Tangling with Aussie Foamboard

by MikeRobey | October 14, 2015 | (17) Posted in Tips

Have you ever observed that the devil is always in the detail? In diagnosing the cause of one problem I made an assumption. Generally this assumption turned out to be true. However the way I interpreted the assumption was not true and therein lies a story that I hope others can benefit from. Along the way I encountered two other simpler problems and so I hope my solutions help people there as well.

Living in Australia I can only dream of using Adams foam board. The only foam board that I can get my hands on comes from Fix-a-Frame Pty Ltd at foamboard.com.au (hereafter refered to as AFB – Aussie Foam Board). APNewton posted an article (http://flitetest.com/articles/foamboard-in-australia) where he compared AFB with various other foamboards (including Adams) as well as Depron. He established that AFB is about 30% heavier than Adams Foamboard. Red20RC posted an article (http://flitetest.com/articles/ft-spitfire-australian-foam-board) where he used AFB to build an FT-Sprifire and showed it could be very successfully used to construct FT models.

Basically the differences between Adams foam board and AFB is that AFB is about 30% heavier and has a much stronger bonding between the foam and the paper. The stronger bonding between the foam and paper is good in that it results in a model which can take quite a bit of wear and tear and last quite a while. I have used it to construct a number of models and have not noticed any deterioration on models that I have flown lots. However it does present problems during construction. The paper being well bonded to the foam means that two Flitetest construction techniques need a different technique to get the required result.

Firstly removing paper from a section of foamboard requires more than just a gentle peeling of the paper. Secondly removing the little strips of foam as part of creating an A, B or C fold is more difficult and also requires a rethink.



I read on various forums that rubbing alcohol could be used to remove paper from an entire side of foamboard. I doubt its possible to remove the paper from an entire side of AFB but rubbing alcohol ( methylated spirits wroks as well) can be used to remove a small section of paper from AFB. The technique is straight forward. Rub the area concerned with rubbing alcohol until you can see it soaking through the paper. Give it another few seconds and then start to peel the paper away. If you are really lucky the paper will peel away in one piece. However it sometimes tears and leaves a lot of paper behind. When this happens you need to apply more rubbing alcohol and gently but firmly rub the paper of with your thumbs. You need to press firmly but not so much that you end up squashing the foam. Practice with a bit of scrap first and you will have no problems.

Similarly peeling the foam strips away from the areas where there are A, B or C folds also requires more work than simply bending and peeling the foam away. My solution is to do the score cut as per normal and then fold one of the sides involved 180 degrees so that it is flat against the other side. I then run a knife along the edge cutting into the foam the width of the fold trench as close to the paper as possible. I do not try to get the knife exactly between the foam and the paper as this will most likely result in cutting through the paper. When doing this I proceed slowly leaving a small amount of foam behind. The cut foam is then removed and the remaining foam removed using the technique demonstrated by Josh of gently scraping the blade across the top of the paper. The remaining foam tends to come off easily. When scraping go slowly. If you get too carried away you will start scraping the paper away as well. Keep in mind that both the foam and the paper are white in colour so it can be hard to tell from the bits flying off whether or not you have gove too far. Again practice with some scrap and you will get the idea.

The extra weight impacts the finished model in two ways. Firstly, being roughly 30% heavier, sometimes you need to use a more powerful motor. Secondly the CG will typically move aft making the final balancing of the model more difficult. However it puzzled me as to why the CG seemed to move backwards. My assumption was that if the weight of the material used to construct the airframe increased by 30% then the entire aircraft would increase in weight by 30%. This assumption is, in point of fact, wrong. However I did not question it.

I built an FT-Flyer which was massively tail heavy. In the end it needed so much weight up the front to balance that I gave up on it. The next encounter was with the Mini Guinea. The solution here was to build a battery tray that extended forward into the nose. That fixed the problem so, even though I was puzzled by it, I moved on.

I built three FT-Spitfires and none of them suffered from the CG issue (one for me and two for friends). Problem gone or so I thought, its just one of those strange and random problems that will never occur again. I went on to build the aileron wing version of the Tiny Trainer. Again no problems. Now I am feeling really confident that the rearward CG issue is done and dusted.

Then I built the Bloody Baron and the rearward CG issue was back with a vengence. I decided to forget about why it had happened and simply fix it. I did so by adding some decoration in the form of dummy engine cylinders and machine guns which looked cool but didn't really help. I then decided I would move the elevator and rudder servos forward. However before I did that I tried putting a spinner on the front. Suddenly my Bloody Baron balanced beautifully. My success was dampened by why this was happening.

The next model on the building board was the Bushwacker and this was by far the worst example of the rear moving CG issue. At this point I could have simply done everything I could to get the plane balanced but I was tired of being haunted by this issue. I was sick of the pleasure of a good build being soured by the unpleasant surprise of having to move everything around to rebalance the plane. I decided that before I tried to fix the problem I really needed to understand why this was happening. I had not read anything about this CG issue happening with others so either the universe had it in for me or there was a sensible, rational explanation for why this was occurring and why it wasn't occurring with every FT model I tried to build.

Okay based on my initial assumption. If the entire aircraft increases in weight by 30% then this increase is uniform and therefore the CG should not move. In my case I had the evidence of the CG moving aft on some models (i.e. the assumption was not holding) and not on others (i.e the assumption is holding). Okay, given that the universe is currently not making sense I decided to question my intial assumption. If there is more foam behind the CG (and there usually is) then maybe that is why the CG moves aft. My daughter, who is pretty good at maths and physics, rolled her eyes when I suggested this was the cause and she told me that if the weight of the entire aeroplane increases uniformly in weight then there is no possible way the CG would move. When she said “the weight of the entire airplane” the lightning bolt struck me. I realised the error in my thinking. It suddenly hit me that the entire model doesn't increase in weight. Only the weight of the foam has increased 30%. The motor, battery and electronics have stayed the same. If a bigger motor is used then their final weight of the electronics would increase but there are no guaranties that the increase would be 30%. The most significant part of that weight is the motor and battery which usually reside in the nose. If the final weight of the motor and battery was significantly less than 30% then the CG would move aft. Eureka! Now it all makes sense. Now I looked back at all my past builds to see if my new understanding can explain what happened with each model.

Firstly I considered the FT-Tiny Trainer which did not have a CG problem. I used a 24 gram Hextronics motor with the Tiny Trainer. That motor is quite a bit heavier than the Emax one recommended by Flitetest and also stuck out further forward. By using a different motor I had accidentally resolved the problem.

I next considered the three Spitfires. Mine was pre-foam board and made from Depron. Weight wise it was only slightly heavier than the Adams foam board version so the CG issue did not arise. The other two I built for friends who both elected to use bigger and heavier motors. They both managed to balance their Spitfires with the battery as far forward as it could safely go. Again the use of a heavier motor meant the weight increase of the model is more uniform and so, again the issue was resolved.

The Mini Guinea puzzled me a bit. I used the same motors as the Flitetest guys so that should move the CG aft by a lot. However, being a twin, the motors are much closer to the CG than with a single engine model so that should reduce the amount aft that the CG would move. I decided that the evidence showed the lack of motor weight was more significant because the problem did in fact arise.

My Bloody Baron uses a different motor that the FT one but its about the same weight. Similarly with the bushwacker. At last what was happening to my models made sense! The universe and I were at peace again.

However I was still left with a massively tail heavy Bushwacker. If I had known this at the beginning then I would have known that I needed to move everything that I could forward. The fact that the model was finished narrowed my choices in this regard. I decided that moving the rudder and elevator servos forward would only help a little and would result in a lot of mucking about so I left them where they were. I looked at the power pod and decided to get rid of it given that most of its weight was behind the CG. Not much of an improvement but it was easy to do. Finally I elected to move the motor and battery forward by extending the nose. I was a bit worried about destroying the looks of my Bushwacker so I decided to start by moving the motor 10mm forward. This meant creating a suitable motor mount and a nose cone that covered the motor. I have a 3D printer so I banged away at Sketchup, fired up the printer and finally tried it all on my Bushwacker. There was an improvement but I was still way off. Okay time to forget about how the nose will look and really get serious here. Back to Sketchup and the 3D printer. My next attempt had the motor positioned 25mm ahead of its original position. It almost balanced but it was still tail heavy. Okay third time lucky. My final attempt had the motor 35mm in front of its original position. With the battery pushed hard up against the motor mount it finally balanced. Success! I had a balanced bushwacker. As an added bonus I think my nose extension looks okay so my Bushwacker didn't look like a hacked up mutant Bushwacker.

You can see the three nose cones for each motor position I tried.

I think my Bushwacker still looks okay with its longer nose.

So how does this help future builds? Next time around I can calculate the weight of the Adams foam board version by taking the published weight without battery and subtracting the weight of the electronics used. I can then multiply that weight by 1.3 and this will give me the estimated weight of an AFB constructed airframe. Then once I have decided what electronic components I am going to use I can determine if I need to compensate for the AFT CG shift. From there I could modify the plans to make the nose longer, use a heavier motor, bigger battery, move servos forward or whatever. At the end of the day its going to be a much easier journey if I am allowing for this before I put a blade to foam board. Okay its still going to involve a bit of guess work but I think I can get much closer to the mark and so there will not be any more unpleasant surprises.

So to conclude. If you are using a different foam board then you will need to look at the differences between the Adams foam board and your chosen foam board. You will find ways around the differences but they will be much easier to deal with before you start your first build than during your first build. As far as the AFB is concerned I think its great. My mistake was ignoring a confusing issue and then trying to fudge my way around it in the middle of the build.

Finally if your experiences and the universe seem to disagree then don't ignore it. If you think about it long enough the reason will come to you but only if you pay attention to the detail (e.g. an airframe is not the same thing as an airplane!).

I hope that AFB users and users of non Adams foamboard have found this article helpful.

Happy building and happy flying.



COMMENTS

Goose on October 22, 2015
Yeah good one. So all the foam board in Australia comes from the same place?? I have never had any CG problems but when I think about it I use one of those motor and ESC combo's from HK and I think they are quite heavy. The work really well and fly all my FT scratch builds well. I really like using AFB that I have and like it better than the FT foam board from the couple of kits I have bought.
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MikeRobey on October 23, 2015
Hi Goose,
You can get other types of foamboard in art and craft shops but the price is not good and also they are usually very heavy. Someone did tell me you can get AFB in Jacksons Drawing Supplies (I think they are only in W.A.) but again price is an issue. I agree that AFB is fantastic. The fact that a difference in motor weight has in impact on the CG issue is what made it difficult for me to realise what was happening as well.
I finally got my hands on some Adams foamboard and I completely agree with you. I am quite happy to deal with the differences and even the extra cost because it is much stronger, smoother and the paper sticks on better.
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Goose on October 23, 2015
Yeah I forgot bout it being smoother too. That makes a difference when you paint it. How are you doing the graphics on your planes they look great. I get a 40 inch by 60 inch sheet (102cm x 153cm) for $25, it was $20 two weeks ago!!! I can get a few planes out of it. I just get it from my local picture framer. It still seems to have the same problem when you paint it (warping), after I found out when I got the kids to paint it.
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MikeRobey on October 23, 2015
I order a box of 25 30 x 40 inch with a friend and we go halves on it. The box of 25 comes out at about $225 with shipping to W.A. For the finishing, I either use acrylic paints mixed with 50/50 water and windex or contact. The Bushwacker is contact, the Bloody Baron is airbrushed yellow and the Tiny Trainer is airbrushed. I have also just discovered a brand of spray can paints called Dy-Mark that seems to go on nicely without damaging the foam. I have just sprayed my latest creation silver using it.
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canuck on October 25, 2015
Well done, I'm sure this will be very helpful. Even though I have access to Adams foam board I build my first FT design using foam board I already had which is very similar to what you use. I've never flown it since finding out about the weight issue but this may ease my mind if I do decide to go that way. Keep up the good work.
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MikeRobey on October 25, 2015
Thanks much appreciated.
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pete stanford on October 25, 2015
Another source for foam board is your local Office Works store. I've built several FT planes with this but it is expensive for what it is.
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MikeRobey on October 25, 2015
I never tried the office works foamboard because of the cost. The negative for foanboards.com.au is that to get a good price you need to order a box of 25 which, while working out to about $5 per equivalent of a sheet of Adams foamboard, it is a lot of money to fork out in one hit. However if you plan to do lots more building its well worth it.
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danield on October 25, 2015
I built a FT Flyer kit and no CG problem. Built another FT Flyer scratch built, same on all parts and very tail heavy. added 2" to front to get to balance, Why, maybe differences in Adams foam board.
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MikeRobey on October 26, 2015
That does sound wierd. I don't have much experience with Adams foamboard so I don't know how much variation in weight from sheet to sheet. If you used the same electronics then the only other two possible causes are the amount of glue used and whatever paint you put on. I would not have thought that either of those would cause such a large weight increase though.
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RockNBurn on October 26, 2015
I think that your Foam Board is the same we have in Brazil. A thick paper well glued into a dense foam.

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RoGuE_StreaK on November 3, 2015
I get my foamboard from Kmart and Riot Art. Kmart's stuff is relatively small, a bit smaller that the DT board, but readily available. $6 a sheet, which is OK, much cheaper than the same size at OfficeWorks. Riot has much larger sheets available, and much larger than the DT boards. Price-wise Riot's is about the same per cm2 as Kmart, and they seem very close in finish and weight; I prefer Riot where possible. These are definitely from different suppliers, one is from China and I think the other is from Korea?
My FT Dusty uses Kmart for the body and Riot for the wings. My modified red20rc mini KFm4 wing is purely Riot. Depends on availability and whether you need an uninterupted larger span; can usually get away with butting two sheets together.
Dusty definitely needed the battery all the way forward.
I haven't had any issues with the foam not separating on A folds; just slice halfway through, crack the foam backwards, and pull out the strip of foam. A little skin of foam gets left, but not much at all.
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MikeRobey on November 3, 2015
I bought a sheet from Riot but it was really heavy as the paper on each side was almost cardboard. That was a few years ago so maybe they have changed suppliers. I'll check them out. I would never have thought of Kmart in a million years. I'll check that one out as well. The foamboards.com.au sheets come out at about $10.00 per sheet which is exactly twice the size of the Adams sheets so its about $5.00 per Adams sized sheet. It really is great foam the only real bummer is having to order 25 sheets at a time. I will check out Kmart and have another look at Riot.
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RoGuE_StreaK on November 3, 2015
FYI just checked sizing, Kmart is about 640mm x 510mm (25in x 20in?) for $6, the biggest Riot one is 1000mm x 800mm (about 39.3in x 31.5in) for $15.
Supposedly Adams (DT) boards are 30in x 20in? So the big Riot one is a tad under twice as big, or $7.50 per Adams sheet(ish)
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MikeRobey on November 3, 2015
I think it comes down to how many models you expect to build. If the answer is lots then a box of 25 sheets from foamboards.com is the way to go. On the other hand if that isn't the case then buying as needed and paying a bit more per sheet makes more sense. Of course the other issue is its a lot easier to come up with $10 or $20 for a few sheets that $225 in one big hit. The one I got from Riot is smaller so they must have changed where they get them from.
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banatijano on November 4, 2015
Here in Hungary I use Depron or similar but much cheaper XPS foam (which should go under wood floor tiles) it is 6MM thick so I usually enlarge all the FT design by 30%. Anyway I found the electronics need a little more space than what is inside an FT design. I use color packing tape to give the foam more a lot more strength. I also love foam PVC and balsa to put some more strength into the frame…
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MikeRobey on November 6, 2015
A friend used tape on a Bloody Baron and its amazing the abuse it can take with the tape. Happy flying..
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aerogriffics on November 6, 2015
Bushwhacker looks fine, better than the original, methinks
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MikeRobey on November 6, 2015
Thanks. Much appreciated.
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janithpriyanga on November 7, 2015
HI Mike
I have the same problem yesterday.I used 5mm Foam board and the tail was too heavy resulting crashing.But no damage to the bushwacker.Can you please suggest the best way to hold the battery carefully (i dropped it during cruising).It will help me to fly again with safe manner.
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MikeRobey on November 8, 2015
I use a strip of velcro running the length of the battery (like they do on most of the Flitetest videos). However I also run a velcro strap underneath the battery tray and around the battery. That way if one failes the other is a backup. The velcro strap I use is one intended to go around cables to keep them tidy. If you search on ebay for velcro cable ties you will find the sort of thing I mean. Nothing worse than watching your battery fall out and knowing what is going to happen next. Hopefully if you double up the way I do it won't happen again. Best of luck.
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bobmox on November 11, 2015
I just commented on the Mosquito build article but try this place for foam board
Big Banner
4/71 Strezlecki Ave, Sunshine West VIC 3020
1300 550 168
A1 size sheets 5mm thick
Box of 25 sheets i picked up for $50.00
Compared to the ones from office works they are a lot lighter and the paper peels reasonably well
They come in from China i believe
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MikeRobey on November 11, 2015
Wow. That sounds brilliant. I am over in Western Australia though so I can't go there. I did find their website but they don't have foamboard listed as a product they sell. I will phone them and ask if they are willing to send some over here. A0 is roughly twice the size of Adams foamboard so that makes it really cheap. Thanks for the tip.
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Greggo62 on February 9, 2016
I have gone through the same issues as this article and suspected that there was a difference in the board density but only made a very basic attempt to prove it for my self. I thought it was just me at first making the craft too heavy some how. I was astounded that my first builds of the Nutball and FT Flyer weights were way over 300g without the battery! My results were inconclusive. I usually source my AFB from Office Works ( you're right, it is pricey) and occasionally from K Mart. The K Mart board seems to be heavier and the paper is more difficult to remove so my preference at this time is Office works. I'm in Qld and so would love to find a supplier at this end of the world for AFB at better prices. Thanks for the info and keep up the good work.
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MikeRobey on February 10, 2016
I think Foamboards.com.au is actually in Queensland. I have checked out the K-Mart, Riot-Art, jacksons Drawing Supplies and Office works. You are correct in that Officeworks has the only usable foamboard, the others have a paper layer that is really thick and heavy. Honestly I am really happy with their stuff.
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jkexpress on January 8, 2018
Try https://www.artshedonline.com.au/?rf=kw&kw=foam+board
about $23 for the white 32x40 inch.
I had Cg issues but it seemed lighted than expensive officeworks.
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Jackson T on May 1, 2018
I'm not sure which foamboard I am using, but it weighs about 495g per square metre. I buy it from Riot Arts and Crafts. 80x100cm sheet for $15.
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MikeRobey on May 1, 2018
That is a lot lighter than what I could get from Riot Arts. Perhaps they have changed their supplier. The foamboard I am using is a little lighter at 469gms per square metre. Its also cheaper at around $10 for the same sized sheet. Of course buying from Riot is more convenient and you don't have to buy a box of 25. I will check them out. Thanks for the info.
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Jackson T on May 2, 2018
No worries. How much is postage for a box of 25 sheets?
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MikeRobey on May 2, 2018
The last box of 25 that I bought cost around $230 including shipping. I think the actual shipping was about $25 or $30.
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Jackson T on May 2, 2018
That's pretty good, thanks Mike.
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Tangling with Aussie Foamboard