I have stopped using 2721's on anything but nosewheel steering on the KingCat where they seem to hold up well on heavy takeoffs on our grass field......All the other control surface servos are 8411's....

I have about 140 flights on my KC with zero problems......my total current draw on those 8-8411's is always no more than about 400 maH/10 minute flight.....I use a SR 2200 maH pack 5-cell Nicad pack with no regulator.....

A certain percentage of 2721's and 4721's have had that jitters problem dating back into the mid-ninety's when they were the JR servo of choice on Big Bird Prop jobs....always blamed on vibration-induced deterioration, but obviously not the cause with jets...I noticed at the Minnesota Jet Rally that one of my Bandit 4721 flap servos started jittering, bad enough to replace again.....that is 4721 servo #5 in about 150 flights on the Bandit....one of these days I am going to go to 8411's....

With 8411's, you just must be careful setting them in the full up position on flaps so they are not stalled......I use an in-line ammeters.....takes a couple of minutes.....advantage then is that you have a digital servo with all it's improvements holding very tight around center which I consider important for rudders, which in my experience has been a common surface to experience high speed flutter on our model jets.....plus, it definitely prevents blowback of the flaps if you happen to deploy them at a higher airspeed, within the limits of the play and geometry of the linkage, of course....

Had the 8611's been out when I built the KC, I would have used them....I have exercised them and compared with 8411's....they draw just a bit more average current than the 8411 during normal motion, but do draw somewhat more when stalled....bottom line, if you are using digitals, just be sure they never stall.....

Tom