Flite Fest 2017: Bugatti 100P

[bstanley72]

Speaking of sanding! I was going to start a new thread today or ask in your other thread about glassing foam.

I've just started working with the pink foam and I'm having a tough time sanding and not grooving the surface. It seems as though the dust clumps and I scar the piece. I'll fill that with spackle, but then I'll create new groves while sanding the spackle and the cycle continues. This happens to me sanding the bare foam, as well as foam I've coated with sanding sealer, and with primer. I'm sanding both with sanding sponges and just holding the paper by hand.

I know it must be me and my technique, but this foam is a lot more fragile than I thought it would be.

Any advice is greatly appreciated!

 

[hackofalltrades]

Try finer sandpaper and perhaps a lighter touch. IME, it is hard to avoid the symptom you are suffering. What grit sandpaper are you using now?

 

[willsonman]

If you notice in my video I am clapping the block against my hand to free the clumps and dust to avoid this. The important part is to notice your work as you go and adjust your technique. As with any other new medium, it takes practice to know how to work with it.

 

[bstanley72]

Try finer sandpaper and perhaps a lighter touch. IME, it is hard to avoid the symptom you are suffering. What grit sandpaper are you using now?

If you notice in my video I am clapping the block against my hand to free the clumps and dust to avoid this. The important part is to notice your work as you go and adjust your technique. As with any other new medium, it takes practice to know how to work with it.

Mostly using 220 and 320 and even some 600. However, I suspect that I'm too heavy handed. Did some wood projects when I was I kid, so I suppose I'm attacking the foam like it's a walnut plank. I'll try to be more delicate and see how it goes.

Thanks for the input!

 

[willsonman]

Yeah, foam is not wood by any means. The initial sanding should be done with at least 80-120 grit to knock off the whiskers and correct bumps. Finder sanding with 220 and 400 are really all that should be needed prior to glass or other finish work. Its also helpful to try and vacuum the surface to get as much dust off as possible. I use the brush attachment so I do not damage the foam.

 

[saiga556]

I have found that trying to get the foam perfect is a waste of time. Try to get it as good as you can then fiberglass and do your bodywork. You have to make sure that none of your pre glass imperfections are high spots but a few shallow lows of scratches are OK.

Your going to bodywork the glass anyways. The small gouges were driving me crazy. I finally said screw it I'm glassing this thing. Then the filling and sanding went much easier. Also a tip I was told is to scrape your fiberglass with a razor blade after the second resin coat and it becomes very smooth. You also avoid accidentally gutting the glass cloth with the sand paper and you reduce resin weight.

B1 Bob showed me that tip. YouTube channel hornitpilot.

 

[bstanley72]

I was experimenting with foam, a couple of layers of sanding sealer, primer then paint (so no glass). On the next attempt I'm going to go with glass and a slurry of baby powder and polycrylic like Joshua demonstrates in one of his other threads. I also bought some Zpoxy recently so I may go all out with it. Right now I'm learning to work with the foam by making some superhero wall art for my son. I figure this way I can get it all figured out before I start on an actual plane.

 

[willsonman]

Stanley, Sounds like a great idea! Best of luck and I am sure you will learn loads in the process.

Moving along with the build through the boring stuff. To get the clean lines I need there has to be some balsa reinforcement. This also will ad some rigidity to the structure. Always a good thing. I first shaped the wing tips.


Then, I traced the outline of the flaps and ailerons from the 3-view onto the panel, top and bottom.


I cut about halfway into the foam from the top and bottom to separate out the control surfaces.


Around the perimeter of the control surfaces, I removed 1/16" to account for the thickness of the balsa that will line the pockets. I applied balsa using TitebondII, my favorite glue for this job. It adheres the wood to the foam very well and the overage can be sanded (unlike gorilla glue). I'll further line the parts perpendicular after these dry and are sanded.


I cut away 3/32" of foam from the sides and capped them with 1/16 balsa. This should give me a gap of 1/32" between the wings and control surfaces. A little more between the flap and aileron. I followed up with trimming off 1/4" from the leading edge of the surfaces and glued 1/4" balsa to it. This balsa adds quite a bit of rigidity as well as provide a better surface to bevel for the hinge line. Again, I used Titebond II for this.


Once I complete the wing's lining I will cover making the pockets for the control surfaces. Its fairly straight forward but the effect and performance gain will be worth it. I prefer to do it before I glass the wing. Some prefer to do it after but I find it easier to blend it into the wing before I glass.

 

[willsonman]

A bit of progress. I got all the wood sanded to where it needs to be. The good part is that I can glass the control surfaces. The bad news is that I cannot yet glass the wings. I still need to form the pockets for the control surfaces. My current stock of 1/64 ply is not sufficient. So, I'll try stopping by the LHS and pick some up. I also need some 3/16" ply for the spar. If I cannot find what I need for this I may have to make an order with National Balsa. BUT, in the meantime I can move onto the fuselage plug. With cooler weather coming I can more comfortably do this in my garage. I would like to get the glassing done before the cold really hits and my resin seems to flash (or blush) more in the cold and I do not have a heat box for curing.

I do want the wings glassed BEFORE I install the wings with the spar. Reason being that I need this forward sweep to be as precise as possible. My studies on FSWs revealed that the majority of designs in full scale and in models tend to show weakness in wing torsional rigidity. This is catastrophically bad for FSW design. I do not want to risk that the spar install with GG will change the airfoil profile or warp the wing in any way. Traditional wings may be more forgiving in this way but I am not risking it with this model.

 

[Aeronaut]

how did you hinge the control surfaces? they look very good

 

[willsonman]

Not hinged yet. I will be using pin hinges.

 

[HilldaFlyer]

Very nice.
Looks like you rounded the balsa to provide a nice rolling surface for the hinge... is that right?

 

[willsonman]

Correct. With the hinge point being set into the control surface a bit you need to have the edge rounded so that it does not bind. The pockets will hide this and make a cleaner transition between the wing and control surface.

 

[DharanFlyer]

So I am a bit confused.

If this is your entry for the Air Races and those require the foundation in FT processes this seems to be pretty far advanced compared to those.

Or am I missing something completely?

 

[willsonman]

This is NOT an entry, as stated previously.

 

[DharanFlyer]

This is NOT an entry, as stated previously.

That's what I missed. Thank you for clarification.

 

[ztoon]

Following the build.
please keep up some video(s) update(s) if possible, always nice to see (watch) what's going on

 

[willsonman]

I've included a single shot to describe the following:

Getting the pockets for the control surfaces is pretty simple. I made a tool to regulate how far into the wing I needed to go and applied some sand paper to cut back into the foam. After this, I cut a length of 1/64 ply to the width and length I need and glue in place with wood glue. You can see the overhang for the flap in this picture. Since it will be hinged from the bottom, this is all that is required. The ailerons will get top and bottom treatment. 1/64 ply is not cheap stuff. My 12x24" sheet was $26 at the LHS. But it pays off in details and strength.

I could have used heavy cardstock here as I will be eventually glassing the wings with epoxy but this build up with wood is adding a lot of torsional strength, which is essential for any forward-swept wing. With the glass and spar I'm certain it will be a non-issue.

 

[willsonman]

I'm such a dummy sometimes. I took the tape off the last pieces of ply yesterday evening and forgot to snap pictures. Nothing glamorous anyway but the pockets turned out quite nice. I applied spackle to the seams and other places that needed some minor touching up. Glass work is quickly approaching. I have a busy weekend ahead but the weather forecast shows that cooler weather is on its way. I would like to get the major glass work done before the cold gets here. I just get better results.

 

[willsonman]

No updates right now but there will be a very big one in the next week or two. Stay tuned.