NJR Blob Build

 

NJR Models “Blob”

The Blob is a 40″ span 2 channel one-piece sports model originally designed to be a slope soarer – a power version is also available.

This is my second NJR Blob. The first, shown here, was damaged beyond repair after a wing—previously reattached twice—came off again during an unexpected arrival.

I’m very fond of the Blob. Designed by Alan Head, it’s a simple, easy to build kit, inexpensive, easy to transport, durable and quite fast. So, missing it, I decided to build another and share the build with you.

In 2026 excluding postage in the UK, the kit is about £77.00 and available from NJR Modelling on - .https://www.njrmodelling.co.uk/product/sas-blob-40-slope-soarer/

Delivery was very prompt. Instead of me describing what’s in the box, look at -https://www.youtube.com/watch?v=HxC2sueWQoo Where Nick himself does it for me.

The wings are veneer‑covered foam, with the ailerons partially band‑sawn during manufacture. The fuselage and top decking are laser‑cut ply, while the tailplane is formed from laser‑cut balsa. A generous selection of quality balsa strip wood is supplied, and the fittings pack is very good, with well‑made control horns, linkages, and hinges. As it’s quite an old plan, the kit includes parts for a single standard servo aileron arrangement, although—as with my first Blob—I’ve opted to fit separate servos outboard in the wings. I’ve also made one or two other changes along the way.

With the kit inspected, it was time to get started. The first task is to fully release the ailerons from the wings using a razor saw. Once the sawn edges have been cleaned up, the balsa leading edge and the false trailing edge are glued to the wing, held securely with tape and pins while the adhesive cures. The leading edge of the ailerons is then glued into place in the same manner. The kit includes balsa strip for facing the trailing edge of the ailerons but I didn’t feel it necessary.

With this done, the wing and aileron leading edges, together with the false trailing edge are carefully dressed and blended. Finally, the inboard aileron facing is added to the wing, along with the corresponding facing on the aileron itself, completing this stage of the wing preparation.

The instructions suggest hinging the ailerons using the “fuzzy” hinges supplied. I prefer to top hinge using Blenderm tape and covering material, which in my view gives a more pleasing line to the wing. More on this later. The L/E of the ailerons were planed at an angle to accommodate the top hinge.

The wing tips were added and rough planed. The assembly drawings show the tips the “other way round” but I prefer a more rearward tapered look. The ailerons could then be cut to length and the outboard facing added.

The servo mounting plates were cut from Liteply and used to mark out the position of the servo recesses on the underside of each wing. I decided to move the servos to a more central position on the wing and extend the servo wire to suit.

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The Veneer was removed from the wing and the recess routed out with a Dremel to accommodate mini servos.

Similarly, a slot was made from the recess to the wing root for the servo wire, to be covered later with a strip of balsa, sanded flush.

A recess in the top of the wing for the elevator servo is cut and routed to suit the servo chosen. The plan shows a standard servo, again I opted for metal geared mini servo.

The kit includes fibreglass tape to reinforce the wing join after the wing has been installed in the fuselage. While this is very effective at preventing the wing breaking along the join line, it also moves the weak point to outside the fuselage, as I previously discovered. To help overcome this, I cut a 10-inch length of carbon-fibre tube, drilled the wings, and epoxied it into place as the wings were joined.

With the wings inverted, they were epoxied together. A hole was drilled aft of the elevator servo recess to route the aileron wires, the wing tips were shaped to their final profile and, after a little filling, the whole wing was sanded smooth. I’ll add the servos and filler strip later. Finally, two lines were drawn on the upper and lower surfaces to indicate the position of the fuselage sides.

On to the fuselage. The instructions wisely suggest making a template of the fuselage side and the wing cut-out to make covering easier later. The edges were lightly sanded to remove the soot from the laser cutting, and the upper edge of the wing aperture on each fuselage half was sanded until the wing was a snug fit on the inside of the lines drawn earlier on the wing.

The fuselage sides were pinned to the building board, the ¼” triangular section glued to the inside of each side and set aside to dry.

The fuselage sides are epoxied to the wings, aligning the sides to the previously drawn line on the wings. NJR provide a pair of spacers to aid parallel and vertical alignment. It is very important that the line drawn on the wing is on the outside of the fuselage. If its on the inside, the precut fuselage bottom, front top, rear decking and hatch will not be a good fit.

The join between the wings was reinforced with glass fibre cloth (supplied) and fibreglass resin, after curing, the elevator servo recess and the aileron servo wire exit were opened out and after checking for fit the elevator servo bearers added and drilled.

 

While the fibreglass was curing, the fin was assembled and together with the elevator and tail plane sanded to shape.

The centre line of the nose block was marked, and the fuselage / wing assembly was aligned to ensure it was true before epoxying the nose block into position. A jig is helpful here although not vital.

The fuselage bottom was fitted, and the elevator servo screwed into place. NJR supply dowel and pushrods to make up the linkage from the servo to the elevator. On my last Blob I used a “snake”, but this time I went with 2 mm carbon-fibre rod, supported at two points along the fuselage to keep the run straight and secure.

I added the top front and rear decking, aligning them with the marks on the inside of the fuselage. The hatch was cut to length and the locating tabs added..

The corners of the fuselage and the hatch were rounded off and the nose shaped.

When installed, the elevator horn will be nearly inside the rear of the fuselage. To accommodate this, the triangular stock was eased with a file so as not to foul the horn on full down elevator.

The kit includes ¼” triangular stock for a strengthening fillet between the tailplane and the fin. Personally, I think this detracts from the lines of the model. Instead, I drilled 4mm diameter holes, 50mm deep, into the fin and corresponding holes in the tailplane. I’ll epoxy 4mm diameter carbon-fibre tube in place to provide the reinforcement.

I’m confident that modern epoxy and lightweight carbon fibre will provide adequate strength, even for my less-than-perfect landings.

I will, however, use the triangular stock on the tailplane-to-fuselage joint where it is less obtrusive to support the tailplane.

 The aileron servos are installed and the wires fed down the slot through the fuselage and out of the top of the wing. 2mm soft balsa strips were then cut and glued flush with the wing.

The inevitable building dings and dents were then filled with lightweight filler and the whole model sanded ready for covering.

 I trial assembled the tail plane and fin to ensure everything was true.  My personal choice is not to assemble the tail plane and fin to the fuselage before covering as I find that I get a better result if they are covered separately.

The instructions recommend that the top and bottom of the airframe are covered in different colours. The model is relatively small, and orientation easily lost. I chose Ferrari red for the topside and white with red stripes for the underside of the wings and fuselage.

 Covering isn’t my favourite job but somehow, I made a half decent job of it.

Next, I installed the Rx battery in the nose. This must go as far forward as possible. I wedged it in with shaped rigid foam to prevent movement. The receiver is situated on the floor of the fuselage in front of the wing. I prefer not to use a switch, preferring a short extension lead from the receiver plugged directly into the battery lead. The elevator servo is installed on the bearers and the elevator horn secured to the elevator – note the horn is tucked away in the rear of the fuselage

 The aileron linkages can be made up from the parts supplied in the kit. I used vac formed covers to improve the appearance.

 The hatch offers easy access to the elevator servo and the battery connection

 To achieve the balance point of 5 ¼” (old plan) from the trailing edge, I had to add 62 gm of lead in front of the battery.

 I would wholeheartedly recommend this model for all the reasons given in my opening statements. If you have little or no experience in building, The Blob would make a good first build.

 So, there we are finished and looking forward to a suitable flying day. I’ll update this blog with the results but I’m confident that like its predecessor, it’s going to be a lot of fun.

 

 Martin Jones  ©