Unbraced tailplanes Bf109F-1

[Paul Wicht]

I have an old Anthony Pritchard Messerschmitt book from 1975 that mentions on page 60 the unbracing of the F-0 and F-1 tailplane that ultimately caused several fatal crashes in tests.

Is this structural error be the fault of engineers trying to make the tail lighter or more rigid? Or does this have to deal with the rudder?

[klemchen]

Hello Paul,

I will try to give an answer. - To understand the problem one has to be aware that for the transition from the "angular" to the "rounded" Me 109 the whole tail section underwent considerable constructive changes:
On the angular models the empennage bearer (i.e. the rearmost section of the fixed fuselage) was simply a geometric extension of the rear fuselage. To that the fin was attached; therefore the (rather high positioned) tailplane had to be made in two halves, which were attached to the fin seperately. Since the angle of incidence of the tailplane was to be adjustable in flight these halves had to be braced additionally to the fuselage by two struts.
On the rounded models the empennage bearer was heightened to the level of the tailplane (which remained in its position), with its upper portion simultaneously forming the lower part of the fin. Therefore the tailplane now could be made in one piece and be attached on top of the empennage bearer, so the bracing struts became unnecessary.
Now the reason for the tail failures on several early F aircraft does not seem to be in the empennage itself but rather in the way of fixing the empennage bearer to the fuselage (which indeed incorporated an engineering fault, being too sensitive towards certain vibrations which could arise under certain conditions). This weakness was remedied temporarily by adding four external strips connecting the empennage bearer with the fuselage; later on (still during F production) these strips could be omitted again because the attachment of the empennage bearer was strengthened internally by adding four connecting bolts.

Regards,
klemchen