Structural failure due to harmonic vibration

Bertie

2P is twice propeller speed. With two blades it means each blade
caused one of the vibrations points each revolution.

The T-28B (Navy) version had a 1425 HP Wright R-1820. They must have
added some strength to wing for big engine? I never saw what mods they
did to 'A' version to make the 'B' ??????

The AF also modified some A's for VN with the R-1820 (think they were
called T-28D's???)

Long time ago in a far away land )

Big John

*****************************************

On Fri, 9 Nov 2007 00:36:27 +0000 (UTC), Bertie the Bunyip
wrote:

Big John wrote in
:

Bertie

I did some service testing at Edwards on the T-28A. Things found
there. Bird had a bad 2P vibration in cockpit. Was caused by each of
the big wide blades of prop blowing big chunk of air back on the
original canopy which was much taller that the one ending up on bird.
Felt like sitting inside a base drum.


OK, you're going to have to tell me what 2P means...

A C-47 or T-29 (forget which one) 3 blade'd prop was cut down to the
correct size and the three thinner blades cured the problem but Aero
Products had completed their order for the big fat props and they were
in storage in a warehouse so it was felt too expensive to can them and
put new props on bird.

Also the engine was a 7 cylinder 800 HP Wright and not the smoothest
running engine ever built. Almost 115 HP per cylinder. Chug,
chug,chug.

Oh, OK, I thought they had 1830s or R2000's In fact, didn;t they
eventually go to R2800's with them? an awful lot bigger than a T-6 for a
"mere" 800hp.

I ferried one of the first group (5) of birds delivered to the USAF
from LA to Enid, OK. Willie refused to accept the birds like they were
scheduled to due to the prop problem. Give to the multi engine school
)

We didn't have much trouble with the T-6 and students. When we finally
got the T-28A at Willie (after they machined the crank) there were
several wings bent which would have broken off and crashed if plastic.
I like metal wings.

I like wood ones!


Bertie