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Scale Model RC Helicopters > Semi-Symmetrical Blades???
 
 
Ironside
Senior Heliman
Location: Baltimore, MD

My Posts This: Topic  Forum		Thinking about trying out some semi-symmetrical blades for my MultiBlade Raptor 50 MD530. Wondering if anyone has tried them and if so what you thought. Pros and cons.
10-29-2009 05:06 PM
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Jag72
Elite Veteran
Location: 20 minutes south of Boston Mass...

My Posts This: Topic  Forum		Flat Bottom Blades

I treid Flat bottoms before

They have a self righting property to them and are very stable upright...but if you try flipping inverted ...LOOK OUT!

Kind of like a flat bottom winged airplane



not something you can do with flat bottom blades...I think for a scale bird you might just want to stick with regular blades....I think the flat bottos are best for AP...but I'm not sure?

Esprit Model Flight Team
10-29-2009 05:13 PM
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doorman
Elite Veteran
Location: E.Berne, NY

My Posts This: Topic  Forum		Semi's

These will provide you with a bit lower hs along with more lift....I use them on my "heavy" helis.....
But if you are going to really try loops and rolls with your scale heli then I would agree to stay with the symetrical blades...

Good Luck, Stan

Team Hirobo/MRC --- RCLIGHTS.NET ----- If there is a cure for this, please don't tell me about
10-29-2009 06:03 PM
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89X-CELL60
Heliman
Location: Denver, Colorado

My Posts This: Topic  Forum		Hello Ironside,

My 89 X-cell 60 had the the best blades that MA ever made in my opinion. They were the All WOOD 660mm Reflex flat bottom blades. I got them by mistake when I upgraded my X-Cell 50 to the 60 it is now. I learned basic aerobatics with these blades. I did loops, rolls, split S and my favorite rolling stall turns. As long as you have the speed, flat bottom blades will do just fine with sport flying. Just don't mow the grass with them

Pros: Hover was at 4.5 degrees not the 5 to 5.5 it use to hover at. Climb outs were better, and my top speed was dramatically better!

Cons: Can't get them anymore

David
10-29-2009 09:18 PM
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darrens
Key Veteran
Location: United Kingdom

My Posts This: Topic  Forum		Semi's are ideal for a scale application for the following reasons;

1. They are more efficient as they generate more lift which means less pitch which means less drag. As you are already carrying the extra weight of a fuse any help in this area is a good thing.

2. You can get enough lift at a more scale like headspeed.

3. They auto better (as they produce more lift) and we have already mentioned the negativity of weight of the fuse.

4. They actually fly more scale like as they move from hover in to transitional lift.

The negative is they don't perform well inverted i.e. for inverted hovering, but they are fine for the odd roll or loop if that's what you really want to be doing with a scale ship.

The final negative, they are hard to come by in some sizes.

Hope this helps

He who dies with the most toys is the winner!
10-29-2009 10:12 PM
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kennethw
Senior Heliman
Location: Singapore

My Posts This: Topic  Forum		I've been looking for Semi-Symmetrical Blades for CCW rotation, but can't find any. Does anyone know where I can find some?
10-30-2009 03:08 AM
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oldfart
Elite Veteran
Location: Vancouver, Canada

My Posts This: Topic  Forum		Lift is a function of rotor blade size, airfoil, rotor speed and angle of attack (pitch).

The maxium rotor speed is dictated by power available to overcome the blade drag that results from all of these considerations.

So a well designed symmetrical can be just as good at creating the lift required, as can a semi-symetrical.

At the same rotor speed it may take a little more pitch but it may well do so even with less drag (more efficiently). And all without the center of lift changing (causes unwanted pitching moments) with control pitch and rotor speed changes. This is why I find itmuch easy to land a scale heli without any balloning with a symmetrical rather then a semi-symmetrical blade...ditto for landing an auto.

Consequently, I have found that one cannot make a blanket statement that one airfoil shape may do better then another, in most of the applications in which we use our blades, without taking all of the other perameters into consideration at the same time.

The only area I have found that some semi-symmetrical blades may have an advantage is in a system where I am lifting a very much heavier then normal airframe sith a limited upper pitch range and/or with a limited rotor speed...e.g a highlly disc loaded photo heli (where I might just prefer going to a longer symmetrical). Otherweise I prefer a well designed double S-cambered symmetrical.
10-30-2009 05:58 AM
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Ironside
Senior Heliman
Location: Baltimore, MD

My Posts This: Topic  Forum		Thats good info. As mentioned I am flying a relatively light airframe in a Raptor Titan SE with a MD530 body. With the Raptor not really having the optimal gear ratio for multiblade heads, my thought was maybe trying semi-symmetrical blades would allow me to slow the headspeed down while still achieving the lift that I would be looking for. Any ideas?
10-30-2009 01:11 PM
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broggyr
Key Veteran
Location: Naugy, CT

My Posts This: Topic  Forum		Stan:

Where do you get your semi blades? I might want to try a set of 690's or similar on my gasser (no loops or rolls here )

- Brian
irony [ay-ruh-nee', ay-er-nee'] adj.: Like goldy or bronzy, except made of iron
10-30-2009 03:00 PM
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Hoverup
Elite Veteran
Location: Gulf Coast

My Posts This: Topic  Forum
Quote 
Stan:

Where do you get your semi blades? I might want to try a set of 690's or similar on my gasser (no loops or rolls here )

- Brian

http://www.starwoodmodels.com/produ...iblades.php#800

Cheers - Boyd
AMA 80393
IRCHA 3355
Major USAF
Retired
10-30-2009 04:46 PM
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broggyr
Key Veteran
Location: Naugy, CT

My Posts This: Topic  Forum		Hey Hoverup, thanks fo that. I actually saw those, but failed to notice the "Airfoil S" and what it stood for.



- Brian
irony [ay-ruh-nee', ay-er-nee'] adj.: Like goldy or bronzy, except made of iron
10-30-2009 06:08 PM
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oldfart
Elite Veteran
Location: Vancouver, Canada

My Posts This: Topic  Forum		Ironside,

What blades are you using now? What pitch range are you using now?

With the much higher drag profile of a multi-blade head, you can use shorter blades for similar power loading for your engine. e.g. some good symmetrical 550's or 570's.

These will work very well:

http://www.centuryheli.com/products...m?prtnm=CNF5533

They groove in FFF and auto very well.

And for lift at lower rotor speeds, just use more pitch.

The Raptor's gear ratio is fine for lower head speeds on scale machines.

You should have no problem setting for head speeds in the 1400 to 1500 range.

Just remember that the high end needle is for adjusting top end settings (carb wide open) and the hover needle is more effective for setting a smooth burbling hover and smoothe transition for lift off and climb out.
10-30-2009 06:37 PM
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Ironside
Senior Heliman
Location: Baltimore, MD

My Posts This: Topic  Forum		I am actually using Helimax 530mm now with a pitch range of -3 to +9 and a headspeed of 1450. Don't get me wrong my heli flies great. I was just thinking of trying semi's to see what they were like and wanted to get others thoughts on them before I went out and bought them. Helimax blades (in my opinion) are cheap blades and I really think that set a good blades would probably make a real difference in the way it performs. Thanks for the info however.
10-30-2009 06:46 PM
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darrens
Key Veteran
Location: United Kingdom

My Posts This: Topic  Forum
Quote 
So a well designed symmetrical can be just as good at creating the lift required, as can a semi-symetrical.

I don't agree that symmetrical blades can be as "good at creating lift" as semi-symmetrical. Yes they can produce as much lift, but to do so have to run a higher angle of attack and thus make more drag. Semis are producing lift at zero degrees and are without doubt, more efficient all things being equal. You would have to be comparing the best designed symmetrical blades with the worse ever designed semis for the above statement to be true.
look at any aircraft which does not look to go inverted flight and they all run a semi-symmetrical profile on the blade or the wing......,there is a logical reason for this!
Semis will always auto better too as they have less drag in the auto and creat more lift at a given rpm. Whatever "perameters" you consider (with the exception of inverted flight) the semis will perform better if you are considering "better" as less drag, more lift, more efficiency.

He who dies with the most toys is the winner!
10-30-2009 08:45 PM
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doorman
Elite Veteran
Location: E.Berne, NY

My Posts This: Topic  Forum		SS Blades

Hi Brian,

As Boyd mentioned Starwood has an assortment, but just about all of my blades come from East Coast Scale.... Vario blades for Vario machines and heads, and CCW operation!!!.....
I also picked up a nice set of SAB 800 High Lift from MA a couple of months ago.... but I am running mostley 800mm on my machines....
V-East also has some nice ss blades.....
They are not the easiest to come by, but if you look you can come up with them, even though most may need to be specail ordered...
On the R-50 with the 5 blade head, I would stay with symetrical 550's and you should have a lot of fun with it....

Good Luck..,.. Stan

Team Hirobo/MRC --- RCLIGHTS.NET ----- If there is a cure for this, please don't tell me about
10-30-2009 09:26 PM
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Hughes500Pilot
Key Veteran
Location: Anaheim, CA

My Posts This: Topic  Forum		I use Zigsaw GP7's (600mm) semi's on my Sceadu 50 with a Funkey Hughes 500 body. They fly great. Way better the full symetrical with that heavy body. Plus, they have a white top. I really like the white, makes it easy to see the rotor disk in flight. -Steve

10-31-2009 05:48 AM
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kennethw
Senior Heliman
Location: Singapore

My Posts This: Topic  Forum		Saw the Semi's CCW blades at the Starwood and East Coast sites, but they are all for larger helicopters (my dream one day soon). I'm looking for mere 600mm blades.

Also, why are CCW blades called Right-Handed? When I look at the rotor spin from the top, CW spins to the Right.

Pardon my stupidity.
10-31-2009 06:46 AM
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2tall
Heliman
Location: Crystal Lake, Illinois, USA

My Posts This: Topic  Forum		Source for "Non-Symmetric" 600mm Blades

After reading this thread I spent a bit of time surfing for 600mm semis. Found these from "SWE" at Helidirect.

http://www.helidirect.com/swe-semis...lade-p-7493.hdx

My Rex 600E in a Funkey Jet Ranger fuselage flys way too heavy - of course it is way too heavy. I'm hoping these blades, or another alternative, will help a bit - as the thread suggests. Has anyone tried the SWEs? Is there a 600mm alternative readily available from a US dealer?



"Don't worry, I crash better than anyone else I know."
10-31-2009 06:32 PM
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darrens
Key Veteran
Location: United Kingdom

My Posts This: Topic  Forum		Century sell 600mm semis, my friend runs them on a funky JR with Trex 600e. he gets 8 mins flight time on a 5amp pack with over 20% left.

He who dies with the most toys is the winner!
10-31-2009 06:34 PM
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kennethw
Senior Heliman
Location: Singapore

My Posts This: Topic  Forum		Thanks for the links.

Good for my CW scale, now looking for CCW Semi's.
10-31-2009 07:00 PM
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Scale Model RC Helicopters > Semi-Symmetrical Blades???
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