Give Me Exponential Rates
by Matthew George of the Northern Utah Radio Control Aircraft Club
| I wanted to
take a few minutes and talk about the use of exponential rates as supported
by most of our RC transmitters. After getting back into the hobby over the
last several years, Iím surprised at the slow adoption rate (no pun
intended) of using exponential rates.
I have even heard recommendations that you shouldnít use exponential rate features on your radio. I can tell you by experience, that any pilot serious about becoming accomplished in aerobatics will make his life much harder if he tries to fly precision maneuvers without incorporating exponential rates into his control surface throws. I am of the opinion that almost any aircraft should be set up with exponential rates on the control surfaces. You will immediately see an improvement in your flying once you understand and start dialing in exponential rates for all your aircraft. Trainers to unlimited IMAC birds, gliders, sport planes, flying lawn mowers, etc Ö
What is the definition of using an exponential rate on a control surface? Exponential rate is where the servo movement is not directly proportional to the amount of control stick movement on your transmitter. Over the first half on the stick travel, the servo moves less than the stick. This makes control response milder and smoothes out level flight and normal flight maneuvers. Over the extreme half of the stick travel, the servo gradually catches up with the stick throw, achieving 100% servo travel at full stick throw for aerobatics or trouble situations.
All the newer radios support this feature and the best part is the fact that no physical change is required on the aircraft. Itís a simple matter of programming your radio to use exponential rates on some or all of your control surfaces including your throttle.
Have I convinced you to give expo rates a try? Itís not scary; I promise. Pull out your transmitter manual and start reading. Itís usually a simple matter of scrolling through your on-screen setup menu and finding the option to set expo for each control surface.
There is only one caveat I know of, if you have a Futaba radio, make sure to dial in your exponential rates as a negative number. All other radios use positive numbers when setting up expo rates.
I would start by static checking your control throws after you dial in some expo. Start with your ailerons and dial in about 30% expo for channel one. Now watch your aileron control throws as you move your stick on the radio. You will notice a soft, easy movement while you are at the center of the stick and as you move the stick to full left or right, the controls will begin to move faster to their current end-point setup. This will make your aileron response much more soft at the center of the stick and you will be doing full, slow rolls all across the field. When you need some quick aileron for a quick correction or faster aileron roll, you will still have the throw you need when the stick gets to its extreme position. It will make your flying much smoother. If you are using the newer faster servos, you will see much more effect by using expo rates.
So how does Matt have his radio set up? There is no exact formula, but this may give you a place to start:
My expo setting on my Composite ARF 330S for precision non-3-D flying are below. Keep in mind I have a lot of throw in my control surfaces even on low rates, so you will want to experiment and find the best settings for your aircraft. (Note: Iím using a Futaba radio, so these numbers are listed as negative. For other radiosóJR, Airtronics, etc.óyou would dial in positive numbers.)
Aileron: -50% (left and right)
Elevator: -40% (up) -20% (down)
Throttle: -38% (this smoothes out the throttle response across the whole stick movement)
Rudder: -80% (left and right)
If you are skeptical, start with lower numbers, 0% would equal no exponential at all. Try a different setting after each flight and get to a point where you see your flying get smoother.
You have heard all the top aerobatic pilotsí names: Frazer Biggs, Quique Somenzini, Mark Leseberg, Christophe Paysant-LeRoux, Chip Hyde, Mike McConville, Bill Hempel, Kenny Lauter, Jason Noll, Jason Schulman, etc. Iím not even in the same league as these pilots, but guess what all these pilots have in common? Yep, they all make heavy use of exponential rates when setting up their radios.
So pull out that radio manual and start dialing up that expo! You will be glad you did and your friends will be asking you what you did to improve your flying.