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Old Jul 27, 2007, 12:48 AM
Its not that windy...
United States, CA, PORTER RANCH
Joined May 2007
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why does big heli=better performance in wind

I always hear that the Lama has no tolerance for the SLIGHTEST wind. And yet most CP's have more overall control. I just want to know. Why can the Cp have so much control. I always thought that it would be because of its CP. But im i correct in saying that its because it can counter it with have some sort of better forward flight or to fly against the wind. Thanks. I just wanted to know.
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Old Jul 27, 2007, 04:21 AM
21st Century Space Cowboy
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Chipping, Lancs, UK
Joined Oct 2006
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Lama is fixed pitch, super stable co-axial - you only control the lower rotor: The upper rotor is constantly fighting your inputs, trying to keep the heli level.

CP are single rotor - it goes where you point it AND keeps going! Also, you have direct control over the pitch angle of the blades. If the wind makes the heli balloon upwards, you don't have to slow the motor down like you would with a FP EDIT: thus lowering headspeed and control authority, you just lower the collective pitch.

A larger heli has more inertia. It needs more of a push to move it around, hence the wind needs to be stronger. So, unless you're flying in really windy conditions, your 90 heli won't be bothered anywhere near the same extent as, say, a Trex or Mini Titan.... generally!
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Old Jul 27, 2007, 04:58 AM
Big Will
Sydney, Australia
Joined Jul 2007
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Co-axials are generally quite slow and light so wind can be faster than your heli can travel.

Imagine a 15km/h wind and your flying head on but only capable of 10km/h you will get pushed back.

I flew my Lama in some reasonable wind a few weeks ago, it was getting blown all over the place lol but always landed relatively gently on the grass just not where i planned it to.

A few mods could possibly make it slightly more wind friendly but at the end of the day it's a co-axial.
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Old Aug 02, 2007, 11:57 PM
Genius or Madness?
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The Evergreen State
Joined Jul 2007
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Bigger helicopters just have more mass than smaller ones, to state the obvious.

Single rotors provide more stability than counter-rotating blades. The rotor on the tail also makes a big difference against the wind.

TachyonDriver and will2k do a great job of explaining how it all goes, so I need not say more
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Old Aug 03, 2007, 01:00 AM
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Necron,

I think you might have it backwards. coaxial rotors tend to be more stable than a similar single/tail rotor. a tail rotor might have a bit more flexibility to combat changing wind conditions, that might be true.

a larger helicopter, as has been said, takes more energy to throw around. The heli has more energy to move itself around, but the same amound of wind has less effect, especially with a higher and steady head speed.

Lowering head speed for decent or hover on most micro-sized coaxials also lowers their rotors' effectiveness against side loading wind, in addition to the airframe's light inertia.

I'd personally love to see a 50 or larger size coaxial heli, with full collective pitch controls on both rotors. That would probably be a closer match to a CP or CCPM single-rotor machine.
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Old Aug 03, 2007, 01:19 AM
Genius or Madness?
Necron Xen's Avatar
The Evergreen State
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Quote:
Originally Posted by CanardianFan
Necron,

I think you might have it backwards. coaxial rotors tend to be more stable than a similar single/tail rotor. a tail rotor might have a bit more flexibility to combat changing wind conditions, that might be true.

a larger helicopter, as has been said, takes more energy to throw around. The heli has more energy to move itself around, but the same amound of wind has less effect, especially with a higher and steady head speed.

Lowering head speed for decent or hover on most micro-sized coaxials also lowers their rotors' effectiveness against side loading wind, in addition to the airframe's light inertia.

I'd personally love to see a 50 or larger size coaxial heli, with full collective pitch controls on both rotors. That would probably be a closer match to a CP or CCPM single-rotor machine.
Oh my, I left out a minor detail, lol.

When I was saying that the single rotor/tail was more stable than coaxial rotors, I meant to say that while they're in windy conditions.

Thanks for pointing that out
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Old Aug 03, 2007, 05:11 AM
21st Century Space Cowboy
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I'd love to see a proper, full function 50 size co-axial KA-50 ... oh yes!

Tach.
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Old Aug 03, 2007, 07:08 AM
MK
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NJ
Joined Feb 2001
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Boeing 747 vs. Cessna, same theory.
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Old Aug 03, 2007, 07:51 AM
Crashin' n learnin'
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Hopkinsville, KY
Joined Dec 2006
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Rock vs. feather, same theory.

klondikes
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Old Aug 03, 2007, 09:44 AM
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Whale verses minnow.
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Old Aug 03, 2007, 09:48 AM
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Quote:
Originally Posted by CanardianFan
Necron,

I think you might have it backwards. coaxial rotors tend to be more stable than a similar single/tail rotor. a tail rotor might have a bit more flexibility to combat changing wind conditions, that might be true.

a larger helicopter, as has been said, takes more energy to throw around. The heli has more energy to move itself around, but the same amound of wind has less effect, especially with a higher and steady head speed.

Lowering head speed for decent or hover on most micro-sized coaxials also lowers their rotors' effectiveness against side loading wind, in addition to the airframe's light inertia.

I'd personally love to see a 50 or larger size coaxial heli, with full collective pitch controls on both rotors. That would probably be a closer match to a CP or CCPM single-rotor machine.

You are lucky if any heli maker can come up with a class 450 coaxial heli with full CCPM rotor.But it seem to me none of them are really interested any more than just a indoor heli.
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Old Aug 03, 2007, 09:52 AM
Si Vis Pacem Para Bellum!
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22 Long Rifle vs. .50 BMG.
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Old Aug 03, 2007, 10:41 AM
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Upstate NY
Joined Feb 2006
499 Posts
One thing universal to all helicopters is translational lift. As you get a bit of wind, it blows the rotor wake out from under you, and the power required to hover goes down. This is good, especially in a big helicopter if you don't have a lot of power margin. In a regular big helicopter, or even a bigger R/C helicopter, you leave the RPM mostly constant and adjust the collective pitch. So, hovering in a wind the primary effect is lower required engine power, control power is unchanged. But in a fixed pitch helicopter, if you are hovering in wind, the translational lift will make you climb unless you reduce RPM. As you reduce RPM, control power goes away with it. That's bad.

Our little coaxes would also do better if there were two swashplates. With one rotor swashplate controlled, and one gyro bar controlled, they mostly fight each other. A lot different than my old Kyosho concept 30, where the gyro bar input summed with the servo input, combining stability with manuverability. Even a light helicopter that has adequate control authority can fly in horrendous and gusty winds. I used to fly the concept 30 in worse conditions than I would take the Enstrom out in. The enstrom had a max gross of about 2300 lbs, compared to 5 lbs for the concept 30. Of course, the concept 30 was also cheaper to repair!

These little coaxes are amazing exercises in packaging helicopter functionality in a very small, easy to fly package. One thing that suffers is control range, i.e. how many degrees of cyclic are available to generate a moment at the head. This reduced sensitivity both fits in the small package better, and makes it easy to hover indoors (with no wind). But, out in the world of wind and gusts, it works against us.

In one of my old posts, I look at what it takes to get my esky happy baby to fly in forward flight. Warning, this is geeky stuff. But, it's what I do.

http://www.rcgroups.com/forums/showthread.php?t=494569

-- Bryan
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