I'd love to see that. I've got a body cut of the dual boomer for some Aero Ace guts but haven't put it together yet. Please post photos! All the info on building hot wire cutters can be found early on in this thread.

For those interested, just updated the homemade foamie Mustang thread in this forum. She's almost ready to fly again and I'm loving the new motor mounting method....which should also work great for our dual boomer.

Just had a thought....Anybody care to bother to make prints of the dual boomer with graphics. I so much like just spray gluing prints on the Mustang that I'm going to try to go that route for all my planes now. Really helps stiffen up the foam as well.

I made a foam cutter and attached it to a table saw using a c clamp last night and cut out 4 2.5" x 2.125"x4' pieces of the pink Dow foam for fuse. Slow day at work so I drew all the cutouts for the fuse. Now I need a way to cut it out ... I am thinking of going to home depot and getting one of those snap off blades and using that to cut the foam since they are real long, thin and sharp.

wish me luck ....

I love my homemade table bandsaw style hot wire cutter. Early in this thread you can see some good pictures of that. It makes precision cutting easy by free hand without the need of wood templates for body parts.

SmellTheNitro,

As many folks have observed you could probably cut out your foam shapes with a pissed off gopher and be able to sand them down quite nicely. Hot wire cutters simply help keep the mess down and can add some real precision if used properly. The scaled down version sounds great. Keep us informed. Then you could get a dozen planes out of one sheet of foam. At $0.79 each it would be the plane for the masses.

We’re pullin for ya!

Originally I was just "scratch bashing" planes out of foam before I made a foam cutter, it's messy, but you can literally build the entire plane without any fancy tools at all. I was using my jig saw to cut out the pieces and used a rough file and sandpaper to get it to the general form, then finer sandpaper to get it to it's final form. Hacksaw blades are a popular low tech choice when cutting out pieces and I use my table saw and chop saw for the booms still since they are just simple shapes.

I used Critterhunters bandsaw technique simply by mounting the bow to the side of the table, mainly for the purpose of making a foam flying saucer, but making perfect circles with it, there are some extra steps to do one of those, especially when making a circular symmetrical wing, again, remounting the bow at a few angles around the pivot point, the tool does have major advantages with saving time and to get more precise cuts not to mention as fisher said, addressing the mess factor.

Fisher's right, hot wire cutting is mainly to keep the foam dust down and requires much less sanding to finish it off. I normaly use my large wing bow to rough cut a piece off the 4x8' sheet, then cut it on the table cutter more precisely. Regardless, I still have to sand a bit. Where a hot wire cutter really shines is for cutting the wing airfoils. You could sand one out but talk about time intensive. I'd go mad. Which reminds me, another quick and dirty way to make a wing airfoil and strengthen it at the same time to boot. Simply take some flat foam (any type will do) and fold it over a balsa spar which will be at the leading edge of the wing. The balsa creates a nice curve airfoil and does double duty but strenghtening the thing. A friend showed me this though he used it on a coruplast wing (talk about something that can take some punishment).

Love the table cutter. I don't even bother with wood body templates to guide me anymore. One thing I need to figure out is how to keep the wire straight and the foam. The wire, if rushed, will bend and create an angled cut. I would guess I need to increase the tension of the spring or heat the wire a little hotter and move slower? That's mainly where most of my sanding comes in. Another thing I need to figure out is how to guide the foam along a straight line for a perfect straight cut. I've done it with a straight edge by holding it with my other hand. I guess a straight board or something simply clamped down on the table cutter's face to use as my guide would work.

Also have another idea I'd like you guys to kick around. I've been toying with the idea of building my first biplane. Any good bi-plane should have a round fuse, of course. Want to use the regular white foam we use for the So plane for that. So, how to do it? I'm thinking I could heat up a metal ring of some type held in a vise with a propane torch. Then take a piece of foam that has already been cut into a long rectangle that is slighly larger than the diameter of the ring and simply slide it through the ring to cut it into a round shape, or cylinder more precisely. Ideas? Thoughts? Put Downs?

Well I took 30 min or so and roughed out the fuse.... looks to be a bit too fat ... might take .25" off the width maybe .5". What you all think so far? 2.5 tall 2.125" wide 10" long

Critter,

That will give you a straight cylinder. I have a feeling that the ring will cool part way down also, and it may be hard to keep straight.

An easier way to do this, and also produce a taper, would be to simply cut out a circle template for the nose in cardboard, or aluminum flashing or thin ply, etc.

Then cut out an oval section for the tail end, same way.

Spray a very light coat of 3M 77 on the ends of your blank. Stick the templates on.

Set your foam cutting bow in a vice with the wire end up, and running horizontal.

Cut the foam blank by holding it in your hands and rotating it over the foam bow. You have to keep the cut even at both ends. Don't let one end get ahead of the other. Let the weight of the foam keep it on the wire, don't push -- use a delicate touch. Don't run too hot. Go slow.

This will make a conical section fuselage -- at the end, an oval cone.

For complex curves you can't use this method, you have to shape by hand, but it's also not hard:

Draw out your top view on a squared up foam blank. Then cut it out and save the cutoff pieces.

Reassemble the new blank and cutoff pieces with tacks of hot glue. Draw the side view on this re-assembeled block.

Cut out the side view. Remove the cutoff pieces. You now have a square fuselage but it has tapers all around.


Now to make it round sectioned.

To do this, you take an even amount of material off of all the corners by eye with a sanding block to make an 8 sided cross section.

Then take these corners off to make a 16 sided cross section.

Finally round by eye.


This is how we make perfectly round tapered masts on boats without a 25 foot long lathe (there is no such thing in boatbuilding -- people always asked me when I had a boatshop -- where is your lathe -- how do you make masts?).


The last method is very fast -- longer to explain than to do in foam. A sanding block takes material off quickly and evenly. The disposable sponge type used for smoothing drywall works well.

This has the advantage over the first method that the tapers can be curves -- like on a real airplane, not just conical tapers.

This is how I did the model of the Gee Bee Z (pictures at post # 834 in this thread) which has very pronounced compound curves that eventually end in a flat section at the rudder.

One final easy way to get a cylindrical fuselage in foam ( and I'm working on a plane this way now) buy a swimming pool "noodle" at Wally World -- a kids toy float -- cylindrical foam -- it's EPE foam, basically indestructible. Will need some skewer stiffening for most projects.


Try your idea first -- if it doesn't work to your satisfaction, these others might help.

I rolled a FFF tube with my bendfoam tool but it wasn't true round but I'm going to try tapeing a piece to a round something and rolling. Heat gun does wonders. Slick way to build is a block for the nose and a cylinder behind. I have seen cones rolled for the rear of fuselage. Like around a coke bottle. Cylinders are great as you can move your innerds where you need them Theres a SE5a 32" bipe in RCGroups that I want to build. He used a block up front and FFF behind. Undercambered wings & skewers for braces.

Ken

And if you're going to build in sheet foam material instead of solid EPS foam, many successful models have been made by enlarging paper models with your computer and printer, such as the ones at Fiddler's Green. There are many historical biplanes there.

Generally, to convert them, you have to butt instead of lap the cut-out skin pieces, and add some formers internally for stiffness. The wings can be sheet style undercamber airfoils, or wire cut foam -- undercambered single sheet style wings would tend to make a lighter and easier build for a biplane, but you could do a double surface or solid core if you really wanted.

Course if you want to come up with your own design, rather than a scale bipe, any of the other methods should get you there

This would be perfect for what you want to do critterhunter.
flat board metal or whatever attach a vertical rod to it..... take 2 large wheel collers and tack weld them together at a 90deg. offset slide them down the vert rod insert 2 horizontal rods into those. Take 2 more collers drill an tiny whole in it to feed a cutting wire through. That can be for angled cuts..... take another coller make it the same way and the other 2 fix it to the tip of the top rod and pass through a whole for a band saw type .... drill wholes further and further away from the center and you can put a wood screw in it for a lathe type ... mahe sure you make another coller with a point on the top to hold in place too ...

Nice! I've thought about a lathe with shaped wire -- but this is much simpler than the headstock and tailstock I imagined.

Wonder what thickness wire they are using for the cutter, and how many amps it takes? That's the real key to it.

The thicker the wire, the more amps are needed -- but you need a fairly thick wire to hold its shape. I wonder wht is being used here?

I've also got a foam lathe of a different type somewhere on my hard drive -- this one copies any profile shape, uses a dremel tool in a moveable base as a cutter, and the lathe part is turned by an old hand mixer.

The application was for making foam patterns for metal casting (I have a foundry I built -- so I found the info for this) but I don't see why it couldn't be used for planes.

Only problem is any cutter other than hot wire makes foam dust -- this one probably a lot -- but still, might be useful to somebody for something -- I'll post it when I find it.

bandsaw wire is a 32 gauge ... you can get it at michaels in the bead section ... cheap too ... the other I will research .... I am using at home som ... mig welding wire @ .030 ... takes about 8 amps for a 8-9" long piece ... and I know for sure this will hold shape

Well if it's .030 or so, then piano wire comes in .032, and other sizes. It has some carbon in it to harden, so the resistance is a little higher than mig wire I think -- resistance would be a good thing -- it will provide more heat with less amps. The big problem with thick wire is too low a resistance and too high an amp range.

Stainless wire is usually even a little higher in resistance than carbon steel. I have used solid stainless fishing leader (single strand) for my hot wire bow -- but I went with as thin a gauge as I could find for a thin cut, and low amp draw (I think it's .018"). Maybe leader material in heavier weight would work well for this.

One thing I forgot to point out -- this lathe will still only make a shape of rotation -- not a flattened side shape. If you think of the Gee Bee, the nose section is circular, but the tail section is flattened. Most planes are that way, more or less -- you can't do an oval section, only circular with the lathe

The only way I know of to do a true compound fuselage shape in a solid foam construction is the profile and top view cutout, then trim and round corners as required.

There are many built-up methods for complex shapes -- but not many solid carving ones.

Wow, all great ideas! I was just looking at those pool noodles the other day. Some Stryker owners make noses out of them for more cushion on a crash. I just woke up so I'll re-read the messages later when I can make more sense out of them. Had another idea, though...aluminum beer cans glued end to end for a round fuse. Use those energy drink red bull cans for a smaller diameter. Then again, pretty much any plastic cylinder shaped bottle would work great too. Red Bull aluminum cans would probably work real well for a Wart Hog type fake nacell. Did I ever tell you guys about the plane I saw being made using detergent bottle plastic lids for the nacells? Man did it look like it was meant for that plane.

here is the best I have found on stainless .... many sizes too

Aircraft saftey wire

[link]http://www.skygeek.com/ms20995c15.html[/link]

Critterhunter

check this out
[link]http://cgi.ebay.com/Crafters-Styrofoam-Cylinders-Variety-Pack-19-pieces_W0QQitemZ180109871585QQihZ008QQcategoryZ412 00QQrdZ1QQcmdZViewItem[/link]

Here's a foam lathe used in making a rocket body and nosecone:

http://www.info-central.org/construc...mturning.shtml

And here's the foam lathe I was talking about that uses an egg beater and a Dremel.

Noptice that it's a copying type lathe. It copies the two dimensional pattern at the bottom. The way it works is a pointer the size and shape of the dremel bit follows the pattern, and so the dremel cuts the same shape above it. Kinda like the way keys are ground at the hardware store.

http://www.abymc.com/Articles/Submitted/foamlathe.html

ok this is the 4th time writing this (forum issues)

my 1/2 scale SO 11 is running into some issues ....

all electronics and hardwear is adding up to a little over 3oz

wing area is 72sq" (4"chordx18" span)

all in all it may turn out to be a 5 oz bird .....

will my power plant putting out 4.5oz thrust be enough to keep this little sparrow in the air? I may be going full size after all


thanks,
Robert

That should be plenty of thrust if your AUW is 5 oz!

Another half ounce of thrust and you'd be able to hover a cube of that weight, never mind a SO.

You also have the wing area to weight ratio of about a 20 oz full sized SO. So the plane ought to fly well -- probably fast and a little control sensitive. I'd keep the throw conservative on the elevator for first flights maybe even 1/8" on a baby SO.

If you have a single aileron, be sure to trim it down a little for first tests, or be ready to correct a roll into the aileron wing on launch. I've also found now with three different pushers I've built, they all required a little up elevator trim and also angling the motor down aft to counteract a diving tendency.

The combination of a diving tendency and roll toward the single aileron broke my first SO on its first glide test.

Others may have different experiences -- please add them if they contradict this.

I agree along the thrust ratio, it's plenty.

I also like the low tech lathe ideas, it looks simple enough.

FYI the 32 guage SS wire @ micheals was .99$ and the 28 guage was 1.50 I think. 24 yrd spools ... I think I will have enough for a while.....

I wanted to mention something about CG, trim and airfoils I haven't seen mentioned in regards to the SO.

The SO is designed for a Clark Y airfoil. The Clark y airfoil is called a flat bottomed airfoil, but it is only flat in its rear section. The forward section lifts off of the bottom line.

If you draw a line through the furthest forward part of the leading edge to the furthest aft point on the trailing edge of a Clark Y, it will form a line that is angled up compared to the bottom flat part.

This is the "chord" line. The angle that this line makes with the fuselage centerline is called the "angle of incidence".

For a Clark Y when used on a SO type plane the angle of incidence is a positive amount -- a few degrees above horizontal.

A couple of things -- some builders don't cut a true Clark Y -- they just cut the top surface and leave the bottom flat. This will lower the angle of incidence of the wing to zero degrees. Such a plane will need to fly faster or, at a higher angle to the line of flight to provide the same amount of lift. It will likely therefore either require more elevator up trim, or a more rearward center of gravity to maintain this angle in flight.

A solution to this for true flat bottomed airfoils would be to mount the wing a few degrees positive on the fuselage -- this will reduce the amount of elevator trim needed. A small wedge set to the proper angle of incidence under the wing would trim the plane better.

I have found that even with the 15% Clark Y I use, that some up elevator trim is needed for level flight.

Another point for those, who, like me cut a true Clark Y:

Because the wing is actually already at a positive angle, the location of the CG is not accurately determined by measuring from a vertical line dropped from the leading edge to the bottom of the plane.

From a practical standpoint, it can be done this way if the measurement is in inches, not a chord percentage, and supplied by the designer -- he has corrected for the difference.

But if a precentage of wing chord is specified, it would actually need to be measured along a line parallel with the wing chord line. Since the botom of the fuselage isn't parallel, to the chord -- it isn't accurate.

The practical side of this on the SO is that planes with a true Clark Y will fly with a more forward CG location, in inches measured along the bottom, than a true flat bottomed foil will. The difference could be a fair amount -- and this explains why different people will find their SO planes fly with different CG locations (measured along the bottom).

I hope this solves the mystery of different results by different builders on the same type of plane.