Tag Archives: Build a hotwire foam cutter

Combat Wing Build Log

Have been having so much fun with the gremlins & wings, as fun to fly no stress scratchbuilds, that its time to build wings for Combat.

First they have to be Cheap to make, and take little time to build since the expectation is they will be crashed in short order!

I started looking at A. Newtons site, where he hot cuts wings based on the FT mini wing plan. Well, the LAR principle kicked in as I started copying his template, and it just did not:
Look About Right!

I wanted a wing with the CG easier to meet, based on some ZRM motors I have from an old quad, a 3s 1300 pack and enough reinforcement to keep these wings together for a while….

My template,  when the LAR principle kicked in, has a wing span of 735mm, Root chord of 315, Tip chord of 163 and a sweep of 234mm. All this translates to a calculated CG of 145mm.

More to come as I add motors, corroplast fins, etc!

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Finished – coroplast winglets, 2300kv swinging 6×4 prop with blheli matched esc’s.

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The Pitt-Tastic….

Ok, so I started with the plans from an old balsa FSW called the spintastic…. It was forward swept with a profile fuse and a rudder. This is an exceptionally odd design so thought I would try it.

However, once I had the wing built I noticed an old HK pitts biplane that I had badly smashed many months ago…

It had a partly intact fuse, no wings, busted elevator, and crushed motor shaft, and really should have just been scrapped.

Being over tired, using this pitts with the spintastic wing seemed like an awesome idea!

Sooo, I cut the fuse apart to take the FSW at midpoint, repaired the motor mount, elevator etc, and glued it all together!

I really need to stop building planes late at night!

Building the wing from 2″ pink insulation:

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Gluing it all into one and using packing tape rather than laminate:

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Scratchbuilt FunJet

After totally destroying a multiplex funjet, I used what was left of it to take measurements.

The hardest part of this build was creating and hot cutting the wings.  Each wing is built by using symmetrical airfoils that scale down in both cord and thickness as they move toward the wing tip.

Once glued, a carbon spar was laid in for strength. The fuse is simple, just 2″ foam block hot wired to shape. As this foam will not take an impact,  I heated a steel rod, and drove it perfectly center down the length of the fuse. This permitted the insertion of a square carbon fiber rod, that will hopefully keep the fuse from breaking on a nose impact.

Power system is currently a Greyson super megajet motor, 6×4 prop and a 40 amp esc.

Maiden will be interesting!

Hot Wire Cut Wings:

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Glue up of the wings:

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Adding the Spar:

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scratchbuilt funjet
scratchbuilt funjet
scratchbuilt funjet
scratchbuilt funjet
FunJet Scratchbuild
FunJet Scratchbuild









LAR Plank

Continuing with the flat plank style, here is a design with a fully symmetrical airfoil, and the LE cut at each corner to prevent tip stall.

Apparently the winglets are not required with the this cut, however, decided to play it safe.

Running an 1100kv motor and an 11″ prop, this design flies like a dream.

*Update – got caught in some wind, drove the plank into a building… this is No More!


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Corsair Profile

The gull wing design is interesting, but I have no clue as to what advantage it is supposed to provide…

That said, thought why not scratch build one!. Here  is a 46″ wing, built a jig to cut the angles with a hot wire, using the LAR principle, so don’t know what the actually degrees are.

Since this was a build that came together with no real thought, the awful paint job is appropriate.

Powered by a Park 450, a 9×6 prop and a 40a esc, the maiden should be interesting…..

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LAR #3 Extended Wing

Building on the previous wing, I added an 9″ center section to permit more equipment mounting area, and to widen the stance of the wing to see if more stability is created. CG for maiden is via the online cg calculator for wings.

I’ve powered this with a blue wonder 1750kv, swinging a fairly mild 7″ prop. It appears to have enough gumption to be able to fly, but I’m not expecting a speed demon. Should be fairly docile.

The wing is hot wire cut out of white styro, with a clarkX airfoil (scaled by 70% for end). Appears very light and cg when using a 3s-850 battery is difficult to set, thus I added the fuse/canopy to give me that few extra mm’s to meet the CG I think it should be at.

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LAR #1

Welcome to my new series, no more WTF XX, it will now be the:    LAR XXX Series!

Looks About Right #1

Noticed the scratch built sBach full fuse, so decided to make a version.

Had a hot cut wing laying around from when I was trying out cutting a tapered wing, so that became the base unit, with all other dimensions based on this wing.

This thing balances nicely with only a 3s 1300, and the motor is an old 28 series 1200kv I had on a tricopter – prop is very small for me, 8×4.5, but seems to hold the LAR #1 in the air at only half throttle, so should be interesting to fly.

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WTF Four

Well, WTF 3 was a complete disaster. It was a clark airfoil and it looks as if I set the wing incidence too high. This resulted in its complete destruction on maiden!

Introducing the WTF 4 – This one I’ve gone back to the sipkil airfoil, mid mounted, at 40″ span. Slight changes to the rudder and elevator to help overall balance.

This one had to be designed while it was being built, as a motor from the Durafly Tundra is powering this one. I chose this motor as its base design is to use a 12×6 prop. It is much heavier than other 28 series motors I have tried, but accounting for this during the build/design stage ensured CG @ 1/4 was easily achievable. As typical for this design, a 3s 2200 lipo powers the plane.

The wing is hotwired from expanded foam, body is built from the 6mm grey depron (much less ridged than the white depron!) and tail section from 9mm depron.

May it fly as well as the WTF 2.

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ScrPush1 Twin Boom Scratchbuild

So I have an urge to build a double boom plane, pusher style, using the hotwire wing method, and possibly the fuse in full foam design.

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I came across an interesting article about the “SO” series, a guy that does many scratch builds, and has perfected the two boom pusher plane. His website and rough plan outline can be found here:

He is using the stepped wing design, basically foamboard stepped back to create a KMF2 style wing. As well, his design is a 30″ wingspan.

In my mind, I want a slow flyer, that is very stable in the air, so I am changing the design to what I think may work. The wing is cut from a standard clarkY airfoil design, flat bottomed to accept the rear booms or spares, and with some form of dihedral.

Since I do not want a standard dihedral wing that angles up from center, I built a wing (38″ total span rather than the suggested 30″) that has it tips angled up – I have no clue what this is called, nor if there are measurements I should be following…

I used some short pieces of foam, hot wired the airfoil shape, fired up the table saw, and tilted the blade a few degrees – darned if I know if it will even work!

One interesting article I also found was making spars using foam board, but in a Triangle Shape for strength – so that’s how the spars will be done, rather than wood or carbon.2016-02-20 14.42.18