Rudder Travel Needed

[Binty]

I am Re-Rigging my Rudder. Does anyone have the Degrees of Travel available? Otherwise a measurement of the distance between the Rudder at Full Deflection and Elevator (Elev in Neutral Position) would be a good start..(see pic)

 

[mike mcs repair]

so they don't hit.....

but officially 25 deg

 

[Gordon Misch]

Yep, 25 on PA-18, but only 20 on PA-12 (per TCDS). And 30 on J-3 & J-5. Any ideas on why so low on the 12? Any reason to not set an experimental -12 to 25 or even 30 deg (given adequate elevator clearance)?

 

[jgerard]

I give them as much as I can and you need to make sure the elevator goes full swing up and down with out rubbing on the rudder. If you grind too much metal off the stop you can always stick a screw in there as an adjustable stop. I learned about that by not paying attention to the first part of this post.

Jason

 

[skywagon8a]

Any ideas on why so low on the 12? Any reason to not set an experimental -12 to 25 or even 30 deg (given adequate elevator clearance)?

There is a flight test maneuver for "rudder lock" which is done on multi engine airplanes. I doubt that this would apply to our Cubs. When they did the flight testing for the 12 they probably just found that 20 worked. In the early days with low power, tail skids and no brakes, more rudder was needed for control on the ground. By the time they got around to building the 12 they had refined the numbers.

 

[Fortysix12]

The other item to consider is the travel with regards to cable length if in fact you are making new cables at any point along the system. One of the first items I correct on cubs is the full deflection travel as it relates to the firewall. If you have heal brakes, the closer you deflect to the firewall the easier the brakes are to use when in the nuetral centered location. My Supercub rudder pedals travel to with in an 1/8th inch of the firewall. The cable between the front and rear rudder pedals is critical as well for the same reason. Be sure that the rear rudder pedal does not contract anything before the rudder hits the rear rudder deflection stops.

 

[Superchub]

Also account for a little cable stretch. You can also shorten the cable a tiny bit by twisting but I try not to do this if I can avoid it...

 

[Gordon Misch]

There is a flight test maneuver for "rudder lock" which is done on multi engine airplanes. I doubt that this would apply to our Cubs. When they did the flight testing for the 12 they probably just found that 20 worked. In the early days with low power, tail skids and no brakes, more rudder was needed for control on the ground. By the time they got around to building the 12 they had refined the numbers.

I looked up "rudder lock", and found this at http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/FLNotebookpdfs.pdf, pg 9 which I thought it was real interesting. In fact the whole thing is well worth reading and contemplating, in my opinion. Kinda like "Stick and Rudder" on steroids - - - Especially the "Flight Notes", beginning on Pg 7.

•Flat Turn: The next maneuver is the basic flight test for static directional (z-axis) stability. When you depress and hold a rudder pedal, causing the nose to yaw along the horizon, you generate a sideslip angle, β. Sideslip creates a side force and an opposing moment. Notice the increased pedal force necessary as rudder deflection increases. For certification purposes, rudder pedal force may begin to grow less rapidly as deflection increases, but must not reverse, and increased rudder deflection must produce increased angles of sideslip. The rudder must not have a tendency to float to and lock in the fully deflected position due to a decrease in aircraft directional stability at high sideslip angles as the fin begins to stall. If it did, the aircraft would stay in the sideslip even with feet off the pedals. (Things could be dicey if the pedal force needed to return a big rudder exceeded the pilot’s strength. Many well-known aircraft had rudder lock problems during their early careers, including the DC-3 and the early Boeing 707, and the B-24 Liberator bomber.

 

[skywagon8a]

I looked up "rudder lock", and found this at http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/FLNotebookpdfs.pdf, pg 9 which I thought it was real interesting. In fact the whole thing is well worth reading and contemplating, in my opinion. Kinda like "Stick and Rudder" on steroids - - - Especially the "Flight Notes", beginning on Pg 7. •Flat Turn: The next maneuver is the basic flight test for static directional (z-axis) stability. When you depress and hold a rudder pedal, causing the nose to yaw along the horizon, you generate a sideslip angle, β. Sideslip creates a side force and an opposing moment. Notice the increased pedal force necessary as rudder deflection increases. For certification purposes, rudder pedal force may begin to grow less rapidly as deflection increases, but must not reverse, and increased rudder deflection must produce increased angles of sideslip. The rudder must not have a tendency to float to and lock in the fully deflected position due to a decrease in aircraft directional stability at high sideslip angles as the fin begins to stall. If it did, the aircraft would stay in the sideslip even with feet off the pedals. (Things could be dicey if the pedal force needed to return a big rudder exceeded the pilot’s strength. Many well-known aircraft had rudder lock problems during their early careers, including the DC-3 and the early Boeing 707, and the B-24 Liberator bomber.

This *Flat Turn maneuver is taken into consideration when installing floats on a plane. Since, with floats you are adding area ahead of the aerodynamic center of balance, you are reducing directional stability. This helps to explain why some float installations require additional fin area. Some do not, depending on the design shape of the floats. Rounded floats, like EDO 2000s, demand less fin area than squared flat top floats since the air flows sideways over the bows with less resistance. Thus better directional stability. A PA-18 does not require an extra fin when on EDO 2000s. A PA-12 does, since it has just enough extra area forward to fail the above test with the floats. Those of you who are flying your 12s on floats without the extra fin, which is required by the Type Certificate, should think about why the PA-18 is more stable directionally.

I'm sorry Binty. I have digressed from your original post. It just seemed to be appropriate at this time.

 

[Binty]

No problemo. I now have what I needed plus the link you provided is an interesting document.