“XP-82 Restoration Project”
#44 83887 Twin Mustang Progress Report
What a wonderful year 2008 has been!
|Lefthand aft fuselage|
The XP project is on or a little ahead of schedule. The wing spar scenario for the center section started out quite ugly as to cost, but, I have resolved the cost issue quite uniquely. Instead of using extrusion dies for all four spar caps at a cost of $38K+ with 1600 lbs. of useless scrap aluminum left over, I decided to purchase seven 4” x 6” x 19’ billets (the aluminum order of 2024 T 3511) and have Peter Lesche, a first class machinist, cut and mill the spar caps out of the billets.
Two caps are able to come out of one billet, and the other two will require one billet each due to cross section size. This leaves us with four remaining billets to make most of the rest of our angles, arms, bellcranks, hinge brackets, etc., etc., out of the remaining aluminum. Peter used to work for me in Florida during the entire Collings B-24 restoration where I learned his outstanding machine shop abilities.
I am choosing him over the other machine shop we are using because he has a new computer mill large enough to bolt down a battleship to it (not quite). But it’s real big, making the 19’ cuts on the spar caps much more efficient. I estimate, including his shop charges, that we will come out with a much better price and minimum scrap than if we used the extrusion die method.
|Duplicating fuselage parts|
Explanation of Extrusion Dies versus Milling of Billets
The most efficient method to manufacture spar caps would be the extrusion method if we needed multiple feet or pieces of one cross section. The problem is that we need only one 19’ section of each of the four cross sections--way below the forging company’s minimum order.
During the extrusion process, the forging company must use a large log-shape of partially molten aluminum and push this log through an extrusion die, and out the other end comes the shape of the desired spar cap. This rough spar cap will require additional machine work for final size and shape.
The foundry also charges an enormous price for the dies because they know we must have them! $3,800 each for the three small spar cap dies and $8,900 for the one large die which drives the end cost ot over $38K plus the finish machine work. The foundry also requires a minimum weight order which gives us a huge amount of scrap left over in sizes that we cannot use. I asked about changing the dies during the push or just using a small amount of aluminum to start with, and both replies were that they could not.
|More duplication forms & parts|
So, I chose our second option of buying the 4” x 6” x 19’ billets, cutting and milling our four spars and the multitude of additional required parts out of these billets--in the long run, saving us a substantial number of dollars. A $20K down payment has been paid to Sigma Aerospace with delivery scheduled for late February or early March at which time the billets will go to Peter Lesche in New Jersey for the required machine work.
We have started duplicating all of the aluminum parts in the lefthand fuselage. We are also now heavy into making the wood forming blocks for all of the fuselage ribs. These are male press blocks made out of high density fiber board and mult-laminate fir plywood glued together. Duplicating each part takes five steps:
Step 1: A 40-ton hydraulic press is used to press a 3” thick slab of medium
density rubber down on the new piece of rib sheet metal and over the form
block. The sheet metal part will conform to the male block almost precisely.
Step 2: We do a little additional hand forming.
Step 3: We send the part off for heat treating. It comes back to us in dry
ice and we final fit the part to the location as the heat treat process tends to
lightly warp the part.
Step 4: After the final fit, a 72-hour air quench at room temperature allows
the part to reharden to 2024 T-3 temper, which is our final desired hardness.
Step 5: Now we drill all of the required holes as the heat treating tends to
shrink the part slightly. This is why we must wait on the holes till the end.
While in Florida this part week, I met with Rick Reeves and inspected his work on
the outboard flaps that he is doing for us. And, as always, his workmanship is excellent.
Please see the attached pictures of the new manufactured aluminum parts, the wood patterns, the fuselage with all of the aft ribs removed to make patterns from, and other miscellaneous shots of the great progress the crew has made this past month.
I am going to Tehachapi, CA, 8 January 09 to inspect progress on our two Merlin engine overhaul.
|Oak Form Blocks|
We were able to complete our labor force by hiring Barry Hutton part-time. He is an extremely experienced metal bender (parts fabricator). He works full time for Pratt & Whitney Engine Division and comes to work for us on his days off. We now have a crew of eight: Dwayne Branch, Chuck Cecile, Jason Cecile, Paul Flora, Barry Hutton, John Marshall, Weezie Barendse and me.
Bumps in the Road
One minor. One of the lower longerons salvaged out of the Colorado parts had a corrosion spot which looked minor until we ground it out. The spot went almost all the way through, scrapping the piece. It could be repaired, but not on this unique restoration. I will use part of one of our 19’ billets to mill a new one.
Everyone is off for the holidays with the exception of John Marshall, who is continuing to make wood patterns, and Kleko, the cat, who is keeping track of the work progress.
Merry Christmas & Happy New Year to Everyone!