Iranian Army Bell 214 ‘Big Lifter’. Builder/pilot – Rob Leigh.
The mechanics in this model are over 30 years old and it has undergone numerous transformations over the years. It started life around 1978 and was purchased from Dave Neiman models as a UH-1B Huey ‘Iroquois’ in kit form from Hirobo. Utilising a 45 size IC engine, it performed well until a light crash prompted my father to upgrade the head to the MkII, extend the blades, upgrade the power plant to an OS 61 FSH and with the purchase of a new Bell 214 Fuselage, it was transformed into a ‘HeliSwiss’ rescue Helicopter. This was flown for a few years, until she was retired to the loft. In January of 2011, I decided it would be nice to get ‘the old bird’ back in the air. I completely stripped her down to the last nut & bolt and rebuilt from the ground up.
After approx. 400 hours and around seven months she was finally flight ready. She was started for her initial test and it was soon apparent that due to the extra ‘scale’ weight generated by the cockpit, paint and extra detailing. The old ‘OS’ was not going to be able to sustain her in the air, without overheating!
In this latest re-incarnation, she has now been converted to electric power, utilising the original mechanics, exhaust holes filled and re-sprayed and keeping the original clutch. This gives an authentic sounding spool up, which was the hope with this new design. The heli sports a Scorpion 4035 400KV motor, with a Hawk 120Amp High Voltage speed controller.
It is running 2 x 6S 2600MaH packs.
My ratio is 10:1 and this gives a head speed of around 1200rpm, although the KV/Cell count is a little too high, as I am only running the throttle curve at about 35%. Ideally it should be around 80% for maximum efficiency.
I perhaps should have gone for a 330KV motor and ran it on 10S, as opposed to 12S. Running as above though, the packs, motor & speed controller barely get warm, so it’s not really a problem. The choice of using 2 x 6S packs was because I have a T-Rex 500 using the said packs, and I wanted to be able to use the same ones. I probably could have gotten away with a 4025 Scorpion motor as well, as it’s got loads of power. But it was difficult to know as it was a bit of an unknown quantity.
Rob.
Single-point threading, also colloquially called single-pointing (or just thread cutting when the context is implicit), is an operation that uses a single-point tool to produce a thread form on a cylinder or cone. The tool moves linearly while the precise rotation of the workpiece determines the lead of the thread. The process can be done to create external or internal threads (male or female). In external thread cutting, the piece can either be held in a chuck or mounted between two centers. With internal thread cutting, the piece is held in a chuck. The tool moves across the piece linearly, taking chips off the workpiece with each pass. Usually 5 to 7 light cuts create the correct depth of the thread.
The coordination of various machine elements including leadscrew, slide rest, and change gears was the technological advance that allowed the invention of the screw-cutting lathe, which was the origin of single-point threading as we know it today.
Today engine lathes and CNC lathes are the commonly used machines for single-point threading. On CNC machines, the process is quick and easy (relative to manual control) due to the machine’s ability to constantly track the relationship of the tool position and spindle position (called “spindle synchronization”). CNC software includes “canned cycles”, that is, preprogrammed subroutines, that obviate the manual programming of a single-point threading cycle. Parameters are entered (e.g., thread size, tool offset, length of thread), and the machine does the rest.
All threading could feasibly be done using a single-point tool, but because of the high speed and thus low unit cost of other methods (e.g., tapping, die threading, and thread rolling and forming), single-point threading is usually only used when other factors of the manufacturing process happen to favor it (e.g., if only a few threads need to be made,[6] if an unusual or unique thread is required, or if there is a need for very high concentricity with other part features machined during the same setup).