KeeeRack!

That might be a wonderful sound to a baseball fanatic, but to an RV-8 builder and pilot, it is one of the last things you ever want to hear in flight.

?Hello, My name is Paul, and I have a cracked RV-8 Canopy??

All RV?ers take pride in their canopies, but let?s face it ? the canopy pretty much DEFINES the tandems and single-seater. That big beautiful bubble is a statement, not just a cover ? it says ?I can see in every direction, and I can rule the world!? Well, yeah ? but it also has a lot of stored stresses in all those wonderful curves. And when the temperatures drop and the material tries to contract, those stored stresses are just waiting for an opportunity to be released?.

I left Big Bear Lake at 6750?when temperature had risen from the overnight single digits to the ?balmy teens. It was just a quick flight down the hill to Cable Airport (KCCB) to visit the workshop of R.C. paisley, RV builder and inventor of neat things. Unfortunately, the strong north wind that brought the cold temperatures also brought some sharp bumps over the mountain ridges and the funnel of Cajon pass. Although I slowed things down to maneuvering speed, it was tough trying to lose the altitude I had to get rid of in the distance I had to go while keeping the speed reasonable. I hit a series of sharp bumps, not unlike what I have experienced before, but never at these temperatures. I thought that at one time, I heard a ?Snap!? behind my head, but was busy enough flying the airplane to not give it undo attention.

Sure enough, when I got back to Big Bear, and we were rolling the airplane back in to the hangar, there it was ? the mother of all cracks. Starting at a rivet hole behind the passenger on the right side, it went straight across to the middle of the canopy. Down where it started, the gap was almost 1/16th of an inch ? the canopy was still very cold, and that showed how much it had shrunk.



These kinds of things always happen when you are away from the shop, but fortunately, there are a couple of independent mechanics on the field, and Louise was able to chase down a portable drill and a Plexiglas bit. Stop-drilling the crack didn?t take too long, and to secure it for the trip home, we added some silicone and two layers of clear packing tape to seal it from leaking too much air.



A test flight with some mild aerobatics and a few ?G?-pulls showed that it would probably last the trip home, and it hadn?t moved at all when I pulled in to Houston., Some more aerobatics this afternoon gave me confidence that it is flyable until I get a chance to replace the bubble. I have amazed myself at how calm I have been over the episode ? knowing a few others that have experienced this and lived through the process probably make it easier. I have since talked to a number of other -8 drivers who have flown with similar cracks for several years, so it is more a matter of cosmetics than airworthiness in my mind ? and it will also be replaced as soon as I formulate a complete plan.

I?d love to take advantage of this episode to go with a Todd?s canopy (we have one for our -3), but after talking with a couple of folks that have had to replace -8 bubbles, this probably isn?t practical (due to different thicknesses and shape than the Van?s product) unless I virtually start over with the windshield, fairings, and skirt ? something that really doesn?t seem worth it. Yes, the Van?s canopy is a lot more money, but time is of value, as well as the amount of down-time it would take to re-do the whole top of the plane.

If I learn anything important about replacing the canopy along the way, I will ? of course ? share it here with the community. In the meantime, should you see the Val with a crack at the back of the canopy, you?ll already know the story?.

Paul

Ouch.

That sucks, Paul. Having replaced a cracked canopy (with a little help from Sky King) just prior to painting, I feel your pain.

However, if you do replace it with another Van's bubble, it's really a pretty painless process. Contact Danny. We drilled out my old bubble and replaced it with a new one in ONE day. Of course, you'll still have some painting to do then, but he has a pretty slick method of duplicating the bubble and it just slides into place.

Wow Paul this just hurts to read. Sorry

Will you re-rivet or go the Sika route?

No. Черт побери.

RV8R999 said:

Will you re-rivet or go the Sika route?

Click to expand...

If Sika had been mature and proven when I was building, I probably would have gone that way. Now I would have to rework a lot of stuff due to the different dimensions, so I will probably go back with the same setup to avoid resizing the skirt, windshield interface, etc.

While I am clearly disappointed with the event, I am heartened by the fact that it lasted for 1250+ hours using Van's installation method, and I know that it was an unusual set of circumstances that caused it to go when it did. If anything, I am a bit mad at myself for not remembering Danny's advice when his cracked under the same circumstances - "slow down and be careful when it is very cold and very bumpy!"

I have been seriously considering Sika only for the bubble on the -3, and will look at that more intensely now!

Paul

{Vlad - I agree! But I won't translate it here....}

Fly it up to 52F, Paul. Danny will fix it just to fly it back down to you.

Sika & Rivets

Hey Paul, you might oughtta think about using both. At work, our helicopter plexi is secured using both proseal and then pop riveted in. This gives additional support beyond the small stress area from the rivet. Anyhow, it works well and I used both sika and rivets when I did my 8's canopy (the jury was still out at the time whether or not Sika was adequete by itself). However, I have yet to fly my 8 yet and can't back it up with honest data whether this will work or not. Something to think about anyhow. Sorry to see the Val blemished like that, she's a beaut.

Sorry to hear that Paul. Replacing a canopy is a lot of work and expensive. The cold must be a big factor. Today a good friend of mine flew his RV8 from Denton, TX to Alamosa, CO. and the very same thing happened to his canopy. Temperatures at the departure point were in the mid 20's, around 0F aloft and in the low teen's at his destination. His airplane is 10 years old and his canopy never cracked before but today was the first time he flew in temperatures close to zero.

Martin Sutter
Building and flying RV's since 1988
EAA Technical Counselor

Aww, that sucks, Paul. Hope you get 'er fixed soon. Glad it wasn't anything worse (i.e. safety).

Ouch!

I'm sorry for the damage Paul! That was a really bad crack too! I'm glad there wasn't any additional safety-related happenings in the turbulence.

Your experience (slow down in cold bumpy weather) came very timely for me since I fly alot during winter and needed a reminder.

So for what it's worth; thanks for the reminder!

Looking forward to see pics of the new canopy when it's in place!

Ouch. A canopy crack is one of my bigger nightmares. I feel your pain.

You needed a break from building the -3b anyway Paul.

Canopy Attachment

Paul,

There is good discussion and a couple construction diagrams in the August 1997 RVAtor (page 8-9) on plexiglas expansion and contraction versus steel and aluminum. Over a total temperature range of 160F, acrylic changes dimension about 1/16" per foot more than steel frame. The article discourages riveting and promotes drilling the canopy to 5/16" for 6-32 screw and nut arrangement. Oversize countersunk holes will allow for acrylic expansion and contraction both at the skirt and canopy frame tube. I tapped the canopy frame tube holes.
The article cites seven reasons to adopt this approach, and I did this on my slider 6. I have less than half your total hours, but have flown in northeast winters prior to moving to Louisiana without problems. I may have gone 1/4" hole in the plexiglas to accommodate the (approx.) 1/8" shank of the 6-32 screw, leaving 1/16" radius clearance. Just thought I would throw it out there if you are reconsidering rivets.

Bob Gordon said:

Paul,

There is good discussion and a couple construction diagrams in the August 1997 RVAtor (page 8-9) on plexiglas expansion and contraction versus steel and aluminum. Over a total temperature range of 160F, acrylic changes dimension about 1/16" per foot more than steel frame. The article discourages riveting and promotes drilling the canopy to 5/16" for 6-32 screw and nut arrangement. Oversize countersunk holes will allow for acrylic expansion and contraction both at the skirt and canopy frame tube. I tapped the canopy frame tube holes.
The article cites seven reasons to adopt this approach, and I did this on my slider 6. I have less than half your total hours, but have flown in northeast winters prior to moving to Louisiana without problems. I may have gone 1/4" hole in the plexiglas to accommodate the (approx.) 1/8" shank of the 6-32 screw, leaving 1/16" radius clearance. Just thought I would throw it out there if you are reconsidering rivets.

Click to expand...

Thanks for the reference Bob - I'll go try and find that article. Screws are one thing I am thinking about, since I don't want to change the fit by going with Sika.

Ooh that hurts

Paul, a 4 driver friend of mine had a similar crack occur during building in almost the same location. It was out of the field of view from the back seat and the crack was fairly symmetrical from left to right, so he put a 2 or 2.5 inch fiberglass bow across the canopy. It looks similar in size to the bow on the 8 joint between canopy and windscreen and actually looks very good. It has been that way since new in early 2000's. You could always put a piece of black duct tape there, to see what it would look like, if the crack doesn't vary too much laterally. If you are interested in considering that route, I can see if he has a picture of what he did. Just another possibility.
John with a "Sikaflexed" 8 canopy but our 4 with rivets has two cracks

OUCH! and OUCH!

I'm sure it'll be good or better than new in no time

Happy New Year regardless

Riveting & solid fixing of Van's plexi has bugged me for years. You almost never see "fixed" plexi on a production plane. Even pressurized windows are set with at least a little provision for movement. As I'm finishing a 10 with totally fixed & flush windows, it still bugs me. No way can pop riveting plexi to a steel frame be good, but thats the way we do it. Gluing them in with Weld-on also seems like poor practice, although "fixing" plexi to fiberglass won't create as much stress as "fixing" it to a steel frame. If I was to do another 8 I'd seriously think about oversize holes with screws and pro-seal. Few production planes even drill through the plexi. Most of it just rides in channels with sealant & felt around them, of course they often leak.

Just a thought..........

I would think something like we do for mounting servos in R/C aircraft would work well.

Rubber grommet to allow a bit of movement, and a bushing inside the grommet to prevent the mounting screw from crushing the grommet.

Mike S said:

I would think something like we do for mounting servos in R/C aircraft would work well.

Rubber grommet to allow a bit of movement, and a bushing inside the grommet to prevent the mounting screw from crushing the grommet.

Click to expand...

That's exactly what I did... oversize holes with bushings made from soft silicone tubing to fill the gap between the fastener and the glass:



(Disclaimer: Not flying yet!)

mcb

For the tip-up portion of my canopy I also used loosely tightened screws and oversize holes, except at the front. That was what was on my old Schweizer 1-26 that I flew in temperatures from 110 F to -40 F with no problems. I did attach the small aft portion of the canopy with pop rivets and I still do have nightmares about what happened to you Paul.

canopy

So sorry you got that crack. A really bad deal. Are you going to make holes in canopy larger this time and augment with Proseal or Sikkaflex? Any thoughts are appreciated as my canopy is just cleco'ed at this point. I need to decide how to attach! Flew yesterday with Jim Phillips in his RV-8 which just developed a short (fortunately) canopy crack in cold weather after several years of flying. This extended a few centimeters up from a rivet hole. He has stop drilled it and all hope it doesn't extend. Should the hole be filled with anything? Bill

Bill Dicus said:

So sorry you got that crack. A really bad deal. Are you going to make holes in canopy larger this time and augment with Proseal or Sikkaflex? Any thoughts are appreciated as my canopy is just cleco'ed at this point. I need to decide how to attach! Flew yesterday with Jim Phillips in his RV-8 which just developed a short (fortunately) canopy crack in cold weather after several years of flying. This extended a few centimeters up from a rivet hole. He has stop drilled it and all hope it doesn't extend. Should the hole be filled with anything? Bill

Click to expand...

For now, we filled the stop-drilled hole (and the gapped portion of the crack) with clear silicone, and that seems to be doing well.

My original install was exactly per Van's directions at the time (I am going to have to dig out the drawings, aren't I?), but or the repair, I will do more over sized holes, and either the screws or the little tubing "washers" like Matt showed - something to give it more freedom of movement. Of course, the original lasted over 5 years, 1250 hours, and some of that in cold conditions, so it is not all bad....I will also do a Sika "filet" like Danny King did after his replacement - we have no hard data, but a guess that this will take some of the load between the frame and Plexi; load that might otherwise go through the fasteners.

Thanks for all the condolences guys - it's fixable, and flyable, and not a safety issue, so it could be a lot worse! (The worst part is that I'll probably have to redo some paint on the skirt, and that might mean I have to replace the vinyl lettering of my name and call-sign. One of those - the right or left - took a special trip around the earth about 187 times before it got applied to the airplane...hate to lose that...)

Paul

Hi Paul,

Sorry to hear about the canopy crack.

Reference the use of screws vs rivets I did the following:

Drilled the holes from the inside out with a new step/unibit -- then did the outside countersink with a new sharp countersink bit. This insured that the small "break out fractures" that always occur when the bit breaks thru the glass are polished out and eliminates stress risers. I used the unibit after test drilling some scrap plexi with both a new uni and a new plexi bit--under a magnifying glass the entry hole was cleaner with the uni--the exit hole was not as important since I was using a counter sink bit to finish that side.

Drilled the holes oversize. Bought some small rubber vacuum line (the kind that in the old days was used on vacuum driven windshield wipers) from the local NAPA, cut to individual bushing size. Used ss phillips screws, ss finish washers, and the rubber bushings into the threaded frame (size 6) as opposed to rivets--set just snug. On the 9 tipper the side skirt screws go all the way through so there I used thin ss flat washers and ss nylok nuts.

Sorry we missed you and Louise this New Years.

Good luck with your repair.

Cheers,

db

Alternate Method

Paul,

Some years ago I built an Acro Sport II with a Pitts canopy. In the build process I had many conversations with the Pitts factory and other Pitts builders and re-builders. So much for the background. The Pitts canopy is held to the steel frame with small 1/4" flush head sheet metal srews (countersink in the glass) and then a 3M product (Scoth Weld #2216 Structrual Adhesive) is used to "weld the glass to the frame. The #2216 is a 2-part extremely strong adhesive. Once cured it takes a cold chisel or grinder to get it off the frame and glass. It takes a bit to put it on your canopy as it migrates when being applied. You apply it in sections. For example, the bottom rails are done in two sessions (one inside and one outside). To do the bottom outer rails, place your canopy assembly on padded supports with the inside facing up. Using clear packing tape, make a dam to keep any adhesive from leaking through on the inner tube to glass contact area. Sand the tubes and glass with 60 grit at the bottom of the canopy where the adhesive will be applied. Vacuum and clean thoroughly with MEK. Mix the adhesive and apply along the bottom of the canopy. It will migrate and settle to a shape that fills the groove smoothly. Let dry, flip the canopy so it sits on the bottom canopy rails and repeat the adhesive application on the top of the bottom rails (you won't have to dam at this stage). Just be sure to think through your taping dams, rough sanding and cleaning prior to applying the adhesive. It will take several days to complete all the individual sessions, but well worth it. Just look at a factory Pitts canopy....
If you or anyone else is interested in the whole process, just give me a call.
Good Luck!

I have heard of several 8 canopies cracking in flight, but honestly I don't think I've ever heard of one cracking on the SBS RVs.

I'm curious if there is there something pertaining to the 8 geometry that makes it more susceptible to cracking? I.e. the very long length of the canopy, riveted to the very long aluminum frame.

I know that the rear of the -8 canopy generates a lot of lift (as evidenced by peoples' difficultly in getting it to seal well) so I'm curious if this could have an effect as well.

More good responses and methods - thanks folks! I was talking with AeroPlastics yesterday, and Jeff filled me in on the Scotchweld process as well. I am going to look in to that, but am still thinking that I don't want to use a process that changes the fit of the canopy to the frame, as I'll have to rebuild the skirt (I am still thinking Sika for the -3 BTW).

I will most likely go with screws and rubber tube spacers with larger holes in the plex on this re-install, as suggested by several here. I think we'll have a new van's canopy on the way soon, but as long as the cracks don't grow, it might wait a couple of months until the weather warms up - and maybe I'll even talk Danny into coming down for a weekend visit and I can talk him into "whitewashing the fence"....

Jamie, I think that you are correct - I believe that the much longer bubble on the -8's subject them to more bending loads than the shorter canopies on the SBS's, so they are more susceptible to cracking in the cold/bumps. Just a WAG - no science behind that though.

Paul

Ironflight said:

Jamie, I think that you are correct - I believe that the much longer bubble on the -8's subject them to more bending loads than the shorter canopies on the SBS's,

Paul

Click to expand...

Also, they grow/shrink with the temp change more than a shorter canopy.

The incremental growth will stack up, and the longer the total item, the greater the stack up.

crack repair

Ouch, tough break.
It is possible to repair the crack without replacement of the canopy. It will be better to replace it but if you want to buy some time and you are able to fly up to utah so I can help you with it, let me know and we can make a plan. My process is not perfect yet, but it does work. The quality is directly related to the amound of time alloted for the repair. Cost is minuscule compaired to the cost of a new canopy but then you would have to fly up here or fly me down there and then what is time worth.

Fly it and love it.
let me know if you think you want my help. Best wishes.
sgjackson

Modify instead of replace

Paul,
Just a thought but because the crack is quite low and to the rear that maybe cutting out the small section of broken canopy and replacing with a formed metal or fiberglass fairing would be better than replacing the entire thing. Also cutting out just the crack and making a fiberglass seam designed to act as an expansion joint may work and would look something like the slider at the roll bar. The crack in the picture seems to be fairly symmetrical and would seem to be easily worked into the profile of the canopy. I think you could develop a repair that would actually enhance the looks, prevent future occurrences, save money and limit downtime. Just a thought.

New FAQ

While we are on the subject of canopy issues, check out the latest FAQ on canopy care and feeding on the Vans website. This should be a compulsory read for anyone in close proximity with an acylic canopy or lexan materials...


http://www.vansaircraft.com/pdf/Acrylic_Canopy_and_Lexan_Window_Hints.pdf

crack = cold

Paul,

The day The 'Doll' cracked her canopy two others here in the metro mess cracked also. One was in its hanger and was not moved. The other one was flying and was in turblence. I was able to replace it and use the origional skirt with out much modification needed.

Another cold winter day two of my friends wanted to see if they could go up to 18K?? One came back with a crack that day.. bummer...

Sorry this happened to you. It seems these canopys do not like cold.
I do not take mine out much below +30.... this is a hobby for me and outside activity is supposed to be fun and comfortable?

DeltaRomeo said:

Fly it up to 52F, Paul. Danny will fix it just to fly it back down to you.

Click to expand...

If you take Doug's advice Paul, just be sure you get an affidavit and witnesses on the readout from your Hobbs meter beforehand. Otherwise, Danny might wind it backwards knowing how much you two compete for highest hours .

Best of luck.

Chris

New Canopy "In House"....

....and it is TOO COLD to care!!!

Many thanks to those who offered ideas on how to fix the old canopy, or hide the crack (actually, some very clever and good ideas - very practical too. I just like the uncluttered look of the full bubble), but in the end, I decided that I really wanted to have the full bubble back. It doesn't really even make any sense, as you can't really see it (except in the mirrors) when you're flying - but looks from outside are important too.

Anyway, I was able to buy a new bubble from Airplane Plastics - Jeff and Becki were great to deal with - and it showed up in a large crate last week. The only problem is that it is so cold down in Houston (sliding scale on what "so cold" means for my northern friends, but freezing is too cold to do Plexiglas work in my book...) that I didn't even want to try and take it out of the crate. It can wait a month until we are back in the 70's, and I can attract Danny down here for a weekend of work...uh, I mean beer!

We'll try to remember to take pictures of the process.

Paul