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Cutting a Foam 4412 Profile
By WXYZCIENCE, Section Mechanical Posted on Tue Nov 7th, 2006 at 07:51:02 AM MST
First Test Cuts

I have been watching several others on this site building foam wings.
Good idea, so adding a foam cutter to my xyz machine seemed feasible.

Three 4412 test cuts produced this wing. My cord length is 6".

The cutter allows me to obtain both inside and outside forms.
The reduction of 5% in each cut makes the profile fit together well.
I am trying to produce a plug and a mold.
These blocks will be used for the mold experiment.

The next picture is the foam clamp with a taper/twist control drive.
The resolution allows me to get 4 divisions per degree.

The last picture is of the cutter in action. A small fan removes the fumes from the cut and they are vented to the attic. The 22 gauge nichrome wire is controlled by a light dimmer on the primary of a 120volt transformer. The secondary, 12 volts can be set just right to cut at the correct speed.

The cutter worked very well.

Joseph.

Cutting a Foam 4412 Profile | 19 comments (19 topical, 0 editorial)

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#1)
by SamoaPower on Tue Nov 7th, 2006 at 08:12:51 AM MST
(User Info)

Neat machine Joe. It would sure be nice if you could cut the whole blade length in one swipe but I can see the limitations.

Please don't depend on THAT profile being a NACA 4412. The 4412 is quite different.

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#3)
by WXYZCIENCE on Tue Nov 7th, 2006 at 10:35:22 AM MST
(User Info)

SamoaPower, yes the profile is slightly modified to be the root section. The test wing will be 48". I will switch to the 4412 next and will add the twist through too the end. Any suggestions of other profiles would be wonderful. It only takes a minute to re-program the cutter. I will be trying out a twisted section later today. Thanks for the input.
Joseph.

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#4)
by WXYZCIENCE on Tue Nov 7th, 2006 at 12:33:47 PM MST
(User Info)

SamoaPower, In the future I will probably increase the cutters length. There are some problems that would have to be addressed.

I have successfully cut 24" in the horizontal but in the vertical the heat is uneven and the cut is tapered. Not such a problem for wings or blades but with other cuts we lose dimensional accuracy.

Maybe a dual machine, one to cut a rough blank and the other to do detailed work.

Another idea would incorporate a circular moving nichrome cutter. Like a band saw. This way temperature over the length of the nichrome would be constant.

The next challenge would be a horizontal adjustable arc cutter. I haven't any workable ideas in this area yet.
Joseph

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#6)
by SamoaPower on Tue Nov 7th, 2006 at 02:45:30 PM MST
(User Info)

Seeing your skills, I wouldn't be surprised to see you come up with an excellent machine.

Don't be afraid to use linear taper and twist in place of the progressive types out of some of the blade calculators. It only costs you a few percent in performance. Linear twist and taper can be cut with a hot wire cutter, of course.

For other possible tested airfoils you may want to take a look at:

http://www.ae.uiuc.edu/m-selig/uiuc_lsat/vol4/NREL-SR-500-34515.pdf

They tested at low Reynolds numbers which is what we need for wind turbines.

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#12)
by WXYZCIENCE on Wed Nov 8th, 2006 at 01:12:40 AM MST
(User Info)

SamoaPower, thanks for the pdf link. There is a lot of technical data but I gleaned a profile and some info on it's performance.

I will give this one a try for the last 3 or 4 section of the wing.
Joseph.

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#15)
by SamoaPower on Wed Nov 8th, 2006 at 08:40:09 AM MST
(User Info)

Fine Joe. The only problem I see with the E387 is that being a thin section, it doesn't have a lot of room for the spar system.

You'll need some of the data from the drag polars to design the blade. You need the CL (Lift Coefficient) at best L/D and the Angle of Attack at that CL. The L/D will be the primary factor determining blade efficiency.

I'm using something very similar to the SH3055 on my 16' rotor.

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#7)
by RP (russp located-at fidnet (dot) com) on Tue Nov 7th, 2006 at 04:56:14 PM MST
(User Info)

"Another idea would incorporate a circular moving nichrome cutter. Like a band saw. This way temperature over the length of the nichrome would be constant."

Maybe, but if there's much length of wire on the "infeeding" side, the wire will pre-heat and be hotter on this side. The only reason I can see for the vertical unveness is convection carrying cool air up through the bottom of the cut.

I wonder: For twist could you pre-twist the bulk foam and cut it while twisted?

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#8)
by WXYZCIENCE on Tue Nov 7th, 2006 at 05:24:38 PM MST
(User Info)

RP, I believe you are correct in the understanding of the convection causing the underside to be hotter than the top. My cutter wire is 8" and by moving the foam lower there is less taper. This is a desirable outcome because the profile tapers fit together very well. The underside melt can be made 1/8 wider than the top.
Joseph.

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#2)
by pepa on Tue Nov 7th, 2006 at 08:49:02 AM MST
(User Info)

very nice Joseph, pepa.

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#5)
by DanG on Tue Nov 7th, 2006 at 02:37:06 PM MST
(User Info)

How about columnar forced air or even a gravity dropped coolant flow - just enough to keep melt film collateral damage down. The oscillating wire idea is good but the melt film still will collapse anything it touches until it cools...

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#9)
by willib (willibur at comcast dot net) on Tue Nov 7th, 2006 at 08:21:40 PM MST
(User Info) http://www.njwind.com/webcam.html#

Hi Joseph ,
if you could regulate the current better i think you could cut it more accurately
did you try turning down the current?
my stainless wire (0.01)dia , starts cutting at a tad over 1/2 amp , but i usually cut the foam at 3/4 of an amp.
Carpe Ventum (seize the wind)

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#11)
by WXYZCIENCE on Wed Nov 8th, 2006 at 12:58:23 AM MST
(User Info)

Willib, I have a bunch of stainless wire and will give it a try. The nichrome came from an old hotel ice maker fairly heavy gauge.
Joseph

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#10)
by Experimental (harogate@whidbey.com(no spam)) on Tue Nov 7th, 2006 at 11:35:10 PM MST
(User Info)

Hi Joseph,
I have built aircraft wings using the nichrome wire method in leingths of 8 feet, it is a very simple process, but I strongly suggest using the high density blue foam, sold as building insulation !!
It is very small cells, stronger and easier to sand, than the styrofoam you are using and much easier to work with !!
There used to be a book out on news stands, called "building composite aircraft" -- if you can find that paper back publication, you will see very easy methods of building your blades..
Somewhere around the house, I still have that book, if you want to email me your address and I can find it, you would be welcome to it..
If I can figure out how to do it, I would show that process on this board -- unfortunitely, I,m old and computers intimidate me !!!
Happy building to all, Bill H........

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#13)
by WXYZCIENCE on Wed Nov 8th, 2006 at 01:21:28 AM MST
(User Info)

Bill, I have lots of the light green foam. It came from an insulating cover for a hot tub and is 4" thick on one side down to 3" on the other. I tried the blue stuff and get a very clean cut with it. Thanks for the input.
Joseph.

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#16)
by willib (willibur at comcast dot net) on Wed Nov 8th, 2006 at 08:44:44 AM MST
(User Info) http://www.njwind.com/webcam.html#

The blue foam and the pink stuff (both insulation) come in 2" thicknesses. i think the pink stuff ,does not taper down at the corners ,like the blue stuff does, and can be purchased in smaller widths than the blue , 8'x2' and around $14 per sheet at Lowes.

Carpe Ventum (seize the wind)
[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#14)
by Chagrin on Wed Nov 8th, 2006 at 03:31:15 AM MST
(User Info)

Tower Hobbies sells nichrome wire for foam cutting if you're looking for a small amount. A 4' piece was under 5$. I can't remember the price.

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#17)
by bj (jackbp996@msn.com) on Fri Nov 10th, 2006 at 07:33:11 PM MST
(User Info)

Joseph--your work is art. Have had some experience cutting Foam, as I worked at Dow for 25 years. They did cutting, with Hot Wire for about
ten years. All types of foam. What they came up with, was a bench, 16 ft, long, with a hot wire attached, on a swinging boom. Not applicable
to what you are doing, but, what they did do that might be, is attach
springs to the hot wire. It grows in length lots when heated, to below
Yield temp, and the springs kept it taught. Made straight cuts after
that Mod. Maybe you could adapt.
If help, Great.
If not, sorry.
bj
BTB I now own the bench.
thanks all bj

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#18)
by keithturtle (keithturtle@msn.com) on Fri Nov 10th, 2006 at 09:12:56 PM MST
(User Info) http://www.disappearances.info

You might also want to consider the modulus of the foam when figuring out which way to cut. It has a "grain" to it much like wood, and thus more strength [resistnce to bending]. Support it on the ends and put a weight in the middle, measuring deflection. Do this in both directions, the "grain" will yield the lesser deflection. Cut accordingly. This is more prominent in the blue and pink foams.

Keith

[ Parent ]

Re: Cutting a Foam 4412 Profile (3.00 / 0) (#19)
by bj (jackbp996@msn.com) on Sun Nov 12th, 2006 at 04:59:39 PM MST
(User Info)

Joseph--after re-reading some of the comments, YES some foams
do have a grain. It depends on how they are made. Extruded foam
has a grain, like wood, and runs from end to end. It is how the
assembly line works. Some foams are made from compressing foam
beads under heat. They insulate, maybe even better, but lack
structural strength. You can break them with a light hand blow
in any direction. Extruded foam IS stronger along the long axis.
Maybe, or not, on the face.
So, after a lot of words, what I am saying, is for blades, use
only extruded foam. Blue is DOW. Pink I am not sure. I have a lot
of experience with blue. If I can be of further help, please
E-mail me.
Love your work.
bj
thanks all bj

Cutting a Foam 4412 Profile | 19 comments (19 topical, 0 editorial)

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