DC-7 tanker: revisiting ballast, weight and balance, and fuselage stations

Some of you may remember the series on the DC-7 tanker that I wrote last December, with the help and cooperation of Larry Kraus. Recall that Larry has been the pilot-in-command of T-62 for 27 years. One article in that series was an article that I wrote on ballast.

I am writing this article to follow-up on that article on ballast that I wrote last December with some information that Larry sent me in e-mail a few days ago. But first, let me review and summarize weight and balance.

All airplanes, large and small, have weight and balance limits that are set by the manufacturer and periodically checked by airframe and powertrain (A&P) mechanics. It is crucial that all airplanes must be within these weight and balance limits for safe flight. Every airplane has a center of gravity (CG), the point at which the plane is perfectly balanced. If you will, you could suspend the airplane from a string at the CG and the plane will be level. A plane with weight distributed too far forward will result in a nose down condition and if the weight is distributed too far aft (in the rear) will result in a nose up position. Both conditions can have fatal consequences for the crew.

In order to bring the airplane, in our case, the DC-7 tanker within her weight and balance limits, ballast is secured at carefully designated stations, known as fuselage stations. Fuselage stations are measured from a point known as a datum (aka fuselage station zero).

When I wrote the article on ballast as applies to the DC-7 tanker last December, Larry wanted to show  you a graphic from one of his DC-7 manuals showing the location of the datum and the fuselage stations in the DC-7 tanker. The problem at the time was that the manual that Larry needed was on a laptop that was comatose at the time, so he was unable to share the fuselage station diagram. The only manual that he had was a Douglas manual for a very early DC-6, showing the datum at a different location. Larry's comatose laptop revived, at least temporarily, a few days ago and Larry sent me a copy of the fuselage station diagram for the DC-7 tanker. You might want to click on the image below to enlarge the image for better viewing.

I'll let Larry explain:

It turns out that I was right about the location of fuselage station zero after all.I was sure that it was the front pressure bulkhead in front of the cockpit.As the radome nose on the DC-7 was an option and was several inches longer than the stock metal nose,I couldn't understand how the end of the nose could be the reference point.The early DC-6 must have been different than the later DC-6 and the DC-7.The DC-6 didn't add weather radar until later in production.The only reference picture that I had without the DC-7 manual was a Douglas manual for a very early DC-6.