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Scriber

by Robin Butler

Plan No. 678

Specifications:  
Wingspan 1.83m (72")
Radio: 3 Channel

 

Plan Detail

Plan No. 678
Price:
AU$30.00 plus P&H (AU$2.00 within Australia).
Canopy: AU$27.50 plus P&H (AU$7.00 within Australia).

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: 
PO Box 30 Tullamarine Vic, Australia, 3043


The Wing

The wing has a semi-symmetrical section of conventional build up construction. With the double ply wing joiner, spruce spars and shear webs, this wing should take just about any punishment you can throw at it in the air.

With a tapered wing, cutting ribs can be a real pain. I first photocopy all the ribs on the plan, then, with the covering iron on high, I iron the photocopy face down, onto the balsa sheet. This gives a good print of the rib to cut out. (Photocopiers use a thermal transfer process, which is easily reversed to our advantage).

 

You can usually get at least 2 prints from each copy this way, so one for each wing, with the added benefit that if the plan was drawn with labels in the parts, the balsa parts are labeled for you (as long as you can read backwards). In fact I do this for all the smaller bits that need cutting out, including fuselage formers and so on. Just be careful that the photocopier you use makes a true copy. Some of them can distort things a little too much to be useable.

Cut out all the wing ribs, including ailerons. Make strips for the leading and trailing edges as shown. Fix the main spar and trailing edge down over the plan, and then assemble the ribs onto the spar and trailing edge. Put the aileron spar in at this stage.

Fit the top spar and false leading edge now. Before going on, plane the aileron spar top edge and false leading edge to match the rib curvature. Take care here as it is easy to break the ribs. Glue the top trailing edge on and leave the assembly to dry.

Fit your chosen aileron control system, mounting servos as shown. Run the servo leads at this time if you are using outboard servos, as once you sheet the centre section it is harder to get them through the ribs. Make sure your servos are set up centred because you won't be able to get at the horns later. If you are bellcranking, you can leave this step until after the wing is assembled.

Cut away the centre ribs at W1 to W3 either side of the spar to allow the dihedral braces to go in. Glue the braces into one wing, then sheet the leading edge and centre section of that wing after putting in the filler blocks for the wing dowels and bolt. Sheet the bottom of the other wing, put in the filler blocks, then mate the 2 wings together adjusting the dihedral to match the brace.


The wing and tail surfaces are quite conventional construction.

 

The dihedral is only minimal and is more for looks than stability, since a high wing model with a straight wing makes the wings look droopy in the air. Once you are satisfied with the fit of the wings, glue the braces into the free wing, then when the glue is set finish sheeting the top of the wing and centre section.

Fit the leading edge and wing tips, then plane and sand to shape. Fit the shear webs and cap strips and you are nearly there. Leave the wing dowels, top fairing, and wing mounting bolt hole until later.

Make the ailerons by fixing down the bottom sheet and glue the aileron spar and ribs to it. Plane the top of the spar to match the ribs then fit the top sheet. Sand the back edge of the sheeting straight and fit the trailing edge, sanding to final shape when the glue is dry. (Build the rudder the same way while you are in the mood). Don't forget to put the control horn mounting blocks in. Plane the aileron leading edge to shape and trial fit the hinges to ensure everything lines up.

Fuselage

Begin by making the fin, as you will need this to finish the fuselage, but don't sheet it because you need to feed the control cable through it once it is in the fuselage. The leading and trailing edges project down into the fuselage. The leading edge is larger than the front of the ribs because the sheeting will butt up to it later, so make sure you get the overhang symmetrical.


Fuselage ready to be assembled.

Cut out all the fuselage formers, sides and ply doublers. Glue the doublers to the fuselage sides, making sure to do a left and a right.

Glue the triangular stock onto the fuselage sides. Don't worry about the formers fitting neatly to the triangle stock; as long as they clear it, you are OK. Glue the sides to the formers. Using a fuselage jig will ensure a straight fuselage, providing you have one. Sean Foley has shown some excellent ideas to make fuselage jigs in earlier editions of Airborne.

Glue the fin into the rear of the fuselage. Take extra care here because the fin must be square to the fuselage. Since the fin also holds the tailplane, it needs to be strong as there will be a fair bit of loading on it, especially in those rough slope landings! The top of the fin where the tailplane seats must line up as shown on the plans to give the correct zero incidence to the wing. Check this carefully.

Sheet the fin after feeding the control cable snake in. The control cable exits the side of the fin, although you could put the cable through the centre of the fin for a much neater finish as I did. You can also put in the rudder control run at this point.

When you are happy with the tail end, fit the wing mounting plate WP and ply over F6a. Drill a pilot hole rather than the final hole in WP at this stage. Now is the time to mate the wing to the fuselage. Make sure the wing is square with the fuselage before proceeding. Sand the wing saddles to make it level and square to the fin, and also measure to ensure the tip to tail distance is the same both sides.

With the wing lined up on the fuselage, drill the front dowel holes in the leading edge through the holes in F4, then glue in the dowels. Drill a hole through the wing for the mounting bolt by drilling a pilot hole from the bottom of the fuselage through WP. Now tap WP out to suit your wing bolt, and check you can secure the wing to the fuselage.

Fit the top and bottom sheet, noting that the bottom sheet is cross grain from F6 forward. Glue on the nose block. You should now have a rather square looking fuselage. Take your trusty razor plane and get stuck into removing the square corners. The plan shows the detail.

Fix the wing to the fuselage, ensuring it is still square, and fit formers F4a, F5a and F6a in place. Slip a bit of 1.5 mm ply between F6a and F6b to space them. Glue on F5 both sides, then plane some 6.5 mm balsa to fit neatly against F5 and glue it on. Plane the top flat and sheet the top. Sand to shape to match the fuselage, and glue the ply spacer onto the back of the wing fairing.

A word of caution at this point. The T tail offers lots of twisting moment on the slender rear fuselage in a rough landing. Some fibreglass reinforcing is definitely in order around the bottom of the fin and around the fuselage area from about the fin main spars to half way to the wing. Reinforce, but minimise weight in this area. While you're at it, reinforcing the underside of the nose with some fibreglass is also a good idea, as most slope sites are hard on the belly in landings.

Make up the canopy as shown. Airborne Plans Service has a suitable canopy available for $27.50.


The fuselage ready to cover. Nice Lines!

Horizontal StabiliSer

Tailplane construction is straight forward and can be built up over the plan. Make sure you use light wood, as extra mass in the stab will increase the risk of a fuselage or fin breakage in a rough landing. Fit the spar, leading edge and ribs together. Plane the leading and trailing edge to shape, then sheet the stab and add the tips.

The elevator is a little tricky. Because of the double taper, you can't just lay the ribs over the trailing edge sheeting. I used a bit of eyeball engineering here and glued the ribs directly to the spar, ensuring they were all in line. The trailing edge sheeting can then be added one side at a time, and the cap strips fitted. Glue the trailing edge strip on last and sand to shape.

Trial hinge the elevator to the tailplane. Make the tailplane mounting holes as shown, and tap the ply mounting plate in the fin. Fix the tailplane on and make sure it is square to the fin (parallel to the wings) and most important, that the angle of incidence is zero as shown. Any error here will affect the plane's performance.

The elevator control horn should be mounted to line up with the control run. If you exited it through the fin as I did, a little experimentation may be required to get good operation. The horn should be as short as possible to limit the fore and aft travel as the elevator moves. I actually made a ply horn.

 

Finishing

Cover the model with your preferred material. Mine is black lace ... oops, wrong type of model. Actually I used Monocote for the wings and tail surfaces, and tissue, dope and paint for the rest.

Fix the control surfaces, making sure you pin the hinges. A few toothpicks make cheap insurance. There is nothing worse than a control surface parting company at high speed.

Install the radio gear as shown. Adjust the aileron and elevator control throws to 20 mm each way and 25 mm rudder and balance as shown on the plans. Make sure everything moves in the right direction, charge the batteries, chant an incantation to the wind gods, and you are ready to go.

 


Radio gear installed and ready to go. Notice there is plenty of room in the fuselage.


I differed from the plans and brought the elevator pushrod up through the fin on the centre line

Flying

After a month of bad weather in Adelaide, time and weather combined to provide a flying opportunity. Not a great opportunity, with winds forecast as gusting 25 to 30 knots, but at least they were from the right direction. So it was off to my favourite flying site at Hallett Cove.

With the wind as forecast, and certainly at the upper limit at what I would normally fly in, I prepared to launch Scriber to the elements. Standing at the slope edge battling to hold the model in the gusty wind, I wondered if I was doing the right thing. Much to my relief, Scriber made her way out over the slope, without any more trim adjustment than a few clicks of down for better penetration.


Great scenery and a great flying site.

Scriber is a delight to fly. The control throws and large surfaces provide plenty of control authority without being twitchy. Loops, rolls and inverted flight are all a breeze. Even snap rolls were fun, with recovery easy at wings level. In the prevailing conditions I wasn't ably to try out the slow speed characteristics but I am confident Scriber will be a pussycat in mild conditions. It would be an advantage if your radio can mix rudder and ailerons for smoother rolls, or you can be a real pilot and mix manually at the thumbs like me, but this is not essential!


Scriber makes a low pass at Hallett Cove.

After 30 minutes in the air, I managed to make a nice soft landing with no drama at all, which is a credit to Scriber's flying characteristics in the rough conditions.

Scriber is an excellent plane to build, flies a treat and looks great. I thoroughly recommend this model to anyone who enjoys slope soaring. To those who haven't yet experienced the thrill of this exhilarating form of flying, order your plans now and get out on the slope. You won't regret it!

Plan Detail

Plan No. 678
Price:
AU$30.00 plus P&H (AU$2.00 within Australia).
Canopy: AU$27.50 plus P&H (AU$7.00 within Australia).

Order Details
By Phone: (03) 9333 5100
ByFax: (03) 9333 5099
By Email:
By Mail: Airborne Plans Service: PO Box 30 Tullamarine Vic, Australia, 3043
Airborne Plans Service: P.O. Box 30 Tullamarine Vic, Australia, 3043