May 15, 2012, 01:40 AM
Eflite UMX Carbon Cub handling checklist
Given the flurry of questions this plane has generated regarding the use of flaps, flight-trimming, landing techniques, and ground-handling - I decided to put together a checklist for those who may be new to scale planes and/or planes with flaps. If you are experiencing difficulties such as ground-looping, difficulty flaring, sluggish control response, odd behavior in turns, or handling problems with the flaps extended - here are a few things to check:
- Visually inspect the alignment of all flying surfaces with respect to the fuselage & each other. Also check the alignment of the tailwheel with respect to the rudder. For best results, any visible misalignment should be corrected before proceeding further.
- Be sure that the plane remains motionless during the first 5 seconds after connecting the battery. The plane can be on its back or in any other position during initialization, provided that it remains motionless during the process.
- Move the aileron pushrods to the innermost or second hole out. Move the rudder & elevator pushrods to the innermost holes. If the plane seems overly sensitive, try adding a bit of expo, rather than reducing throw - as there will be times when full control authority is needed.
- Mechanically trim the plane so that little, if any tx trim is required for straight & level flight in zero wind at 50-75% throttle. AS3X interprets excessive trim (more than a few clicks) as command inputs, so tx trim should be used sparingly. Also - never use sub-trims with AS3X. Ideally, flight-trimming should be done in dead-calm conditions. The next best alternative would be flying directly away from yourself into a light, but steady headwind.
- Measure the CG, then perform an in-flight CG test & adjust as needed: If you need up-elevator trim (mechanical or on the tx) for level flight at 50-75% throttle, the plane is overly nose-heavy. If the nose drops like a rock in turns and/or when power is reduced, the plane is overly nose-heavy. If the plane is trimmed for level flight at 50-75% throttle and it balloons when you go to full power, it's overly nose-heavy. If the nose comes up or doesn't drop at all when you cut the power, it's very tail-heavy. If the plane seems to be overly sensitive to micro-turbulence, it's also tail-heavy. (You can actually hear the difference by listening to the sound of AS3X working the servos.) When the CG is about right, the nose should drop slightly as the plane slows after the throttle is pulled back. If the plane is trimmed for level flight @ 50-75% throttle and you go to full power, the plane should gain altitude, but the nose should come up only slightly, if at all. Measure the CG again after the final adjustment for future reference.
To reduce the tendency for ground-loops:
- The CC is not a bank & yank plane. It needs rudder in the turns. Practice using the rudder in conjunction with ailerons for coordinated turns. For the best-looking scale turns, use mostly rudder & manage the bank-angle with ailerons. During tighter turns, a slight amount of opposite aileron may be required to maintain a modest bank-angle.
- Make sure that you aren't over-trimming the rudder & then compensating for the induced roll with opposite aileron trim. Even a small amount of cross-trimming (mechanical or tx) can cause handling problems.
- On takeoff, roll into the throttle smoothly. Use rudder to compensate for the effects of P-factor, torque, slipstream, and gyroscopic precession during the takeoff run. Those who fly the Beast 3D are used to letting AS3X take care of these effects. On this airframe, AS3X dampens, but does not eliminate them - therefore, some pilot intervention is required.
- Use smooth rudder inputs while taxiing, during the takeoff run, and during the rollout. Hold full-up elevator while taxiing to keep the tailwheel firmly planted on the ground. If the rudder seems overly sensitive, try adding a bit of expo, rather than reducing throw - as there will be times when full rudder authority is needed.
For easier power-off/power-on flares & three-point landings:
- When taxiing in crosswinds, try to taxi at an angle into the wind, if possible. Apply aileron into the wind to reduce the chance of wind getting under the wing & flipping the plane. For instance - if the wind is off your port wing, use left-aileron. Avoid taxiing in anything more than a 5-6 MPH crosswind.
- On approach, remember that throttle controls descent-rate & elevator controls airspeed. If you're coming in short, add some power to decrease the decent-rate. If you're coming in too high, reduce power to increase the decent-rate. If you're coming in a bit hot, ease back on the stick a bit to raise the nose & slow the plane down. If you're coming in a bit too slow, relax the stick slightly to drop the nose & pick up some speed.
- Use the maximum elevator throw that you can, but avoid servo over-travel. Be sure the the elevator pushrod is in the innermost hole. Make sure that it doesn't bind. If the elevator seems overly sensitive, try adding a bit of expo, rather than reducing throw - as full elevator authority is needed for the flare.
- Make sure that the flaps are fully retracted in the 'up' position. Even a small amount of droop can introduce enough downward pitching moment at low speed to make power-off flares difficult.
- Make sure the plane is not overly nose-heavy. A forward CG can reduce elevator authority enough to make flaring difficult, if not impossible - even power-on.
- As recommended in the manual - always carry some power all the way down to about 6 inches or so off the runway. Carry a bit more power when landing with flaps, and carry it all the way down to just a couple of inches off the deck.
To improve handling when flying & landing with flaps:
- Due to the CC's high thrust-to-weight, a small change in throttle setting can make a large difference in thrust when slow-flying with partial flaps or when executing a power-on flare. If you find the throttle a bit too sensitive, set up a throttle curve to mellow the throttle-response a bit on the low end - if your tx allows.
- If this is your first flap-equipped plane, get used to how it handles clean before experimenting with the flaps. If this is your first or second aileron plane, you will most likely find the plane to be a handful when slow-flying with the flaps even partially extended. Make sure you are flying at least 3 mistakes high until you get used to how the plane behaves when there is little air flowing over the control surfaces. If you think you're about to lose control - retract the flaps, smoothly go to full-power, and get the nose down. Keep the nose down until the plane is flying again.
- Make sure the plane is not tail-heavy. With the CC, even a slightly-aft CG will result in mushy handling when flying circuits with partial flaps.
- Do not fly around with the flaps fully extended. Full-flaps are for steep approaches - not slow-flying. If you are stuck with one flap setting, reduce the throw to 50% or less if you want to fly slow circuits with the flaps down. If you are serious about the hobby & think you may want to try more full-featured planes in the future, consider upgrading your tx.
- If your tx allows, set up at least two flap positions (half & full). Three or four positions would be better. If your tx has flap delay - use it! Alternatively, assign the flaps to a conveniently-located proportional knob or slider, if one is available. Preferably, one with a center detent position that you can use for slow-flight. The CC uses channel 5 for flaps, which is typically the gear channel on the tx. If you're flying with a DX6i, see the following post for a way to mix the gear channel to the flap channel & have 3-position flaps: https://www.rcgroups.com/forums/show...postcount=1841
- If you find managing the airspeed, throttle, elevator, and flaps all at once to be overwhelming, try the flap-elevator mix. But don't make the mix so aggressive that you can drop the flaps at cruise speed without ballooning. As you get more comfortable with the workload, slowly reduce the mix. You may find that you don't need it anymore. Those who would like to add a little taste of full-scale flying to their RC flying may even find that they enjoy 'feeling the plane' - as one pilot put it.
- Reduce power & wait for the nose to drop slightly before extending the flaps.
- Manage the throttle carefully when flying with the flaps extended. Be sure to retract the flaps before adding power - as stated in the manual. For instance - if you're doing a slow flyby with partial flaps, retract them before adding power after the pass. If you're on approach with partial or full-flaps and need to abort the landing - immediately retract the flaps, advance the throttle, wait for the plane to gain speed, and then ease the stick back. The plane will most likely lose some altitude as you retract the flaps, but resist the temptation to abruptly haul the stick back. Wait for the plane to gain speed, then smoothly pull up & make your go-around.
- Be smooth & deliberate on the sticks (including throttle) when slow-flying with partial flaps. Remember that control authority will be significantly reduced, due to the lower airspeed. The reduction in control-authority becomes more pronounced as the flaps are extended further & the plane slows down. Avoid steep bank-angles when flying with the flaps extended. Make gentle, coordinated turns. Initiate the turn with rudder & maintain bank-angle with ailerons. Don't let it get too slow. Do not abruptly increase the throttle, as this may cause an abrupt pitch-up, followed by a stall. At low altitudes, this often results in a crash. If you find yourself in this situation, immediately retract the flaps, smoothly go to full-power, and push the nose down to build airspeed & get the plane flying again.
- Avoid flying & landing in gusty and/or turbulent conditions with the flaps extended.
- Avoid crosswind landings with the flaps extended.
- When landing with flaps in anything more than a very light breeze, retract them immediately after touchdown to help keep the plane planted on the runway.
Here's an example of how she can fly when set up & flown as described above. I am flying with the GWS 5030 prop & a TP 325 mAh 65c 'UMX' pack from RCBabbel
(TP's factory pack does not have the UMX connector):
Last edited by turboparker; Aug 09, 2012 at 04:43 AM.
Reason: Added landing approach & coordinated turn info