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icanfly

Elite Veteran

ontario

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OK, let's get a few things straight, seems some forums serve non other than fanboys and manufacturers for the most part. A year ago I got into a certain topic titled the very same way as this one. They tossed my azz out of there because as much as the mathematics used in the topic had accuracy there were yet unsolved mysteries regarding setting phase angle on a essentially rigid rotor head.

After the topic ran I had a chance to experiment and was duly rewarded with helis that flew very well compared to stock form, I modified mine to allow mechanical adjustment of phase angle.

I'll now try to give you a picture of what was learned and how it is phase angle is NOT 90°. First, the axis of a blade flapping up and down during rotation lags in angle, it lags more with each degree input, 12° pitch= 12° lag etc same goes for - and + pitch inputs, (average 6°). Imagine the "less than" > sign as the pathway the tips take in a cw rotation.

One thing I threw into the mix in the original topic was drag, the blade will be pulled back further in high stall events and return due to centrifugal force, with each rotation.

Lets take a look at the fulcrum point along the blade, on a rigid head it is usually most somewhere between halfway out, and to where the blade clamp ends outward that the blade flexes and gives the blade's vertical pendulum it's fulcrum. This would dictate how quickly the blade will oscillate and return to it's neutral position after a pitch event, The shorter the pendulum the shorter the time it takes to return to neutral. The highest point in a 360° rotation of the blade will be it's point of "peak displacement" and the blade will compress air as it's returning to neutral pitch (hover or 0) and cause the disc to rotate about it's other axis of ail and el to react since the heli is suspended in a non fixed environment.

What happens with a blade that has a shorter fulcrum point toward the tips outward from the main shaft axis is that it will snap back to neutral position before it's completed it's 180° cycle and the peak amplitude of the blade will come earlier when the phase is at 90°, the phase angle has to be retarded to make the peak amplitude event happen a bit later (further back) in the 180* cycle.

Phase angle on center teetering heads IS 90°, on rigid heads it can be as low as 72° (Robinson 22) and would be zero if the blade peak amplitude event took place all at 0°, (seen as a flap event in the rotation cycle). Phase lag on rigid heads depends on what is called "Advance angle" and even though you don't see it the blades automatically have some delta 3 (third angle) they experience due to all the factors mentioned. Phase is less than 90° by that general delta3 angle to begin with.

Want a graffic portrayal of all of the above? Fix the skids to a solid object, turn the heli on without throttle, try pitch events and go to extremes while flexing the blades in their appropriate + or- pitch extremes, pull the blades in the grips a few degrees lagging and go through the same process while rotating a blade in it's 360° rotation, and most of all have fun.

My helis do NOT TIP OVER because the gyro is overworked and trying to mitigate what I'll term "phase harmonics attributed to incorrect phase lag settings. That is even worse on small helis.

They said icanfly didn't know what he was talkin 'bout? This lag dilemma came to me over two years before the topic of last year co my angel the Lord, and I didn't listen until I broke enough things to say "what the hey", broke something significant and DID something about it.

Here's the topic in question, be prepared to learn. http://www.helifreak.com/showthread.php?t=699669

Peace all, much better thanks, and I thought it was me who was doing all the crashing back then.

Maybe I'll try to draw up some visual graffics too, maybe.

And THEN toss in gyroscopic precession to complicate things just that little bit further, lol. good luck as that's helis for you.

How this all came about now? I was doing some research on the net for a related topic and saw the pl topic listed, investigated and was reminded how people and mods can be poopers, that ban cost me some important contacts in my pm's (but this isn't about them, the other site).

07-08-2016 04:00 PM
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helifanatix

Veteran

Fountain Valley, CA

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Adjusting the phasing lets you:
- adjust the timing of the elevator / aileron
- compensate for CG
- compensate for main shaft angle in relation to frame & etc

Example 1: When you do an aileron roll
- might not be perfectly circular,may be oblong
- the phasing will let you adjust / tune this characteristics and let it be spherical
- quite handy when it comes to multi-head design

Example 2: Interactions
- if you line the blade parallel to boom
- when you give foward / backward elevator Input
- there should be no Aileron movement
- if have a swash drivers that allows adjustment, you can adjust to cancel out any unwanted interactions

You can do the same mechanically and electronically
- just make sure you understand
- if not, you know enough just to be dangerous.

- Scott

07-08-2016 04:18 PM
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Chris Bergen

Elite Veteran

cassopolis, MI USA

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Sorry to hear you were tossed about icanfly, there are a lot of fan boys who will NOT allow a particular design or feature be discussed as less than PERFECT (especially if its their current sponsor)...

I can agree mostly with your results and why I have resisted over these many years to make my machines like all the others, why I have resisted CCPM and FBL heads with fixed phase angles.

Yes, you can electronically adjust out certain deficiencies, and for the most part and for most people out there flying in the hobby, that's "Good Enough".

But when someone such as yourself wants it to be correct mechanically and willing to do the work needed to achieve that, its sad that those persons are ridiculed and tossed out....

We may not always agree on results or ideas, but I will ALWAYS defend your right to be wrong..

Chris D. Bergen

07-08-2016 06:40 PM
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icanfly

Elite Veteran

ontario

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good to hear from you serious players first.

It would not have been an issue to point out a simple mechanical flaw in the design regarding engineering for optimal flight control, it's only when time after time and time again the same nasty tip overs and control biases popped up in other flyer's experiences did I examine more closely the problem and solution.

A recent 450 nose in lift off proved to be the most comfortable and stable lift off ever. A 300 I tried to lift off nose in without the adjustment (and not quite the thorough understanding of the problem) tilted on the ground no matter what I did on the tx.

It would suffice to say the lack of confidence due to associated control errors made learning a lot less fun and actually made me second guess my abilities in control and recovery in difficult situations. My 550 had vibes last year and hicup'd mid flight right in front of me careening right at me. A quick jab to the right and some auto pitch and it came down rsu while turning 180° on the ground. That made me feel good about this education. A poorly controlled small heli is realy going to mess with your confidence.

The 700 and larger helis are all great and everything but you really have to be on top of every nuance before you go risking your neck to fly one. (I've read of the near misses over then years).

Do you like this?

Watch at YouTube

07-08-2016 07:05 PM
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ICUR1-2

Key Veteran

Ottawa, Ontario

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An easy simple trick for avoiding tip over's ( provided set-up is correct)

When you spool up do so with some neg pitch ( ~-4* )as the head reaches speed correct the tail as needed and cyclic as needed and when the head is levelled and the tail is neutral lift off.

spending time, paying attention

07-08-2016 08:42 PM
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icanfly

Elite Veteran

ontario

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that doesn't sound like the consistency I got with phase lag correction. You have to remember the rotor system is a resonant one.

Now, I have a 700dfc align product and checked to see where the pl would be when all I did was rotate the pitch arms 180°. The stem portion that encases the bearings is now leading in rotation. It puts the swash balls back to about 78°. Being a rigid head sytem I then measured where the blade would flex most (in order to flap) at 130mm from the main axis, about 1/6th the entire length to the tip.

When I took my tape measure and placed one end at the main vertical axis then rotated the entire 770mm tape toward 90° I lined up the end point at 90° to the point outside the blade clamps at 130mm and it got generally a 78° angle (blades placed parallel to the boom).

So mechanically setting phase lag could be as simple as that, phase lag being 90° but 90° from the point the blades flex to allow them to pendulum/teeter with every flapping motion, is------all, not the 90° to the main shaft axis everyone's had to be subjected to by the industry. Remember not all gyros have a swash rotation function and especially not the 3gx that came with my 700.

This is just reasoning with all the info that's been gathered over the past couple of years. This hobby can teach you a lot about yourself, and others,

07-09-2016 04:29 AM
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icanfly

Elite Veteran

ontario

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this site is pretty tame, in any other situation guys would be all over me for expressing ideas without mathematical formula by which to stifle the critics, haha.

Instead of editing the last reply I thought it necessary to inject something to spruce up the air around here. I read of a micro 180 size heli that's got some bad behavior and knowing it's not possible to reply to help the guy out it'll have to be left to his own management )and other members ignorance) to sort it all out. The "micro" heli will show flaws much quicker than a large heli.

Here are two pics of my dfc head mechanically set for about 78° phase lag, ohh soooooo simple (my 300 with ALdfc head has this done to it)

what you don't know is that in a resonant system there are harmonics which can confuse a controller and it will manifest in ugly wobble behavior. How I know? That wobble is exactly what a heli of mine produced as long as the phase was as manufactured. I broke the part that set phase and repaired it to allow phase adjustments mechanically, thing flew like never before, no wobble, no tip overs, easy to fly and predict, raised my confidence miles.

In fs helis a pitch event will not act on the heli until 1 second later. perhaps the delay is there on a rc heli but it would be miniscule in comparison, yet still there. One must master the art of anticipation or as stories of students in fs chasing the stick disclose, you have to stay ahead of the swash inputs to instinctively fly the heli well. That got to be troublesome in the non perfect engineered rc heli product I and you bought into when we first entered the hobby.

since messing with my helis's performance and adjusting where possible there's no turning back, they are a joy to fly compared to just flyable mostly, not perfect, now they're awesome.

07-09-2016 03:12 PM
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revmix

Key Veteran

NJ

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phasing angle [78~90] is not critical as the swashplate & rotor disk respond to the position of the Tx cyclic stick; just have to feel it

07-09-2016 03:17 PM
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icanfly

Elite Veteran

ontario

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that's pretty good, ever see how some guys rotate their gimbles on the Jeti they own?

My instincts want my rh forward movements to parallel the actions of my left control, comes from riding bicycle and motorbike for many many years, both hands/arms parallel at all times fixed position especially in high intensity riding. That subconscious control action makes itself apparent when actuating the gimbals.

With phase corrected at the heli there's a lot it solves in the helis performance, a lot.

07-09-2016 03:24 PM
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revmix

Key Veteran

NJ

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on one of my Tx cyclic right stick the 2 springs are removed & the gimbal has no preload friction, just have to get the hang of it

07-09-2016 03:38 PM
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icanfly

Elite Veteran

ontario

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The rotor is a HARMONIC system. When there's some form of flex in the blades there will be a teeter fulcrum, in fs they call that offset hinge. If your fbl gyro isn't able to get a lock on oscillation due to the micro delay in the control reactions it will end up chasing the resonance manifest as wobble and or tip over.

I had a pair of blades on a 450 that were very flexible, glass fiber, and they wobbled like mad on the old unmodified unadjusted pl head set up. I then did a mod to allow pl to be set where the flex point on the blades was the 90° junction 80mm from the main shaft axis (of 350mm total to the tip) and adjusted pl angle to intersect that point at the disc's perimeter, Wobble went away, heli was flyable.

Some things can't be masked at the tx is all I'm saying.

If you want to experiment and make the heli more locked in just run a screw into the head button hole and tighten it onto the spindle.

Then there's the matter of rotor height, lol, just read about a fs prototype where the mast had to be raised or else the rotor would oscillate, HARMONICS. You have to know a little about sound frequency to understand the dynamics of resonant frequencies, everything has one.

07-10-2016 02:18 PM
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revmix

Key Veteran

NJ

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the Schluter Magic has 45 degree phase

right stick cyclic;
down (back); Swash is tilted to the right and rearward
up (forward); Swash is tilted to the left and forward
left; Swash tilts to the left and rearward
right; Swash tilts forward and to the right
~
regarding vibration; 2 per rev in the rotor disk

07-10-2016 03:26 PM
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Agilefalcon

Key Veteran

Fort Worth, Texas

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I don't think the Magic has 45 degrees of phase. That's a consequence of the frame, servo location and linkage run design.

At the head (which is where you need to be measuring) you'll find it's the same as any other model helicopter. That is, to roll right on a clockwise rotation helicopter, you essential push up on the aft portion of the rotor disk (by increasing lift on the blade passing over the boom).

Chris Berardi
Team BobbyJack's Hobbies

07-10-2016 04:30 PM
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revmix

Key Veteran

NJ

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the washout is 45 degree in relation to the head hence the swash movement,
the 90 degree phase is ahead for the blades

07-10-2016 04:54 PM
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icanfly

Elite Veteran

ontario

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here's a quote from a fs forum about mast height and aero effects on a h60.
Posted 01 May 2014 - 22:06

FWIW, the prototype of the H60 originally had a shorter mast than when it went into production; one of the requirement of the bid was for minimal maintenance to load into a C130 or C141. However, Prouty's book mentions undesirable aerodynamic vibrations with the short mast so a 15 inch extension was installed which solved the vibration problems.
I remember reading of a Compass or Cell 500 that had mast height vibes which afterward were corrected with a longer main shaft. This has also helped uncover another mystery regarding the interactions between phase and cross coupling with the mast, all good to know on an engineering level for future reference.

07-10-2016 05:23 PM
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John Benario

Veteran

Las Vegas

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Icanfly, the phase delay is related to the hinge offset, as you stated.

The Robinson is a teetering head, even though it has flapping hinges, in flight as the blades flap up the rotor disc teeters on the center hinge no different from a Jet Ranger. The individual flapping hinges simply take the bending stress off the rotor head, allowing the rotor head to be so small. (Frank Robinson was a design genius)

The mathematics show that as the hinge offset increases the phase offset increases. The Brantley helicopter is extreme as the flapping hinges were about 30% out the blade.

So why does the Robinson and Jet Ranger, with a teetering head, have swashplate offset when you wouldn't expect it, and the BO-105, BK-117, Aerospatiales, etc, have phase offset when you do expect it?

It comes down to flight testing. The Bell 222 has swashplate lead of about 60 degrees, which is very large, but they made the main shaft splined so the swashplate could be moved, and flight testing showed that the pilots liked the feel best with the large swash lead.

The 222 had a elastomeric center hinge with the seesaw being flexible titanium, and very substantial metal blades.

"Aerodynamics of the Helicopter" by Gessow and Myers is the classic helicopter text, with "Helicopter Performance, Stablity and Control" by Prouty and "Rotary Wing Dynamics" by Stepniewski and Keys more modern texts.

Knowing calculus certainly helps understanding the mathematics, but something I realized many years ago in college when I was trying to analyze a model head, performance is of overriding importance in full scale design since payload and fuel efficiency sell helicopters, and in the model world performance is not important, we just put a bigger engine or motor.

In the model world we care about stability and control because that affects how we like the model, but in the full scale world, lousy stability and control don't matter, the pilot or electronics can overcome deficiencies.

John Benario

Team highest quality
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John's Ultimate building school

07-10-2016 10:29 PM
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icanfly

Elite Veteran

ontario

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So why does the Robinson and Jet Ranger, with a teetering head, have swashplate offset when you wouldn't expect it, and the BO-105, BK-117, Aerospatiales, etc, have phase offset when you do expect it?
"Pitch flap coupling"

In net pics viewed of the bo105 head you can see pl set less than 90.

As one info said about removing one of either axis of blade freedom, engineers were playing a game of Chinese checkers trying to take out one function then having to add another to solve the original problem of blades needing to be free to move on both vertical and horizontal axis to flap and lead/lag respectively.

Rc helis have spindles that bend and dampers that allow some freedom, only when you have hard dampers, locked spindle, and or dfc do things change while high rpm masking the coupling somewhat.

It's understandable why a high rpm 300 could be flown nobar except for ballooning in flight and wind and why guys in the early days had a hard time conquering the scale size model without electronic masking since rpms were a lot slower than today's machines.

I'm certainly not interested in correcting pl on the tx, so I finally did something about the manufactured flaw and was duly rewarded with much more confident control, CONFIDENCE is what wins the day every time. Some guys get real down on themselves when things don't work out like that of their ability to succeed in mastering rc heli flight control. May not sound like much to some people but it can be a big deal to guys with sensitive characters, and a big deal to down time repair and subsequent expenses incurred by so called "dumb thumb" mistakes. All about feeling more "connected", connected is good, very good. I personally never felt comfortable nor connected when controlling the heli with off axis control before the tiny issue was repaired.

One unexpected and astounding benefit to my pl corrective surgery, lol, was flying in high winds, the heli wasn't tossed around quite like it was beforehand.

07-11-2016 03:37 AM
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