Vacuum Bagging - Noob build log

[thenated0g]

I have come to realize that there are a lot of very experienced builders here so i wasn't sure if anybody would be interested in following along as i figure out vacuum bagging. I started a thread over in the Flite test forums. I could double post here as well if anybody is interested.

https://forum.flitetest.com/index.p...our-bags-ie-how-to-laminate-foam-wings.55426/

 

[Konrad]

Flitetest? These are the guys that are focused on fold and smash models? Looking at many (most) of their videos, the crash seems to be the highlight and focus of their existence.

I'd think it would be better to host your questions and techniques here at Aloft and then link to this forum site.

After all Aloft Hobbies is a provider of higher end products. I'm sure any member of the Flitetest forum that is planning to progress in the hobby, would want to know about the better product, material and processes available. They might grow in the presents of members committed to the advancement of our little part of aviation.

Flitetest might be a fun entry point for some, but the skills you are trying to develop and share are a bit beyond their scope.

Are you looking just to use vacuum bagging to press down the laminate (balsa wing skins) on to the foam core? Or are you looking to use vacuum bag and pump to aid in the creation of composite structures?

If working with a EPS foam core please be aware that the vacuum pump can easily crush the foam. it is wise to have away to regulate the vacuum.

If using balsa how are you doing to control soak up of the glue into the wood. With a vacuum bag it is easy to force a lot of glue in the wood pores making for a heavy wing.

I like to seal the wood with a thin coat of nitrate dope. I'm now using polyurethane (Gorilla) glues to good effect. (Read slowly moving away from slow cure epoxies).

All the best,
Konrad

 

[Konrad]

Well, I held my nose and actually went to the FT forum.

I think you are starting a bit at the deep end of the pool. 1/32 balsa is a bit more difficult to handle than some coverings. When spreading the glue keep the skins in tension. If you swipe in compression (towards your holding hand) you run the risk of buckling the 1/32 balsa.

I also find that it is a bit more difficult to spread out PU than epoxy. I like to think that not enough is still too much when trying to keep the AUP weight down. I do keep things a bit wet at the perimeter and over the spars.

I find that Red Oak veneers are great skins over foam. These have a fine cloth layer that helps keep the skin from splitting as it tries to go over the airfoil curves. It is strong and a lot less expensive than some other laminates. I get these from hardwood lumberyards.

I still think 1/16 balsa is best for your first attempts.

 

[thenated0g]

I am interested in mostly sharing the progress with others who haven't done it which the ft forums are great for.

Unfortunately in my small town i don't have access to anywhere nearby that has veneers. Possibly down in santa rosa, about 1.5 hrs away, i can find a place. I have been trying to find veneer or even 1/64 ply online but its pretty expensive. I was able to get some balsa for pretty cheap ($0.86 for 3x36 sheets plus shipping) so i will do what i can with it. Mainly at this point i'm trying to get the entire process down and not worrying too much about the actuall material. Than when i feel like i can do it move on to the good stuff as it were.

I have used gorilla glue for almost all my builds over the past few years and am a lot more competent in its use than epoxy at this moment. I don't want to add to many new variables at once.

The ply on the blejzyk wings is nice. Thats a goal in the future for sure. Also saw a guy use something called rhinohide to cover his foam. Some kind of composite.

 

[Konrad]

I am interested in mostly sharing the progress with others who haven't done it which the ft forums are great for.

I’m sorry. I thought you wanted to gain from those of us that have actually done this. Please allow me to make a few observation and then I’ll leave you to your own devices.

Unfortunately in my small town i don't have access to anywhere nearby that has veneers. Possibly down in santa rosa, about 1.5 hrs away, i can find a place.

LOL, It often takes this big city slicker over an hour and a half just to cross town!

I have been trying to find veneer or even 1/64 ply online but its pretty expensive. I was able to get some balsa for pretty cheap ($0.86 for 3x36 sheets plus shipping) so i will do what i can with it. Mainly at this point i'm trying to get the entire process down and not worrying too much about the actuall material. Than when i feel like i can do it move on to the good stuff as it were.

Now I have sheeted with 1/64 plywood and would like to caution you that it is often difficult to get the plywood to form against the cross grain of some of the plywood layers. While it can be done there is a risk of distorting the foam core with the force needed. (Small wing are more at risk than larger wings, this is a rate of change issue).

I have used gorilla glue for almost all my builds over the past few years and am a lot more competent in its use than epoxy at this moment. I don't want to add to many new variables at once.

I’m glad you are comfortable with PU Glues. I find that the thick viscosity of the PU glues makes them much more difficult to spread out into a thin layer than any of the slow epoxies. This difficulty spreading out the glue (PU or Epoxy) is why sealing the balsa is advantageous. This sealing also saves on weight from the wood soaking up the glue.

The ply on the blejzyk wings is nice. Thats a goal in the future for sure.

To the best of my knowledge the wing skins on the Blejzyk kits are not plywood but a single layer wood veneer.

Also saw a guy use something called rhinohide to cover his foam. Some kind of composite.

Don’t know about Rhino-hide but Rhino-Skin in my industry (Aerospace) is a 3M PVC film with self adhesive used to protect notch sensitive surfaces when we are working adjacent to them. This is probably what some folks are looking for from the Laminating film.

All the best,
Konrad

 

[Wayne]

Actually Flight test has a good active forum that thenated0g has been very active on. I am very pleased he is posting up here also.

I have never used a vacuum pump when sheeting wings with wood, I have always used contact cement and basically rolled the wood onto the foam cores. The bagging should give better results. I don't think your foam will be smooshing down under the vacuum, but it is a valid concern. I forget what you said you used for a pump. Somewhere around here I have a really nice pump. I bought it as a rebuild from a guy that gets them from dental places. It is basically the same as used for commercial A/C repairs.

I have seen a wide range of things used for vacuum pumps ranging from pretty low end stuff like hand pumps from auto parts stores, converted fish air pumps, neither of these worked well. The most common seems to be an old refrigerator compressor, and semi-cheap vacuum pumps from the composite shops. These tended to be good and have a fair price. More recently I have heard of people using vacuum pumps from diesel cars, seems the newer cars have electric pumps that can be had for very little. Look for diesels that still have vacuum boosters for the brakes, they will have some sort of pump.

When it comes to glue for the skins, you can use anything that will not melt your foam. I have seen people use elmer's, all forms of contact cements, foam glues, Gorilla, epoxies even carpet tape in the old days.

For skins we used to hit up a wood importer in So Cal that would bring in pallets of 5 layer ply that was 1/64". This was super nice stuff. Seems it was usually destine for high end cabinets. It was not cheap. The hobby suppliers will milk you dry for lower quality 3 layer 1/64" ply, so best off looking elsewhere if you really want this spec of ply. For balsa, I liked a good quality balsa that was around a 1/16 or even 1/8" thickness. I was usually looking for a light wing that I could sand nicely. I would not use balsa for anything that was going to be abused.

We had a guy sheet some EPS cores with aluminum sheets, do not do this! His cores melted while sitting in the sun. They looked pretty darn cool before they got too hot. Again, if you can glue it, you can use it.

 

[Konrad]

Wayne,
When I say I despise a forum (hold my nose) it is not for the forum participants but rather the forum's management and the implementation of their often poorly defined policies.

I will say that vacuum pumps designed to draw down refrigerator systems can (will) crush white expanded polystyrene beads (styrofoam) at their max draw. The extruded stuff might hold up.

I've never tried wood glue in a vacuum bag. Does one need to keep the pump on as the water boils off?

I will say that the desired adhesives for vacuum bagging are different from "normal" skinning adhesives. I never liked contact cement ( or double sided tape) as it was far too easy for me to induce a warp as I rolled the cores on to the skins.

All the Best,
Konrad

 

[Wayne]

When you get into bagging you quickly learn about how much pressure to apply and how to regulate that pressure. I prefer to have a larger pump that is on a vacuum switch and has a reservoir. The pump might turn on once an hour at most. Many of the cheaper options can't pull as low a vacuum and have no reservoir or vacuum switch so they run all night long. Also some of the big ones are very quiet.

Yeah, if I had a pump when I was younger, I would have used it for sheeting wings. I was just stating that I have only used contact methods when using wood to sheet wings.

I forgot to mention, Sean at the office here has been bagging some DLG parts and he has found that our laminating film works great for making the bags!

 

[thenated0g]

I found some older well written posts on rcgroups about balsa and gorilla glue. I have a kit waiting for me to build that uses the spray adhesive method to quickly get the sheeting down, Again this is just a cheaper easy way to get some of the process's down before going to better materials. I have a vacuum gauge and from what i have seen in a few posts i think i will be trying about -8 inHG as my starting point and leave it under vacuum for 3 hours with the brown GG.

 

[thenated0g]

Thanks for the tip! I have a 28x200ft roll i thought i would have for life as that was the smallest it came in. I will definitely try that. How is he sealing the end? Food sealer bag style, just resealing and cutting as needed or does he have some clips?

 

[Wayne]

He uses rope caulk on the open end, it is kind of like play doh. Other sides he just seals with an iron. You could easily seal all sides and cut to open.

 

[thenated0g]

Had a good dry test run, no glue. Couple little leaks to fix but everything is working. Closed the loop pulls down to -20 inHg. I was in a hurry sealing my bag but even with leaks i was getting about 12 inHG. I will want to add a few quality of life things but its working enough to keep progressing with this setup. I grabbed some food saver vacuum bags to test this week.

 

[Wayne]

Sweet - Looks like you might need a brushless upgrade in the future. LOL

 

[thenated0g]

 

[thenated0g]

One Jart wing Bagged. Crazy how stiff this makes the wings. I think i could get away with no laminate on top.

 

[Wayne]

The joys of composite structures. When you bond 2 materials with different physical characteristics, you get a new result.

 

[thenated0g]

Its not a light wing, but it is the stiffest wing i have ever had or made.

 

[thenated0g]

I had debated doing the horizontal stabilizer/elevator as two seperate pieces or a single piece, but after seeing how strong the wing was after getting laminated I realized i really want that strength of a single piece in the tail.

So i first leveled and glued the two beds together and than used white GG to glue the two wing cores together.

The possible bad things here are that this has some compound curves. It is high in the center going down towards each wing tip. It also needs to go around the LE and TE curves. Guess we will see what happens.

Next i need to trace the shape on to two pieces of balsa and start bagging.

 

[thenated0g]

 

[Wayne]

Sweet! That elevator looks great! You are doing super on this build!