Jump to content

AR9350 Use of expo


Andy J
 Share

Recommended Posts

Setting up a md size warbird (5ft wing) using an AS3X AR9350 Rx.  Would like to use expo on the aileron channel in all three flight modes which vary the degree of heading gain set. The App I am using which I recently downloaded from Google Play states exponential is NA in any mode.  So should expo be set on the TX as I thought I have read you should only apply servo settings in the Rx not the Tx.

Link to comment
Share on other sites

OK Denis, was recommended to use heading hold by a club mate today so will await your comments.

Have set 30% expo on two channels for flight mode 1 with zero gains using the Tx settings so would have liked to use an identical setting on the other two modes to get a similar feel for the required deflection of the sticks. Currently have the heading gain set at 20% for flight mode 2 and 30% for flight mode 3.

Link to comment
Share on other sites

I am more or less with dennis on this one apart from saying no gyro either. 30% expo is massive for and i dont use any on most of models. where i do it is 10% on one channel. 

 

My big question is why. Why are you adding all this stuff? is the model hard to fly as it is or is this a pre-emptive strike? What exactly are you trying to achieve? Your post implies the model is unstable in in roll, which makes very little sense as its normally yaw and pitch that show instability. 

 

A mid size warbird is what, 65 inch? if so it should not need anything special other than low low elevator rates. 

 

Just a bit confused. Knowing the end goal might clear the fog ?

Link to comment
Share on other sites

You don't need expo with a gyro because the effect of a gyro is to create expo.  For example, you command a roll, and the plane starts rolling which the gyro senses and feeds in an opposite command.  The gyro's opposition to your command will be less than your command so the effect is to reduce travel.  However the gyro should reduce its effect the further you move the stick so by the time you reach full stick deflection the gyro no longer opposes your command (some cheap and older gyros don't do this).  The net effect is that the gyro reduces travel at small stick movements and has no effect at full stick movements, which is what expo does so the two feel like the same thing to the pilot.  If you have tx expo and a gyro you are doubling up the expo.

The max roll rate (and the same for pitch and yaw) should be exactly the same with and without the gyro, because a decent gyro is programmed by its manufacturer to reduce its gain to zero at full stick.  If you get a slower response at full stick when the gyro is switched on, this means that the gyro is still opposing the stick, caused by using servo travels less than 100% at full stick deflection so the gyro never thinks you are at full stick and is still giving some opposition to you.  This means that it's important to use full servo deflections as close to 100% stick movement as possible by adjusting the linkage setup to allow this.

It's a while since I read the Spektrum rx instructions to find out what the built-in gyro does, but I think that your 9350 rx will zero the gyro gain at full stick deflection when the system is set up in accordance with the instructions. There is a series of youtube videos on setting up the Spekky AS3X gyro rx's.

 

  • Like 1
Link to comment
Share on other sites

Purchased this receiver quite a few years ago as I thought it would improve takeoff swings and dampen over controlled movements during landing.

Whilst I did fly the model back then  I can't recall if I used any gyro settings as my flying site proved far too small for the model and this coupled with retract issues led to multiple wheel up landing which subsequently damaged the laser 75 needle so the model was relegated to the back of the hanger.

Then after the loss of two other models I lost faith in Spektrum gear and purchased frisky equipment which  has not been straight forward in use, but that's another story.

After a 24 month  layoff from flying and a recent club change to one with a far larger landing strip I thought I would get some stick time on a faster model before moving onto a couple of 90inch models I have waiting for test flights.

The Hurricane with the Ar9530 seemed an appropriate choice so I dug out the spektrum Tx charged up all the batteries and went and flew the model. Of course I had completely forgotten about flight modes so I have no idea what settings were being used for the flight.

First flight proved over sensitive in roll so I noted no expo was set on the Tx and dialed in 30%. However a series of retract issues then prevented further flying.

After changing one retract and then reading on how to set up an AR9530 I reset the Tx model settings as instructed in the set up procedure. This then proved to be a disaster as coupled with relearning how to use the AS3X App nothing worked as it should.

On talking to a club mate at the weekend who has used an AS3X system he advised heading hold was the way to go so have spent the last few days resetting up the system such that all controls now work as they should,

So as I say the aim of using the AS3X is to improve takeoff yaw stability and particularly over controlled attitude changes during landing. So in my mind heading hold should be the mode to use but open to other options other than ditch the Rx.

Roll expo is now set to 30% irespective of any mode changes and 0 gyro gains for mode 1. Now wondering if I should try using a smal gyro gain value for mode 2 and an identical value in heading hold for mode 3 then slowly increase settings on each test flight to see the difference.

 

Link to comment
Share on other sites

Ok so overcontrolling seems to be the main thing you are trying to cure. If so, i would look into the root cause of the problem rather than trying to bandage it with tech. 

 

If the model was over sensitive in roll, why not reduce the rates? if you do not need the full aileron deflection you have available then you have too much and should reduce it. I recommend a setting where you have the maximum roll rate you want at about 75% of your stick deflection. This should always be the first port of call before adding loads of expo. 

 

If landing approaches are a problem again i would look at why. Is the model out of trim on approach? if so an elevator/flap mix might be an advantage to trim the model for the landing configuration. I use this all the time. If its not that and its just over sensitive, are your elevator rates too high? Warbirds have very sensitive elevators and most of the time they are set with excessive movement. My small 63 inch Hurricane has about 5mm movement on low rate and i think 8 on high? Its very small. 

 

Incidentally Hurricanes are known for a strong pitch down with gear/flaps deployed so this could be contributing to your landing woes. 

 

Finally...Are the problems simply due to lack of practice of a given skill? Even if the model is nicely set up there is no substitute for practicing the thing you are struggling with. I have even set up cones on the runway and got my students to taxi figure 8's round them at higher and higher speeds to force them to practice using their rudder and throttle. Landing approaches with warbirds tend to require a different technique and if this is the cause of your trouble then i would just keep practicing them. I deliberately practice things all the time be it a cross wind landing or engine out operation on my twin. There have even been days where i have dedicated an entire flight to landing approach practice with a given model following a flight where i didnt feel totally comfortable with it. Flying my P39 the other week after a year of not flying it left me feeling very much behind the model. It took 4 or 5 flights to slowly work up and get comfortable with it again. 

 

While we have a vast array of very clever gadgets available to us these days they do seem to get viewed as a quick fix and that is not always the case. Even if it was, i would rather tame the beast myself and improve my skills as much as i can. I am sure there are those with a different view, but that is my 2 cents. As with the chap on the other thread who wanted to go straight to an aileron rudder mix rather than do it by hand i would strongly recommend getting all the basics right before you go down the electronic route. Make sure the core setup of the model is good, perfect and practice skills that may be rusty. If you do all that you will probably find that you no longer need gyro assistance anyway. 

 

 

  • Like 5
Link to comment
Share on other sites

Cant recall if I had elevator coupling with deployed flaps as lost all that in the reset of the model settings. Probably best if I give it a flight in mode 1 with zero gains and see what happens when I deploy the flaps.

Model is a RW Hurricane so will take a look at that old thread to see what was recommended for the elevator deflection.

Link to comment
Share on other sites

1 hour ago, Andy Joyce said:

Measured the elevator deflection this afternoon and it was +/- 25mm so have reduced that to 10mm as likely this is one of the reasons for over control. Also have added up elevator on deployment of flaps.

Sorry Andy if that is a typing mistake.

I think you should apply some down elevator as flaps are deployed.

Link to comment
Share on other sites

Well that's what I would have expected Denis given the flaps produce extra lift so the nose would pitch up so to compensate a similar force is required at the tail. However Jon above said that the Hurricane has a strong pitch down when flaps are deployed. Confirmed that statement on Google given the flaps are behind the centre of pressure.

 

Link to comment
Share on other sites

Most aircraft, but WWII fighters in particular, pitch down in the landing configuration due to c/p movement and also because of factors like the drag of the now lowered undercarriage, c/g shift with undercarriage deployment and the fact that they tend to fly fairly fast so they are a long way out of trim when they are slow. 

 

If a model pitches up with flaps deployed it is likely due to it being either too fast or too light to need flaps in the first place. Things like fun cubs etc are a prime example but my clubmates black horse 80 inch spitfire is another example as its flaps are oversize and it is very light for its size. We are going to abbreviate the flaps and add a few lbs of lead on the c/g to get it to the right weight. Blasted thing is like a baggy old paper bag at the moment. 

 

My little Hurricane is a Warbirds one as you know and dropping gear/flaps turns it into a lawn dart. I have a fairly substantial up ele/flap mix and use a higher elevator rate for landing. 

 

When it comes to setting the ele/flap mix i get it all set up and enabled but with only 1 or 2% movement. I then leave the menu open on the tx while i fly, and once i drop the gear and flaps i adjust the travel on the tx while its in the air. If you struggle to find your buttons without looking get an assistant to poke and prod. Anyway i keep trimming up until i reach the stall, and then dial it back a few% and its all set. Landing approaches are then a simple case of using ailerons to keep level and throttle to control decent/pitch. 

 

If you continue to have trouble with the hurricane check the incidence of the wing as mine was a dog until i discovered an incidence issue with the wing. Once adjusted it was much better. 

 

 

Link to comment
Share on other sites

Looking at the programming instructions for the AR9350, you can set both expo and gain via the smartphone app. All expo trim etc settings on the Tx must be at factory defaults. Set the expo to a figure that you are comfortable with in respect of the models response to input around the center stick position, on a couple of twitchy models I have set expo as high as 40%, it calms the response down but allows for rapid response if you need/want full stick deflection. The gyro gain should be set low to start with and gradually increased until a satisfactory response to uncommanded movements about the 3 axes result in the model flying in a stable manner for example when flying in gusty conditions or to correct take off yaw. If you go too high on the gain settings the model may start to oscillate on one or more axes as the gyro over corrects and tries to right the model resulting in over correction the other way. For this reason it's good to be able to turn off the gyro with a transmitter switch before it all goes very wrong. It may be possible to adjust the gain from the transmitter. As usual with Spektrum instructions they are a bit vague, I'm not sure of the difference between rate gain and heading gain,  but they are explained here Rate and Heading

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...