Flying Fires -- Fog, Smoke, and VFR or IFR: Inversions

Cold air is denser and heavier than warm air, so cold air sinks and warm air rises.

In a normal airmass, the air cools as altitude is increased. That is, the air is cooler aloft, and helps to move smoke and pollutants out of valleys. An inversion is the opposite of a normal airmass. In an inversion the air aloft is warmer then the air near the ground. Remember that cold air sinks, so the warm air aloft acts like a trap door, trapping the cool air below.

If the airmass is holding enough moisture, fog will form in the inversion because the temperature of the air near the ground is at or near the dewpoint. Smoke and pollutants sitting near the surface are trapped in an inversion.

Like clouds and fog, inversions inhibit visibility, hampering VFR operations.

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Note (added July 2012): I'd like to thank a couple of my tanker pilot friends whom I corresponded with as I was preparing the articles in this series for their time and help. Here is a complete list of articles in this series with hyperlinks:

1. Introduction (Jan 4)
2. VFR, I can see (Jan 6)
3. IFR, I can't see but I have instruments (Jan 8)
4. Fog (Jan 11)
5. Inversions (Jan 12)
6. Flying fires: VFR or IFR? (Jan 13)
7. Reflections (Jan 18)

Flying Fires -- Fog, Smoke, and VFR or IFR: Fog

Low clouds that form below 6,500 feet above ground level often reduce visibility thus making VFR flight impossible. There are different types of clouds, forming at different altitudes. If you read a book geared for student pilots, you are likely to find a discussion of different types of clouds. I am not going discuss these different types of clouds here, but if you are interested, NOAA has a nice website on cloud classification that may be found here. For a discussion of cloud types for aviators, The FAA's Pilot's Handbook of Aeronautical Knowledge is available online. Their chapter on weather, which is found in chapter 11, includes a nice discussion of cloud types with some nice pictures.

Low clouds, those that form below 6,500 above ground level (agl) often reduce visibility making VFR flight impossible. Fog is one type of low cloud, and I am going to discuss fog in a little more detail. Fog typically forms when the air temperature near the ground is at or near the dew point. The dew point is the temperature at which the air can hold no more moisture. I found out recently that there are five, no six types of fogs. For those of you who are familiar with discussions of fog, I am using the six types of fogs as referenced in the glossary (under F) of weather terms from the Mt. Holly office of the National Weather Service.

I'll start with the sixth type of fog, ice fog. Ice fog forms in very cold temperatures, e.g. 25 to 30 degrees (F) below zero. It forms in conditions similar to radiation fog (below). Because it forms in such cold climates, ice fog is generally not a factor in aerial wildland fire fighting.

Radiation fog frequently forms at night when the ground is still warm and moist radiates against cold air near the surface. It frequently forms in mountain valleys. As the sun rises and the temperature increases, the radiation fog burns off.

Advection fog forms somewhere else, usually over water when warm air moves over the cooler surface. Wind moves the fog over land.

Sea fog occurs when a very cold and dry airmass moves over warmer water. As the water evaporates, it rises forming fog. Sea fog is then moved along by the wind. Sea fog is sometimes referred to as sea smoke or steam fog.

After a heavy rain, often near a warm front, precipitation or rain induced fog will form. In this case, the atmosphere is saturated with moisture and little if any cooling is required. G, a former air tanker pilot and certified flight instructor offers this observation about precipitation induced fog:

These are the "water dogs" seen rising out of the tree tops after a heavy rain. They are frequently mistaken as smoke by over zealous look-outs in the forest.

The final type of fog is upslope fog. It forms when a moist airmass is forced uphill by wind and the up sloping topography found in areas such as hills and mountain ranges. As the air expands and is forced uphill into the cooler air upslope, the airmass cools to the dew point forming fog.

Why are these different types of fog important to aviators? G explains:

The reason you might want to know the six reasons fog will form is so that you can predict it and decide if its potential will affect the safety of your flight. Fog is fog, but it forms in very predictable circumstances. For example, "It rained like hell this morning, but it is clear and calm this evening. I think I'll go up for a sunset flight and just have some fun." That little scenario is setting you up to where you might not be able to land back at your home port because it fogs in while you are up enjoying the sunset. Did you bring along enough gas to get to a safe place to land? That alternate airport might be a long way away.

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Note (added July 2012): I'd like to thank a couple of my tanker pilot friends whom I corresponded with as I was preparing the articles in this series for their time and help. Here is a complete list of articles in this series with hyperlinks:

1. Introduction (Jan 4)
2. VFR, I can see (Jan 6)
3. IFR, I can't see but I have instruments (Jan 8)
4. Fog (Jan 11)
5. Inversions (Jan 12)
6. Flying fires: VFR or IFR? (Jan 13)
7. Reflections (Jan 18)

Flying Fires -- Fog, Smoke, and VFR or IFR: IFR, I can't see but I have instruments

IFR aka instrument flight rules, means that the pilot can not see because conditions are below the minima to allow for visual flight rules. Literally.

A few months ago, I purchased a small scanner and began finding and then listing to the radio frequencies used by near by air traffic. Most of these conversations are one-sided, pilots only, because air traffic control is too far away for my little scanner to pick up. One day soon after I got my scanner, there was a pretty significant rain storm going on. It was clear to me that the pilots I was listening to were not able to see, so had to be flying under IFR. One pilot came over the scanner asking "what's going on down there?" Meaning she may have been asking the controller what she might expect when she reached her destination airport. Or perhaps she was just curious. I could not hear the controllers response, but did hear her say thank-you. A short time later, I heard another pilot ask the same question.

I recently found out IFR student pilots use special glasses where the lateral and forward vision is clouded leaving only clear vision for the instruments. One brand name is foggles. Unless they cheat, wearing foggles means that they can not see out side the cockpit, and must rely on their instruments. Of course, the plane must have IFR instruments that include navigation equipment, one example being a Garmin GPS.

Flying under IFR means that you can fly a plane in or above the clouds. You navigate by flying from way station to way station. Each way station is assigned a specific radio frequency. As I understand it, the pilot tunes the navigation equipment, e.g. garmin GPS, to that radio frequency. Using the instruments in the plane you fly towards that way station. When you pass that way station, you get the frequency for the next way station from your flight plan, which may be on a knee board in your lap and fly towards that way station.

Finally, you are ready to approach the airport where you will land, with what is known as an ILS (instrument landing system) runway. You continue to fly from way station to way station until you reach the assigned frequency for the final runway approach. You pop out of IFR at about 200 feet above the runway, on final approach. When you pop out of IFR, you will be lined up with the extended center line of the runway. (Yes, there is a line down the middle of the runway.) Since you are already lined up with the extended center line of the runway, you do not have to maneuver at low altitude. You make the actual landing under VFR. Many GPS devices used in IFR planes will have these ILS approach plates loaded into memory, when you pass one way station, the GPS finds the next way station from memory and so on up to and including the final ILS approach.

I learned about these way stations, by the way, by listening to my scanner. I often listen to the band used by planes approaching and preparing to fly through the NY airspace in the vector over my house. To give you some perspective, I live on the edge of the class B airspace surrounding Newark-Liberty International Airport. Thanks to my copy of the sectional map covering this airspace, I learned that one of these way stations is located only a few miles from my house.

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Note (added July 2012): I'd like to thank a couple of my tanker pilot friends whom I corresponded with as I was preparing the articles in this series for their time and help. Here is a complete list of articles in this series with hyperlinks:

1. Introduction (Jan 4)
2. VFR, I can see (Jan 6)
3. IFR, I can't see but I have instruments (Jan 8)
4. Fog (Jan 11)
5. Inversions (Jan 12)
6. Flying fires: VFR or IFR? (Jan 13)
7. Reflections (Jan 18)

Flying Fires -- Fog, Smoke, and VFR or IFR: VFR, I can see

Look at the term, visual flight rules (VFR), it means that pilots can see when minimum visibility requirements are met. These minimum visibility requirements (visual meteorological conditions) -- visibility, distance from clouds, ceiling -- vary by the class of airspace you are flying through.

I have read enough materials geared for student pilots to know that all pilots begin by flying under VFR. When pilots first obtain their private pilot's certificate, or sports pilots certificate they are restricted to flying under VFR. Some where along the line, I learned about "see and avoid". This means a pilot flying under VFR pays very little attention to the instruments in his/her plane. Rather they are constantly keeping their eyes focused on what is ahead. For example, you see another aircraft and avoid. Before flying you plan your route, looking at sectional maps where obstructions are mapped along with their height and plan to maintain a minimum required height above the obstruction (tall buildings, antennas, mountains, utility wires, etc.).

You may still be navigating using radio beacons or NavAids, but you can see. For example, charts used by VFR pilots in their flight planning may include charts depicting visual approaches to their destination airport. These charts will include a map and notations such as follow Route 3 (westbound) to Giants Stadium (west of NYC) where you turn north to make your visual approach to runway 1 at Teterboro NJ. Go here to download the chart, Cedar Grove Visual Rnwy 1, that I just described

Just about all planes that VFR pilots use have radio equipment. VFR pilots may be in contact with air traffic control, and when they are they are still seeing and avoiding.

Part of pre-flight planning is checking out weather forecasts to see if weather conditions will allow for VFR conditions along your planned route. Pre-flight planning also involves selecting alternate airports in case weather conditions at your primary airport do not allow for VFR landings. Of course, fog, clouds, etc. create conditions where VFR flight is not possible. These conditions are known as instrument meteorological conditions (IMC) because meteorological conditions -- visibility, ceiling, distance to clouds, etc. -- are below minima for visual meteorological conditions (VMC). IMC, even if there is no precipitation, will ground a VFR pilot. A pilot flying under VFR entering into IMC conditions can not see, meaning that pilots can not see obstructions in their flight path. This can have fatal consequences.

A pilot flying VFR must be flying in VMC in order to see.

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Note (added July 2012): I'd like to thank a couple of my tanker pilot friends whom I corresponded with as I was preparing the articles in this series for their time and help. Here is a complete list of articles in this series with hyperlinks:

1. Introduction (Jan 4)
2. VFR, I can see (Jan 6)
3. IFR, I can't see but I have instruments (Jan 8)
4. Fog (Jan 11)
5. Inversions (Jan 12)
6. Flying fires: VFR or IFR? (Jan 13)
7. Reflections (Jan 18)

Flying Fires -- Fog, Smoke, and VFR or IFR: Introduction

My first memories of fog go back to our family vacations (long before the days of GPS) camping on the Maine coast. Fog was a not infrequent visitor to our corner of the Maine coast. We couldn't see. I still remember the sound of the fog horn from the light house on the island across the way. I knew that fog horn was important to marine interests because it warned of rock outcroppings, shoals, and the like that were shrouded by fog. I continued to run into fog as an adult, most of these encounters were inland. I always try to drive carefully when it is foggy.

I have a few second hand experiences with smoke as a hindrance to visibility, and these experiences. For several years I lived about four miles from an exit to the NJ Turnpike that was near the Hackensack Meadowlands in NJ. See the image below, look north of I-280 and west of the road marked 95 (actually the eastern spur of the NJ Turnpike). You will see a rather large undeveloped area, that is one portion of the Hackensack Meadowlands.

Every so often there would be fire in the Meadowlands that was bad enough to affect traffic on the NJ Turnpike, I-95, and I-280. There may have been traffic accidents on these interstates where smoke was a major player.

But fog, and smoke are not the only hindrance to visibility. Clouds are also a hindrance to visibility for aviation interests. Not having flown on a commercial airliner until I was about fifteen, I never gave much of a thought to clouds as a hindrance to visibility as a child/. I wasn't to fly again until I was in my early twenties. By that time, I saw that planes could and often did fly above the clouds. Sometimes we wouldn't pop out of the clouds until we were getting ready to land. I had a vague realization that the pilots were using instruments, combined with communications from air traffic controllers to navigate. As time went by, I picked up the vocabulary of visual flight rules (VFR) and instrument flight rules (IFR).

After I wrote my article on winds as affects aerial wildland fire fighting, I got interested in the question of fog and smoke as affects these aerial operations. After some e-mails with a couple of my tanker pilot friends, I knew that I had to begin this series by introducing VFR and IFR where I will provide an overview of each. I'd like to thank the tanker pilot friends whom I corresponded with for their help in this series of articles.

Here is a list of articles in this series (revised after the fact to include links to each article):

1. VFR, I can see (Jan 6)
2. IFR, I can't see but I have instruments (Jan 8)
3. Fog (Jan 11)
4. Inversions (Jan 12)
5. Flying fires: VFR or IFR? (Jan 13)
6. Reflections (Jan 18)

Great footage of Airtankers in action

Happy New Year everyone, a couple of days late. A friend told me about this very cool video of a P-3 Orion in action so I am sharing it with you today. Beautiful footage!

Tomorrow, I'll be starting a new series of articles on fog and other visibility concerns as applies to flying fires. Stay tuned.

Addendum: A couple of tanker pilot friends pointed out to me that much of the footage in this video is several years old. But it is a great montage of tanker footage. Enjoy!

Updated on August 3, 2015: The US Forest Service terminated its contract with Aero-Union for their Lockheed P-3's, going out of business a month later. (see my articles of July 30, 2011, August 17, 2011, and January 18, 2012). 

Tanker 9 - Flying in favorable winds

Some of you may remember that I wrote about the loss of tanker 9, a Lockheed P2V Neptune, several months ago. Just last night some e-mail came across my desk that provided me a poignant reminder of tanker 9 and her crew: Gene (Pilot), Gonzo (co-pilot), and Zach (flight engineer). One of the first things that I did this morning was to go back to that post (from April 2009) and watch that video, a nice photo montage of tanker 9 shot at Fox Field in 2007.

So, in memory of tanker 9 and her crew, please take about seven minutes and go here to watch this photo montage of tanker 9. The crew gave it their all. She is flying in favorable winds.

The embedded video shows another Lockheed P2V, tanker 7, taking off.

Australia: bush fires continue

Bush fires continue in Australia. Bill Gabbert of Wildfire Today is reported on these bush fires, yesterday and again today.

Thanks Bill!

Up close and personal with DC-7 tankers: reflections

See, I told you it is complicated, Nothing is ever easy in the tanker business. (Larry Kraus to K. Tyler Miller).

What can I say about this magnificent airplane, her pilots, co-pilots and all those behind the scenes who keep Butler's three DC-7 tankers in the air, flying fires? I can say that I feel an affinity for these tankers because of their original service as commercial airliners. I don't know if I ever flew on a DC-7, but I was a passenger on planes of a similar size and vintage. So, in some sense, even before I began the series on the DC-7, I had a relationship with these aircraft.

What I have gained from writing about these aircraft is a love for these three tankers. Three tankers that I call magnificent. It has been a joy to get to know these tankers up close and personal. I also know that these tankers are loved by their pilots, co-pilots, those in the shop who maintain the planes, and the ground crews. A bond between humans and aircraft that ensures that these fire engines in the sky are flying. A bond that ensures that some of us can get to know these magnificent aircraft up close and personal.

There is a another bond, that is the bond among fire fighters, both in the air and on the ground. I think of this bond as the raison d'etre. Larry speaks of this bond:

We have a bond with the other fire fighters that we work with, both in the air and on the ground. There is a mutual respect similar to that which develops in a military unit that has been in combat. It's always a pleasure to work with people who know their jobs. We all know that we can depend on each other and we do so every day. There's a great deal of satisfaction in being a useful part of that team.

Nothing is simple in the world of flying tankers, those fire engines in the sky. I have learned a lot in writing this series about the DC-7 including but not limited to weights and balances, a view inside the cockpit, quick engine changes (Q.E.C.), and multiple door retardant systems. These are important, but the most important point that I want to pass on to you is what Larry kept saying to me over and over in our e-mail correspondence:

See, I told you it is complicated, Nothing is ever easy in the tanker business.

Larry should know, he has been piloting DC-7 tankers for some 27 years.

Wildfire season in Australia

I don't want to forgot our friends in Australia where it is wildfire season. For example, I recently read about fires that were burning last week in Port Lincoln in South Australia, go here and here for more information. The video that I embedded here, was just posted to Youtube the end of last week with some footage of the Port Lincoln fire.

Still to come on DC-7 tanker series

I took a short break for the Christmas holidays and will be finishing up my series, up close and personal with DC-7 tankers this Wednesday with my own reflections.

Happy Holidays

The Shepard by Fredric Forsyth

A friend of mine told about this wonderful aviation themed Christmas story: The Shepard by Fredric Forsyth as told by "Fireside Al" and broadcast on CBC radio. This same friend sent my a link to youtube where the story is told in four videos with aircraft photos. I post them here with warm wishes to all for a happy holiday season and safe and happy New Year.

part 1



part 2



part 3



part 4

Up close and personal with DC-7 tankers: in action (2 of 2)

When I first wrote this entry in December 2009, there was a very nice 20 minute video on Patrick's Aviation from Bob Webb shot from the cockpit of a DC-7.  The Patrick's Aviation website has since been taken down. So I am embedding a couple of Bob Webb's You Tube videos shot from a DC-7 tanker.

I will never get a chance to ride in the cockpit of an air tanker, but thanks to Bob's videos, I can say that I have experienced what it is like to ride in the cockpit of an airtanker. Enjoy.

I will be posting my own reflections based on my experience writing this series on DC-7 tankers in a few days after the original date of the post (December 23, 2009).

Edited on November 8, 2016

Shot during the 2005 fire season, DC-7 Tanker. pilots are Webb/Rowe. 

Direct link to video by Bob Webb

Shot during the 2005 fire season southwest of Cedar City Utah, DC-7 Tanker. From Bob's description of the video: "flying down into a deep hole to get to the fire, not once but twice!"

Direct link to video by Bob Webb

Up close and personal with DC-7 tankers: in action (1 of 2)

Now for the fun stuff. Here is a sequence of photos (below) of Brian Lash and Rick Langstrom in Butler's tanker 66 on the Deer Ridge Fire near the Medford OR airport on or about September 22, 2009. Mike Bitney took these photos and sent them to Larry. It is a great sequence of photos. For those of you who are interested, here is a link to Warbird Information Exchange (WIX) where Larry posted these and other photos of tanker 66 and tanker 62 in action. There are some other nice action shots on this same WIX thread of tanker 62 in action in 2008 here.

I expect to make two more posts in this series of articles on DC-7 tankers, one more on DC-7 tankers fighting fires and a final post where I offer my own reflections. So, stay tuned. In the meantime, enjoy these photos.

So as not to confuse, the video is taken at Fox Field in Lancaster, CA (probably in 2007).

 

 

 

 

 

 

 

 

 

Up close and personal with DC-7 tankers: retardant drops pt 2 of 2

In my last post, I was writing about the Aero Union multi-door tank system (8 doors) used by Butler's DC-7's. I'll let Larry explain to you the sequence he goes through making a typical retardant drop:

To drop a full load at Coverage Level 6, I would have the co-pilot arm the tank system, and I would set the intervelometer to the 12 o'clock position (1), set the timer to 0.4 and set the doors to open selector to 8. Assuming that we'd gone through the Descent Check List while descending into the drop pattern I should be set. All that I have to do next is to determine the correct place to begin the drop and hold down the drop button (located on the yoke) until all of the doors open.

I know that there are times when tanker pilots must make an emergency drop of a retardant load. If an emergency happens near a tanker base, there is usually a designated place, e.g. coordinates, where emergency drops can be made. Otherwise, the pilot tries to look for a safe place -- no houses, no people on the ground, away from water sources, etc. -- to make the emergency drop. As I understand it, if a tanker pilot were to drop the entire load at once (aka a salvo) while making an emergency drop, the nose will do a sudden pitch up because of the sudden loss of 27,000 pounds of retardant. Often the pilots have a few hairy moments when this happens as they bring the tanker under control.

In the case of the DC-7, Larry tells me that emergency dump switch (outlined in blue in the photo) is centrally located on the cockpit panel. When Larry or his co-pilot lift the guard and activate the system by flipping the switch to the up position, the doors open at an approximate coverage level 5 drop. If I am thinking about this correctly, an added benefit is that an emergency drop at an approximate coverage level of 5 means that any pitch up of the nose of the tanker will not be nearly as bad as a sudden salvo of all doors at coverage level 8 (or higher). Larry provides some more details on emergency drops:

As far as having to jettison retardant in an emergency, it all depends on the severity of the emergency, the location and other local circumstances. In most cases, such as an engine failure deep in a canyon, there will be time for some quick (maybe 15-30 seconds) of trouble-shooting followed by determining if there is time (and the terrain allows) to fly to a suitable drop area. If we really are deep in a canyon, a suitable drop area will be anyplace nearby that doesn't contain a water source, people, vehicles or structures.

Again, it all depends on the circumstances. Generally, it will be possible to fly a few miles to an open area, but it's better for a spot on the ground to be covered with retardant than the flaming wreckage of an airplane. It would be unlikely that we would climb out of a canyon with 3 engines to carry the load to a designated jettison area. However, if the failure occurred enroute to the fire at altitude, that could be an option. There are also other emergencies not involving engines. Hydraulic problems being high on the list. I also once had a failure causing the loss of the fabric on the rudder on Tanker 62 during a drop run.

As I've mentioned before, nothing is ever easy in the tanker business.

Up close and personal with DC-7 tankers: retardant drops pt 1

The tank system used in the DC-7 is an Aero Union multi-door tank system with eight doors where each of the eight tanks holds 375 gallons.Up until now when I have written about retardant tank systems in use by firefighting aircraft (e.g. the Erickson AirCrane and the AT-802), I have written about constant flow tank systems with either one variable single door or multiple doors. As I understand it, both of these systems are controlled by computers. Where the PIC has only to set the desired coverage level and possible the quantity of retardant to be dropped. These systems are easier to use, but come at a price. According to Larry Kraus, an Aero Union constant flow variable single door system for the DC-7 would cost at least$250,000 (perhaps more), representing a significant hunk of change out of Butler's budget.

The panel shown in this photo is located on the co-pilots side of the cockpit. The red light over the drop arming switch marked "off" is constantly on until the tank is armed, in which case it goes off. By the way, this switch is configured the same way across all of Butler's DC-7 tankers. Moving on, the switch on the left side of the drop panel marked "Flow/High/Low has been disabled as they no longer use the flow feature.

 

The dial in the photo above is called an intervelometer. Larry uses this dial to set how many tanker doors open at once. In this photo, it is set to safe, meaning that the doors will not open, moving clockwise:

LFT is the four doors on the left opening at once,
RT is the four doors on the right, and
ALL is the salvo of all eight doors opening at once

Continuing clockwise, to open double doors at a time, the dial is set to 1-2, and to open a single door at a time, Larry sets the dial to 1.

Larry provided an interesting piece of history about the intervelometer: "As far as the intervelometer, it was a surplus military item, as were a number of parts in the Aero Union 8 door tank. It originally was used for selecting the firing sequence for air to ground rockets on fighter bombers."

 We are not done yet, there are two more dials Larry uses, one sets the interval between door openings in tenths of second when pilot-in-command (Larry) presses the drop button that is located on the top left side of the yoke. The second dial sets the total number of doors to open. Larry explains the settings in this picture:

"In this picture,they are set to 0.4 seconds and 8 doors. At 130 kts. and 150 ft. above the terrain, with the intervelometer set for single doors, I would get approximately a coverage Level 6, or 6 gallons of retardant every 100 square feet (a 10 ft by 10 ft area) on the ground."

On Friday, I'll be writing more about retardant drops, so stay tuned!

Up close and personal with DC-7 tankers: the cockpit

I don’t know about you, but I have always been interested in airplane cockpits. When I have flown on commercial flights, I often will sneak a pike in the cockpit as I am boarding the flight. My intent here is to present some of Larry’s photographs of the cockpit of his tanker, T-62, along with some selected DC-7 manual pages that Larry had on file in his working computer.

What I have done, with Larry’s assistance, is to take the graphic and numeric key of a typical DC-7 cockpit arrangement (prior to conversion to its current use as a tanker) and match up some of Larry’s cockpit photos with the numeric key for the graphic of the cockpit arrangement. First I present the two images of the cockpit arrangement graphics then I present his pictures.

Please don't forget to read the comment after the pictures.

 

 

cockpit (radio stack on left in foreground)

control pedestal (36)

control pedestal (36)

control pedestal (36)

pilot-in-command instrument panel (25)

engine instrument panel (26, above control pedestal)

co-pilot instrument panel (27)

main fire control panel (in 16, above engine control panel)

heater fire panel (2)

upper instrument panel (8)

forward overhead panel (3)

aft overhead panel (1)

As Larry told me recently, "see, I told you it was complicated!"

Up close and personal with DC-7 tankers: former passenger cabin, floating beam

Before going any further, it is very important for you to know that this photograph of the passenger cabin of tanker 62 was taken before the ballast items were loaded.

Ok, moving on, do you notice the box like structure running across the cabin floor? That is, according to Larry, the floating beam. The floating beam secures the retardant tank to the aircraft. But Larry says that it is another important purpose, it helps to distribute the "considerable weight of the retardant tank (1,500 lbs.) and the retardant (27,000 lbs.) across the front and rear wing spars." Larry told me later that the floating beam acts like a shock absorber. As I understand it, by acting like a shock absorber, the floating beam will absorb the shock as the tanker is taking off, flying, and landing.

Not only is the retardant tank, located below the floor of the passenger cabin (in the belly of the tanker), attached by means of the floating beam, there are attach points fore and aft. Larry explains:

Along with the floating beam, the tank has attachments at the forward and aft ends as well. The four attach points at the floating beam distribute the majority of the weight of the tank and retardant to the wing spars, but there are also two attach points near the front of the tank on top near the outboard corners.

These attach to a reinforced area of the fuselage where the forward baggage compartment and the hydraulic compartments meet in a bulkhead. There are two similar mounting attach points at the other end of the tank where the rear baggage compartment meets the heater and air conditioning compartments  All of these are belly compartments below the floor of the passenger compartment.

These mounting attach points don't have the shock absorbing qualities of the floating beam and I've seen individual mounting bolts break on a couple of occasions. Nothing serious, but on a preflight check you can see the tank sag near the broken bolt when it's loaded. On the plus side, I haven't seen one break in the last 15 years.

Up close and personal with DC-7 tankers: former passenger cabin, ballast

 The image above is interesting to me for a couple of reasons. First, remember that Butler's DC-7's once saw service with the airlines. Obviously, part of the conversion process from passenger plane to tanker has been stripping the old passenger cabin. Moving on. Now in this photo it is obvious that there is something going on. This is Butler's tanker 66 and the gentlemen in the photo is Brian Lash, the pilot of T-66. Larry Kraus tells me that in this photo, taken on May 26, 2008, Brian is doing a preflight check for a maintenance test flight of T-66. More importantly, Larry sent me this picture because it shows ballast secured in place on the aircraft.

Ballast represents additional items (for example the tires in back of the cabin in the above photo), is carefully stowed and secured at specific points called fuselage stations to add weight to bring the aircraft within manufacturer designated weight and balance parameters. It isn't just the weight of the plane that is important but how the weight is distributed within the plane that is crucial for safe operations. For example, weight that is distributed too far forward will put the plane into a nose down situation with possible fatal consequences for the plane and crew. Aviation mechanics, aka airframe and power train or A&P mechanics, periodically reweigh the plane and then check the planes center of gravity. Once the center of gravity is known, there are calculations that are performed that determine weight and balance parameters. Then additional ballast is often needed to bring the plane within these weight and balance parameters.

The photo above, a little fuzzy, shows one of these fuselage stations (F.S. 860) for tanker 62. What this means, according to Larry, is that this station is "860 inches aft of the weight and balance datum (F.S. 0, located at the tip of nose of the DC-7)." As I understand the weight and balance datum is also known as reference datum and is:

an imaginary vertical plane from which all horizontal distances are measured for balance purpose (FAA, Aircraft Weight and Balance Handbook (2007), Glossary p. 5).

From this ballast station, F.S. 860, additional ballast stations (fuselage stations) and their assigned weights are calculated to assure that tires, parts, ladders, etc equal the required ballast. According to Larry T-62 carries somewhere around 1200 lbs. of ballast. Most of it is behind (aft) of F.S. 860 and some of it is forward of F.S. 860.

Larry wanted to show you a graphic from one of his DC-7 manuals (electronic files) showing the location of the fuselage stations. Unfortunately, computer troubles with the computer where these manuals are stored prohibit him from doing so. Thanks for the effort, Larry.

I want to close this article on ballast by letting Larry share with us about how the weight of the retardant tank (1,500 pounds empty and an additional 27,000 pounds when carrying 3,000 gallons of retardant) affects tanker 62's center of gravity (CG).

With the retardant tank installed, the DC-7 is out of the forward center of gravity range in the empty condition unless several hundred pounds of ballast is located right aft, or a higher total weight spread over the aft part of the fuselage. We originally used sandbags at the rear pressure bulkhead,which is as far back as you can go inside the pressurized cabin, just behind the seats in the old passenger lounge at the rear of the plane.

The weight varies from airplane to airplane. I think that it's around 660 lbs on tanker 62.We now carry spare tires.tools,parts and other supplies that are carefully weighed in place with the fuselage stations noted (in inches from the bulkhead forward of the cockpit) to be sure that we get it right.

The mechanics changed things around in T-62 this year after doing a new weight and balance and I think that they got the CG slightly too far forward. At least it felt that way on take-offs and landings.There's a heavy box that we can move fore and aft over several feet to easily adjust the CG, but it wasn't bad enough to adjust, although I thought about moving it a couple of feet aft to see if I was right, but the season ended before I got around to moving it.

References

A wikipedia entry on an aircrafts center of gravity and the related concept of weight and balance may be found here. A somewhat more technical publication (cited above) called the Aircraft Weight and Balance Handbook (2007) is published by the FAA and freely available on the web, Much of it is written for A&P mechanics and other aviation experts. But the first chapter or two have an overview that I could follow as well as a glossary.