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Flybarless Helicopter Systems CSM Cyclock, Helitronix Multi-mixer, Spartan AP2000i, Firmtronix Digimix-3, Gyrobot, SK360and AC3X |
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11-25-2009, 04:48 PM | #1 (permalink) |
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Positive / Negative / Neutral Delta
In order not to hijack this thread (https://www.helifreak.com/showthread.php?t=174481) too much, let's continue this here were it might be more appropriate.
BobOD, I now understand what you're saying, it makes perfect sense. In fact with my setup I noticed the collective is very responsive, maybe too much. When I flip my grips and setup to leading edge control, I guess I could also decrease the amount of negative delta by using a longer standoff grip ball (even if the ling from mixing arm to grip wouldn't be 100% straight any longer) or increase it with shorter ball. In short, I suppose the amount of offset from center is in relation to the amount of delta you get? Just for curiosity, how does the phenomenom you describe shows up in a flybarred heli? All Align helis that I know of are trailing edge. When positive pitch is applied to the blade, the same should occur? I don't understand why they use trailing edge and how the flybar come into play -------------------------------------------------------------------------------------------------------------------------- Here is the beginning of the discussion for those who are joining: QUOTE: Originally Posted by BobOD The picture directly above is such a perfect shot to demonstrate delta offset. This configuration produces +delta offset since the grip ball is offset from the center of the head block. The result is that when the blade pitch is increased, the added lift on the main blade causes upward deflection in the dampers. So, as the grip deflects up, and the link is on the trailing side, the pitch will be increased....thus it is called +delta. This presents a bit of a problem that is very difficult for a gyro system to deal with. Every time there is a pitch increase, there is an addition of pitch. Then the gyro has to back off and this results in another additive change. It leads to constant back and forth hunting. It also slams the servo at the end of every pitch change. It's going to work but it's not optimal from my experience with closed control loops. It does create one benefit and that is a bit more "pop" but at the expense of precision and durability. If this could be switched to leading edge control, this would result in -delta. When pitch is increased, the resulting lift decreases pitch a little...not even a degree but enough to create smoother pitching control. This creates a situation where the blade pitch will "settle in" much more smoothly because the gyro only has to "follow" it until it reaches it's desired goal. No opposing results to cause hunting. This creates faster, smoother and more precise control overall. Sorry if this was not such an appropriate place for this, and please do not take offense...none intended. It was just a perfect picture to show +delta so I thought I'd share a little insight on the subject. END QUOTE None taken, and on the contrary, although I do not fully understand how the offset or absence of it can make a difference, I will try and change to leading edge see if I can feel a diference and if the amp draw from my servos is less. Thanks, that the kind of comments I seek, and I will be thinking your explanation over!
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Ben Goblin 500 IKON w/ gov, Quantum 4115-1200, Hitec 5245, BLS251 DX8, RF6 |
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11-25-2009, 07:43 PM | #2 (permalink) |
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Thanks for the information.
I'm trying to digest it, but don't quite get it. From the picture of the setup, what I see is that there is a 90 degree phasing required. So, I'm confused to what the difference between Phase and Delta is. I think I understand when you talk about Leading and Trailing edge pitch changes due to lift because of damper flex, but if it is a fully rigid system, this should be minimized, correct? Sorry for the ignorant questions as I have not setup any of my FBL heli's like in the picture. Mine are all direct links to the swash and I try to make the control links as straight as possible and phase using the SK360 (or whatever electronics I have) to compensate for 'slop' between the swash and the grip that cause pitch differences. |
11-25-2009, 08:58 PM | #3 (permalink) | |
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Regarding Align's flybar design, it is actually difficult to lay out this setup as leading edge without reversing swash direction. It's hard to explain why unless you actually try to design it...with all the appropriate lever ratios. As a result, it is indeed + delta. And, it has always been my belief that this is what has led most to go to harder and harder dampers. You see, without give in the dampers, there is no delta. And when there is +delta...it's best to have none. Get it? Better result would be the right amount of dampening, so as not to be a rattle trap, and good -delta for stable operation. FYI, some manufacturers do have leading edge on their flybared helis. I forget which but at least one of them has the swash moving down for increasing pitch...likely for this very reason. Anyway, it matters less in a flybarred heli since the flybar is very stable...usually too much so...thus we are all exploring flybarless. |
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11-25-2009, 09:02 PM | #4 (permalink) |
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Kenneth,
I know there are debates for fully rigid systems. I do not believe that a fully rigid head will ever be as good as a well designed, dampened head. Rigid is only going to be better when compared to a poorly designed dampened head. And, with the direct swash to grip setup, you absolutely cannot have offset because if it is angled to the swash, it'll be twisting the inner swash ring with every push and pull. The intermediate lever setup solves this problem by having the levers mounted to something that won't twist. The link from the lever to swash will always be straight. |
11-25-2009, 09:59 PM | #5 (permalink) |
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Hi Bob,
I've only been doing this for less than a year, so still learing and your information has been invaluable. If I get you correctly, Delta is only experienced in Damped or Flapping Heads and Rigid Heads do not display Delta's. So, if my understanding is correct, Delta is the inevitable change in pitch due to Damper flex. Being so new and still learning how to fly, the difference between Rigid and Damped heads is 'greek' to me. However, I have noticed that Damped heads seem to be more 'forgiving' and smoother, and therefore seemingly easier to setup. I have both types: my Hirobo 30-sized 3-Blade and RJX 50-sized 2-Blade are Damped while my Gaui 450-sized 2-Blade, HeliArtist 450-sized 4- and 5-Blade and Century 30-50-sized 4-Blade are Rigid. Can't remember what the Gaui 430-550-sized is (I think it is Damped). Thanks. Ken |
11-25-2009, 10:16 PM | #6 (permalink) |
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Here's the way I see it. If you are a beginner pilot, go for something pretty cheap. Get the best you can afford but not something that will be so upsetting when you crash. The idea is to get in as much flight time for your budget. Once you get proficient, then it is a good idea to get something higher end. The better precision really does help you build confidence as the heli becomes more predictable.
Wow, for someone who is into it for a short time, you seem to have quite a nice collection already. Welcome to the addiction. |
11-26-2009, 02:59 AM | #7 (permalink) | |
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Quote:
If I understand this correctly, phasing is when the grips are not perfectly 90 with the inner swas ball, which lead to cyclic interactions (you give an elevator input which translates also in a slight aileron reaction) Delta is when the grip ball is not in line with the feathering shaft tilt axis, thus inducing even more pitch as the grips tilts up if delta is positive. If the grip ball is in the center of the head block, it is aligned with the axis, so when the grip tilts up, the link doesn't move further. Bob, thanks for sharing this great info. In a setup that has delta (or even zero delta for that matter), in a damped head, what are the effects of lead - lag movement? When you apply pitch to the blade, the grips goes up and I would think back also, as the air resistance induces lag? Then the geometry of the link from whatever to the grip is slightly modified? ie in my setup (picture), the link would angle further, which would bring the ball further down and induce more pitch? I'm just guessing, but that would lead me to think lead - lag movements work in the same direction as flap movements to make it worse in a positive delta setup and even better in a negative delta setup. Just a thought
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Ben Goblin 500 IKON w/ gov, Quantum 4115-1200, Hitec 5245, BLS251 DX8, RF6 |
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11-26-2009, 12:35 PM | #8 (permalink) |
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I did the Heli Magazine Trex 500 FBL mod and I had the same issue with positive delta but not as bad as Benoah. I had let a couple of heli veterans fly it and they both commented that they weren't used to that much colllective pop and we attributed it to the FBL less inertia and drag but now I'm sure it was the positive delta now. I just did the grip flip to switch to leading edge control and did a test hover with major collective pumps and it really does feel more controllable in collective now, more like my 600N. It was very windy (15+ mph) and I was able to keep it at the same altitude much better. I flew 135 flights with the positive delta and it was not terrible but hopefully this will help me progress a little better.
Thank's for the great explanation Bob! My next FBL head will deffinately be an I2. Anyone wanting to flip their grips with the Heli Magazine mod also has to flip the mixing arms. The ball link will pop right back onto the grip after the mixer arm flip but the end going to the swash will be 180 off. I did not want to mess up my setup so I just popped it on anyway but probably would have been fine to give them both a half twist in the same direction. I double checked midstick low and high and they were still right on. Only change I had to make within the Skookum software was to change collective pitch swashmix from positive to negative (maybe it was the other way?), anyway reverse the sign for collective pitch in swash mix. No changes in radio. Here's a couple pics of the mod to the mod.
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11-26-2009, 12:58 PM | #9 (permalink) |
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It is my pleasure.
That arrangement is getting there. The biggest issue I see is that the control link going from swash to lever is angled. This will cause phasing issues as the link is pushed and pulled. To demonstrate this, set your swash at an angle and then twist the grip back and forth. You will see it rotating the swash back and forth. Not good. Try a longer ball on this lever. Obviusly it has to clear the lever on the other side but get this link as straight as possible. Next, you might want to put a short ball on the grip and move the link to the other side of the lever. This will let you take advantage of -delta for cyclic as well as collective and will also open the clearance for getting that other link straight. |
11-26-2009, 05:36 PM | #10 (permalink) |
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Any thought on the lead-lag effect on pitch? My guess is it would have the same effect as delta offset
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Ben Goblin 500 IKON w/ gov, Quantum 4115-1200, Hitec 5245, BLS251 DX8, RF6 |
11-26-2009, 05:43 PM | #11 (permalink) |
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Lead lag would have little effect. It's mostly perpendicular to the control rod. Also, there isn't as much deflection in this direction. Lift force is greater than drag.
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11-26-2009, 08:09 PM | #12 (permalink) |
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Thanks for the information. I think it suddenly clicked in my little brain and the bulb went on.
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11-27-2009, 02:45 AM | #13 (permalink) | |
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Quote:
Also do you think a negative delta offset setup would be easier on the dampers and not need too hard ones? I'm using the stock black ones and was a bit concerned with durability on my setup.
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11-30-2009, 02:35 PM | #14 (permalink) |
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Parachuting into the discussion here,
If I'm not mistaken, + Delta is adding pitch in the same direction of the flapping motion, -Delta is REMOVING the pitch from the direction of flapping. IOW, in the Example picture above, if the blade flaps Upward, that setup will ADD (+) to the pitch of the blade. Agreeably, that IS the wrong direction we want to go. Better to have (-) negative Delta, removing the pitch from the blade when it flaps in either direction. How much depends on your flying style, how you like the feel of it. Most prefer a Neutral or ZERO (0) Delta, with NO correcting of the pitch with blade flap. Ok, apparently my reading skills are NOT improving, this is exactly what BobOD wrote... Pardon my intrusion into his Fantastic explanation!!
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Chris D. Bergen Bergen R/C Helicopters |
11-30-2009, 03:57 PM | #15 (permalink) |
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Yes, that's what Bob explained (if I got it correct anyway :o)
I tested some different setups based on my head: - Origninal setup (picture): most amount of + delta - Less + delta using the stock long ball (ball closer to center) - same but flipped grip = little - delta - Same as original setup but flipped = much - Delta I have to say with the two negative delta setups I was not able to get the heli to fly correctly... I had a strong rapid oscillation in hover and after any cyclic input that would not disappear by any mean. I tried taking the hiller gain, damping gain, bell gain, all way down without finding the winnig formula. Whit the least +ive delta, the heli is flying good, no too twitchy on collective and flies without wobble, tracks well... I only have a little bounce back that I have to sort on elevator, no big deal. I don't get why it didn't work out for me with negative delta. Maybe the gyro was working back and forth and chasing too much... Even with hiller gain down at 15% it wouldn't disappear, and the heli was too lose.
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Ben Goblin 500 IKON w/ gov, Quantum 4115-1200, Hitec 5245, BLS251 DX8, RF6 |
11-30-2009, 04:13 PM | #16 (permalink) |
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If you like the way it flies with the + delta, man RUN with it!!
Theory's are only good until there are FACTS to back it up. The fact is your heli, for whatever reason, likes the positive Delta, no need to try to fit it into the "proper" mold of negative delta if you're happy with the way it is.
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Chris D. Bergen Bergen R/C Helicopters |
11-30-2009, 05:05 PM | #17 (permalink) | |
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11-30-2009, 05:16 PM | #18 (permalink) | |
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Anyway, can you post a pic with your - delta? I'd love to know the reason for the opposite finding. Here's mine FYI. |
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12-01-2009, 10:29 AM | #19 (permalink) |
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Well, my first positive delta setup was the exact same as the pic in my first post (above), but with the grips and arms flipped. I then tried with the longer stock balls to reduce the delta (ball closer to center).
It was similar to your head, only the arms were 90 to yours, used the other 2 swash balls and therefore I had 90 degrees phasing. EDIT: I flipped the pic, it looked exactly like that (with the align logo and blades the right way ) If you get opposite results as I have, that's indeed strange... what gains are you using? Chris, I checked you website, that's some serious stuff you have there Wish Santa was more generous
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Ben Goblin 500 IKON w/ gov, Quantum 4115-1200, Hitec 5245, BLS251 DX8, RF6 |
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