Update on Graupner Amateur

The Graupner Amateur built in 2014 is still flying. It has become my go-to model for calm morning or evening outings to the field.

Recently added a 3D-printed dummy 'Cox' cylinder head from a design found on Thingiverse:

Graupner Klemm 25

The original Klemm 25 was first available in 1928 as a light two-seat touring and training aircraft. My model is based on a Graupner Klemm 25 kit from a lucky EBay find, which then became a Corona Summer of 2020 project. Built as per instructions, except replacing the vacuum formed part for the cockpit with strip-planked wood. Fuse is covered with cloth/epoxy, wings and rear with 'Nelson light fab'. All coloring is Tamiya paint, both glass and rattle can. Filled the cowling from the kit with plaster, then vacuum-formed a copy to have replacement part. Pilot is 3D printed.

Wingspan	130 cm
Weight	830 g w/o Battery
Battery	3S 2200 mAh Lipo, 185 g
Motor	Speed 400, gear

Full-throttle current draw is 10 Amp, 120 Watt. First flight in June 2020. Motor's gearbox is quite loud. Barely climbs at full throttle, but can fly nice slow circles at 1/3rd throttle. Uses about 100 mAh of battery capacity per minute flight time. Makes for enchanted early morning or late evening flights in zero wind. Very convenient that whole plane fits into car, no need to remove wings etc. Only downer are the water-slide decals. As applied from the kit, the transparent backing shows up shiny/silvery. Tried to 'melt' them into the paint by dabbing with vinegar as well as acetone. The latter helped a little, but masking and then spraying the numbers would have been way better.

Simprop Zaunkönig

The Simprop "Zaunkönig" ("wren", small bird) is a small biplane design from way back (30 years?). At the time it must have been the smallest commercially available RC kit. It was powered by a small cox engine, and with the RC gear of the time the weight resulted in a model that's fast and challenging to fly.

First flight on 05/05/2018.
Wingspan  410mm
Weight 290g
Motor 1000 RPM/Volt
Prop APC 7x4 SF
Battery 3S, 800mAh LiPo

Found a kit on ebay, and created my own CNC-cut duplicate from that.

Some of the parts:

Assembly (and sanding) required:

Graupner BO 209 Monsun

The original Bölkow BO 209 "Monsun" was built around 1970, with almost exactly 100 copies being manufactured. As long as I can remember, Graupner always had at least on model in their catalog, from a small free-flight, rubber-powered variant to larger R/C types.
This model is based on a plan of the older 1973 Graupner kit for a 40-sized model.While the kit included foam-core wings, the rebuild has traditional ribs-and-spars balsa wings.

Wingspan	1.5m
Length	1m
Weight	2180g (kit used to be 2700g)
Motor	AXI 2816/12 V2, kV 760
Battery	4S 3000mAh LiPo
Prop	12x8
Max current	40 Amp

First flight: Evening of April 1, 2018.

Initial cockpit detail.

Special challenge in the rebuild were the bubble canopy and the motor cowling, which were vacuum formed. Above is example of the wooden cowling plug used to pull the cowling.

Graupner Chico

Built from plans, but with electric motor, removable wing, hatch on nose for battery replacement.

Weight	830 g
Prop	9 x 5
Battery	3 cell LiPo 2200 mAh
Max Current	18 Amp

First flight on Sept. 22, 2017. Roll rate with mostly original aileron setup is a little underwhelming, and slight tendency to pull down with increased power. But generally easy to fly, floats nicely, very gentle stall.

Most important: Terminally cute 70s look.

Graupner Mosquito

Graupner offered the Mosquito kit from about 1975 on. At the time, it was one of the first electric (under-)powered gliders, also usable as a pure glider, or with a 0.8 to 1.5 ccm Cox motor.

What's somewhat special about it is the sleek nose section, accomplished by moving the electric motor back from the front, using an extension to the prop.

Built from plan in about 6 months. Total weight in the original glider version was 1100g. With 'Jumbo 540 F G6' motor, 6:1 gear and NiCd battery, it was around 1600g.

Wingspan	2500 mm
Length	1100 mm
Wings Area	44 dm2
Tail Area	7.5 dm2
Weight	1300 g
Motor	MVVS 2.5 1350
Prop	9 x 5, folding
Battery	3S LiPo, 2200 mAh

First flight June 3, 2017. Very slow, majestic, low sink rate, flat glide. Typically flights of about 15 minutes require motor run time of only about 3 minutes, leaving the LiPo 80% charged.

Graupner Bugsier

Very slow progress, but progress nevertheless over the holidays on Graupner Bugsier.

ARRL Field Day

Put up a Super Antennas YP-2 2-element portable Yagi for 20m, on temporary mast leaning against the house. Antenna was about 5.5m above ground.
This antenna used to be offered by W6MMA.

Graupner Cherry Rebuild

Had flown a Graupner Cherry II when it first came out. Was comparably heavy back then with NiCd batteries and somewhat under-powered.
Recently found one on EBay, which had a fiberglass fuse compared to the soft plastic fuse of my earlier one. Unfortunately, crashed on the first landing. Reason was probably that I had the airlerons mixed to both move down to slow the plane for landing. While the plane did slow down, it also suddenly rolled over and fell out of the sky.





Decided to build up a Cherry look-a-like as a purely wooden construction. Used the one remaining wing from the crash as a template. Compared a scanned copy of the airfoil with others in Profili, found a good match in the Eppler E211. The wing is fully sheeted, with a slight undercamber. To build the wing, the bottom sheeting was placed onto standoffs with a contour matching the underside of the ribs; ribs and spars were added, then the top sheeting.

Wingspan	2.2m
Length	1.02m
Wing Area	35.5dm2
Weight	1.250 kg (with battery)
Airfoil	E211
Motor	MVVS 3.5/1200
Battery	3cell LiPo, 2500mAh
Prop	10x6 Aeronaut CAM
Max Current	About 30 Amp

First flight was in January 2015. Rapid vertical climbout on full throttle. Can easily take off on half throttle. Slows down nicely when just gliding around. Now pulling ailerons 'up' for landing instead of 'down' to avoid tip-stalls. Still needs long approach because of flat glide path.

What would have been nice: Rudder control for better looking tight circles, and inner wing flaps for landing.

Still, fun airplane and the MVVS motor turned out to be terrific: Easy to mount in comparably tight glider noses, amazing climbout. Example for flying it one summer morning: About 2 minutes of motor runtime resulted in 18+ minutes of flying!



On another summer morning, achieved a 28 minute flight with 4 minutes of motor runtime. Still having trouble spotting thermals "right then" when flying thought them, but at the end of a flight it's pretty obvious when there must have been some. KCRC Model-of-the-month in August 2016.

Eindecker Model IV

Roughly 100 years ago, most airplanes had at least two wings. Biplanes. Anthony Fokker went against this trend. Based on his experience flying radio control airplanes, he was well aware of the "Ugly Stick" type of model airplane. So he created a full-size ugly stick, which became known as the Fokker Eindecker. Most people are aware of the Model III: Round engine in the front, machine gun that could fire through the propeller arc, wing-warping for roll control.

My model is about the lesser known Model IV variant of the Fokker Eindecker: Upright cylinder engine, ailerons. The cylinder block in front of the pilot provided a certain amount of protection from incoming fire, but unfortunately prevented mounting a machine gun, so the Model IV was mostly used as a reconnaissance plane. For this reason, Manfred von Richthofen had little use for the airplane. Nor had his brother, Lothar. But his girlfriend, the Baroness von Kräsch, loved the plane, which is why my model includes a replica of her in the control position.

Today, there is no surviving example of the Fokker Eindecker Model IV, mostly because I made it all up. My model is actually an 80% sized copy of the Balsa USA Eindecker 40 model which I had built several years ago. That one used an OS Max 40, this one uses an OS FS 26.

ISS SSTV

SSTV image sent by international space station on 145.800 FM on April 11, 2015.

Each image was sent in about 3 minutes, with 3 minute pause between images.
This pass was very low and thus short. First image had a little noise as ISS rose over the horizon. Second image started as ISS already vanished below horizon, so missing most of it.

Another pass, only about 15 degree max. elevation, resulted in this image:

Final pass on April 12, very low, only got end of what could have been an interesting image:

Audio Attenuator for PSK/RTTY/SSTV/...

Been using a RIGblaster plug  & play interface between the computer and the radio for digital modes. Works OK, but to get the proper output level to drive the radio, the computer volume needed to be quite low, around 10%. Since the same computer is also used to play music, I always had to adjust the volume way down for radio use, then back up to listen to music.

Finally got around to build a simple attenuator. The junk box happened to contain a 4k potentiometer with nice knob, so I used that. Computer output connects to the pot, and its wiper goes to the RIGblaster. The computer (laptop) output volume is now simply set to "100%", which is easy to reproduce, and the attenuator was once adjusted to give proper audio drive to the radio.

People with more patience should be able to put a smaller trim pot inside the RIGblaster, but I preferred to keep that as is and instead plugging the attenuator in-line.

 In the picture, the pigtail on the right side of the black box goes into the computer's headphone jack. Audio from there is then attenuated, fed via the blue/green plug into the rigblaster and on into the radio.

Eclipse SWT CheckboxCellEditor hangs on Mac OS X

.. when using the wrong value type.

The CheckboxCellEditor requires an Integer as its value, i.e. the index of one of its labels. When instead providing the label text, the SWT event loop will hang on Mac OS X. The combo editor's setValue method has an assertion to check the value type, but this doesn't result in an Exception with normal settings. Instead, the debugger will typically show that the main loop is stuck in handling the mouse-down event which activated the cell editor.

The fix is simply to provide the correct value, but unfortunately the reason of the hangup is not immediately obvious, there is no exception or log message that indicates the wrong value type as the reason for the hangup.

Graupner Amateur

Built by using parts from an original kit found on EBay.

Wingspan	110 cm
Area	18dm2
Weight	650g
Motor	Atlas AM2312/26
Prop	9x6
Battery	3cell LiPo, 2200 mAh

Started building just before Christmas 2013, first flight on 1st of March 2014.
Compared to the original, built as tail-dragger and with electric motor. Hood and front window are held by magnets, removed to access battery. Completed weight matches what original estimated for the free-flight configuration, without radio!

Flying it couldn't be better in no-wind conditions. Current draw is up to 10Amp, but plane still slightly climbs at 1/3 power, so full throttle is rarely necessary.

I happened to have grey Monokote around, so I tried to cover it as shown on the kit's box art. I'm surprised how pleasant the color combination turned out. The lettering and "Graupner" logo were cut from Monokote based on copies from the plans.

LEGO Mindstorms RCX 2.0 in 2014...

I still have a LEGO Mindstorms RCX 2.0 from 2003, and once more the question was: Is it still possible to program the device?

The Windows XP computer that I had used in 2010 (with difficulty, see post from back then) is no more. A brief search only indicated that there's no driver for Windows Vista/7/8, let alone 64 bit. BUT: I always preferred using the RCX with LeJOS, i.e. Java, instead of the Windows based GUI. Then it turns out that Linux actually contains a `linuxusbtower` kernel driver in most distributions. So overall, this sounded easier than ever?!

After installing a current Ubuntu release, the LEGO USB tower was indeed recognized, creating `/dev/usb/legousbtower1` whenever plugged in. But LeJOS 2.1.0 just didn't work, giving various communication errors in the `firmdl` program. I tried to compile the `linuxusbtower` kernel driver from the 2.1.0 sources, but could not find an easy way to get the required kernel source includes.

The solution was to use the LeJOS 3.0.0 "release candidate" (from 2006). It communicated with the Ubuntu-provided `legousbtower` kernel driver just fine. Only quirks:

• `lejos/bin/*` scripts needed to be `chmod`ed as executable
• `lejos/bin/lejos` needed the same "export LD_LIBRARY_PATH" and "java -cp .." for the `*.so` shared library that was already in `lejos/bin/lejosjc`

These changes might be included in the latest CVS checkout, but the `*.tgz` download has the advantage that for example `firmdl` can be invoked right away without having to build anything.

Used Eclipse by creating a plain Java project, then removing the default JRE links and instead adding the `lejos/lib/*.jar` files to the build path.

So with Linux and Java, it's possible to use a 10+ year old LEGO brick, and it works just fine.

Compared to an Arduino, it is actually still quite attractive as an into to computer fun for teenagers: In one box, with batteries, you get a motor controller, sensor reader, and simple display and "beeper". With an Arduino, you'd have to add a battery box, speaker, motor shield, LCD, plus put that all into an enclosure.

Great Planes ElectriCub

First Cub was an ElectriCub in 1996, with original Mabuchi 550 type can motor and NiCd. Flew OK, but nothing outstanding.
Second was the 20-sized Great Planes Cub with OS FS 26. A lot of fun in the air, but often hand-launched because hard to control on the ground.
Now found another ElectriCub kit on EBay. Came with yellow MonoKote, though unfortunately plain yellow, not the special Cub Yellow. Built it in about 6 month.

Outstanding flyer with 3 cell LiPo, brushless motor. Added ailerons, approximately scale sized, but forgot to remove dihedral from original kit design, so very little effect.Mixing rudder to airleron for relaxed flying. Second image shows transmitter in 'winter bag' for cold weather flying.

Futaba 9C Throttle Lock

To get a "Throttle Lock" for electric motors on the Futaba 9C while not in a heli mode:

• Select one of the programmable mixes
• SW: E, Posi: Down
• Mix: On
• Mas: Thro, Slv: Thro
• Link, Trim: Leave Off
• Offset: 0% (Throttle stick to idle, then hold rotary for 1sec)
• Rate 'down': +100%, 'up': -100%

Similarly for the T8FG:

• Offset Y at -100
• Rate -100 for both directions

Super Slinky

This was a free plan in the January 2013 R/C Model Aeroplane magazine, by Alex Whittaker, including
 "...ye olde health warning. Super Slinky is the Yorkie bar of simple sportsters. She's not for girls, the faint-hearted, Guardian readers, those of a nervous disposition or Southern jessies. She's no trainer, follow-on trainer or first low winger. She's for experienced pilots, aerobatic hooligans and unrepentant throttle benders. The truth is, she's a very bad girl."

With a warning like that, I couldn't resist. The original idea of the plan is a very quick build. One type of rib, box fuse, plank tail. Of course it took me 3 month, using stick-build tail, one extra wing bay, and in general every attempt to not rush it.

Wingspan	110 cm
Length	90 cm
Area	27.5 dm2
Weight	1275 g
Loading	46.4 g/dm2
Airfoil	Semi-Symmetrical
Engine	OS 25

First flight was on 2013/08/01, thanks to Bill L. for providing the wing rubber bands! Very easy to fly, maybe as a result of slightly larger wing and CG abt. 2cm in front of main spar, since several internet posts warned about a CG that is too far back. Later used the "Brush Script Std." font as template for wing marking.

"Throttle Hold" for RC boat or car

The Futaba T8 has a "smart" throttle hold option, meaning: The throttle hold will only engage when the throttle stick is close to the low position. Makes sense for an airplane or helicopter that uses a range of idle-to-full throttle. Does not help with a car or boat where you want reverse/stop/forward.

For a boat I wanted the throttle hold to hold the throttle output at 50%, but the built-in throttle hold function would only engage after moving the throttle stick near the full reverse position.

Fix: Use throttle curves.
Curve 1: usual 0..100% linear curve.
Curve 2: Always at 50%, with switch "SF" to engage, the same one I otherwise use for throttle hold.

How to Glue ABS?!

.. can be like trying to nail Jello to the wall.

While starting on a model boat project that involves an ABS hull, the question came up how to best glue things to plastic: Wooden bulkheads, deck, metal drive tube, other plastic parts, ...

This specific boat I'm about to build is a Graupner Bugsier 3. Its hull is made from ABS plastic. For what it's worth, the site http://www.kuederli.com/bugsier3/ has a very nice description of building this kit. It does mention re-enforcing and sealing the hull with epoxy and glass mats, but doesn't mention a specific type of epoxy. Based on what I learned, plain epoxy will not work at all. The kit's instructions recommend Stabilit Express. Stabilit Express is a very good 2-component glue:

• Nicely bonds to ABS, wood, metal, anything
• Gap-filling
• Sets in a short time
• Can be drilled, sanded

...but it's very hard to obtain outside of Europe. http://www.hobby-lobby.com/ used to sell it, but won't any longer. Ordering it from German companies like Conrad seems impacted by shipping restrictions.

So I tried various glues in a very unscientific way: Glue snippet of ABS plus piece of wood to ABS, see how it holds up to me trying to pull it apart.

Here's what didn't work:

• Various Epoxies (Tower Hobby, DevCon 30 min, UHU Plus endfest 300, Loctite Heavy Duty 5min, ...) - Usually a good bet for any glue task, but doesn't stick at all to ABS.
• JB Weld MarineWeld, PC-11 Marine Epoxy - May be more resiliant to UV and water, but don't help with ABS.
• Alumilite casting resin - Seemed like a good idea for flowing into bottom of hull to make is watertight, closing every little pinhole, but peels right off the ABS when hard.
• JB Weld - Won't stick.
• Gorilla glue - The foaming polyurethane variety. Very messy, doesn't stick to ABS. 
• Contact cement - Spread on, let dry, then press parts together. Seem to stick, but separate easily once the glue dries.

While most of the above would initially appear OK, the hardened glue will simply 'pop' off the ABS as soon as you slightly deform the ABS or pull a little stronger.

What works with ABS:

• Stabilit Express - we knew that.
• UHU Hart - Nice for bonding wood to ABS, but also hard to obtain in the USA.
• Acetone - sneaks into smallest gap, melts the ABS, gives perfect bond, but needs perfect 'fit'. Not gap-filling at all, doesn't bond to anything else. 
• ZAP Slo, gap-filling CA - May be even better if surface is wetted with acetone just before adding CA. Since the
• DevCon Plastic Welder, 'cream' colored - Smells a lot like Stabilit Express, may be the closest to it.
• Loctite Plastic Bonding System - A pen-type heptane activator plus a CA-type glue. 
• Loctite Plastic 5min Epoxy - Not to confuse with regular epoxy, this one somewhat works on ABS, but not as well as DevCon Plastic Welder nor the CA-type Bonding System.