Varga/ShinnVG-21 Squadron

MAINTENANCE ITEM #5

*** FLIGHT CONTROL RIGGING ***

By Lee Beery

Overall, the Varga Maintenance Manual is fine except there is little information on fixing an airplane that won't fly hands-off. I have found that very few Vargas fly the same. I am convinced that this is due to lack Of tolerance in the assembly of the aircraft. There is no attempt made to check for proper alignment or is there any way to adjust anything when mounting wings to fuselage or stabilizers to fuselage. The manual simply gives control surface

travels and instructions on how to reach these values. According to the manual, the only way to correct for a plane's tendency to turn (they call it wing heaviness), is to bend the fixed tabs found on the rudder and left aileron. What they didn't tell you is the out-of-trim condition could be caused by nose wheel steering inputs and/or a flap surface out of rig. We also know that worn out engine mount bushings can have a real effect on engine thrust line

and cause trim problems.

To be honest with you, it takes considerable time and a lot of test flights to fix a Varga that is way out of rig. It is often a matter of small adjustments in more than one area. One exception to this is the correction to pitch trim forces. Pat's Varga required large amounts of nose down trim in cruise flights. This was caused by poor positioning of the horizontal stabilizer, which required a great deal of elevator down trim, which, in turn, produced what is called "out of trim drag." In one hour, three adjustments and test flights were made which reduced the elevator down forces needed for level flight (same RPMs each flight) and increased the normal cruise speeds by six (6) MPH. When we brought Pat's Varga home from Ohio some five years ago, it's corrected airspeed was 112 MPH, now it is 150 MPH, but it required more than a good wax job for that kind of increase. At our next meeting at our home field (Lampson), time permitting, I would be happy to work with any Varga owner that has a trim or rigging problem. Only a very few of the club members have responded to the request for copies of FAA approved Varga modifications (337 forms). It is very beneficial to someone trying to get FAA approval on a mod if that person can show the FAA that your project has been done before and approved by the FAA (such as our engine change to 160 HP). Anyone now changing to a 160 HP engine could use our paperwork to gain approval. Also, besides having a library on 337's, we are building a listing on special Varga tools, fixtures, testers and hard-to-find parts. Please help.

INDEX - PREVIOUS MAINTENANCE ITEMS

#1 ENGINE MOUNT FAILURE

#2 HIGH ENGINE OIL TEMPERATURE

#3 FUEL QUANTITY SYSTEM

#4 FUEL VENT SYSTEM/FUEL SHUT-OFF VALVES