Embraer Revisited. . . My Bad

Well it seems that in my haste to wrap up the regional jets, I skipped Embraer's other line of regionals, the ERJs. Although certainly less impressive than their E-Jet relatives, the ERJ 145 family of aircraft is nevertheless an important member of the global regional fleet.

The ERJ 135/140/145 are very small turbofan powered regionals that actually fill the niche below the Bombardier CRJ100/200 that was mentioned in the previous post. The 145 family was developed starting with the largest version, the ERJ 145. It first flew in 1995 (in its final design; it originally flew in 1989 but was deemed unsatisfactory and was redesigned) with a passenger capacity of 50. As a side-note that I found interesting, the ERJ 145 was designed from Embraer's turboprop, the EMB 120. Although the ERJ 145 that first flew in 1995 was quite different, it shares the same seating arrangement, range, and T-tail arrangement. To my knowledge, it is rare for a turbofan/jet aircraft to be derived from an existant turboprop airframe (please correct me if I'm wrong). The ERJ 140 variant seats 44, while the 135 seats 37.

Seeing as the both versions have at least 95% commonality with the ERJ 145, with the biggest visible difference being the shortened fuselages, telling these apart from one another is very difficult. To me, attempting to pick apart aircraft that have less than a 15 person capacity difference across three models is pointless. Instead, I'll just describe how to tell the ERJs apart from their closest lookalikes, the CRJs.

As you can see above, the ERJs have very, almost comically long noses, which taper entirely from top to bottom. Both these characteristics are exaggerated compared to the CRJs. The other easy way to tell them apart are the ERJs' engines. All ERJs have Rolls-Royce Allison AE3007 engines, which are entirely encased by the bypass air nozzles (the white casing around the engine in the picture above). That is quite different on the CRJs that have the rear portion of the engines, namely the combustion chamber and the turbine, exposed.

Currently there are a total of 697 ERJ 145 variants in service. The airline that I most associate with the ERJs is American Eagle Airlines which operates 200, as they use a ERJ 145 to connect to the American Airlines hub in Chicago from Rochester, such as the one below at O'Hare:

But the overall largest operator is ExpressJet with 244 ERJ 145s. ExpressJet operates under the banners of both Continental Express and United Express.

Bombardier. . . Those Damn Canadians

(CRJ200)

The final key Western commercial airplane manufacturer is Bombardier. Boeing, Airbus, Bombardier and Embraer are the four largest Western airliner manufacturers, in that order. Bombardier is a Canadian company that specializes in regional jets, turboprops, and corporate jets. Bombardier owns both Learjet and deHavilland Canada, which explains the later two of its specializations. But out of respect for deHavilland's amazing designs, I will cover the turboprops (the Dash 8/Q series) in a separate post focusing on deHavilland Canada.

Once you push aside the Learjet and deHavilland families, Bombardier only has two lines of regional jets, which are quite prevalent. In fact, Bombardier's regional jet families are very similar to the Embraer E-Jet families in their composition. There are two "sets," the CRJ100/CRJ200, and the CRJ700/900/1000. Each subsequent type is simply a stretched or larger version of the previous model. So realistically, you only need to be able to identify the families as a whole, instead of each type, just as with the Embraers.

First I will explain how to identify Bombardier regionals in general. They are very easy to spot, with the only similar plane in their class being the increasingly rare Fokker regionals. What stands out the most is that the engines are mounted in the rear on the fuselage. The wings are swept back at a steep angle. They are like much smaller McDonnell-Douglas MD80s, except the noses are different. The Bombardiers are similar to the Embraers as the noses are like the bullet trains, with almost the entire taper being down from the top to the bottom. To me, they kind of look like pencils as two-thirds of the narrow fuselage is forward of the sweep wing and the nose is pointy. Finally, the engines are quite distinctive. They have a very cylindrical forward section (bypass duct) and a cone-like, metallic colored rear section that is almost equally long (which is unusual), as you can see here:

(CRJ100)

So what's the difference between the CRJ100/200 series (which are the two above pictures) and CRJ700/900/1000 series? Simply put, size and a few added bells and whistles. They all have similar ranges, speeds, and ceilings. They also increase in capacity at quite regular intervals, unlike the Embraers, so they cover a lot of the regional market. Instead of differentiating each type, I'll just give you the range of capacities and first flights.

The CRJ100 and CRJ200 are the same capacity at 50 passengers. The CRJ200 is just a reengined version with slightly better range and fuel economy than the 100. The CRJ100 first flew in 1991.

The CRJ700/900/1000 series transports 70 to 100 passengers, with each subsequent model carrying about 20 more people. The CRJ700 first flew in 2000, and the CRJ1000 (which looks almost awkwardly long for the size of its engines, see below) first flew in late 2009 and has yet enter regular service.

(CRJ1000)

How do you tell the difference between the two families? Well, you can always count the windows and estimate the seating capacity, but that's boring and difficult. Sometimes you can just eyeball the fuselage length and know if at least its not a CRJ100/200. The only way I know to tell between the CRJ200 and CRJ700/900/1000 is that the latter series has leading edge slats. From a distance slats can be very hard to spot if they aren't deployed (they shouldn't be on the ground or in cruise). But if you do happen to see slats on a CRJ, then you know that it has to be CRJ700/900/1000. (If you don't know what slats are, just tell me and then I can make a post on them)

Who uses Bombardiers in the U.S.? Well, almost everyone. These are extremely popular aircraft with the legacy carriers as they can be used for gazillion smaller airports around the country (including, surprise! Rochester) Delta Connection alone (or its subsidiaries) operates an incredible 381 CRJ200s, 66 CRJ700s, and 101 CRJ900s. Considering that Delta/Northwest, the largest airline in the world (for now, United/Continental is forecasted to surpass it), only operates 18 B777s and 16 B747s, you can see the huge numerical difference between the big widebodies and the regionals. Low-cost airlines tend not to use the Bombardiers as they are too small for their operations, which stipulate larger aircraft (usually E-Jets, A320s, B737s) to lower the cost per passenger seat per mile.

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