Online Community of Zenith Builders and Flyers
My STOL 750's Snap-Vent always fit rather loosely in the passenger's bubble door. I tried another Snap-Vent that had a spring to increase tension and reduce the sloppy fit. However, the next day I came back to the hangar and there was an approximately 1" crack in the acrylic radiating out from the edge of the hole! Yikes! I stop-drilled it and re-installed the original loose Snap-Vent to take any tension off of the crack. The crack remained stable with the stop-drilling and I tried 2-3 times to fuse the crack with acrylic solvent cement, but it was so thin and with one end of the crack unsupported, it never seemed to permanently fuse. I was concerned because sometimes I would find the two sides of the cracked acrylic out-of-alignment, worrying me that it might crack further.
I found that a Vista-Vent would fit in the existing hole without drilling any screw holes. The screws just clear the edges of the original hole. I took a piece of rubber edging, put it on a steel ruler, and cut it down using a straight edge and a razor blade:
I then lined the original hole with the rubber edging material:
I made a retaining ring from .050 that overlapped the original hole by about 1/4" all the way around - it corresponds to the diameter of the Vista-Vent flange. The retaining ring was drilled to match the Vista-Vent, powder coated, and then bolted. The Vista-Vent includes shiny silver hardware, but I elected to use black button-head 6/32 x 1/2 machine screws and black nylock nuts:
The nylock nuts allowed me to precisely control the pressure on the retaining ring. I wanted it "just snug" and no more so as not to create pressure points and potentially new cracks in the acrylic!
The primary reason I took this approach is now the crack in the edge of the hole is cushioned in the rubber edging and held firmly (but gently!) between the retaining ring and the Vista-Vent flange, eliminating the possibility of future fretting of the edges and potentially expanding the crack.
The Vista-Vent has an advantage in that the tension of the vent is adjustable, so no more sloppy, loose fit or rattling. It also can be closed off completely with no leaks. I also find it easier to lean over from the pilot's seat and adjust the vent when flying solo. It has the disadvantage that the vent area is much smaller than the Snap-Vent, so it doesn't flow nearly as much air. I think with the pilot's Snap-Vent the ventilation this summer will be OK - we have relatively mild summers in East Tennessee - but that remains to be seen!
I thought this might be of interest to anyone with an excessively loose Snap-Vent or a crack in the bubble door vent hole.
John, Nice fix! if worse comes to worse and you want/need a new door, I verified with Roger a few days ago that these type doors are still available.
Awesome, thanks for sharing! I'll check out these vents.
I finished riveting my bubble doors and a small 10 mm crack appeared next to one of the rivets.
I KNOW that there as an entry in the forums about a repair adhesive, but the "search" function turns up nothing incorporating either acrylic or plexiglas.
Could you direct me to that entry as I would like to avoid having to stop drill the small crack
Thanks, Ted Galdi
There are thin acrylic solvent cements that you wick-into a crack like SCIGRIP 3. Also, there are thicker cements if they don't have to be wicked-in like SCIGRIP 16, but you have to be able to open up the crack or deflect the surfaces so you can apply it. (The water-thin cement that wicks-in sounds like what you'd need.)
However, even if you cement it, I would think stop-drilling would be advisable just to ensure the stress concentration is relieved ... the crack could still extend, otherwise!
I will try the really thin stuff first and keep a close eye on the crack If needed will stop drill same..
A major part of the problem is trying to get the bubble door to fit under the folding wings crossbar. The upper rear gusset in the normal door --and I guess the STOLwith folding wings--nicely covers the top and rear of the door.
It appears that the wing on the Cruzer is fatter than the STOL so that one has to cut an arc into the gusset 35 mm deep to clear the cross tube. Looks like s....
Reading between the lines of my conversations with Roger, it appears that they have never sold the folding wings option for a Cruzer as he requests images so that they can but it on the Zenith site.
Gents, To all with cracks in your plexiglass: in order to stop the crack from getting larger you MUST place a small drill hole at the growing end of the crack. (Use a 60 Deg. plexiglass drill bit and let the bit do the work...nice and slow don’t force the bit through the plexiglass) Then if you can get a hold of it and since aircraft plexiglass is hardened the only solvent that will actually work to glue the crack by fusing the plastic crack is methylene chloride. Use a 1 ml syringe and place the solvent in a freezer before withdrawing a 0.5 ml sample into the syringe. (Your syringe needle should be cut to form a flat rather than angled needle end). Then after practicing on a sample piece quickly apply a small amount of the solvent to the crack by simply moving the needle along the crack while gently pushing in the syringe. The solvent will quickly seep into the crack, dissolve a small portion of the crack surface and as the solvent rapidly dries it then fuses the plastic together. Do not attempt this unless you have the crack on a level horizontal surface as trying to repair a crack that is vertical is impossible. Any solvent based fogging can be easily removed by dipping a paper towel into the same solvent and in single strokes wiping the area to a shiny surface. ( do not use a cloth as the fibers will bind to the plastic) Practice on a piece of scrap first so you get the hang of it before attempting to fix a door crack after removing the door from the plane and positioning the crack so that it is suspended over a table horizontally. You can see this done on UTube while watching people make plexiglass aquariums but keep in mind that Aircraft grade plexiglass requires methylene chloride solvent for crack repairs. And yes I have done this on my windscreen successfully before I installed it. The drilled hole can be filled with clear silicon glue after the repair is done. Finally this will not work unless the two sides of the crack are aligned with each other.
Hi John, though already flying my Cruzer I opted not to attempt to add the kit supplied vents because I found them very difficult to get into the door holes and did not want to crack mine. Thus I came to this page and found your idea an excellent one. What I don’t undersand is if you made 2 retainer rings to keep the Vista Vent in place since the holes in the Vista Vent are smaller in diameter then the door hole meaning the the retaining bolts and nuts require external support aka your retainer ring.....but don’t you need two rings? One for the outside and one for the inside of the door to hold the new vent in place? Once I have your answer and maybe a pic from the bolt side of your installation then I’ll order the vents. Please advise and keep up the excellent work. You are a great moderator and a good contributor too. I plan to add the front gear donut system too as time permits and thank you for that posting too John.
Hi John M,
The Vista Vent itself has an acrylic retaining ring of sufficient diameter to grasp the interior edge of the bubble window hole, so no additional hardware was necessary on the interior side of the vent. Since the bolts were passing through the hole in the door and not through individual bolt holes, I had to make a retaining ring to capture them for the exterior side only. Here's a picture from the Spruce website showing the acrylic ring or plate:
Thanks for your kind comments - I love to design and install mods ... guess I'll quit when the plane goes over-gross and will no longer fly! ;>)
Thanks for the quick reply John! Got it and no need for a picture now (it’s in my mind!).