Need For Speed: Goblin Comet

Need For Speed: Goblin Comet

SAB Helidivision comes with a completely new refined and exclusive model called the COMET. The goblin COMET delivers a new concept to the market for the speed freaks with its innovative structural layered carbon fuselage. The Comet supports three functional modules, the main rotor, tail rotor and battery pack which guarantees a low parts count, delivers easy maintenance and all of this defines the Comets elegant simplicity.

UNBOXING

The Comet kit comes in a very large but thin box with the famous green Goblin logo printed on the outside. When I first received the kit I thought there were two Comets inside but when I opened it up, it was clear to me! A very big box for the canopy that comes very well protected in a foam mould and off course the fuselage is a one-piece part that is quite long. After opening the box we find five smaller boxes that are all marked and makes it easy to find the parts we need later on in the manual. The CNC parts come protected in foam trays to avoid scratching. The rest of the parts come all well marked in plastic. All are numbered and correspond to the assembly procedure in the manual.

The manual is visually appealing, it’s printed in full colour. Inside we can find the different ratios and configurations suggestions. It is very important to choose the correct ratio that maximizes efficiency depending on the motor, pinion and rpms we want to fly.

SAB also included a useful sheet with points to be reviewed during maintenance. Includes a full list of spare parts with images which is very useful when we need to order any part.

The goblin is a helicopter which needs regular maintenance and does not only need to checked after a crash. Therefor SAB has included a sheet that explains the important parts to check.

THE MODEL

Thanks to its design, the performance level is very high. The patented drive system by SAB that is used all other Goblins has been used on the COMET. It uses a belt drive system that efficiently transfers engine power to the rotor. The 19T motor pinion uses a belt that moves a 60T pulley. This pulley has mounted below one transmission pulley that drives the tail-belt. At the top of the pulley we have the steel helical pinion that attacks the steel main gear, which eventually moves the rotorhead.

Different to the standard goblins, the servos are now mounted vertically instead of horizontally. The linkage rods are connected directly to 120° CCPM swashplate. This forms a very rigid and accurate assembly. This method allows the maximum lowest center of gravity, and increase performance to the max.

We are used to see with all the other goblins a central part made of a aluminium frame tray but with the Comet SAB did a complete new design on the frame and made like a small very strong aluminium cube. All the servos are mounted to this cube and on a later stage also the motor mount and the ESC tray. This frame is easily removable from the Comet fuselage for maintenance whenever we need.

The tail uses a simple belt drive system with a tail belt idler made of column tensioners mounted on the motor mount. The comet is designed to work at 14S (58.8V). Current Brushless motors are very powerful, and it is important to take advantage of that energy. With the double belt system, the Goblin Comet handles this energy very efficiently.

As with all the other Goblins the Italian design is unique. Visually its very attractive as the canopy binds with the tail boom made fully of carbon fiber. Its streamlined design gives the Goblin incredible speed capabilities. The tail system eliminates vibrations of the tail rotor at high rpm. It is strong and lightweight.

The new rotor head of the Comet comes with black matte components. This new head is has been completely redesigned Pivot center hub. More details on the rotorhead later.

SAB is known worldwide for manufacturing RC carbon fiber blades. The Comet had to include them. In the box we find a set of the new Thunderbolt 720mm main blades and 105mm tail blades in Black, white and red colours.

MAIN FRAME

The frame is composed of two aluminium side cases. In the front part there is mounted a special ESC support were we need to install later the carbon tray to install the ESC. The carbon fiber ESC anchored to the support with two M3 screws and can be regulated in height depending on the size of battery packs we are going to use. The battery tray is made of carbon fiber and aluminium and has a very clever locking system onto the frame with a newly designed locking system.

The standard landing gear on the Comet is a two shaped fin. Goblin offers an additional retractable landing gear if you would like to change it or if you are going to do some serious speed. In this review we used the standard landing gear but after making the picture we decided to use the optional landing gear since we decided to do some real speed with this model at the competitions around the world. The original landing gear that comes with the kit is made of carbon fiber and comes in a red color and is mounted directly to a special support inside the tail fuselage.

Its very well explained in the manual were to put which glue or locktite but we always recommend those screws threaded into metal to apply a little lock tite to the screws. It is very important to use it well to prevent stripped bolt heads or broken screws. Its sufficient to apply a little on the tip of the screw (aprox.1mm).

This structure comes standard with two bearings mounted in the main support and top plate. The bearing for the 12mm main shaft on the main support plate is really big to support the great forces when flying at high speed. The other two bearings are for the 10mm secondary shaft. Between these trays we need to mount the full transmission system.

Some parts are factory pre-assembled. I always check everything to ensure the correct assembly and if threadlock is applied. The frame is held together with M3x8mm socket head screw. The carbon fiber anti rotation guide is mounted directly to the upper main support. The 68T main drive gear is helical and comes in Aluminium instead of delrin to hold out all the forces applied to the mechanics when flying fast. The tail belt tension columns are mounted on the lower part of the motor mount. The tension of the tail belt idler is adjusted moving the whole mainframe assembly on the fuselage.

The SAB manuals one of the best I’ve seen with very clear and detailed drawings. The manual indicates us that we have to grease the one way bearing of the 60T pulley and on the main gear, we recommend to use Dryfluid Heli and Gear Lube here, in our opinion its one of the best grease on the market. The motor mount is located in the rear of the main frame. On the Comet no damping springs are used like with the other goblins. Depending on which motor we mount we have to take into consideration the length of the motor shaft, the manual gives you the ideal length (34mm) so its easy to find the appropriate shaft or shorten the one already on the motor. The kit comes with a 21T pinion. In my case with the Kontronik Pyro 1000-48 I mounted the optional 24T pinion to achieve the 8.9:1 ratio and get 2800 RPM maximum. This pinion does not attack directly the main gear but uses a belt drive system.

MATT BLACK PIVOT HPS ROTOR HEAD

The Pivot rotor head comes pre assembled in a box. The manual explains very well where we need to apply thread lock and grease. The rotorhead consists of a newly designed pivot center hub, blade grip arms, radius arms, linkage rods and dampers.

Dampers used are made of delrin and together with a O-ring are mounted inside the center Hub. Each blade grip has two radial bearings and one thrust bearing. In kit includes several washers to control the play of the spindle shaft. In the manual recommends using one 1mm washer and one 0.2mm washer on each side. If the blade grip feel very rigid we need to removed the 0.2mm washers. Its recommended to check for axial play of the spindle after the first flights. If the play has changed you can add one or two 0.2mm washers.

The linkage system used is with turnbuckles. In the middle of the linkage we can find a small hole through which you can pass a 1.5mm hex driver to accurately adjust 0 pitch on the head.

The swashplate on the Goblin Black Thunder comes also in a matt black colour to match the rotorhead.

FUSELAGE

The tail is one of the characteristic items of a Goblin. The boom has nothing to do with a traditional tail boom and even less on the Goblin Comet. SAB manufactured a fully carbon fiber fuselage that comes factory painted to continue the colours of the canopy. The comet hast two different paint schemes available, Black/Red and Yellow/Red. We decided to go for the Yellow/Red version because of the visibility when going very far away during speed runs. It is rigid enough so no need for tail boom supports. Another curiosity that the whole frame assembly just anchors into the fuselage and is held in place by six screws. This makes it really convenient if we need to do any maintenance to the model.

The tail servo is mounted upside down on the lower front part of the fuselage. The fuselage has a oversized carbon rod through which we need to slide the tail push rob. The tail push rod is made carbon fiber. It is important to protect the tail servo cable and use some servo braid to avoid the cable can be damaged, it is also very important to secure all the wiring very well inside the fuselage before mounting the main frame assembly on top.

Nowadays we are very used to see all the helicopters using torque tube drive system but the Goblin also decided to go for the proven tail belt drive system on the Comet. The overall design is very simple and easy to assemble with very few parts. Most of the parts like the locking reinforcements and tail servo locks come pre-assembled by the factory in the box. Although you need to check everything and ensure correct installation. The tail rotor assembly comes also entirely in matt black aluminium. It uses a traditional double tail pitch slider. The tail box is formed of two matt black aluminium case side plates. To mount the whole tail case its done by four M3x6mm button head cap screws. The tail uses a 27T pulley on the tail.

The COMET canopy uses a magnetic locking system. Use the specially designed carbon fiber lever to remove it. Fit the canopy starting from the bottom pins. During the speed flight SAB recommends the use of elastic to hold the canopy in position although in the latest kits there has been a small upgrade with a specially designed screw to hold the canopy in place. This is done because when performing a hard upward pitch it may cause the fuselage to deform making it high risk that the canopy will move from it’s original position.

A small note which also can be found in the manual is that the boom zone uses a „carbon sandwich“ solution. Excessive localized pressure can damage the structure internally. Please be careful, for example, do not crush.

RETRACTABLE LANDING GEAR

Optional motorized landing gear (H0742-K) pushes the boundaries even further maximizing the unrivalled speed performance. Any standard landing gear acts like an airborne brake. To get the best performance, the landing gear must retract into the fuselage.

This KIT uses an electric motor that powers the landing gear allowing full retract. The device functions just like a servo. You will need to use a receiver channel and combine it with an on-off switch powered directly from the receiver channel (7.4V). With a 0-100 signal, you can control the extension and retraction of the landing gear.

COMET FRONT AIR INTAKE

The front air intake forces the air through a narrowing channel accelerating the air flow. The super accelerated air maximizes the streamline effect as it sweeps away the vortex generated in the landing gear area.

SETUP

The basic setup of this model used in this review is the following with a VBar Control transmitter and VBar NEO Flybarless system.

Since this was the first Goblin Comet and speed machine I have ever build I was unsure about the settings and setup so I took the basic setup of the Vbar NEO as a starting point. We tested various settings and this is how we liked it the most. On the main rotor settings we use an Expo of 40, Style is set to 100, Rate++ to 110 and a head gain of 60. For the tail we use expo at 20, Rate++ at 90 and tail gain is set to 45. The settings are always a personal choice but this is the way we liked the model the best, if someone has any further questions about the Comet and its settings just send me a message on facebook. We used a Kontronik CoolKosmik 200A so we can set 3 different head speeds and programming the CoolKosmik with Mode 4. The correct ratio as previous explained with a 24T pinion and a 480KV motor is 8.9:1. The motor has 480KV and we used a 14S setup with SAB 4800mah Competition 60C packs and the 24T pinion.

THROTTLE CURVE

Flight mode % Aprox. RPMS
Bank 1 60% 2100rpm
Bank 2 75% 2600rpm
Bank 3 90% 2800rpm


Pitch curve have been set in all flying modes to -10 at low stick, 0 at mid stick and +16 at high stick like recommended in the manual.

BREAK-IN

As recommended in the manual and it is important that you need to make sure you break in the heli for a few flights before you go crazy. SAB recommends a few flights at around 2100RPM mainly to get the metal-on-metal main gear system to bed in a bit. I spent about three five-minute flights doing some smooth and light 3D, circuits, and simple big air manoeuvres just to put the system through some varying loads and flight conditions. Be sure that for these first flight you keep the main gear and drive pinion well lubricated. The lube tends to get spun off the gear while flying, so I re-lubed it before each of the first few flights. Once you’re done with this break-in period, you can fall back to lubing it the earlier of once every 20 flights or when it starts to look dry.

GENERAL FLIGHT CONSIDERATIONS AND SPEED FLYING

Now that the heli has been broken in a bit, we can move on to actually speed-flying it. For this, I set my transmitter up with two main speeds. In bank 1/2 we set to a lower head speeds around 2100RPM / 2600RPM. This gives me the ability to take off and land in a safe and low-speed condition or do some sport flying. Then, my bank 3 was set to the speed that I planned to fly my speed runs for that flight. I decided to go for 90% throttle curve to avoid regulation of the governor during a speed run and gives me with my ratio the head speed of 2800RPM and the collective has been set to 16 degrees.

Take off in bank 1 or 2 at your low head speed setting and observe the heli for a few seconds. Check for shakes, wobbles, sounds, wags, or anything else that doesn’t quite seem normal. Remember, when you raise to higher head speed in my case 2800RPM, there’s a whole lot more stress on the machine than at 2100RPM, so something weird-looking in bank 1 or 2 may turn into something catastrophic in bank 3. Please don’t start your heli at 2800RPM at take-off, it’s unsafe, scary, and isn’t going to do your batteries any favours once you get to the actual speed portion of the flight. I know that there are some ESC that doesn’t allow you to start with lower head speeds so maybe they can lift off a little bit more out on the flight line.

I can recommend you practice your right-to-left and left-to-right turns on another, slower heli so that you’re equally comfortable on both sides. It was time to go for the first speed run, the Comet already flew very fast to the right hand side of the fiel at about an 100 meters were I started to pull up into the turn, this can be a stall turn or a roll and coming back down. This part of the run shouldn’t be any different than your typical, everyday turn.

Once you’re at the top and turned around check for any unwanted roll attitude. In other words, at the top of your turn when doing a stall turn, you want the disk facing directly across the field in the direction you’re going to be traveling and your nose pointed straight down. Now, let the heli drop into the “course” and begin adding back elevator and positive collective until you level out at around 20 meters in altitude (higher if you need to still get comfortable with things).

When you first start flying speed you don’t really need to worry about using up all your collective…instead, focus on a smooth addition of both elevator and collective and a clean (not jerky) transition from vertical to horizontal flight. Eventually, you’ll get better and as your heli turns the “knee” from vertical to horizontal, you’ll get your timing down to the point where you will have full collective applied just as you hit level with the field and you’ll be able to hold a straight line with little to no elevator input and the nose tipped forward at a 15-30 degree angle.

After this its not over yet the Goblin Comet is still moving really fast, so pay attention! You’ve got to get yourself back up into your next turn before it’s too far away. Again, let the heli travel about 100 meters past you in the opposite direction and then begin to remove collective while simultaneously adding back elevator. This is a really important part of your run because if you pull up with too much elevator or too much collective, you can cause your power system to over-current. This is because you’re at the end of a 5-10 second sustained run at 150-200A, which puts your battery in a vulnerable position due to voltage sag and then you accidentally pull up with too much pitch and there will be a huge current spike!

The kit includes a sheet named (important tips for proper assembly). Here SAB explains some of the key points of the helicopter where you should pay attention. Although helicopters are prepared today for more speed and 3D all have wear and require maintenance. Sounds like a good idea that SAB includes a sheet with Tips & Tricks.

THE NEW THUNDERBOLT BLADES

The „SAB Thunderbolt Blades“ are made to grow the performance of your helicopter. The amazing design was developed not only for an esthetical purpose, but it also improved the visibility of the tip of rotor, higher visibility is necessary in very low manoeuvres. The variable profile along the radius of the rotor makes the „SAB Thunderbolt Blades“ 20% more efficient in comparison to the „SAB black line blades“ and gives great stability to the whole helicopter without compromising the agility of the rotor. The chord varies along the radius of rotor (Shorter at the root, larger at tip); thanks to the aerodynamic of the rotor, gives more thrust exactly where the rotor generates it, that allows harder and more precise manoeuvres in flight. To improve the stiffness the „Thunderbolt Blades“ includes double layer of unidirectional carbon fiber.

In order to guaranty safety in the event of a crash, we include a steel safety wire alongside the leading edge of the blade.

SAB GOBLIN COMET

General Specifications:

  • Main rotor diameter: 1626 mm with 720 mm size blades
  • Pivot Head
  • Tail rotor diameter: 282 mm with 105 mm size tail blades
  • Approximate weight RTF: 4280 grams (excluding flight battery)
  • Cyclic Servos: Standard size (40mm)
  • Tail Servo: Standard size (40mm)
  • Typical battery setup: 12S – 4200mAh, (from 3700 to 5200)
  • Typical ESC setup: 200A
  • Motors: Max Diameter: 64 mm, Max Height: 80 mm 4530, 4540, 5030 series (480 to 560 kv)
  • Battery compartment: 2x 165x55x55 12S-5000mAh, 14S-4300mAh, 14S-5000mAh

Manufacturer: SAB GOBLIN
Web: www.goblin-helicopters.com

Kit Includes:

  • 720mm ThunderBolt main blades
  • 105mm ThunderBolt tail blades
  • Motor Pulley 21T (other pulley sizes available)
  • 1 Battery Tray

Equipment used…

Blades: SAB Thunderbolt 720mm
Flybarless: Vbar NEO
Cyclic servo: BK Servos BLS8001HV
Tail servo: BK Servos DS-8005HV
Battery: 2x SAB Competition 60C 4800mah 7S
Motor: Kontronik Pyro 1000-48
ESC: Kontronik CoolKosmik 200A