That's a lot of if's there, Redfish.

You also have to figure out a way to charge that LiPo. There is, of course, only one way, and that's to buy a LiPo charger. You cannot charge it with your NiMH charger. There is a lot to consider here. And, oh, that's "solder". It took me a minute to figure that out..

Size does not equate to capacity. If your NiMh pack is, say, 1000 mah, then if you get a LiPo of the same size, you have a few other things to consider. One is the number of cells in that pack that will provide the voltage that you have with your NiMh packs. Then, as I said, no matter what you do, you have to get a higher capacity than what you have if you want longer flight duration. And, of course, that's one flight, then on the charger for over an hour (with the right charger), or buy another pack of the same voltage (number of cells) and capacity.

You also have to remember not to overload that LiPo pack. They are not like NiMh or NiCd packs. Those are pretty robust. So, is a LiPo if you get one that has the right max current (listed as C on the pattery pack.. such as a 10C pack can handle a discharge rate 10 times the capacity). And, LiPo packs are, can be, somewhat dangerous. They are not to be charged in your house or in your car. If there is a problem, they have been known to be the cause for burning things down, or gut cars and trucks.

You sure you still want to do this in a plane that may or may not have been designed for LiPo packs? If you are ready to answer all the if's and go forward, keeping in consideration all the things that could be a problem for a novice, well, knock yer self out!

CGr.