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Rudder bungees and Highlander tail

PostPosted: Wed Feb 19, 2014 12:48 pm
by Fresnoredneck
Hi all

I don't know if my rudder bungees have past their sell by date but they don't seem to offer much in terms of centering assistance on the rudder, am I asking too much of them? Is there a poundage test that can be done to check them and has anybody made any changes to springs or alike, would appreciate any feedback.

I noticed that the Highlander has what could be described as a spade on the rudder, the section that goes over the fin, what difference does that make to the handling?? does it increase the directional stability??

Rich

Re: Rudder bungees and Highlander tail

PostPosted: Wed Feb 19, 2014 3:07 pm
by moving2time
Rich, I believe you are talking about the part of the rudder that is used to provide a balanced feel to the rudder. Similar balanced surfaces are on the elevator. As you deflect the vertical control surface (rudder) to the left with the rudder pedals the air flow catches on the leading edge of the top of the rudder and the air pressure that develops on that surface assists the movement of the much larger surface of the rudder into the flow of the air. The "balance surface area" on the rudder is located in front of the rudder's hinge point so that the force exerted on that area assists your feet as you push the rudder into the flow of the air creating your left turn. Without the balanced area on the rudder the forces required by your feet to push the rudder into the flow of air would feel much greater. These areas are often weighted with lead to actually balance the control surface at the hinge. The same applies to the elevator and the force that your arm would need to exert on the control stick to move the rudder.

It has been my experience that the rudder cables are usually slack and the pressure you apply to the pedals is used to hold the rudder in place while you are flying. Usually you keep pressure on both pedals at all times while you are flying so I don' think the bungees are intended to do anything but take up the slack. I’m not an expert by any means but I thought it would be fun to try to explain this. Hope I was successful. Joe B

Re: Rudder bungees and Highlander tail

PostPosted: Wed Feb 19, 2014 4:04 pm
by gkremers
Rudder bungees?? Not something I received with a standard Highlander kit.

Re: Rudder bungees and Highlander tail

PostPosted: Wed Feb 19, 2014 5:44 pm
by Fresnoredneck
Hi Joe B and gkremers

On the bungee thing my Escapade has bungees from the rudder pedal to the firewall both sides, I think they were fitted to provide some self centering to the rudder. Flying today and being low time on the type showed up directional stability issues, flying straight and level I dumped in left rudder and took my foot off both pedals and the aircraft made no attempt to return to straight, likewise right rudder and when I throttled up it just got worse, fine if you are skywriting, but not conducive to relaxed flying which is why I asked if the spades increased directional stability.

Rich

Re: Rudder bungees and Highlander tail

PostPosted: Wed Feb 19, 2014 6:16 pm
by SheepdogRD
Fresnoredneck wrote:I don't know if my rudder bungees have past their sell by date ...

Builders have used a variety of rudder pedal return systems, but my impression was that they were to keep the rudder cables from going slack. Here's one installed by Steve Henry:
Rudder Pedal Return System - Steve Henry SS.JPG

... and another by xpflyer:
Rudder Pedal Return System - xpflyer.JPG

Bungees would probably work, too ... but not past their "sell by" date. :wink:

Re: Rudder bungees and Highlander tail

PostPosted: Thu Feb 20, 2014 6:27 pm
by Fresnoredneck
Hi SheepdogRD

Thanks for the snaps, interesting, how do you find your rudder in flight? Do you find in straight and level flight if you input either port or starboard rudder then release both pedals that the aircraft returns to a directionally stable flight? Or does it stay in a flat turn?

Being low time on the Escapade I was quite surprised that with the fin and rudder area that mine certainly doesn't want to return to straight flight, that's why I asked the question about the highlander?? Didn't know if the overhand on the fin that sort of acts like a spade also had directional stability benefits, bungees certainly will give a bit of benefit on that front. To get the 1,2,3 pressures right on the controls I have extended the rudder control horn by an inch either side, makes a world of difference and takes out sensitivity on the pedals.

Rich

Re: Rudder bungees and Highlander tail

PostPosted: Thu Feb 20, 2014 8:38 pm
by danerazz
Are you keeping the wings level during this rudder exercise? AC-90-89a as a lot of information on testing to include stability tests. Most aircraft do not have any kind of centering springs on the rudder, they just have a "closed loop" cable system, like the second picture above.

Re: Rudder bungees and Highlander tail

PostPosted: Thu Feb 20, 2014 9:52 pm
by SheepdogRD
Fresnoredneck wrote:... how do you find your rudder in flight?

I wish I could tell you, but we're not flying her, yet. Just getting started on covering. Still 90% to go. :wink: I haven't noticed anything amiss in the small amount of Highlander time I have. Everything seemed pretty normal. I did notice that my cheeks were kinda sore from grinning, though ...

Re: Rudder bungees and Highlander tail

PostPosted: Thu Feb 20, 2014 11:07 pm
by gkremers
On my RV7A and most if not all RV's the rudders at set up similar to the Highlander. No return springs, the airflow in flight keeps the rudder centered. If the rudder doesn't return to center (neutral) in flight something must be binding or holding it up somewhere. When the plane is on the ground does the rudder swing freely, do you hear any binding when pushing on the rudder pedals?

Gary

Re: Rudder bungees and Highlander tail

PostPosted: Fri Feb 21, 2014 7:27 am
by Fresnoredneck
Hi danerazz

Yes straight and level and just input rudder gently through to the stop then take your foot off, the rudder tries to center but does not and the plane continues in a flat turn, it really indicates that there is not enough fin to give directional stability, this can sometimes be corrected and assisted with either bungees or springs which sort of prompted my first question and if you give it gas whilst in the flat turn it just tightens the turn up significantly.

Has anybody extended their rudder horn to take some of the sensitivity out of it??

Rich

Re: Rudder bungees and Highlander tail

PostPosted: Fri Feb 21, 2014 8:45 am
by danerazz
Is this always in the same direction? And how does it fly if you just take your feet off the pedals, no input applied?

Re: Rudder bungees and Highlander tail

PostPosted: Fri Feb 21, 2014 1:13 pm
by moving2time
I only have two demo flights in a Highlander but I have been spending time in on a Citabria working on my tail wheel endorsement. The cables to the rudder are not tight until you put your feet on the pedals and apply pressure which is what I remember on the Highlander. While flying if you started turning with just the rudder and then took your feet off of the rudder pedals the rudder would basically center and the turn would stop. Just like the Highlander both the rudder and the elevator are balanced but that balancing will not hold the control surface into the air stream without pressure from the pedals for the rudder or the stick for the elevator. The surface area of the rudder or elevator is so much larger than their balancing tabs so I think they tend to want to align with the vertical and horizontal stabilizers.

Re: Rudder bungees and Highlander tail

PostPosted: Fri Feb 21, 2014 1:49 pm
by Familyflyer
It is interesting reading all this. I use to fly an Avid Aerobat. My first airplane. If you lost rudder, the plane became almost uncontrolable from all the adverse yaw, the plane would go into a slipping turn and when leveling you never really could stay in full control. If you leveled the wings after the turn without rudder use, it would stay flying slipped over per say. Not sure if you could even get it on the ground safely. I do not think the rudder would center on its own. If you lost aileron, the rudder was so sensitive and twitchy that you would have a hard time landing with it alone. You needed to use both all the time. Don't dare take your hand off the control in turbulance. I sure hope these aircraft are not like that :shock:

My guess is they are somewhere in between the Avid and the RV. They are short coupled so the yaw stability will not likely be perfect. Someday I will be able to give a helpful comment on this. :D

Re: Rudder bungees and Highlander tail

PostPosted: Fri Feb 21, 2014 5:26 pm
by Gil T
IMG_2254.JPG
IMG_2248.JPG
IMG_2244.JPG

This is my solution for having the rudder cables sag when I don't have my feet on the pedals. I don't think it has anything to do with the airplane wanting to go left or right. I just felt uncomfortable having the cables sag without my feet resting on them. As to flying straight ahead, I have a small rudder tab that takes care of it at 5100 rpm. Any other setting requires me to work a little by actually having to touch the controls. I guess that's not too much to ask of us once in a while.

Gil T

Re: Rudder bungees and Highlander tail

PostPosted: Fri Feb 21, 2014 5:50 pm
by moving2time
Actually, I can't really say what happens with the rudder if I take my feet off the pedals in the Citabria because I can't say that I have actually done that. It just seemed to make sense that it would follow the stabilizer and level out. Working towards my Tail Wheel endorsement I am not really playing around much since we are always concentrating on the lesson at hand. I have about 5 hours into the training but that was back in early December. I haven't been up in months now and it seems like forever and I was very close to getting signed off. Next time I get up I will check it out just for fun. The CTLS is a ery stable aircraft and I know I can trim for level flight without the Auto Pilot using the trim tab on the elevator and let go of the controls. Given my limited time in the Highlander I would say that it seemed very stable to me. Very much like the CTLS.