WIX Archives
Flutter control...
Posted by bdk on Wed Aug 07, 2002 07:11:05 PM
In reply top Re: Fabric control surfaces posted by Kenneth on Wed Aug 07, 2002 04:50:15 PM
Fabric was lighter, thus less counterbalance weight was required forward of the hinge line to balance the surface. Most control surfaces had a front spar with an integral leading edge, forming a D-section torque box to resist control surface twisting. The ribs and trailing edge trailed behind and were relative light, only needing to react the airloads forward into the torque box.
Post war, many aircraft had control surfaces "metallized" by riveting sheet metal over the fabric areas (after the fabric was removed naturally). This required the control surface to be rebalanced. The resultant surface was heavier, but by that time durability in service had become more important than performance.
You can see the progression of knowledge on aircraft like the P-51 where some of the fabric surfaces on the earlier model aircraft became metal in the later models. Others like the P-47 had metal surfaces throughout their career, but this aircraft was a later design. The Seversky predecessors all had fabric covered surfaces.
Flutter was a relatively new phenomenon back then, but it was known that balanced control surfaces could in most cases alleviate the tendency.
There may have been a thought that the fabric tension might help to reduce flutter (since it wasn't well understood), but who knows for sure!
: This is a question which has been puzzling me too for very
: long. I have always been wondering why designers after th
: e discovery of metal monocoque construction persisted with
: fabric covered control surfaces. I doubt that the answer
: is related to damage repairability since, for example, civ
: ilian aircraft from the pre-war period (e.g. the DC-3) had
: them. Could it be related to flutter problems, i.e. are f
: abric covered surfaces easier to balance?