B727 Reversers Options

[The Airbuser]

Hey, guys, I have a question for ya.

I've never seen a B727 opening any... "clamps" (I don't know how they're called in English! ) in the engines, like the MD-80 when on reverse thrust . So how does the reversers on the B727 works?

[Aspiring Boeing ...]

I am imagining it is the little rectangular spaces seen here, if you look closely at thefront part of the engine exhaust.

http://www.jetphotos.net/viewphoto.php?id=6089452&nseq=0

I am assuming that the square panels close in and block the thrust from escaping out the rear, so it re directs out of the spaces.

If you want a special modified VIP one:

http://www.jetphotos.net/viewphoto.php?id=5724789&nseq=3

Just the old PW's used on the DC9 family.

Regards,
Chris

[Piltdown Man]

Or try this one. And I think the word you are looking for is "clamshell" or "bucket".

PM

[Aspiring Boeing ...]

Yes that is the word. Clamshell. Just not the one I usually refer it to, as the clamshells must be internal on the 727.

I know that PW designed loads of subvariants of The JT8D that was used on the 727. like the -8, -15 etc. I did not know that they all used different reversers for each 727 subtype (-100, -200 -200adv etc) Its quite strange.


Regards,
Chris

[rjb4000]

http://cobweb.ecn.purdue.edu/~propulsi/pro...cs/Frevers1.jpg

[The Airbuser]

I see...Different thrust reverser for different B727 types...

Just that I've never seen the B727 with bucket-style thrust reversers like, for example the MD-80/DC-9 series. Most 727's have clamshell reversers, if I recall correctly.

[AirRabbit]

Yes that is the word. Clamshell. Just not the one I usually refer it to, as the clamshells must be internal on the 727.

I know that PW designed loads of subvariants of The JT8D that was used on the 727. like the -8, -15 etc. I did not know that they all used different reversers for each 727 subtype (-100, -200 -200adv etc) Its quite strange.
Regards,
Chris

No, that’s not what was said. Rjb4000 provided a link that simplistically, but clearly, shows how “clamshell,” “bucket,” and “By-pass fan” reversers work. While a lot of people use the term “clamshell” to describe “bucket” reversers (because the buckets look like clam shells folding and unfolding; and, therefore, it has become quite acceptable to do so – as not many are confused by the term), a true “clamshell” works very much like the “buckets” do, but they do so internally. As you can see, in the first two diagrams all the thrust is reversed, but in the last diagram, not all the thrust is diverted, just the major portion that is derived from the by-pass fans. In the case of these “”By-pass fan,” or “cold air,” reversers and for the “clamshell” reversers, the diverted air passes through the engine cowling via what are called cascade vanes; some of which encircle the entire engine housing, and some of which are located in specific ports around the circumference of the engine. The “ring cascade vanes” are usually exposed through a sliding of the aft portion of external cowling. The specific port located cascade vanes can usually be seen from the outside of the engine – whether or not they are in use at the time – and when not in use the blocking plates are in place over the vanes on the inside, keeping the exhaust gases within the engine and allowing exit only at the rear.
(Thanks, rjb400)

I see...Different thrust reverser for different B727 types...
Just that I've never seen the B727 with bucket-style thrust reversers like, for example the MD-80/DC-9 series. Most 727's have clamshell reversers, if I recall correctly.

Again, no, that’s not correct and that’s not what was said. Different types of thrust reversers are used on the B727. Some B727-100s are equipped with “buckets” and some B727-100s are equipped with “clamshells.” The same is true on the B727-200 series. Look again at the photo that PM posted.

[Piltdown Man]

Again, on looking up my "Boys Book of Jet Engines" we find three reversing systems. These are the Clamshell doors, Bucket Target system and Cold stream reverser. The Clamshell system is an "internal system" where internal doors close and divert all of the efflux forwards(ish) through a series of cascde vanes. Allegedy these are pneumatically operated. See AB's link above. The Bucket target system is probably best seen on a 737-200 series or a F70/100 where two wacking great big doors on the very end of the engine close and achieve the same thing. Apparently these are hydraulically operated (definitely on the F70/100). In cold stream reversers, internal doors similar to the clamshell doors close and again divert air forwards via cascade vanes. In flight these cascade vanes are covered by a moveable secton of engine cowling. But when comparing this system with the other two you find that only the cold stream (or fan or by-pass air) is diverted with the exhaust still exiting to the rear providing forward thrust. Apparently this system is powered by an air motor or hydraulics. The 737-300 series onwards has this system of reverse thrust.

PM

RJB's post has the diagram from the book.

[The Airbuser]

OK, I see. So the "high bypass engines" (it's that how are called the "round" engines" like B757, A320?) use the cold stream reversers...It's all clear now.

[rjb4000]

That is correct.

High bypass turbofans rely on a large compressor fan driving air rearward with a small compressor core driving the fan:

http://en.wikipedia.org/wiki/Image:Turbofan_operation.png

A low bypass turbofan relies high pressure air exiting the nozzle at a relatively high velocity:

http://en.wikipedia.org/wiki/Image:Turbofa...n_%28lbp%29.png

An ultra-high bypass ratio turbofan is called a turboprop:

http://en.wikipedia.org/wiki/Image:Turboprop_operation.png

[Fluffdoc]

Early 727's had target type reversers. Somewhere during the production process a switch was made to the clamshell type.

There was a modification developed by an outfit named Valsan that replaced the pod engines JT8D-7, -11, -15, etc) with JT8D-200 series engines (same type used on MD-80s). The original center engine was left in place but the thrust reverser was removed.

[27driver]

I am imagining it is the little rectangular spaces seen here, if you look closely at thefront part of the engine exhaust.

I've always called them cascade vanes...the JT8D engines use either the cascade (7,9,11,15,17, etc) while the 217,219 etc. are equipped with target reversers. It's not about the type of 727, it's about the engine. I've flown 100's and 200's with either and both different types. I've also also understood clamshells, buckets, and target reversers all to be called the same thing...at least that's what the "old guys", aka: those that have been flying longer than I've been alive...have called them.

[Ranger]

There was a modification developed by an outfit named Valsan that replaced the pod engines JT8D-7, -11, -15, etc) with JT8D-200 series engines (same type used on MD-80s). The original center engine was left in place but the thrust reverser was removed.

Absolutely the best B-727 derivative in the air! I loved flying the Valsan. But I don't ever want to set foot in another 727 as long as I live. I can't hear because of that airplane. Well, that and 5,000 of turbo-prop time with no hearing protection and a couple of frags that got a bit close.

[AirRabbit]

Various thrust reverser designs are commonly known, and the particular design utilized depends, at least in part, on the engine manufacturer, the engine configuration, and the propulsion technology being used.

In order to get “reverse” thrust from a jet engine you’re going to have to re-direct the flow of the hot gaseous exhaust. That means you’re going to have to use some sort of blocking mechanism placed in the flow of that exhaust. The “name” of the system used is dependant on several things: what the engine manufacturer chooses to call it; what observers of the operation choose to call it; what those who use or repair it choose to call it.

1. Perhaps the most prominently visible method is to use large, scoop-shaped, diverter plates, mounted on the aft sides of the engine exhaust when stowed. They are moved out and away from the engine, and then through an arc that positionss them against one another immediately aft of the engine exhaust in such a manner that all of the exhaust impinges on these scoops and is re-directed up, down, or to the sides of the engine. These are commonly called “buckets.” Sometimes they are called “target buckets.” Sometimes they are called “clamshells.” However, there are other methods.

2. There are those methods that use large, scoop-shaped, diverter plates that are hinged differently than those described above, such that when deployed the plate is deflected inward from the sides of the exhaust ring, and sometimes a portion of the plate is deflected outward, away from the engine cowling. These diverter plates also come together, but they do so inside of the engine exhaust ring, effectivly diverting all of the exhaust through the newly created openings on the sides of the rear of the exhaust ring. These are also called “clamshells,” but I think is a more accurate use of the reference because the action of these plates more closely mimics the operation of a true clam shell.

In both of these cases the engine exhaust has completely escaped or has almost completely escaped from the rear of the engine before it is diverted.

3. There are those methods that use similar scoop-shaped plates, but they’re not as large and because there are more of them used, each one is less “scoop-shaped,” and when deployed are deflected into the exhaust flow further forward in the engine, but still aft of the burner section. The diverted exhaust still has to exit the engine in some direction other than aft. The exhaust ports used are the ones that were “uncovered” with the deployment of the diverter plates – but the openings are actually a set of louvers, or vanes, the shape of which assists the extraction of the exhaust gases. Because of the row upon row of these louvers, or vanes, they are commonly called cascading louvers or cascading vanes. As a result, this is often called a cascade reverser system.

4. There are those methods that use blocker plates (the numbers of which vary) that are positioned into the by-pass air flow from the fan section of the engine – and do not deflect into the exhaust gas flow. These diverter plates, mounted entirely internally to the engine cowling, are usually moved into the blocking position as part of a movement of a section of the engine cowl (usually aft) that also opens to expose a ring of cascading louvers, or vanes, that often encircle the entire engine, diverting the by-pass air flow out of the sides of the engine all around the circumfrence of the cowl. Obvisously, these, too, are called cascade reverser systems.

5. There are those methods that use blocker plates (again, the number of which may vary, but the vast majority use only 4 – with 2 mounted on each side of the engine cowl) that are positioned into the by-pass air flow from the fan section of the engine. They do not deflect into the exhaust gas flow, but are hinged so that a portion of the plate is deflected outboard of the engine and the remainder effectively blocks all (or almost all) of the by-pass air. The redirected air escapes out of the openings made when the blocking plates open outboard. These are often called pivot door reverser systems.

Oh, one more thing. I have seen high by-pass engines that use BOTH a cascade system described in number 4, above, to reverse the by-pass (fan) portion AND a bucket system, described in number 1, above, to reverse the core engine exhaust! They are not common, but they do exist.