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.