East Bethel, MN USA
Joined Jul 2009
E-Flite UMX Carbon Cub SS handling checklist
Due to numerous requests, I have decided to also post my Carbon Cub handling checklist here, which should make it easier to find. I hope it helps newcomers & others who may be unfamiliar with flying scale planes and/or planes with flaps.
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. Check the wings for twist. There have been a few reports of the fore & aft strut lengths being slightly off on one or both sides, which can twist the outer section of a wing enough to affect flight. For best results, any visible misalignment should be corrected before proceeding further. The metal ends in the struts are threaded. If yours are off, you can adjust them with needle-nose pliers, or other suitable tool. For reference - from what we've seen in the Carbon Cub SS thread, nominal fore & aft strut-lengths seem to be 197mm & 200mm, respectively.
- 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 by adjusting the pushrod U-bends 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.
On the subject of ground-loops - it's just a Cub thing combined with the effects of scale. Full-scale Cubs are even prone to ground-looping if the pilot doesn't stay on top of the rudder until the plane has slowed to a fast jog. The tendency is magnified as scale is reduced. From what I've seen, the most common causes of ground-looping with the CC are (in no particular order) a misaligned tailwheel, cross-trimmed ailerons & rudder, a draggy or misaligned main wheel, and poor taildragger landing technique.
- Make sure that the mains have a couple degrees or so of toe-in. Just like your car's front wheels, a bit of toe-in or toe-out on the mains is required for directional stability. If the mains are out-of-whack, no amount of work on the tailwheel will solve the problem.
- Make sure that the rudder & elevator pushrods are all the way in. Due to the true-scale empennage, this plane needs all of the rudder & elevator authority you can give it. Even then, there's just barely enough elevator to execute a decent power-off flare.
- Be sure that the ailerons & rudder are not the least bit cross-trimmed. Even a few clicks of cross-trim can cause handling problems both in the air & on the ground. After you've got the trim sorted out, and have transferred any tx trim to mechanical trim & zeroed your tx trims, make sure the tailwheel is aligned with respect to the fuselage when the rudder stick is centered. Be sure to do it before you arm AS3X. Assuming the mains roll freely & are properly aligned - if your CC has a tendency to ground-loop at touchdown during 3-point landings & it also tends to ground-loop in the same direction when the tail touches down during 2-wheel landings, it is likely caused by one or both of the above.
- 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.
- If you're doing 3-point landings, you'll want to touch down with the stick nearly all the way back. At touchdown, pull the stick all the way back & keep it there during the rollout. Stay on top of the rudder until the plane stops moving, but be sure to make smooth, fluid corrections. Over-controlling the rudder during the rollout is a primary cause of ground-loops as the plane slows down.
- If you're doing two-wheel landings with the tail flying until it decides to come down on its own, be sure to keep flying the plane until it stops moving. Also, remember that the gyroscopic precession you compensate for with extra right-rudder just as the tail rises on takeoff is also present when the tail drops during the rollout if the prop is still spinning. But of course it now acts in the opposite direction, so the plane yaws to the right as the tail drops. Since the prop is spinning a lot slower during the rollout, the induced yaw will be a lot less than what is experienced during takeoff - but then rudder authority is also much lower during the rollout, so it's probably somewhat of a crapshoot. Just be ready to compensate with a touch of left rudder as the tail drops & then immediately relax the rudder just as the tailwheel touches down. When you get it right, your reward will be a nice two-wheel landing with the tail flying halfway down the runway, followed by a nice straight rollout on all three wheels. If you get the timing exactly wrong, the plane will punish you with a nasty ground-loop either as the tail drops or right afterward - depending upon whether you're early or late. If you get the timing sorta close, you will be rewarded with the Cub's infamous 'S-turn rollout' as the tail touches down. Not pretty - but it's a lot better than ground-looping, and it's a good sign that you're getting close to nailing the timing. It's one of those things that doesn't work right if you have to stop & think about it. Sorta like how when a musician plays a fast riff, he/she does not have time to think about the individual notes. The riff just happens. Thinking about each note would make it sound awkward & mechanical. And the riff would also be very slow in comparison to how fast one can play when the mechanics of playing become automatic. Just as a musician does not have time to think about individual notes during a riff, a pilot doesn't have time to consciously think about each move on the sticks. This is especially true during takeoffs and landings. Even more so when flying a taildragger. Thinking about each move guarantees that you will be chasing the plane rather than commanding it, as all of your corrections will be late.
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 descent-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 - unless you are an experienced pilot, with good throttle-management skills. Full-flaps are primarily for steep approaches and extreme slow-flight. 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 three flap positions (retracted, half & full). More positions would be better if your tx allows. 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 takeoffs & slow-flight. The CC uses channel 5 for flaps, which is typically the gear channel on the tx. This makes it difficult (or impossible) to set up multiple flap positions on some transmitters. If you're flying with a DX6i, see Kalmon's (Brian) post for a way to mix the gear channel to the 3-position switch: http://www.rcgroups.com/forums/showp...postcount=1841. Here's a setup for the original DX7, courtesy of Habitforming: http://www.rcgroups.com/forums/showp...postcount=7856. If you're flying with a tx that doesn't have an assignable proportional knob, multi-position switch, or the ability to mix the gear channel to the 3-position switch, you can put a Y-harness on the ailerons, plug the Y into CH2, plug the flaps into CH6, and change the brick from REV CH2 to full 6-channel operation. See the AS6410NBL manual for info on reprogramming the brick to 6-channel mode & using the servo reversing cable to reverse one of the aileron servos. A Y-harness for UM servos is available from Glenn at RC-connectors & Horizon.
- 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.
Tips for flying off water:
- 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.
The floats move the CG back a bit, so you'll probably want to move the battery forward a few millimeters or so from where you like it when flying on wheels. The CC has plenty of power, so the extra weight & drag isn't a problem, and she gets on step in just a few feet at WOT. The factory & 5030 props work well on floats. I'm using the factory prop in the video below. The Yak prop is the best choice for scale flying with tundra tires & for flying off snow with the floats, but it's not a good prop for ROW, as it picks up too much water.
There is no water-rudder, so maneuvering on water can be a bit challenging at times. There has to be air over the rudder to turn, so you need to use blips of throttle to turn when taxiing slowly. Always keep the elevator stick fully-back while taxiing. Crosswinds are challenging. Anything more than a 3-5 MPH crosswind is too much to taxi in without a water rudder. If you have to taxi in a 3-5 MPH crosswind, try to taxi at a 45-degree angle into the wind, and be sure to hold aileron into the wind to keep the upwind wing down. Use throttle & rudder to combat the tendency to weathercock. Avoid taxiing downwind. Simply let the plane weathercock into the wind & let it drift back to you, instead. Take off and land into the wind if at all possible. Roll into the throttle smoothly on takeoff, and keep some back-pressure on the elevator stick during the takeoff run. Stay on top of the rudder as the plane gets up on step, and again as it rotates just before liftoff. You can see what happens if you don't in the video below. (S-turn takeoffs!) On approach, keep the nose up. Bring her in a bit nose-high on the landing & keep some power on all the way down. The elevator stick should be almost all the way back just as the floats touch the water. You always want to land nose-high on floats so that you don't 'submarine' a float. Trust me - you really don't want to submarine a float! Taxi back with full up-elevator, and remember to use throttle to assist with turns.
Here are a few examples of how she can fly when set up & flown as described above.
Here's a scale flight & proper use of flaps demo:
Flying in a stiff breeze:
My first-ever ROW flight:
In these clips, I'm flying with the GWS 5030 prop & a custom lightweight TP 325 mAh 65c 'UMX' pack from RCBabbel
Having some fun in the yard:
Extreme slow-flight maneuverability demo with full-flaps:
Testing the 2300Kv motor/2.75" x 2.5" Yak prop combo at the club field - scale flying, checking the low-end thrust, plus lots of touch & gos and scale two-wheel landings with straight rollouts. Landing practice starts @ 6:00:
Flying in the yard - using the 2300Kv motor, 5.75" x 2.5" Yak prop, Hyperion VX 500 35c Babbelbatt, and a set of E-flite L-4 Grasshopper 250 wheels as 'tundra tires':
The CC can also carry a large payload. Here are a couple of on-board video clips, using a 17g 808 #16 cam. The first one was shot from the SW shore of Lake of the Woods in Warroad, MN (my hometown). The second one was shot from my yard - flying ROS with the floats on. AUW was 129g, yet the CC still had ample power. Even managed a loop from level flight.
Here are a few useful links.
RCBabbel makes the lightest, highest-performance, highest cycle-life packs available for the UMX planes. His workmanship is exemplary, as is his customer service. Get your Babbelbatts here. Just send him a PM & let him know what you're flying & what you want to do: http://www.rcgroups.com/forums/showthread.php?t=1540831
Ben's (bhoov128) scale 36" Alaskan Bushwheels are the ultimate wheels for your CC! Just send him a PM & he'll make a set for you: http://www.rcgroups.com/forums/member.php?u=415738
1.25" & 1.5" DuBro Mini Lites work well as tundra tires on the CC. They're great for flying off AstroTurf, short grass, dirt, gravel, and sand. They don't look scale, but they're cheap and readily-available: http://shop.dubro.com/p/1-1-2-mini-l...essories?pp=12
E-flite's Grasshopper 250 wheels are a direct fit, and they make a good tundra tire for the CC that looks much more scale than the DuBro Mini Lites. They're great on AstroTurf, short grass, dirt, gravel, and sand: http://www.horizonhobby.com/products...er-250-EFL5031
The 5.75" x 2.5" Yak prop is an excellent choice for scale flying. But you'll also need a set of tundras or Bushwheels for clearance: http://www.horizonhobby.com/products...54-EFLUP575225