I'm considering purchasing one of the new Cirrus Micro Joule airborne systems for a RoadKill Electra I'm about to start.

Would use of the Micro Joule allow addition of a 3rd servo for rudder. The alieron/rudder mix can be done from my TX. The same system may also be used in a Wright Junior, DC-3, and BF-109F. Your thoughts please.

From : Don Stackhouse

I think you're worrying way too much.

I haven't seen any actual specs (particularly torque) for the new 3 gram Cirrus servos, so I can't really comment on whether they're strong enough to operate the ailerons or rudder on the Electra, but the weight-carrying ability of the Electra does not require these small servos in the first place, particularly if you're using the new Li-poly batteries. The weight savings and power increase from these new batteries will make it totally unnecessary. Even with the old NiMH batteries, the planes you mention can handle the weight of three conventional 6-gram servos.

Of the four you mention, the Electra and Junior are particularly good at tolerating reasonable weight increases.

In addition, in the case of the Junior there really isn't much need for separate rudder and ailerons anyway. The Junior's ailerons are not very effective (the full-scale Junior also had very ineffective ailerons), so the roll rate with ailerons is not significantly different from the very nimble roll response you get from building it with the extra dihedral and just rudder (no ailerons). The stability is also better with that version, so unless you have a desperate obsession for doing forward slips on final approach, or you want the ailerons and scale dihedral for scale competition reasons, there really isn't any need for the ailerons in the Junior in the first place.

The DC-3 likes to fly faster, but it does have quite a bit of weight carrying ability. I've flown it successfully with a Hitec 555 receiver and a 6-cell 600 mah nicad battery, which puts its flying weight far above what you're contemplating, and without a significant change in power from the 230 mah 7-cell NiMH pack we typically used to recommend for it. Yes, it flies better if you keep it light, but it does fly quite well with some heavier equipment. The weight of an extra 6-gram servo like the GWS "Pico" or Hitec HS-50 will not be an issue.

Of all the RK Series models, the Electra is one of the best for hauling a load. Joe has one with an extra servo and a 5" tall plastic skydiver and parachute he used for parachute drops. On a 170 mah 7-cell NiMH pack, he typically got about 6 takeoffs, climbs to about 80 feet, skydiver drops, descent to landing and re-loads for the next run, all on one charge and without turning it off during the re-loads.

The Me 109 is more of an issue. "In the beginning" there were the first six Roadkill models. They originally flew on 6-cell 110 mah NiMH packs that had no room for error or extra weight on power. The Me 109 was the worst in this regard, a "current hog" with a high minimum flying speed and a strong desire to be flown at all times during its relatively short flights with the throttle most of the way open.

However, an Me 109 with a 230 mah 7-cell NiMH pack and one of our new twin-motor systems was a new animal altogether. The extra power made all the difference. With today's new Li-poly batteries, we can use a 2-motor MPS-2A powerplant with a 700 mah 2-cell pack, or better yet an MPS-2B (that uses a 5-4.3 prop instead of the 6-5 prop we use on the -2A) and a 3-cell 250 mah Li-poly pack. The Fokker Triplane is even more of a current hog than the Me 109, and I get typically 15-18 minutes of wild aerobatics from it with the -2B and the little 3-cell pack. The excess power is so great that I almost never use more than 3/4 throttle, even on vertical maneuvers. The weight savings for that motor and battery (in comparison to the old single-motor powerplant and NiMH battery) is a little more than the weight of an extra servo, so you'd be looking at a small net weight savings. The Me 109 with this setup will still need to fly fast, but it will have enough power and battery capacity to do so for a very long time.

The new tiny Cirrus radio systems are exciting, and I'm already looking at what sort of models we can design around them, but you don't need something that exotic to have four channels in any of the current Roadkill models. Investing in the new batteries will give you a much bigger return.

Don Stackhouse
DJ Aerotech