Skymaster F-16 rudder flutter fix
11-19-2009, 07:26 PM
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Skymaster F-16 rudder flutter fix
I have given a lot of thought to the modification suggested for the rudder linkage in the SM F-16 1/6, to prevent rudder flutter.
I am not convinced that the placement of the rudder servo in the fin is an optimal solution. I think that such set up has more negative than positive consequences:
Negative:
-Looks ugly !!!!!!
-The force applied to the servo is asymmetric with respect to the servo output shaft. The original SM system (pull-pull) is symmetric, i.e. less play.
-The structural integrity of the horn/glue/rudder system is by far weaker than the steel rod imbedded in the bottom of the rudder.
-There is no torque or force gain at all. By the contrary, the original system allows to connect the rods closer to the servo output shaft; thus, reducing play.
-Heavy duty ball links can not be used.
Positive:
-No play in the rudder horn/link contact. In the original SM system there is some play between the torque rod head and the rudder rod bar. This has probably been the cause of flutter.
So, installing the servo in the fin is not giving any mechanical advantage, but is aimed to eliminate the play generated in the contact between the rudder rod and the torque head.
What I did was to focus on eliminating this play without the negative consequences.
I have logged 25 flights, with "no mercy" regarding top speed, and have not had any sign of flutter (I am using 38 pounds of thrust).
Here is what I did:
-Make sure the torque head is oriented so that the deeper part of the slot faces fwd. (this is an easy mistake, and could cause the rod to disconnect from the torque head at full deflection if placed backwards).
-Wrap a 1/4" by 1/4" piece of aluminum tape around the rudder steel torque rod.
-"Force" the fin-rudder assy over the torque head.... absolutely no play at all !!!
- I use a JR 8611 servo without the rubber grummets. Rods are connected to the innermost hole of the servo arm, and I use HD ball links on the torque arm.
Rudder has absolutely no play at all now.
Hope you guys find these tips useful
Regards
Jack
I am not convinced that the placement of the rudder servo in the fin is an optimal solution. I think that such set up has more negative than positive consequences:
Negative:
-Looks ugly !!!!!!
-The force applied to the servo is asymmetric with respect to the servo output shaft. The original SM system (pull-pull) is symmetric, i.e. less play.
-The structural integrity of the horn/glue/rudder system is by far weaker than the steel rod imbedded in the bottom of the rudder.
-There is no torque or force gain at all. By the contrary, the original system allows to connect the rods closer to the servo output shaft; thus, reducing play.
-Heavy duty ball links can not be used.
Positive:
-No play in the rudder horn/link contact. In the original SM system there is some play between the torque rod head and the rudder rod bar. This has probably been the cause of flutter.
So, installing the servo in the fin is not giving any mechanical advantage, but is aimed to eliminate the play generated in the contact between the rudder rod and the torque head.
What I did was to focus on eliminating this play without the negative consequences.
I have logged 25 flights, with "no mercy" regarding top speed, and have not had any sign of flutter (I am using 38 pounds of thrust).
Here is what I did:
-Make sure the torque head is oriented so that the deeper part of the slot faces fwd. (this is an easy mistake, and could cause the rod to disconnect from the torque head at full deflection if placed backwards).
-Wrap a 1/4" by 1/4" piece of aluminum tape around the rudder steel torque rod.
-"Force" the fin-rudder assy over the torque head.... absolutely no play at all !!!
- I use a JR 8611 servo without the rubber grummets. Rods are connected to the innermost hole of the servo arm, and I use HD ball links on the torque arm.
Rudder has absolutely no play at all now.
Hope you guys find these tips useful
Regards
Jack
11-19-2009, 07:56 PM
#3
RE: Skymaster F-16 rudder flutter fix
ORIGINAL: Jack Diaz
I have given a lot of thought to the modification suggested for the rudder linkage in the SM F-16 1/6, to prevent rudder flutter.
I am not convinced that the placement of the rudder servo in the fin is an optimal solution. I think that such set up has more negative than positive consequences:
Negative:
-Looks ugly !!!!!!
-The force applied to the servo is asymmetric with respect to the servo output shaft. The original SM system (pull-pull) is symmetric, i.e. less play.
-The structural integrity of the horn/glue/rudder system is by far weaker than the steel rod imbedded in the bottom of the rudder.
-There is no torque or force gain at all. By the contrary, the original system allows to connect the rods closer to the servo output shaft; thus, reducing play.
-Heavy duty ball links can not be used.
Positive:
-No play in the rudder horn/link contact. In the original SM system there is some play between the torque rod head and the rudder rod bar. This has probably been the cause of flutter.
So, installing the servo in the fin is not giving any mechanical advantage, but is aimed to eliminate the play generated in the contact between the rudder rod and the torque head.
What I did was to focus on eliminating this play without the negative consequences.
I have logged 25 flights, with ''no mercy'' regarding top speed, and have not had any sign of flutter (I am using 38 pounds of thrust).
Here is what I did:
-Make sure the torque head is oriented so that the deeper part of the slot faces fwd. (this is an easy mistake, and could cause the rod to disconnect from the torque head at full deflection if placed backwards).
-Wrap a 1/4'' by 1/4'' piece of aluminum tape around the rudder steel torque rod.
-''Force'' the fin-rudder assy over the torque head.... absolutely no play at all !!!
- I use a JR 8611 servo without the rubber grummets. Rods are connected to the innermost hole of the servo arm, and I use HD ball links on the torque arm.
Rudder has absolutely no play at all now.
Hope you guys find these tips useful
Regards
Jack
I have given a lot of thought to the modification suggested for the rudder linkage in the SM F-16 1/6, to prevent rudder flutter.
I am not convinced that the placement of the rudder servo in the fin is an optimal solution. I think that such set up has more negative than positive consequences:
Negative:
-Looks ugly !!!!!!
-The force applied to the servo is asymmetric with respect to the servo output shaft. The original SM system (pull-pull) is symmetric, i.e. less play.
-The structural integrity of the horn/glue/rudder system is by far weaker than the steel rod imbedded in the bottom of the rudder.
-There is no torque or force gain at all. By the contrary, the original system allows to connect the rods closer to the servo output shaft; thus, reducing play.
-Heavy duty ball links can not be used.
Positive:
-No play in the rudder horn/link contact. In the original SM system there is some play between the torque rod head and the rudder rod bar. This has probably been the cause of flutter.
So, installing the servo in the fin is not giving any mechanical advantage, but is aimed to eliminate the play generated in the contact between the rudder rod and the torque head.
What I did was to focus on eliminating this play without the negative consequences.
I have logged 25 flights, with ''no mercy'' regarding top speed, and have not had any sign of flutter (I am using 38 pounds of thrust).
Here is what I did:
-Make sure the torque head is oriented so that the deeper part of the slot faces fwd. (this is an easy mistake, and could cause the rod to disconnect from the torque head at full deflection if placed backwards).
-Wrap a 1/4'' by 1/4'' piece of aluminum tape around the rudder steel torque rod.
-''Force'' the fin-rudder assy over the torque head.... absolutely no play at all !!!
- I use a JR 8611 servo without the rubber grummets. Rods are connected to the innermost hole of the servo arm, and I use HD ball links on the torque arm.
Rudder has absolutely no play at all now.
Hope you guys find these tips useful
Regards
Jack
Absolutely no play on "the mod" either. It's rock solid. Ask anyone who has seen me fly my F16.
Andy
11-19-2009, 11:22 PM
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RE: Skymaster F-16 rudder flutter fix
Thanks for the post, Jack. I'm building this jet right now and have been going back and forth on whether to use the stock setup or do the BVM-recommended modification. I'm installing the same engine you used (or the equivalent): a JetCat P160-SX. My biggest qualm is that Bob and Dustin strongly recommend the external linkage, and I have the utmost respect for both of them.
What did you mean by "Wrap a 1/4" by 1/4" piece of aluminum tape around the rudder steel torque rod?" Where did you place the tape?
What did you mean by "Wrap a 1/4" by 1/4" piece of aluminum tape around the rudder steel torque rod?" Where did you place the tape?
11-20-2009, 12:42 AM
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RE: Skymaster F-16 rudder flutter fix
I have had 3 1/6 F-16's all with the external link rudder mod. I ran a 180 in one of them and P200 in the other two..
Over 150 flights on my current one with no problems at all and the owners of the other 2 have had no problems either.
I strongly recommend the external link mod as i have seen the stock setup types of mods fail.
Over 150 flights on my current one with no problems at all and the owners of the other 2 have had no problems either.
I strongly recommend the external link mod as i have seen the stock setup types of mods fail.
11-20-2009, 03:56 AM
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RE: Skymaster F-16 rudder flutter fix
With a 160N turbine I can see how this seems to work, however, I tried the same solution
and still had flutter (the first time). The connection between the rod with the slot and the
steel rod in the rudder is so short that even an extremely small mismatch will allow for
slop, and we have seen this too many times - after a few flights (mine occurred after 40-
50 flights) any tape or glue wrapped around the rod will wear off or be compressed, and
you will get flutter.
There was a similar post here recently, and in that post I confirmed that the slot in my
plane and the 3 others in Scandinavia were all placed the right way, and still we all had
flutter - so my conclusion is: There is no way you will avoid flutter with the original
setup.
Tor
and still had flutter (the first time). The connection between the rod with the slot and the
steel rod in the rudder is so short that even an extremely small mismatch will allow for
slop, and we have seen this too many times - after a few flights (mine occurred after 40-
50 flights) any tape or glue wrapped around the rod will wear off or be compressed, and
you will get flutter.
There was a similar post here recently, and in that post I confirmed that the slot in my
plane and the 3 others in Scandinavia were all placed the right way, and still we all had
flutter - so my conclusion is: There is no way you will avoid flutter with the original
setup.
Tor
11-20-2009, 08:55 AM
#7
RE: Skymaster F-16 rudder flutter fix
We have had 3 F-16 1/6 here in Chile with the original setup and some modifications like what Jack did, all with Rhino's for power. We have never seen a flutter problem and I have seen the F-16 go quite fast and hard.
Jack, I am glad you are enjoying your jet my friend...
Send me some pics when posible...
Michel
Jack, I am glad you are enjoying your jet my friend...
Send me some pics when posible...Michel
11-20-2009, 10:38 AM
#8
RE: Skymaster F-16 rudder flutter fix
I don't like the idea of "tape" as a perm. solution to anything. If anyone wants pics of the mod which is a permenant solution, I will be happy to post them.
11-20-2009, 12:45 PM
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RE: Skymaster F-16 rudder flutter fix
I experienced some rudder flutter on my SM 1/6 F-16 but the rudder did not break loose (very lucky). After dis-assembly of the rudder, I noticed the steel pin that is mounted in the rudder had moved back into the balsa block that supports it, leaving the front of the pin free of its hole in the radius of the rudder. I began to drill a series of small locatiing holes in the bottom of the rudder to find the end of the steel pin. I discovered the hole for the pin in the balsa block had originally been drilled 1/4" too deep, allowing the pin to move rearward and dis-lodge itself from the front of the rudder. The pin was only making contact with the rudder shaft drive about 1/2 way in the slot. This was an easy fix...i filled the balsa block with Aeropoxy after moving the pin forward. I wonder if this has been some of the problems all along. I have a friend that lost his on the first flight because of flutter and the fin and rudder separated from the fuse at a crucial time. We didnt think to check the pin...too much damage anyway.
Richard
Richard
11-20-2009, 02:47 PM
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RE: Skymaster F-16 rudder flutter fix
Jack
Good to hear from you!
I too was also concerned for the rudder setup. This mod has been flight tested with a P-200. First I installed a vertical spar made from .080 carbon plate to help support the rudder hinges, and the vertical stab. Making sure to go the full length of the stab. I injected around 8-10 CC of Aeropoxy in each hinge hole. I made my own control horn and made sure it went the full depth of the base of the rudder. Keeping all mechanical advantages short and tight. Servo install is just like Jeff Tolemos instructions. I also drilled and tapped a 4-40 set screw into the forward carbon support section. This also secures the forward carbon tube. There is quite a bit of flexing in this area. This setup is working great.
Justin
Good to hear from you!
I too was also concerned for the rudder setup. This mod has been flight tested with a P-200. First I installed a vertical spar made from .080 carbon plate to help support the rudder hinges, and the vertical stab. Making sure to go the full length of the stab. I injected around 8-10 CC of Aeropoxy in each hinge hole. I made my own control horn and made sure it went the full depth of the base of the rudder. Keeping all mechanical advantages short and tight. Servo install is just like Jeff Tolemos instructions. I also drilled and tapped a 4-40 set screw into the forward carbon support section. This also secures the forward carbon tube. There is quite a bit of flexing in this area. This setup is working great.
Justin
11-20-2009, 10:28 PM
#13
RE: Skymaster F-16 rudder flutter fix
ORIGINAL: BeanerECMO
Do ya think that Airbus could use this fix in their aircraft?
Do ya think that Airbus could use this fix in their aircraft?
David Gladwin
11-21-2009, 12:32 PM
#14
RE: Skymaster F-16 rudder flutter fix
ORIGINAL: SinCityJets
please do!!
Chad
please do!!
Chad
11-21-2009, 01:59 PM
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RE: Skymaster F-16 rudder flutter fix
That's what's called the Norwegian mod, and if you do it right, it will work well. Just remember to reinforce
the copper/brass tube so it doesn't break from fatigue... (Ask me how I know!!
)
the copper/brass tube so it doesn't break from fatigue... (Ask me how I know!!
)
11-21-2009, 11:51 PM
#16
RE: Skymaster F-16 rudder flutter fix
ORIGINAL: icepilot
That's what's called the Norwegian mod, and if you do it right, it will work well. Just remember to reinforce
the copper/brass tube so it doesn't break from fatigue... (Ask me how I know!!)
That's what's called the Norwegian mod, and if you do it right, it will work well. Just remember to reinforce
the copper/brass tube so it doesn't break from fatigue... (Ask me how I know!!
)
