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Bergen R/C Helicopters > Minicopter Acrobat gear ratio and head speed help

lookdigital
New Heliman
Location: Poland

Hi all,
I want to put a ZG20ei engine on Acrobat helicopter
(there is an Octan Domintator heli that uses this engine, so I will
not be the first to use it for a helicopter)

according to your drawing http://www.toni-clark.com/ftp/ZG20_english.pdf
the best speed for ZG20 is around 9500rpm
according to Acrobat manual it has a gear ratio 8.15

for a heli main rotor should turn around 1500

9500/8,15=1165 on the rotor - this is a bit too slow

Am I right thinking that I should have gear ratio around 6,3
(9500/1500=6,3) to get the right rotor speed for the best ZG20ei
performance on 9500rpm

thank you

02-04-2008 09:29 AM

Chris Bergen
Key Veteran
Location: location

Your calculations look to be correct, but would need some in helicopter testing to be sure.

Chris Bergen

02-04-2008 01:32 PM

lookdigital
New Heliman
Location: Poland

Thank you Chris,
I have one more question

I think there is a rule: the longer blades, the lower rotor speed - I worry, that the engine may not be stron enough for 700mm blades, on the other hands according to the above rule - shall I try longer blades and lower rotor speed?

the Acrobat is designed for rotor speeds between 1350-1700

thanks

02-04-2008 02:26 PM

Chris Bergen
Key Veteran
Location: location

You will probably get better advice from Gerd at Minicopter. I'm happy to offer my thoughts, but I have no experience with the Minicopter Acrobat or the G20 engine.

We chose NOT to make an airframe with this engine due to it's low power to weight ratio. I'm sure it's great in an airplane, but the one time I saw it in a heli, I was not impressed....

You may have better luck in the Acrobat. My suggestion would be to keep to the smaller blades (680 or less) and gear the heli to run them at the highest speed the heli can handle, in your case, 1700 RPM in idle up.

Good luck,

Chris Bergen

02-05-2008 01:52 AM

lookdigital
New Heliman
Location: Poland

thank you Chris
I will contact Gerd about it, hopefully he will find some time for me

Darek

02-05-2008 07:22 AM

Chris Bergen
Key Veteran
Location: location

I have heard that Gerd is very good with customer service, sometimes that makes for a very busy day....

Chris Bergen

02-05-2008 01:15 PM

lookdigital
New Heliman
Location: Poland

He is, I used to mailed him and nearly bought an Acrobat, but then I changed my mind (someone convinced me) to go for a Cuatro and I gave up Acrobat

but I liked the Acrobat that I bought one on eBay 1/4 of the price

I hope he is not offended

02-05-2008 01:33 PM

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Bergen R/C Helicopters > Minicopter Acrobat gear ratio and head speed help

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