Canopy - Latch

This blog cover the installation of the canopy latches.

Overview

The original opening in the side panel for the pilots latch actuator was totally inadequate and a larger opening was required as shown below with a cover to be fabricated later. 

Opening showing brass rubbing plate with the polished area 
showing mating faces with the handle flange

Latch Location
To determine the front latch pins relationship to the hook two AN4 area washers and washer spacers were fitted to the threaded rod then a series of lock nuts fitted allowing the assembly to be adjusted until the hook landed on the center of the assembly.

Verner's were then used to determine all dimensions with the rear pin location fixed no measurement was required.

Front Latch Installation
The original aluminium latch had to be move out into the cockpit about 10 mm supported only on the M6 threaded shaft. Rather than add washers a single piece brass latch was machined with a 1.5 mm fiber washer placing it about 0.005'' from the brass rubbing plate [shown above]. 

Once the correct position was established the brass latch was fixed to the shaft using high strength Loctite.

Note: The intent is to transfer uplift load via the stringer face and the M6 shaft. 

Front Latch Pin

The hook was installed after begin located from the inside of the cockpit using the latch as a reference. Its location is critical as it has to allow the hook to engage with the latch pull fully back and then allow the latch to engage the hook when closed. Initially fixed with four [4] clecos in a triangular pattern to allow the operation to be checked

Rear Latch Installation
The rear hook required a 1.5 mm spacer behind it to clear the latch flange and was located as described for the front latch.

Rear Latch Pin

Note: The M6 threaded rod at the rear was not long enough and the brass latch was used to remedy this issue - make sure there is about 30 mm projection from the face of the stringer then trim as required and the factory catch will fit correctly.

Latch
Operation was checked from the outside and adjusted until both hooks engaged smoothly by using a fine file to adjust the length of the nose of the hook along with the entry ramp only with relation to the latch pin. Only the lightest of dressing is required if the geometry is set up correctly at he start

Both hooks were fixed using tri-fold 4.8 mm pop rivets in a belief that these will resist side loads in a superior manner compared to pop rivets in the fiberglass side.

Note: The smallest tri-fold available is 4.8 mm

Handles
The handles were removed from the original latches with a razor saw and then machined square for re-installation onto the brass latches. Holes were drilled at the ends to allow a Tommy bar to be used to lock up the assembly.

All handles will be coated with liquid red plasti-dip with each component dipped twice [min] to achieve suitable coating. The finished coating creates a tough soft grip but once opened the contents has a limited life so it will be done with a lot of other items at a later date

Comment
Worked as designed with adjustments - see gas strut install re alignment issues.

Why the front latch had to move so far is unknown.

Canopy - Struts

This blog covers the addition of  gas strut aid lifting and holding canopy open.

Overview

ERRES the Brazilian dealer's Tucano installed a gas lift cylinder to support the canopy when open. The factory forwarding the images below as a reference with a cylinder specification of 150 mm stroke / 150 N force mounted onto a commercial 50 x 25 aluminium extrusion.

ERRES

Installation
The first problem was availability of a suitable length of extrusion with only 6 meters offered by a commercial distributor so it was decided to fold two 50 x 25 channels from 2024-T3 x 0.020'' aluminium sheet which is practical for the hand bench folder.

A series of 20 mm holes at a 80 mm pitch were drilled and flared on the front side to achieve a small amount of lighting and stiffening. Holes were drilled on the opposite face to provide socket access to the cylinder nut and a power cable for the passenger I-Pad or other device. 

Note: Weight was a major part of the decision with the fabricated channel & doubler's weighing in at 160 g versus 700 g for the extrusion [3 mm wall thickness].  All weights estimated.

The first task was to remove the original spreader that was now inadequate for the loads created by the gas strut. After removal the channels were assembled by riveting the flanges together using 3.2 mm pop rivets pitched at 40 mm. 

Next the assembly was trimmed to match the profile of the original and as there had been brackets previously installed it was decided to reuse them and add additional ones on the opposite face.  A packer [0.030''] was placed under both ends at assembly to allow the end of the spreader to move freely across the frame and to create a gap between the fiberglass and spreader.

With the front clecoed two new brackets were installed at the back and both the frame and spreader drilled. All brackets were secured to the frame using 4.8 mm Tri-fold rivets then fixed to the spreader with 3.2 mm pop rivets. 

Note: The smallest tri-fold available is 4.8 mm

Aluminium 2024-T3 0.030" gusset was added at the point of cylinder attachment spreading the load with another 0.020'' triangular gusset at the base to control the torque. Another was added on the port side to stiffen the overall assembly.

Note: ERRES used an aluminium angle extrusion as an attachment with high density foam backing to solve the problem of the slight angularity of the canopy side - this is a tidy solution.

Reference only

Trial installation verified the geometry and after tweaking the dummy it was re-made using a piece 45 x 20 x 1.5 aluminium extrusion fixed onto the spreader bar with four [4] x 4.0 mm stainless steel pop rivets. Commercial aluminium was used for convenience and ductility over aircraft 2024, there is a little flex when opening up to the cylinder stop.

All attachments to the gas strut were treated with Loctite thread lock at assembly with the clevis on the cylinder using a reinforced nylon and metal locking clip with a engagement of about 10 mm onto the cylinder - refer notes in comments.

Gas strut assembly

Note: The 343 mm dimension came in at 335 mm and the cylinder has about 10 mm travel left - why ? - the geometry shown is an estimate only of the actual shape. All rivets were primed before riveting .

When installed a problem was noted on the starboard side, the canopy was pushed out about 5 mm plus from the side of the fuselage, it had been aligned as enough filling and sanding had been done previously but it was realized that thrust [140 N] created by the cylinder geometry was creating the problem. 

As a result of this thrust component the center locating pin and canopy latches now do not line up by about the same amount. This is now a issue for this project requiring some additional guidance for the canopy to place it where it has to go.

Comment
Once the drawing geometry was verified it became an assembly task however replacement of the original spreader created additional small alignment issues and will be covered in another blog. The balance with 15 kg of thrust is excellent with the strut balancing the canopy at about 50% closed

The cylinder used has a 6 mm shaft, doing it again would have selected an 8 mm shaft model - use of thread lock is critical as these struts can undo themselves as they do not use a lock-nut.

A safety cable will be added around the strut using 3/32 cable because if the strut was ever to fail at a connection from a gust of wind, the damage would be unimaginable as an open canopy is a huge heavy bucket...!

Doing it again I would look at the ERRES method of canopy attachment and install all the components before fitting the canopy leaving its as late as practical, it's the frame that shapes the canopy but once it's fitted access becomes the real issue, especially one up.

Rivet Heads

This blog cover the filling of the pop rivets

Overview
After viewing a Sling at AUSFly 2015 I had to do a double take and ask if it was solid riveted. The answer was NO, it was explained that the factory filled each rivet with epoxy micro with a toothpick and sanded after curing.


Installation
Returning to the home base I was still struck with rivet envy, so starting with a small quantity of lightweight filler was applied with a syringe fitted with a needle.  Before use the sharp point was removed using a small grinder.

Purchased from farm supply chain CRT - $9 for the box

The filler was small batches of West Systems 105 resin with the slow hardener. This was mixed with a small amount of blue powder pigment to improve visibility. The needle was inserted into the rivet opening with just enough pressure to allow a continuous drop to be formed at the top between each application with a paper towel at the ready to wipe any excess from the needle. This process is quick with the whole elevator taking about 30 minutes for one side.

The fresh adhesive was first applied to horizontal surfaces as it went off the vertical surface were then filled. 

Rivets filled ready to sand

The vertical surfaces were done with the left over from the horizontal surfaces. When it had begun to gel the process was repeated and as extracting the needle the excess was wiped onto the rivet with a upward motion onto the top face. 

When complete the syringe was cleaned with acetone and wiped down. A watch was set up with any runs cleaned using a towel and acetone. 

Note: After a cold night to cure only about 5% showing runs which were cleaned as described.

The application of a coloring agent is critical and coloured chalk powder was use, clear is a real trap for that reason and once cured onto the skin has to be removed mechanically.

When cured, the excess is carefully sanded off using a piece of metal equal with a hole diameter and thickness equal to the rivet for sanding. A thinner piece of plastic is used to clean the sides if required so obtaining a nice blob on the top side of a rivet saves time

Thanks to Craig at Flying Frontiers in Africa for his input and advising its took about 100 hours plus - woo hoo, happy days....!

Comment
Application was quite quick and my guess with this combination it would take a long hard day to apply resin and a lot longer to sand plus rework. The sides require small batches to be mixed, loaded into a syringe and allowed to start to gel before application.

Undertaking this on a cool night is the go as I managed to use all the resin prepared.

The short needles work well and may have helped the speed but I would make sure the resin was tinted much darker before application.

This idea was found on a RV 12 blog with much thanks.