RABE RUDDER ON A FANCHERIZED TWISTER

[Phil Coopy]

I've been having inboard yaw tendencies on my outside squares when flying my Fancherized Twister, so I thought I would take a lesson from Al Rabe and try out his rudder concept.  The rudder hinge line on the Twister being pretty close to the elevator hinge line required a bit of shade tree engineering, so the attached pic is what I came up with.  I flew it this morning in dead calm (where the problem was worse) and what a difference it made. Yaw tendencies are completely gone.  I used the same rudder offsets he described in his article and they worked perfectly.  Thanks Al.

Phil

[Paul Taylor]

WOW Phil,
Very Kewl. I wish my Twister could to do outsides squares. Oh, maybe it can, but the guy on the other end has problems with outsides.

How about showing off the whole plane?


Paul

[Bill Adair]

Hi Phil,

Neat installation! 

Showing my ignorance here, but it looks like your setup produces more rudder offset for outsides, and less for insides.

Seems I've read that the Twister flys well with no rudder offset, so is your rudder set up for neutral during insides, or....?

Guess I'll have to do a search for that Al Rabe article, just in case I ever build my ten year old Twister kit. 

Bill

[steven yampolsky]

I don't mean to imply anything, but FTwisters don't generally need a rabe rudder for two reasons:

• Typical prop on a model of this size is 10.5". Yaw tendencies are directly proportional to prop swept area. 10.5" prop has too small of an area to generate any significant yaw tendencies. A 10.5" prop has 1/6 area of a 13" prop. Al's models generally use large diameter props and therefore Rabe rudder is an ingenuous answer to the 6x more yaw.
  
• Ted gave the model enough side area behind the CG to offset any yaw tendencies.

I have had the same soft on the outside problem with my models as well. In one case, stab's trailing edge was not parallel to the wing's trailing edge. This misalignment effectively turned elevators into rudders. In another case, tank was not shimmed properly. Even though the model flew at the same speed level and inverted, it had different speeds in inside vs. outside sections of horizontal 8.

Point I am trying to make is that this model does not need Rabe Rudder. Something else if off here. 

[Leo Mehl]

Great way to use your tail wieghts!

[Bob Reeves]

Now why didn't I think of that when I was trying to come up with a way to put a Rabe rudder on my Nollearf. Very good and think I will steal the idea.

As far as the Twister needing a Rabe Rudder, my TwistMaster sure could use one but no way to do it. It has served me well and is straight but I had to learn to fly soft corners or it wiggles it's tail all over the sky.

[Mark Scarborough]

At the risk of oversimplification, I think every airplane would not be hurt by having a RAbe rudder. However in specific the ratio of prop to size of plane is probably more a relevant set of parameters than simply stating the prop is to small to need compensation. Your going to give the poor 11.5 and 12 inch props a complex about being to small if you arent carefull

[Alan Hahn]

The gyroscopic effect is a function of prop diameter (goes as the square of radius), the blade area, the mass, and rpm, the last 3 being linear. For those of you who remember your freshman physics  , this is just the angular momentum of the propeller, which goes as I*w, I=moment of inertia and w= angular frequency.

So a small prop running at high rpm could generate as much of a wiggle as a larger prop at lower rpm (depending on the actual values of mass, rpm, and things like number of blades).

So yes, large heavy blades usually do end up having more gyroscopic problems, but you could still experience problems with a smaller prop if it is turning fast and is relatively heavy. So like everything, it depends...

[Bradley Walker]

A RABE rudder

on a

FANCHER plane?

Watch out, the rudder might get insulted and separate from the rest of the plane...

[Larry Cunningham]

I built about 9 Twisters in during the late 1980s. Two things I will mention:

1) The (stock) Twister will easily do the entire pattern, including outside squares.

2) The only mod needed for the stock rudder is to build it flat, the plans show an
excessive offset. I don't feel a wiggling rudder is required at all. The model flies quite
with WITHOUT a rudder at all (try it).

The stock Twister with a Fox .35 is a bit skittish, and the additional weight of an OS .40
FP-S tends to make it smoother and easier to fly, as well as improve line tension.

L.

"The rule is perfect: in all matters of opinion are adversaries are insane." -Mark Twain

[Phil Coopy]

Brad, I'm all for integration....

Phil

[Bob Reeves]

<snip>
The stock Twister with a Fox .35 is a bit skittish, and the additional weight of an OS .40
FP-S tends to make it smoother and easier to fly, as well as improve line tension.

L.

Or a 10 1/2 ounce 4 stroke swinging an 11 inch prop 

[Trostle]

(clip)

• Typical prop on a model of this size is 10.5". Yaw tendencies are directly proportional to prop swept area. 10.5" prop has too small of an area to generate any significant yaw tendencies. A 10.5" prop has 1/6 area of a 13" prop. Al's models generally use large diameter props and therefore Rabe rudder is an ingenuous answer to the 6x more yaw.
  

Point I am trying to make is that this model does not need Rabe Rudder. Something else if off here. 

Steve,  I am not sure what you base your calculations on but there is hardly the 6x difference in area between a 10.5 inch Prop and a 13 inch prop.  The 13 inch prop has only about 53% more area than a 10.5 inch prop.  Your 600% is a far reach, like more than an order of magnitude, from the actual 53% difference.

Many will argue that a Rabe rudder is not necessary on any airplane, and on a Twister in particular.  One thing that can be said is that properly installed, a Rabe rudder cannot hurt the performance of our stunt models.  In this case, by the report of Phil Coopy, it helped correct a problem, whatever that problem was.  And besides, Phil employed a rather elegant method to incorporate the movable rudder.  Thanks for sharing.

Keith Trostle

(edit for typo correction)
(second edit for dumb mistake on names - apologies to Phil Coopy)

[Trostle]

Hi Phil,

Neat installation! 

Showing my ignorance here, but it looks like your setup produces more rudder offset for outsides, and less for insides.

(clip)

Bill

It appears that Phil understands the ideas that Al Rabe has behind his movable rudder.  The idea is to have more right rudder on outside maneuvers while less rudder offset is needed for the insides to offset the differences in gyroscopic precession.  As stated elsewhere, a properly installed Rabe rudder concept with the correct differential movements between inside and outside maneuvers cannot hurt the performance of a stunt ship.  (Others may argue that a properly designed/properly trimmed stunt ship does not need a Rabe rudder thing, and there have certainly been successfull airplanes without it.  If the correct differentials or if the correct movements are not incorporated, the Rabe rudder can cause more problems than it helps.  On the other hand, a Rabe rudder that is properly installed and adjusted cannot hurt.)

Phil Coopy came up with a really neat way to incorporate the idea.

Keith Trostle

(edit for dumb typo's  - sorry Phil C.)

[Ted Fancher]

A RABE rudder

on a

FANCHER plane?

Watch out, the rudder might get insulted and separate from the rest of the plane...

Oh, oh, Brad.  I wasn't going to go there! I am, however, a big fan of "whatever works".  Glad it helped make his plane fly better.
Ted

[Phil Coopy]

I've have two identical Fancherized Twisters and they both display that same yaw characteristic.  I'm using an LA40 with 11.5 x 4 or 11 x 5 prop (depending on the wind) on both.  I like the low pitch 'cause I like to fly slow, which I suppose, also makes the plane more sensitive to precession. My shade tree, Rabe rudder Rube Goldberg arrangement corrected the first one, so I'm gonna try iton the second one.  Easy for me to do because I have hinged rudders on both anyway.  Bottom line for me is that the Rabe rudder feels a lot better.

PHIL Coopy 

[steven yampolsky]

Steve,  I am not sure what you base your calculations on but there is hardly the 6x difference in area between a 10.5 inch Prop and a 13 inch prop.  The 13 inch prop has only about 53% more area than a 10.5 inch prop.  Your 600% is a far reach, like more than an order of magnitude, from the actual 53% difference.

You are correct Keith, I went back and plugged the numbers again.
Area = Pi*R².
10.5" prop area  = 3.141592*5.25² = 86sq. in.
13" prop area = 3.141592*6.5 = 132sq in.

Which is exactly that: 53% more. Now I am not sure how I got the 6x number... Late nights at work and lack of sleep play tricks on my.

Many will argue that a Rabe rudder is not necessary on any airplane, and on a Twister in particular.  One thing that can be said is that properly installed, a Rabe rudder cannot hurt the performance of our stunt models.  In this case, by the report of Phil Coopy, it helped correct a problem, whatever that problem was.  And besides, Phil employed a rather elegant method to incorporate the movable rudder.  Thanks for sharing.

I agree that adding Rabe rudder will not hurt performance if setup properly. I also like the way Phil implemented it. But I am still of the opinion that a LA40 swinging 11.5" wood zinger Pro running in rich 2-cycle is not enough weight or diameter to generate any adverse yaw on the Fancherized twister. The fuse side area behind the CG plus hefty rudder size on that design is plenty. I flew Fancherized Twister with 40FP swinging 10.5" APC and have not had any trouble with yawing on outside maneuvers.

Besides, it doesn't hurt anything to check the alignment...

[steven yampolsky]

"whatever works"

Good point

[Larry Cunningham]

Phil,

Your Twisters are entirely too attractive!

I believe nearly all classic CL stunters can benefit from longer tail moments.

L.

"It were not best that we should all think alike; it is the difference of opinion that makes
horseraces." -Mark Twain

[Bradley Walker]

Oh, oh, Brad.  I wasn't going to go there! I am, however, a big fan of "whatever works".  Glad it helped make his plane fly better.
Ted

I just thought it was funny...  I got a chuckle out of it!!!

Maybe next someone can build a Bearcat and paint it metallic purple!!!

[Doug Moon]

I just thought it was funny...  I got a chuckle out of it!!!

I thought it was funny too.  Just good fun. 

[Shultzie]

"HOW MUCH IS THAT STUNT DOGGY IN THE WINDOW..THE ONE WITH THE WAGGLEEE TAIL?  WHERE IS OUR BELOVED SCHOOL OF RABE!  MAYBE IT'S TIME FOR YOU TO JUMP IN ON THIS CONVERSATION AGAIN?

[john e. holliday]

Hey Phil glad to hear it works for you.  When I built my F-Twisters I couldn't tell if they were flying correctly or not.  I know that I have not had a plane that flew as good as the Mustunt I built according to Al's article and set the rudder up to his specs.  Just didn't have the time to get out and practice that much back then.  By the way, the planes look great.  Have fun,  DOC Holliday

[Bradley Walker]

Are those white patent leather loafers?

Dang, he be pimpin!!!

[Shultzie]

I'm not sure.....but I think it might have been our friend Al Rabe that borrowed those purty white shiney loafers  from inside my closet when he used to visit us NWsters. It was always a pleasure to have Al visit us NWsters' on his Lay-over flights during the years he was a Captain with Braniff Airlines. I lived only a short distance from SEA-TAC and would arrange hanger-trash talkin' sessions at my small apartment hanger pad.

Living near SeaTac airport in those day...I do remember how those  shiney white leathers shoes of mine used to really dazzel and glow under those dance floor lightings at that topless disco-dive  called "MY PLACE" next door to the Braniff Airlines hanger.  I can't remember if I ever invited Al to join us at that place or not....but those white shoes really helped your feet fly...where few mere mortals dared to fly n' allthatjazz.

Actually those white shiney shoes might have belonged to either Tim Dunlop, Bob Parker, Joe Dill, Ted Fancher, or Paul Walker.

However they do look very much like the ones I used to fly in contests with. Shiney white leather doesn't stain with castor as easily as my old White Bucks or tennie' shoes seem to do. Which leads to one burning question??

OK! WHO OWNS UP TO BE THE FIRST STUNT GRUNTER TO WEAR ALL WHITE? I know we used to razzz
 Bob Gialdini who was the first ICON CLPAster' that wore all white.We used to yell at him...."HEY NURSE!!...CAN U BRING ME SOME SUN TAN LOTION OR A BEDPAN!" (or whatever we needed.

 Anyone who has either judged stunt or worked as a contest director knows just how little time one has to go get a drink of water...or use the bathrooms during contests.
 Jim VanLoo used to razz all of us...when we showed up "wearing our NAVY WHITES" and in those days....folks would do anything that might help influence that NAVY staff of judges.

Did it pay off...NAW! I HIGHLY DOUBT IT?
Here is a shot of the lateTim Dunlop who really influnced all of us to wear white here in the NW! Tim and I really enjoyed having our Al Rabe drop in for a visit. Time flies...huh?

[Circlejerk]

Good reference for understanding GP   http://geocities.com/CapeCanaveral/Galaxy/4707/Aeronotes/GYROWEB.htm

[Bradley Walker]

Actually those white shiney shoes might have belonged to either Tim Dunlop, Bob Parker, Joe Dill, Ted Fancher, or Paul Walker.

My new pit crew signaling the judges for a start.

[Dennis Adamisin]

Phil C:
So how much rudder movement did you end up using?

[Phil Coopy]

Right now I am adjusted at 1/8" outboard at neutral, 5/8" outboard at full down, and 1/8" inboard at full up.  It feels great with this setup for my level of flying, but I'm sure I'll tune more on it, especially when I get it installed on my second Fancherized Twister.  I'm playing around in the dark here, and just have AL Rabes article from the net to go by, I would guess he has refined things a bit since he wrote it.  But my first experience with is exciting, and I am convinced that I am not compensating for any misalignment that I can find in the plane.  With all that said, I am no expert,  just a retread that got bored with too much RC.

Phil

[john e. holliday]

Phil,  that is one of the things that has kept me going at this model airplane stuff for so long.  There are so many things to try and do.  Like when I was flying F2C, was told that when I was told something new, try it.  Some times it works and some times it doesn't.  I am glad to hear yours is working.  Have fun,  DOC Holliday

[Phil Coopy]

Doc, I know what you mean...when I was drag racing they used to call it the "hot lick of the month club"...gotta be careful you don't join that gang.

Phil