To overhaul or not to overhaul?

[Thermalseeker]

So, lets say you have a Rotax 912s that was built in 2002. It's approaching calendar TBO, but only has about 600 hours TT. So, it's nowhere near Hobbs time TBO. Compressions are excellent and it runs like a top. Doesn't burn or leak oil and it's the smoothest 912 you've ever flown behind. You've done all the regular maintenance items (carb rebuild, new rubber, etc) and kept up with all the AD's. Do you:

A) Overhaul the engine.

Keep flying "on condition" even though your insurance might not cover an engine out.

C) Keep flying "on condition", but have the gear box overhauled before something lets go (they usually go at about 700 hours)

d) Buy a new 912s to replace the old one. Then, sell the old one in the Experimental market because, price wise, this is about the same as overhauling.

D) None of the above.

[Thermalseeker]

So, lets say you have a Rotax 912s that was built in 2002. It's approaching calendar TBO, but only has about 600 hours TT. So, it's nowhere near Hobbs time TBO. Compressions are excellent and it runs like a top. Doesn't burn or leak oil and it's the smoothest 912 you've ever flown behind. You've done all the regular maintenance items (carb rebuild, new rubber, etc) and kept up with all the AD's. Do you:

A) Overhaul the engine.

Keep flying "on condition" even though your insurance might not cover an engine out.

C) Keep flying "on condition", but have the gear box overhauled before something lets go (they usually go at about 700 hours)

d) Buy a new 912s to replace the old one. Then, sell the old one in the Experimental market because, price wise, this is about the same as overhauling.

D) None of the above.

[Guest chasers03]

I have a 2005 80 hp Rotax with 1350 hrs and like yours it runs like a top. My block dictates a 1500 TBO but I intend to go for the new 2000 TBO of course taking care of maintenance such as the gear box washers again. The bigger question is how is the plane gel coat condition. My Lambada is cracking a little and will need repair somewhere down the road. I would like to get it painted at least on the top surfaces like the Diamonds have but preparation for all this is a big effort I am told.

[Guest chasers03]

I have a 2005 80 hp Rotax with 1350 hrs and like yours it runs like a top. My block dictates a 1500 TBO but I intend to go for the new 2000 TBO of course taking care of maintenance such as the gear box washers again. The bigger question is how is the plane gel coat condition. My Lambada is cracking a little and will need repair somewhere down the road. I would like to get it painted at least on the top surfaces like the Diamonds have but preparation for all this is a big effort I am told.

[Thermalseeker]

My Ximango is urethane finish. So, no cracking or crazing issues at all. It has about 1100 hours on the airfame now, but still looks very good. I do quite a bit to keep the finish up, though, i.e., regular waxing and buffing, taking care of dents and scratches as necessary, etc. it gets wiped down after every flight, too. If you leave the bugs on the finish they can stain, not to mention they're much easier to get off when they're fresh (i.e., not baked on after sitting in the hangar on a hot summer day)

We do composite repair and refinish in my shop. Mostly on racing sailplanes, but we did a refinish on a Lambada from up in Virginia several years ago. The hard part for us is our shop isn't tall enough to roll something like a Lambada in (low ceilings). So, the wings have to come off. Most everything we do comes to us in a trailer. So, the low ceilings usually aren't an issue.

There's a couple of ways you can go about a gel coat refinish. One is to sand 90% of the gel coat off using a long block (2' or better) with 220 and 320 wet. You can use a linear air sander, but you have to be very careful sanding at alternating 45's to the curve of the airfoil so you don't ruin the profile. As I recall the gel coat wasn't that thick on the Lambada, so gouging wasn't really a problem. Something like a Grob, where the gel coat can be a 1/4" thick, you have to be very careful using an linear sander.

The key with this method is taking it down very evenly. The longer block you use the better. Once you have it sanded down to near (but not at) the cloth most of the crazing will be gone. Anything left that is visible is filled. The biggest thing about sanding is knowing when to stop. You don't want to get into the cloth. We then overshoot with about 5-7 coats of urethane, then color sand after it's cured with 600, 800 and 1200 wet, then buff. Comes out looking brand new, but it's a hell of a lot of work. There's another method we've had very good success with, too, and it's not quite so labor intensive, but still a hell of a lot of work.

We've done several "quick" refinishes by block sanding the wing tops, removing most of the spider cracks, but leaving the larger ones. Then, we grind out the worst of the crazing so any loose chips are removed and the bigger cracks are tapered to accept filler. Then, we fill with "dry" micro (the consistency of very light whipped cream) wiped very thin. Larger cracks will take multiple wipes. After it kicks the wing (and/or fuselage) is block sanded until it's nice and smooth, usually we use 320, but sometimes 220 to start, then 320. Usually a pass with 220, and a couple of passes with 320 will do it. Then, overshoot with 5-7 coats of urethane, then color sand with 600, 800 and 1200 wet, then buff. It comes out looking very nice and you shouldn't have to do anything for many years. Urethane is the preferred finish. Gel coat gets brittle over time from UV exposure. That's why the cracks. Urethane remains flexible, so it doesn't crack over time. It doesn't yellow like gel coat, either.

The first method takes anywhere from 150-200 man hours for something the size of a Lambada. The second method about 150-180 man hours. Of course, these times are generalities. How long it takes will depend on how bad the crazing is and whether there is any damage that needs repaired. Using method 2, depending on how bad the crazing is you might be able to see where the major cracks were in a year or two if the light is just right because the filler and paint both will shrink, but it's minimal and can only really be seen under florescent light if you get down at a low angle. This is called "print through". You can see a similar effect on just about any composite airplane where there are internal bulkheads, ribs, stiffeners, etc. The crazing should not return because when you top coat with urethane you have stopped the gel coat from being exposed to UV. We did an LS-4 about 7 years ago using this method and it still looks good. We try to post cure when we use micro filler so most of the shrinking takes place before it's shot with urethane. Whatever you do you really do need to fix it because if the crazing goes all the way to the cloth the UV is cooking your underlying epoxy resin and ultimately will compromise the structure.

What we usually tell folks with gel coat airplanes is to lightly sand it periodically, say every 3-4 years from new. UV damages the gel coat from the outside in. So, periodic sanding will remove the micro-fine crazing before it becomes cracks. It also helps with the yellowing. After about the 3rd or 4th sanding (12-16 years since new) you'll be ready for a refinish, but most of the sanding is already done. Most of the gel coat used these days won't last that long anyway before it crazes. Most people don't listen, but we tell 'em anyway. Hope it helps!

[Thermalseeker]

My Ximango is urethane finish. So, no cracking or crazing issues at all. It has about 1100 hours on the airfame now, but still looks very good. I do quite a bit to keep the finish up, though, i.e., regular waxing and buffing, taking care of dents and scratches as necessary, etc. it gets wiped down after every flight, too. If you leave the bugs on the finish they can stain, not to mention they're much easier to get off when they're fresh (i.e., not baked on after sitting in the hangar on a hot summer day)

We do composite repair and refinish in my shop. Mostly on racing sailplanes, but we did a refinish on a Lambada from up in Virginia several years ago. The hard part for us is our shop isn't tall enough to roll something like a Lambada in (low ceilings). So, the wings have to come off. Most everything we do comes to us in a trailer. So, the low ceilings usually aren't an issue.

There's a couple of ways you can go about a gel coat refinish. One is to sand 90% of the gel coat off using a long block (2' or better) with 220 and 320 wet. You can use a linear air sander, but you have to be very careful sanding at alternating 45's to the curve of the airfoil so you don't ruin the profile. As I recall the gel coat wasn't that thick on the Lambada, so gouging wasn't really a problem. Something like a Grob, where the gel coat can be a 1/4" thick, you have to be very careful using an linear sander.

The key with this method is taking it down very evenly. The longer block you use the better. Once you have it sanded down to near (but not at) the cloth most of the crazing will be gone. Anything left that is visible is filled. The biggest thing about sanding is knowing when to stop. You don't want to get into the cloth. We then overshoot with about 5-7 coats of urethane, then color sand after it's cured with 600, 800 and 1200 wet, then buff. Comes out looking brand new, but it's a hell of a lot of work. There's another method we've had very good success with, too, and it's not quite so labor intensive, but still a hell of a lot of work.

We've done several "quick" refinishes by block sanding the wing tops, removing most of the spider cracks, but leaving the larger ones. Then, we grind out the worst of the crazing so any loose chips are removed and the bigger cracks are tapered to accept filler. Then, we fill with "dry" micro (the consistency of very light whipped cream) wiped very thin. Larger cracks will take multiple wipes. After it kicks the wing (and/or fuselage) is block sanded until it's nice and smooth, usually we use 320, but sometimes 220 to start, then 320. Usually a pass with 220, and a couple of passes with 320 will do it. Then, overshoot with 5-7 coats of urethane, then color sand with 600, 800 and 1200 wet, then buff. It comes out looking very nice and you shouldn't have to do anything for many years. Urethane is the preferred finish. Gel coat gets brittle over time from UV exposure. That's why the cracks. Urethane remains flexible, so it doesn't crack over time. It doesn't yellow like gel coat, either.

The first method takes anywhere from 150-200 man hours for something the size of a Lambada. The second method about 150-180 man hours. Of course, these times are generalities. How long it takes will depend on how bad the crazing is and whether there is any damage that needs repaired. Using method 2, depending on how bad the crazing is you might be able to see where the major cracks were in a year or two if the light is just right because the filler and paint both will shrink, but it's minimal and can only really be seen under florescent light if you get down at a low angle. This is called "print through". You can see a similar effect on just about any composite airplane where there are internal bulkheads, ribs, stiffeners, etc. The crazing should not return because when you top coat with urethane you have stopped the gel coat from being exposed to UV. We did an LS-4 about 7 years ago using this method and it still looks good. We try to post cure when we use micro filler so most of the shrinking takes place before it's shot with urethane. Whatever you do you really do need to fix it because if the crazing goes all the way to the cloth the UV is cooking your underlying epoxy resin and ultimately will compromise the structure.

What we usually tell folks with gel coat airplanes is to lightly sand it periodically, say every 3-4 years from new. UV damages the gel coat from the outside in. So, periodic sanding will remove the micro-fine crazing before it becomes cracks. It also helps with the yellowing. After about the 3rd or 4th sanding (12-16 years since new) you'll be ready for a refinish, but most of the sanding is already done. Most of the gel coat used these days won't last that long anyway before it crazes. Most people don't listen, but we tell 'em anyway. Hope it helps!

[Steve Sliwa]

Hi John

Are you able to roll upir Ximango into the hangar when you work on it or do you take the wings off?

Steve

[Steve Sliwa]

Hi John

Are you able to roll upir Ximango into the hangar when you work on it or do you take the wings off?

Steve

[Thermalseeker]

Hey Steve,

Not in the area where we normally paint. The ceiling and roll up door are too low. We did a repair on a Ximango a few months ago that sustained belly scrapes from a gear up landing. Since we were only shooting the belly with a small detail gun it was easy enough to contain the overspray and drift by just draping plastic over the airplane. We shot it right out in the middle of the hangar, about 30' from where I keep my Ximango. No problems at all. If we were going to do a full on refinish on a Ximango we'd have to fabricate a tent to contain the overspray drift, but I have plenty of room. I would limit it to the wing tops. If someone wanted the wing bottoms on a Ximango done the wings would probably have to come off. Since the wings are high off the ground and are so easy to pull on a Lambada, we pulled the wings on the one we did the refinish on, but the Lambada's wings come off a hell of a lot easier than a Ximango. It was much easier to sand with the wings off, plus the owner wanted top and bottom done.

A bigger issue with urethane is temperature. Gel coat not so much, but urethane is very sensitive to temperature. It really needs to be about 80F (and preferably 90F) when you shoot or if you're not really careful it will run and sag. Runs and sags in urethane can be sanded out completely, but it just adds more labor. When I do work on my X I move it to my other hangar which is heated, but I don't like to shoot a big paint project over there because I keep my Europa, camper and other toys in that hangar, too. We could definitely do a Ximango without removing the wings, but we'd have to section off an area to do it with plastic and throw a couple of heaters in if it were going to be painted this time of year.

[Thermalseeker]

Hey Steve,

Not in the area where we normally paint. The ceiling and roll up door are too low. We did a repair on a Ximango a few months ago that sustained belly scrapes from a gear up landing. Since we were only shooting the belly with a small detail gun it was easy enough to contain the overspray and drift by just draping plastic over the airplane. We shot it right out in the middle of the hangar, about 30' from where I keep my Ximango. No problems at all. If we were going to do a full on refinish on a Ximango we'd have to fabricate a tent to contain the overspray drift, but I have plenty of room. I would limit it to the wing tops. If someone wanted the wing bottoms on a Ximango done the wings would probably have to come off. Since the wings are high off the ground and are so easy to pull on a Lambada, we pulled the wings on the one we did the refinish on, but the Lambada's wings come off a hell of a lot easier than a Ximango. It was much easier to sand with the wings off, plus the owner wanted top and bottom done.

A bigger issue with urethane is temperature. Gel coat not so much, but urethane is very sensitive to temperature. It really needs to be about 80F (and preferably 90F) when you shoot or if you're not really careful it will run and sag. Runs and sags in urethane can be sanded out completely, but it just adds more labor. When I do work on my X I move it to my other hangar which is heated, but I don't like to shoot a big paint project over there because I keep my Europa, camper and other toys in that hangar, too. We could definitely do a Ximango without removing the wings, but we'd have to section off an area to do it with plastic and throw a couple of heaters in if it were going to be painted this time of year.