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Viper Rudder Help

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Old 03-31-2011, 03:53 PM
  #1
vetagator
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Default Viper Rudder Help

Hi guys, I just purchased a turn key, never flown, large Skymaster Viper. The builder addressed all of the modifications to this jet EXCEPT for the Rudder. The rudder was assembled using the 3 robart-like hinges. The hinge knuckles are located far from the trailing edge of the vetical stab. This causes alot of flexing of the rudder. How can I remedy this without causing too much wreckage to the rudder and vert. stabilizer? Someone has to have been in my position as this was a major issue with this jet. Do you think I can maiden it as long as I take it easy on the speed and rudder usage? Thanks, Alex.
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Old 03-31-2011, 04:47 PM
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Default RE: Viper Rudder Help

Can you get in there and cut it apart? A hot wire would do the trick. I know it would not fly like that if it were mine....I have seen two come apart that way....ugly!
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Old 03-31-2011, 05:40 PM
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Default RE: Viper Rudder Help

I built one and did the mods. I was glad it did it as there isn't a lot of material for the 3 hinge points as it is.

Sorry, but you need to fix it or don't expect to keep the airframe for long.

Also, watch the stall, the flight characteristics are very docile and forgiving to a point....

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Old 03-31-2011, 05:52 PM
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Default RE: Viper Rudder Help

Cut it loose and mod it.
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Old 04-01-2011, 03:13 AM
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Default RE: Viper Rudder Help

Inbound, Thanks for the hot wire Idea! That should work fine to cut the hinges. The dilema I was having was getting the rudder off without screwing things up. I will fix it before I maiden it then. Thanks for the heads up on the stalling, Alex.
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Old 04-01-2011, 03:21 AM
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Default RE: Viper Rudder Help

Hi Alex

I used 3 robart hinges, but used brass tube to support the part of the hinge that stuck out the back of the vertical stab. The 3 hinges worked perfectly when supported, Ali flew it more than i did and the rudder never gave me any issues.

cheers

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Old 04-01-2011, 04:16 AM
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Default RE: Viper Rudder Help

Duncan, that's what I want to do. I'm planning on installing a total of 6 hinges with the brass tubing. It's a long rudder.
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Old 04-02-2011, 07:16 AM
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Default RE: Viper Rudder Help

I have a 2M viper (smaller one) and I was looking at the rudder with its 3 supplied hing points and thought that it was marginal, so I added two more hing points.

In doing so I found that the vertical fin is constructed with 1/8" balsa web running the entire length, there is minimal backing behind the three factory supplied holes and no doubler in the area where I drilled the two new holes. Also the hinges protrude quite a ways out from the balsa web, my solution was to make hard balsa blocks for the hinges to have additional bonding area. I found that I had to change the thickness of the blocks based on their positions.

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Old 04-02-2011, 07:21 AM
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Default RE: Viper Rudder Help


Quote:
ORIGINAL: vetagator

Hi guys, I just purchased a turn key, never flown, large Skymaster Viper. The builder addressed all of the modifications to this jet EXCEPT for the Rudder. The rudder was assembled using the 3 robart-like hinges. The hinge knuckles are located far from the trailing edge of the vetical stab. This causes alot of flexing of the rudder. How can I remedy this without causing too much wreckage to the rudder and vert. stabilizer? Someone has to have been in my position as this was a major issue with this jet. Do you think I can maiden it as long as I take it easy on the speed and rudder usage? Thanks, Alex.

I know a guy in the Pittsburgh PA area who totaled his due to the vertical fin failing, I would recommend to do the mods

BTW a helpful hint, as mentioned a hot wire can be used to cut them off, to remove them from the holes take a pencil tip soldering iron and run it it down into the hing holes, it will melt the original pins away

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Old 04-02-2011, 07:33 AM
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Default RE: Viper Rudder Help

Oh by the way, I would check everything over no matter who built it, I was doing the install on my Viper and went to install the servo in the Horizontal Stabilizer, I did one side first with no issues, then I pulled out the other side and found that Skymaster QC isn't quite what it should be, the sheer web was missing. I could take my fingers and squeeze the outer skins in the area where the web was missing and move them quite a ways. This is a major structural flaw in my mind and could have been catastrophic if it would have gone unnoticed, I made a sheer web and glued it in place...come on Skymaster, lets concentrate on your QC a bit more!

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Old 04-02-2011, 07:43 AM
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Default RE: Viper Rudder Help

One last thing ... I know these are made in China and English is a second language...

Come on guys if you going to offer a paint out of the mold super duper paint job , then get the details right!!![>:]

Also keep your graphics straight, not sagging[>:]



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Old 04-02-2011, 07:54 AM
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Default RE: Viper Rudder Help

I used a small zonas saw with the spline removed to cut the hinges, thanks for the idea Joser. I used the soldering gun with the thin pencil tip to melt away the old hinges. Worked like a charm. I added 2 maple block hard points between the 3 existing hard points. My friend Bill gave me 5 new robarts with the brass tubing modification on one side. This is going to be solid. I have the hinges glued into the rudder now. Next step is to glue the brass ends into the fin. I had time to look through everything. Looks like a maiden flight is set for Tuesday. Great Ideas all around, thanks guys. I will post pics of the maiden.
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Old 04-02-2011, 08:08 AM
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Default RE: Viper Rudder Help


Quote:
ORIGINAL: RCISFUN

One last thing ... I know these are made in China and English is a second language...

Come on guys if you going to offer a paint out of the mold super duper paint job , then get the details right!!![>:]

Also keep your graphics straight, not sagging[>:]



Is that really the way it came? Did you give them a piece of your mind... http://www.youtube.com/watch?v=yytbD...eature=related


Marty
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Old 04-02-2011, 08:23 AM
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Default RE: Viper Rudder Help

Marty
Yes, that is really the way it came!
It will be an easy fix with a bit of white paint

I like the video
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Old 04-04-2011, 12:32 PM
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Default RE: Viper Rudder Help

I have bought a second hand large viper that has the 3 hinges, and the servo seems to sway the rudder side to side with flex, Im fairly new to jets and Im not really happy with the way this has been made (not by Skymaster but by the builder who glued the hinges in)

Im an inexperienced builder, does anyone know of a good builder familiar with viperjets in the SE of England area who would beef up the rudder, and also get me the 68mm travel talked about on these forums.... and how much of the readies they would want.

The airframe has flown 25 times fine as it is... but I doubt its ever knife edged like this.

Phil
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Old 04-06-2011, 12:45 PM
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Default RE: Viper Rudder Help

Fellas,

I'm in the midst of this drama with my 2M right now. I snapped one of the original SM hinges and was pretty sure I had sideloaded it at some point (copy, fat thumb error).

I cut out that hinge and then replaced it with a Robart. To get the hinge out, I clamped a section of brass tubing in my drill, and cut little grooves into the end of the pipe (making it sharp). I then simply fit the brass over the exposed portion of hinge and fired the drill up, cutting around the hinge until I reached the correct depth. To get all the melted hinge out of the brass tubing, I stuck a drill bit in a second drill and just left it sitting on the bench...when I'd clog up, I'd simply run the drillbit inside the brass. Innovative Man strikes again!

I added three sections of the hardest balsa I could find and then filed a round that matches the leading edge of the rudder curvature, and once I was satisfied that the pin hinges were supported fully, I thin CA'd the blocks to harden them. I then glued the rudder on and the blocks in with hysol.

While setting up my radio I noticed that my rudder was moving more than I thought it should at the top...upon closer inspection I noticed that the top SM hinge had failed. I had to cut the entire rudder off (I used a very small (1.63mm) Dremel cutting bit that I accessed the hinges with a fully deflected rudder). I then had to cut out all three hinges from the rudder and the vertical using the method described above, refill some of the excess material that had been liberated with hysol, and glued the whole damn thing back together.

I've also snapped two of the gear door hinges. I'd HIGHLY recommend replacing all the plastic hinges in this kit...they are made of too-brittle a material.

Dave
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