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HIROBO Turbulence - SDX - Freya - Sceadu > Using 700 mm blades in a Freya is like using 720 mms in other helis
 
 
AugustoElite Veteran - Location: US - My Posts This: Topic  Forum
I've seen this question about 700 mm in Freyas posted over and over so I decided to post this analysis by itself to be used as a reference.

If you run 700 mm blades and 95 mm tail blades AND fly HARD you WILL hit the tailrotor blades with the main blades.

The main rotor diameter on a Freya with 686 mm blades is actually 3 mm bigger than for instance a Fury with 710s so you don't need blades bigger than 686s. Here's why:


Here are the two heads. Notice the large difference in the hole to hole separation.

Here I'm measuring the X-Spec Main Rotor diameter with MAH 685 blades.

62-7/16" long. The Fury with 710's is 62-3/8"


Here I'm measuring the Fury Rotor Diameter with 710 MAH blades.


I taped both tips to compare

Here they are taped and aligned for comparison.

The X-Spec one (white with black tips) is a tiny bit longer giving about 3 mm
difference. This is comparing 685 blades with 710mm blades on the Fury Extreme.

You can see the difference due to a larger bolt to bolt distance.


The Disc Area of the X-Spec with 686's is just a bit larger than the Extreme with 710's so being of the same weight the load in oz per square inch of disc area should be the same.


Tail Rotor Blades

Here's also an explanation on the rotor diameter of a Freya.


The tailblade bolt distance in the Freya makes the disc of a 95mm tailblade the same size as a 102 disc in a Fury. Even doing terminal-velocity piroueting side vertical falls with the 95 MS fiberglass blades the piro rate stays constant. In reality you are flying a 102mm disc. I also tried longer ones and the main blades hit the tailblades and destroyed them. Also the tail RPM speed of the X-Spec is higher than most helis so a 95 mm tail blades with the equivalent 102 mm dic diameter performs much better in the Freya than a 107 mm equivalent diameter in other helis without the extra load that might break a tail hub.

Here are the diameters of the hole to hole centers for both the Fury and the X-Spec:

X-Spec tail


The two tail hubs compared.


Fury Separation is 72 mm.

X-Spec separation is 87 mm. There is a difference of 15mm or 7.5 mm per blade. So in order to have the same Disc diameter I have when using 102mm in my Fury I can use 102 - 7.5 = 94.5 mm in the X-Spec. SO a 95 mm tail blade in the X-spec gives you a little bit more tailrotor disc area than a 102 in the Fury.

Conclusion:

Use 690 and 95mm as the MAXIMUM size on an X-Spec or Freya and also use the lower main shaft hole to increase the clearance between the blades and the tail rotor blades and the blades and the tailboom.

and as a final statement:



Using 700 mm blades in a Freya is like using 720 mms in other helis

So there is absolutely no need to use anything longer than 686 mm main blades and 95 mm tailblades.

Augusto.

Avant Aurora Ultimate
04-08-2003 Over year old.
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z11355
rrMaster
Location: 10000 is enough time wasted.

My Posts This: Topic  Forum		this post is brought to you by the RC heli
Dept. of Wishful Thinking.

My money is on less than 2 weeks before this
question is asked again. Just call me cynical.
04-08-2003 Over year old.
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MG
Key Veteran
Location: California

My Posts This: Topic  Forum		But does this mean I can't use 710 blades? Hehehe... I just had to do it
04-08-2003 Over year old.
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Augusto
Elite Veteran
Location: US

My Posts This: Topic  Forum		If you read the post you can see that I said "to be used as a reference" that's because I know it will happen again.

When someone asks the same question again it can just be directed here so there's no need to repeat the explanation over and over again.

That's also why when I posted this as an answer to another post I said "I think I'm going to post this by itself as a post to refer to".

Augusto.

Avant Aurora Ultimate
04-08-2003 Over year old.
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Dave_D
Key Veteran
Location: Philippines

My Posts This: Topic  Forum		Amen...

I knew this 3 years ago and a lot of flyers replied to my insistence on using 660m (w/ OS61) on a Freya like I was nuts or something.

The impetus of stuffing long blades without actually knowing why is just typical "mine is bigger than yours" or equating blade length to penis size.

When I used a YS80 on the Freya, I NEVER used anything longer than 680mm. I even use 680mm on the Fury and it seems alot happier with less flutter during hard cyclic turns or tumbles.

IMO bigger rotor discs are better suited for the FAI crowd than the 3D enthusiasts.
04-09-2003 Over year old.
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davehour
Key Veteran
Location: Guayama, Puerto Rico

My Posts This: Topic  Forum		680's...

I ordered some carbon 680's for my Freya 60. Hope the OS 61 WC and Muscle Pipe work ok with them...
06-20-2003 Over year old.
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davehour
Key Veteran
Location: Guayama, Puerto Rico

My Posts This: Topic  Forum		Light is comming...

Feel better now .

Thanks.
06-21-2003 Over year old.
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Kinger
Elite Veteran
Location: Columbus, OH

My Posts This: Topic  Forum		I know this is an old post, but I have a question regarding this 690 on the Freya is like 710's on a Fury thing. Considering the rotor head is larger on the Freya, does it really contribute anything to extra lift or help in autos? I thought that was the main reason folks started using longer blades in the first place?
09-30-2003 Over year old.
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Augusto
Elite Veteran
Location: US

My Posts This: Topic  Forum		Because the tangent speed of the blades around the center is so low, the center of the blades contribute almost nothing to the lift. Other than different blade selections, the disc diameter is the determining factor for both lift and auto performance. You get to have the same performance with the same disc diameters.

Augusto.

Avant Aurora Ultimate
10-01-2003 Over year old.
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Kinger
Elite Veteran
Location: Columbus, OH

My Posts This: Topic  Forum		Great explanation. Thanks Augusto!
10-01-2003 Over year old.
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HIROBO Turbulence - SDX - Freya - Sceadu > Using 700 mm blades in a Freya is like using 720 mms in other helis
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