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collective pitch or fixed pitch

Old 01-20-2003, 09:38 PM
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Default collective pitch or fixed pitch

ok i'm new to the rc heli's and i was wandering what the difference was between colective pitch and fixed pitch. i am getting a lhm next week that has fixed pitch, so i was courious which was better. and can i upgrade if need be.
metrospider
Old 01-21-2003, 09:39 AM
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Default collective pitch or fixed pitch

Note that the following is ONLY theoretical knowledge, I haven't even finished building my LMH. So please correct me if I'm wrong.

All helis use pitch changes for nick and roll functions: E.g. if you decrease the pitch angle on the right, the heli will roll to the right, because the rotor produces less lift there.

To make the whole heli go up or down, most helis use collective pitch: the swashplate is moved up or down to change the pitch angle of all rotor blades (hence "collective") all around the rotor circle. With CP helis the rotor rpm stays the same all the time (an electronic mixing function sees to that).

Fixed-pitch helis employ pitch changes only for nick and roll functions by changing the angle of the swashplate relative to the rotor shaft. The swashplate does not move up or down the shaft, which allows for a much simpler construction, one servo less and the use of a 4-channel controller. To make the heli go up or down, you change the rotor rpm (as with a plane).

The LMH has fixed pitch to make for lower cost and higher crash resistance. AFAIK, CP helis fly better and react faster, and they offer aerobatics capability, but they are much more likely to hurt your wallet in the event of a crash, since the complicated rotorhead is more vulnerable.

The LMH can be upgraded to CP (there are some websites with how-tos), but it takes a considerable amount of time and skill.
Old 01-22-2003, 10:47 AM
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Default CP

In a hover with a fixed Pitch you have more of a rise and fall with the wind. In forward flight it likes to pitch up a little more. From what was explained to me from a Pilot who converted his LMH to collective, he had less crashes do to having a more stable heli.
From what every thing I have read from others so far, the converted LMH's don't cost any more to crash. I still think what makes the LMH so tough is it dose not have that much power to trash its self. A tail boom strike with a .06, .07 ,or a AT, is not going to be as bad as a boom strike with a size 30 motor.
This also makes it a little less dangerous than the bigger machines.
Old 01-22-2003, 05:37 PM
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Default collective pitch or fixed pitch

thanks guy's that what i needed to know. i guess i will try the fixed pitch and convert i later if i need to
Old 01-22-2003, 05:59 PM
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Default collective pitch or fixed pitch

I seen a video of a guy who was suppose to be flying a CP LMH. My kid said that guy dont know how to fly all that good. There was a few time I thought he was going to bury it not only landing but also taking off. I think he said he was flying in high winds. my question was, Why? I havent modified my LMH much except for putting a semi-scale fuselage on it. I think the fixed pitch flys just fine. Alot of plank pilots wont fly in high winds so my thinking is, why would a heli pilot want to? I flew in some high winds but they were not high when I started. I couldnt bring it back to me it kept getting further and further away. So, I had to ditch it. It took me about two hours to find it. When I found it, it was laying over on its side and the only damage was a Z link on the main rotor was gone.
Old 01-22-2003, 11:50 PM
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Default CP LMH

Does anyone know where I can find any good info on how to convert to collective pitch?
Old 01-23-2003, 10:10 AM
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Default CP

Why fly in high winds? because when you need a heli fix you must have a heli fix.
Maybe I should consider AA FOR HELI'S
Try this.
E:\PBASE PHOTO GALLERY IN BOX.HTM

Motorhead did one too using raptor parts.
http://www.rcuniverse.com/showthread...ghlight=CP+LMH]
Old 01-23-2003, 12:41 PM
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Default collective pitch or fixed pitch

Originally posted by Darthdrk
why would a heli pilot want to?
I think the main reason people are always looking for CP upgrades is something like this...
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Old 01-23-2003, 01:16 PM
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Default collective pitch or fixed pitch

yeah but from what Ive read the people who have made LMH into CP cant do inverted anyway, lack of power I guess,not sure..Rog
Old 01-24-2003, 03:52 AM
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Default collective pitch or fixed pitch

Inverted CP Corona with the stock blades is the reason. You need symetrical blades to land on the hub.
Old 01-24-2003, 11:04 AM
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Default collective pitch or fixed pitch

The main reason is that the rotor head remains closer to the same speed on a collective pitch.
On a fix pitch you decrease the rotor head speed to come down.
This slows down the reaction time (control response) of the heli. It is then difficult for the rotor head to then pick speed back up. before you hit the ground HE HE.
Old 01-25-2003, 04:17 AM
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Default collective pitch or fixed pitch

Try this thread about a collective conversion:

http://www.rcuniverse.com/showthread...56&forumid=192

As for the video of the person flying a collective conversion LMH my machine doesn't fly that way, it is very stable and controllable, even in high winds..
Old 01-28-2003, 12:07 AM
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Default collective pitch or fixed pitch

That would have been my video. I don;t fly that bad do I?
Actually, I later found out that the eratic flying was due to a bad servo. If I moved the pitch stick past neutral then the servo would recenter about 30 deg the other direction. It was windy and to hover required about 1/4 foreward stick. When I landed and let off of the foreward stick the servo would recenter and try to get the heli to do a foreward flip as I took off. After I changed the servo out it went back to being very stable. I can hover hands off for several seconds.
As for FP vs Cp. I would not suggest it for a beginner. it is just not worth the extra complication. For those who are flying the pants off of theirs, they would enjoy the extra control. I have considered putting symetrical baldes on mine to see how the inverted is but they would only be good for one crash. I like my LMH as a good bang around heli.
Mike

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