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HelicopterBlades and Night Flying › Difference between 68 & 71 Cm blades
09-01-2003 01:11 PM  14 years agoPost 1
mvhf

rrApprentice

Antwerp, Belgium

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What will be the difference when changing from 71 cm blades to 68 cm blades, all the rest remains the same (91 engine en 60 Heli), using a governor, so head speeds will not be affected.

regards

Marc

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09-01-2003 01:37 PM  14 years agoPost 2
Heli-Driver

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Arlington, TX

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I have a Fury Extreme with 710 MAH blades. I also have a set of MS680 night blades for night flying. I noticed that swapping the blades I felt the 680's had much less collective response than the 710s.

Going to the smaller blades may require raising your pitch curve and/or reducing your throttle curve slightly to maintain a balanced system.



Raymond

Predator Gasser SE/231 X 2
Century Helicopters

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09-01-2003 01:44 PM  14 years agoPost 3
mvhf

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Antwerp, Belgium

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What will be the difference for auto ?

Raptordriver:
I will nog have to reduce the throttle, as my governor will handle this

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09-01-2003 04:21 PM  14 years agoPost 4
Twobeers

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Toronto, Canada

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the difference is obvious 71cm-68cm=30cm. The difference is 30cm. More power is required from the engine to drive the blades round & round, but with a 90 sized engine with the proper gear ratio it will run more happily. Auto's will be much more pleasurable with considerably more hang time down at the bottom. What was the question again?

I lost my infamous tag line.

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09-02-2003 02:30 AM  14 years agoPost 5
shawgl

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Murrieta, CA

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Depending on the type of blades your collective response will be alot different. And as far as auto's your 710's will carry alot more inertia than 680's. Why are you going smaller? I am thinking of going to 720's on my Vigor CS with the 91.

In God we trust, everyone else we monitor.

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09-02-2003 06:18 AM  14 years agoPost 6
mvhf

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Antwerp, Belgium

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I was thinking in the case of cyclic movement, what will it do to rolls, flips etc, it should be more stable not ?
I understand it will be different in collective response, but when you have the same engine, you can pull more pitch, without the blades slowing down, which increases the power again.
As for the autos, I understand the bigger the blades, the more intertia.
twobeers, I understand the difference is 30mm, even if you do some math, you can calculate there is a 10% difference in size, if you take the complete circle of the blades.

regards

Marc

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09-06-2003 10:15 AM  14 years agoPost 7
Reesy

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In the doghouse ... Nottingham UK

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Hi Marc
I'd do the (pi x Rsquared) bit to see the AREA is quite a bit bigger, A well regarded Raptor 60 flier using a YS880 much preferred 680 > 710 for doing 3D I'd guess your on the money with the bogging bit .. to maintain headspeed the 680's might give more headroom.

I know some nutters use 550 blades in their raptor 50's

Paul

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09-10-2003 09:02 PM  14 years agoPost 8
Dragon2115

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New England

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understand it will be different in collective response, but when you have the same engine, you can pull more pitch, without the blades slowing down, which increases the power again.
That's not necessarily true. At a certain point the blades will stall and lose lift. I think that's at around 14 degrees. Remember to add collective and cyclic pitch together for the total pitch on the blade. You can see how that could add up to stalling quickly. Bigger blades, at the same rpm, will lift the same weight on less pitch because they have more lift.

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09-10-2003 09:14 PM  14 years agoPost 9
Futurac

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Belgium , Europe

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Blades

Gents

all you saying is correct.
one thing - Load.
when flying with 61 size, the gear and 66-68cm are the correct load to the motor. then it runs at optimal power, fuel consumption, temp, and all others.
when changing the motor to Motor x 1.5 ( 91 size) you have to adjust the gear and load.
if you continue flying 68cm, it will have more power for the heli, what is not necessary even with 71, but it will not correctly split the load.
many people continue flying with 68cm, and it works fine, but its not the correct thing to do.

minimum size is 69-70cm for 91 size.

Alex (Formerly Known as RCMarket )

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