what do you usually use for rudder servos?
I will use jr8411 for ailerons and 8611 for elevons...
for the rudders I was wondering if it was required to have over 100oz.in servos...

what do you think?

What will they be going into ? As far as I know you do not need huge torque for rudder servos!

It will really depend on the aircraft. If it is a Euro, 8411 or similar as this is a huge rudder. The torque is really required to stop any flutter that might start if did not get the support right. I have heard of one EURO that ended up with rudder flutter and the model was almost lost. If it is a T33, a smaller servo could work. I would not consider anything less than an 8411(or similar for the Hitec, Multiplex, Futaba, etc fans!!!!!!!) on any flying surface on a turbine jet as this is a small price to pay if you look what the total investment is!

My Kangeroo flys with 4 8411's on the wings!

Zane

Zaney

I thought that the deflections are quite small on jet rudders .... are you saying that the torque is important for hold at neutral to prevent flutter?

I agree fully that the servo cost is quite small when looking at everything else but, I don't see the point of a $80 servo when a $30 is perfect for the job.

I'm not criticising your points - Just interested to know!! I always tend to buy good servos as well but try to avoid over doing it.

I agree that very little rudder torque is required for most jets and you could get away with less. With the Euro, the fin is large and you do not want flutter on this surface as it would cause possible loss of the aircraft. I have also seen flutter on a Rafale rudder which is very similar in shape to the Euro. I have also seen terminal flutter on a very small elevator suface with very short linkages, so I don't know if we appriciate the loads that these aircraft go through. For me, I would err on the side of safety! I as said earlier, if it is a T33 with a very small rudder, you could consider a less powerful servo.

I was hoping that some of the other more experienced jetjocks would pipe up and give thier opinions. Once again, please don't put anything less on a Euro! Mechanical advantage can also be gained from linkages, etc.

Zane

Presuming that you are going to use it in your F-22, there is a neat servo from Futaba : the S3050
that is metal gear, digital, 90 oz/in at 6v and dead cheap. (don´t know if this matters to you) plenty
of torque for a knife edge loop if the airframe is capable of it...

Rgds, Enrique

I will put only JR in my f22...probably 8411 or 8611....

Don't skimp on your rudder servo....put in as large a metal gear as will fit......IMO, the most common surface to flutter is the rudder, followed by the elevator......

Tom

On many occasions thumbs and knees flutters first! LOL

Hpghost, Jr´s 8611 has 220. oz/in at 4.8 V and you will use 2 of this in the rudders.. I also presume that your plane has a 1.4 meter wingspan. this servo is not required there, but if you want to go this way, no problem. It will work anyway.

Rgds, Enrique

Tom, In my opinion (for what its worth) you and all the others who recommend the largest, metal geared digital servo on rudders and in fact all other control surfaces, all of which could possibly flutter are absolutely, 100% dead, right !!! Flutter prevention is absolutely essential on high speed machines and the best protection, apart from accurate mass balancing , is a powerful digital servo with the tightest possible holding torque, and "digitals" beat "analogue" servos hands down in this area . (A slop free linkage is taken as read .)


And that is exactly why I was so critical, in my review of the BobCat, on the original BVM tail servo specification for that machine ! Perhaps those who hassled me for raising that issue might now care to revise their opinions ! Opinions can be changed, the technical truth can't !

Regards,

David Gladwin.

considering the surface area of the 10th scale f22, I was thinking of 1 JR DS8611...260oz.in torque per elevator.
will it be ok or 2 per elevator are required?

One of the reasons you need holding power more so on the rudder is the fact that the rudder is neutrally loaded most of the time. With the ailerons, flaps, and elevators there are aero loads trying to displace the surface under normal fight conditions with the servo resisting that displacement. The rudder however is just trailing in the airstream most of the time and any slop in the linkage, gears, mounting, or deadband will induce flutter well below the flutter speed of the plane. As I am sure all of you know every plane (model and full scale) has a flutter speed above what is usually called out as the VNE by the manufacture.

I live and have learned - thanks

A lot depends on the rudder size, hinging (gaps) and weather or not it is pushrod or pull - pull. A properly engineered surface (rudder, elevator, flap, aeil etc.) is equally important.

Smaller oftern requires less and larger normally requires more. Pull - pull is the most efficent, but is rearly used in todays models.

By the way, for those of you new to the hobby, it wasn't that many years ago that a 100 oz servo was a mosnter.

Some of todays airframe manufacturers do not go through the exhaustive design as testing that should be done prioro to the release of a a new model. Too often maxi servo torque is used to overcome that lack of proper design. In the end problems are often incurred.

I had a BVM Bandit which is a very fast airplane that used pull - pull on the rudder. I employed a Futaba 3002 55oz metal gear servo and worked flawlessely for 400 flights. This is a very well engineered system the didn not require a "maxi" servo. The elevators on the Bandit were equally well engineered. I ran 70oz servos on them and again, never had any problem. I guess it's the old saying; how well is it engineered?!?!

Actually the torque of the servo isn't as important as the gear train. As I was taught many years ago, servo specs usually never reveal anythig about what's inside the servo.

Hope this helps some.

hpghost,

I would advice you to go with VOLZ servos Hands down. I had a large SU-27 that I almost lost last year due to a massive flutter. The jet had JR digitals But Not metal gear. I replaced the servos with the Analog 285 Oz of torque and HOLDING power,we flew the Jet 6 HARD flights and it was rock solid. They cost $96.00 each and you will never have to worry about flutter unless you brake a hinge or something.

The stabs of the SU have 2 8411 on each side due to its massive surface.

Johnny Hernandez

Johnny:

I have a couple of sources for the small Volz Wing-Maxx Servos that I have used in rudders before, but where are you getting your big Volz Servos?

Tom