are there benefits?

[James C. Martin]

I remember seeing a large stunt ship with a push rod hooked to the rudder , but did not get any info on it . are the rudders on some of these large stunt ships working with the elevator ? and is there any benefit to this kind of set up?

[Randy Cuberly]

I remember seeing a large stunt ship with a push rod hooked to the rudder , but did not get any info on it . are the rudders on some of these large stunt ships working with the elevator ? and is there any benefit to this kind of set up?

What you most likely saw is a Rabe Rudder.  Named after Al Rabe who either invented the actuation method or at least used it with great success to win a lot of stunt championships with very scale like, very competitive stunt planes.
It is coupled on short control horns to the elevator in an offset manner to allow adjustment and biased control of the rudder as elevator control is given.  It's aim is to overcome the effects of precession that tend to make the airplane yaw in one direction with up elevator and the other with down elevator.  The rudder overcomes the yaw effect if properly adjusted and you hold your mouth just right.
Everyone agrees that they work.  Not everyone agrees that they work well.  They seem to be more effective on some airplanes than others, and can be a real headache to get properly adjusted...hence the mouth holding comment!
You can learn all the details about them here on the forum simply by searching for Rabe Rudder...there are tons of discussions about them.  Some from the Master himself Mr Al Rabe!

Some use adjustable hinged rudders that are simply coupled to a push rod ridgidly fixed to the fuselage, and can be adjusted by means of a screw thread on the pushrod.

Randy Cuberly

[Clint Ormosen]

Keep in mind that there's a notable disadvantage the the Rabe Rudder as well. During outside corners, there will be a distinct "wiggle" of the rear of the model. Outside rounds will not affect it much, but banging an outside corner sure does.

[Doug Moon]

Keep in mind that there's a notable disadvantage the the Rabe Rudder as well. During outside corners, there will be a distinct "wiggle" of the rear of the model. Outside rounds will not affect it much, but banging an outside corner sure does.

If this is the case then there is a good chance the rudder is not adjusted properly per the style/corner that is being flown.  It is very important that the rudder be adjusted so that on the outside corner only the amount of rudder is added to offset the amount yaw created by the outside input .  This can take hours and hours and hours of flying to get it really correct.  And in my experience it is actually a very tiny amount of movement once its all said and done.  Or a larger amount on a very small amount of moveable surface.

It is also noted that the rudder is only to add nose out yaw for outside corners and the rudder should go almost dead straight/no input on inside corners.

When I was running Saito 72/56 on 14" wide blade props I ran my connection point from a horn placed on the bottom of the elevator.  I would move 1/4" back from hinge and then move 1/4" down from the hinge line and make my connection there on the installed horn.  It's tedious for sure but once its working right it can really give you clean corners with minimal to no line oscillation contributing to clean corners and steady tension all the way through. 

[Trostle]

Keep in mind that there's a notable disadvantage the the Rabe Rudder as well. During outside corners, there will be a distinct "wiggle" of the rear of the model. Outside rounds will not affect it much, but banging an outside corner sure does.

The Rabe rudder is NOT a "notable disadvantage" if it is adjusted/trimmed properly.

In fact, the Rabe rudder, properly adjusted, does precisely the opposite.  It removes the adverse yaw encountered when turning outside corners due to gyroscopic precession on models with counter clockwise turning engines.

The problem that some have with the system is that there is too much rudder movement for the given elevator movement.  Is it necessary to have a winning model?  No.   However, properly adjusted, the system can only help throughout the pattern.

Keith

[Kim Doherty]

I will echo what both Doug and Keith have said. I have mine adjusted just like Doug with no movement on insides and "just enough" on outsides to yield a clean corner with good tension. Looked at another way, it takes little time to install and can easily be made neutral so now you have another trim adjustment play with. As a wise man once said, "If you can't make it accurately, make it adjustable!"

Kim.

[Sean McEntee]

Keith, Doug, et al,

     Would you say then that rudder area is a factor--less deflection with a larger rudder (for example Mustangs, McFarlands Akromaster, ect) then on non scale stunters?

[Trostle]

Keith, Doug, et al,

     Would you say then that rudder area is a factor--less deflection with a larger rudder (for example Mustangs, McFarlands Akromaster, ect) then on non scale stunters?

Well, absolutely.

I have a moving rudder on my Rabe Bearcat.  (It has been around for a few years.)  It took awhile to get the rudder throws to work.  That rudder, compared to a "typical" non-semi-scale stunt ship is fairly large and sits will above the fuselage/thrust line.  I originally set it up for the rudder to operate much as I had on some other of my stunt ships (which, by the way, have placed at several Nats).  With all of that area, on the outsides, the airplane would yaw excessively to the right and roll to the left.  In the intersections of the eights, I would see portions of the airplane that one does not want to see when standing in the middle of the circle holding a control handle.  It took numerous flying sessions and numerous variations of the sliding cam I use to program the rudder movement to get what I now consider a really nice flying airplane.  The amount of rudder deflections I use are much smaller than what Al Rabe uses on his models.  His throws work for him.  I think part of the differences in this are a result of his overall trim of his models, but I do not think it necessary to go into that detail here.  The point here is to be prepared to make some significant adjustments to the rudder deflections in order to get the full benefit of the Rabe Rudder concept.  As I have said, as well as others, the Rabe Rudder concept, properly installed and trimmed, cannot hurt the performance, it can only help.  I would never ever consider building a stunt ship for Open competition without a movable rudder.

Keith

[James C. Martin]

thanks for all the advice everyone need to practice more and someday build that large precision ship and try the rudder

[Brett Buck]

Looked at another way, it takes little time to install and can easily be made neutral so now you have another trim adjustment play with.

    That's sometimes a liability, all by itself. What happens in the vast majority of cases is once someone has a movable rudder, they then fixate on it to try to solve every trim problem they find. The result is that nearly no one manages to get it adjusted correctly, in which case it would be better to have left it off.

    Same thing happens with tuned pipes, every engine run problem is suddenly a problem with the pipe length.

    Brett

[Tim Wescott]

Same thing happens with tuned pipes, every engine run problem is suddenly a problem with the pipe length.

That sounds like a good reason to use one, then -- that way you always have an excuse!

[Tim Wescott]

More seriously, if you're smart you'll approach that Rabe Rudder as something to be fiddled with after you get everything else optimized, and then when you tweak it, go back and re-check everything to see if there's not more optimization to be made.

[john e. holliday]

People need to go read Al's articles on the Mustunt series and why he uses the Rabe Rudder.   Then go and read Ted Fanchers articles on the Doctor/Medic on why learning to fly stunt should be kept simple as possible.   I've seen too many newbies get tied up with all the gadgets trying to learn the pattern.   My 1/2 cent opinion.

[Brett Buck]

People need to go read Al's articles on the Mustunt series and why he uses the Rabe Rudder.   Then go and read Ted Fanchers articles on the Doctor/Medic on why learning to fly stunt should be kept simple as possible.   I've seen too many newbies get tied up with all the gadgets trying to learn the pattern.   My 1/2 cent opinion.

   You're right but in this case it's not just newbies. Even most NATs qualifiers can't get it within country mile of right. Windy never managed it, and it was a big factor in his problems once he got to the finals.

   It's a very powerful adjustment but most people would be far better off without it, until they can learn to trim to the optimum without a moveable rudder. I would guess that narrows it down to less than 10 people in the country.

      Brett