PDB Posted June 18, 2024 Share Posted June 18, 2024 I've only had a couple of sessions with a new Multiplex AcroMaster so still trimming and getting to know it however I'm finding rolls in one direction a problem. If viewed from the rear the model performs axial rolls anti-clockwise with only small inputs nicely but if I try clockwise the model corkscrews around badly. I've checked the TX model settings and the channel monitor to ensure the throws are equal and there's no odd mix going on and I cannot see any warps in the airframe. Any guidance on troubleshooting this appreciated. 👍 Quote Link to comment Share on other sites More sharing options...
Robin Colbourne Posted June 18, 2024 Share Posted June 18, 2024 Could it be the torque from the motor/propeller which assists the anticlockwise roll, hinders the clockwise roll? Maybe try starting with a dive, throttle back to say half throttle (to reduce the torque effect from the motor) and then try the clockwise roll? Let us know your findings. 1 Quote Link to comment Share on other sites More sharing options...
Brian Cooper Posted June 18, 2024 Share Posted June 18, 2024 The bottom line is attention to detail "trimming". I don't mean the beep, beep trimmers on the Tx, but actual airframe trimming. It involves setting up every aspect of the airframe from incidence angles; balancing (front to back and left to right); control throws; differential throws; exponential settings; servos; engine thrust lines; and even the correct propeller for the model, etc., etc.. After that, we have to learn the characteristics of the model. I.E. the best entry speeds and power settings for any particular manoeuvre. How the wind speeds affect the manoevres, etc., etc.. Fine tuning and trimming is a great journey. Have fun. 1 Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted June 18, 2024 Share Posted June 18, 2024 (edited) Many, many, years ago I had one of the MR Gangster clones that a lot of model manufacturers produced. It was a great model, dead easy to fly and never threatened to catch you out. It did have one very odd foible. If you flew at full speed at full chat and then gradually closed the throttle the model would slow down normally and cruise around as expected. However, if the throttle was quickly snapped shut from full popwer then the model would do an uncommanded full axial roll, don't recall in which direction after so long - was a party trick of mine to demonstrate it. I checked that model out to within an inch of its life and never found the cause, which was surprising given how blatant and obvious the effect of the 'fault' was - just got used to it. Hundreds of flights on that model and eventually sold it on. Edited June 18, 2024 by Cuban8 1 Quote Link to comment Share on other sites More sharing options...
Lindsay Todd Posted June 18, 2024 Share Posted June 18, 2024 I Have the latest version, actually a review with the Ed but it is a very neutral airframe and have had none of the issues you describe so it does sound like something is amiss. I would suggest revisit the basics as something simple can be overlooked so easily. Also just be sure you are not inadvertently adding some rudder or elevator when your roll one way or the other, very easy to do with a sensitive airframe. Also just make sure the motor is secure and you don't have a subtle amount of offset thrust coming into play. As Brian says you get the best out of an airframe when it is correctly trimmed but I am surprised by the issues you have had. Which version did you get, was it the Pro RR ? Linds 1 Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted June 18, 2024 Share Posted June 18, 2024 It pilot related or model related is first port of call, you ok with other models ? 1 Quote Link to comment Share on other sites More sharing options...
J D 8 - Moderator Posted June 18, 2024 Share Posted June 18, 2024 I have similar issues with my Citabria Pro but in doing a loop, While good at every other scale type maneuver, rolls, barrel rolls, stall turns, spins, getting a decent tidy loop is difficult in that it just likes to screw off one way or other. Model only has OS La 40 so one has to start with shallow dive but even with plenty of speed just as the nose reaches the vertical off it goes. Only answer I have found is a quick dab of rudder at the just the right moment as it starts heading off but timing this is not easy. Still keep trying mainly because it's a challenge. 1 Quote Link to comment Share on other sites More sharing options...
PDB Posted June 18, 2024 Author Share Posted June 18, 2024 3 hours ago, Lindsay Todd said: I Have the latest version, actually a review with the Ed but it is a very neutral airframe and have had none of the issues you describe so it does sound like something is amiss. I would suggest revisit the basics as something simple can be overlooked so easily. Also just be sure you are not inadvertently adding some rudder or elevator when your roll one way or the other, very easy to do with a sensitive airframe. Also just make sure the motor is secure and you don't have a subtle amount of offset thrust coming into play. As Brian says you get the best out of an airframe when it is correctly trimmed but I am surprised by the issues you have had. Which version did you get, was it the Pro RR ? Linds It is the Pro RR new out of the box, I have checked the channel monitor and mixes on the TX and all looks fine. 3 hours ago, john stones 1 - Moderator said: It pilot related or model related is first port of call, you ok with other models ? My first thought was I must be doing something to cause the issue but I'm fine with other models. 5 hours ago, Brian Cooper said: The bottom line is attention to detail "trimming". I don't mean the beep, beep trimmers on the Tx, but actual airframe trimming. It involves setting up every aspect of the airframe from incidence angles; balancing (front to back and left to right); control throws; differential throws; exponential settings; servos; engine thrust lines; and even the correct propeller for the model, etc., etc.. After that, we have to learn the characteristics of the model. I.E. the best entry speeds and power settings for any particular manoeuvre. How the wind speeds affect the manoevres, etc., etc.. Fine tuning and trimming is a great journey. Have fun. I've a long way to go yet with trimming so will be sticking at it. 6 hours ago, Robin Colbourne said: Could it be the torque from the motor/propeller which assists the anticlockwise roll, hinders the clockwise roll? Maybe try starting with a dive, throttle back to say half throttle (to reduce the torque effect from the motor) and then try the clockwise roll? Let us know your findings. It's possible however the corkscrewing is very pronounced and I'll give that a go. I've an very experienced pilot who I fly with but isn't around at the moment so I will also get him to have a look on his return to see if he spots anything. I'll keep you updated on how I get on. Quote Link to comment Share on other sites More sharing options...
Bruce Collinson Posted June 18, 2024 Share Posted June 18, 2024 Lateral balance? My Supra Fly was screwing out of loops and bunts until I added quite a bit of weight to one wing to counterbalance repeated retract mount repairs on the opposite wing. Think either 30 or 60 go from memory. BTC 1 Quote Link to comment Share on other sites More sharing options...
Robin Colbourne Posted June 18, 2024 Share Posted June 18, 2024 This video covers torque reaction, spiralling slipstream, precession and assymetric thust. It was the thought of spiralling slipstream hitting one side of the fin, that lead me here, but any of these could play a part. 1 Quote Link to comment Share on other sites More sharing options...
Lindsay Todd Posted June 18, 2024 Share Posted June 18, 2024 What rate of roll would you say you have? At full deflection you should be getting a very rapid (Blurr) rate of roll, if too slow though it will show up every little error in your inputs. Linds 1 Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted June 18, 2024 Share Posted June 18, 2024 When I was practicing for my B, I set up an aileron rate that with full stick deflection gave a rate of roll that I could time my elevator inputs with accurately. Some time later, I mentioned that I had a roll rate of almost 2 secs and I was told the this was a slow roll. So, I went away and decided to check the roll rate. Quite surprisingly, I found that rolling to port, i.e. with the engine torque, the roll rate as half a second faster than when rolling against torque. This wasn't noticeable until I timed it. The other issue is that the ailerons might be moving at different rates even though the end deflections are identical. On my F3A aircraft, even using expensive servos, I have to use the elevator balance function to get both elevator servos to move the elevators the same amount. It is quite surprising how even expensive servos need this trimming. The same goes for the ailerons and since they are not as easy to measure you will need to make up some card templates with the degrees or some other interval marked off and check that they deflect the same amount for the same stick movement. This is sometimes referred to as differential but it isn't the same differential to which we refer when talking the aerodynamics of ailerons. This differential is to get the ailerons to move exactly the same amount, in opposition of course. If there is a significant mismatch on right stick then that would cause the corkscrewing you are experiencing caused by the big difference in drag that may be being generated by mismatched aileron movement. 3 1 Quote Link to comment Share on other sites More sharing options...
SIMON CRAGG Posted June 19, 2024 Share Posted June 19, 2024 Having had my fair share of pattern ships over the years, it could be caused by an array of faults. There are several excellent trimming guides available on the internet, which go through the trimming stages step by step. Assuming the model is built square etc. etc. It should be fairly easy to find out what is causing the problem. It takes a bit of time, and probably a few visits to the patch, but in the end you should end up with a much better model. Good luck!. 1 Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted June 19, 2024 Share Posted June 19, 2024 13 hours ago, Peter Jenkins said: The same goes for the ailerons and since they are not as easy to measure you will need to make up some card templates with the degrees or some other interval marked off and check that they deflect the same amount for the same stick movement. This is sometimes referred to as differential but it isn't the same differential to which we refer when talking the aerodynamics of ailerons. This differential is to get the ailerons to move exactly the same amount, in opposition of course. If there is a significant mismatch on right stick then that would cause the corkscrewing you are experiencing caused by the big difference in drag that may be being generated by mismatched aileron movement. A friend invented this cheap and simple device to measure control surface throws and I must say that it works very well Deflection meter * Chris * Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted June 19, 2024 Share Posted June 19, 2024 50 minutes ago, Christopher Wolfe said: A friend invented this cheap and simple device to measure control surface throws and I must say that it works very well Deflection meter * Chris * Unfortunately Chris, that falls into the necessary but insufficient category. You need both to set the required deflection to be the same but also to have the servos moving in synch with each other over the whole range of movement that you set. I have been flying in F3A competition since 2011 and the FAI Preliminary schedule since 2015 - not as well as I would like! - so I am well aware of what is required as regards trimming and the techniques used. The photo shows that once I've used my throw meter to set, in this case the elevator throw for normal aerobatics - I generally start at 10 deg each way and then reduce as necessary - the next task is to ensure that the 2 elevator servos move together over their entire range. I use a pair of new pencils (hexagonal cross section and not round) having first checked that their points align when both are placed flat on a horizontal surface. I then tape them to the elevators as in the photo. (You may need a gap to clear the rudder if either the pencils are too short or the rudder extends aft too far.) You can either use a mix between the two elevators or your Tx might have an elevator balance function. Then it's a matter of adjusting the slaved servo to ensure the pencil points remained aligned throughout the range of movement. Of course, this is less easy with ailerons but at least ensuring both have the same deflection is a start. Then, make up a jig that can be taped to the wing adjacent to each aileron that holds a graduated scale and do the same exercise as for the elevators. Remember, for a single prop aircraft, the roll rate with torque will be faster than sgainst torque for the same aileron deflection. If you use a contra rotating prop setup then you won't get this problem. In reality, you may not even be aware of the slight difference in roll rate. 1 Quote Link to comment Share on other sites More sharing options...
Adrian Smith 1 Posted June 19, 2024 Share Posted June 19, 2024 I like that simple idea, Peter 👍 1 Quote Link to comment Share on other sites More sharing options...
PDB Posted June 20, 2024 Author Share Posted June 20, 2024 On 18/06/2024 at 13:22, Lindsay Todd said: Also just be sure you are not inadvertently adding some rudder or elevator when your roll one way or the other, very easy to do with a sensitive airframe. I had a session yesterday and over 7 batteries practiced nothing but rolls managing eventually to perform them well in both directions. The problem was me moving the stick off centre without realising it. I've only flown high wing models to date and this is my first mid wing so I've been a bit tense flying it, when relaxed I was moving the right stick left and right without any vertical movement. 3 Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted June 20, 2024 Share Posted June 20, 2024 Ah, well done on working that out. Do you fly thumbs? After I started flying in aerobatic competitions I found flying thumbs was not so good for me. When I got tense I tilted the Tx towards my body and cramped my thumb movements. Moving to a tray took me a couple of months to get used to it and flying with finger and thumb but after that it's been an absolute boon. I still occasionally use thumbs to fly but it just doesn't feel as comfortable nor as accurate to me. It is very easy to apply right aileron whdn you pull up to loop or push down to bunt because of the geometry of a thumbs movemsnt when holding the tranny - as you have found. If you suffer from neck ache when using a neck strap there are shoulder harnesses that overcome that problem. There are specialist ones (Revoc for one) but some camera shops might also have something suitable. I also found that when I got tense, I could just let go of the tranny, without it wobbling around to stretch my hands and arms when the aircraft was flying S&L between a msnoeuvre at box edge and one in the crntre. Another huge help was being able to use the wrist supports to brace my hand when flying a long inverted section where the aircraft needs to be dead level. Switch operation is also, for me, much easier - I don't need the sliders on the back or side of the Tx for my flying so that's not an issue for me. 1 Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted June 20, 2024 Share Posted June 20, 2024 Glad you're sorted PDB, been there, done that. 1 Quote Link to comment Share on other sites More sharing options...
PDB Posted June 20, 2024 Author Share Posted June 20, 2024 1 hour ago, Peter Jenkins said: Ah, well done on working that out. Do you fly thumbs? After I started flying in aerobatic competitions I found flying thumbs was not so good for me. When I got tense I tilted the Tx towards my body and cramped my thumb movements. Moving to a tray took me a couple of months to get used to it and flying with finger and thumb but after that it's been an absolute boon. I still occasionally use thumbs to fly but it just doesn't feel as comfortable nor as accurate to me. It is very easy to apply right aileron whdn you pull up to loop or push down to bunt because of the geometry of a thumbs movemsnt when holding the tranny - as you have found. If you suffer from neck ache when using a neck strap there are shoulder harnesses that overcome that problem. There are specialist ones (Revoc for one) but some camera shops might also have something suitable. I also found that when I got tense, I could just let go of the tranny, without it wobbling around to stretch my hands and arms when the aircraft was flying S&L between a msnoeuvre at box edge and one in the crntre. Another huge help was being able to use the wrist supports to brace my hand when flying a long inverted section where the aircraft needs to be dead level. Switch operation is also, for me, much easier - I don't need the sliders on the back or side of the Tx for my flying so that's not an issue for me. Yes I do fly thumbs and it appears this isn't working very well for me. I've been mindful for quite a while now of the advice from yourself and in your book regarding finger and thumb on the sticks for more precision, now's a good time to try that. Thank you 👍 1 Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted June 20, 2024 Share Posted June 20, 2024 First thing I did in the early days, was stiffen my sticks, helped me feel the centres better. 5 Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted June 20, 2024 Share Posted June 20, 2024 8 hours ago, john stones 1 - Moderator said: First thing I did in the early days, was stiffen my sticks, helped me feel the centres better. Might be worth looking at how you hold the TX and position your thumbs as its easy to position your grip so that your thumb pulls an arc. Try thumbs on top or just go to finger/thumb before its too late! 1 Quote Link to comment Share on other sites More sharing options...
PDB Posted July 13, 2024 Author Share Posted July 13, 2024 (edited) Been experimenting and have now got nice smooth rolls but it still doesn't feel accurate so going to give a tray ago. Also have a harness to try. Edited July 13, 2024 by PDB 1 Quote Link to comment Share on other sites More sharing options...
Philip Lewis 3 Posted July 13, 2024 Share Posted July 13, 2024 Good luck with trying that, just don't expect immediate results, it takes quite a bit of time to transition over (at least it did me), you might also want to lengthen the stick ends by unscrewing them a bit or get new longer stick ends. After a while of gettiing used to the new feeling though you will never want to go back. 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted July 13, 2024 Share Posted July 13, 2024 Some transmitters (usually higher end i.e. expensive) allow rotation of the stick units to compensate for personal human physiology. Worth experimenting with if yours allows this. 1 Quote Link to comment Share on other sites More sharing options...
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