Is this legal?

Have you ever been plotting along in your Cessna, Piper, Cirrus, Beechcraft, or Diamond and wondered, hey can I throw my bag of flour out the window and not be hunted down and killed by the FAA? I know I have. Just in case you were, I thought I'd clarify the Federal Aviation Regulations (FARs) on dropping objects from airplanes.

To most new pilot's surprise, it actually is legal to drop objects from your airplane... that is only if no property or person is damaged, maimed, or killed. So as I'm flying over the Allendale Columbia campus, I could drop a sack of flour onto the courtyard, as long as nothing is damaged and I don't hit anyone. Although I'm sure they could sue the bejesus out of me.

But you'd better have amazing aim or trig skills because you won't be able to fly very low. The FARs put the nail in the coffin for low-level flour bombing (at least in monitored areas). There are three regulations that make up the "minimum safe altitudes" rules.

Over congested areas: An altitude of at least 1000ft above the highest obstacle within a horizontal radius of 2000ft of the aircraft must be maintained over any congested area of a city, town, or settlement, or over any open-air assembly of people.

Over other than congested area: An altitude of 500ft above the surface must be maintained except over open water or sparsely populated areas. In that case, the aircraft may not be operated closer than 500ft to any person, vessel, vehicle, or structure.

General Anywhere Rule: The pilot must maintain an altitude which, in the event of an engine failure, will allow an emergency landing without undue hazard to persons or property on the surface.

The 500ft rule is the most important one when it comes to bombing anything, although the FAA could screw you with the Anywhere Rule anyway. Normally, flour bomb competitions (which happen quite often, as it is a major event at National Flight Team competitions) have the target on a closed runway, as there are no altitude restrictions set in stone (the anywhere rule is still applicable as long as the aircraft is not landing or taking off) over airports.

So in summary, yes dropping objects is legal, but it comes with a laundry list of ifs and buts. Of course you could just fly off the beaten path where there is no radar coverage and then obscure your aircraft registration so no one could report you.... but I won't never recommend or condone such actions. ;)

The Embraer Regionals

Instead of doing all of the regionals at once, I have decided to do them in separate posts to encourage me not to be lazy. Before I start talking about the E-Jets though, I should define what is a "regional" airliner. Regional jets or turboprops are usually short-to-medium haul (topping out at around 3,000nm) and seat up to 120 passengers. This includes the smaller B737 and A320 variants that are considered large regionals. These rules are not absolute. For example, some might considers the smaller MD80s as regionals, but I don't. Most of the time regionals feed larger aircraft and airlines by connecting low density markets (such as Rochester or Springfield, Illinois) to airline hubs or larger airports such as JFK or LAX.

The Brazilian aviation company Embraer has largely produced business jets. But since the E-Jets series introduction into commercial service in 2004, Embraer has been steadily becoming a bigger player in the regional airliner market. The E-170/-175 and E-190/-195 are medium haul, narrowbody twins. They are considered "large" regional jets with their passenger capacities ranging from 80 to 122 passengers in high density configurations (i.e. single class, no leg room seating arrangement). The E-Jets or ERJs as they can be called are essentially four variations on the same general design. Each variant is really just a stretched version of the previous one. The E-170/-175 have the same wingspan, fuselage height and width, and engines. The E-190/195 are also similarly paired with the same wingspan, fuselage height and width, and engines. According to Wikipedia, the E-170/-175 and E-190/-195 families have 89% commonality, whereas each family pair has 95% commonality.

Anyway, how do you spot the ERJs? Telling them apart from one another is probably really difficult, so I won't get into that.

The best way to differentiate an ERJ from say a A320 or B737 is the nose. The nose slope is similar to the much larger B757 in that its a straight angle from the top of the fuselage to the bottom, like a high-speed rail locomotive*. They kind of look like mini B787s as well. Also, I believe the E-Jets are the smallest (especially the -170/-175) twin engine jet liners with the engines below each wing in pods. The E-190 and E-195 are similar in size to its chief competitor, the A320. Finally I have noticed that the windows on the ERJs are spaced farther apart than most other below wing twins, i.e. the B737 and A320.

The E-Jets are beautifully designed, efficient aircraft, which explains their success. Their largest operator is JetBlue, who operates 41 E-190s with 64 still on order. If you ride JetBlue, either you're on a E-190 or A320.

*Here is a picture of a high speed locomotive just in case you don't know what I'm talking about:

What do flaps do?

The 747's (pre-747-800) beautiful triple-slotted flaps. These have DRAMATIC effects.

The old 737's deployed slotted flaps.

This diagram is a good basic summary of wing components. Of course, every plane is different, but this can act a general guide. When you're actually in a plane, it often easier to figure out what everything is based on what movements its making when.

As you can see, normally on larger airliners there are two sets of flaps, inboard and outboard. On smaller planes, the wings are too short to have two sets of flaps be practical. Flaps are usually only used during landing and takeoff and have two functions. When lowered, flaps increase the wing area, thus increasing the amount of lift the wing is generating. Another way of looking at it is that flaps decrease the stall speed of an aircraft, allowing it to fly more slowly without dropping out of the sky. The second force resultant of lowering flaps is an increase in drag. Since flaps drop down (at varying angles depending on the aircraft) from the wing, they create lots of drag, helping the aircraft slow down. Flaps are especially useful as they allow the pilot to decrease the angle-of-attack of the aircraft without increasing the airspeed. (Angle-of-attack is a fancy pilot word for pitch. When a pilot lowers the nose, he is decreasing the angle-of-attack. Normally this would increase the airspeed. But with flaps down, the aircraft will accelerate much more slowly as the flaps are generating tons of drag.)

Flaps have variable settings, measured in degrees that will determine how dramatic their effects are. I will use my little Cessna 152 as an example:

0 degrees: Flaps are not deployed and are thus not generating any additional aerodynamic forces.

10 degrees: Flaps are 10 degrees down from the chord (the line from the leading edge to the trailing edge of the wing). At this setting, they are sensibly (as in I notice) only generating additional lift. Typically I will use this when I want takeoff in a slightly shorter distance.

20 degrees: The flaps start generating some drag, meaning that if during flight I were to lower them straight through to 20 degrees, you would feel some negative acceleration. Otherwise yet more lift.

30 degrees: This is the normal landing setting. The plane significantly decelerates and you would be thrown forward into your seat belt if they were deployed to 30 degrees midflight. (As a side note, flaps can only be deployed below a certain speed (Vfe), usually well below cruising speed, otherwise the pilot risks damaging both the flaps and the wing.) Here the lift and drag is very high. Normally, in my Cessna, 30 degrees of flaps was the setting that would allow me to fly the slowest without stalling.

40 degrees: I rarely use this puppy. At 40 degrees, far more drag is being generated than lift. This is used to lower your altitude as fast as possible while staying within a certain airspeed envelope. I never would land with 40 degrees unless absolutely necessary, as the flaps are at such a steep angle that the wind can catch them like a sail at low speeds and balk my landing.

The summary of what each setting is used for basically demonstrates how flaps are used in general. Low flap settings are used for takeoff to increase lift for a given speed, thus shorting the take-off distance, and to slightly help slow the aircraft during landing. High flaps settings are using during landing to allow the plane the fly much more slowly while not risking a stall, as well as aiding the pilot in slowing the aircraft down during approach.

There are many different types of flaps, each with their own advantages and disadvantages. But instead of overwhelming you with all that unnecessary knowledge, I'll just show a little diagram of what they look like and end there. My boring little Cessna had plain flaps of course.

Why do three engines have humps and one does not?

You'll notice that the outer engine in the third picture is the only engine without a "hump" that runs all the way to the cowling. And, if you remember, no other engines in the pictures I've shown you so far have had these humps. These four engines are from the Boeing 707 (first flown in 1957), the plane that ushered the world into the jet age in the late 1950s. I thought that the interesting question (to me) of why those engines are different would be a good introduction into Bleed Air Systems and their outdated counterparts, Turbocompressors.

Bleed air systems are (or soon to be "were") a key system within most commercial airliners. Bleed air is quite simply air that is taken or "bled" from the jet engines, usually from after the compressor stage and before the combustor (so there is no fuel in it). Since the air is bled from after the compressors, it is both very hot and under very high pressure. This hot and high pressure air is fed through pneumatic lines into the aircraft and can be used for a variety of functions including heating, de-icing, pressurization, and actuators. Bleed air is being (very) slowly phased out of newer aircraft designs because of its inherent inefficiencies. Bleeding air from the engines increases fuel consumption for a given output of thrust. Also, the air that leaves the engine through the air lines is far too hot to be immediately used in the cabin, so it has to be refrigerated (entailing more weight for chemicals and electrical components). Next generation planes such as the Boeing 787 (which first flew in late 2009) rely on electrical generators for heating, de-icing, etc. instead of bleed air.

So why the weird engines on the 707? The Boeing 707's comparatively archaic turbojets were not powerful enough to loose air to the bleed air system without seriously decreasing the performance of the Pratt & Whitney JT3Ds. Instead, the Boeing 707 has turbocompressors mounted above three of its four engines (thus explaining the humps). The turbocompressors are mini turbines that are mechanically driven by the main turbojets, and compress air from their own independent air inlet directly above each turbojet's cowling (so as not to draw air away from the JT3Ds). Since three turbocompressors could provide ample air for the other systems on the aircraft, there was no need to add the unnecessary weight of a fourth one on the port outer engine.

Just as a final useless factoid, the first commercial engine designed to provide bleed air was the Pratt & Whitney JT8D. The JT8D was first used on the Boeing 727 (first flown in 1963), the next airliner designed and built by Boeing after the 707.

Why the "Step"?

I decided that in the interest of me posting more, that I'd change my writing strategy. Instead of doing infrequent long posts, I'm going to try to do daily short posts. Perhaps every once and a while I will do a novel, but for now, I will change to something akin to the "Fact-a-Day" method.

For my first act, I'm going to answer the seldom asked question, "why do flying boat hulls have the step on the bottom?" The step is the abrupt decrease in the hull chord usually about midway down the bottom of the aircraft, as can be seen on the Bombardier 415 in the picture above. First it is important to understand the difference between a flying boat and a float or seaplane. Put quite simply, a flying boat is a plane that lands directly on its hull into the water, just like a boat (who would have guessed?). A flying boat is (I am pretty sure) always primarily designed to be mainly operated on water, although most also have retractable landing gear for landing on tera firma. A float plane or sea plane usually lands on floats that are positioned similarly to traditional landing gear, and can be originally designed for use on land and then retrofitted with floats. Here is an example:

So now that we have that clear, the step on a flying boat or actually on all floats, its designed to aid the plane in breaking away from water during takeoff. When the plane is attempting to takeoff, two forces try their best to keep the hull or float firmly attached to the water's surface: adhesion and vacuum pressure. Adhesion is of course the molecular attraction between water molecules and other compounds. The vacuum pressure is caused when the aircraft pulls up on the water's surface without allowing air into a pocket under the hull, creating a low pressure (which causes the water to "pull down" on the aircraft). In calm seas, vacuum pressure is a particularly annoying problem since when the water is choppy, there won't usually be an airtight seal between the water and the hull. By adding a step, the hull is no longer a long, continuous surface. Thus when the aircraft is at speed, the water flow is broken up underneath the hull, lessening the strength of adhesion and vacuum pressure.

In addition to the step, most flying boats in particular have "breather tubes" which are located just aft of the step. These tubes run from the bottom of the hull to another location on the aircraft that is always exposed to open air. In turn, the spot most prone to vacuum pressure (the area just behind the step) can never form a low pressure as air will be immediately drawn into the pocket through the breather tubes. The tubes can be seem in the picture at this link if you zoom in and look closely behind the step on the hull: http://cdn-www.airliners.net/aviation-photos/photos/1/7/6/0770671.jpg

The Hard One

here we go, same as last time.

#1

#2

#3

#4

#5

A Little Quiz like You Asked For

Just comment the corresponding name to each number over the photo.

#1

#2

#3

#4

#5

Another Plane Spotting One

Now that I've finished up the Boeings and Airbus's, the plane spotting game becomes more difficult as there are a lot of different models and makes out there. This is especially true in the regional market, where there are a large number of players all competing in the more generous short haul market.

But before getting into the regionals, there is still one formerly big player in the medium-to-long haul market: McDonnell-Douglas (MD). McDonnell-Douglas was at one time just as important as Boeing and was Boeing's chief competitor in the 1950s, 60s, and 70s. But in 1997, Boeing and McDonnell-Douglas merged, creating just The Boeing Company. Large MDs are rarer now in the passenger aviation market since they are outdated both technologically as well as by design (for example, the widebody MD is a trijet, which as I explained in the previous post, has fallen out of use). But there is one MD that is still operating in large numbers and its reputation as loud, antiquated, and as fuel guzzlers makes it my least favorite currently operating large commercial aircraft... can you guess which one? The suspense must be palpable. We'll find out in a little bit. Besides that one plane, most MDs have been relegated to the cargo industry. By the way, DC means Douglas, which implies that the type received its designation before McDonnell and Douglas merged in 1967.

DC-10/MD-11

The DC-10 is one of the classic widebody trijets that I wrote about in the previous post. It was first flown in 1970 so it is quite old. The MD11 is simply an updated version of the DC-10, first flying in 1990. Both are medium-to-long haul airliners. The DC-10/MD11 are easy to differentiate from other planes because of the third engine mounted on the vertical stabilizer. It is important to note that the engine cowling/body is not fused to the main fuselage of the aircraft, but is instead raised, a key feature in distinguishing it from its former chief rival, the L-1011 Tristar. In terms of the telling a MD11 from a DC-10, there are a few little tells. A MD11 is longer and has a bigger wing span. But what can more easily viewed from a distance is that MD11s have winglets unlike DC-10s, as can be seen here in this photo of an MD11 (the above photo is of a DC-10):

Both aircraft have been largely removed from passenger service. But they are huge players in the cargo market. Fedex is actually the largest airline in the world in terms of freight tons with its fleet of 74 DC-10s and 59 MD11s (along with a wide variety of other types).

MD-80s/MD-90s

Well if you haven't guess it, then here you go: this is my least favorite aircraft. I hate flying medium demand, medium-haul routes on American Airlines or Delta because invariably you get one of these. MD-80s (with the MD-88 being the most common is U.S. legacy carriers) and MD-90s (for this post's sake, just an upgraded version of an MD-88) are narrowbody, medium-haul aircraft. They are easy to spot, as I believe they are the largest twin aft engined, T-tail airliners in service (the Fokkers might be similar in size but they are far rarer aircraft in the U.S.). They also have the little eyebrow windows above the cockpit like the B737. T-tails (the elevators or horizontal stabilizers being at the top of the tail or vertical stabilizer) are unusual in large airliners, due to the increased weight resulting from the reenforced tail structure and the ability of the aircraft to enter a deep stall and in turn a flat spin, from which it is aerodynamically impossible to recover (in other words, you are 100% screwed). If you would like to learn about deep stalls (buM, bUM, BUM!), just let me know. Well, in my opinion, enough said about this airplane that I don't like at all.

DC-8

This is the oldest plane I have ever talked about in my various plane-spotting posts. It is from the first generation of American jetliners, with the first flight being in 1958. The only reason its on here is that the DC-8 is still used for cargo operations in large enough numbers that I have seen them at airports multiple times. This one is easy to spot, as 99% of the time, they have no passenger windows since they are cargo aircraft, they have four engines despite their small (compared to the A340, A380, and B747) size, and they are the only four engined aircraft with the eyebrow windows above the cockpit. These aircraft are true relics and it is a testament to their sound design that they are still operating in force. Only the B707 trumps it in awesomeness from that era (I suppose that's subjective...). But I figured I would cover the B707 in either an old airliner post or a military post (since the largest current role for the B707 is as an aerial tanker for the USAF) as I have never seen one with my own eyes.

That about wraps up the MDs/DCs, but before finishing this post and moving onto the regionals, there was one now extinct* player in the large airliner market: Lockheed.

Lockheed L-1011 Tristar

The L-1011 was Lockheed's only foray into the widebody jetliner market. It is essentially a double of the DC-10, being a widebody, medium-to-long haul trijet. It also first flew in 1970 like the DC-10. Despite similar specs, the DC-10 outcompeted the L-1011 for reasons I don't feel like getting into here (its a long story). Today, L-1011s are extremely rare in the U.S., but are still used by a few young carriers in developing markets such as Africa and the Middle East. But in the event you run into one (I would be quite jealous), there is a simple way to tell it apart from its only look alike, the DC-10. The L-1011's aft engine cowling is molded into the fuselage, not separated, and the engine's exhaust is directly behind the fuselage. This is because the L-1011's engine is actually inside the fuselage (although separated by an intense bulkhead, in case there is an engine fire or it sheds a blade), unlike the DC-10, which has its third engine entirely in the tail, separated from the fuselage. So if you look at a L-1011's aft engine intake, it forms a stretched "S", which is in turn called a S-duct. Why the different engine positions? Its all about what the designers were looking for. Wiki says it best:

"The main visible difference between the TriStar and the DC-10 that emerged at Douglas is in the middle/tail engine; the DC-10's engine is mounted above the fuselage for more power and easier maintenance, while the TriStar's engine is integrated into the tail through an S-duct (similar to that of the Boeing 727) for improved quietness and stability."

So there you go: the final Western large airliners I believe are worth mentioning in a plane spotting discussion. Next time, I'll go into the nitty-gritty world of regional airplanes, which include the Embraers, Bombardiers, ATRs, Fokkers, Saabs, and de Havillands.

*To clarify, Lockheed (now Lockheed-Martin) itself is not extinct, it just has no offerings in the commercial airliner market, instead focusing solely on defense.