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HelicopterMain Discussion › New Approach to Collective Pitch Setup
07-10-2008 01:46 PM  9 years agoPost 1
buburub

rrApprentice

Bayside, NY

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Hey Guys,
I was thinking about this the other day. Even when you setup the pitch on your bird perfectly (+13/-13, 0 degrees in the middle, everything 90 degrees and swash is leveled). The bird does not climb the same on full positive and negative. So let's say you have the bird tracking perfectly but positive pitch climbouts are more powerful than negative. Put the bird down and turn clockwise or counter clockwise both long links from the swash to the grips or bell mixers. Do this until the "Feel" of positve climbouts and negative is the same. You'll probably end up with something uneven like positive 11.5 and negative 12.5. You want to make sure the swash is not binding on full positive or negative.

If you really think about it, the goal of setting pitch is to make the bird feel equal and linear on the positive and negative side. So who cares if you are technically off a bit as long as the bird flies perfectly. Don't take me wrong...we take great pride in setup and having a very nice ship. I just think the feel of the bird and sheer performance outweights a meticulously anal pitch setup.

Best Regards,
Bub

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07-10-2008 02:09 PM  9 years agoPost 2
ErichF

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Sutton, NH

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This is not a bad idea. Even when using hard dampers, free floating axle heads will compress the dampers slightly during positive and negative G forces, which also affects the collective inputs to the pitch arms. Depending on wether you have trailing or leading pitch arms, you would have to either lengthen or shorten your pitch links to achieve the desired balance.

The only problem with using the pitch links as that you upset the neutral point in the head. Let say you do a vertical climb, or tailslide, where the head has 0G load. The zero point in the collective may be off either way positive of negative. You can either get used to it, or adjust your pitch curve in the radio to balance the head, as opposed to adjusting the links mechanically. Adjusting the radio pitch curve will still keep the center collective neutral point.

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07-10-2008 07:34 PM  9 years agoPost 3
KYLE 05

rrApprentice

Houston,Tx - USA

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Great idea

Bobby Watts,shared the same thing with me. There is only so much you can do on the bench. When flying,do a full accelleration upright,then do a full acc inverted untill the heli responds the same. We adjusted the short double links going to the grips. Turn them the same untill the desired effect is achieved. It makes a big difference in the feel of the heli.

Kyle.

Dont walk in my footsteps----I think I stepped in something!!!!

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07-10-2008 07:56 PM  9 years agoPost 4
Heli 770

rrProfessor

USA.

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KYLE 05
On your testing, First test did you find that flight was faster inverted? To me it should have been.

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07-10-2008 08:04 PM  9 years agoPost 5
SSN Pru

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Taxachusetts

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what is the fundamental reason behind the negative climbouts being slower than positive climbouts?

Something tells me airflow into the rotor disk is disrupted by the fuse or pod when inverted...

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07-10-2008 08:05 PM  9 years agoPost 6
nmrs

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Austin, TX

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This seems like a good idea to me, though I don't like the idea of doing it mechanically which will move 0 pitch away from center stick. I tend to agree with ErichF:
The only problem with using the pitch links as that you upset the neutral point in the head. Let say you do a vertical climb, or tailslide, where the head has 0G load. The zero point in the collective may be off either way positive of negative. You can either get used to it, or adjust your pitch curve in the radio to balance the head, as opposed to adjusting the links mechanically. Adjusting the radio pitch curve will still keep the center collective neutral point.
You should be able to achieve the same effect by setting a pitch curve that looks something like:

0 25 50 70 90

This way center stick will still give you 0 pitch, but climbouts will feel the same on both ends. You would obviously need to tweak the endpoint (could be 97, could be 84) to get the correct feel, and then either inhibit point 3 so it will be exactly between 2 and 4, or do the math correctly to get it in the middle.

If you were finding it needed more on the positive side, use something like:

10 30 50 75 100

450 se v2

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07-10-2008 08:07 PM  9 years agoPost 7
Aox

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Irvine, CA

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what is the fundamental reason behind the negative climbouts being slower than positive climbouts?
On my Logo 500 and my Synergy, both climb noticably faster in negative than positive. I thought this was a "feature" of negative not needing to blow air past the heli body. Sounds like I just need to "even up the power" as this post notes.

-Aox

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07-10-2008 08:23 PM  9 years agoPost 8
Girard Ibanez

rrVeteran

Tucson, Arizona (formally from Guam)

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Static and Dynamic adjustments.

Different blades (airfoil shape) respond differently under Actual Conditions.


Team Thunder Tiger
since 6/2005 to 12/2014

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07-10-2008 08:26 PM  9 years agoPost 9
ErichF

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Sutton, NH

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what is the fundamental reason behind the negative climbouts being slower than positive climbouts?
I stated one of the reasons already:

...free floating axle heads will compress the dampers slightly during positive and negative G forces, which also affects the collective inputs to the pitch arms...

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07-10-2008 08:26 PM  9 years agoPost 10
SSN Pru

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Taxachusetts

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I thought this was a "feature" of negative not needing to blow air past the heli body.
In the world of Fluid Mechanics, the airflow after the rotor disk wouldn't matter. The airflow into the disk is important though.

It is interesting that Aox claims to have better negative climbouts than positive.

Now I am really curious as to what is causing this.

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07-10-2008 08:51 PM  9 years agoPost 11
Topher

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Rochester, Michigan

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I think you had it right the first time umdpru. The affect of the airframe itself on the disc inflow and delta pressure.

will wash your heli for a quarter

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07-10-2008 09:11 PM  9 years agoPost 12
Billebob

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Tim-buck-2

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Nick's Used Cars....new to you

BB

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07-11-2008 12:15 AM  9 years agoPost 13
buburub

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Bayside, NY

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Changing the throttle curve might not be a bad idea either as mentioned by nmrs. I like the idea of keeping 0 at center. The change is probably 1 degrees to the positive/negative collective at max which would mean +1/-1 at center. Bobby doesn't seem to mind or feel the difference. This approach hold true for swash leveling as well. Full positive and negative climbouts to see if it torques aileron or elevator wise.

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07-11-2008 12:50 AM  9 years agoPost 14
Morris

rrApprentice

Hong Kong

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I agree but what would happen in invert? anyone try that? I mean, set up as we discuss here, then invert and try.

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07-11-2008 12:58 AM  9 years agoPost 15
nmrs

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Austin, TX

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I agree but what would happen in invert? anyone try that? I mean, set up as we discuss here, then invert and try.
Unless I missed something, that is the whole point, to get climbout speed equal whether right-side up or inverted...

450 se v2

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07-11-2008 01:05 AM  9 years agoPost 16
Aox

rrApprentice

Irvine, CA

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In the world of Fluid Mechanics, the airflow after the rotor disk wouldn't matter. The airflow into the disk is important though.

It is interesting that Aox claims to have better negative climbouts than positive.

Now I am really curious as to what is causing this.
Good to know. I'm definitely a newb when it comes to fluid mechanics/dynamics.

I had just installed new very hard dampers in the Logo head (K&B Oranges) when I first noticed this on my Logo. It had some pretty soft dampers previously, and I never really noticed a negative/positive difference.

My 0 pitch is set to midstick, but the Logo definitely has more vertical power inverted than not. My N9 is like that too, and even my Mini Titan. Much more pronounced in the Mini Titan and Logo than the N9. I've got a little Trex 450 SE V2, and it doesn't seem to have this characteristic at all.

-Aox

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07-11-2008 01:42 AM  9 years agoPost 17
KYLE 05

rrApprentice

Houston,Tx - USA

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Heli770

No,I think it was just the opposite. It had to much positive/upright climb-out.(depends on your initial set-up)

Nmrs,yes that is the whole point. Your trying to duplicate performance wheather it is upright or inverted.

I not going to get into the dynamics of this,but just do a good symmetrical initial set-up,then tweek the pos/neg untill a good performance inv/upright is achieved.

Kyle.

Dont walk in my footsteps----I think I stepped in something!!!!

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07-11-2008 02:06 AM  9 years agoPost 18
Riq

rrKey Veteran

ND

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Ok, minus the scientific dynamics,(im a chemist, not a physicist ) ive read/viewed (somewhere!?!!?) that a heli requires less pitch in a negative hover then in a positive, we can go from there....

Yet if UMDPRU is correct, then this isnt true.

I ran a test in my lab. I taped a paper plate to the front and back of a box fan and tryed to decide which kept me at a greater comfort level.

Test results are inconclusive as of yet; my lab assistants were unable to decide whether or not their opinion was subjectively biased.

They have no fan.

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07-11-2008 02:06 AM  9 years agoPost 19
Torkroll

rrApprentice

Bakersfield Ca

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People have been doing this for a long time.
It's more important the heli feels the same both ways, than the pitch gauge numbers, it's a good starting point, also there is not any flight stress on the machine at that time.

Anyone who says it's a small world never tried to walk to Zimbabwe.
Jerry

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07-11-2008 02:40 AM  9 years agoPost 20
SSN Pru

rrElite Veteran

Taxachusetts

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Im not claiming to be absolutely correct but from what I can remember of my fluids courses tells me that the lift is created at the surface of the blades. the surface of the blades have no effect on the air far away from it. this has a limit though as I could imagine a solid plate disk mounted to the skids that would be large enough to serious affect the lifting capacity of the rotor disk.

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HelicopterMain Discussion › New Approach to Collective Pitch Setup
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