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Humbug |
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Humbug |
This model was a cheap rubber-powered freeflight kit, which I am completing for another modeller. Our intention is to convert it to electric power with radio control. Empty airframe weight is 50gm, so I am aiming for a flying weight of about 100gm. The model's wingspan is 520mm (20.5 inches) with wing area of 5dm 2 . This gives a wing loading of 20gm/dm 2 (7oz/sqft), which should be acceptable for a model of this size.
A small but powerful motor is required. I extracted the film-advance motor from a broken 35mm camera. It weighs 12gm and draws about 1.2 Amps on 4.8V, when geared 3:1 and driving a 180mm (7 inch) prop. The gearbox is homemade, using a floppy drive head guide rail for the prop shaft, ball bearings punched out of a 2.5" hard drive, and nylon gears from a trashed CDROM drive (I have collected a lot of old computer parts!).
To mount the propellor I superglued a nut and aluminium retainer onto the end of the prop shaft. This holds the propellor securely using a short rubber band, but allows it to bend out of the way if it strikes the ground. This was absolutely required to prevent damage during landing, and it works very well (I just have to keep a spare rubber band handy in case it flies off into the grass and gets lost!).
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| prop retained with rubber band | prop adapter detail |
The fuselage is made from 1.5mm sheet balsa and has enough room to house a 110mAh Nicad pack, GWS 4P receiver, Kontronic Micro10 speed controller and HS50 servo. These components are very light and meet my requirements admirably, but unfortunately my supplier was out of stock of GWS receivers. Therefore I took the opportunity to experiment with a Tyco "Canned Heat" radio system.
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| Tyco Rx and Nicads installed | "Still Life" with the Tyco Tx |
25th Jan, 2001:
Have done several flight tests. No rudder control yet, which makes for 'interesting' flights. Landings are quite hard without any ability to flair (no elevator) and the small wheels do no good in short grass. The body has suffered a few splits (easily repaired with superglue) due to badly trimmed flights. It also didn't like flying into a softball net! Handles wind surprisingly well. Climbs well but needed more positive wing incidence (must make a trimmable elevator).
The Tyco radio is reliable but has poor range. I have to run after the model to maintain control! Have since increased Tx antenna length (may need retuning).Installed a charging jack in the plane, so that the wing can be more permanently attached (still using rubber bands for now).
I am now working on making a BIRD (Built In Rudder Device) actuator. Latest attempt has a coil resistance of 40 Ohms. Will use a magnet taken from a floppy disk drive index sensor. All-up weight is now 105gm. Final weight is estimated at 110gm. Motor run-time in flight should be about 5 minutes. Hopefully sufficient power can be maintained to keep the plane in the air for this long.
3rd March, 2001
I have now installed a BIRD rudder control. Despite the rather weak force it produces, there is plenty of control in the air. I will have to straighten the motor's thrust-line as the plane tends to pull to the right under power. Range is still poor, but I notice that it gets better at higher altitude. Next tasks are improve range and finish painting the model!
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| BIRD installed in rudder |
23th August, 2001
Changed the "Canned Heat" Tranmitter battery from 2 x AA Alkalines to 4 x 110mAh Nicads. This increases RF output power by about 400%, doubling range. Removed the plane's undercarriage, as it just caused the plane to nose over when landing in grass. Added some artwork, and painted on a cockpit window so the pilot can see where he's going!
11th November, 2001
First public flight. This model has no elevator control, so CG and decalage are critical. Today I must have got the trim just right, as the plane was responsive and relaxing to fly (I even managed a low pass for the camera!). Flight time was over 4 minutes of good climbing ability. After 5 minutes it could only just maintain altitude, time to think about landing...
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| Movin' on out ... | Low pass (pulsing the throttle!) |