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Rotaroc-A Instructions

(as written for a limited production kit sold for BRB contests)

Rotaroc-A

 

Use THIS LINK for PLANS in PDF format  

This model really should be built using Cyanoacrylate (CA) glue. The polypropelyne plastic hinge material does not stick to most glues. So, if you do not have any CA glue, I highly recommend you get some. You will also find it incredibly useful for building other models, not just contest models but also Estes & Quest kit types.

For more information on CA glues, here is a link to a FAQ

Here is a link to the Bob Smith Industries website. A lot of the local hobby stores sell this brand of CA and accelerator.

The Rotaroc kit includes a single edge razor blade, to use for cutting up the short launch lug material for the half-arc pieces to hold the rubber bands in place on boost. Please use GREAT care with the razor blade since it is VERY sharp. Younger builders should ask a parent or other adult for help with cutting the parts with the razor blade.

Also see the Helicopter Tips Page

 

Read the following rows left to right, then down to the next row.

 

Blue foam block was used in the kit to store various parts.

Left: 5/8" long Launch Lug
Bottom: Offset Head Model RailRoad Spikes
Right: Straight Pins (hinge pins)
Taped on Top: three Loose Hinges (DuBro)
Underneath: Single Edged Razor Blade

Parts shown separately from left to right top row:

5/8" long Launch Lug
Offset Head Model RailRoad Spike
Straight Pin (hinge pin)
Loose Hinge (DuBro)
Bottom row: Single Edged Razor Blade

 

Balsa blades & fins - Refer to the PLANS

Top: 12" long 1/16" thick 3" wide balsa sheet for rotor blades, marked for three 1" chord blades.

Bottom: 7.5" long 1/16" balsa sheet for Fins

BEFORE cutting, sand the rotor blade trailing edges using the method shown in the plans.

The model will fly without any airfoiling, but the better the airfoil, the better it will tend to fly.

Cut away one blade 1" wide, and sand the trailing edge for the third blade on the remaining 2" wide sheet.

Cut out the remaining two blades from the 2" sheet, for three 1" chord blades. Round the leading edges. In this photo the tapered trailing edges are at left, the rounded leading edges are at right, on each blade (not the best airfoiling job, but adequate). This photo is showing the TIP end of the blades.

The Hinge Hub assembly is prefabricated, much as it would be by some big-time kitmakers (except theirs would be molded). The three hinge halves have been glued to a piece of 14mm tubing to act as a Hinge Hub Assembly. Thread has been wrapped and glued to prevent the glued-on hinges from prying off. The Hub Assembly slides over the BT-5 (13mm) body tube.

Shown below the hub assembly is one of the loose hinges and a #16 straight pin to be used for the hinge pin.

DO NOT GLUE at this time.

Simply slide the hinge hub assembly over the body tube while preparing for the process of gluing the loose hinges to the rotor blades.

First, use a straight pin to temporarily attach the loose hinge to the hub.

 

Trim the hinge end (root end) of the rotor blade to match the skew angle of the hingeline. Draw a reference line in the middle of the rotor blade (1/2" on the 1" wide blade).

Remember that the rounded leading edge of the rotor blade goes to the right of the hinge, and the tapered trailing edge goes to the left of the hinge. Or as seen in this photo, the leading edge is at top and trailing edge is at bottom.

Using Cyanoacrylate (CA) glue, apply just one drop of CA to the loose hinge, and press the rotor blade in place, centered. Be VERY CAREFUL not to allow any of the CA glue to get into the actual pivoting hinge area, as the CA then will tend to glue the rotor's hinge and the hub hinge together. If you have CA "Accelerator", spray on some to help make the drop of CA cure very fast. Otherwise, you may need to hold the parts together for a minute or two. Take note that if you use too much CA, it will take a lot longer to cure, so that is the reason for just using one drop at first. Once the CA is cured, then carefully slide out the hinge pin, and remove the rotor with the newly tack-glued hinge. Hold the hinge side of the rotor blade face-up and apply more CA around the edges of the hinge so the CA will soak up under the hinge and also glue around the sides of the hinge, to more securely glue the hinge. Apply "accelerator", or set it aside level so the CA can cure without running elsewhere.

 

 

The kit includes a piece of 3/32" balsa with the balsa grain running diagonally (bottom part in photo). This is used for the Rubber Band standoff/Rotor dihedral angle support braces. Use the plans as a guide for cutting out three of them.

Be CAREFUL when using the single edged razor blade!

Use the razor blade to cut the 5/8" long launch lug material into two pieces about 1/4" to 5/16" long. Then, CAREFULLY use the blade to split them into halves. These half-arc halves are used for holding the rubber bands in place during boost.

Glue three of the half-arc lugs to the three Balsa Rotor angle supports.

Carefully glue the Rotor supports to the rotor blades.

Use needle nose pliers to help push a model railroad spike into place, as seen on the left side of each rotor support in this photo. Locate the offset part of the spike head to point "down" at the blade as seen in the photo. Apply a drop of CA to help glue the pin into place.

A couple of blades after the rotor supports and hinges are glued into place.

Put a rotor blade in place on the hinge hub, sliding the hinge pin into place so the round pin head touches one side of the hinge. Use needle nose pliers to bend the excess part of the pin about 90 degrees. Then cut off the excess (pointed) part of the pin, leaving a 1/4" long bent "L" portion so that the hinge pin cannot fall out.

Carefully dispose of the pointed end of the pin. Repeat this for the other two blades.

Photo of Rotor Assembly after all hinge pins have been put into place, bent, and trimmed.

Now slide the Rotor Assembly off of the body tube, so that the fins can be glued on.

(Not shown)

Cut out the 1/16" balsa fins, and sand the leading and trailing edges round.

Use the marking guide to mark the location for the three fins. Glue them on so that there is a 1/4" distance from the bottom of the fin trailing edges and the bottom of the body tube. This will allow you 1/4" to apply tape to both the tube and engine to help the engine to not kick out at ejection.

Drill a 1/16" diameter hole into the body tube for the burn-thread to run through. See the plans.

(Not shown)

With the fins glued on, slide the rotor assembly back onto the body tube. Fold the blades back so that the bottom (tips) of the blades are even with the trailing edges of the fins (with the body tube sticking out by 1/4"). This will orient the hinge hub assembly in just the right place relative to the fins, and at the correct distance along the body tube.

Apply a couple of drops of CA glue to bond the 14mm rotor hub tube to the BT-5 body tube. CAREFULLY using the single edges razor blade, cut out a 1" long 1/4" wide ejeciton exhaust port, exactly in between two hinges (if the ejection vent points at a rubber band, it could melt the band).

Push the nose cone into place and apply a couple of drops inside of the ejection vent port to glue the nose cone to the BT-5 tube.

Push three offset head model railroad spikes into the nose cone, and use CA to secure them. The spikes need to go up pretty far onto the nose, as in the photo, to provide the correct rubber band tension.

Check that the blades open up to the proper dihedral angle. If the angle is too flat, the model might come down nose-first rather than flip upright (nose up) for descent. If the angle is not enough (see the plans), CAREFULLY use the single edge razor blade to trim some balsa from the rotor supports, where they touch the hinge hub when deployed.

The completed model, rotors tied for boost.

The Elastic thread runs inside of the model through the two 1/16" holes ahead of the fins, to be burned at ejection, allowing the blades to deploy. See the plans for how the elastic is run inside the holes then around the blades.

Some of the ejection gases get out thru the 1/16" holes, and char the balsa blades. So, for the areas of the blades exposed to the 1/16" holes, apply a bit of CA to the bottom of balsa blades to provide some protection. Be sure not to let any of the CA run anywhere else until it cures.

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