Fuselage Frame Repairs


When N-5490 was surveyed at at Harvey Field before being rescued, slack fabric was noticed on the port side of the fuselage.
A closer inspection revealed that there was a bent vertical tube in the port sideframe, caused almost certainly by a heavy landing.
Once dismantled, the full extent of the damage was apparent - the main 7/8" square tube directly above the port undercarriage
compression leg was bent and the 7/8" circular tube immediately forward of this member was split just under the top rail.
Described here is the method of repair employed.


N-5490 being de-rigged at Harvey Field during recovery.  Note the slack fabric just under the front cockpit door - a sign of serious damage beneath.

A closeup of the slack Ceconite.

Hidden horror.  The cause of the slack fabric was found to be this bent main vertical member in the port sideframe
directly above the port undercarriage compression leg.
There was clear evidence that the fabric had been opened up in this area and then patched, so the conclusion must be that
this Tiger had been flown in this condition for some time!
The wooden front seat frame bolts to this vertical member and was also found to be damaged, so a new seat frame is being made.

The replacement section salvaged from an otherwise damaged sideframe.  This section will be welded into the port sideframe.
Note that the vertical member has a round 3/4" 4130 steel tube inserted.  Once installed, this vertical member will be
far stronger than the original.

From the Tiger Moth Maintenance and Repair Manual, these are the various fishplates to be used in the repair of Tiger Moth fulseage frames.

These are some original DH repair fishplates that will be used to weld in the repair sections.  The three fishplates at top right are 20 SWG and used on the top longeron (H35774 Mk. 1).
The two lower fishplates (H35774 Mk. 2) are the heavy duty 16 SWG plates that will secure the vertical square member.  The two 3/4" diameter round fishpates (H35771) at top left
will be used to replace some 5/8" tubes in the rear pylon, and the flat plate (35773 Mk. 2) will be used to repair a small dent in one of the engine bearers.
These fishplates are the totality of original plates that could be found during a worldwide search.  Additional plates needed to complete the repairs have been made
to the specifications in the Repair Manual from 4130 steel plate and tube.
During the repair process, the two sideframes will be bolted directly together to make sure that there is perfect symmetry between the two frames.

A correctly executed weld repair of another Tiger Moth fuselage frame showing the pair of fishplates in place.

Once the rear fuselage had been stripped of fabric, this damage was discovered in the aft bay of the rear pylon.
Two of the 5/8" diagonal tubes were found to be badly bent.  Luckily there was no damage to any of the surrounding structure.
How these tubes became bent in this manner is a complete mystery.  However, before the fabric was removed, a pair of
large patches were noted in the area of the damage, indicating that someone in the past knew of this damage, opened up the fabric
to inspect, and then decided to leave it and patch the fabric!

The bent tubes have been cut out and replacement 4130 steel tubes have been prepared to weld in place using the fishplates discussed above.
(After this photo was taken, the stub ends of the cut tubes were carefully re-aligned.)

Once these welding repairs have been completed, the fuselage frame will be finished in interior grey/green ('cockpit green') and re-assembly will commence.


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