GPH Goblin 570 Conversion - Just Add Nitro

[ticedoff8]

Since this is the "600 Class Nitro Helicopters" section, I thought I'd contribute this here too.



I finished my G570 Nitro conversion using the kit from JC Designs sold by Gas Powered Helicopters
JC Designs Goblin 570 Conversion

I traded email with Carey at GPH and asked for two changes:
-- A 32t motor pulley (instead of the standard 34t)
-- The extended flight options (2nd fuel tank).

The extended flight frames add a 2nd (8oz (236cc)) fuel tank mounted at the back of the frame.
It is easily removable so I can decide when to use it or not.

The 32t motor pulley changes the main gear ratio to 6.46:1 instead of 6.08:1.
I was told there is a 30t motor pulley, but it requires a smaller belt

I am using a YS 96SR-X whose "sweet spot" is 16,500 RPM.
At 6.08 (34t), that is a 2700 RPM headspeed. Too fast for me.
At 6.46 (32t), that is a 2554 RPM headspeed - this is much closer to what is needed.

I also bought a "600 stretch kit" from Lynx (this makes it a "600 Class Nitro Helicopter)
I plan to run 600mm blades.

The kit is well engineered, well thought out and the manufacturing quality was top-notch.

After building it, I think the only question I have is:
"Why isn't the motor mounted with the glowplug facing front and the tank under the main-mast".
With the tank up front, it will suffer from the same old CG issues a fuel burns off as any of the old-school helis out there.

But, other than that, I think this turned out great

The kit comes with a 12oz (354cc) Sullivan tank (this was listed as optional, but is now standard), but I replaced it with a 16oz (475cc) DuBro tank
https://www.amainhobbies.com/dubro-1...-dub416/p29336
I drilled holes to locate the nipples and it is (I think), the maximum size that will fit under than canopy.
As a point of reference, the Trex 700 has a 660cc tank and the Goblin 700 Black Nitro has a 650cc tank.
At 475cc, the flight times with the DuBro tank will still be within a minute of the larger heli's tanks.

There are Align parts (I think) used in the kit's starter / clutch hub and shoes. But, based on about 500 flights on my Trex 700N, I don't expect any problems with those.

The machined parts are perfect.
The frames are a fiberglass / CF laminate (from what I can tell).
The outer layer is black material. I don't know if is CF or just black colored fiberglass.
But they are good quality and perfectly cut and drilled.

The conversion kit requires a "donor-copter".
I totally lucked-out in finding the perfect solution. A "once in a lifetime" opportunity
A seller contacted me about a complete G570 airframe with motor and a box of new in-the-bag parts from a 2nd kit.
The 2nd kit had been raided for parts to rebuild a different heli and "all that was left" was all the parts needed to build a donor-copter.
Literally, all I needed to buy (besides the nitro conversion kit) was a new Fusuno canopy (with the custom graphics "Nitro" logo added) and the Lynx 570 to 600 stretch kit.

The "ready to fly" (full fuel) weight is 9lbs 6.8oz compared to my stock G570 "ready to fly" (w/ 12S Glacier 3300mAh) at 8lb 3oz.

[Helicrow]

Hope to see a flying report shen maidened or maby a vid ? 😉 . Its seems heavy for its size 4.2kg compared to trex 600n 3.2kg. But maby the higher headspeed will make it feel abit lighter.

[Dennis Everett]

whats the cg like on a empty tank ?
to check if the frames are cf , use a ohm meter , cf is conductive.

[ticedoff8]

It weighs 9lbs 6.8oz full fuel and "Ready to fly".
At full fuel, the CG is spot-on perfectly on the main mast.
The "0 fuel" weight is 8lb 9.6oz and it is definitely tail heavy

I am going to remove the OptiPower Ultra-Guard 430 - that removes 1.5oz from behind the main mast and maybe offset some of the tail heaviness at 0-fuel.

But, I also extended the tailboom using the Lynx "570 to 600 stretch kit", so that moved the tailrotor mass out 30mm.
I expect that means I need to add about 15% of the tail rotor weight to the nose to compensate

And, I am using 600mm Align blades instead of the SAB 570mm blades (125g vs. 120g). They add a few more grams to the total weight, but doesn't affect the CG.

Due to the "conventional" placement of the tank (at the front), CG will be the same old compromise we have had for the last 30 years of RC nitro powered helis - a little nose heavy at full fuel and a little tail heavy at 0 fuel.