Chapter 18 - Section 22

Canopy Stop


The mounting location of the gas spring strut varies quite a bit among Cozy builders. The plans' method is to mount the anchor end at the left side of the passenger headrest and the extended side to the canopy bulkhead. However, I haven't decided what headrest I was going to use, therefore the plans' mounting location is somewhat out of the question. In addition, I do not care for the gas strut position when the canopy is closed - it blocks the through space between the front and back seats in flight. On the other hand, if I do not follow the plans mounting method, I have to come up with a new set of geometry and mounting locations. I decided to search through the Cozy forum and builders' web pages to educate myself on the subject.


Both John Basol and Clark Canedy have a nice mounting scheme that does not involve the head rest. Al Wicks describes his in the Cozy forum (similar to Canedy's approach) but no pictures. One of the highly recommended features is a lock on the gas strut when it is fully extended. Evidently, if the wind catches the canopy just right when it is at its open position, it could slam down on your head and ruin your whole day. The extension lock is to prevent that from occurring.


Due to the variations in mounting methods among Cozy builders, there are many gas struts recommended. The bottom line is, it really depends how you plan to mount it. The deciding factors are its overall length, its stroke and its force. I found mine from McMaster-Carr (P/N 9425k14) that is 19.72" overall length and 7.87" stroke. Note the auto extension stop (button) at the middle of the strut? Pulling the button will release the strut for collapsing/closing the canopy. The nice thing about this strut is that it comes in different forces (15 to 120 lbs) - all in the same dimensional configuration. In other words, I can change the force of the strut without changing its mounting locations and methods - just in case. I bought a 50 lb force first, but felt it was too stiff. So I exchanged it for a 30 lb for initial mounting. I'll finalize the force after I complete the mounting.


With the strut in hand (30 lb), I mimicked both John Basol's and Clark Canedy's mounting methods (using clamps and temporary fixtures). The following result is based on MY temporary mounting method and MY selection of strut, your mileage may differ. I recommend you contact them for more informed directions, because both of them are VERY gracious and helpful to Cozy builders and I want to thank them for their support! Both mounting methods work well.  With Basol's approach, my gas strut effectiveness starts a bit sooner (~41o, and I expect it to be even sooner with a higher strut force) than with Canedy's approach (~44o). Actually I was really surprised by the small difference. On the other hand, Canedy's approach has the strut standing vertically behind the passenger's headrest when the canopy is fully opened. Conversely, with Basol's approach, my strut will be positioned at an angle stretching from the center of the seatback to the canopy bulkhead. Its a tough call because I liked the early effective support. After some pondering, I decided to go with less blockage space per Canedy's approach, trading off with higher effective angle (height) - its just a personal preference.    


Fabricating a Mounting Anchor

The aft face of my canopy bulkhead lines up almost flush to the back edge of the seatback. There is no room to mount an anchoring block (hard point) for the gas strut per Canedy's mounting method. I also prefer not to have the strut taking up space in front of the canopy bulkhead (& on top of the seat back), which is reserved for the headrest and whatever electronics goes there. Therefore, the only logical space I have is at the back edge of the seatback (passenger side).


I started with a .25 x 1 x 1.25" aluminum hard point embedded in a triangular shaped foam block (as shown). I carved out some of the foam edges for flox-fill later on. Notice I shaped the back side (top .25") of the hard point to fit the slope of the seat back.





I mixed some wet flox with 5-min. epoxy and held the foam/hard point block against the seat back until the 5-min epoxy cured. Then I packed flox around all sides of the hard point. I wrapped the entire mounting anchor with 2 layers of BID. Note that I wrapped some of the BID over to the top of the seat back - the wood block and weight were there to hold the BID down during cure. Then I peel-plied and allowed it to cure.  








Drill and Tap for Gas Strut

After the BID cured, I re-marked the center of the hard point, and drilled and tapped for 5/16-18 threaded hole for the anchor end of the gas strut. I also added a flat washer to spread out the compression force. 










Establishing the Mounting Location of the Extended End

The extended end of the gas strut will be mounted to the canopy bulkhead. With the anchor end mounted (above), I held the gas strut vertically and propped the canopy up to 64o per plan. The mounting location can be determined by the intersection between the gas strut tip and ~.5" from the bottom edge of the canopy bulkhead. That establishes the mid-point position of the hard point (to be installed).


Installing the Hard Point

The mounting hard point for the extended end is a bit thicker than the anchor hard point because the canopy bulkhead (foam) is 3/8" thick. I cut up a 1x1x3/8 aluminum square for the purpose. I then pre-marked (above) and cut out a 1"x1" slot (including the aft BID layers) at the mounting location on the canopy bulkhead. I added wet flox and embedded the hard point in place. Then I laid up 1.75" x 4" BID (6 layers) and UNI (2 layers) over the hard point and along the canopy bulkhead. I peel-plied and clamped down for cure. You can see the hard point embedded in the foam.






Mounting the Extended End of the Gas Strut

Once the glass / hard-point was cured, I drilled and tapped the hard-point for the extended end of the gas strut. Note the digital level mounted on the canopy bulkhead for determining the canopy opening angle.


A small change in mounting location changes the opening angle quite a bit...I ended up with 65.7o instead of 64o per plan. 


Note the masking tape? That would be the mounting location if I employed Basol's mounting configuration. The strut will be extended from the center of the seat back to some location on the masking tape. As you can visualize, Basol's approach will give you a lower effective support angle than my approach, which is a nice plus. Unfortunately, we cannot have it both ways...








Effective Support Angle

The effective support angle (by the gas strut) starts at 44.3o. In other words, the gas strut takes over when the canopy is opened to 44.3o. Bare in mind that I am using a 30 lb force strut for this measurement. If I used a higher strut force (i.e. 40, 50 lbs etc.), I believe the effective support angle will be lower. However, there will be more stress against the hard points when the strut is compressed (i.e. canopy in closed position as shown below). I felt the 30 lb was quite adequate for my installation and will leave it as is for now...         








Gas Strut Stroke Used

When the canopy is closed, the digital level showed 0.0o. The white tape marks the maximum stroke. If you look close, I have ~0.5" of stroke left before bottoming out the gas strut (i.e. the distance between the right edge of the white tape and the large body of the strut). Therefore, my installation used up 7.27" of the available 7.87" of stroke.









[Hindsight] A seasoned Cozy flyer once told me that his canopy opened in flight - it has got to be one frightening experience! Here's what I learned...The instant the canopy flips open in flight, a 160 mph gust of wind will smack you head on. Your hat, glasses, head set, pencils, maps, knee board will depart without any hesitation. The force of wind will stretch your facial skin backwards, keeping your eyes shut but a big smile (though it won't be amusing to you at this point). You'll loose all communication with the Tower and you have to duck low to look forward (while avoiding the head wind). Now, your death grip is on the control stick and you'll be screaming to yourself "fly the plane". Fortunately you are still strapped into your seat...


Gaining your composure, you want to close the canopy...but the gas strut has a button lock. Now you realize it is impossible to release the lock and at the same time pull the canopy back down with just a single hand (assuming my type of lock strut and you have to fly the plane with the other hand). The extra pull rope is waving in the wind and cannot be reached. The Cozy flyer was cool headed and returned safely. I am not sure I could do the same, hmmmm.... A lock on the gas strut may not be such a good idea after all... Well, I can certainly switch to a non-lock gas strut - same configuration from McMaster (4138T575) for $14.47.


Now I have an interchangeable set up for lock and no-lock gas strut to support my canopy. However, neither one solves the lock coming loose in flight problem. As a matter of fact, both struts help to push the canopy open, once the lock is released . I need to figure out a better solution.... 


Enter dual actuator control side canopy - continued in Ch18_22A