Friday, June 17, 2016

FF-1202 Pitot Tube Instillation Completed

Wednesday and Thursday the FF-1202 pitot tube assembly was worked on and finally installed. Assembly of the pitot begins by placing tape on the FF-1202 pitot tube 1 ¼" inch in from the threaded end of the tube and screwing the pitot into the FF-1201 pitot block until the tape touches the block so alignment marks can be made on the tube and the pitot block.
Placing a tiny alignment mark on the threads and the pitot block.

The above procedure is used for properly positioning the pitot tube in the pitot block so a dimple can be drilled into the pitot tube. To drill the dimple a #36 drill bit is inserted through the screw hole in the pitot block until it touches the pitot tube. A pile of washers are slipped over the shank of the #36 drill bit until the flutes are completely covered with washers. A drill is slipped over the shank of the drill bit and pressed onto the washers as the chuck is tightened down.
A pile of washers is placed over the #36 drill bit until the flutes are completely covered.
With the pile of washers still in place on the drill bit’s shank, the drill’s chuck is pressed against the washers and tightened down on the #36 drill bit.

Next, only one of the washers is removed and the pitot is then drilled. By removing the single washer, the drill bit will only slightly penetrate the pitot tube making a small dimple in the pitot tube. This dimple is then used as a centering dimple for a larger #29 drill bit. This is where the wheels fell off Wednesday … in that, the DOG Aviation procurement department dropped the ball a few years ago when ordering all of the required drill bits for the project and apparently failed to order a #29 drill bit. Drilling the pitot tube was put on hold but the FF-1201 pitot block was installed on the backside of the gear box with two cap screws and then safety wired.  The cap screws are to be made finger tight, then given another ¼ turn with a 5 mm Allen wrench and safety wired. Once the pitot block is installed, a long screw is run down the #36 hole in the top of the block to self-thread or “tap” the block. The long screw will be used to lock the pitot tube in the pitot block.
Running a long screw down into the hole in the top of the pitot block to self-thread or “tap” the #36 hole.

Savvy builders may have noticed the mistake made while safety wiring the nearest cap screw shown in the photo above … the wire coming up the side of the screw head should pass behind the wire coming up through the hole in the cap screw and not in front of it. Caught the error, removed the safety wire and reinstalled it correctly.

Thursday, armed with a #29 drill bit the final step to prepare the FF-1202 pitot tube for final assembly was completed. The tiny dimple made in the pitot tube the previous day is to be used as a positioning dimple for the #29 drill bit. This next step requires going slow … very slow! In a nut shell, the #29 drill bit is used to continue drilling the FF-1202 pitot tube to create a recess for the locking screw to seat into … which will prevent the pitot tube from turning. The goal is to stop drilling the recess just before the pitot tube is breached. This requires shining a light inside the pitot tube and continually looking inside the tube until the metal can be seen distorting just prior to the drill bit coming through. Fortunately, I was able to stop when a tiny spot appeared on the inner wall of the pitot tube and did not breach the tube.
The setup used for drilling the #29 recess into the FF-1202 pitot tube. While looking up inside the tube with a light, small amounts of material were drilled away until the metal could be seen beginning to distort as the drill bit became close to breaching the pitot tube.
Completed recess for the locking screw … accomplished without breaching the pitot tube.

Once the recess for the locking screw is completed, the pitot tube is slipped inside the center hole in the propeller flange and threaded into the FF-1201 pitot block until the previously made alignment marks align and then the locking screw is snugged up against the recess in the pitot tube. To complete the instillation, the FF-1216 pitot line previously installed across the top of the engine is cut to length and slid half way into a 1" coupler sleeve, then the coupler sleeve is slid onto the aft end of the FF-1202 pitot tube.
A 1" coupler sleeve is used to join the aft end of the FF-1202 pitot tube and the FF-1216 pitot line together.

The coupler sleeve needs to be safety wired to the pitot tube and line with a double wrap of safety wire as shown in the photo of the plans below. Builder tip: Rather than trying to fish the safety wire around the sleeve/pitot tube assembly in such tight quarters, consider tightly wrapping the safety wire around a scrap piece of tubing then sliding the pre-formed safety wires over the sleeve then twisting the wires tight using safety wire pliers.
Two pre-formed safety wires that will be slid over the sleeve and twisted tight to compress the sleeve onto the Ff-1202 pitot tube and FF-1216 pitot line. Forming the safety wire in advance is far easier than trying to fish the wire around the sleeve in such tight quarters.
Shaping the two pieces of safety wire around a piece of scrap tubing then slipping them over the 1" coupler sleeve worked out great! Fast and easy.

By having the pitot tube extending so far in front of the engine, until the prop and spinner is installed, a lot of care will be needed every time the front of the engine is passed by so as to not become a victim of the pointy pitot tube.
The eagle has just grown a very pointy beak begging to rip skin from any who dare get too close and let their guard down. A lackadaisical passerby WILL be punished!