FBL blades

[extrapilot]

Originally Posted by dunkonu23

R,

Sometimes, a couple of degrees is all it takes to make a model helicopter act as described earlier. I don't know if this is still so, but Align flybarred helicopters had about 2 degrees of phase lead built into their heads. There's a Finless video where he talks about his and shows it (I think it's a T-Rex 500 video). Depending on the blade, it can and does cause the problems mentioned earlier.

2deg phase error in your flip resolves to an aileron stick input of approx 0.7mm. Maybe you can detect that, but most pilots just automatically correct things like this- as they do with inherent roll from FFF, etc. FBL may not like a 2 deg error- I have not tested it- perhaps it is a disaster. Considering the Lock number on blades of different types will change the phase by more than 2 deg, that scenario is hard to imagine.

Originally Posted by dunkonu23

Yesterday, I did a lot of research. You're spot on with your statements of lead/lag/flap... etc... where they apply to full sized helicopters. There are scale factors in model helicopters where small changes can often yield huge results.

Scaling is an issue, but what makes you think smaller = more sensitive? And, we are talking about phase angles- which scale exactly.

Originally Posted by dunkonu23

Blades do settle on spool up. Most of us have experienced a wobbly helicopter on spool up. I'd venture to say that virtually all of this wobble is because the blades haven't settled and as RPM increases, centripetal forces force the blade to seek center.

Lead/lag of the blade in flight depends on the factors you state, but I don't believe it happens to the degrees you stated originally and then later...

Blade flap is there, for sure, but I don't think it's at the degrees you state. Since there is little research on model helicopters in this direction, it would make a great project to define parameters, but I just don't have the equipment to do so.

Yep, it is there. It is not difficult to see (do a runup with a 450 securely mounted, with a camera safely offset but level with the rotor plane, and run the cyclic around…). You will be surprised- 5-10deg disc tilt (flap) is pretty typical.

Have a look at this video. It is not ideal because the head itself is bending, which masks the extent of the blade flap. And the framerate is too slow to catch the lead/lap oscillations- though you will catch some jiggles now and then. But there are times when he has lots of collective in, or changes of direction, when you can see many degrees of lead or lag bias in. This is happening to us all during our flights-

Interesting topic- nice to revisit some old assumptions and dust off some books!

[ame]http://www.youtube.com/watch?v=xV0GkdGxEuo[/ame]

[dunkonu23]

Originally Posted by extrapilot

2deg phase error in your flip resolves to an aileron stick input of approx 0.7mm. Maybe you can detect that, but most pilots just automatically correct things like this- as they do with inherent roll from FFF, etc. FBL may not like a 2 deg error- I have not tested it- perhaps it is a disaster. Considering the Lock number on blades of different types will change the phase by more than 2 deg, that scenario is hard to imagine.

The two degree phase error I mentioned is something that is seen, depending on the blade. Seriously. When I get back from work (and flying.. the weather is great here), I'll post the link to the Finless video I mentioned. As I recall it was seen in rolls. Sure, you can correct, but you don't know to correct unless you can see it. As I recall, Finless corrected the problem by using different blades. So, yeah blades make a difference, but that's never been the debate topic.

Originally Posted by extrapilot

Scaling is an issue, but what makes you think smaller = more sensitive? And, we are talking about phase angles- which scale exactly.

Head speed and the differences in design between full scale and model helicopters. Yep, 90 degrees is 90 degrees.

Originally Posted by extrapilot

Yep, it is there. It is not difficult to see (do a runup with a 450 securely mounted, with a camera safely offset but level with the rotor plane, and run the cyclic around…). You will be surprised- 5-10deg disc tilt (flap) is pretty typical.

I'll give you that, if you hold it down there will be that much tilt. But in flight? I don't know. Depending on model size, I think any tilt will be quickly transferred to the airframe--smaller equals faster--which will cause the model to assume nose down or up attitude for elevator inputs, roll for any aileron input. Damping matters.

Originally Posted by extrapilot

Have a look at this video. It is not ideal because the head itself is bending, which masks the extent of the blade flap. And the framerate is too slow to catch the lead/lap oscillations- though you will catch some jiggles now and then. But there are times when he has lots of collective in, or changes of direction, when you can see many degrees of lead or lag bias in. This is happening to us all during our flights-

Interesting topic- nice to revisit some old assumptions and dust off some books!

http://www.youtube.com/watch?v=xV0GkdGxEuo

I'll have to check it out this afternoon and get back to you.

Scott

[dunkonu23]

I watched the video. Very interesting. I had seen similar videos, but nobody took the time to stabilize the background nor did they put a reference line on the screen. You're right. I'm wrong. It woujld be nice to know what size helicopter was being used and if the blades were tilt and tap tight or tighter. But you're right, sir.

I don't know about the head bending, I think what was seen was damping allowing the flap. I would also be nice to know degree of damping.

I still think I'm right about Chord CG and how it affects phasing.

Thanks for all this, sir. I stand enlightened. Now... off to make blades flap.





Scott.

[extrapilot]

Hey Scott

I would be fascinated to see a system with a true 2deg phase error yield a 30deg yaw in a flip. If you lived closer, I would ask to instrument your machine so we could see exactly what is happening. More probably, the Lock number of the changed blades is significantly different, so the phase delta is more in the 10deg range.

On the scale thing, the problem is that certain things work to our benefit, and certain things do not. For example, our rotors have lower tip speeds, but higher accelerations (centrifugal force). Our disc loading is much lower, but our chord to length ratio is higher. Etc. But the physics all work the same way- you just have to break out the vector math etc.

Yep, in flight- it is of that magnitude. Imagine you enter a full-stick flip. The chassis has inertia. Its angular rate increases, but so does that of the rotor, until the required chassis rate is achieved. Likewise, in FFF, the advancing blade sees higher airspeed, which means, at a given AOI, more lift. It must flap up to drop the AOA. The retreating blade sees slower airspeed, and must drop to increase AOA. That is the dissymmetry of lift thing- where the rotor flaps to equality. If this did not happen, the machine would roll uncontrollably.

Even if the dampers were solid metal, the blades would still bend- just not as much- and the phase would change yet again. Something to think about- this is analogous to the tail rotor- where for most designs, there is no provision for flap (it is all in the blade). So, in FFF, you have a nasty dissymmetry, which gets worse with increased blade stiffness. That creates all kinds of hell on the tail subsystem.

On the video, yea, both flap an lead/lag are masked to a large degree. The reason is that the cam is synched to the rotor RPM (well, it attempts to…). So you really are seeing just one quadrant. What you are not seeing is the opposing quadrant, where flap and lead/lag are generally reversed. So, it is not a very complete picture of the dynamics in question, but it helps to see at least some of the magnitude.

Peace
R

[dunkonu23]

Hi R,

The old Align flybar head/swash combination did have a two degree or so phase error as I've read but can't seem to find, now. (I didn't look too hard after watching the video you linked, though.) I don't use those heads, though. Mechanically, my phasing is at 90 throughout the head and swash so when I spoke of about a 30 degree tail movement, it was with a 90 degree mechanical setup. And it's true that the only thing or could do to fix it was install blades. It just so happened that the blades were from a different manufacturer. I'm thinking I got a bad set of blades... it happens, no biggie. I've sent the blades to a friend so he could be the third person to test. He does use a different head than I use, so we'll see. Prior to this, I had done everything in my power to take my stick control out of the loop, including tightening the aileron and rudder tension on my transmitter and having another person fly the helicopter with my transmitter. Everything was as I stated.

It would be cool to test this stuff. After thinking about it, there's no way to determine whether damping or blade flex caused the flapping in the video. Either way, it happened. I'm not surprised it happened, but I am surprised it happened to the degree it happened. I agree on the physics, but like I wrote, I'm surprised at the extent.

Scott

[extrapilot]

Scott

Phasing is tough to adjust. People assume it is 90, but for our machines, it rarely is- and is often much less- 70deg-80deg-ish. One way to check is to do a tethered runup, and apply pure forward cyclic. If the disc has any lateral tilt, the phasing is off. As I hinted, I suspect 2deg is not relevant in this- there is more slop than that, more lead/lag than that, etc, and even without those things, it still is debatable if a less-than-master pilot could detect it; it can move around by a few degrees in flight for various reasons, so 2deg is less than the noise floor.

Re: flapping- it doesn’t matter if it is blade flex or damper hinge. Changing the damper stiffness (increasing it) should decrease the phase angle. If you have no flap, then you inherit problems with asymmetric lift, and lots of vibration.

Rob

[helidude71]

Originally Posted by extrapilot

Scott

Phasing is tough to adjust. People assume it is 90, but for our machines, it rarely is- and is often much less- 70deg-80deg-ish. One way to check is to do a tethered runup, and apply pure forward cyclic. If the disc has any lateral tilt, the phasing is off. ....
...
Rob

Cool! I think I see this.
When I'm in a hover and give forward cyclic only, I see the disk tilt to the left a bit.
The opposite happens when I give backward cyclic only.

Can I adjust this by NOT setting my swash driver perfectly in line with my blade grips?

What do you mean by tethered runup? (Sorry, I'm a none native speaker and I don't understand this.)

Thx.

[extrapilot]

Helidude-

Your English is perfect- I wish I could speak Dutch!



Phase (aka Gamma) is defined as the relation between the peak offset of the swash, and the peak offset of the disc (tip path plane) in motion. So, if your Gamma angle is not what you want, you have to figure out what your options are electronically or mechanically to change that relationship. Seems some heads have capability for this mechanically. I don’t recall if the uB has electronic phase adjustment via the PC yet… If neither of those work, you may have to experiment with different blades (different types).

A tethered rununp is where you have your machine tied (tethered) to a massive object, in a way that the frame will not move during ground tests. If it is just held by the skids, then the skids can deform and cause the tilt to seem biased. If you are looking for just a couple degrees total tilt, and the left/right tilt is even less, you have to make sure it is rotor only and not from the chassis twisting. And, it could be that your servo/swash geometry is not quite right, so that the Gamma is 90, but your swash itself is not moving as you expect it to.

Cheers-
Rob

[dunkonu23]

No, the head's at 90, R. It's hard set. There's no way to adjust it on 4 of 5 of my flybarless helicopters, so I change blades.

Scott

[extrapilot]

Sorry, I was not clear. I meant to say that the phasing is often assumed by designers to be 90, and their initial designs become templates for later designs (or cloned by others...), but the actual value may be significantly less.

[helidude71]

All clear now Rob.
Thx for the explanation.

I can adjust phasing by twisting the swash driver a bit.
Currently it's not possible with BeastX software, you have to select 120* swash for my setup.

I will play a bit with this to see the effect in a hover. It scares the hell out of me to do the tethered rununp.
(Now I know what this means.)

P.S. Thx for the compliment you're welcome to learn Dutch if you like.

[airjawed]

So what is a reasonable way for us to adjust/check phase angle? Assuming that you can either adjust the swash mechanically or electronically.

I was previously under the impression that the heli tilting on cyclic on the ground was normal. I assumed that in the air it would flip cleanly which it does end up doing or appears to. Perhaps the heading hold gyro masks the tilt since the tail will track straight in a flip.

Any scale fliers with multiblade rotors out there know a good way to set phase angle?

[dunkonu23]

Originally Posted by extrapilot

Sorry, I was not clear. I meant to say that the phasing is often assumed by designers to be 90, and their initial designs become templates for later designs (or cloned by others...), but the actual value may be significantly less.

Sounds snobbish, I know... but I don't buy clones, bro. The only helicopter I have that I can adjust phasing on is a Velocity 50 with an Outrage head. I made it 90 at the head (no way to adjust the rotating portion of the swash) was to twist the swash driver while holding a glass strip against the head--it's flat on opposite sides--and the swash driver arms. I twisted until the glass was flat against both surfaces. Flips great! Pain in the ass, but worth it. I much prefer phase neutral swash driver/head designs. Of course, in all of models there are tolerances, but I don't think it's significant enough to stress over.

Scott

[dunkonu23]

Airjawed,

There are two or three flybarless controllers out there that I know of--don't want to mention names in the BeastX forum--that allow phasing adjustments, electronically. I don't own a three or more bladed rotor, so I don't know the process. You're right, it'd be nice to know.

Scott

[extrapilot]

Originally Posted by helidude71

All clear now Rob.
Thx for the explanation.

I can adjust phasing by twisting the swash driver a bit.
Currently it's not possible with BeastX software, you have to select 120* swash for my setup.

I will play a bit with this to see the effect in a hover. It scares the hell out of me to do the tethered rununp.
(Now I know what this means.)

P.S. Thx for the compliment you're welcome to learn Dutch if you like.

I have not tested how this plays out in an FBL. The problem is that, if the FBL is mounted to the chassis, and the chassis moves, the swash will be caused to counteract. So, example, say you tie the skids to a test mount, and do a runup at 0deg collective. You then add forward cyclic (should be 12 o-clock rotor tilt). Say the phase is off 10deg, and this causes some unintended roll. The FBL will detect that chassis roll and command a counter-roll.

Since the system has decay, it is possible that this effect will not be so major, and that even if the chassis rolls a bit, that the head will eventually settle in the same place it would. Hard to know without testing. But, that is a reason for trying to secure the chassis- so that the FBL is not seeing chassis pitch/roll.

It might be better to bypass the fbl for initial phase testing, but realistically, you will need to adjust phase for different blade types. Hopefully, the uB guys will include some electronic phase adjustment- the math is not difficult, since they already have the swash ring logic done.

Cheers
R

[extrapilot]

Originally Posted by dunkonu23

Sounds snobbish, I know... but I don't buy clones, bro. The only helicopter I have that I can adjust phasing on is a Velocity 50 with an Outrage head. I made it 90 at the head (no way to adjust the rotating portion of the swash) was to twist the swash driver while holding a glass strip against the head--it's flat on opposite sides--and the swash driver arms. I twisted until the glass was flat against both surfaces. Flips great! Pain in the ass, but worth it. I much prefer phase neutral swash driver/head designs. Of course, in all of models there are tolerances, but I don't think it's significant enough to stress over.

Scott

A core problem is that, even among aero engineers, there are few who really understand rotary aero.

Some faulty assumptions made in the 40s-50s made it into books, and that made it into classrooms, etc, and these bad assumptions just get ingrained/entrenched. Even now, you will see fundamental concepts presented in aero engineering texts that are simply wrong. So, it is sort of a comedy of errors, where some guy built something based in part on faulty texts, and some other guy copies his work, etc.

So, yea, there is fair argument about the IP theft aspect, or the mfg quality of a cloned system, but a more important question is- were the errors cloned also?

[helidude71]

Maybe just wait for the microsettings become available for v3?
Really cool to adjust it electronically and make it perfect for the blades you are running.
(And leave the swash driver as it is.)



(Image found on beastx.com forum.)

[airjawed]

My question isn't how its done so much as how you know it is done right. I've got a 450 pro with BeastX... when the V3 with swash phasing comes out what should I do? Is it trial and error?

[dunkonu23]

I hear you. When I was researching this stuff, I found a lot of contradictory information. I suppose because a lot has been assumed as you wrote. My own assumptions were based on the readily available information from forums and from cursory reading on the Internet. Unfortunately, the Internet is what it is and chaffe abounds. So, now that I have been set straight on many things, there are things that I'm not clear on, but I did do some checks on some blades I have laying around and discovered that the FBL blades I have all have their span CG further from the root than their FB equivalent. I also found that on the blades where they do not scissor when suspended from their mount mount, apparently chord CG and span CG are damn near spot on with each other. So, there I go.

Scott

[fusionsx00]

ok,
so after a few rounds back and fourth,,,


what are the best fbl blades for helis. edge fbl?

post and why?

X5- edge 523 fbl, great improvment over stock and rjx blades.
these are balanced very well chord wise and 1 thin tape on one blade
to balance them out.
just everything down the line is better, but the biggest is flips, rolls, tictocs