Why The 3rd 727 Engine

SAAB340 · Wed Oct 17, 2001 8:47 am

Hey All!!

Can anyone tell me what the third engine purpose is??

I know this sounds like a dumb question but I really dont know. Thanks

PAUL

Bill Bob · Wed Oct 17, 2001 9:26 am

Extends its glide when the other two fail. Smile

Guest · Wed Oct 17, 2001 9:38 am

Not to be flippant, but the -27 has 3 engines because it needs 3 engines. At the time it was the most economical way to get the total amount of thrust to meet the design requirements.

AA777-200 · Wed Oct 17, 2001 12:41 pm

cuz it can barely get off the ground with 3 engines. could you imagine it only having 2??? Why do you ask us these questions. Ask boeing. why did the DC10 have 3 engines? why did the MD11 have 3? why does the 747 have 4? Its the design for the plane!!!

Minuteman · Wed Oct 17, 2001 1:04 pm

ETOPS didn't exist when they were making the blue prints on the walls of the cave for this plane.

AJ · Wed Oct 17, 2001 2:42 pm

During the development of the 727 Boeing was taking input from US airlines. SOme wanted a twin engine aircraft for economy, others four engines for field performance.
The compromise was a three engine aircraft.
Such compromises have also occured on the 747. Pan American wanted a 40 degree sweepback for speed, Boeing a 35 degree sweepback for field performance. The tradeoff? A 37.5 degree sweepback!

cedarjet · Thu Oct 18, 2001 1:31 am

The 727 is a lot heavier than the 737-200, and remember it was designed in the late 50s and early 60s when engines weren't perceived to be as reliable. Notice that the engine fire buttons are at the top of the centre panel, in later designs they've been moved overhead because of course they're almost never needed, but in those days the prop mentality remained, when it was quite routine for a longhaul prop (Stratocruiser, Connie, DC6 et al) to arrive at the end of a trans-Atlantic or trans-Pacific flight with one engine shut down.

Gregg · Thu Oct 18, 2001 8:59 pm

Also in the early 60s we designed a/c around the enginees, instead of designing engines around the a/c. Most enginees had simular power rating of around 20,000 lbs. So a 707 has 4, the smaller 727 has 3, the smaller 737 has 2 .....

exnonrev · Fri Oct 19, 2001 2:47 am

AJ is right. It was a compromise between American (who wanted two) and Eastern (they wanted four). United was happy with three from the start.

QANTAS747-438 · Fri Oct 19, 2001 6:47 am

727 sucks!

AJ · Fri Oct 19, 2001 9:11 am

That's quite a statement 747-438!
The Boeing 727 built Australia's air travel industry, and formed a vital part of TAA/Australian, which ultimately made the airline strong and able to be merged with...Qantas!

Notar520AC · Fri Oct 19, 2001 10:36 am

Yeah you dolt!

QANTAS747-438 · Fri Oct 19, 2001 1:58 pm

AJ---

Well zippidydooda for Australia... I live in Los Angeles so whatever Australia has to thank the 727 for has nothing of concern to me. I just love seeing Qantas cruise into LAX like it owns the place, hence the screen name. And the 727 still sucks.

Turtle · Sat Oct 20, 2001 1:22 am

747-438

What are your reasons for saying the 727 sucks? Just curious.

drgreen757 · Sat Oct 20, 2001 2:24 am

A true aviation fan doesn't think any aircraft sucks. They're all great in their own way.

MX727 · Sat Oct 20, 2001 5:25 pm

Saab340.
If you have time to come to Mexico City (7341ft. elevation), come by April or May (30 degrees celcius), then you can try to fly MEX-LAX, MEX-PTY, MEX-MXL or some route like that at 2pm full of passengers.
I can assure you that after takeoff you will realise why the 727 needs 3 engines.
Regards.
MX727

railker · Fri Oct 24, 2008 6:42 pm

I personally love the 727 to death, it's like the American Muscle of the aviation world, as it were. Their engines may not be huge, and performance may not be great at some have said, eats up the entire runway to get off, but I love the look of that plane and most definately the sound of of its engines roaring -- and to think those engines have a hush kit on them, can only imagine how loud they were when the aircraft first came out and didn't have any such hushing. Instead of everything being all quiet and hushed down, when one of these takes off, it's 100% brute power, a rumble you feel in your chest, and if your car's parked on a slope at your favorite observation post near the runway, you'd better hope you have a good strong handbrake.

((That actually happened. My dad's 1992 Ford Thunderbird SC had a weak handbrake. Parked at the emergency entrance gate at the base of runway 25 at YOW, First Air leaving for Iqaluit. Handbrake came loose and the car rolled across the road.))

roseflyer · Fri Oct 24, 2008 7:12 pm

When the 727 was designed, takeoff performance was very important. In the 50s, a 7,000ft runway was considered long. The days of every airport having 10,000ft runways were far off into the future. Airlines wanted a plane that could operate out of a 5,000ft strip. Engine out performance was a major issue with a twin engine design on such short runways. The 727 was designed to be operated on regional routes and domestic routes where the larger 707 did the transcon and international flights. The 727 had higher capacity than any of the other twin engine planes designed earlier or at similar times like the Caravelle and DC9. They could have made a 727 with two engines, but they would have been pushing the performance capabilities to get over 100 passengers off the ground.

The 727 was influenced heavily by United, American and Eastern. United was the airline pushing for three engines and eventually won. 4 engines were not efficient, and 2 did not offer the required performance. 3 was the design settled on, and it was a runaway success being the first jet to sell over 1,000 airplanes.

RussianJet · Fri Oct 24, 2008 7:15 pm

Quoting AA777-200 (Reply 3):
Why do you ask us these questions. Ask boeing. why did the DC10 have 3 engines?

That's a totally unnecessary thing to say. This is an aviation forum. We all have different interests and depths of knowledge, and we all have different jobs and can all bring different things to the table. Hell, just a wild guess, but I expect there ARE people that work for aircraft manufacturers here. THAT is why we ask questions here. Because the range of people here often leads to a satisfactory answer and an interesting discussion. If he has a civil aviation query, no matter how elementary or pointless it seems to the likes of you, he should ask about it. You do not have to bother yourself answering the question if you are not interested.

Quoting AA777-200 (Reply 3):
Its the design for the plane!!!

Yes, and the reasons it was designed the way it was, for the purposes it was built for, are many and complicated. Basically, he asks why it has or needs three engines. You basically say "because it has". Nice one. Why don't you try talking about the role the plane was intended for, the places it was intended to serve, the aerodynamic issues, the engine technology available at the time, ETOPS issues and so on, and so on, and so on.

unattendedbag · Fri Oct 24, 2008 8:26 pm

Quoting SAAB340 (Thread starter):
Can anyone tell me what the third engine purpose is??

It balances the aircraft. This looks kinda odd...

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Photo © Brian Harrison

speedracer1407 · Fri Oct 24, 2008 10:10 pm

Quoting RussianJet (Reply 18):
You do not have to bother yourself answering the question if you are not interested.

Well, he's had 7 years to think about it since he posted that response (reply 3). Perhaps he's older and wiser now.

Viscount724 · Fri Oct 24, 2008 10:36 pm

Quoting Speedracer1407 (Reply 20):
Well, he's had 7 years to think about it since he posted that response (reply 3). Perhaps he's older and wiser now.

Quoting Railker (Reply 16):
I personally love the 727 to death

Just a sidenote, but when a thread is resurrected after being dormant for years (7 years in this case), it would be courteous to mention this so other users are aware they're replying to an old thread. In this case, the original poster isn't even a valid A.net user ID now.

airbuster · Fri Oct 24, 2008 10:41 pm

Quoting QANTAS747-438 (Reply 9):
727 sucks!

If you can't be constructive to the discussion, why post?

Now, the thing i was wondering was with the engine retrofits available these days for 727's do they also replace the middle engine? As the 2 outer engines would already greatly increase performance, and i suppose cramming a larger engine into the middle S duct would be quite challenging....any info?

rgds

Ab

Starlionblue · Sat Oct 25, 2008 1:32 am

Quoting Drgreen757 (Reply 14):
A true aviation fan doesn't think any aircraft sucks. They're all great in their own way.

All aircraft suck air. That's how turbine engines work. duck

To sum up the reasons for the 727 having three engines:
- Engine technology at the time was not quite up to powering a twin of that size.
- Reliability for over water flights. This was way before ETOPS.
- Reliability period. Engines failed more in those days.
- Customer requests.

The third engine, specifically its s-duct, was a bit of development headache for Boeing, but in the end the 727 was a great success for the company.

boeing767mech · Sat Oct 25, 2008 3:40 am

Quoting Airbuster (Reply 22):
As the 2 outer engines would already greatly increase performance, and i suppose cramming a larger engine into the middle S duct would be quite challenging....any info?

D Howard did it for UPS on there -100's, they took all three JT8's off and replaced them with Roll-Royce Tays. You can tell the tay airplanes because of the bludge on the #2 inlet, like an DC-10-40 or MD-11.

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Photo © Tim Perkins

David

railker · Sat Oct 25, 2008 3:51 am

Quoting Viscount724 (Reply 21):

Whoa ... I really have no idea how I managed to get on this thread and think it was current, to tell you the truth. I did not mean, at all, to resurrect a 7-year-old thread.

Daaamn, this has been an overall wierd day ... sorry for disturbing anyone! haha.

Max Q · Sat Oct 25, 2008 4:15 am

You have to remember, also, the much lower thrust levels of the older JT8D engines on the 727,

The -9 was only 14,500 lbs thrust.

Thats only 43,500 lbs thrust total or about the same as one RB211 on the 757 !

She really needed three ! I remember seeing both ends of the runway on a regular basis..

She was the first Jet I ever flew and what a dream machine, I was fortunate.

RussianJet · Sat Oct 25, 2008 9:16 am

Quoting Viscount724 (Reply 21):
Just a sidenote, but when a thread is resurrected after being dormant for years (7 years in this case), it would be courteous to mention this so other users are aware they're replying to an old thread. In this case, the original poster isn't even a valid A.net user ID now.

And, not all of us can remember every post from seven years ago, and in the course of seven years many people come and go.

jush · Sat Oct 25, 2008 11:20 am

Can I just ask who pulls out a thread from 2001 answers it and then alot of other people talk about a thread which was done almost 7 years ago.

And then you discover the facts and still people are answering...

Very strange day.

[Edited 2008-10-25 04:20:36]

767nutter · Sat Oct 25, 2008 2:01 pm

Quoting SAAB340 (Thread starter):
Hey All!!

Can anyone tell me what the third engine purpose is??

I know this sounds like a dumb question but I really dont know. Thanks

PAUL

As what everyone else said it needed three, the 727-100 would have been ok with two on light loads but the 727-200 was described as a 'dog' to handle, way underpowered

I remember reading a article from a retired United pilot who flew the DC-6, DC-8, 727, 737, 757/767 and finished on the 777. ( this might help people remeber if they have read this as i can't remeber the chaps name)

He said he was sitting in the cockpit waiting for a storm to clear, it was hot, muggy and they were fully loaded, while waiting the topic of engine failure came up and with the head stewardess in the flightdeck at the time she asked what would happen if they did lose a engine, the Captain turned round and said ' sweetie, if we did lose an engine we would be the fastest boat on Tampa bay '

CosmicCruiser · Sat Oct 25, 2008 3:12 pm

Quoting QANTAS747-438 (Reply 12):
Well zippidydooda for Australia... I live in Los Angeles so whatever Australia has to thank the 727 for has nothing of concern to me. I just love seeing Qantas cruise into LAX like it owns the place, hence the screen name. And the 727 still sucks

I can't believe I'm responding to such an ignorant post BUT I do want to address the 727 sucks comment.

The 727 was/is the DC-3 of the jetage and was the most fun jet I've flown. It was rugged and you can do things with it you certainly won't do with newer "high tech" jets. I flew all 3 seats in the 72 and even with it's little quirks it was a hoot to fly. I'll always be glad I got my 91/2 years in the grand ole 727. Some of ours had the Valsan mod and it definitely wasn't under powered. Granted our ex-Air Canada -15s were a little sluggish coming out of Toluca.

OldAeroGuy · Sat Oct 25, 2008 3:56 pm

Quoting SAAB340 (Thread starter):
Can anyone tell me what the third engine purpose is??
Without it, the 727 wouldn't have been a copy of the HS Trident.

Quoting Cedarjet (Reply 6):
Notice that the engine fire buttons are at the top of the centre panel, in later designs they've been moved overhead because of course they're almost never needed
I think you should check the location of the fire handles on the latest generation of Boeing Twins. They're still on the center pedestal.

http://meriweather.com/777/ped-777.html

Look just above the CDU.

[Edited 2008-10-25 09:20:03]

LY777 · Sun Oct 26, 2008 8:45 am

Quoting QANTAS747-438 (Reply 9):
727 sucks!

what an interesting comment!
Are you sure you are a true aviation fan?

Viscount724 · Mon Oct 27, 2008 2:58 am

Quoting Boeing767mech (Reply 24):
Quoting Airbuster (Reply 22):
As the 2 outer engines would already greatly increase performance, and i suppose cramming a larger engine into the middle S duct would be quite challenging....any info?

D Howard did it for UPS on their -100's, they took all three JT8's off and replaced them with Roll-Royce Tays. You can tell the tay airplanes because of the bulge on the #2 inlet, like an DC-10-40 or MD-11.

The #2 engine intake on the 727-100s with the R-R Tay conversion was also round, not oval like the P&W 727-100. (The 727-200 also has a round #2 intake.)

727-100 (P&W)

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767nutter · Mon Oct 27, 2008 2:46 pm

Quoting QANTAS747-438 (Reply 9):
727 sucks!

Why? i would have loved to be able to fly that beauty, it didn't have none of this high automation we see nowadays. it cried out to be hand flown in all phases of flight ( ok maybe not cruise ) but it meant that all landings and approaches were hand flown and it showed how skillful a pilot can be. ( unless of course any CAT II / III or autoland features were installed ) CosmicCruiser coud you answer that please.

Northwest727 · Tue Oct 28, 2008 1:08 am

It was a compromise. In the early 1960s, during the aircraft's birth, UA wanted another 4 engined aircraft to operate out of KDEN. EA wanted a more efficeint twin engined aircraft, to operate out of KMIA. Boeing came up with a compromise...3 engines instead.

acNDTTech · Wed Oct 29, 2008 1:48 am

Also, back in the mid to late 80's, there was a proposal for a mod to make the 727 a twin by removing the center engine - S-Duct and all. I wish I could remember what periodical the article was in - maybe Aviation Week & Space Technology???? I'll try to find it and add to this thread.

Starlionblue · Wed Oct 29, 2008 2:48 am

Quoting AcNDTTech (Reply 36):
Also, back in the mid to late 80's, there was a proposal for a mod to make the 727 a twin by removing the center engine - S-Duct and all. I wish I could remember what periodical the article was in - maybe Aviation Week & Space Technology???? I'll try to find it and add to this thread.

This one is bogus I think but it gives an idea of the direction.

acNDTTech · Wed Oct 29, 2008 4:17 am

No, not this one. I saw that a while back. The one that I remember was a 200 without the winglets. It may have had UDF engines on it. It may have been called 727-300.....also, this was also about the time of the Lockheed FanStar.

TSS · Wed Oct 29, 2008 5:13 am

Quoting AcNDTTech (Reply 38):
The one that I remember was a 200 without the winglets. It may have had UDF engines on it. It may have been called 727-300.....also, this was also about the time of the Lockheed FanStar.

You're thinking of the Boeing 7J7, a proposal from the 1980s for a successor to the 727. It looked much like the illustration above, except it featured UDF engines. It also featured a twin-aisle cabin with (depending on the source) either a 2-2-2 or 2-3-2 Y-class seat layout.

DocLightning · Wed Oct 29, 2008 9:49 am

Quoting Drgreen757 (Reply 14):
A true aviation fan doesn't think any aircraft sucks. They're all great in their own way.

Except the A320 duck

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