Jur's RV7 Aircraft Factory
4267 hours and counting

Day 2 of the construction of the windscreen fairing in fibreglass cloth using west system epoxy.
As I used peel ply over the last layer of the first session, so I could continue laying up glass without having to sand in between. I only cut down some rough points but it was really minimal. The peel ply really does a greatjob in keeping the cloth well glued to the bottom surface, even where it had the tendency to curl up due to the curvature.

As described in previous article, I am wetting out the surface, then laying the dry cloth onto it and use a brush to add epoxy glue onto it.  Cut the hairs on the brush short for better control.

I never thought I would say this about epoxy work, but I actually started enjoying doing this. Laying up dry and wetting it out allows you to keep your hands and tools clean. I only used 2 pair of gloves for the 4 layers... 
Once the part is wetted out, I roll over it with a 10cm wide epoxy roller To spread out the resin. Then Alain used the heatgun to gently warm the surface. This allows the resin the spread itself in the cloth. Then use the roller again to remove the excess epoxy.
The video below show the wetting out of the pilot side rear corner piece on the final layer.

The final layer is very important. The cloth has been cut as precise a possible to the templates and covers the fairing surface from the tape on the windscreen to the forward tape on the top skin.
Take your time laying it up as precise as possible aligned with the 3M tape. Then start wetting it out. The corner pieces are the most tricky as I wanted to get a nice angular corner in the transition of the bottom of the fairing to the top fairing over the rollbar.
The images underneath show the final result after completing the 8th layer. 8 layers should give me a thickness of about 0.105". On the top over the rollbar, I have 1 layer less (7) which is about 0.092". The plan section K-K on DWG43 specifies 0.08" aproximatly. I will see how it looks once the rear line is cut to size and might sand it down a bit but it actually looks good now.

Close up view on the front left side. Pay attention when laying up so the parts don't overlap and bulge up. It only means more sanding work later if they do overlap. A minor gap will be filled with additional layers of epoxy in the next steps anyway.

Pilot side left view. The rear end of the upper fairing has been made too long on purpose. Once the canopy is open again, I will measure for 1/2" overlap and cut back the excess.This ensures that the thickness will be uniform all over the width of the slider.

Passenger side front view.

Close up shot of the transition corner towards the rear part of the fairing. Patience and carefull cutting and fitting makes this nice round corner.

With all layers on, it's time to cover the epoxy with peel ply. Once this all cures, some sanding will begin and then some thin layers of glue with microballoons will be spread on to close gaps and fill pinholes.

I made mixes of 30 grams of epoxy each time. This is the amount of times I mixed a new batch for these 4 layers.

Time for a beer... the garbage bin is full again and curing time has begun. What a mess...

Next day, I removed the peel ply. The epoxy has cured nicely against the windscreen and skin without any bulges or curtain forming at the edges. Very glad with this outcome.

I thought I had covered the electrical tape with black epoxy and that it would become difficult to find the sanding edge, but when removing the peel ply, a lot of that very thin layer came off and as you can see, most of the tape is exposed again which will make sanding easier. In the next session, I will start sanding and try to get the surface a smooth as possible before applying the first coat of microballoons.

images/finishing/fin-windscreenepoxypart2-625

All right... the edges are masked with double 3M electrical tape, the canopy slider received 3 to 4 coats of wax and some additional PMA liquid plastic so it won't stick to the front. (would be embarrasing not being able to get back into the cockpit wouldn't it ?) The additional buildup up flox on the sides worked well. The fillets in the front are ready, gently sanded and dusted off and degreased. The slider, windscreen and skins are well protected and masked. A centerline is drawn do indicate the initial placement of the first narrow pieces.
I think I'm fully ready for laying up some fibreglass cloth... No kiddin... 

I got some good tips from an friend who used to work in epoxy repair shops. He told me to layup the dry cloth directly on the plane and wet it out on the spot instead of wetting it on a plastic on the workbench and transferring it wet to the plane. Both work but the wet transferring method makes a mess of your hands. Everything starts sticking right away. Wetting on the plane allows you to keep your hands much cleaner for a longer time. Once the cloth is wetted out by applying it with a brush or roll, use a heatgun  from a distance to warmp up the glue. Don't heat it !, just apply some warm temperature at a distance and the resin will start spreading itself much more easibly into the fibreglass cloth. You can also easily spot excess epoxy in this way which I then roll off with a roller.

The image below shows positioning the cloth on the front of the windscreen I had first wetted out the surface and then positioned the dry cloth. Once it's in the right place, start using a brush and dip additional epoxy resin on the new piece. Make sure when laying down pieces that you don't have overlaps (this will create bulges when dried) But layers up as precise as possible..

With the part wetted out, Alain held the heatgun at 120degress C high up and moved over the pieces. This generates a nice warm but not hot flow of air over the piece. As I see it saturating the cloth, I use a epoxy roller door press is on (to avoid trapped air bubbles) and pick up the excess epoxy resin.

As it's a sticky job, I didn't take a lot of pictures during the proces. We layed up 4 layers, each time going 3/16 wider on either side. Be carefull to keep centering the higher pieces over the lover ones so you create a nice smooth transition by the staggered layers to end up with 1 layer  on the sides.
When 4th layer was on, I cut peel ply and covered the hole thing with it. The peel ply has a triple purpose. 1. it sucks up some of the excess epoxy from the top layer. 2. When hardened and pulling the peel ply off, it creates a rough surface on which you can immediatly start laying up the next layers without need of additional sanding. and 3. very important, it keeps the wet layers in the desired shap. You will see that the parts that curve a lot - especially around the top rollbar - tend to pull up de edges of the cloth and it's hard to keep them down. Once the epoxy becomes more sticky, it's easier to push it down again with a brush. Once it's down, put peel ply over if and wet the peelply so it sticks well to it's surroundings. This ensures that the cloth will not curve up again and stay nicely in place.

 Next day, I removed the peel ply. I'm satiesfied with the result so far. This is ready to receive 4 more layers of fibreglass cloth.

The world these days is full of Artificial Intelligence LLMs (large language models) and AI tools that have become available to the everyday user. Knowledge that used to be hidden in libraries and dusty books has now become available and is easily accesible to the average person, which is certainly a positive thing. Most people's knowledge of AI is limitted to the usual chat prompts.

Lately, I have been experimenting with more advanced usage, and I wanted to share my experience and knowledge with other builders as I think it could also benefit their information research.

A word of caution, which is valid for my method as well as for simple prompting using any AI chat engine: Always cross-check the response you receive from the AI model by visiting the referenced websites or sources before actually using the information in the response on your project.

LLM AI tools do "hallucinate". Hallucination is a technical term to indicate that if AI doesn't find a definite answer to your question, it may sometimes invent information based on other - probably non-relevant - sources it identifies. This causes the user to read and rely on false information. Always double-check the responses you receive, certainly if you use them for your aircraft project.

I have been playing with different AI models to see how AI can help me look up information from the web and guide me through the list of manuals that keeps getting longer and longer as I progress in the building process.

For a few months, I had been looking up information through ChatGPT with prompts like, for example: "What is the torque value for an AN924 jam nut on an AN833-6D fitting for 6D fuel lines on my RV7?" It usually comes up with a good answer as it can find the relevant information in torque tables online. It gets more difficult if the information is not publicly available, like with information in proprietary Van's builder plans and manuals.

It would have been useful if AI could actually search my Van's PDF documents and DWG plans as well as other technical install manuals all at once. I discovered the use of "projects" in Google Gemini but soon hit the boundary of how many files you can upload with the free plan of Gemini. Then I discovered Google's Antigravity app. Antigravity is very similar to Gemini, but it is more oriented toward projects and coding assistance and it also uses projects and skills. The main difference seems to be that Antigravity can also work on local folders and the information that resides in them when it searches for information. And the amount of files in the folder does not seem to be limited.

Last days, I have been busy figuring out how to cut the epoxy cloth in such a way that it fits as good as possible in order to avoid a lot of sanding once it's cured. As mentioned in the previous post, I have decided to lay up the glass permanently on the airplane such as it is described in the Vans manual. There are other methods where the windscreen is removed  after laying up, sanding and finalizing it off the airplane and then using sikaflex to attach it such as described in a kitplanes article (Easy slider: part 2) by Larry Larson.
If you go for the Vans method, the layup will have to be more accurate as all sanding can only be done on the airplane, very close to that beautifull PMMA windscreen. 

I decided to make templates just like a tailor would do when making clothes. The Vans method describes starting at 1/2" in the center and gradually increasing the width up to 8 layers by cutting each layer of cloth 1/4 inch wider than the previous. That would bring you to 2 1/2" wide. My masked 3M lines are more or less 3.2" appart. The plans state a distance between 2.5" and 3.5"is fine.
So I have increased the step a bit. Increasing by 13/32" for the first 4 layers, then by 3/8 on the last 4 layers. This will increase the width on each layer by 3/16 on each side, creating a nice step up to 3.2".

The final layer is the most critical one as that one will have to fit as good as possible between your electrical tape masking lines.
The best way I could find was to use plastic sheet which I taped to the windscreen and then used a red sharpie to draw the contours of the tape to the plastic sheet. In the image below, you can see the sheet over the side of the windscreen and upper top fuselage skin.

Below another shot of a plastic sheet to create a template by tracing the exact location of the windscreen fairing

Then I cut out the shape from the plastic and layed it on thick paper and transferred the shape on to the paper. Here you can see the two corner pieces and two curved front pieces.
Then cut out the paper shapes.

Now that all pieces are cut for the final layer. I copied the paper shapes 8 times full size.
Put layer 8 on the side and start sizing down the other paper copies per layer, stepping down 3/8 on each template. Pay attention on which side you need to transition down in width. (eg: on the top of the fariring over the roll bar, you need to transition down to the front but can remain full thickness over the rear as this part will be trimmed down later. You'll have to think about this when trimming down the paper templates. It's a job that requires patience.

All templates are finally done, 72 unique paper templates ready to be transferred to epoxy cloth.

Next day took it all back to the garage and started cutting out the templates from a roll of epoxy weave.

A circular cutting knife works best here. The direction in which you cut the cloth is not important for the windscreen but you'll have learned by now that cutting the cloth at different angles causes different degrees of stability in the cloth and can cause the fibreglass cloth to fray.
I cut out 4 layers and next step will be the actual lay up work.