Note that not all NiMH cells have a high internal resistance -- some are lower than NiCds of the same capacity.

The real problem is the use of the wrong NiMH packs.

In my profiles, I regularly fly with 4x digital servos (HS5925) and a 1050mAH NiMH pack with zero problems -- despite some pretty serious throws and violent manuvers.

The NiMH pack I'm using however, is rated at 20A continuous and consists of five 2/3A cells.

Sometimes people think that more capacity means more current-handling capabilities but they're usually dead-wrong.

I've got some 1650mAH NiMH packs that start to sag with just a 5A draw -- but they're AA-sized cells. I use these with standard servos and they're fine but I'd never use them with digitals.

On a larger plane such as your Yak I'd never use anything smaller than a sub-C sized cell and make sure that you're buying a pack with low internal resistance, regardless of its capacity. In fact, the use of two packs would be a very wise move.

Note also that because they have their own processor, Hitec servos do seem to exhibit a "reboot" delay if the voltage feeding them drops below a certain level. This manifests itself as a period of up to 1 second when they simply stop responding. However, if you have your batteries and wiring up to scratch you should *never* experience this in flight so it's not usually a problem.