I have a few questions concerning my A6M2 Zero. It doesn't seem to perform as I think it should. It weighs 2.27 oz.
It has a 250 MAH li-poly battery and Cirrus 5.4 gram servos. I used the Pixie 7P speed controller!
From : Don Stackhouse
That's a very good weight. With the old 7-cell 110 mah NiMH packs and GWS Pico servos, a typical weight was around 2.8-2.9 ounces, and the 2-cell Li-poly battery typically shaves about half an ounce off of that. The full-throttle power from a really good 110 maH NiMH 7-cell battery is very slightly higher than from a 2-cell 250 mah Li-poly battery, but the weight difference more than makes up for that.
It climbs at a leisurely pace and feels like it is getting ready to stall when I pull up more than a few degrees. It is difficult to self hand launch, which I usually have no trouble doing with other small models.
That sounds abnormal.
Are you sure you have the prop on the right way? The frosty (convex) side should face forwards and the shiny (flat) side of the blades should face aft.
The other thing to check is that your propulsion system is performing normally. If you have a Wattmeter, it should be reading about 6 watts at full throttle. You should also be getting about 5500 prop RPM at full throttle after that initial peak in the battery voltage has burned off (battery voltage at that point should be around 7.6 volts for a 2-cell pack). If not, you could have a bad motor. The usual cause of this is getting the terminals too hot while soldering on the leads, which then melts the plastic end bell. The brushes can then shift in their sockets, losing contact pressure against the commutator. The motor will still run, but will not develop full power.
One other question - what's the elevation of your flying field? If you're at higher altitudes, such as Denver or Albuquerque, it could be that in the thinner high-altitude air you need a prop with more pitch.
It does, however turn around in about three feet. What am I doing wrong?
Hmmm.... I see...
Let me guess, it turns around in three feet in one direction, but not the other, or else you have only had time to try turns in one direction. Am I right??
The A6M2 is one of the tightest turning of the entire Roadkill Series, but three feet is definitely tighter than normal. The fact that it's able to turn that tight without falling out of the sky suggests to me that your motor is probably performing OK. My guess is that you may have a rudder trim problem. If the rudder trim is off, the plane flies in a yaw all the time. That profile fuselage makes massive amounts of drag when you make it fly through the air sideways. Because of this, a rudder trim problem usually looks like a power shortage problem. The Triplane is especially sensitive to this, but it's definitely something to consider with any model that uses coupled ailerons and rudder, such as the Zero. Fortunately, once it's been set properly, it should not be a problem after that.
First, make sure the ailerons are trimmed for level flight in cruise. Now, try some turns in BOTH directions using moderate (start with 20-30 degrees) bank angles, with bank angles equal in both directions. If everything is correct, the plane should turn equally well in both directions. However, my guess is that it will have a tighter turning radius one way than the other, and that it will be yawed to the inside of the turn in the tighter-turn direction, and yawed to the outside of the turn in the wider-turn direction.
Leaving the ailerons alone, adjust the rudder trim by shifting the wire pushrods in the heat-shrink coupler on the pushrod running from the aileron horn back to the rudder horn. When you have everything just right, the plane will fly wings-level in cruise, and will turn equally well in both directions.
The key to remember in all of this is that you have a coupled aileron and rudder system. Whenever you retrim at the servo (i.e.: with the trims on the transmitter), you change BOTH the ailerons and the rudder simultaneously. If the problem was with just one of those (such as a roll trim problem with the ailerons), you have to readjust the other control through the mechanical linkages to put it back where it was. Yes, it's a little more complicated than just resetting the sub-trims in your transmitter, but it saves you the weight of a servo, which on a model this size is very significant.
Yes. Either the MPS-2A (the one with the 6-5 prop) or -2B (the one with the same 5-4.3 prop as your present MPS-1A) will work. I'd recommend the -2A, the one with the bigger prop.
With the twin motor system the current per motor at a given throttle setting is lower, so the motor efficiency is higher. Therefore, for the same watts coming form the battery you get significantly more watts actually delivered to the prop shaft. In addition, the twin motor system will pull a lot more total watts from the battery.
If you REALLY want some excitement, try using a 3-cell 250 mah pack with a -2A. At full throttle it should pull about 22 watts with that battery, almost four times the total power! That's the setup I fly in my Triplane, and it's awesome, bordering on downright scary. Performance will be very "non-scale".
BTW, the same motor with a 3-cell 700 mah pack pulls about 29 watts in the Ryan ST, but don't try that in your Zero. You will find that you will almost never need full throttle, even with the 250 mah battery.
Note, with these batteries it is possible to overheat and even damage the motors if you try to fly with the throttle wide open for extended periods. It's fine for short bursts, say 5-10 seconds with enough time between for the motors to cool back down. With just about any of the Roadkill Series models you shouldn't need full throttle anyway, except for very rare occasions. I normally leave the throttle on my Triplane at 40-50% most of the time, occasional bursts to 75% throttle stick position during extreme aerobatics, and I almost never need full throttle. The Triplane is a notorious "current hog", and your far more efficient A6M2 should get by with even less throttle than that. Still, it's nice to have all that power available for those "special occasions".
Not necessarily. The torque from the motor is greater, but most of the damage is done by the mass of airplane behind the point of fracture. The motor is ahead of that point, so the extra forces required to decelerate that bigger motor mass goes into the point of impact, not the airframe.
If you want more durability in the nose for a small increase in weight, try cutting two 1.25" wide strips of 1 or 2 ounce fiberglass and laminating them to both sides of the nose, running from the forward portion of the wing to the cutout for the motor in the nose. Thin C/A, laminating epoxy or water-based polyurethane varnish ("Varathane" or equivalent) all work fine for this. This gives you a fiberglass load path to carry the impact loads from the nose to the wing. It's easiest to add while you're first building the model, but you also can add it later.
I already broke mine off once when I hit a fire ant mound on landing. I have to maintain a bit of throttle to land. Maybe if the prop was not turning it would not have broken.
The torque can be a contributing factor if you still had the throttle open at the moment of impact, but in a model of this class it's a minor issue. Most of the damage comes from the speed of impact and the mass of the model aft of the point of fracture. Switching to the bigger motor package will not change the mass whose kinetic energy in a crash has to be absorbed by the section between the nose doubler and the wing.
Don Stackhouse
DJ Aerotech
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