vetagator

My Feedback: (5)

I need a recommendation on which gyro you guys are using. I need to install one on the rudder of my Der Jet Cougar to stop it from wiggling. This would be my first experience using a gyro.

weasel33

Nothing expensive just use a simple single axis gyro like this

http://www.hobbyking.com/hobbyking/s...idProduct=6755

i use them on steering and rudder

regards brian

Dave Wilshere

Fit an aileron gyro, I think the Cougar needs this more than the rudder.

Dave

sailing1

My Feedback: (134)

Dave,
What would you suggest for the aileron Gyro. I am building a Skymster Gripen and want to put a gyro on the steering an ailerons. I have a Futaba 352 gyro which is a dual axis gyro, but don't know it that will work for this application. I know I can use a simple one channel gyro for the steering.

Dave Wilshere

You don't need a gyro in pitch, so a "wing" gyro like the ACT one would be perfect. I think Futaba do a wing only one too?

I've never run a gyro on my own models, but have flown a few and it makes a big difference, plenty of European pilots use them.
The Global Jet Club Skyray I have flown a few times improved greatly with the gyro

Dave

vetagator

My Feedback: (5)

Thanks for the advise. The cougar seems to wag the tail side to side on straight and level flight, keeping a straight line without any radio input. I figure this is due to the swept wing and short coupling of this jet. A friend mentioned using the futaba dual axis gryo on rudder and ailerons. The jet is flyable, but can be a little work to land sometimes. I may have to consider this one. Alex.

rcand

I have an Airworld cougar. I have a gyro on the ailerons and it works great to smooth everything out, especially on landing. Unfortunately, the gyro i have is no longer available, but any simple gyro without taillock should be fine.

Dave Wilshere

ACT gyros are available and used by most of the German JWM team...

HarryC

My Feedback: (1)

The primary problem is in yaw, not roll. The plane has no roll stability, or it is very low in frequency and is highly damped, so it will not wiggle in roll on its own. It does have yaw stability but poorly damped so it will wiggle in yaw, "fishtailing" or "snaking" on its own. Because of the dihedral effect of a swept wing, this yawing causes a secondary wiggle in roll. Stop the fishtailing and you stop the wiggle in roll, but stopping the wiggle in roll will not stop the fishtailing.

The gain between yaw and roll varies from plane to plane, some have a little yaw causing large roll and some have lot of yaw causing little roll. The former looks like it is just wiggling in roll, the latter looks like it is just fishtailing. Both will be stopped by a gyro on rudder, however with the model that has a high yaw to roll response there is more for the gyro to work with if you put it on ailerons and treat the symptom rather than the cause. That will still leave you with a wiggle in yaw which in some cases may be too small for you to notice, or a small noticeable wiggle which a yaw gyro will remove.

If you only see fishtailing, then a simple gyro on rudder is what you need, not an aileron gyro.

Do consider the quality of the gyro that you fit. Your commands from Rx to servo pass via the gyro's processor and a failure of the gyro system will usually lead to no signal getting through it, and thus a loss of control of that servo.

Harry

vetagator

My Feedback: (5)

Thanks, Harry. What you describe seems to be exactly what I am experiencing. The plane really doesnt have a rolling issue, just a yaw instability. Like I said, without radio input, the plane flies straight and level, it just fishtails. The wings dip cyclically but correct themselves in level flight. I think I'm going to try just a rudder gyro first. Dave, I will look into the ACT Gyro. Who sells these? Im not one to judge things too much on their cost, but I feel weird installing an inexpensive gyro in a jet. Thanks for the help guys.

siclick33

You'll be happy with the ACT gyros then Having said that, I've just checked their website and, I'm not sure if they have lowered their prices, but they aren't too badly priced at the moment.

Made by ACT in Europe. Sin City Jets have sold ACT gyros in the past.

http://www.acteurope.de/html/flachen...ane_gyros.html

http://www.sincityjets.com/store-accessories.htm

Dave Wilshere

Mmm Having flown Colin's DerJet Cougar a fair bit, I think although a yaw (rudder) gyro will help, it needs an aileron gyro! When flying slowly in a breeze it wags its wing...
But there is no down side to fitting a rudder gyro first and seeing if it does what you want. ACT gyros are not cheap, they also are not made in anything like the quanties as helicopter tail gyros...

Dave

DavidR

My Feedback: (1)

What you are describing is classic Dutch roll. Swept wing one side starts developing more lift so it rolls slightly, then loses lift as the other side starts gaining lift. Put a gyro on the rudder and it smooths it all out. Any number of gyros will work, lately I have used the JR 770, but hearing good things about the 270. Don't use it in heading hold mode.

DR

Dave Wilshere

Yep, it is dutch roll. I'm sure the rudder gyro will help alot. Adding an aileron gyro smooths out the whole flight pattern, look at pilots like Steffen Volker, Tommy G, Ali, Seb Silvestry that use them on quite a few models.

Aero65

My Feedback: (2)

Hi Everone

I have used Futaba GY-401's on rudder

Futaba GYA-351 on Aileron / Elevator www.keimod.com Got to get them from Taiwan dealer (single Axis dual servo)

Futaba GYA-352 works good on Aileron and Elevator for Deltas. (dual axis dual servo)

I put A GY-401 on rudder, and GYA-352 on the taileron, of my F-4D Skyray from Global Jet club, made it really lots of fun to fly. I can fly it without them but then you have to work too hard to make it look smooth lol.

The GYA-352 dual axis gyro is a little different to setup. You have to let the gyro take care of the mixing not the radio.

I also have used the ACT fuzzy pro2 its a very nice gyro, has built in stick fade out which is nice. When you have a gyro on a surface like aileron when it is active it feels like it fights you when you fly, so with the ACT has the ablity to disable the gyro stabization as you move the stick. When you use a futaba gyro you have to make a mix to accomplish this. (You have to be very careful not to have your mix drive your gyro in to AVCS while fading out its gain)

Aloha

Duke

vetagator

My Feedback: (5)

Thanks for the advise guys. I went ahead and ordered the JR 770. I will let you all know how it goes.

HarryC

My Feedback: (1)

Only use low gains on rudder gyros. Any turn is a combination of yaw and pitch, so a yaw gyro will try to oppose any turn by adding opposite rudder. Helis get away with it because the yaw control is a primary control in a turn and the gyro can be suppressed when it sees a control input, but we rarely touch the rudder when turning our jets so the yaw gyro will not be suppressed and will oppose the turn. Using only low gain will minimise the effect and be prepared to add a little bit of into turn rudder if required when the gyro is active.
H

Malcolm H

I built a Fei Bao F18F with a Wren XL200 as my first foray into jets. Being an F3A aerobatic flyer, correcting the track of the model over the ground is second nature but I was shocked to discover that this particular airframe has so much yaw/roll couple that rudder is totally useless for this purpose. Also when flying in any turbulence it exhibits the dutch roll phenomenon.

I fitted an ACT gyro on ailerons reasoning that this would cure the dutch roll and should also supress if not eliminate the roll response from rudder inputs. Initial flight tests have been dissapointing in that I was only able to turn the gain up marginally in flight without instigating roll instability and with the gain set just below this point no significant reduction in yaw/roll couple or dutch roll were observed.

The ACT gyro with its fuzzy logic does have another adjustment other than gain which I have yet to try so there is still some experimenting to do. Also has anyone tried heading hold mode on roll?

Malcolm

Duncan

Is it dependent on the type of model Dave, mostly being scale?

I've worked/helped Ali on pretty much all of his models in the last 3yrs, and never seen a gyro in any of them. Are you getting a gyro confused with his super smooth thumbs?

HarryC

My Feedback: (1)

Malcolm, it sounds like your F-18 is mostly a yaw problem, try the gyro on rudder instead.
The other setting on the ACT gyro is the fade-out, which won't affect its response to wing rocking. Fade-out reduces the gyro's actions when you move the control stick, otherwise the gyro would always be trying to counter any roll input that you make.
You can set the ACTs max travel, which governs how much it would use at 100% gain. Clearly this affects how much gain you will need. If you servo travels in your Tx are quite different to the normal 100%, the gyro could be reacting much more than required, so if your tx travels are well below 100% use the ACTS max travel function to reduce the travel that the gyro is trying to use.

Ali

My Feedback: (5)

Every F-18, F-15, SU27 and Mig 29 that I have ever flown has that massive rudder to roll coupling mentioned above. I personally think its too big a task for a gyro to eliminate that ( Certainly without messing with the flying of the model )
I look at and use Gyros in "certain" models as a damper more than anything. The cougar is a classic example. I have owned three of them now, and only one was not equipped with an aileron gyro, and it was visually obvious, as it used to fidget almost all the time. An aileron gyro sorted that, and if personally I will never set a Cougar up without one.
The way I look at it is that we spend all this time, money and effort to make our models look as scale as possible on the ground. Every rivet, panel line is applied as standard now almost. We fit out cockpits out with all the dials, and gauges.. we even make inside of the gear doors scale now a days. I see it as a shame to see all of that accuracy in scale fiedelity wasted as soon as the model breaks ground.. Where it proceeds to wobble, fidget, shimmy and shake across the sky [:'(]
I often show people a demo when I have a model with a gyro fitted. I will make a few laps with the gyro on. Then I turn it off ( I always have my gyros switchable from the tx) I then make a few more laps.... The difference is always very obvious! In the same demo I also bank the model hard over to one side and let go of the sticks.... Just to show the model diving toward the floor of its own accord.. That is to try and put across, how my gyro set ups work as just a dampener, and without the input from me that particular model will ( If uncontrolled by the pilot ) hit the floor just as quickly as the same model without a gyro. It does make me chuckle to hear comments like " It only flies like that as it has a gyro fitted" I never use heading hold modes in any of my gyros, as I hate the feel that a gyro is infringing on my flight controls.
I also find gyros to be very model/ type required. Right now in my display models, I only have two equipped with any sort of gyro. I find the others just dont need it as much. Some models just have better natural stability than others, so I dont bother fitting them. For example.. My T-33.. That has the feel of having a gyro fitted to the ailerons, when infact it is just super locked in on the roll command. Flip side of that is my Airworld Mig.... Those thin, short wings never ever seem to settle without a gyro. Yet with a Futaba 351 fitted they just dial in perfectly. My Skymaster Vipers ( Both big and small ) are super solid on all controls, where as my Epic Victory was a wobbly thing ( Especially in a wind) till I fitted a Gyro to the ailerons and rudder.
I have had a play with quite a few different types of gyros. I know my sponsor may not like to hear this, but the best results for me have come from the Futaba range of Aero gyros. Those with the GY prefix. GY 350, 351 and 352. I tend to favour the 351 as most of the time I have only used a gyro on single axis. Although I have set a few customers planes up with the 352 which is dual axis ( So I can cover Aileron and rudder through the same unit) The 350 is basically a re branded 401 heli gyro and works really well on a single servo application such as nose wheel or rudder.
I like the 351 as its an ideal aileron gyro. It has dual in puts and out puts.. So you can still have individual aileron servos. Its gain adjustable via the TX.. It does require an extra channel, but in my opinion its well worth it. I can adjust the gyro gain in flight ( if you fit it to a slider or rotary dial) although I tend to have mine set on a 3 position switch Two positions being off, and then last position being on.. I do this to make sure there is no way I can have the model set in AVCS ( Futaba for heading hold) I then just raise or lower the ATV's till I get the gyro set up which I am looking for. Thats one where the flight control does not wobble, or bounce or hunt which it can do if the gain is set too high. I have used the Futaba gyros without using the gain control, as the gyro unit itself has manual rotary dials that you can set it up from, but I like the tx switchable option... if only for the ability to be able to turn it off in flight and adjust it easily.
The main reason why I use the Futaba gyros is that I have found them to be the most accurate, and least effected by "drift" Drift will show itself in the form of the model needing to have trim adjustments made to the control which the gyro is fitted. Some one more intelligent than me will explain how and why this occurs. All I can tell you is that the Futaba Gyros I have used have suffered almost 0 drift, and when it did occur it was a tiny amount resulting from me flying in some environments with big temperature changes.
Sorry to make the post so long winded, and I hope it is of some help?
Regards Al

Malcolm H

I suspect Ali is correct that the gyros won't help with the yaw/roll couple so I'm going to concentrate on getting it to smooth out the flightpath and yes Harry I suspect that playing with the gyro travel setting may be useful

Malcolm

mark handley

Hi Gents
As a Derjet Cougar owner I'm finding this thread very interesting as I too am having the same dutch roll problem. I have never fitted a gyro to a fixed wing aircraft before but having read Dave and Ali's posts I will be doing now. The question is do I put it in the roll axis or the yaw axis?....On the B757 I fly the dutch roll is damped in the yaw plane exactly as Harry described and yaw damping is how full size swept wing aircraft stop dutch roll. Having said all this I cannot ignore Dave and Ali's advice as they have the time on the swept wing models and regardless of full size aerodynamic principles if the gyro works better in the roll axis you cannot argue as we've all seen Dave and Ali fly. I'm open minded about this and welcome the results of the gyro experiments as Ali hit the nail on the head we want it to look good flying!
Regards
Mark

HarryC

My Feedback: (1)

Mark, it depends how powerful the rudder is. If the rudder has the authority to stop the fishtailing then the problem is solved. Many scale model jets have tiny rudders, e.g. my F-86, and they may not have sufficient authority to stamp out the fishtailing. Where there is a high gain from yaw to roll, it only needs a tiny amount of fishtailing to remain, and a decent wing rocking action will still be present. Where you have those high gains, a very small fishtailing provoking a large wing rocking, putting the gyro on the ailerons really will stamp out the wing rocking and any fishtailing may be too small to worry about.
My Grumania Eurofighter has a lot of wing rock, and it has no rudder for me to try a gyro on that, so I put an ACT Fuzzy Pro on the ailerons and that has locked the model's flightpath, greatly improved its handling and enjoyment, and yet there is no perceptible fishtailing.
H.

HarryC

My Feedback: (1)

To be fair to the model Malcolm, you should never use rudder to adjust your heading. Turning by banking is the only proper method. Yawing it is a trick used in competition aerobatics to try to fool the judges so that they don't see the bank and don't realise you are adjusting course! I gather that the full-size F-18 has some nasty yaw characteristics and particularly on approach to land the computer has to keep it within a very narrow yaw envelope otherwise things become unpleasant.

As to heading hold, the advice is not to use it on fixed wing models. Rate mode which damps out disturbances works well enough for us, and HH mode can have unexpected consequences. It works fine on helis which have very light tail inertia and fast servos and very fast yaw response that can keep up with where the gyro thinks you are adjusting your heading to. It's a different matter with the inertias and roll rates of fixed wing which will lag some way behind where the gyro thinks the wing should be.

H