Diamond Aircraft DV 20 KATANA, Maintenance Manual

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AIRCRAFT
DV 20 KATANA AMM
Structures
Doc # 4.02.02
Rev. 13
51-10-00
Page 15
15 Dec 2018
4. GFRP Repair
When the airplane is damaged, proceed as follows: Carefully visually inspect the surface and damaged
area. Often other parts are affected as well. Occasionally the crack continues invisibly under the
surface. Classify damage using paragraph 2. DAMAGE CLASSIFICATION.
All repairs must be carried out with care and precision. The exterior surfaces of composite airplanes
are load carrying members. A failure of this structure can lead to a plane crash.
The resin-hardener mixture ratio must be adhered to exactly (± 0.5 %), and clean containers must be
used. The ratio between the weight of the glass fiber cloth and the weight of the resin should be
approximately 50 : 50. The damaged area must be sanded immediately before applying the wet
laminate to prevent dirt from entering that might inhibit a strong bond.
As in the case of plywood, the orientation of the individual cloth fibers (lengthwise or diagonal) is of
great importance for the strength of the structure. The number of layers required to rebuild the strength
of the damaged area can be determined from the layup drawings. It is necessary to determine the
remaining number of layers in the damaged area in order to arrive at the original number of layers.
In any case, the thickness of the damaged laminate must be measured. If a small piece is broken off
the damaged area and set on fire, the resin burns, and the remaining layers can be counted and their
type determined.
Even though chamfering is time-consuming, the area must be sanded down far enough to ensure that
the new cloth layers are flush with the existing contour.
To reduce the hardening time, a fan heater may be used to raise the surrounding air temperature.
CAUTION: EXCESSIVELY HIGH TEMPERATURES CAUSES THE FORMATION OF
LARGE AIR BUBBLES IN THE CLOTH. LOCAL EXCESSIVE
TEMPERATURE CAN BE AVOIDED BY USING A FOIL TENT GUIDING
THE FLOW OF THE HOT AIR. THE INDICATED CURING CYCLE MUST
ALWAYS BE ADHERED TO. THE PRESCRIBED TEMPERATURES ARE
TO BE UNDERSTOOD AS MATERIAL TEMPERATURES. A
THERMOMETER MUST BE USED TO MONITOR THE TEMPERATURE.
AFTER REPAIR WORK ON THE CONTROL SURFACES, THE MASS
BALANCING MUST BE CHECKED.