Spring Air gear are are the way to go. As mentioned in one of the earlier posts, they will lock down if you lose air pressure. They now have a line of .60 sized gear that uses their "oleo" struts. The struts have a large 3/8 diameter aluminum post that mates to the retract unit. No need to worry about bending tiny 5/16 music wire, these units are strong!

I've used them on my models with great success. My Top Flight 190D has scale length struts (9" long! Lengthened two inches more than the stock struts) and have proven sturdy and reliable. Also, as stated earlier, they require air pressure in only one direction (retraction) so the air cylinder is much smaller and easier to conseal. Use the Ultra Precision control valve to slow down the upward travel and to dampen the quick action of the gear extension.

SC