I grabbed this out of a long thread, lots of good info here.
Some of the recommended mods for the Predator that I remember (probably apply to the Viper as well) are:
1)Drill holes through the fuse into the hold-downs through the fuselage and pin them with epoxy covered round toothpicks. You should also do the same thing with the landing gear plate. Add some fiberglass or carbon fiber re-inforcement to the firewall area if you think it needs it.
2)Place a piece of 3/8" triangle stock under the wing hold downs and glue well.
3)Re-Tap the metric wing hold downs to 1/4-20 for ease of replacement. Before you do, check the wing alignment by triangulating to make sure it's square to the fuse and not sqewed. If it's off you can correct it when you re-tap by epoxing dowels in some of the holes and redrilling an tapping. The 1/4-20 bolts are easier to come by if you lose one. (Only Ed Smith has metric stuff in his box )
4)Mix epoxy and micro balloons and make a fillet between the wing hold-downs and the fuselage. How to techniques is somewhere in this forum.
5)Change the torque rods in the ailerons, especially if you're planning a really strong engine. The change is easy. Simply cut down both sides of the torque rodsabout 1/8" wide and lift the piece out to expose the torque rod. Remove the 2mm torque rods and replace them with one bent from a 4-40 Dubro threaded rod bent to the same dimensions that the 2mm were bent. Put them in the slot and put the 1/8" piece back in the slot. Press it down on the new rod and Ca it in place with thick Ca. Do not glue the 4-40 rod. Carefully drill the holes in the ailerons to 3/32. Install ailerons as instructions.
6) Check the finished airplane for lateral balance as well as for correct CG.
7) Want more? Instead of bringing the wood pushrods out the top of the fuselage, Darrol Cady suggests the following Darrol Cady mods.
Sharpen a piece of1/8" brass tubing and use it to cut holes in the side of
the fuse under the stab on the angle that the pushrods would exit the fuse.
Use two pieces of Dubro 4-40 threaded rod to make control horns that fasten
to the elevators and go to the bottom. Bend them so that they are about 1/8"
from the side of the fuse and run free for their arch. Then make up carbon
PushRods with the 2-55 threaded rod long enough to go through and exit the
fuselage. Install ball links on the control horns and attach the PushRod.
The extra that you cut off the 2-56 threaded rod should be glued into the
other end of the PushRod and made to a Z bend to attach to the servo.
There may be others, but that's what I remember. Also see these threads:
http://www.rcuniverse.com/forum/m_11...tm.htm#1120726
http://www.rcuniverse.com/forum/m_11...tm.htm#1141469
Stan Douglas