Hello, how do I know whether I can substitute a cretin servo for one that is being called for in the Arf I purchased? I know the speed and torque play an important roll in that but does brand matter much? If I’m running some digital servos can I run analog ones with them or will the conflict? The servos that are being called to use in my giant scale p-51 mustang are jr ds811 but there discontinued and was wondering if they are just because there is a better one out now from jr. The servos that I have that I would like to use in place of the ds811 is the spektrum ds821 just because I already have them, would those work well in comparison? Thank you in advance for any help and advice on this matter also I’m new to rc universe so was wondering is there a way to make the post I post easy to get back to after I complete it? The only way I found one I posted before was via e-mail but was unable to locate it otherwise.

When you go to the forums you can just look for your name at the top of the page and click it to go to your profile and find your recent posts.

You can mix digital and analog servos with no problem. Also, I think its generally best to stick to name brand servos, Futaba, hitec, JR with the recomended torque for the plane. Other than that there is a lot of flexibilty with servos. For some aplications you could go with standard analog servos that go for $15 or digital coreless that go for $75. It just depends on the style flying. For warbirds high end servos arent really necessary as long as they meet torque requirements for the plane.

First off, what is your experience level? I see that you have only a small handfull of posts here on RCU (not that it means anything) but you are considering using 54 oz/in servos on a Giant Scale P-51 ...that should send bells and alarms ringing to a lot of modelers.

What P-51 is it? That tid-bit of information wouold better help us help you.

Please do not us JR DS811 servos in a giant scale warbird. 54oz/in servos will not work on ANY flight surface. Throttle, choke, retract valve, yes, but not on the ailerons, elevators or rudder. Please check the torque requirements as indicated in the build manual for the airplane. You may be able to get away with the DS821's on ailerons, go with something 120 oz/in or better on elevator and 250+ oz/in on rudder.

Spend the money on quality servos unless you want a quality trash bag full of quality airplane.

Seriously, stronger and faster servos will be much cheeper in the long run than a crashed airplane.

The plane is a giant scale p-51d mustang 150 hanger 9 and my skills are newbie for sure, I have never flown planes before just helicopters but I’m not planning on bearing this bird in the dirt just building it, getting a trainer plane in the mean time, also I have a flight simulator. The servos that the bird recommends in the manual are the ds811 which are now discontinued. They may be discontinued because there working to hard in those big crafts like you say and been having complaints on them. I don’t want to cheap out on this but don’t want to waste money where it isn’t needed like over killing things that don’t need to be. I am new to RCuniverse but planning on being around a long time so my posts should improve.
I am considering using the ds821’s that I already have in the bird would any of you or would that be cheeping out? Thanks for any and all help.

Do a search on that plane I am sure there are many posts with lots of good info on what works well with that plane.

Servos, I like to always get the biggest and best I can afford these days.
People seem to forget that just A couple of years ago, about 8 years ago, A 50oz/in servo was a big one. On big giant war birds and stunt planes we had to gang them together but these were big IMAA and IMAC planes. Today everyone is stuck on the big digital servo must have thinking. It just isn't so. Go by the weight of the plane and how you plan on flying it. There are some good sites with charts showing the type and weight of A plane and the servos required to fly it.
Today I installed some JR 8411 digital servos with 155 oz/in {4.8V} in A very old 60 size Bridi Kaos. I have flown this plane with servos from 48 oz/in and bigger for years. Why the big ones?? Just for fun, I just happened to have them and not being used for anything at the moment.
Pick the servos needed for the plane then if you have the money buy even better ones, they will be with you for years and have A lot of different uses over time.

thanks again guys