Rabe Rave

[TomLaw]

Generic Model

[Trostle]

This curve is perhaps based on a design by Rabe that shows the location of the pushrod activating the rudder and the specific locations of the horns/pivot points for that pushrod.  There are vertually any number of horn pushrod configurations using the Rabe approach to give any number of rudder reactins for given elevator deflections.  The problem that some people have had with the Rabe rudder is that excessive rudder deflections have been used for both the up elevator (as shown giving more right rudder - which is not always what Rabe has advocated) and down elevator (as shown giving even more right rudder).

For "normal elevator deflections", even during square maneuvers which may not exceed 25 degrees,  your curve is showing not that much difference in rudder reaction between the inside and outside turns, more right rudder in both cases, but more right rudder on outsides, which may be a good way to trim a specific model.  However, some of Al's published plans do not show linkages that can give this kind of probably better rudder response to elevator position.

Before I go on with this discussion, I want to emphasize that I am a strong advocate of the moving rudder that Al Rabe pioneered the way for us.  I will never build a stunt ship for Open competition without a "Rabe" type moving rudder.  (Al and I have been friends ever since we first met at the 68 Olathe Nats.  That Nats is another story.)

The point I want to make here is that it is possible to find positions for the horns and the pushrod to impart rudder deflections similar to the curve shown.  I will suggest that the movement shown on the curve is far superior (probably in most cases) than a system where more neutral rudder or even some left rudder is imparted on inside maneuvers as Al has sometimes outlined in his written material.  What is important is to install a system that will give some degree of flexibility to adjust the amount of rudder travel for given elevator deflections.  This can be done to some degree by having alternate locations for the rudder pushrod to connect to the elevators and different locations, angles and lengths of the rudder horn.

[TomLaw]

I agree. I am already working on a more realistic model including non-intersecting elevator and rudder hinge lines. I just got excited when I saw the graph.
In fact, I have already decided that the graph is backwards according to Rabe's Snaggletooth article.

[Brett Buck]

What is important is to install a system that will give some degree of flexibility to adjust the amount of rudder travel for given elevator deflections.  This can be done to some degree by having alternate locations for the rudder pushrod to connect to the elevators and different locations, angles and lengths of the rudder horn.

   Your system is the best, it's almost unlimited in the ability to get what you need. And apparently you are one of the few people in the world able to figure out what is needed, it works great on the Bearcat.


    Brett

[Trostle]

I agree. I am already working on a more realistic model including non-intersecting elevator and rudder hinge lines. I just got excited when I saw the graph.
In fact, I have already decided that the graph is backwards according to Rabe's Snaggletooth article.

Then, what is the basis for that graph?  What part do you think is backwards?  The plot certainly does not follow the rudder movement that Rabe advocates for inside maneuvers, but in my opinion is an approach towards a better way to go.  And I am not the only one who has determied that a bit more right rudder is desirable even in inside maneuvers, totally opposite of what Rabe explains for his system.

And what do you mean about "non-intersecting elevator and rudder hinge lines".  What are "non-intersecting hinge lines" and what are their differences with "intersecting hinge line"?

Keith

[Trostle]

   Your system is the best, it's almost unlimited in the ability to get what you need. And apparently you are one of the few people in the world able to figure out what is needed, it works great on the Bearcat.


    Brett

Brett,

Thanks for the comment.  As I mentioned earlier, I have talked with others who have experimented with different rudder responses different than what Rabe advocates.  Several have been able to do this with a carefull relocation of where the rudder pushrod attaches to the elevators and still use the external rudder pushrod.  Ron Burn (who certainly does not need an introduction on these forums) uses a system similar to mine that takes input directly from the elevator pushrod to actuate the rudder, but I do not think he uses the sliding/slotted cam approach that I use.  His approach, like mine, keeps everyting inside the fuselage with no external horns or pushrods.  Ron does use a movable rudder in all of his outstanding super semi-scale models including his latest (I think it his latest) Zero (third model in the lineup below).

I am not sure, but I think the rudder motion that Rabe advocates suits his models partly because of the way he trims the models for flight.  I will not go into any more detail than that for this thread.  I certainly do not want to sound like I am critical of what he finds what works best for him, because obviously, it does work for him.  And he certanly desrves credit for coming up with his totally original idea to counter gyroscopic precession in these CLPA models of ours.

Keith

[Brett Buck]

And what do you mean about "non-intersecting elevator and rudder hinge lines".  What are "non-intersecting hinge lines" and what are their differences with "intersecting hinge line"?

    I presume that he means that the elevator hinge line and rudder hinge line are not even with each other, i.e. the rudder is aft of the elevator like most of them are. A drawing would certainly help.

    Brett

[TomLaw]

First let me say that I am not offering my graph as any kind of ideal. It is simply minimal evidence that my program is working. There are indeed an infinite number of outcomes. By non-intersecting hinge lines I meant that the  rudder and elevator hinge lines are not the same distance from the bellcrank. By backwards I meant that in Rabe's article, he suggested twice as much rudder deflection on max down as up.

[Trostle]

(Clip)

 in Rabe's article, he suggested twice as much rudder deflection on max down as up.

And what I am saying is that deflection may work best for Al and the way he trims his ships.  Others may and have found more desirable deflection schemes.

[TomLaw]

Back to the drawing board.

[Brett Buck]

And what I am saying is that deflection may work best for Al and the way he trims his ships.  Others may and have found more desirable deflection schemes.

     And of course if the only thing you were fixing was the precession, it would require the rudder to move in either direction. What Al seemed to have missed (or at least had downplayed in several of the discussions I had with him) is how the leadout position would affect the desired rudder motion.

   Unfortunately, what nearly everyone else seems to have a problem with is the adjustment of it. First, they fixate on the rudder as the cause of/solution to every trim issue they have (just like newbie pipe users fixate on the pipe length), and second, they seem utterly incapable of seeing or feeling the effects of the adjustments and thus wind up with it *grossly* maladjusted, usually with an order of magnitude to much movement. Numerous examples abound, even at the NATs at the highest levels. Most people would appear to be far better off just gluing the rudder on straight ahead, than what they end up with after adjusting it.

    Brett

[TomLaw]

Last one:

Here is the equation I am plotting. It is entirely general. If I couple it to my previous L-O/Bell/Flap/Elev program, it will include all. I am not proving anything here, just sayin'.

(rE'rR'Cosχ)Cosη - (y'rR')Sinη = rE'rR'Cosλ0Cosβ0 - y'rR'Sinλ0 - z'rE'Sinβ0 + z'rE'Sinχ

[EddyR]

The one thing that has not been mentioned here is the height of the rudder. On a normal sized PA stunt ship the moving rudder effect is quite small  compaired to the huge tall rudder on the Bearcat. When that tall rudder moves it has a very big effect on the plane. It is like a aileron rolling the plane counter clockwise. Mine works perfect on outside turns but once in a white it does "something" on hard insides. I am not sure what the something is but I felt it and I don't like it. I think there is a very fast snap roll in but it corrects so fast I haven't seen it. Last corner of the triangle    60+++++ ounces 13/5 prop
Ed

[Trostle]

(Clip)

 On a normal sized PA stunt ship the moving rudder effect is quite small  compaired to the huge tall rudder on the Bearcat.

(Clip)

Ed

You are finding something similar to what I found on my Rabe Bearcat.  As on all of my stunt ships, I emply a moving rudder inspired by the Rabe idea.  However, on my Bearcat with that tall rudder, all well above the centerline, I had to completely change my thinking abut the amount of travel that rudder should have.  When I first started flying this thing, I would sometimes see parts of the airplane that I did not want to see when it was going through the pattern, particularly in the intersections of the eights and even more so the overheads.  With all that rudder, it was yawing left and rollling right.  Not pretty nor very comfortable.  I still use a moving rudder, but the throw is probably reduced to no more than 1/8" to 3/16" right rudder on full down, and probably about 1/16" more right rudder on full up.  The thing has a very nice clean turn.  It is quite comfortable with the overheads, particularly the outside turns at the top of the hourglass.

Keith

[EddyR]

Keith   I have mine set up like yours. I took your advice on setting it up. I have less through than you do. Maybe 1/8" on full down and less on full up. I am not sure what it is doing. I feel that snap as when a plane is going to chase you across the field but it is over so quick I am missing what the plane is doing. It has happened four times in 18 flights. The plane goes through the pattern easily. I have been working up to the hard maneuvers slowly. Not hard for me hard for the plane.Overheads and four leaf clovers not a problem. I am not seeing any roll yawing. When a plane is new it is hard to watch it everwhere. On conventional planes I know what to look for. I do not know if the plane is rolling  in, inboard wing dropping or turning in ,nose pointing in. I need to fly it just watching for the problem. I have not had anyone who knows what to look for watch the plane. At my field they do not know much about trimming. I may need to take a trip to south Georgia and have Derek or his dad watch it fly.
Thanks again Ed

[Trostle]

Ed,

I canot help very much.  Out here, we get to fly with some of the best who can watch an airplane fly and give some suggestions on how to improve the thing.  I am sort of spoiled with being able to share a flying field with at least one of those golden arms.  However, I could suggest that you play around with leadout positions and tip weights, but you probably already know that and are doing so.

It took me more than a year to get my Bearcat to where it became a lot of fun and easy to fly.  After you get some more time with yours, I am interested in how you feel about the Rabe rudder.  I know many top fliers have tried it and have concluded that they do not need it.  Indeed, there are outstanding pilots/airplanes that do not use it.  My feeling is that there are no negative aspects to using it and that it can only help.  (And no, I do not consider the added complexity, regardless of the system, nor the added weight to be negatives given the dividend of the system.)

I am able to essentially disengage my movable rudder and fly it in a fixed position..  I have done this several times over the years when the airplane has been in various stages of trim.  After I got the movement down to what I have described, I can say that, at least for me, the rudder is a definite asset for this airplane.

By the way, your machine really looks good.  Congratulations on a job well done.

Keith

[Air Ministry .]

With a Low Wing , Diheadraled Semi Scale A/C , you can notice the moveable rudders Not There ,
at the top inner outside square eight turn , and in 20 knot winds , into the Clover Leaf , and the
top of the Hour Glass . When the wind gets under the tail and blows it out . Therefore the nose in ,
and the plane disapears over your shoulder upwind , lines slack , and moveing hard .

[EddyR]

This is a old thread but I did get rid of the roll. I have the rudder movement down to almost nothing. The rudder was causing the roll.
I had endless motor problems and gave up flying it so I have put a different motor in the Bearcat and will fly it soon.
Ed
Matt  I guess that would be a scale crash

[Air Ministry .]

Very Nearly . 

I used to walk to the field , so was limbered up , and could run really fast . 

Glad to here its sorted . Nitros good for tourque , if not the finish .

Been inclined to do another , The G 51 sounded a bit odd on the 10 x 4 three blade ,
so I picked up a G 40 Ringed . Should do the trick . I miss the terror . Comparison was
a Dodge 440 on oil with the throttle stuck doing a precission driveing test .

Keeps you focused . 

[Brett Buck]

This is a old thread but I did get rid of the roll. I have the rudder movement down to almost nothing. The rudder was causing the roll.

  That's certainly what I have seen, most people have WAY too much movement and it causes more issues than it solves. If all you are doing it compensating for precession, it seems to work but it takes very little movement.

    Brett

[Lauri Malila]

Hi.

Would it be possible to have more details, pictures perhaps, of this K. Trostle system?
I' just pondering what to do with my new model, I could certainly benefit from  rabe rudder as our engine likes big props.
 I'm also considering a servo operated Rabe rudder, either with gyro or a hall sensor at bellcrank. That would be cool.

Lauri

[Tim Wescott]

I'm also considering a servo operated Rabe rudder, either with gyro or a hall sensor at bellcrank. That would be cool.

My knee-jerk reaction to that statement is that I feel that on a PA ship none of the flying surfaces should be electronically actuated -- if you can't do it mechanically, you shouldn't do it.

That's a totally irrational bias, particularly given that I have no problem with the idea of electronic control of motor (or engine) speed.  But since we're getting judged on controlling the airplane's direction of flight, I just feel that we shouldn't allow even the smallest part of that to be taken over by electronics (once again, and totally irrationally, barring motor or even whole-plane speed control).

[Igor Burger]

I tried it ... may be some 10 years ago, I posted this picture already several times, worked perfectly (much better then mechanic linkage) but
1/ in on edge of actual FAI rules (means can start long speach if it is legal or not)
2/ I think we should not include anything else then mechanic in controlls

[Lauri Malila]

I think, maybe Peter Germann can confirm it, that it is OK according to the current rules. If it's OK for rules, it's OK for me.
Apart from movement simultaneous to elevator movement one could get much more joy from the system, like quick change from one trim to another, caused by a differend prop or weather for example. Or, perhaps a rudder kick in corner and a delayed return to neutral position, as per plane acceleration.
I allready have possibility to stop the engine with radio, that's cool too! I feel like a child in a candy store.
But still, any more details of the K. Trostle's mechanism? If my ideas don't become reality I can without doubt make a mechanical setup work somehow. L

[Brett Buck]

I think, maybe Peter Germann can confirm it, that it is OK according to the current rules. If it's OK for rules, it's OK for me.
Apart from movement simultaneous to elevator movement one could get much more joy from the system, like quick change from one trim to another, caused by a differend prop or weather for example. Or, perhaps a rudder kick in corner and a delayed return to neutral position, as per plane acceleration.
I allready have possibility to stop the engine with radio, that's cool too! I feel like a child in a candy store.
But still, any more details of the K. Trostle's mechanism? If my ideas don't become reality I can without doubt make a mechanical setup work somehow. L

  Keith wrote an article on his system in SN; unfortunately, I don't know which issue (about 10 years ago).

   Brett

[Howard Rush]

I think we should not include anything else then mechanic in controlls

You'd best pay attention to Igor's advice.  Igor can see where electronic flight controls can lead, and you (except maybe one or two) cannot. 

Keith's rudder system is one of the cleverest things I've seen in stunt. 

[Trostle]

Hi.

Would it be possible to have more details, pictures perhaps, of this K. Trostle system?

Lauri

The article on my variation of the Rabe Rudder theme was in Stunt News, March/April 2008.  It has drawings, pictures and a description of the system.

I have not been able to compress the scan of that article to get it attached here.

Keith

[Igor Burger]

I think, maybe Peter Germann can confirm it, that it is OK according to the current rules. If it's OK for rules, it's OK for me.

Rules say something about "path" so probably you are right, yes, it is OK, but may be only by mistake  ... but I can imagine arguing about it and I am sure someone can bring valid arguments that it is not OK  so it is on edge of rules at best

well ... I have working solution, tested, I thing better then mechanic solution, but I also know that I am not going be first having servo on controll surface on official plane, because I simply like "mechanic" definition of controlling

[Lauri Malila]

Of course you are right, Igor. I can see very similar discussion coming than when electrics came in free flight models. They very soon banned the "closed loop" control systems, which is good. But still, I think that rules are badly written if there is a contradiction with "spirit of rules" and the written rules. Also, I feel that nothing ever changes in Stunt, it would be nice to see some new things being used. I don't feel that it will kill the sport, actually quite opposite. One can say that the new technology (availability of ready made models & components, electrics, carbon construction stuff) has saved the Free Flight categories from extinction and same is happening now thanks to electric motors and also Yatsenkos; a huge improvement in flying quality of sportsmen who used to be stuck as mid-level flyers.
Anyway, Keith kindly sent me details of his rudder system and I like the idea a lot. But I still like the idea of a servo rudder, if not in contest use, as a trimming tool. Just to find out the parameters to be duplicated in the mechanical system. L