T-34 question

[pmanton]

Due to the recent posting of a T-34 crash, I was reminded of something concerning the T-34 that I have wondered about,
The T-34 rudder has a small triangular section cut out at the bottom. When the plane is converted for civilian use that triangular section is filled in with a piece that is riveted to the tail cone.
Why? What difference does that small piece make?

Thanks

 

[Spring Ford]

Perhaps at some point someone became concerned about the spin characteristics?

Also according to Wikipedia - Civilian fleet was grounded 2004. Fully restored to flight status 2011. Mainly structural changes were made. I have no idea if this might have been one of them.

One from Wiki.


Red Bull one.

 

[Pinecone]

Hard to tell due to people painting planes all sorts of schemes, but it may be an A versus B model thing also.

A number of differences. Starting with the B having 1 degree more dihedral. It really makes them feel different in roll.

 

[midwestpa24]

Perhaps at some point someone became concerned about the spin characteristics?

Also according to Wikipedia - Civilian fleet was grounded 2004. Fully restored to flight status 2011. Mainly structural changes were made. I have no idea if this might have been one of them.

One from Wiki.
View attachment 130045

Red Bull one.View attachment 130043

If I remember right, that grounding and subsequent ADs had more to do with wing spars failing. T-34s were a popular choice for companies offering "dogfighting experiences" to the public until several lost wings due to over stressing. Most of those outfits have switched to Extras or other aerobatic aircraft.

 

[Pinecone]

The AD for the wing spar was in 1999 and did not ground the planes. You had to adhere to new operating limitations (lower Vne, low max G, and no aerobatics) until a spar inspection with eddy current was performed. Most planes were modified so as to not need the inspection.

Later there was a ground AD that was due to the carry through structure. A couple of different fixes were developed to get the planes flying.

For the first one, the AD was due to a single spar failure during flight. Based on the video tape that was recovered, the plane exceeded 12G while in a hard roll. Inspection found some cracks on other aircraft. A finite model analysis determined that if there had been no cracks, that spar would not have failed. Even though it was subjected to double the symmetrical G limit AND rolling.

A second plane (at another company) had a spar failure, but it is likely that they were not adhering to the revised limits.