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HomeAircraftHelicopterBergen R/C Helicopters › Minicopter Acrobat gear ratio and head speed help
02-04-2008 09:29 AM  10 years agoPost 1
lookdigital

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Poland

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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

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02-04-2008 01:32 PM  10 years agoPost 2
Chris Bergen

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cassopolis, MI USA

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

Chris D. Bergen

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02-04-2008 02:26 PM  10 years agoPost 3
lookdigital

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Poland

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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

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02-05-2008 01:52 AM  10 years agoPost 4
Chris Bergen

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cassopolis, MI USA

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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 D. Bergen

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02-05-2008 07:22 AM  10 years agoPost 5
lookdigital

rrNovice

Poland

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

Darek

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02-05-2008 01:15 PM  10 years agoPost 6
Chris Bergen

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cassopolis, MI USA

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

Chris D. Bergen

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02-05-2008 01:33 PM  10 years agoPost 7
lookdigital

rrNovice

Poland

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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

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