I just got the Curtis Wright Jr. . I just read Bob Aberle's article on the Li Poly cells. Could I use 2 of these cells for the CW-1? Or do you reccomend sticking with the Nimh set up.

From : Don Stackhouse

Until just a short time ago, I would have recommended the standard 110 or 230 mah NiMH setup. Things are a little different now, although the NiMH cells are still a very viable option for the Junior. Here's a summary of our Li-poly test results, including the tests involving the Junior:

First of all, the Kokam cells:

Two cell packs of the little 145 mah cells don't seem to have the power output and the necessary max current capacity, except for the most efficient MPS-1A models that don't need more than about 40% throttle for cruise. The Cub, A6M2 Zero and the Curtiss-Wright Junior may be OK based on this. Flight times might be acceptable, as long as you're willing to put up with a significant loss of full-throttle power. They do save a great deal of weight, but not enough to offset the loss of power due to the max current limits.

Two cell packs of the larger 500 mah Kokam cells do reasonably well in our twins and MPS-2A powered models, about the same performance as the 230 mah NiMH cells but with more flight time. The shorter-winged models with a single MPS-1A do not seem to like the weight of the KoKam 500 mah cells. The Junior and Cub might tolerate the extra weight, but I'm not wildly enthusiastic about that option, I think there are better alternatives. Read on...

Regarding the new E-tec cells that are just now becoming available: These seem to have more current output than the Kokam cells, and come in sizes that seem better suited to our models.

A two cell pack of the E-tec 250 mah cells is fully 1/2 ounce lighter than a 7-cell 110 mah NiMH pack (our standard recommendation for indoor flying with a single MPS-1A). Full-throttle power is very slightly less, but with the weight savings the overall performance seems to be about the same or slightly better, and the flight times are far better. Power at cruise is about the same as the old NiMH cells, and power available near the end of the flight is a little better. I recently flew the Junior with a 2-cell 250 mah E-tec pack outdoors in measured winds averaging 10 knots with frequent gusts to 12 and occasional gusts to 15. This required about 75% on the throttle stick position (we can normally cruise the Junior at about 1/4-1/3 throttle stick in calm air), and with the old 110 mah NiMH pack I would have expected about 7-8 minutes at these power settings. The E-tec cells lasted a very solid 22 minutes, despite very high throttle settings throughout nearly the entire flight! It appears that the E-tec 250 mah 2-cell pack may be the best all-around choice for models powered with a single MPS-1A.

On the Junior you'll need to mount the Rx under the front cockpit and the battery leading edge even with the leading edge of the ply nose doubler to get the C/G to come out correctly without noseweight. I've attached a photo of the installation in my Junior.

I also have logged a fair amount of time recently on the Ryan ST prototype with an MPS-2A twin-motor system and an E-tec 2-cell 700 mah pack. This pack weighs 0.1 ounces less than a 230 mah NiMH pack, but provides a HUGE 55% increase in power at full throttle, and provides flight times in excess of 35 minutes (I'm not sure how much in excess, I haven't had a chance to run one all the way to the end yet, but end-of-flight voltage measurements suggest another 10-15 minutes or so). In comparison, the 230 NiMH pack goes about 8-9 minutes at those power settings. Note, that's not 35 minutes of "economy cruise", but rather it's regular sport flying with periodic takeoffs and landings to a full stop, and loops and other maneuvers throughout the flight. There is no question in my mind that this is the best available option today for models with the MPS-2A or a pair of MPS-1A's. I'm really looking forward to trying this setup in a P-38, or the super-efficient Electra. BTW, the MPS-2A is also available as an upgrade for any of the single-motor RK models except the Junior (it doesn't need it, and there isn't enough prop clearance above the tailboom for the MPS-2A's 6-5 prop), and the MPS-2A should work especially well in the single-motor WW II warbirds.

We have a 2-cell E-tec 1200 mah pack that I'm hoping to try in the Boeing B-17 soon. Based on what I saw with the 700 mah cells in a twin-motor setup, I expect the 1200's to do very well. The Boeing currently flies extremely well on a 6-cell 600 mah NiMH battery, so I anticipate it will see roughly double the flight time and a big increase in available max power. It should be interesting.

We've ordered batches of the E-tec 250 mah and 700 mah two-cell packs, and hope to have them available for sale in the next week or two. You'll also need a good Li-poly compatible charger. The Plantraco LPC-400 does an excellent job with these and for a very reasonable price. I also hear that the E-tec charger is very good, although I haven't had a chance to test one yet. It's about $10 to $15 more than the Plantraco, but can charge at up to 1.5 amps, while the Plantraco has settings for 100, 200 and 400 milliamps. We're supposed to be getting one or two E-tec chargers with the first batch of E-tec packs.

Also make sure your ESC is compatible with a Li-poly pack, in particular that the cutoff voltage is correct. The Castle Creations Pixie 7-P is our preferred choice for this.

Until now I've been less than thrilled with the available litium options for our models. Obviously I've now changed my mind!

Don Stackhouse
DJ Aerotech