Anything wrong with this servo?

[Chuck McHugh]

The JR DS821 servo that comes with the Spektrum DX-7 is quite the powerhouse at 72oz of torque and I have used them on a few E conversions of 120 size. I am starting a build of the KMP OV-10 Bronco for E conversion, is there any reason I shouldn't use these servos in this plane? At $19 each they are a good deal if they will work.( the Bronco needs 10 servos) Looking for any input.
Chuck

[sun.flyer]

The JR DS821 servo that comes with the Spektrum DX-7 is quite the powerhouse at 72oz of torque and I have used them on a few E conversions of 120 size. I am starting a build of the KMP OV-10 Bronco for E conversion, is there any reason I shouldn't use these servos in this plane? At $19 each they are a good deal if they will work.( the Bronco needs 10 servos) Looking for any input.
Chuck

What kind of weight do you think you will come in at on the Bronco? I have a know one of our club members is flying an 18lb. GP Stearman with them on 6v and they are do just great.

Tim

[Chuck McHugh]

What kind of weight do you think you will come in at on the Bronco? I have a know one of our club members is flying an 18lb. GP Stearman with them on 6v and they are do just great.

Tim
I am hoping for 20lbs, the ad says 19 and the manual says 25 I am sure it will be lighter than that.
Chuck

[Wufnu]

I seem to remember the general rule for sport flying to be 1 oz-in for each square inch of control surface area the servo would be deflecting. Just pop out the ruler and do some measurements for a general idea of how big a surface the servo has to deflect.

Justin
www.CommonSenseRC.com

[GWRIGHT]

weight of the model doesn't really matter,..it's the size/shape/deflection of the control surface and the speed of the aircraft that all determine torque requirements for the servo. I've never heard of the 1 oz/in per sq in of surface, and I wouldn't agree with it, but at least it's somewhere to start. for example, I have one plane with 108 sq inches of aileron surface (6 in root, 3 inch tip, it's a 3D plane), and I deflect them 65 degrees. Plane is intended for slow flight speeds, but can get up in the 50 range at times. 132 oz/in servos weren't enough for full deflection above 1/4 throttle or so. Now with 192 oz/in they're Ok up to 60%~70% throttle, which is as high as I ever go with speed when hitting full aileron. So, in this example, almost 2 oz per inch isn't quite enough to be optimal. In others, 1/2 oz per sq inch has proven to be more than adequate. They were very low deflection, narrow chord surfaces on faster style planes.

[Chuck McHugh]

Thanks for all the input. My main reason for this post is learn of any problems with the 821 servos themselves. At least I am feeling confident they are strong enough to do the job.
Chuck

[desert_flyer]

I would go with something stronger on the control surfaces on a 18-20lb plane. This might push the price up to $50 per servo, but how much money do you risk losing if the elevator servo(s) strip in flight?