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I didn't expect the door frames to be anywhere near the right shape. The manual says they’re not and sure enough – they’re not. First off, I wasn’t happy with the way the standard body screws held-off the door frame mouldings in some areas around the frames so I decided to change all the body panel screws from the plated Gold Pan Head to Stainless Countersunk set in countersunk Screw Cups. I figured this would make a more pleasing finish to the proposed silver paint job, reduce turbulence and drag (albeit marginally) and make possible a better fitting job of the doors. The four pictures below show the saw cuts I made to correct the shape of the pilots door. I’ve highlighted the cut lines with Magic Marker. Incidentally, the recommended cardboard packing around the door reveal sounds dead crude - but it works OK.
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The saw cuts relieve the stresses in the GRP allowing the frame to follow to the actual shape of the opening without any spring or tension. Cuts on the outer edge allow the frame to be reshaped in the same plane as the Plexiglass whilst cuts on the inner edge allow reshaping at right angles to the Plexi. Although I could have pulled the frames into shape and taped them there, the sprung strength of the frames would be far stronger than any inherent strength in the Plexiglass so, with the tape removed, the frames would return to their original shape taking the Plexiglass with them. I removed approximately only 1/4 inch of material from the top and the bottom. The passengers side (not shown) was cut into three pieces and sawn & reshaped. One section was moved around one inch leaving a gap to be filled with a fillet cut from another joint - whatever it takes.
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With the sawn frame pieces still taped in position I ground a shallow ‘V’ half way through the frame at each saw cut with the flap disc in my small hand grinder. The frames were taped and wedged in position and one inch strips of matting were laid-up across the joints. The cured frames were then removed and the joints and saw cuts ‘’V’d on the inside face through to the new GRP on the front side. More GRP was laid up to rebuild the level.
The fully cured new GRP was sanded down to leave the frames a uniform thickness all round. I used a large flat block on the outside faces and folded 40 grit by hand on the inside.
You can see by the above picture the finished frames sitting flush with the body all-round with no spring or tension.
I marked a black pencil line around the frame one half inch from the edge to act as a drilling guide for the Clekos. Laying the Plexiglas in position over the frame is no problem — simply centralized to give a good average overlap all round. I laid a band of 1/4 inch PVC masking tape around the edge of the Plexi with one side of it directly over the pencil line on the frame. This helped smooth out the pencil line and reduce any potential staggering of the rivet holes. I marked the 2 inch hole spacings using a pair of dividers, starting at the centre top and working left and right. If any spacing corrections were needed this could be done along the bottom of the frame where it would be least noticeable. Luckily it worked out perfectly.
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I slid a thin steel rule between the frame and the body beneath each hole position and drilled through 1/8 inch for the Clekos. The rule was thin enough not to push the frame away from the body and strong enough to act as a drill stop. Removing the assembly showed uneven gaps between the frame and the Plexiglas — just as expected. To pull rivets at this stage would certainly distort and crack the panel. I removed all the Clekos and countersunk the Plexiglass with a single flute, solid carbide countersink bit (expensive but well up to the job on GRP, Acrylic and 4130).
I peeled back the plastic coating on the inside face of the Plexi and masked an area two inches wide around the outside edge with 2 inch clear packing tape to act as a mould release. Overlapping the tape is no problem so long as no air bubbles beneath the tape are formed.
I reassembled the panels with Clekos and filled all the gaps around the frame, inside and out with Easy– Sand Body filler (Bondo?) An old credit card works perfectly on this job (If you can find a card that’s not already worn-out from the financial spanking of a Helicopter Build!!).The panels were again temporarily assembled with Clekos and the edge of the Plexi ground and sanded down to meet the frame.
When the filler had cured I removed all the Clekos and easily separated the panels. Any gaps in the filler were bridged with more filler. I rubbed down all the edges and smoothed & levelled the inside edge of the frame. At this stage I decided to ’eye’ around the filled edge of the frame for low spots and gentle depressions that were distorting the natural curve of the Plexi. I built up these areas with more filler and sanded them to a continuous smooth shape with a large flat sanding block.
Surface imperfections were smoothed with Acrylic stopper and flatted with 260 grit Wet & Dry abrasive ready for painting.
I masked the inside of the Plexi right up to the frame edge to prevent Epoxy from the joint squeezing onto the Plexi. A thin smear of Epoxy resin was all that was needed to bond the two panels together. I inserted all the rivets and only partly pulled them — just enough to spread the Epoxy evenly in the joint. When the epoxy had cured the rivets were fully pulled, the balls knocked out, excess rivet ground off flush and the inside face filled and sanded.
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The Stall Strip is supplied as a two dimensional folded piece of aluminium. To accurately fit the front edge of the door with no stress or tension that would, in turn, misshape the door, it must be made a 3 dimensional shape. We need to curve the narrow side of the V to sit flush on the exact area of the door where it will eventually be riveted. I marked the hinge and stall strip position on the Plexi as a reference. We have an old cast iron Surface Plate that we use for flattening plates and rough marking out. I covered the surface with masking tape taking care to butt the tape joints together exactly. Using a slightly domed panel beater’s hammer I gently tapped away along the wide surface of the strip, effectively stretching the aluminium into a curve. This is a slow and painstaking process involving checking and re-checking on the Plexi. Eventually you’ll have a perfectly mating pair of parts. If in doubt, I recommend that you practice on a piece of scrap material first.
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Here’s one fitted. Looking at the front edge of the door
I wasn’t happy using the sponge foam rubber door sealing strip supplied with the kit . I figured it would collect dirt and soak up water like a sponge in the rain. so I searched around our local hardware stores and found a neat, self-adhesive, skinned ‘P’ section Draught Excluder product. It’s very soft and will fill gaps of between 3 mm and 5 mm - perfect for the Exec doors. At less than £5 it’s cheap enough to sacrifice a pack to get you doors aligned perfectly prior to painting, then put on some new after.
I decided to make stainless steel door hinges. A local company scanned the Rotorway Templates and cut the shapes from a sheet of .060 in polished stainless steel using a high power water jet machine. This machine works just like a laser but without the burning around the edges.
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Unless you have a really good quality industrial sheet metal folder it’s difficult to fold a clean, tight bend on small components, especially stainless ones. Here’s my method. I lined the jaws of my bench vice with thin steel angle pieces to protect the polished face of the material. I made a few practice parts from similar material and marked the proposed fold line on them. The parts were clamped in the vice with the marked line just visible above the jaws. I then used an aluminium block and hammer to dress over the material, striking the blows as close to the fold line as possible. The fold will have to be slightly over 90 degrees to allow for the curvature of the door so, for the final few degrees of fold, I released the part and slid a thin welding rod into the corner thus raising the material enough to allow a few extra degrees of fold with a few more blows.
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It’s almost impossible to form the folds on the hinge components to exactly follow the contours of the Plexi and be perfectly in-line with each other. My solution was to bend each part to fit as accurately as possible, mask the Plexi with the usual packing tape to act as a mould release then bolt both hinge parts loosely to the door on a bed of epoxy resin, using a 18 inch length of 5 mm (or 3/16 inch) studding bolted between them to hold them parallel. The cured epoxy can be trimmed off to leave a perfectly mating male and female curve between the two faces.
It was necessary to fold the upper screen pillar hinge plates at an angle to maintain clearance with the door frame. I reinforced the inside of the screen pillar moulding with an extra layer of GRP matting at the hinge areas.
DOOR LATCHES
A popular modification to the door latching mechanisms is the fitting of a ‘Southco’ Lockable Latch. This standard component is made in the UK but available throughout the world and is an ideal design to simplify the door shutting process and provide a locking facility. The Southco Part Number is M1-41.
First step was to cut the 2 inch hole as close as possible to the door frame. I decided to position the striker where it could be secured with the two existing screws on the return joint of the side panel to the tub. This determined the position of the latch. I started with a 44 mm Hole Saw.
And gradually opened the hole with a Flap Wheel until the latch was a good fit.
In its standard form the Southco Latch it’s easy to fit but inevitably requires either a protruding striker of some cutting to the door frame. Neither were options I wanted to take.
So I folded and drilled a thin piece of stainless steel to a ‘U’ section that fitted around the door reveal return.
This formed a non-protruding striker that doubled as a reinforcing plate around this potentially weak body joint. The latch hook would slide between the screw heads.
I modified the sliding Pawl component with an extended replacement that I machined from a billet of black Acetal.
I actually extended the Pawl inwards and rearwards by about 6 mm (1/4 inch) in each direction.
And here it is fitted. I trimmed the inner latch retaining ring to clear the door frame.
Neat, lightweight, secure and lockable. All I now have to do is get Rotorway’s and the CAA’s approval for the mod.
I’ll still use the other two standard rotating catches top and bottom on each door.
I made some stainless steel wear plates for the lower door catches. The inside edge is rolled slightly and the plate is secured with countersunk screws and Rivnuts in the floorpan.
I cut the slot at a slight angle and put a matching twist in the catch so that the door is pulled in tighter on the seal as the catch is closed.
COCKPIT VENTS
I’ve used these things for many years in our cars and I happen to be UK agent for ’Snapvent’, the company that makes them. This is the fitting method that works best for me.
I left the doors mounted on the ship and used masking tape and a compass to mark, as accurately as possible, a 3 1/4 inch circle. A timely tip on ROG ensured that I didn’t fit them behind the stall strip where they wouldn’t be so effective.
I use a stubby 1/8 inch drill with dulled cutting edges to drill a ring of holes, as close together as possible, slightly inside the 3 1/4 circle. The outer line here shows the outer edge of the vent.
This is the dangerous part. With the drill leaning over at an angle I carefully join the holes using the sides of the drill as a ‘milling’ cutter. If you try this method practice first on a piece of scrap material. Run the drill slowly and support it firmly with both hands.
Finally, I clean up to the line with a flap wheel
My Digital Vernier is the best tool to measure the hole size. I aim for spot on 3.250 in.
When it’s to size and I’m happy with the way the vent operates, I’ll polish the hole edge with 240 then 800 grit wet & dry paper.
This is the version of ventilator I’ll be using - It has a lower profile than the ones supplied with the kit and is rated at 200 mph - way more than it’ll ever see in the Exec but it works just the same. I’ll only install two at the moment but I’ve been advised that four will give much better ventilation on a hot day.
I made two strikers/sliders for the upper door catches from thin stainless. They’re secured with one countersunk screw on the underside (hidden from view here), through the door pillar return and into a nut plate on the inside of the liner
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