Loading retardant onto the S-2 is a reasonably simple process. The yellow hoses in the photo are called pit supply lines, running from the storage tank to a high capacity, high volume pump. Each storage tank has it’s own pump. TL Stein tells me that “as the pump pulls the retardant from the storage tank it sends it into the pit supply line.” Once the pit supply is fully charged, the black loadout hose (see picture) is connected to the hot load at the tail end of the aircraft (see photo). The gate valve at the end of the load-out hose is gradually opened allowing the retardant to flow into the tank on the aircraft. He explains how they know when the tank is full:
On some of the S-2T’s, there are a series of loading lights on the right side of the aircraft that light up to indicate how full the tank is getting. On others a mass flow meter is watched to indicate how much retardant has been pumped into the aircraft. As the aircraft fills, it will tend to settle due to the addition of weight and the tail will drop about six to eight inches. This settling action is not slow, but a rapid drop and signals the loader that the aircraft is getting close to full. When this happens, the loader will close the gate valve about halfway until either the full light lights up or the mass flow meter reads the desired amount of retardant has been pumped into the aircraft.
After the aircraft has been filled, the gate valve on the loadout is closed and the hose is disconnected from the aircraft. The ground crew leaves the area, and the plane is ready for take off.
Take a look at the annotated close-up of one of the panels in the cockpit. I will be talking more about the controls on this panel in my next post. On the top right, is a switch labeled “open - closed control for tank backflow valve.” This valve, also known as a flapper valve sits between the retardant tank and the hot load. To put it simply, the flapper valve seals the system. It serves three important purposes: (1) the valve is open when retardant is being loaded into the tank (2) when closed, prevents retardant in the tank from flowing back to the rear of the plane to the fill point, and (3) is left open when the retardant tank is washed out at the end of the season or when maintenance is necessary (more on this in a later post).
Recall from the post on S-2T specifications that the S-2T holds 1,200 gallons of retardant. There are times when the retardant tank will not be filled to capacity. One of these times is when it is very, very hot outside. TL Stein tells me that Ryan sits in a large basin, and when it is hot, it is very, very hot at Ryan. During times like this, the air density is lower. And when the air density is low, heavy airplanes do not fly very well. So, on a really hot day, the weight of the air tanker needs to be lightened. So, less retardant will be put in the tank on the S-2T. Retardant weighs about 8.5 pounds a gallon. Filling the tank with 1,000 gallons of retardant instead of 1,200 gallons saves 1,700 pounds. Lowering the weight of the air tanker by 1,700 pounds on a really hot day, according to TL Stein, makes a huge difference!
Still to come in this series of posts on the S-2T are (1) the retardant drop; (2) videos of the S-2T making retardant drops, and (3) cleaning out the retardant tank at the end of the season.
No comments:
Post a Comment