevator hinges under the covering material – can also be applied with tissue-covering.

For those unfamiliar with state-of-the-art plastic covering material, Oracover is quite an eye-opener. No pre-treatment of the wood is required and vast amounts of heat may be applied in order to achieve the desired shrinking in difficult areas. The result is a very resilient covering job that even withstands glow fuel The material price may seem stiff but all the sealer and dope (not available through mail order!) that is no longer needed is not cheap either. Probably the biggest bonus is the absence of solvents and sanding dust, permitting good old kitchen table builds.

6 months after the first construction steps, the Monitor is “job done”.

In recent weeks a picture of the original kit box contents was found. A close look reveals that this model can be constructed within 3 hours. No comment!

The second example will probably differ from this one in that the undercarriage will be left off and the engine mounted sideways. Covering material will be silk (nylon) and power will have to be from an old English diesel. Do you happen to have a neglected Elfin, ED or AMCO lying around?

Meanwhile, Monitor No.1 has moved to it's new home and now has Toledo steel under (and over!) the hood – a Zom engine.

A year after the build started, the Junior Monitor flies. Picture taken in Almere.

Yet another year has passed and the time has come to complete Monitor No.2 Here the bottom half of the fuselage log has been marked off with a paper template (plan view) and cut out by jigsaw.

The next step is marking the side view of the fuselage, including the wing seat.

Sawcuts down to the wing seat line.

The wing seat is chiseled out.

Finally, the wing seat is filed out to match the wing profile.

This build follows the original engine mounting plan (and no undercarriage). The 8 mm beech engine bearers seem somewhat light in view of some of the engines considered suitable for this model – such as the 3.5 cc AMCO. I chose the 2.5 cc AM because it came from the same stable as the model did: Henry Nicholls' Mercury brand.

Following the plan, the engine mounting bolt heads are buried in the fuselage log and must be secured with a piece of wire (soldered). The tinplate addition is my own futile attempt to beef up the engine mount.


The picture below depicts the start of construction of a fuel tank. Before scribing the metal a cardboard mock-up was made and this step always exposes things not thought of beforehand. The biscuit tin material used for the tank had rust under the glued-on label but both label and rust were removed by soaking in vinager.

The first tank (right) gave a motor run of only 2 minutes and 15 seconds, obliging me to make a bigger one. The tank (left) is 20% larger, follows the “Uniflow”-principle and has a baffle halfway.

The engine bearers are installed. Bit-by-bit the log is hollowed out to ensure a snug fit for the bearer unit within the soft balsa surroundings.

Although the sidewinder engine setup was thought to be far simpler than the upright installation in the first model, this can no longer be upheld: the “hollow log” build is fiddly whichever way you go about it.

Sandpaper heaven: my “hollow log” is not factory-turned lathework but hours of careful manual labor and worrying about going all the way through!

All done. Now for the construction of the tail and cockpit – and the takeoff dolly!