FBL ,... Am I backwards :-S

[LaurenceGough]

Hmmm, the tail is a bit different right, but if set-up for the same travel in both directions it shouldn't matter. The 450 pro comes with not enough tail pitch in one direction so the trick is to either reverse the grips to trailing edge control or to extend the tail shaft (flys miles better then).

[coolice]

Hey.

There will be a difference between leading and trailing edge control, anyone remember the old Raptor grip flip trick to make it fly better? The latter was on a flybarred setup, but it highlights there is a difference between the two options, in this case it cured a flutter problem.
Having said this however, on a FBL model running dedicated FBL main blades which have a chordwise centre of gravity on the bolt hole centre line, one would assume there should be no difference as the feedback to the swashplate should be the same. But from memory there is a difference.

If the conversion is meant to run leading edge control and you're running trailing, to rule it out as a possible cause to any problems it wouldn't take a lot of fiddling to flp those grips. Flip them over and change the pitch direction and any other FBL controller settings.
.

[waveydavey]

[QUOTE=coolice;760633]Hey.

There will be a difference between leading and trailing edge control, anyone remember the old Raptor grip flip trick to make it fly better? The latter was on a flybarred setup, but it highlights there is a difference between the two options, in this case it cured a flutter problem.
Having said this however, on a FBL model running dedicated FBL main blades which have a chordwise centre of gravity on the bolt hole centre line, one would assume there should be no difference as the feedback to the swashplate should be the same. But from memory there is a difference.

If the conversion is meant to run leading edge control and you're running trailing, to rule it out as a possible cause to any problems it wouldn't take a lot of fiddling to flp those grips. Flip them over and change the pitch direction and any other FBL controller settings.
.[/QUOTE]

There you go, about to type the same. But written by someone far more knowledgeable than me, thanks Ian

[coolice]

[QUOTE=LaurenceGough;760626]Hmmm, the tail is a bit different right, but if set-up for the same travel in both directions it shouldn't matter. The 450 pro comes with not enough tail pitch in one direction so the trick is to either reverse the grips to trailing edge control or to extend the tail shaft (flys miles better then).[/QUOTE]

Hey buddy.

Not only did this help balance out the tail travel on either side but users were also able to raise their gyro gains as a result of flipping the grips.

There is an aerodynaic difference between the two but its not in my memory currently, its been a long time since i setup a machine for smooth F3C flying ;-) but I bet Noel Cross would probably be able to answer this straight away.
.

[J-S-Q]

It can make a difference if there is delta in the head (i.e. if the balls on the blade grip are not in line with the centre of the main shaft). This is because as the feathering shaft rocks up and down in the dampers, the pitch of the blades will be altered by a very small amount. Depending on whether you have leading or trailing edge control, this effect will either be corrective (i.e. as the blade grip moves up, the pitch will be reduced, thus bringing the blade grip back down) or it will be non corrective (i.e. as the blade grip moves up, the pitch will be increased and tend to pull the blade grip even further upwards). Supposedly, the corrective effect can lead to a more stable feel, with lower current draw on the cyclic servos. The non corrective effect can lead to a slightly more snappy cyclic feel, with higher current draw and more vibrations.

So, IF you do have delta in the head (i.e. short balls on the grips, that don't go far enough to line up with the main shaft centre line) then it might be worth changing to leading edge control and see if it cures the wobble.

[trillian]

[QUOTE=coolice;760640]Hey buddy.

Not only did this help balance out the tail travel on either side but users were also able to raise their gyro gains as a result of flipping the grips.

There is an aerodynaic difference between the two but its not in my memory currently, its been a long time since i setup a machine for smooth F3C flying ;-) but I bet Noel Cross would probably be able to answer this straight away.
.[/QUOTE]

I was going to mention the Raptor grip flip as I had the Raptor 'woof' and flipped the grips, but I think that was due to
some quirk of the Raptor head geometry. There was also a grip flip that used to be done with the Compass Knight in
order to get punchier collective.

Basically, if you have zero delta then as far as I know the only difference is that when the feathering shaft floats
up or down (and granted, it's a pretty small movement) you will have either a positive or negative collective effect
depending on leading or trailing edge control. So for example, if you punch the collective up, for just a moment the
feathering shaft is compressing the upper portion of the dampeners and riding upwards slightly as the blades pull
on the rotorhead. So the grips are moving upward slightly but the links to the swash stay still. So if it's leading
edge control this is causing a momentary decrease in the amount of overall collective (or put another way, the
leading edge control tends to 'correct' for this movement of the feathering shaft. If it was trailing edge control
the effect would be opposite and would slightly increase the amount of collective.


---- You managed to jump in there Jamie while I was still typing my comment. :-) Basically I think if there's
no delta I think the difference is pretty minor but when I converted the Ely.Q head to FBL it
just seemed like all the FBL heads I looked at were leading edge control so that's the way
I did it.

[coolice]

Hey.

On a flybarless head with direct links from swash to blade grip (not a JR FBL head with mixer arms on the grips) you won't find any delta at all, reason being it would introduce a phasing problem.

I think one of the main side effects is as Sheryl has said above, with any wind gusts acting on the advancing blade and exploiting any soft damper issues.
I'm also of the feeling there is something to do with the pivot point in relation to the blades chord, I think in this case there is less force or feedback to the servos with leading edge control. Again it doesn't seem that way in theory but I think there is something along those lines dictating why some follow a leading as apposed to trailing adge control.

I was thinking last night that Colin Mill would be another great oracle on this subject, as would Curtis.
.

[coolice]

Hey.

I just found this and it sounds spot on;

" Why do the blades stabilize with leading edge control?

Make some simple experiment: Take a heli with soft dampeners where you can move the blade up and down a bit, it should have leading edge control. Set the swash at 0° and somehow fix it there (or at least try not to move it). Now push on the end of the blade and watch how some positive pitch is added to that blade (as long as the swash and the linkage rods are fixed in their positions). In flight, any external influence on that blade will cause some minor change in pitch that counteracts the influence. So that system is self-stabilizing, because it always tends to go back to the position it came from. Now switch the blade grip and watch what happens at trailing edge - any deviation of the blade produces a pitch change that adds to the deviating force. Your flybarless unit will have to fight this.

The flybarless unit will not care about the difference, but todays servos are the limiting factor, as they have limited power and speed. So the self stabilizing approach should be the better one. If you use HV servos together with blades with much aerodynamic lead and want to do Crack Stick 3d, the other way might give you some quicker cyclic and collective response.

Thorsten"

While we have good servos and hard dampers, it makes me wonder if leading edge is preferred so as the dampers start to loosen up any movement in the feathering spindle doesn't cause any artifical inputs to the rotor disk that upset it.
.

[ModelGuard.Com]

A couple of posts from someone who knows about flight theory.

[B]This is an interesting thread! There's a lot of missunderstandings out there regarding this issue. So working from basic principles....and trying to answer the question.....Actually it's not which type to use, but which way has been designed into the head! You see, either will work, but the head must be designed so that cyclic pitch controls from the swashplate provide a "stable" movement of the rotor disc. For example, if we wish to roll or tilt the rotor disc to the right, as the disc moves and follows the swashplate (also tilted to the right), it is vital for stability that as the disc approaches the plane of the swashplate, that the cyclic pitch changes of each blade reduce to zero, so the disc ends up parallel to the swash. This also means that any "disturbance" to the disc plane is "resisted" and it is always brought back parallel to the swashplate. So whether a leading link or a trailing link is used, is actually irrelevant!
To put it another way, if a cyclic positive pitch is applied to a blade, as the blade rises, the blades pitch MUST decrease, so that as it becomes parallel to the swashplate, it stabilises and then stays parallel to the swashplate.
I hope that's clear?
It's taken me a long time to have a pretty good idea what's happening at head level, and I haven't mentioned gyroscopic precession or the reason for the flybar yet!
Enjoy![/B]

[B]
The answer is to realise that for a trailing link the pivot point for the blades rising and falling vertically, is moved out away from the hub centre, usually well past where the link connection is. On my Concept 60 (fraid I only fly vintage helis), which uses trailing links, a quick waggle of the main blades up and down will confirm that this is true. And this means that as the blade rises, its pitch decreases, an obvious requirement for disc stability!
To conclude, neither is best. Both will work, with the correct mechanical design!
I hope this helps?[/B]

[ModelGuard.Com]

If it were me, i would change it round, wont take a sec and if your wobble goes you know why. Otherwise youll always be wondering.

[coolice]

[QUOTE=ModelGuard.Com;760713]A couple of posts from someone who knows about flight theory.

[B]This is an interesting thread! There's a lot of missunderstandings out there regarding this issue. So working from basic principles....and trying to answer the question.....Actually it's not which type to use, but which way has been designed into the head! You see, either will work, but the head must be designed so that cyclic pitch controls from the swashplate provide a "stable" movement of the rotor disc. For example, if we wish to roll or tilt the rotor disc to the right, as the disc moves and follows the swashplate (also tilted to the right), it is vital for stability that as the disc approaches the plane of the swashplate, that the cyclic pitch changes of each blade reduce to zero, so the disc ends up parallel to the swash. This also means that any "disturbance" to the disc plane is "resisted" and it is always brought back parallel to the swashplate. So whether a leading link or a trailing link is used, is actually irrelevant!
To put it another way, if a cyclic positive pitch is applied to a blade, as the blade rises, the blades pitch MUST decrease, so that as it becomes parallel to the swashplate, it stabilises and then stays parallel to the swashplate.
I hope that's clear?
It's taken me a long time to have a pretty good idea what's happening at head level, and I haven't mentioned gyroscopic precession or the reason for the flybar yet!
Enjoy![/B]

[B]
The answer is to realise that for a trailing link the pivot point for the blades rising and falling vertically, is moved out away from the hub centre, usually well past where the link connection is. On my Concept 60 (fraid I only fly vintage helis), which uses trailing links, a quick waggle of the main blades up and down will confirm that this is true. And this means that as the blade rises, its pitch decreases, an obvious requirement for disc stability!
To conclude, neither is best. Both will work, with the correct mechanical design!
I hope this helps?[/B][/QUOTE]

Hey.

Where did these come from buddy? To me they only sound relevant to a flybarred rotor head, as it will have been designed to self stabilise by having any flybar deflections input corrective inputs to the main blades. Hence why its said it depends on what the heads been designed to use, where as on a flybarless head having the links at the front or back on paper makes no difference.

The more I think about I wonder if the leading edge is considered better as its more tolerant to different blade designs, specifically if they exhibit and lead/lag in flight due to weight distribution within the blade. But again the dedicated FBL blades are designed to fly in their neutral position so as not to lead/lag in flight.

It's a complex science that's for sure and one I'm now keen to hear a definete answer to now.
.

[moyesboy]

I chopped and changed my std trex600n head to flybarless. This involved flipping the grips to leading edge control, and because I used the std grips the links from swash to grip are nowhere near vertical - there is a big negative delta offset. So if the spindle mives up with positive pitch the leading edge grip reduces the collective pitch.
But also the delta offset means the cyclic is stabilised - if the spindle tilts in the dampers the pitch changes to push it back...or does it - problem is the cyclic input to tilt the disc forwards (for example) is applied 90 degrees before, but the pitch stabilisation from the delta offset occurs in the plane of the disc tilt - so that in theory makes a roll input from the pitch input - hence the idea that the delta offeset wil create a phase issue.
Now my 600n seems to fly perfectly staright with its beastX, but maybe the beadtie is working a little harder to correct those errors my cut and carved head is introducing. To correct it I'd need to extend the balls on my grips somehow (butI kind of like them as they are becuase they are more robust in a crash). Sometimes though I do see a little bit of a cyclic wobble when I release the cyclic input in hard 3D manoevres.

[J-S-Q]

[QUOTE=coolice;760705]Hey.

On a flybarless head with direct links from swash to blade grip (not a JR FBL head with mixer arms on the grips) you won't find any delta at all, reason being it would introduce a phasing problem.
[/QUOTE]

I don't know specifically of a direct linkage FBL head that has delta in it but there is no reason why you couldn't have one if you wanted and there wouldn't be any issues with phasing. Phasing is only dictated by the relationship between the blade grips and the ball links on the swash so changing the delta (i.e. moving the balls on the blade grips) will not alter this relationship. Some converted FBL heads certainly do have delta in them.

[rachel]

Just an update ,
I striped the heli and did find a small problem , the rotorhead hub although as thight as it goes is loose on the mainshaft , so maybe thats the wobble ?????
I have looked at a lot of FBL setups and the vast majority inc Align's are Leading edge .
So just for the experament I will flip the grip ,that will llok poo as the bolts will be upside down but hey ho, its Christmas.
lol
Interesting thread too

x Rach

[moyesboy]

J-S-Q - I reckon that the delta offset will introduce some 90 degree out of phase effects when the spindle has some teeter in the dampers (the disc is tilted). So it will give the FBL unit some work to do to correct it. In fact the effects of delta offset will always be 90 degrees off so I'm no longer sure how delta offset works at all!