Headspeed limit for 1.8m rotor diameter

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Home › Scale › ✈️Aircraft › Scale Heli › Vario Scale Helicopters › Headspeed limit for 1.8m rotor diameter

05-08-2020 07:35 AM 18 days ago

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Makiedog

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Headspeed limit for 1.8m rotor diameter

For my cobra, I'm using 419 GRP blades (810mm) mounted to Vario metal grips (don't remember part #). Is it not safe to run at 1300 rpm? Am I supposed to stay under 1200rpm?

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05-08-2020 11:03 AM 18 days ago

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Notar

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1200-1225 is good.Its not the blade grips since they are metal, its the blade or blade bolt which could fail. How big is the blade bolt?

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05-08-2020 08:42 PM 18 days ago

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Makiedog

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Joe,
There bolts are 4mm with the unthreaded shoulder. Here it is running at 1200 rpm, I think I'll live with it.
I was also advised not to use the Vario 40° angled tail gear box with the plastic gears for this size heli. I've since ordered the replacement metal gears which will help me sleep better.

Watch at YouTube

Pat

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05-08-2020 08:51 PM 18 days ago

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Notar

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The only other upgrade would be to get new grips and the 5mm bolts for the blades. But the grips would be GRP, not metal. It should fly fine like it is though.

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05-09-2020 12:27 AM 17 days ago

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Makiedog

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Joe, what about the 40° grear box? Someone now tells me metal gear upgrade will still not be sufficient to handle model this size. They say it is the weak plastic casing that will fail because it will flex when heavily loaded. What is your advice?

Pat

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05-09-2020 11:34 AM 17 days ago

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Notar

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That is a big model and that is possible. At one time the Vario turbine cobra had this gearbox, and it failed, resulting in them using the larger gearbox with the 8mm torque tube. If you have a 6mm torque tube in there i would rethink the drive system.
What is your all up weight?

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05-09-2020 03:49 PM 17 days ago

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Makiedog

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28 lbs with everything. It is about the same size as Vario's own Cobra, which uses the same plastic gear box and drive system.

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05-09-2020 03:56 PM 17 days ago

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Rojoalfa

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Notar The only other upgrade would be to get new grips and the 5mm bolts for the blades.

/
/

That is correct.

Talking about rotors headspeed limits, the weakest part is not the bolts! It is the grip and of course, The blade.

Talking about tail rotors, we know it's handle about 4% of total rotor torque.
The larger the boom, the less torque it handle.
The larger the tail rotor diameter, tail servo handle same force. The difference is the tail pitch angle.

Turbines .vs. gas motor.

Good point.
More torque means more driving forces... So metal gears.

/Saludos cordiales,

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05-09-2020 07:39 PM 17 days ago

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Notar

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Vario Benzin Cobra does use the plastic gearbox. The turbine version uses the metal unit. The turbine version weighs in at 28 lbs while the electric benzin version comes in at 21 lbs. You can see where you end up at as far as weight.

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05-09-2020 08:42 PM 17 days ago

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Rojoalfa

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/
/

Electric helis... I forgot it.

Constant torque... No matter what rpm is working... Metal gears.

/Saludos cordiales,

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05-10-2020 12:56 AM 16 days ago

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Makiedog

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Notar Vario Benzin Cobra does use the plastic gearbox. The turbine version uses the metal unit. The turbine version weighs in at 28 lbs while the electric benzin version comes in at 21 lbs. You can see where you end up at as far as weight.

Joe, despite being electric, mine is heavier because it's larger (1/6) and has a fully stuffed cockpit. Which metal gear box should I go with that requires the least amount of bulkhead surgery? I see that their mounting method is very different than the plastic gear box.

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05-10-2020 06:05 PM 16 days ago

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Notar

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Take a look at the build instructions for the turbine cobra. You will also have to change the torque tube to 8mm to make it work.

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