Stuck with heavyweight foam board.
Worried your scratch build won’t fly?
Of course it will – just a little faster!
As a newbie flyer and newbie scratch builder I was slow to spot that not all foam boards are the same. Apnewton from Australia has a great article on this topic; “Foamboard in Australia” (link below).
After reading his article I realised I was using a foam board that was just as heavy as the ones causing concern in some of the Aussie Flite Test community. Not that it ever bothered me before!
My foam board weighs-in at 0.39 g/sq inch compared to the Dollar Tree stuff at 0.19 g/sq inch - which sounds terrible - but it’s not all gloom-and-doom! UK (and other non-US) foam boards can be a bit heavier, but they're still a pretty light build material.
See if this sounds familiar - you launch a new plane into the air, giving it a good strong throttle setting to make sure it gets airborne and stays there. If it doesn't nose-plant, you fly it around for a while to trim it out, then ease-off the throttle to find the lowest setting that will keep it in the air. Anything below that is a landing setting. You probably try a stall test to see what happens and then chop the throttle to see how the plane glides (hopefully not like a brick). Sound familiar? I think most flyers go about it roughly the same way.
Who knew I was using more throttle than anyone else?
The only time I noticed anything like a problem was with the Old Fogey – for comparison mine’s 690g / 24.3 ozs. With the original 8amp Blue Wonder motor (roughly 90W of power) it took a pretty high throttle setting to keep my Old Fogey in the air – but it flew, and being a newbie that was exciting enough for me! Remember those days?
In contrast, my Nutball and FT Flyer both did what it said on the box - and I couldn’t really see any difference between how mine and the Flite Test ones flew. Both mine fly on the Blue Wonder and both manage near standstill high-alpha flying and all the other stuff – they even cope with stronger winds if I slap-on a heavier battery.
Even my scratch built Tribewt, which weighs in at 570g / 20ozs, flew fine (for a beginner) on an 8amp/90W motor. I later upgraded the motor to 15amp/170W as the first one seemed to be working a bit hard and getting hot.
Ignoring brownout crashes, I never spotted any problem with my Velie Monocoupe. I started with an 18amp/200W motor, had loads of wing area, and, due to a lucky build error that resulted in slight undercamber on the wing, the plane flew fine and slow – even coping with a big pile of extra nose weight to get it to balance.
So what’s going on? I answered that earlier - heavier planes need more power/speed to keep them in the air. Unless you compare a plane made from the different foam boards head-to-head, you probably won't spot any difference.
In fact extra weight can sometimes be an advantage – see David W’s comments during the FT Spitfire build – he says not to worry too much if you’re a bit keen with the hot glue, as more weight gives the plane better penetration.
It was only when I built Cstence’s Smash Drone that I really spotted the weight difference (link below). Those Smash Drones in his intro-article just float around, swooping and looping like they were made from… yes, US foam board.
Mine – I struggled to get it into the air! Not surprising since it weighs-in at 890g / 31 ozs. However once I adjusted it to fly faster - it was fine. You can see my modifications in the article “Yes, it's a Smash Drone!” (link below).
So – yes, build as light as you can, but don’t despair if you can’t get hold of the super-light US foam board. Heavier foam boards can and do still work with these Flite Test designs.
Not convinced - here’s a video of my ‘heavy’ foam board builds defying gravity. Then click the link to see the GeeBee flying!
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I gave on my overweight, tail heavy Old Fogey when it wouldn't fly with the 24g motor and 2C.
Expense was the other factor that put me off paper backed foam board. I now buy depron in bulk packs. Super light and A$5.50/board.
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Took it to the local slope yesterday, and boy that extra weight was great. 15-20kts and nearly kept up with the BeEvolutions. And that's with the pod still attached.
Starting a second tomorrow for dedicated sloping.
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I used foam board from Hobbycraft (£3.99 a sheet) not finished yet but now you have m a bit worried, have you any idea how much heavier the foam board is from Hobbycraft?
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50-70 watts/pound: 11-15 watts/100g Minimum level of power for decent performance
70-90 watts/pound; 15-20 watts/100g Trainer and slow flying scale models
90-110 watts/pound: 20-24 watts/100g sport aerobatic and fast flying scale models
110-130 watts/pound: 24-29 watts/100g Advanced aerobatic and high-speed models
130-150 watts/pound: 29-33 watts/100g Lightly loaded 3D models and ducted fans
150-200+ watts/pound: 33-44 watts/100g Unlimited performance 3D models
From what I've seen people seem to be using much bigger motors than they really need. If your funbat comes out about 400g-450g the Blue Wonder 8amp motor will produce on a 3s battery - 11 volts x 8amps - roughly 90w - which translates to about 20 watts/100 grams and puts you in the sport aerobatic and fast flying scale models bracket. So even on the 'puny' Blue Wonder or equivalent, your plane will still fly. Go for a slighter bigger motor 14-15A and you get about 160 watts - which translates to roughly 35watts/100g which will put you in the unlimited performance 3D bracket when on full throttle.
Hope that helps to reassure you - my FT Flyer weighs-in at 400g with a 3s 500mah battery and 445g with a 1000mah battery - which is a heavier battery I stick-on for flying in wind. You can see it fly in the video above. Also have a look at the "FT Bloody Wonder - Australian foamboard by Red20RC" article for more reassurance :) Very slick! The motor he's using is rated at 15A max. Cheers.
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So I agree with alibopo don't worry about the board being heavier, get your cog right and perhaps consider powering up. (but you may not need to!). Now where is that charger.....
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As you say, this doesn't mean that the whole model will be twice as heavy because the foamboard is only part of the weight. I found it does, however, cause problems balancing the plane. When I built my storch I moved the tail servos up under the wings to get the CG in the right place. My storch is probably a little heavier because I made the wings in two parts for easy transport and storage. It had an all up weight of about 1050g with a 2.2ah 3s battery before I added varnish, flap servos, and covered it in tape. It now weighs about 1160g but seems to fly exactly the same. In fact, as you also say, a little extra weight might help, especially in windy conditions.
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