The aft side of the F-1204 center section gets the F-1204D center section aft bulkhead and F-1204F-L&R aft side bulkheads riveted onto it. The instructions call for the builder to use various rivets depending on location … however, noticed the AN470AD4-4 rivets called out for the F-1204F aft side bulkheads were a tad short … had the necessary half size in stock, so they were substituted with AN470AD4-4.5 rivets that were on hand making for the perfect length. The plans have the builder placing four LP4-3 rivets in the lower four rivet holes on each F-1204F aft side bulkheads … I was able to get solid rivets into all but two rivet holes on each of the F-1204F-L&R aft side bulkheads ... the remaining two rivet holes were so close to the center channel the rivet squeezer could not get close enough to be square on the rivets.
Setting the F-1204D center section aft bulkhead in place to be secured with Clecos.
About to Cleco the F-1204F-L aft side bulkhead onto the F-1204 center section assembly.Riveting the F-1204F-R aft side bulkhead onto the F-1204D aft bulkhead with slightly longer AN470AD-4-4.5 rivets which provided for a good shop head.
While attempting to squeeze rivets at the locations where there were three layers of metal, a small issue with the pneumatic squeezer came to life. It did not have enough power to squeeze the quite long AN470AD4-9 rivets. The issue is no fault of the pneumatic squeezer … it’s the way I have it configured. First, I like having an adjustable swivel/air valve on the end of the air hose. It can be used to slow the speed of the air drill for countersinking and deburring with the Scotch-Brite wheel or as a safety device for cutting off the air to a tool while changing drill bits, countersink cages, rivet sets, dimple dies, etc. While setting solid rivets with the pneumatic squeezer into the wing’s ribs, I found it necessary to add a second swivel to gain more clearance for the hose … but did not have a swivel only attachment, so a second air valve/swivel was attached onto the squeezer. Each of the air valve/swivels (even with the air valves full open) drop the pressure to the squeezer. This has not been an issue since the vast majority of the rivets so far have been a size 5 or less. But when squeezing rivets the lengths of 9 or 10, the reduced pressure won’t let the pneumatic squeezer develop enough power to set the longer rivets … with the current configuration a length of 8 appears to be the upper range. Not wanting to take the time to reconfigure the air hose or squeezer, the dust was blown off the hand rivet squeezer which ultimately did a great job of setting the longer rivets.
Using the hand rivet squeezer for the first time on the RV-12 project to set AN470AD4-9 rivets into the center section. It did a fine job!
After the F-1204F-L&R riveting was completed, the row of rivets securing the F-1204D aft bulkhead onto the F-1204 center section channel were riveted with AN470AD4-8 rivets on the left side and AN426AD4-8 flush rivets on the right side (think the flush rivets are for fuel tank clearances). Both of these rivets are also somewhat shorter than optimum for the location, so the shop head is smaller than ideal. Extra care was taken to not mar the paint while setting the flush rivets by using riveting tape to protect the paint.
Riveters tape placed over the AN426AD4-8 flush rivet to protect the JetFlex paint while setting the rivet.
The riveters tape did a marvelous job of protecting the JetFlex paint. Riveters tape has no adhesive in the center but has adhesive on the outer edges. Its true purpose is to allow for back riveting of flush rivets. Flush rivets are placed into dimpled or countersunk rivet holes on a part. The part is then turned upside down and placed on a back riveting plate and the ends of the rivets sticking out of the backside of the part are pounded with a rivet gun from behind to form the rivet shop head, hence the name, back riveting. The tape has a two fold purpose … it prevents the rivets from falling out when the part is turned upside down and because there is no adhesive in the center of the tape, there is no adhesive to get mashed into the rivet joint. Riveters tape can also be used to protect a painted finish while setting a rivet with a pneumatic squeezer with flat sets ... which is why I used it to protect the JetFlex paint on the F-1204D center section aft bulkhead.
Riveters tape - available at Avery Tools and other fine aircraft supply businesses.Using the pneumatic squeezer to set an AD426AD4-8 flush rivet into the F-1204D aft bulkhead making it one with the F-1204 center section channel. Riveters tape is being used to protect the JetFlex interior paint.
The last parts to complete the center section assembly are skin stiffeners, which are components of Service Bulletin 12-11-09. This service bulletin addressed two issues … it beefed up the landing gear mounting and also improved load distribution to the airframe. The four parts added onto the center channel during the work session are part of the load distribution component. The F-1204T-L&R and F-1204U-L&R stiffeners are added above and below the center channel with strong CherryMAX rivets which, in theory, are slightly stronger than a solid rivet. Of course, my center channel came with the mounting holes predrilled on the outer edges for the stiffeners, but my hat goes off to those builders that added this retrofit after the aircraft was built, I can tell that feat was not an easy task to be sure.
F-1204T&U stiffeners … part of the Service Bulletin 12-11-09. The stiffeners are to be installed above and below the outer edge of the center section channel.
Riveting the F-1204T-R and F-1204U-R stiffeners onto the F-1204 center section channel using CherryMAX rivets … a portion of Service Bulletin 12-11-09.
After completing the riveting of the F-1204T-L&R and F-1204U-L&R stiffeners onto both sides of the F-1204 center section channel, the center section assembly was completed and with that, Section 20 of the plans as well.
Completed Section 20 center channel assembly.