General Category => KRCM Training Course, Flight Safety & Training Nights => Topic started by: Deerslayer on November 21, 2019, 08:29:03 AM

Title: Throttle Curves
Post by: Deerslayer on November 21, 2019, 08:29:03 AM
Another more recent option in many of our radios is the Throttle Curve. Either we are unaware of it or we just never think of it as a possible improvement or solution. In the "good old days" of simple radios and glow engines, we actually did have a "throttle curve", in that the linkages were such that we most likely had an exponential response built in, i.e., degree of throttle barrel sensitivity to stick movement is much different down near Idle and at low range than it is at higher stick settings.

Electric motors can be very sensitive to power commands throughout their range. Unlike internal conbustion engines, maximum torque is available from the start. This is great for most or our work but there are times when having a smoother application of the r.p.m. toward the low end can result in easier or more precise handling.

For instance, you may have something like a WW1 replica where ground handling during takeoff is a handful. Giving the engine a shot of power to get her moving may result in a wild swing due to torque and propwash effects before you have proper rudder control. Note how small and down in the dirt many WW1 rudders are - not exactly made for great control until that tail is hoisted well up into a strong airstream. Now, it suddenly wakes up and yanks your plane around, as you are jockeying throttle and rudder, with perhaps even some aileron thrown in. Slow and steady is more likely to be the way to go, lead by smooth and gradual throttle application.

What about those nasty "bunny hops" we sometimes get into while landing. Manhandling a sensitive throttle, especially if you have shied away from using lots of exponential on your elevator, can lead to pilot induced oscillations.
Or, you may like doing knife edges or hovering and need better control of not only the rudder, ailerons and elevator but the throttle has to be carefully coordinated with all of the above to make it look good and be sustainable for a few seconds.

The neat thing about Throttle Curves, as implemented on most systems, is that you get to plot the points and to choose whether they will be straight lines or smooth curves. There really isn't much you can mess up. Your system most likely is already using a throttle curve, actually a straight line between 0,0 and -100,100 and called Curve 0. Leave that one alone. You can set up and number your new curve(s) and associate one to take the place of Curve 0 or use your Flight Modes to enable different curves for different conditions.

Here is another good use of  Throttle Curve: I often have a plane set up to do something a bit different during landing. In this mode, the lower half or so of the Throttle Stick mostly controls the Spoilerons (Ailerons acting together to become Spoilers in addition to their normal Aileron function) or Flaps+Spoilerons (Flaps moving down as Ailerons move upward, to create "Crow"). This Throttle Curve will be entirely or nearly flat-lined from "0" to a very small percentage while the stick is controlling the Crow via other mix(es) to the stick. Then, as you push the stick forward, Crow is gradually reduced and then eliminate. Meanwhile, the Throttle Curve for the upper half or more of the stick movement rapidly increases, eventually reaching 100%. This setup allows for steep approaches, great handling in high turbulence, spot landing and immediate clean-up and ready to handle a missed approach, if required.

Throttle Curves - just another location on the Learning Curve! Think about it.