EPO Foam alternative for FT Slinger Turtle Deck

This is the finished product of an experiment I did using EPO foam from Home Depot for turtle-deck, as an alternative to formers and poster board. I built the entire plane except for this detail just as shown in the plans and in the FT build video. This was my first Swappable build and I had experience in bygone days building nitro airplanes. I used a Turnigy 250Watt Park480 and a Turnigy Plush 60A ESC that was bought for an 70mm EDF Air Hog Titan Jet conversion - a future project. I got seriously hooked on the FT Review of the Slinger - Josh and Dave really refined something great in this design, built on the experience of all the previous Swappables.

One aspect of the design I wanted to expedite was creating the turtle-deck - and make it more durable. I thought I could do this using common EPO insulation - the cheap, crude stuff - large cells.

Items needed to repeat this, which I plan on doing with other FT planes:

- 1 Hot Wire Foam Cutter - I had a small table to start with but I am sure you can fashion one out of a model train transformer and a couple of sticks. I will show that in the future to demonstrate you can do this cheaply.

- 1 Handheld Hot Wire Foam Shaper. I bought a $20 hot wire "wand" from Hobby Lobby - I think Josh B. showed one in one of the videos showing how to cut foam. Again, in the future I will show a hand-holdable hot wire cutter that will accomplish both tasks - cutting the foam patterns and shaping the foam.

- Gorilla Glue to join two pieces of EPO 1" foam together to create a 2" high block.

- For this experiment, I used DAP Lightweight Sheetrock Joint Compound found at Walmart to fill in the coarse EOP foam after sanding.  I wasn't too sure about this method I read about on RCGroups and thought I would give it a try. (FYI - Walmart sells Minwax Polyurethane $6 cheaper than Home Depot.)

- I used a sheetrock sanding block to shape the foam after rough-shaping with sharp blades and the aforementioned hot-wire wand.

- That's about it, outside of the typical tools the FT guys always use for these planes.

I dug out a 40 year old foam hot wire cutter my father made me back in grade school, dusted it off. I found some neglected EPO 1" foam insulation you can get at Home Depot. I think it was 2' x 2' and I got two copies of the deck out that, plus fair amount left over.

With the Racer/Slinger built up to the point that  I could take a pattern from the flat deck (continued),

I traced the plane outline on DTF and cut it out as usual with a utility knife blade. This would be my pattern for the hot wire cutter. I just turned the plane upside down and traced the outline on a sufficiently large piece of DTF.

This pattern I skewer-tacked to the piece of foam. That is, I borrowed the Bixler bamboo skewer method to spike the DTF outline to the foam - neat and simple. Bamboo skewers rock.

I cut two copies of the decking because I had to lay up two layers of the 1" EPO to get the height needed to get the maximum thickness at the top of the canopy. I used Gorilla glue to attach the two layers.

The following photo shows, in the upper right hand corner,  the corner of my hot-wire foam cutting table which is about 18" x 18" with the hot wire in the center of the table.

Also shown is the sheetrock sanding block which is very useful in getting the final rounded decking shape.

In the center you can see the DTF template I cut - I wasn't too careful as I knew I would do a fair amount of sanding to get the final shape.

On the left is the two-up EPO foam after I cut it into rough shape. You can see the line where the Gorilla Glue is, slightly brown.  You can also see how much of the forward decking I cut off - when I do this again I will just two-up the EPO only where it is obviously needed. that was a pretty big piece of foam to cut off, can use it for something else, someday.

Here is what the plane looked like after I hot-glued the foam decking onto the fuselage, getting ready to fill with Lightweight Spackling Compound - you can see Sharpie marks where I drew guidelines for cutting and sanding the eventual shape:

I left a bit of a "step" between the fuselage and the decking to be able to create a smooth transition between the two using the LWSC. Above, you can see the 2650mAh 4S I was planning to use. This also was originally designated for the 70mm EDF Jet that took a back seat to the Slinger once I saw the FT Review video on Youtube.

Below, RipSlinger all spackled up - looks like an unwilling beauty spa victim.

For the transition to the tailfeathers from the fuselage, I cut a piece of foam to act as the transition. It become fillets for the vertical stab. Below shown in its rough cutout form. A view of the handy hot wire cutter, too. All in all you can do this design mod without a hotwire cutter at all - a knife is fine.

Inserted tail fillet below. "Is this really going to turn out?" I am thinking. I wasn't quite convinced about this LWSC method, but just keep moving forward.

The following is a jump ahead after I roughed out the paint job for RipSlinger, now getting the black skullcap before getting his eyes.

Summary

The experiment was very successful. After painting, the decking is a) very, very durable, b) light, c) easy to get a good finish. I recommend trying it - it will be the way I do all decking for FT planes in the future.

In keeping with the objective of getting airborne, I put "just enough time" into the method to prove the concept out. Originally, I really was really taken by the looks + performance of this Racer in the Review video. I didn't want to "Guild the Lily" and spend too much time on fine detail - this time - before I went through all the steps A to Z on my first FT build. I was careful not to overinvest time detailing when this was my first-ever FT build. I just wanted to get out and fly it(!) Probably should have maidened before even painting.

This is a foamie, after all is said and done. You can see a blemish on the nose of the plane. Next time, now that I know what I am doing, I will be careful to not leave any exposed foam. I sanded the LWSC a little too aggressively in a few places and the paint got to the foam. I was not worried about this - it wouldn't effect flying. Also, I left the LWSC too thick in the windshield area and it partially flaked off along the way. It would have been a simple fix but I knew the eyes would be covering it anyway.

I used Krylon for the green and black. I have to say this - the Krylon splattered paint everywhere and created messes along the way. I haven't used spray cans in a long time and was expecting a better spray pattern. What I got was spray varying from mist to splats heavy enough to run. Little did I fret, though, because I would be at the flying field soon enough - its about the flying. Keep pushing through. I will circle back around and build another one to be very clean, with the experience I now have.  I have access to a range of spray guns from cheap to quality and will use that next time to avoid the overspray of Biblical proportions I got.

The LWSC method is OK. I like sanding to get the smooth finish before painting. It has some challenging characterisics, like you can't get a really smooth finish while it is wet. Maybe somebody knows this method better and can comment on how not to have to leave the LWSC so rough. You end up doing a lot of sanding, taking away almost everything you just put on. I have reservations about how durable LCWS will prove to be, too, in hard landings. I did three applications of LWSC to assure the smoothest finish but the results I got after just the first application proved to be entirely sufficient. The extra two cycles of applying the LWSC, waiting for  it to dry, and sanding produced imperceptible improvements, if any. Just delayed me two days. To get to the point of having a respectable deck and just go flying took about 4 hours, if I didn't add the LWSC and painting steps. After the exercise, I now could reduce the time to 2 hours and that is being conservative. I like to pad times for the unexpected, like having to answer the door to accept a shipment from Hobby King.

Next pass: I have some West System epoxy handy that is left over from a previous project. Instead of LWSC (which is relatively cheap, I might add) I think I will try finishing the EPO with .5 oz fiberglass next time - it is not supposed to create too much extra weight. You can also gut out the foam after you get the FG shell, to remove unnecessary weight. However, the price of epoxy resin is now through the roof so I don't want to spoil the economy of the FT designs with extravagant materials when the point is to look good enough and go fly a performance foamie(!)

Parting Note:

"We're gonna need a bigger field."

The plane came in pretty heavy but I overpowered it from the start. Under its own power it can lift vertically, that is a good sign. The Turnigy 2650mAh 4S is .750 lbs, by itself. I may have to try some 3S's. When I maidened last week, I had an issue with the plane pulling to the right (because of a construction flaw, I believe) but after a trip to the bench and some corrections to keep it in tolerances, I think the next outing will be successful - tomorrow, if I am lucky. I think this powerplant is pushing the edge of this plane. Landing speed is going to be 15-20 mph, not a featherweight.  Again, not to spoil the economy of these foamies, but I also likely need to make a fiberglass Swappable tray instead of the DTS foam due to the weight and thrust of the motor I used. I can observe the tray torquing when I rev the motor.  Very easy piece to do - make an EPO plug and cover it with glass and epoxy - 1/2 hour from start to finish including mixing the epoxy. No extra points for fine finishing the piece, leave it rough as nobdy really sees this. And finally, as a note, the mount for my motor doesn't fit as a "T" on the front of the tray. I had to position  it as an "X" because  it was so big (apologies for color balance of my cellphone camera):

Thanks for reading and I will try to answer any questions. I will post a video of the re-maiden if I can get someone to show  up with a video camera.

Best!

Peter