Heavy foam board blues?

by alibopo | October 28, 2013 | (8) Posted in Tips

  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!

COMMENTS

apnewton on November 8, 2013
Great article and video compilation. You're a prolific builder.
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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alibopo on November 8, 2013
I must just be stubborn! I think the Old Fogey is a good (bad?) example of a plane not flying due to weight. If you've a heavy one you need to drive it faster, and that just makes that wing rocking problem worse. Fly it slow enough and the problem melts away. I needed mine to go faster so I did the research and came up with a design solution that worked - lifting the tail. I now find it a great plane to fly on a blustery day. Foam board in the UK is a stupid price too, unless you buy it in bulk. To be honest I never explored the pricing of Depron in the UK. After I found a cheap-enough foam board I just got caught-up in the whole Flite Test foam board vibe. Of course that 'cheap enough' option was to buy in bulk - hence the prolific building :) Plus it's an amazingly fast build method. I think there's a kind of scalar thing going on, once you get to a big enough plane the weight issue is less critical - a kind of volume to surface area thing.
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FlyingSloth on November 10, 2013
Yea I had the same issue being an Aussie newb, my bloody wonder suffered from the lead blues. But I made a Versa, and after hearing Josh say the extra weight helps the wing penetrate, I decided to hop up the power an make it a high performance ship. Maiden was AMAZING!! nice and smooth, second flight in 10kt winds was a dream and flew as if the wind wasn't there.
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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alibopo on November 11, 2013
I've not tried the Versa build yet, but there's so much positive comeback on it, I'm thinking of giving it a try. I just need somewhere to hide it so my wife doesn't find out I've built yet another plane. Nah.. she'd be fine as long as stick to one wall in the office :)
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rcspaceflight on November 18, 2013
I've build planes with both Dollar Tree Foam Board and with foam board that weighs over twice as much. The nice thing about the heavier stuff is that it's more durable. You can actually get away with making the plane thinner in places to save on weight. Like I've been working on a plane design and I made the wings 40" with a 6" cord. The wings fold almost instantly with the DTFB. I haven't tried it with heavier stuff, but I know I can get away with long thin wings better with the heavy stuff.
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alibopo on November 18, 2013
I did wonder about the DTFB - I'm flying both my Old Fogey and the Smash Drone in some quite windy weather. With the weight of both being pretty high there's a fair bit of wing stress on some of the manoeuvres - but my heavy foam board copes! Likewise I've crashed my monocoupe so... many times, but the wing is still going strong after ridiculous punishment. I'm thinking I might find the DTFB a bit disappointing after mine.
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CStence on November 8, 2013
Interesting info. I wondered about the weight you posted in the your last article on the Smash Drone. That's somewhere close to 250-300Grams heavier than the demonstrated model - heavier foam makes a lot of sense! I've wondered about using alternative foam densities and thicknesses, but haven't played around with that much at all. Thanks for bringing that to light! :)
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alibopo on November 9, 2013
Hi CStence, I tried the plane out with the higher battery platform. Didn't spot much of a difference, but I have managed to lift the motor thrust angle slightly due to the CG shifting. More of the 'push' is driving the plane forward so there must be some efficiency gain. Just to see what would happen I tried 2 x 1000mah batteries, which added another 72g to the AUW - raising it to 962g! I think what's interesting is that - IF - your Dollar tree foam board wing is strong enough - you can carry an additional 250 - 300g payload on your original version of the Smash Drone (though I'd change the A of A to match mine to let the plane fly more freely). This means your original 'lightweight' smash drone would be a great 'cheap & cheerful' platform for FPV. I managed a flight time of 15 minutes on the 2000mah, and about 12.5 minutes with the 1700mah. Rolling all the weight figures down to what you can achieve, that promises quite a reasonable flight time for FPV. Cheers, Alistair.
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alibopo on November 8, 2013
It's that AH- HAH moment when it all starts to make sense - basically I'm flying a very different plane, but it's a great initial design :) I'm already onto my next mod - I've raised the battery platform to get the battery weight more in line with the wing and motor. I'll let you know how it goes.
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Bedrock on November 15, 2013
Well I just came in from a successful second flight with my FT Flyer, using UK foamboard. AUW 350g, stock motor (2822/15/1450kv turnigy) 850mah nano-tech battery. The key thing for me to get it flying nice was the 60g(!) of lead I had to add to the nose area. Once that was in it flew MUCH better than maiden flight which was really hairy. The lead is obviously balancing out the large wing area (made of heavier foam) behind the CoG of the flyer (and tail plane etc.) And yes it still flew perfectly well and for about 10 mins on the batt, in a light breeze.

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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alibopo on November 16, 2013
hi bedrock, I had the same problem with my smaller batteries (500mah) - had to hang them well forward - right under the motor to get the right CG. I later invested in a pile of 1000mah batteries and they work very well. I also made sure my wheels were sticking as far forward as I could get them without hitting the prop. Another approach for you might be to re-site the servos further forward to take weight off the tail? I extended a couple of pushrods on another model by binding a bit of the same wire on as an extension. I just used thread and CA with lots of turns - still a good solid join 3 months on. Glad you got it flying. One advantage over the lightweight models is you can fly in stronger winds!
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paullyjay on November 11, 2013
Wow, I didn't realise this as the case....!!!! Ahhhh.... I'm in the UK and I've just built my first scratch build - a Funbat...

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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alibopo on November 11, 2013
Hi paullyjay, I've no idea what that foam weighs. BUT, and this is a big but - what I'm saying in the article is that the foam's weight has really NOT been that critical. I've not built a funbat (I'm assuming you're referring to the FT bloody Wonder), but I think your funbat will go fine. Here's a chart for typical power to weight ratios in RC aircraft;

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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anonymous rc pilot on January 7, 2014
It turns out i have used this heavier foam-board on my build (Mac odd twin) in my it flies relatively light.
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alibopo on January 7, 2014
...and likely takes more of a beating than the lighter foam boards. A bit of extra weight has worked well for me in blustery Scotland. Cheers.
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SkyLark on May 26, 2015
I've built the nutball, flyer, delta, tiny trainer and storch all using Westfoam board from hobbycraft. It weighs in at 240g for an A1 sheet which I calculate to be 0.31g/sq in, or about 55% heavier than DTFB. The board costs £4 a sheet or 2 for £7 so it's not too expensive, but not cheap either.

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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alibopo on May 26, 2015
Hi Skylark - I've had similar problems (design decisions) with many of my builds and it has influenced the planes I choose to model. Something with a big 'sticky-out' nose is easier to model than a snub-nosed plane. I nearly always try to get my servos as far forward as I can. I find if you scale-up a bit, producing models with around a metre or 900mm wingspan the lift from the wings compared to the weight of the build starts to improve and the addition of a few balance weights on the nose gets less important, a bit like the Storch. What I have found is my heavy foam planes seem to last. I'm still flying near-enough 3 year old planes. Cheers.
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Heavy foam board blues?