Hirobo AH-1W Super Cobra
This will be my second scale helicopter and I intend to add much more detail to this one.
The model specifications are as follows:
- 1/9 scale (approx).
- Main Rotor diameter - 1,550 mm (61.02 “).
- Fuselage length - 1,450 mm (57.08 “).
- Overall weight - 5,800g (12.79 lbs) without engine, electronics and fuel.
- Engine: O.S. 91 RZ-H rear exhaust.
- 120 degree ccpm control system.
- Stainless steel shaft driven tail rotor.
- 130-degree angled transmission.
I will also be adding an onboard start system which means I will be able to start the helicopter from the transmitter.
The build log
The fuselage has now arrived! Shown below is the freshly painted body with the undercarriage temporarily fitted.
This is the M197 3-barreled 20 mm "Gatling-style" cannon in the M97 turret, painted and ready to be added to the SuperCobra.
Shown below is the gearbox for the tail drive shaft. This has had lithium grease applied to the gears, and re greasing will be part of the regular maintenance schedule.
Here is the completed tail assembly. I exchanged the white plastic Hirobo tail blades that come with the kit for these black carbon fiber Align blades. I think they look more scale.
Here is the assembly added to the fuselage plus the piano wire that will be used by the tail servo to control the tail bade pitch.
You can see the piano wire more clearly in the picture below. The wire is threaded through a thin brass tube that is already installed in the fuselage and runs through to the front of the helicopter where the mechanics and servos will be installed.
The next step will be to install the fiberglass tube into the tail section and through this will run the drive shaft. The tube and drive shaft can be seen below.
The tube needs to be epoxed into place and to enable the tail end to be epoxed against the installed bulkhead I will need to make a small plywood washer which I will do on my CNC router.
All the components for the build have now arrived. Some highlights are;
- O.S. .91 RZ-H Ringed rear exhaust engine
- Futaba S9452 digital servos for CCPM and throttle
- Futaba GY401 gyro and S9254 tail servo
- 690mm V-Blades
- JR R921 9 channel DSm2 2.4Ghz receiver
- Gem 2000 HeliLites with 4 Led (for nav / anti colision lights etc)
- Duralite 6 volt regulator with heavy duty switch
I balanced the fan on my Dubro balancer.
This is the lower mechanics assembly with the engine, fuel tank, muffler and clutch all in place. Also attached is the throttle servo which is on the other side of the frame. The tail servo is mounted in the fuselage of the cobra and therefore the mount in the frame is not used.
As I have decided to add a CSM Smartcarb to this model to, I will use the frame tail servo mount for the Smartcarb servo. The metal blocks supporting the assembly are just to keep the weight of the assembly of the muffler underneath.
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This is a close up of the engine mounted in the frame. You can clearly see were I modified the fan shroud to fit around the top of the cylinder head as the head on this particular motor protrudes beyond the shroud.
This is the top frame where the main shaft bearings are mounted along with the three cyclic (CCPM) servos and the onboard starter.
Next to the frame you can see the starter motor along with it's gears. This will ultimately be mounted to the frame.
So now for a little bit of detailing work. I have bought a Gem2000 heli light controller which gives me one flashing red led and a red, green and white leds.
The stock nav lights etc that come with the kit just have a molded plastic "light" with the appropriate color applied.
Below is the stock "flashing" anti-colision light that goes on top of the cobra.
My first task was to cut out the red dome, then fill the remaining hole with a piece of plastic card which was the filled and sanded.
Below you can see the part after cutting a 1/4" hole for the red lens and repainting.
Also you cam see the rear tail light body after carving out the plastic to enable the clear lens to be fitted along with a LED. For comparison I have also included in the picture a unmodified body (the green starboard light).
Here are the two completed parts ready for the LED's and mounting onto the Super cobra.
The lights added to the fuselage along with the front gun.
This picture shows the refueling point added to the fuselage. The cap comes from Slimline Products.
To refuel you pull the cap out, unplug it from the fuel line and then reverse the process when complete.
Here you can see the mechanics temporary installed in the fuselage. The swash plate has now been added and setup.
You can also see part of the tail drive shaft.
I still need to figure out the placement of all electronics which apart from the normal items also includes the onboard starter, light controller, CSM SmartCarb and CSM Revlock 2 governor.
This is another picture of the mechanics out of the fuselage. This is the port side.
...and the starboard side.
...and here is one of the pilots eager for me to get finished so he can go flying. He does not know yet that he will be undergoing major surgery to shrink him down to fit in the cockpit!
I built (using my CNC router) a mechanics test stand to enable me to test and ultimately tune and run in the engine before I put it into the fuselage. I decided to do it this way as it will be easier to get to everthing.
Below is a short video of the first start of the engine using the on-board starter system. In this case I did not use the on-board glow igniter part of the system as the earth lead had not yet been fitted.
I wanted to be able to adjust and run in the engine before installation in the fuselage as it will be much easier (and safer) that way.
There are two ways of doing this. I could just attach the engine to a bench test stand and use an airplane propeller (to give the engine a load and avoid damage to it), but this would not allow me to check all the mechanics, electronics and linkages. A better way is to build a test stand for the whole mechanics, but in this case I needed something to apply a moderate load to the engine. Obviously attaching the main blades could lead to a flying test stand!
Vario offer a engine running-in aid, (check it out here vario run-in aid) , but it costs $74 plus delivery, so I decided to make my own, which can be seen below.
Here it is mounted on the mechanics which are mounted in the test stand I built.
This run-in aid will allow me run the engine in at various speeds without actually having to fly the helicopter. This aid should prevent any damage to the engine right up to about 3/4 throttle.
If anyone is interested in one for a moderate price, please let me know.
more to come...
