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HeliTorque :: View topic - why Rotax couldnot rotate my rotor?!
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HeliTorque Forum Index » Flight Dynamics

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why Rotax couldnot rotate my rotor?!
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sadegh_865
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PostPosted: Sun Aug 30, 2009 10:59 am    Post subject: why Rotax couldnot rotate my rotor?! Reply with quote

hi

i am new here!
today i did an expriment on my gyro(ELA).
i fixed my gyro on the ground(tied down test) then opened the propeller.

then began to rotate the main rotor (by Rotax 912 engine.)

i expected to achieve 450rpm(nominal speed in brochure) by mentioned engine but the max rpm was just 275 !

why it so?
thanks for any answer.
Sadegh
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haggishunter
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PostPosted: Sun Aug 30, 2009 11:27 am    Post subject: Reply with quote

Hi and welcome,

I am not an expert on Gyrocopters, but would you need to have forward speed to increase the rotor to normal RPM? It is possibly a flight RPM that is mentioned in the book. Forward speed will increase the RPM due to the autorotational effect.

I think...

HH
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PostPosted: Sun Aug 30, 2009 12:28 pm    Post subject: Reply with quote

Well, don't know about you, but I am a bit puzzled.

If the gyro is tethered to the ground, how are the main rotor blades spinning at 275rpm?

Most of the gyro-copters with which I am familiar, do not have blades coupled to the engine, but rather develop momentum/lift from the airflow upward through the blades, as Haggis pointed out. (Unless your test was on a very windy day. Laughing

The Rotor RPM quoted in most manuals, even for powered helicopters is the "operational RPM", or the range that you would normally expect under a particular flight condition. I would not expect you to reach 475 RPM unless the gyro was in flight., or at least takeoff speed.

One of the copters I fly for fun, the Schweizer 300, has an in-flight RMP range of 442-471 powered, and 390-504 free-spin (auto-rotation). Keep in mind that I can have the engine RPM at 2000, but the blades will be perfectly still until engaged!

So you see, most of the specs in the manual are for in-flight, or in your case, "moving for flight" conditions.

Remember that even we who fly powered copters.....
"When the engine fails.........WE ARE ALL GYRO-COPTERS!"
Laughing Laughing

Have fun

Gotta go now
Helicopter
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PostPosted: Wed Sep 02, 2009 9:35 am    Post subject: Reply with quote

I can't say I'm any expert, but I thought some/most gyro's had the option to engage the engine to get the blades up to a reasonable speed, just to start them rotating, then as HH says, the forward speed on take-off brings them up to flight RPM (engine is also dis-engaged).
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PostPosted: Wed Sep 02, 2009 1:48 pm    Post subject: Reply with quote

Heliwhore wrote:
....... some/most gyro's had the option to engage the engine to get the blades up to a reasonable speed......


That is a very interesting question. Hopefully, someone here has the answer.
It may very well be that they have some type of belt clutch to start them spinning. I never really got into them.

I will try to find out, and post later on.

"The fun of flying is trying to figure out how we do it" Laughing

AB
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PostPosted: Wed Sep 02, 2009 2:02 pm    Post subject: Flight Dynamics Reply with quote

Ok, I contacted the Popular Rotor Association (PRA) pra.org for information.

Yes, it is possible that a gyrocopter will have an optional "energizer", or "spinner", electrically operated to bring the rotors up to an initial RPM.
The blades will not be connected to the engine directly as this could cause severe problems in autoration.

Forward motion is still the primary rotational force on most gyrocopters.

Thank you Heliwhore.

AB
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Heliwhore
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PostPosted: Thu Sep 03, 2009 4:53 pm    Post subject: Reply with quote

Nae bother.... Very Happy
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