Building a Coot-A and other adventures in aviation
This evening I’m going over Lycoming Service Instruction 1427B in anticipation of breaking in my Lycoming 0235 in the Yankee tomorrow, following the reconditioning of one cylinder. The document describes the engine break-in procedure in great detail, including ground testing the engine with a test club in place of the prop. On page 3 comes the warning:
WARNING: ENGINE TEST CLUBS MUST BE REPLACED WITH APPROVED FLIGHT PROPELLERS BEFORE FLYING AIRCRAFT.
Umm…right. Got it.
As suggested in the previous post, I did end up building new front and rear baffles for my Yankee. Here is the journey for the front baffles.
First, take a look at these dogs:
The first thing to notice is that the rubberized seals are in abominable shape. They are hard and crumbly. But there is more. Notice the big patch on the lower part of the left baffle. At the top of that baffle there is a big ol’ crack (click on the image and it becomes clear). See that bracket on the upper part of the right baffle? that bracket is just about cracked all the way through. Finally, the original steel staples used to hold in the seals have eaten away at the aluminum they contact. Yuck.
Here is the view from the back side:
The crack in the (now right) baffle is plainly visible. The upper seals are clearly very worn.
The first task was to make cardboard patterns from the baffles and cut out new blanks from 0.032″ 6061-T6 sheet aluminum:
The air duct tube on the passenger-side baffle is rolled into the original baffle. Therefore, I simply cut the original out and reused it in the new baffle:
New cylinder baffles were cut and shaped to closely correspond to the original. These were made longer than the original. Upon final fitting, a 45 degree bend will be put in the ends and the front and rear pieces will be safetied together:
And, of course, a new bracket was bent from 0.04″ stock (7075 T6 in this case):
A few bends later:
The next step was to cut out new seal material. I used a product called Cowl Saver™ from McFarlane Aviation:
I used Avex blind rivets with a sandwich of AN-960-6 washers on the aluminum side and AN-960-6L washers on the seal side for holding the seals on. Cherry rivets were used for holding metal parts together:
The next installment will be the rear baffles, followed by photos of the installation.
