Observing certain flight maneuvers

There are various maneuvers that student pilots have to learn. Learning various maneuvers, the specific maneuvers required vary depending on the rating, is an important part of pilot training. Or for training for a commercial rating or to be a certified flight instructor (CFI).

Specific maneuvers teach certain skills, and the student has to be proficient in the required maneuvers as they may be required to demonstrate these maneuvers as a part of their testing to get their pilot certificate or for later ratings.

I recently went on a scenic flight with Mike, a pilot/CFI where Mike demonstrated certain maneuvers, two were more advanced maneuvers that private pilots do not learn but are required for commercial pilots and CFI's. Mike and I had talked prior to this flight about the maneuvers that he would show me, so I was able to read up on these maneuvers prior to our flight.

Before writing about these maneuvers, I need to talk about stalls.I first wrote about aircraft lift and stalls over two years ago. Since that time, I have been to aviation ground school and passed the FAA private pilot written exam. So, I have a better idea of what a stall is. In thinking about how to provide a reference for stalls, I liked what TL Stein told me in this article from March 2009  so rather then reinvent the wheel, I am referencing that article:

stall speed for an aircraft is the speed where the forward speed of the aircraft is not producing enough air flow over the wings to produce life or support the airplane at its altitude. When a pilot is landing an aircraft, the plane is just over stall speed. ... the faster the air moves over the wing, the more lift is created Air speed is in direct relation to life. Lift enables flight. Lose lift and the aircraft sinks. When the forward airspeed no longer produces enough low pressure over the top of the wing to sustain flight . . . this is stall.

There is a nice animation on aircraft stall that may be found here.

With that as background, I will turn to writing about some maneuvers that Mike demonstrated for me, chandelles, steep turns, and power-off and power-on stalls in an article that I will post next Wednesday, June 8. These and other maneuvers required for the private pilot, CFI and commercial pilots ratings are covered in detail in an excellent publication by ASA (Aviation Supplies and Academics, Inc.) called Visualized Flight Maneuvers Handbook. I have the edition for high winged aircraft. I understand that there is one for low winged aircraft as well. I have a hard copy that is small enough to fit in a flight bag, I do not know if you can purchase an electronic file. I got my copy through my local airport.

Aerodynamics is important

When I was in ground school last winter, the first thing we covered on the first night was aerodynamics. At the time, I was gaining an appreciation for the importance of aerodynamics, and it was not just because I needed to have a knowledge of aerodynamics to pass the FAA"s written Private Pilot exam.

For example, I spent some time learning about stalls. One of the things a pilot is supposed to know in order to pass the practical (flying) portion of the FAA examination process leading to a private pilot's certificate is how to recover from a stall.

I have already written that it is unlikely that I may never get a pilot's certificate but that doesn't stop me from learning all that I can about aviation and flying. And to that end, one of the things that I have that I have seen on a few of my scenic flights involve watching the pilot demonstrate stalls. They talk about what they are doing and made sure I knew what the aircraft was doing (stall horn and vibrations in the wings). And they both made sure that I understood how they got out of a stall by lowering the nose and/or increasing thrust.

Then there was learning about weight and balance in ground school so as to not overload the aircraft. Here I did many practice problems that helped drive home the point of proper weight and balance of an aircraft.

Up until a few days ago, I hadn't given much thought to aerodynamics. That changed recently. I'll try to explain.

The other day as I doing some background research for an upcoming series of articles on the B-17 (to post in January), I realized again how important aerodynamics is. This time it was about how aerodynamics affect airplane design. I was wondering what factors affect the speed at which an airplane flies, but I was only thinking about thrust so I was missing a kep point. One of my pilot friends gently reminded me about drag because there are things that can be done to reduce drag in designing aircraft. Reducing drag means a faster aircraft.

So, I am revisiting aerodynamics and reviewing the chapters on aerodynamics in the books I used in ground school. I read about drag, reread a chapter in the B-17 book I am reading, and asked my pilot friend another question about drag. The brain cells kicked in again. It is hard to explain, but I learned (again) how important aerodynamics is.

I knew that I wanted to write about this experience in today's article. But not being any kind of expert in aerodynamics, I wanted to find something simple to provide those of you who are not pilots with a context. So, I found this video that I am embedding here. It is a little old, but I think that it still provides a good overview of basic aerodynamics.

The video, How Airplanes Fly is available from Fed Flix here, and is in the public domain.



revised 5:50 PM, Dec. 13 2010

Tankers don't always carry full loads

I want to briefly mention something that I will spend more time writing about later after I have had a chance to do some research as well as talking to my aviator friends. That is, more often than not, tankers and helos will not carry a full load of retardant or water in their tanks due to aeronautical concerns. So, when the reports are saying that the Martin Mars can carry 7,200 gallons of water/gel mixture or that the Evergreen 747 supertanker can carry 20,500 gallons of retardant, they will carry these loads under "ideal" circumstances. The word "ideal" may be a misnomer, but it will have to suffice for now.

So, the Martin Mars was, as Bill Gabbert pointed out the other day, was carrying a smaller load of water (about 4,600 to 5,500 gallons). Chances are the Evergreen 747 supertanker was carrying a smaller load of retardant. Those of you who are aviators, or firefighters more familiar with aeronautics than I will know that one of the main reasons that tankers (and I assume helos) carry a lower load is because of something called density altitude. I will be writing some articles later about density altitude. I had begun discussions with some of my fire aviator friends several weeks ago about points such as density altitude and retardant coverage levels. I am beginning to revisit these issues.

One final point, while I am on the subject. When the Fox newscasters were covering the other day about the Evergreen 747 supertanker's retardant drops, one of them said that the supertanker could lay down a retardant line 3 miles long. This was also under "ideal" conditions and when the load is dropped in one run. I will add here that they were reading from specifications and other data on the supertanker, as they should. Having read specs myself, what I have to remember is to read words like "maximum" or the data sheet might say something like "the supertanker can drop a retardant line up to three miles long." Point being that I have to remember to think about these words as I listen to newscasts or read articles online.

Returning back to retardant line laid by the Evergreen 747 supertanker, the supertanker split the load into two runs, as all tankers are able to do. Likewise, at full capacity and under ideal conditions, the Martin Mars can cover 4 acres with its water/gel mix. If I understand things correctly, each water/gel load dropped by the Martin Mars covered less than 4 acres. Again, in later articles, I will try to write more about this issue.

I will also be writing about other aerodynamic issues relating to retardant and water drops. In some sense this planned series of articles will be a continuation of the short series of articles I wrote several weeks ago on wing stalls as relates to retardant drops. I won't link to this here, but if you look at the labels on the lower left side of this page, you will see a label that says "aerodynamics." If you click on that label you will get all my posts on aerodynamics to date, including posts on wing stalls.

Look for this series down the road a bit.

avoid stalls during retardant drops

Remember the two stall speeds that I referred to for the AT-802F that I referred to here? There is a V-speed or velocity-speed known as Vs where Vs is the stall speed or minimum steady flight speed for which the aircraft is still controllable. As you can see from this wikipedia article on V speeds, there are many different V-speeds. Now, if I am thinking about this correctly, then Vs should be slightly higher then this AT-802F performance specification:

Stall Speed, Flaps Down: 91 mph (146 kph) at 16,000 lbs (7 257 kg)

The speed that an airtanker flies at when making retardant drops on a fire is related to Vs. This is expressed as a formula (1.3*Vs). According to the specs found on the Queen Bee web site, the drop speed is in the 120 to 130 mph range. For a more detailed discussion of the calculation of the drop speed (from which I based this discussion) using the AT-802 as an example, go to this BLM aviation page, an automatic download of a MS word document.

TL Stein offers this explanation of stalls, retardant drops, terrain, and fire-produced weather:

Stalls are to be avoided in ALL cases, excepting the landing phase of an aircraft.  In the air tanker world, landing is the only place you want a STALL.  Fire produces it's own weather conditions.  A tanker making a drop in a canyon can experience a tailwind on approach to the drop, which drops the forward airspeed.  Over the fire, a severe lift condition can and does occur, due to the heat raising from the fire.  During the drop phase, the aircraft releases it's load and becomes much lighter.  Consider the thermal wind activity over the drop zone, combined with a sudden tail wind.  The aircraft can loose enough forward airspeed over the wing to cause it to stall and crash.  This is why airspeed / drop speed are critical to the aircraft and the mission.  In the real world, stalls are practiced at a good altitude to enable a successful recovery.  This is mandatory for a "type rating" in the aircraft you will be certified to fly.  Stalls close to the ground, in a fire fighting scenario leave no room for recovery.  There are a lot of memorials to pilots who stalled and crashed.  Why?  Constantly changing conditions over the fire is a good start.  You can make two passes over a fire and the flight conditions will never be the same on each pass.  The best tanker pilots on earth know this.  Each drop you make you run the risk of something going wrong, it's a given and we know it.

stalls and icing

One of the factors that can contribute to stalls is icing on the wings and tails of an aircraft. Simply, ice formation interferes with the normal aerodynamic flows over the wing and tail (aka horizontal stabilizer) leading to lower stall speeds and tragic outcomes. Yes, there are various de-icing systems that can be used in flight such as de-icing boots to rid the wings and tail of ice during flight. It is not my intention to get into the world of de-icing an in-flight aircraft.

In my travels on the internet learning about stalls recently, I happened on a link to aviation safety at a US Forest Service website and found a safety advisory from the Interagency Airtanker Board on icing. I found these safety reminders for airtanker pilots to be very poignant. As I read this advisory, what came home to me is that an airtanker pilot has the right to say “no” to flying into a situation where icing might be a problem and/or to get out of an icing condition before making a drop if called for.

Of course, I don’t know enough to know if airtankers even do retardant drops in northern States in America during cold weather where icing might be a problem. I am not an expert in meteorology, but I know enough to know that 33 degrees on the ground is going to translate to something colder at higher elevation. I also know that there is something called rime ice, which I think is caused by “freezing fog.” And rim ice can form on aircraft wings and tail.

Link to IAB safety advisory on icing (this is a pdf filerequiring a pdf viewer)

If that link does not work, go here and look under Interagency aviation safety alerts for advisory FS 09-01 on aircraft icing.

The advisory also provides a good description on ice formation as affects aviation that I found very helpful.

good animation on aircraft stall

TL Stein sent me this awesome animation illustrating some of the concepts that I have been writing about. It may be found here. Note that the animation may take a couple of minutes to load.

Aircraft lift

I am moving on from writing about SEATs. I want to spend some time talking about retardants that airtankers -- SEATs and multi-engine airtankers -- drop on wildfires. But, before doing so, I need to spend some more time on the aerodynamics underlying “aircraft stalls” for reasons that I hope will be apparent in later posts. I will be spending a couple of weeks on this sequence of posts before I move on writing about multi-engine airtankers around the third week of March.

To review, I wrote about stall speed in my post of February 12:

“As I understand it from my correspondence with TL Stein, stall speed for an aircraft is the speed where the forward speed of the aircraft is not producing enough air flow over the wings to produce lift or support the airplane at its altitude.

When a pilot is landing an aircraft, the plane is just over stall speed.”

The engine provides the power or thrust to move the aircraft forward through the air, but it is the aerodynamic properties of the wings that provide the lift: chord, dihedral and anhedral, wing loading, and the shape of the top and bottom of the wing. The leading edge of the wing is thicker than the trailing edge. Recall that the flaps are usually on the trailing edge of the wing. The distance from the leading edge of the wing to the trailing edge of the wing is known as the chord.

Dihedral is the angle, usually upward of the wings of an aircraft in relation to the body of the aircraft. The wings of a bird also are dihedral. Anhedral are when the wings are at zero or negative dihedral. See this wikipedia article on dihedral for a more detailed explanation and some pictures.

Wingloading is the loaded weight of an aircraft divided by the wing area. TL Stein tells me that “the chord, length and ‘hedral aspects determine the amount of lift that can be generated by the wing for any given aircraft.

But, we are not done with lift yet. The standard wing design is a curved top and a smooth bottom, creating a high pressure area under the wings and a low pressure over the wings. TL Stein explains:

“the faster the air moves over the wing, the more lift is created. Air speed is in direct relation to lift. Lift enables flight. Lose lift and the aircraft sinks, When the forward airspeed no longer produces enough low pressure over the top of the wing to sustain flight . . . this is stall.”