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Slipstream plans are available from: Airborne Plans Service for AU$36.30 plus AU$2.00 P&H2.  
Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).
Plan No. 648
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Slipstream picture

by Rick Harris

The Slipstream is a scale looking model with a reasonable wing area and rugged construction most suited to slope soaring. It is not a fast aircraft but is quite aerobatic and would be suitable for novice slope soaring pilots. Although it is designed for three functions it could be flown using a basic two channel radio with coupled ailerons and rudder.

CONSTRUCTION

Pour over the plans then cut out as many parts as possible so you have a fairly complete kit ready to start building. Drill the holes in the ribs equal to the steel rod diameter so they can be slightly enlarged later. I used PVA and cyano glues throughout and epoxy for metal to wood joins.

WINGS

Slipstream picture Lay clear plastic or waxed paper over the plans then pin down the bottom main spar, pack up the bottom rear drag spar with scrap 1.5mm balsa and pin it into place. Dry fit all the ribs to ensure the leading and trailing edges are straight line and all the spar slots line up correctly. Also check the holes for the wing joiner brass tubes also line up correctly as well as the holes for the aileron bellcrank pushrod.

Glue the ribs into place followed by the main spar, the top rear drag spar and the aileron spar (also packed up with scrap 1.5mm balsa strip). Cut and glue the aileron bellcrank plate which fits into the riblets W9a and W10a. Also glue the reinforcement W3a into place. Pre-shape the leading edge with a razor plane then glue it into place. Add the triangular gussets and the top ply brace for the aileron bellcrank and allow the glue to dry. Remove any pins then carefully razor plane any excess off the top of the aileron spa, sand the whole top surface to a smooth contour and add the 1.5mm balsa top sheeting strip over the aileron spar and the rest of the top balsa sheeting in the centre section and leading edge. Lightly dampen the LE top sheeting on the outside and it will develop a curl which makes it easier to pin onto the ribs. Allow the glue to dry.

Cut, fit and glue the rib capping strips onto the tops of the ribs.

Complete the other wing panel to the same stage before continuing. When dry sand the top surface to the final shape including the rear edge of the aileron spar. The tip blocks can be added at a later stage.

Trial fit the brass tubes for the wing joiner rods, it may be necessary to lightly file the holes using a chain saw file so they fit in the ribs correctly. Do this to both wings. Slide the wire joiners into one wing then slide the other wing onto the wires - they should slide on without excessive binding and have the same incidence and dihedral. If the wires fit OK epoxy the brass tubes to the ribs, allow to dry then remove the wires from the wings.

Locate and drill a hole small enough for the bellcrank screw to be actually screwed in to the ply plate and not be a loose fit. be careful not to drill through the top LE sheeting.

Make up the servo aileron push rods with kwik links on one end for adjustment.

Build up the ailerons by gluing the LE and ribs to the bottom sheeting first, razor plane and sand the LE to the shape shown on the plans.

Mark and cut slots for the aileron hinges in both the ailerons and the spars in the wings and dry fit the hinges to ensure smooth operation. Mark, drill and fit the aileron horns. Fit the aileron bellcranks to the wings.

Make up push rods to go from the bellcrank to the aileron horn. Again use wire rods with kwik links on one end for adjustment.

Connect the push rods and check that ailerons move smoothly and easily. I suggest you set up the bellcranks up then down to give aileron differential. If everything works OK partly remove the bellcrank screw and fit a washer and nut (with Loctite to prevent the bellcrank from moving off the brass bearing) and refit the screw all the way into the ply plates.

Remember that once the bottom sheeting is in place you cannot get to the bellcranks.

Now cut and glue the 1.5mm balsa shear webs (grain vertical) between the main top and bottom spars. Plane and sand the bottom of the wing to a smooth contour.

Glue the scrap blocks for the cup hooks to the inside of the root ribs and mark the positions for the cup hooks on the outside.

The bottom sheeting can now be cut, glued and pinned into place. Cut, fit and glue the rib capping strips onto the bottom of the ribs. When dry sand the bottom surface to a final smooth shape. The tip blocks can now be glued in place, carved and sanded to shape. Sand the root of the wings perfectly flat ready to mate up to the fuselage sides. Depending on the type of covering/finish you are going to apply to the wings you could now glue or pin the aileron hinges in place. The pushrods can again be connected and aileron movement checked for easy operation. Do not fit the cup hooks just yet.

TAILPLANE/ELEVATOR AND FIN/RUDDER

Slipstream picture These are fairly straight forward and are built directly over the plans with waxed paper used to protect the plans. When the glue has dried they can be removed from the building board and planed and sanded to shape as shown.

Mark and cut slots for the hinges and trial fit them to ensure free and smooth operation of the elevator and rudder. Again depending on the type of covering/finish you are going to apply you could now glue or pin the hinges in place. The covering could also be applied.

FUSELAGE

Slipstream picture Glue the ply doublers to the balsa sides with PVA glue, pin down flat and allow to dry.

Glue and pin the three stringers on each side in place and remove the pins when dry. Make sure you make a left and right hand side. Mark out the position of the formers onto the sides making sure the distance between F5 and F6 is the same as the distance between the wing joiner rods in the wings as the brass tubes will be epoxied to these two formers.

Lay one side flat and glue formers F4 to F6 in place with F4 at right angles to the side then glue the other side in place ensuring the two sides are parallel to each other when look from the side and with an equal taper when looking from the rear.

Hold these in position with a clip on the back and rubber bands or clamps on the front section. It will be necessary to hold up the front part of the fuselage with a scrap block on a flat board so the fuselage will be "true". Allow the glue to dry.

Glue the remaining formers in place checking the fuselage retains an even taper to the rear. Hold these in place with clamps, pins, rubber bands etc.

Fit the ply ribs (WS) to the fuselage sides and slide the wing joiner rods through them. Make sure the rods are parallel to each other when viewed from the front and the top.

Slide the wings onto them and if everything fits OK then glue the ribs to the fuselage sides. When dry remove the wings and the rods and slightly enlarge the holes to accept the brass rods and epoxy them into position. Again fit the rods through the tube and check they are parallel to each other when viewed from the front and top. (The wings could be attached during this operation).

The top spine from F3 to F6 and the bottom keel can be glued in place and while the glue dries shape the rear post of the fin to shape so it fits into the correct space at the rear of the fuselage. Trial fit the fin and tailplane to the fuselage and pin them in position. Mark out where the push rods for the elevator will exit the fuselage, remove the fin and tailplane and cut out slots for the forked pushrod end.

Make up a forked wire with solder ball links (Dubro Part no. 180) and a threaded rod to screw into the inner part of a flexible snake type pushrod. Epoxy the outer tube to the fuselage formers. Carefully remove the section above the slots with a sharp knife and from the rear slide the inner tube into the outer tube then drop the forked end into the slots. Replace and glue the cut sections back into place.

Fit the fin and tailplane to the fuselage again and pin in place.

Mark out the position for the slots and epoxy short lengths of nyrod inner in place. Slip lengths or wire fishing trace into the tubes and feed them to the front of the fuselage. Fold the ends of the trace over so they cannot be pulled out. Fit and glue the rest of the top spine into place.

The tailplane seat can be cut and glued, and a piece across the sloping face of DB2.

The 3mm bottom strip planking can now be attached. This is a bit of a fiddle and the last piece on either side will have to be specially shaped to fit. Sand the bottom to a smooth shape, fill any holes with your favourite filler then give a final sand. (When the fuselage was finished I added two layer of 3/4oz glass cloth to the bottom of mine as all the slope soaring hills we use are covered in rocks). I fitted the plywood skid after glassing.

Make up a tray for the aileron servo. This must have a slide in section of some sort as you cannot get to the servo once installed. The hooks can be added to the wings which are then fitted onto the rods and the linkage of the ailerons at the servo arm completed. I simply bent the wire at right angles but ball links could be used. The fin and tailplane can now be glued in place, check for alignment by using the wings fitted on the rods as a guide.

Glue a piece of 3mm balsa across the face of DB2 and fit all the top planking as on the bottom. Sand the top smooth and fill any holes. Finish the rear end with filler blocks or sheet as shown on the plans. Finish the fairing of WS to the fuselage sides then sand smooth.

The canopy can be made up and fitted. Paint the cockpit inside before gluing canopy and, if you wish, include a pilot for added realism.

Fit the rudder and elevators and pin the hinges. The linkages at the rear can now be finished.

Fit the wings, lay the radio gear neatly in the very front section of the fuselage then make up servo rails and/or your own method of holding the servos, receiver and battery securely in place. Complete the linkages at the servo ends.

Lay the canopy in place and check the balance point. Fit and carve the noseblock to approximate shape and make the hollow for the nose weight. Mine needed about 100gms. Add the necessary weight then glue the noseblock to F1. When dry finish carving/sanding the noseblock to shape and finish the canopy fitting as shown.

Fill any holes and give the wings and fuselage a final light sanding. The whole model can now be assembled and checked for alignment, balance, linkages, movement of control surfaces etc.

FINISHING

Slipstream picture Paint the fuselage and cover the wings, tailplane/elevators and fin/rudder with your own choice of finish/covering material. (I used full gloss enamel on the fuselage and Solarfilm on the remainder).

Bend 2 bicycle spokes to make up the hooks to pull the wing joiner rubber bands through the fuselage. The flange on the ends make good small hooks. Make a loop at the other end large enough to put your fingers through.

PRE-FLIGHT CHECKS

Range check the radio and all control surfaces for free and easy movement as well as moving in the correct direction for the transmitter stick movement. (The paint can also bind a rudder cable to the fuselage as it did on mine).

Recheck the centre of gravity as painting and covering can add weight changing the balance point.

If using a two channel radio a 'Y' lead can be used to operate the ailerons and rudder from the one stick but an extra servo will need to be purchased or used. This will limit some of the aerobatic manoeuvres but still gives a responsive aircraft on only two functions.

Hand launch the model on a calm day from a flat field to check the trim is correct. Mine travelled about 80 metres from a good hand launch. Make any adjustments before launching the model from the slope.

FLYING
(The best bit)

Slipstream picture Usually the winds are really good in southern NSW for slope soaring from August to December BUT this year we have had very few windy days and several of the ones we did have were wet as well - so test flying has been a prolonged event.

The one day that the wind did blow I managed to only have one flight of about 10 minutes before the wind died. However the model flew without any trim changes and it is quite responsive without being "twitchy".

The model is not particularly fast - due, I feel, to the rather wide fuselage and the reasonably thick airfoil section which gives a large frontal area.

Normal slope flying was quite relaxed and loops, rolls and stall turns were not difficult provided some airspeed was built up first. Inverted flight was also no drama - only a slight touch of down elevator needed to maintain level flight. I did not have a chance to try any other aerobatics as I just scraped back to the top of the hill in the dying breeze.

I feel the Slipstream would be a good model for novice slope soaring pilots who wish to advance from a simple rudder/elevator type aircraft to an aileron type as it does not build up too much speed but is still reasonably responsive. However it does need to be flown all the time but it does provide some enjoyable slope soaring without being too stressful. Its scale like appearance looks good on the slope especially when silhouetted against the sun.

I did not fit a towhook as shown on the plans, so cannot comment on its thermalling ability off winch or bungee launches.

All in all a good model with reasonably good penetration without excessive speed and a good repertoire of aerobatics possible with a little practice.



SPECIFICATIONS Slipstream

Type: Glider Wingspan: 2.2 metre Length: 1.42 metre Weight: 1.81kg 2-3 channel radio control required



Slipstream plans are available from:
Airborne Plans Service
AU$36.30 plus AU$2.00 P&H2
Moulded Canopy: AU$27.50 plus P&H (AH$6.00 within Australia).

Plan No. 648

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This page was last modified on the 21-May-02