Foam board Fun Fly experiment

[Mike Bell]

I have seen some of the excellent foam board creations in the specialist section of this forum but I was curious to investigate whether this stuff could be a viable balsa replacement in the relatively high stress environment of a Fun Flyer. I usually end up building a new model every year or so since they tend to get a bit of a pasting in practice and competition.  I thought that a foam board fuselage would provide a simple prototype to test out what this material is like to use and how resistant it is to being slapped onto the deck in touch and goes etc.  Since I am looking to potentially use this in a competition airframe it will also be important to assess any weight penalty. or advantage.

 

My intention for now is to just build a fuselage and tail group and use the wooden wing of my current model to try it out.  There will be the option of trying a mostly foam board wing structure later if the fuselage performs well.  The design is home brew, although it is to the typical fun fly layout and dimensions, so the experiment should be representative.  Some wood will still need to be used in strategic places but I hope to keep this to a minimum.

 

The pics below show progress so far.

 

I have used a double thickness at the front end of the fuz sides and bottom to help absorb stresses coming through from the undercarriage.  Board to board and board to balsa joints are all medium cyano or Por while the high stressed areas around the firewall and undercarriage mounts used Gorilla glue (foaming PU).  I think it may have been better to use something other than cyano but we'll see.

 

The balsa framing around the tail plane and elevator was 3/16" which was a good thickness match for the 5mm board.  Need to be careful when sanding as the card facings can tear and lift. 

 

I have to say that so far the pros for this material are cheapness and there is scope to speed the build process, but on the downside it isn't so nice to handle and I suspect that the exposed foam edges won't look pretty when covered, although this is going to be a workhorse application rather than concours but I do have some pride.  As for weight, early impressions are that it is unlikely to be lighter than the balsa version, but hopefully any penalty won't be too high.  I'll update as the build progresses.

 

 

 

 

 

[john davidson 1]

The weakest point is probably where the rear fuselage meets the wing, perhaps  a doubler of light ply here?

[Simon Chaddock]

Mikel

That is an interesting project and it will be interesting to hear how it ends up..

 

i would have to say that the original design was sort of optimised for the physical properties of a ply/balsa construction so simply substituting a paper covered foam board for balsa in a 1:1 basis is unlikely to give much advantage unless either the physical shapes and/or the construction technique are altered to better suite the foam board's strength & cost properties.

 

Just an observation from a 'structural' foam builder.

   

[Mike Bell]

You are right, John, that is a favourite place for the fuz to break and I intend to incorporate some local strengthening together with a hard point for the rear wing dowel.  Should have done that before putting the top sheet on  D'oh.

 

Simon, thanks for the feedback, I have anticipated that the structural design may not be optimum for this material.  I hope to get some learning from this prototype to inform future structural design decisions should this first try shows any promise.  I suspect that design optimisation is likely to be about where to place local reinforcement but such additions will have to be tempered by needs to keep the weight acceptable.  On a different note, do you have any advice on applying film covering directly on to this type of product?  I have tried a small test piece and it seems to work if the heat iron doesn't linger too long.

[Graham Davies 3]

3 hours ago, Mike Bell said:

On a different note, do you have any advice on applying film covering directly on to this type of product?  I have tried a small test piece and it seems to work if the heat iron doesn't linger too long.

Hi Mike,

Check out Martin Collins excellent skystreak. He's film covered that and it looks great. There's a thread on here, recently contributed to!

Graham

[Nigel R]

Just don't let the iron sit in one place for too long. It makes the foam swell.

 

I think the problem you may encounter is the foam is equally strong in all directions whereas a wood fuselage has the grain to make more strength in that direction. For a long thin structure that may be somewhat important. 

[Mike Bell]

Thanks Graham, that Skystreak looks really nice.  Looks like most of the material the covering is attached to is Depron, or similar, rather than foam board but I guess the board could be a bit easier if anything.  Anyway, I'm about to find out since I have some parts ready for covering now.  I'll probably start with the tail group then on to the fuz.  

 

The bits you see here weigh 175g which seems quite promising.  The corners of the fuselage box have been cut and sanded to a chamfer rather than a radius since the material seems to be rather resistant due to the characteristics of the card facing.  No problem for an application like this so I'll crack on.

 

By the way, the "lightening" holes were cut quite easily with a compass cutter, although the weight of all the circles was only a gramme or so, so not worth the effort really.

[Simon Chaddock]

Mike

I can't help with film covering techniques as none of my foam planes use it primarily because their size and foam thicknesses have been optimised so the foam is strong enough. Any 'decoration' required is via water based paint.

Most of the foam I use is a Depron type so has no paper covering. This means it is about 1/10 the density of balsa along with a corresponding reduction in its physical properties but there are still there. The task is to end up with a design that makes maximum use of the foam's properties.

 

[Graham Davies 3]

True, not tried covering over the paper. My last build (CAP232) used the paper as the covering, painted directly. However, I wasn't happy with this as the paper comes away from the foam fairly easily, and for me it adds more weight than it adds in strength. I leave the paper on for formers, but for most other parts I find little downside removing it, and loads of weight saving. I'll follow this with interest though, as it's great to share all the collective learning!

 

Good luck, keep posting.

 

Graham

[eflightray]

At least foam board can let you get away from slab-sided boxes with wings on. 

Where's the scratch builders willing to move on ?

 

Ray.  😉

 

[martin collins 1]

 

Very nice work, love the Dauntless, any chance of some more info and build pictures of it, could you stick them on another thread save hijacking Mike`s build, would love some more info 😁

[Simon Chaddock]

Yes indeed.

You can 'build' using foam sheet to create a shape as complex as you wish or have the patience to do.

Foam is not necessarily a "quick and simple" substitute but it can give significant performance advantages from weight saving. 

[Mike Bell]

Got some covering on the parts today and found no problem at all ironing the film onto the paper covering.  I thought that the exposed foam on the chamfered corners of the fuz would be a bit ugly but actually turned out OK, for a utilitarian plane like this anyway.

The only disappointing bit was where the balsa framing of the tail and fin didn't quite sit exactly centrally on the edge of the board leaving a bit of a step.  Not a problem where the balsa is proud, you can just sand it away, but on the other side you can't do much about it.  I should probably have used 1/4" rather than 3/16" and shimmed the board up to have a bit of balsa proud on both sides.  Lesson learned.

I'm really encouraged by the weight, the parts shown below weigh 197 grammes which feels fairly comparable to a typical balsa version.  It feels very rigid and I am perfectly confident it will be strong enough for in-flight loads, just remains to be seen how it stands up to fun fly rough and tumble.  I'll kit it out with a motor and radio and find out in the next couple of weeks hopefully.

 

[Mike Bell]

The fuz is assembled and installation well on the way, hopefully not too long before I can try it out.  The wing in the bottom picture is from the previous balsa version.

 

[Bill Wood]

What size battery will you use and will it go in the front hatch?  Nice job. Much better than my first foray into foam board.

[Lipo Man]

That should do fine - foamboard is surprisingly capable surviving flight loads. I’ve got a little fun flyer that was built in a single evening - it’s got about a hundred flights on it so far and looks as good (or more accurately, as scruffy) as the day it was built. All damage is hangar rash from my clutzy handling!

[Mike Bell]

Hi Bill, I normally use 3S but I want to try 4S for the revised Class 2 formula.  3S will fit via the front hatch but 4S won't so I have cut a bottom access.  I don't really like the idea from a structural point of view and it limits useful space for the radio installation but I've done it anyway.

I messed up a bit by forgetting about the reduction in internal volume from doubling up on foam thickness at the front.  I'll make the fuz a bit deeper next time.

 

Lipo Man, that looks funky and fun.  Good to hear about the durability, I'm quite confident that mine will be Ok too.

[Mike Bell]

While fitting out the radio gear I couldn't resist making some bits and pieces on the 3D printer.

 

 

 

 

 

 

 

 

 

 

Not too much left to do now.

 

[Mike Bell]

Just done a quick weigh in with a 4s 2200 battery and get 1263g or 2.8lb.  I usually fly with 3s and most of my fun flys seem to come in at 2.5lb.  So it does seem to be a bit heavier, though not by that much.  If I put a lighter battery in it I'll have to put a spacer behind the motor to maintain balance.  Next time I'll make the nose longer.

[Mike Bell]

I finally got to fly it this afternoon.  General flight characteristics were as expected, it's the same shape as the balsa version after all.  Did some fairly gently circuit type touch and goes and everything went well.  As expected the strength is adequate for normal flying.

Then on to some looping touch and goes to put a bit more stress into the fuz and when a wheel caught in a bit of a divot i found the limit of the structure in it's current configuration.

 

 

To be honest, if it was going to break anywhere, this was one of two probable locations.  I deliberately only put minimal ply reinforcement in this area, but now it is plain that it needs more for this type of treatment.  At least this stuff breaks nice and clean so it should be an easy repair.

No problem, that's what prototypes are for.  For now I'll mend it and install some thin ply and in the meantime I'll build another fuz with some strategic reinforcement.  I'm still aiming to campaign a foam board fuselage plane in this years fun fly events.

 

 

[Keith Billinge]

I have built a few foamboard models, mostly "Flite Test" and I find it a difficult material to like.
It seems to react badly to changes in humidity and I'd hang a model by it's prop in my garage and find that next time I flew the trim had changed vastly due to moisture changes.
It's not a predictable material and I'd rather build a traditional Balsa airframe covered in film or a foamy ARTF.

I'm sure lots of people have had a different experience but I find it a bit of a dead loss for a model with some logevity.

 

KB

[Ron Gray]

Try Depron, imo a much better building material.

[Mike Bell]

Since my last post I have gone a step further and built a nearly wood free wing to go with the fuz.  This uses the foamboard for ribs with 3mm depron for all the sheeting.  The only wood used was for the spars, leading edge and the core of the trailing edge.  The finished wing doesn't feel in any  way delicate and flight testing so far has revealed no weaknesses.  Interestingly the weight of this new wing was within half an ounce of the balsa version.  While there is little or no advantage in terms of weight saving for the new wing, the cost saving compared to balsa would be considerable.

 

I'm just finishing a new foamboard fuz, this time with more local strengthening included building on experience from the first one.

 

 

 

The foam version is the one on the right.