Maximum recommended cyclic and collective blade pitch

[Carpetbombing]

I have a pretty solid understanding of the basics of aerodynamics. I've read Aerodynamics for Naval Aviators from cover to cover, anyway, and at one time could do all the math. Here's my question. Though there are obviously a ton of variables, from a general advice standpoint, what are the maximum recommended cyclic and collective pitches when setting up a heli? Can useful generalizations be made?

My 325mm helis run from 2,900 to 3,100 RPM.
My 360mm heli runs 2,800 to 3,0000 RPM.
My 425mm helis run 2,250 to 2,650 RPM.
My 520mm heli runs 2,150 to 2,350 RPM.

I ask because I just got a Soko gauge to set up my new 425mm Protos 500. The Soko allowed me to get more accurate pitch numbers for my helis than I had before. The Protos has really limited cyclic throws relative to collective because of the small diameter inner swashplate. The absolute max I could get after shaving away a little frame material was 12.4* of collective in both directions and about 10.3* of cyclic.

In my flybarred Trex 500 days, I found 10* of cyclic wasn't enough to give me the fast flips that I liked. 11* felt much better, so on my FBL helis I've been setting 11.5* of cyclic as the max available. (I set 360* per second pitch and roll in my FBL controller) Collective on my Gaui X3 was actually a little over 13*, and cyclic was over 12*. That thing flew GREAT; it was a monster and really strong, but the flight times suffered.

I never had the Soko when setting up my Gaui X5, so I'm not positive what my pitches were as I tweaked the setup, but on the larger 520mm heli I felt like it really needed a lot of cyclic pitch to wake it up.

I've recently had suggestions that anything over 10* of cyclic is completely wasted and the FBL controller would never command it anyway. I haven't been able to do much flight testing in Minnesota lately. (I refuse to fly under 20*F)

So - any advice for maximum collective and cyclic values that most people should stay below to stay aerodynamically efficient while maximizing performance? At what point are we too far past 'the curve' and far into the point of diminishing returns? I'm not looking to maximize hovering times, I want to throw the heli around, but so far I'm perfectly happy with sane and somewhat efficient headspeeds.

This information would be really useful to the vast majority of us trying to understand the sweet spots of setups. Thank you in advance!

[kumar2494]

The short answer is use whatever you feel comfortable with as long as there is no binding of the swash. On my nitro mostro, I have 12 degrees cyclic with vbar. I like the heli to feel very sensitive around center. With that however, I need to lower the cyclic gain quite a bit in order for the gyro to act normally. The more cyclic you run, the less gain you need. Most fbl units suggest that 8 degrees is optimal, but you can go up to 10 without any ill effects. Going past 10 degrees can bring out weird tendencies in certain gyros.

[helicek]

Hi,
are you asking when there is more drag than lift situation exists?
I had once inquired this to Spinblades but did not get a straight answer either.
I guess one has to try and find out himself.
Ahmet

[kumar2494]

Originally Posted by helicek

Hi,
are you asking when there is more drag than lift situation exists?
I had once inquired this to Spinblades but did not get a straight answer either.
I guess one has to try and find out himself.
Ahmet

Blades stall around 15 degrees, so that should not be the case.

[jbaum81]

Originally Posted by kumar2494

Blades stall around 15 degrees, so that should not be the case.

Why does just about every heli out there have around 45degrees of pitch on tail blades at the limits?

[kumar2494]

You set the tail endpoints to the max to give the gyro room to work , but you never actually max out the throw in flight. The most you use in flight is usually no more than 16 degrees, and that's if you have your rotational rate set high. If you were to use the entire 45 degrees throw, the rotational rate will be well over 1200 degrees per second and stall the tail, possibly stripping torque tube gears or skipping cogs on a belt. If you want to try this yourself, put the gyro into rate mode and pin the rudder. Just make sure you have everything strapped down well.

[extrapilot]

You are confusing physical blade pitch with aerodynamic pitch (AOI vs AOA). When you have axial inflow at the rotor (main or tail)- the AOA is < AOI. This matters a lot- where certain maneuvers like funnels and FF piros can see very high inflow speeds at the tail rotor- taking your 18deg pitch and putting the entire blade into negative AOA (read: no thrust in the desired direction).

Same thing happens with the main rotor when it is canted relative to the direction of travel, or when you have axial flight (i.e. vertical punch), and also just as a result of the rotor accelerating air (where the flow is already accelerated to ½ the outflow speed).

[kumar2494]

Extrapilot, I agree with you that the critical AOA can differ depending on the direction of the airflow and the specific maneuver the heli is in. I should have been more specific. I was referring to a stable flight configuration (hover) with minimum RPM and maximum pitch allowable before a stall (main rotor). With the minimum possible RPM, 15 degrees will provide the maximum thrust. Increasing the pitch will cause the blades to reach the critical AOA, and the heli will no longer be able to maintain flight. With the tail rotor, I was referring to being in an accelerating piro. At some point in that piro (before the max mechanical pitch is reached), the blades will reach the critical AOA and will no longer be able to accelerate the tail any more.

[extrapilot]

No, that is not correct. 15deg means nothing. The foil/camber along the blade’s span, the blade twist, the rotor coning angle etc are not defined. There is also a blade loading component, where that alters the flow profile, etc. Regardless, no one should setup their 3D machine for stall at hover. If you are doing high speed funnels, you will require substantial AOI on the tail for a couple of orientations. In FFF, you will need substantial cyclic to offset lift dissymmetry, etc. Because in all these conditions you have an axial inflow component that can be many times higher than that seen in hover, talking about stall as a function of AOI makes no practical sense. The OP needs whatever pitch is required to generate the thrust needed, and that will be based on a slew of variables which are not defined.

[kumar2494]

This thread has gotten a bit off topic. The OP was just wondering what the max cyclic and collective pitch should be used in a general 3D setup. 14.5 degrees should not be exceeded for collective, and 10 degrees should not be exceeded for cyclic because of gyro performance and possible binding. Some, such as vbar can go past that, but it requires a substantial change in setup.

[Carpetbombing]

I'm not worried about the tail. I set max mechanical throws available and let the gyro do the rest; works great for me. I'm just curious about the collective and cyclic; principally the cyclic. Let's keep it simple and say that I'm only interested in exploring the maximum practical cyclic pitch that should be set for spirited flight. Collective wouldn't exceed 12 or 13 degrees. I'm not interested in extreme, specialized, bleeding-edge applications - speed runs or super hard core 3D.

Just in case I need to specify, let's also presume no mechanical binding anywhere. I also understand that I can do 'whatever works for me,' but I'm seeking to understand this a little more thoroughly than that.

With the Soko and the Skookum SK540 there is NO problem whatsoever setting whatever combination of collective and cyclic the head geometry will allow. 10* of cyclic seems to be some kind of sacred cow, and I'm trying to understand why. I can't think of an aerodynamic reason why cyclic pitches above 10* wouldn't improve roll rates.

Yes, there are innumerable variables, but ultimately people are setting up their helis with SOME maximum value for collective and cyclic. I'm looking for a useful generalization here based on some science. At what point do you stop seeing practical gains from upping cyclic pitch; at what point are you clearly past the point of diminishing returns for amp draw / stalling the airfoil? If anyone here has practical experience pushing this and coming to conclusions, or theoretical knowledge that might be useful, I'd love to hear it. I'm not aware of good information out there on this subject.

[kumar2494]

Technically, you can increase cyclic as much as mechanically possible, and the roll rate will continue to increase as well. However, increasing it that much will force you to decrease the gyro gain so much, that it will not be performing optimally for all flight situations and will be out of its control loop. Gyros are meant to work between a certain parameter for each size heli. For example, a 700 will run close to 70% cyclic gain at 8 degrees cyclic. If you increase pitch to 14 degrees, you will have to decrease the gain to 35%. When you have more mechanical gain, you will need less gyro gain because the gyro correction will cause more of a response with 14 degrees as opposed to 8 degrees. However, because the gyro is now operating outside of its optimal level for a 700 and now have the gain of a 450, it will become less stable in fast flight or high wind conditions. You can try to counter this by decreasing the ball spacing on the servo arms, but the gyro may still have some strange tendencies because you are still not within the control loop. Jason Bell did this with a vbar on his aurora, where he ran high cyclic pitch, low cyclic gain and decreased ball spacing. He wanted the heli to be as fast as possible for smack 3D, but he said that the heli is unstable in big air maneuvers. 10 degrees cyclic for larger helis seems to be the best combination of cyclic response and gyro performance without being outside the control loop. This is because you are only increasing the mechanical gain slightly and decreasing the gyro gain slightly, which still allows the gyro to work correctly. As I said before, it also depends on the control loop of the gyro. A higher end gyro with a faster control loop will be more forgiving with 10 degrees cyclic than a lower end gyro with a slower control loop. This is why you see 10 degrees being used with the vbar, skookum, ikon, and other higher end gyros. Try using 10 degrees on a 3gx and I guarantee it will make the heli feel less stable than it would be with 8 degrees.

[Russell Harding]

All science aside, a very common rule of thumb is for 12 for collective and 8 for cyclic.

You mention your old flybarred heli, but due to the way the flybar interacts with the pitch, the roll rates are much slower with flybar. Remember, with flybarless, you are not actually controlling the cyclic pitch anymore (directly), only the commanded roll rate. Unless you are running crazy rates, you will be fine at 10* of cyclic.

Aerodynamically the blades can go FAR beyond 15* before stalling. There lift/drag relationship isn't very good and the motor usually starts to bog and/or othe drivetrain and power system is overly stressed. For 3D flight, 12-14 degrees is the usual range; and up to 16 for speed.

[Xrayted]

Originally Posted by Carpetbombing

I'm not worried about the tail. I set max mechanical throws available and let the gyro do the rest; works great for me. I'm just curious about the collective and cyclic; principally the cyclic. Let's keep it simple and say that I'm only interested in exploring the maximum practical cyclic pitch that should be set for spirited flight. Collective wouldn't exceed 12 or 13 degrees. I'm not interested in extreme, specialized, bleeding-edge applications - speed runs or super hard core 3D.

Just in case I need to specify, let's also presume no mechanical binding anywhere. I also understand that I can do 'whatever works for me,' but I'm seeking to understand this a little more thoroughly than that.

With the Soko and the Skookum SK540 there is NO problem whatsoever setting whatever combination of collective and cyclic the head geometry will allow. 10* of cyclic seems to be some kind of sacred cow, and I'm trying to understand why. I can't think of an aerodynamic reason why cyclic pitches above 10* wouldn't improve roll rates.

Yes, there are innumerable variables, but ultimately people are setting up their helis with SOME maximum value for collective and cyclic. I'm looking for a useful generalization here based on some science. At what point do you stop seeing practical gains from upping cyclic pitch; at what point are you clearly past the point of diminishing returns for amp draw / stalling the airfoil? If anyone here has practical experience pushing this and coming to conclusions, or theoretical knowledge that might be useful, I'd love to hear it. I'm not aware of good information out there on this subject.

Don't overthink it. Remember, your FBL controller now determines your max flip and roll rate, assuming there is enough available cyclic pitch to accomplish it. Increasing the cyclic pitch changes nothing unless you change the FBL settings.

I'm a Skookum user as well, and your control rate setting in the software is shown in degrees per second. Setting 300 degrees per second will give you that max flip rate at full stick deflection as long as you have enough cyclic there to get there. 10* is typically plenty enough depending on what control rate you have set, and in many cases 8* is all one needs. Adding more cyclic availability won't do anything unless you up the rate in the software, so it's useless and wasted at the risk of binding. I'm a sport flyer and I like the feel of 280-300* degree control rates, but this will vary from one size model to another, and is personal just like most other tuning parameters.

The magic number in the Skookum setup software on the cyclic servo setup tab is in the 60-65 range for the aileron and elevator cyclic settings. Collective can be whatever value you need to get the pitch limits you want. Any more than 65 on the cyclic servos and you run the risk of binding in the event of full collective and cyclic, but there are also exceptions depending on the model.

Getting the values in the 60ish range is also a good indication that your in the best servo resolution range on the swash and won't run into any cyclic gain tuning issues. The values will turn yellow over 65 to warn you that you are pushing the servo travel out of bounds and need to mechanically change things by using a different servo hole farther out if you need more throw.

[Carpetbombing]

Hmm. Interesting. I was thinking purely aerodynamically, but I can see how the mechanical / electronic gain relationship would need to be adequately balanced. I'll have to check where my cyclic gain settings are on my helis - I think everything is between 40% and 50%. Most of my swash percentages are right around 60-65%. I'm still getting a feel for the cyclic acceleration setting - I'm using about 50% on all my helis right now. Bell gains are high 60's or low 70's.

For my Gaui X3 and Protos 500 I have my pitch and roll rates set to 360*/s. That's the max Skookum will allow. Maybe that's pointless, but for some reason it's fun for me to yank it back and do quick backflips. I tend to change my pitch curves so they're more sensitive around mid-stick, too. Yaw rates around 600-640*/s. My 'slowest' heli set-up is my Gaui X5, at 320*/sec pitch and roll. After slowly increasing the rates, I can definitely tell you that those are the rates I prefer the feel of.

Though everything is related, this shouldn't be a FBL controller specific discussion. It sounds like the jury's still out on the aerodynamics of FBL cyclic pitch. I suspect that setting 11 degrees isn't hurting a thing. On the other hand, the new-to-me Protos 500 feels plenty quick with 'only' 10.3* of max cyclic. I wonder how much pitch the Skookum is actually commanding / needing when I do my flips? Is the % output in the hidden SK540 logs? I think I'm trying to understand what's the maximum cyclic pitch my FBL controller ever requests for a given heli, so that I can set up the travel to not be more than that. That would maximize resolution and available electronic gain, correct?

[Xrayted]

Originally Posted by Carpetbombing

Hmm. Interesting. I was thinking purely aerodynamically, but I can see how the mechanical / electronic gain relationship would need to be adequately balanced. I'll have to check where my cyclic gain settings are on my helis - I think everything is between 40% and 50%. Most of my swash percentages are right around 60-65%. I'm still getting a feel for the cyclic acceleration setting - I'm using about 50% on all my helis right now. Bell gains are high 60's or low 70's.

For my Gaui X3 and Protos 500 I have my pitch and roll rates set to 360*/s. That's the max Skookum will allow. Maybe that's pointless, but for some reason it's fun for me to yank it back and do quick backflips. I tend to change my pitch curves so they're more sensitive around mid-stick, too. Yaw rates around 600-640*/s. My 'slowest' heli set-up is my Gaui X5, at 320*/sec pitch and roll. After slowly increasing the rates, I can definitely tell you that those are the rates I prefer the feel of.

Though everything is related, this shouldn't be a FBL controller specific discussion. It sounds like the jury's still out on the aerodynamics of FBL cyclic pitch. I suspect that setting 11 degrees isn't hurting a thing. On the other hand, the new-to-me Protos 500 feels plenty quick with 'only' 10.3* of max cyclic. I wonder how much pitch the Skookum is actually commanding / needing when I do my flips? Is the % output in the hidden SK540 logs? I think I'm trying to understand what's the maximum cyclic pitch my FBL controller ever requests for a given heli, so that I can set up the travel to not be more than that. That would maximize resolution and available electronic gain, correct?

I wish I could give some deeper answers as to the specific relationship between the available cyclic pitch and our FBL settings, but unfortunately I cannot. There is nothing in the software that we have access to and no ability for us to easily know exactly what amount is being used for a given command. The Pro software allows us to see each channels stick command outputs from the logged data, but not the actual servo output data. I do know that Skookum is able to dig much deeper into the logs than the end user can.

It's basically based on feel, and subjective assessment by the pilot. Essentially you set a starting control rate, or use a one of the default setting by the manufacturer, and fly the heli. If the flip and roll rate is too slow, adjust the values up until you achieve the speed you want.

If still not happy one could continue to raise the rates, however the controller can only go as fast as your available cyclic will allow, and at some point there will be no increase in rate unless you have access to more cyclic pitch mechanically.

As stated, the general consensus amongst the SK user crowd is that 10* should be be enough to get the max setting rate in the FBL controller, however there is a lot more to how fast the model will flip and roll than just cyclic pitch. Which blades, how wide is the chord, how many blades, what RPM and on an on, so one could conceivably achieve a rate of 325* per second for example using a lower amount of cyclic pitch than another with a different setup.

This is one reason it would be impossible for Skookum to determine that a certain control rate setting = a known exact amount of cyclic pitch to get there, at least as a blanket statement. It would be model and setup specific.