The 555 is probibly the most popular RX in combat. They work great, even with 12-13 models all up, and in very close proximity (sometimes, a bit too close). The only RF envrionment that I think matches combat for stressing RX's is some of the glider guys who fly WAY WAY out there, and with many up at once.

I've even had one keep working when half the antenna got cut off in the air (don't try this at home). Landed after the round to find a prop cut through my tail and antenna that I never even saw happen! The antenna wire is thick stuff, and the card inside is strong. (Other RX's in that size that I've seen have much thinner guage wire on the antenna). I've had 555's survive multiple head-on mid-airs, where both planes were going 80+ mph. They are the gold standard for durability in an RX. (I did actually manage to scrag one though. It got hit directly by a prop. But Hitec's service center had it back to me in no time flat).

If there's one thing combat pilots know, it's how to durability test equipment . If you want a 6th channel they make a 6 channel that's just as good. I think I have about 10 555's. (I need to clean up the shop and count gear)

I also use HS-81's and HS-85's. I have piles of both (don't ask me how many. I don't know. I lost count a long time ago. My wife just asked me the other day how many I had. that wasn't pretty. Now I have to clean up the shop this week and count them all. Sheesh. Just for starters, 5 2610 class scale combat ships, each has 4 servos, all HS-81 or HS-85). The HS-81 is a fine servo for all kinds of uses. You want to watch for 2 things though. The plastic gears on them are fragile, and easily stripped. (the HS-85 has a stronger gear train). I bought a pile of HS-81's with plastic gears, and a some spare metal gear sets. When I strip a plastic one, I replace the gears with metal. The ones that don't strip obviously don't need metal gears . So, if you have plastic gears, be careful bumping it, and don't put it on the elevator or anything that might flutter, or that is a major problem if it does strip on you. With metal gears, you can put it anywhere the the torque numbers work. I have them on the elevator and ailerons on 3.5lb, 90mph scale combat planes. No problems. (I do usually use HS-85's on elevator, and a pair of 81's, one on each aileron, plus a plastic gear 81 on throttle. But I do have some flying with an 81 on elevator.)

The other "issue" with the HS-81 is that some of them seem to have a pot that is a bit prone to wearing out faster than the HS-85. But every time I've sent in a Hitec servo with a flaky pot, Hitec sent back a brand new servo at no charge, and fast. And it doesn't happen often.

Btw, the HS-81 has been cloned by a number of companies, or Hitec is making them for other labels. The Hobico CS-12 is an HS-81, if I recall.

Anyway, the Hitec HS-81 and HS-85 are a bit more expensive than other micro servos, but worth the money, espeically the metal gear variants.