Main Construction Page

Aug-08

Ludovic Warin (Ludo) arrives from France to help on the project over the next 5 months. A keen competition pilot (French Junior Team) and good workshop helper. Just finished his enginerering studies in France.

With the sliding pushrods for airbrake and retract gear mounted in the fuselage we could now connect these to the controls behind the pilot and check the movements. The pilot can now raise and lower the wheel. Looks OK. The positions of the input/output arms on the airbrake bell crank also look OK.

The linear bearings for the elevator and aileron pushrods were prepared. The locations and space available was carefully checked with the drawings, then the rods and bearings were positioned temporarily to check the movements and clearances. Care is needed with this as we have designed quite a small space under the seat flange,. With some fiddling the clearances are good. The movement range and neutral position of the rods was checked and good.

The misalignment at the breaks in the elevator and aileron pushrods means we are more concerned with the clearances for the linear bearings. The control deflection due to push rod axial play due to linear bearing radial clearance is tiny, but we still wondered about vibration and wear on the plastic balls. So for these bearings we made sleeves with a better clearance by lapping and polishing the inside of a thicker tube.

After final checking of all the clearances the gluing/laminating of all the mounts was done.

Aug-08

The controls behind the pilot were reassembled then checked in the alignment jigs to make sure the bearings were free and the mounting holes matched. Then they were refitted to the fuselage and the output function to the wing root was checked using the mockup rods.

The plan view of the airbrake and retract rods was marked on the seat flange and the slots cut for the handles. The mounts for the rear linear bushes of these rods were located, then metal brackets for the front terminations were made and glued into the fuselage. After an internal bush and sliding plastic plug were pressed into the rods they could be fitted in the fuselage to check the movement and geometry. An aluminum hardpoint (just a piece of aluminum plate was glued in for each rear mount.

July - early Aug - 08

The control column mountings are made, plywood webs between the bulkheads. They were glued in place using the
alignment fixture, before the plated steel bearing sleeves were glued in. Then the sleeves were glued in using an alignment
rod. The column was bolted in and connected to the bell crank to try it out. Seems good. We constrained the stick in roll
and checked the aileron input due to pitch control. This was slightly more than calculated, a result of the bell crank as built
being slightly further forward than the drawings.

The pitch control stop mounts will be glassed onto the bulkheads. The little arm going through the hole in the bulkhead is for
a bob weight for the pitch control.

Jul-08

The main retract gear was assembled and the function was checked in the wheel box. Seemed OK so the acetal bushes
were glued in. The manufactured clearance on these bushes is a little high for the front swing arm so we will probably have to
make our own for that. Pilot holes for the 5mm cap screws that retain the hinge pins (sleeves) were drilled in situ. Side
loads on the front swing arm should load both sides of the wheel box. After fitting the retaining screws the control input arm
was fitted in situ by drilling a pilot hole as before. Again a 5mm cap screw goes trough the sleeve.

Without yet a balance spring or gas strut, a spring scale was attached to the input arm and a peak load of about 17kg was
noted midway through the movement. Seems OK. BTW the wheel looks tiny but is a standard Tost Lilliput (4x4) with a
300mm diameter tire.


Jul-08

A glass bracket in front of the belley hook area is made over a foam form and glued in. An alignment jig for the control column and the aileron bell crank is made referenced to the seat flange and the adjoining bulkhead. The location for the output rod ends can be checked carefully (not much spare room) and the plywood webs to anchor the control column bearings can be made and glued in while this jig is in place. The bell crank is bolted to a mount on the glass bracket..

Once the mounted hardware is fixed we can work on the fuselage control rods. The control hardware in the rear needs to be
reinstalled, and this is raising the issue of access. For development, experimentation, troubleshooting we need good
access so we may revert to the original idea of quite a large hatch just behind the canopy, and sharing a part line with
that.

Jul-08

Most of the metal parts are painted. The rest were plated using an electroless nickel process. This process gives a
controlled thickness, good lubricity for a bearing surface and no embrittlement. A selection of cap screws were also
electroless nickel plated, although some care will still be exercised in the use of these.

The rudder pedals could now be assembled and fitted to the fuselage. So far so good. Tolerances after plating are nice for
the pedals (acetal bushes) but a little tight for the carriage slide. Some cheap springs are used for now on the pedal to see
the function, and no control stops on the pedals themselves at this stage. This will make it easier to experiment with the ideal
pedal position/foot movement.

June - 08

The development of the control column relies on previous studies we did on pitch stability and stick force gradients (which
included a lot of interesting non linear stability contributions)

Various versions of the control column were designed, studying some existing columns and trying to develop features that
best suited our glider and existing methods. With not much time, the ideas chosen are fairly generic again. A torque tube
that sits on the port side of the glider. The pitch axis bearings placed as low as we can without loosing too much width. A
box shape forms the "yoke" for the roll spindle bearings and gives easy roll control stop mountings.

The pitch spindle axis is in plane with the arc of the stick aileron output arm. While the relative height of the end of the output
arm obviously varies, roll inputs due to pitch inputs are ignorable with this geometry.

The pushrod displacements from this system are kept fairly large, pitch +/- 28mm and roll */- 35mm. The pitch pushrod
displacement from 50kn to Vne is about 9.1mm. The estimated displacement on the Discus 2 was 6.9mm. So we have to
relate this to the height of the column pitch axis spindle, the available space affecting the with between the bearings for that
and so on.

On a practical level this column was not difficult to build for a prototype. Simple alignment fixtures set the bearing housings
for welding then they were reamed with an adjustable reamer held in the lathe chuck while the opposite bearing was
positioned with the tail stock. After pressing in the bearings the pitch axis was corrected a bit by bending.

June - 08

The small old lathe in the home workshop is proving very useful. Lots of small parts are made up as needed for the control
hardware. The brass bushes for the wing "main bolts" were made from inexpensive stock bushes, the inside reamed and
polished and then the outer dimensions and flanges cut. The bushes get trimmed to length later. The main bolts themselves
were machined and sized from 4130 tube by Prescot Engineering. They will get a tube steel handle then a 5micron layer of
electroless nickel plate.

June - 08

The Pushrods with handles are made for the airbrake and retract. Also the pushrods that go through the main bulkhead.
These are all made with 0.7mm WT 4130 tube. The tubes that slide inside the front of the airbrake and retract pushrods will
run in plastic bushes. The preferred method for the wheel brake is a hand control on the airbrake handle. If we have
problems with space for the cable geometry the handle will probably shift to the control column.

May - 08

The rudder pedal assembly was built, a fusion of concepts suggested by other designs. We have to keep weight out of the nose of the aircraft, so these parts are carefully stressed and built. The main parts will probably be electro-less nickel plated. The carriage adjustment slides metal on metal dry and the pedals have acetal bushes. Still wondering on whether to have control stops on the pedals. We have them at the rudder horns already. Meanwhile a final shakedown on the design of the remaining control parts in the fuselage goes on.

May - 08

The main retracting undercart is fabricated from 4130 tube and plate. The front swingarm takes all the side loads and the rear swingarm takes the symetric case loads. Steel sleeves (4130 tube) slide into the reamed swingarm cross tubes to form the hinge pins. There was surprisingly little deformation in the cross tubes due to the TIG welding (Nicholas Collier, NC Welding Services Ltd, 09 8171256)

Some last minute revisions were made to the design of the overcentre fittings and the axel brackets, making it lighter and a bit easier to fabricate. There was some concern about the sensitivity of the retract function to missalignments in the construction, so I tried to keep it fairly acurate and use a fabrication process that made accuracy easy. On assembly and fitting in a test fixture the movement seemed fine. A gas strut and maybe a spring will be used to balance the wheel weight and lock the system up or down. Some experimentation may still be needed with that.

March - 08

The form for the seat back was based on the mockup, with some additional ideas on the width and the section shape. The stiffeners have to go around the front of the wheel box to maximize the adjustment range. The crosswise stiffener will sit on packers to give the seat back adjustment. Hinge will probably be a modified household but hinge.

I used up some really stiff glass that would only drape in the vac bag. The first version we were careless with the vac level and the form was crushed badly by the vacuum. So, remembering ideas from the scale model building, the second version was set with vacuum at about 6" .

Still a few composite jobs to do in the fuselage but now we have to prepare and make the rest of the metal hardware.

Feb - 08


The shape of the seat pan form was completed, adding carved foam blocks to form the sides then blending these to the base part. The battery space form was made with sheet foam and MDF. It looks big but with the seat back the normal battery with mount will just fit. Changing the shape of the front of the main wheel box would help. The form for the control column exit was made, with a little lip so we can hold the dust boot on easily. The column exit hole is quite large because the column spindle axes are quite low. We may need to add some stiffeners underneath the pan.

The soft foam for the pan base needed some filling and fairing, then all was covered in packing tape. The cloth was draped in dry basically without joins for the whole part to help minimise the fairing needed layer. The soft finish fabric made it fairly easy to be under our target resin content (Fabric was from Dick, Ironbark Composites in Australia). Although the foam form was a bit rough the surface of the part sanded fair quite easily and will need only a few spots of filler.

Releasing the part was quite difficult. We had to scratch out most of the foam using the column exit hole for access. At that point I was glad I had not skinned the form to accurately fair it. The roughly trimed up part looks ok, a few tiny repairs and it's good.

Jan - 08

The form for the leg pan was checked. It will need a foam coving and then fairing. The origional seat pan form may be ok as a base or we may have to make a new one. Either way the seat pan form will be added to with shaped foam to the sides and some mods like the battery tray space and the hump at the control column dust boot.

The front pedal mount was glued in using a jig, then a foam form for the foot pan was made and left in under the laminate. It's a sealed space with just some vent holes. The port seat flange join to the oblique bulkhead was completed over a foam form, then all the laminates were trimed and smoothed up a bit. Most of the flanges will be part of the one-off seat pan form. The control slots and the perimeter of the seat pan were carefully marked on the seat flanges.

Jan - 08

The front pedal bracket was laid up. A cardboard form was stuck to the base of the form to enable the flange. The layup was done without a cut plan, just guessing the shapes and joins, applying the fabric dry and then wetting and no bag. The result is ok but with a lot of thickness variations due to lots of joins. The front wheel box was laid up using our more normal method - with a cut plan, fabric wetted between plastic, cut wet then applied with one of the plastic layers as a carrier film. The fabric is very soft drape like the Interglass version, so it is easy to control fiber volume in the wetting and layers bed together quickly. No vac bag and we held the form detail really well.

Carbon bearing blocks were laminated onto the front of the wheel box. Plated steel bushes were glued in on a mandrel for alignment. The rear bearing is on one side only. A nylon bush has a light press fit into this glass bearing mount. This has a companion on the starb fuselage wall.

After some local reinforcement in the vertical part bulkhead it was glued in and taped to the main seat flange and canopy sill box section. The fuselage sides are now very stiff . The box was glued in and the "leg pan" flanges and little part bulkheads at the front of the box were laid up.

Dec - 07

A form for the bulkhead under the pilots knees was made of MDF and covered in packing tape. This form was recoverable to be a basis for a later plug. The glass part needs some internal reinforcement, some extra cloth and UDs under the top flange corner. Then the form for the front wheel box was made with the upper part contoured to give more leg room.. A beveled landing will be made so the front pan can screw to the wheel box. Side loads from the front gear are taken through part bulkheads at the front of the box Most vertical and horizontal loads (Fz, Fx) go though one side of the box at the rear.

The main seat flange is interupted by the bulkhead under the pilot's knees, but the line continues forward to give some stiffness to the shell and something to screw the front pan to. The front pan(s) may yet be an extension of the seat pan. It depends how often we think we'll have to mess around with the front retract system.

Also there is a form for a glass bracket that will anchor the front of the pedals. Between this and the front wheel box will be a glued or glassed in foot pan so the pilot can choose to have his heels resting on that.

Dec - 07

After the alterations at the workshop we had to reorganise our floor plan, shift things, tidy up and purge junk, then finally back to the aircraft itself.. The flashlines were ground off the fuse and the rudder cutout was ground to the original specified marks (plastic tape had been placed in the moulds at the cut lines). The cutouts in the wing root were made, the gear doors were demoulded and the lip on the fuselage roughly cut. The edge of the fuselage canopy sill is not yet finally trimed. The thickness at the final cut point will be 4mm, perhaps still too sharp for the pilot's hands, so we may have to add something there. The canopy frame will be laid up over over this edge.

Oct - 07

The next step was to check the basic ergonomics. The pilot seating, the hand control positions and the pedal position and position range. Initially this was done with mockups in the fuse, starting with and comparing to the origional drawings. A quickie seat pan and front pan was hot wired. The front pan, under the pilot's lower legs, is needed to hide some hardware, so it is a good excuse to make a fully contoured seating environment. A mockup of the adjustable seat back was made. The volume of a nodern parachute was allowed for, and we gave the back some contour for support of the pilot's lower spine.

The hand control positions were checked for some different pilots. There was a notible difference in the ideal positions for the trim, brake and retract handles compared to the origional drawings For the pedals mockup an old set from a Schreder design were cut and changed a bit. The mockup did not have the front wheel box volume properly included, but the pilot leg position and spacing made us quite confidant about the space for that.

From the mockup it looked like we could benefit from a more comprehensive set of detail drawings for all the stuff about to be built for the cockpit. Also time was running out for a final review or redevelopment of critical hardware. The time or oportunity suddenly cane up as contractores arrived to add kitchen and bathroom facilities to the workshop which made work on the project there difficult So we shifted to the design office. I started with design refinement, engineering calcs and FEA of of the main undercart and then all the other cockpit internals were developed and drawn. With a couple of old big printers we now have as many drawings as we need.

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