Movable Rudder on Twin Tail

[Ken Culbertson]

I am in the process of adding a CAM rudder to a twin tail.  As I was starting on installing the mechanism into the second stab it occurred to me that I may not need it.  Does rudder offset on a twin need to be on both rudders?

Ken

[Trostle]

I am in the process of adding a CAM rudder to a twin tail.  As I was starting on installing the mechanism into the second stab it occurred to me that I may not need it.  Does rudder offset on a twin need to be on both rudders?

Ken

I would think not.  I would make the outboard rudder be the one that moves.  (Changes in outbaord drag as the rudder moves, even in small amounts, would be more desirable with the outboard moving rudder than if you just moved the inboard rudder.)  You will still have to go through the process of finding the best program for rudder travel relative to elevator position.  Moving just the one rudder may require a bit more travel to achieve the desired results (line tension for inside and outside turns) than if both rudders were programmed to move.  Save the extra weight that the extra linkage would require.

An alternative would be to consider if there is a bit of fuselage beneath/behind the horizontal tail.  Fix both rudders and make a small rudder from that fuselage "underhang".  The height of that "underhang" rudder will probably not be very tall.  Suggest you look at Igor's rudder that he has employed which is fairly small and is a very low aspect ratio affair that needs more travel  for insides and outsides than a more "conventional" rudder design.

Waiting for incoming.

Keith

[Howard Rush]

You should probably do what Keith says.  I'd tend to put the stuff on the inside rudder so's to skew the principal inertial axis clockwise a tad, but I can't defend that. 

[Ken Culbertson]

You should probably do what Keith says.  I'd tend to put the stuff on the inside rudder so's to skew the principal inertial axis clockwise a tad, but I can't defend that.

Amazing the trouble you can get into when you can't fly and have to build in a corner of your office.  The amazing thing is that this gadget works (on the ground anyway).

Ken

[Air Ministry .]

With fixed rudder / fins , youd want the inboard straight & the outer offset to turn right . If you wanted safe ' outer engine ' handling .
Used flat outer , just biased a noth , airfoiled fins on the P - 38 .

Seems a wide engine spacing , to get clear air with the propwash , works good . Close motor spacing seems to have a chance of the prop slipstream
maybe causeing turbulance / interfearance drag , if the prop tips are close to the fuse. Maybe .

Smooth air & running well , most'll do round manouvers below 45 Deg. , & wingovers , on the OUTER only . But any real wind the YAW can get out of hand .

So maybe the rudders a Good Idea . Not overly long lines , initially at least , unless its calm weather .

Al, on about his Hornet , wanted the counter rotateing set up , so as not to need a moving rudder , so He said , of the ' design concept ' .

Ancient Aeromodellor Me 110 Scale Drawings , they prattled on about assymetric fin/rudder airfoils , on that . If youve one handy .

[Scott Richlen]

What's the difference between a CAM rudder and a Rabe Rudder?

[Steve Berry]

What's the difference between a CAM rudder and a Rabe Rudder?

That's what I was wondering.

[Ken Culbertson]

That's what I was wondering.

The CAM rudder which is an improvement over the Rabe allows infinate non linear adjustment of the rudder in both directions.  Keith Trostle, as far as I know, invented it. 

Ken

[Scott Richlen]

ken:

I just did a search of the forum for "CAM rudder" and found a lot of written comments about it, but no actual description of it.  I have used the Rabe rudder to good advantage but have no idea of how to build a CAM rudder.  Are there descriptions and drawings someplace?

[Dan McEntee]

Try adding Keith Trostle to your search words. He has posted pictures of the components required in recent threads. Might have even been related to his new MB-5 stunt model.
   Type at you later,
  Dan McEntee

[Ken Culbertson]

ken:

I just did a search of the forum for "CAM rudder" and found a lot of written comments about it, but no actual description of it.  I have used the Rabe rudder to good advantage but have no idea of how to build a CAM rudder.  Are there descriptions and drawings someplace?

Here is a link to a short video that I did a couple of years ago while building my Endgame design.  It shows the CAM in action.
but doesn't do much for the overall design.  Notice that the rudder does not move much.  Once your permanent offset for level flight is set the CAM gives you additional for both inside and outside.  By varying the shape of the CAM you can determine how much you get in both directions and how soon it kicks in.  The plane flew with this cam and the results were excellent.  The major change that has me using it is not the one Al designed the Rabe Rudder for.  I use it to add a small amount of additional line tension in maneuvers.  It was set to give me an 1/8" extra rudder in both inside and outside rounds increasing to about 1/4" on outside corners.  If you use a CCW prop it is easy to switch that extra to the inside.



Sorry that I don't have the sketches.  Lost all of that and Keith's article on the cam in a fire.  I will post a picture of the profile one I cooked up as soon as I get finished building the "production" version.  A word of caution if you try this.  The mechanism places zero load on the control system and the force needed to move the rudder is very small due to the length of the tiller.  It doesn't have to be heavy or made from exotic materials and a little slop is OK, it just can't bind.  I have made CAMS from thin plywood Bass and tongue depressors. They all worked fine.

Ken

PS - Seems when you post a link to YouTube you get the whole channel.  The patterns that show up were shot just after I came back from a 30 year layoff.  Sort of embarrassing but without video proof of how bad you are you can't fix things!  Great tool for trimming too if you shoot it from 90 degrees off center.  Plane shows you all of it's bad stuff that you don't see from the center.  Again, sorry, I had not intended to post these.

Ken

[Air Ministry .]

Actually , with Two Rudders , with the Rabe set up , you could do a seperate linkage for each rudder .
As theres at least three variables ( Linkage Offsets & rod length plus stagger from hinge )  you could
set each side differant , With so many variables you could keep playing around with it forever . 

Though wouldnt it be easier to just do the external linkage , and have ione on each rudder ?
One would assume twice the movement on the outer side , perhaps .

[Tim Wescott]

What Keith said.  The Sonex Waiex is a home-built that Sonex calls a "Y tail", because rudder control is effected by moving the "V" tail part as well as a small rudder under the tail.

So there's even a full-scale inspiration for it...

[Scott Richlen]

Okay, found it.

For anyone else looking, try these two:

https://stunthanger.com/smf/stunt-design/rabe-rudder/msg501770/#msg501770  reply 25

https://stunthanger.com/smf/at-the-handle/rabe-rudder-on-'pusher'-props/msg563403/#msg563403