Rolls-Royce engined 727's
Thread Starter
Join Date: May 2001
Location: Frankfurt, Germany
Posts: 143
Likes: 0
Received 0 Likes
on
0 Posts
Rolls-Royce engined 727's
I recently saw a picture of a UPS 727 which had been re-engined with Rolls-Royce Tay's. This posed a couple of questions, which I hope somebody will be able to provide answers to.
(a) What advantages does the Tay have over the P+W? (if any - and I presume there must be a reason for the re-engine)
(b) The duct for the centre engine has a very characteristic bulge. Clearly this is nothing to do with the size of the engine as that is mounted well away from the intake, so what is the reason?
(a) What advantages does the Tay have over the P+W? (if any - and I presume there must be a reason for the re-engine)
(b) The duct for the centre engine has a very characteristic bulge. Clearly this is nothing to do with the size of the engine as that is mounted well away from the intake, so what is the reason?
Join Date: Aug 2003
Location: Skagness on the beach
Posts: 882
Likes: 0
Received 0 Likes
on
0 Posts
The main reason was for noise regulations. As a matter of fact they meet Chapter 4 noise regulations as they are around -12.4 EPNdB to Chapter 3 limits. 
Imagine, A Chapter 4 727......
The bulge, if I remember correctly is for engine stall characteristics.
Imagine, A Chapter 4 727...... The bulge, if I remember correctly is for engine stall characteristics.
Prof. Airport Engineer
Join Date: Oct 2000
Location: Australia (mostly)
Posts: 726
Likes: 0
Received 0 Likes
on
0 Posts
The duct for the UPS727 Quiet Freighter centre engine is a special animal, and its characteristic bulge has to do with improving the airflow. Jim Finch got a patent on the design of it. He was a design engineer with Dee Howard, who did the re-engining of the 727 into the QF configuration by putting Rolls Royce Tay engines in all positions.
The duct forward end portion has a cross-section transitioning from a circular cross-section of substantially greater area than that of the original S-duct to an elliptical cross-section for the intermediate duct. The rear duct has a cross-section transitioning from the elliptical cross-section of the intermediate duct to a circular cross-section of substantially greater area than the original S-duct, thereby permitting installation of the Tay engine with a substantially larger air intake diameter;
The radius of curvature of the forward curved portion of the S-shaped intermediate duct portion was greater than the original S-duct and that led to the bulge. The leading bend had an increasing cross-sectional area in the range of about 1500 sq. in. to 1780 sq. in. and a radius of curvature in the range of about 0.5 deg./in.
The initial problem with the original S-duct was that Boeing found that not all JT8D engines would work with all S-ducts. Engines would have to be selected for a high surge factor for placement as the aft engine, supplied by a conventional S-duct. Boeing's S-duct was also limited in the volume of high energy air that would actually traverse the longitudinal length of the S-duct and appear at the engine fan.
The high energy air flow problem was addressed by Boeing in later versions of the S-duct. Boeing's S-duct technology dictated that more air flow from a larger diameter S-duct would solve the high energy air flow problem. However, to Boeing's dismay the larger inlet to the S-duct did not result in more high energy air reaching the engine fan. The principal reason for this failure is that the larger the inlet, the slower the air moves in the duct, therefore less high energy air reaches the engine fan.
The Tay series engine by Rolls Royce required 30% more air flow than the JT8D engine by Pratt Whitney. That increase in air flow, according to present S-duct technology, would dictate a 30% larger S-duct. That wouldn't work using the original S-duct concept.
Finch designed the S-duct for re-engining would have a configuration varying from an enlarged circular cross-sectional area at the forward open end of the air flow inlet to a first elliptical transitional area which has an increasingly reduced cross-sectional area as it approaches the main spar forging of the vertical fin of the aircraft. A second transitional section was provided rearwardly adjacent to the reduced cross-sectional area portion and has an increasing cross-sectional area and a circular cross-section as it approaches the engine intake fan.
The turning of the air was accomplished in the original 727 S-duct at lower velocities in an attempt to reduce boundary layer separation, but this called for a larger cross-section and resulted in more abrupt turns, and an unfavorable pressure gradient. The S-duct configuration of Finch allowed for increasing of the radii of curvature over previous designs and an area profile to accelerate the flow at the proper point in the curve to achieve the proper pressure gradient which maintains the required attached airflow, thereby maintaining a consistent velocity of high energy air presented over the entire engine fan disc.
Hence the bulge.
The duct forward end portion has a cross-section transitioning from a circular cross-section of substantially greater area than that of the original S-duct to an elliptical cross-section for the intermediate duct. The rear duct has a cross-section transitioning from the elliptical cross-section of the intermediate duct to a circular cross-section of substantially greater area than the original S-duct, thereby permitting installation of the Tay engine with a substantially larger air intake diameter;
The radius of curvature of the forward curved portion of the S-shaped intermediate duct portion was greater than the original S-duct and that led to the bulge. The leading bend had an increasing cross-sectional area in the range of about 1500 sq. in. to 1780 sq. in. and a radius of curvature in the range of about 0.5 deg./in.
The initial problem with the original S-duct was that Boeing found that not all JT8D engines would work with all S-ducts. Engines would have to be selected for a high surge factor for placement as the aft engine, supplied by a conventional S-duct. Boeing's S-duct was also limited in the volume of high energy air that would actually traverse the longitudinal length of the S-duct and appear at the engine fan.
The high energy air flow problem was addressed by Boeing in later versions of the S-duct. Boeing's S-duct technology dictated that more air flow from a larger diameter S-duct would solve the high energy air flow problem. However, to Boeing's dismay the larger inlet to the S-duct did not result in more high energy air reaching the engine fan. The principal reason for this failure is that the larger the inlet, the slower the air moves in the duct, therefore less high energy air reaches the engine fan.
The Tay series engine by Rolls Royce required 30% more air flow than the JT8D engine by Pratt Whitney. That increase in air flow, according to present S-duct technology, would dictate a 30% larger S-duct. That wouldn't work using the original S-duct concept.
Finch designed the S-duct for re-engining would have a configuration varying from an enlarged circular cross-sectional area at the forward open end of the air flow inlet to a first elliptical transitional area which has an increasingly reduced cross-sectional area as it approaches the main spar forging of the vertical fin of the aircraft. A second transitional section was provided rearwardly adjacent to the reduced cross-sectional area portion and has an increasing cross-sectional area and a circular cross-section as it approaches the engine intake fan.
The turning of the air was accomplished in the original 727 S-duct at lower velocities in an attempt to reduce boundary layer separation, but this called for a larger cross-section and resulted in more abrupt turns, and an unfavorable pressure gradient. The S-duct configuration of Finch allowed for increasing of the radii of curvature over previous designs and an area profile to accelerate the flow at the proper point in the curve to achieve the proper pressure gradient which maintains the required attached airflow, thereby maintaining a consistent velocity of high energy air presented over the entire engine fan disc.
Hence the bulge.
Last edited by OverRun; 25th Jan 2004 at 05:26.
Join Date: Jul 2000
Location: U.S.A.
Posts: 474
Likes: 0
Received 0 Likes
on
0 Posts
All the UPS 727’s are three crewmember aircraft with no plans on any conversion to two crewmembers.
I seem to remember some years back there was a conversion (proposed? - certified?) that had the engineer panel swing forward so it could be operated by the two window seat pilots. Anyone have any more info on this?
The Tay conversion program was not exactly embraced by the rest of the aviation world. Only one other aircraft other than the UPS aircraft was converted. This conversion was for the -100 series aircraft only – an airframe that is (1) old and (2) small. Not enough power in the Tay series at the time for a -200 conversion (the way I heard it).
The 727-100’s are falling out of favor at UPS. With rapidly expanding volumes at most cities, it is easy to bulk out (most package companies have more of a problem with “bulking out” instead of “grossing out” an aircraft). Their use as a hot spare rescue aircraft is limited for this reason also……it takes more than one to rescue many cities volumes.
I seem to remember some years back there was a conversion (proposed? - certified?) that had the engineer panel swing forward so it could be operated by the two window seat pilots. Anyone have any more info on this?
The Tay conversion program was not exactly embraced by the rest of the aviation world. Only one other aircraft other than the UPS aircraft was converted. This conversion was for the -100 series aircraft only – an airframe that is (1) old and (2) small. Not enough power in the Tay series at the time for a -200 conversion (the way I heard it).
The 727-100’s are falling out of favor at UPS. With rapidly expanding volumes at most cities, it is easy to bulk out (most package companies have more of a problem with “bulking out” instead of “grossing out” an aircraft). Their use as a hot spare rescue aircraft is limited for this reason also……it takes more than one to rescue many cities volumes.
Join Date: Aug 2003
Location: Skagness on the beach
Posts: 882
Likes: 0
Received 0 Likes
on
0 Posts
There is an STC around somewhere that converts the 727 to a 2 man flight deck but I don't think anybody has done it accept the person that developed the STC.
The TAY conversion was not embraced by the rest of the 727 operators because of problems with using digitally controlled engines on an analog based airplane. If UPS was not as big as they are those airplanes would no longer be flying because the FAA came very close to recinding the certification. I believe they have now somewhat fixed the problem.
The digitally controlled engines had to have a "translator" interface between the analog system of the 727 and the engines. As with all translation things don't always come out right. The digital control units would sometimes read the static from the analog controls as a shut down order and shut off the engine, all 3 of them.
They figured it out as being caused by a series of events and airplane attitude . They then convinced themselves and the FAA that one could control the chances of it happening again. Before they got it under control, UPS experienced several instances of triple flame out. One instance brought the airplane to 400 ft above the ground in the middle 
of a city before they got 1 or 2 (I can't remember if the TAY conversion can climb on 1 engine, I know the stock 727 cannot) fired back up again and could climb.
The TAY conversion was not embraced by the rest of the 727 operators because of problems with using digitally controlled engines on an analog based airplane. If UPS was not as big as they are those airplanes would no longer be flying because the FAA came very close to recinding the certification. I believe they have now somewhat fixed the problem.
The digitally controlled engines had to have a "translator" interface between the analog system of the 727 and the engines. As with all translation things don't always come out right. The digital control units would sometimes read the static from the analog controls as a shut down order and shut off the engine, all 3 of them.
They figured it out as being caused by a series of events and airplane attitude
. They then convinced themselves and the FAA that one could control the chances of it happening again. Before they got it under control, UPS experienced several instances of triple flame out. One instance brought the airplane to 400 ft above the ground in the middle of a city before they got 1 or 2 (I can't remember if the TAY conversion can climb on 1 engine, I know the stock 727 cannot) fired back up again and could climb.
Join Date: Aug 2003
Location: Skagness on the beach
Posts: 882
Likes: 0
Received 0 Likes
on
0 Posts
ferrydude,
I don't remember who it was, but I was approached by them when I was designing and selling hushkits for the 727 back pre 2000.
Don't always trust that FAA database for STCs, it has lots of errors.
If the STC is no longer available for sale and is installation specific I am not sure if that would show as well.
I don't remember who it was, but I was approached by them when I was designing and selling hushkits for the 727 back pre 2000.
Don't always trust that FAA database for STCs, it has lots of errors.
If the STC is no longer available for sale and is installation specific I am not sure if that would show as well.
Join Date: Jul 2000
Location: U.S.A.
Posts: 474
Likes: 0
Received 0 Likes
on
0 Posts
747 Focal and all,
The only triple engine problem I am aware of on the Tay converted 727’s was loss of power on all three engines due to a fuel surge then flameout when all cross feeds were (inadvertently) opened, then boost pumps turned on. Apparently, a situation that would have gone (virtually) unnoticed on a JT-8 powered aircraft is a big deal on Tay aircraft. To my knowledge, the fix is procedural and not a hardware fix – some sort of flow restrictors were tested/proposed, but not incorporated. As I recall, the player is different type of engine driven fuel pumps - Tay vs. JT-8, and their ability to handle (feed) pressure transients.
Haven’t heard about the analog/digital anomaly you refer to. Was this is flight testing, or after certification?
The only triple engine problem I am aware of on the Tay converted 727’s was loss of power on all three engines due to a fuel surge then flameout when all cross feeds were (inadvertently) opened, then boost pumps turned on. Apparently, a situation that would have gone (virtually) unnoticed on a JT-8 powered aircraft is a big deal on Tay aircraft. To my knowledge, the fix is procedural and not a hardware fix – some sort of flow restrictors were tested/proposed, but not incorporated. As I recall, the player is different type of engine driven fuel pumps - Tay vs. JT-8, and their ability to handle (feed) pressure transients.
Haven’t heard about the analog/digital anomaly you refer to. Was this is flight testing, or after certification?
Join Date: Jun 2003
Location: Near LOACH intersection
Posts: 497
Likes: 0
Received 0 Likes
on
0 Posts
747focal, The database I am referring to does not belong to the FAA. As I previously posted, there is no record of any FAA certification office issuing said STC. Unless you can produce some credible evidence, I maintain there never was an STC converting any 727 model to a two pilot airplane.
Join Date: Aug 2003
Location: Skagness on the beach
Posts: 882
Likes: 0
Received 0 Likes
on
0 Posts
ferrydude,
And you may be correct..... Who knows this could have been some tally whacker trying to drum up interest or investment. I had no interest in discussing anything with them.
Shore Guy,
This was held a very close secret for a very long time. You obviously know a something about the problem and your knowledge validates it somewhat.....but their is no sense in discussing it anymore than we have. It will just be arguement. Why do you ask silly questions about "flight test" or "cetification".......you should know that no "experimental" aircraft is allowed over populations without extreme examination??? One flamed out over a major US city and almost landed downtown.
And you may be correct..... Who knows this could have been some tally whacker trying to drum up interest or investment. I had no interest in discussing anything with them.
Shore Guy,
This was held a very close secret for a very long time. You obviously know a something about the problem and your knowledge validates it somewhat.....but their is no sense in discussing it anymore than we have. It will just be arguement. Why do you ask silly questions about "flight test" or "cetification".......you should know that no "experimental" aircraft is allowed over populations without extreme examination??? One flamed out over a major US city and almost landed downtown.
Prof. Airport Engineer
Join Date: Oct 2000
Location: Australia (mostly)
Posts: 726
Likes: 0
Received 0 Likes
on
0 Posts
747FOCAL's memory serves us well. The conversion of a three pilot cockpit to a two pilot cockpit was around in the mid 90s – probably 1996/7. I don't know if it made it to STC status but a fair bit of work was done on it. Richard Taylor and Ed Smith got a patent on it. I think it might have been based on something by Richard Shipman in "727: The New Look" in Air Line Pilot, Sep. 1988.
The original type certificate for the Boeing 727 was issued under the CAR 4B Rules, which required redundancy in critical aircraft systems, but not to the extent of requiring fail-safe operation of these critical systems as currently defined by the FAA, the fail-safe level being defined in "Part 25" of the Rules. Substantial modifications to the 727's systems invoke Part 25 of the Rules, which require conversion of those critical systems to a fail-safe level of operation - extremely expensive.
All glass cockpit solutions, involving software associated with the CRTs, required FAA oversight under Part 25 of the Rules, requiring the certification applicant to prove fail-safe operation of all software to a determined level of probability. In short, unless the majority of the supplemental type certificate (STC) observation and documentation procedures could be conducted under CAR-4B rules, the unit costs associated with aircraft modification are driven up to the point that the investment in the supplemental type certificate (STC) for the Boeing 727 cannot be returned. So they set out to make a CAR-4B conversion.
They relocated instrument controls from the flight engineer's instrument panel to positions in the cockpit closer to the remaining two pilot air crew, so the relocated instruments were accessible for monitoring and operation by the two pilot air crew. Although they make use of stored programme computers, they did not involve a "glass cockpit" type of conversion with CRT-based displays, thus avoiding the significant costs involved in the creation of the substantial software required to achieve the reading and conversion of analog control inputs/outputs for display on the CRT screens. Since no existing aircraft systems were changed, the STC could be under the CAR-4B rules of certification.
The installation of the conversion was claimed to be doable in less time than a week. The flight engineer's control panels were relocated to an extended overhead panel added between and over the captain's seat and the first officer's seat, and to a first officer's auxiliary panel mounted to the cockpit bulkhead adjacent the first officer's seat. All relocation of flight engineer instrument panel instruments was done without modification to the aircraft systems except to the fuel panel, the electrical panel, and the environmental control systems panel. The fuel panel, electrical panel and environmental control systems panel were modified to be more compact and include partial automation of these systems to reduce crew member workload. A master caution system was installed in the cockpit to monitor irregular and critical warning indicators out of the direct line of sight of the two crew members. In order that the two crew members not leave their seats during a landing gear extension failure, a mechanism provided gear extension capability from a seated captain or first officer's position.
The original type certificate for the Boeing 727 was issued under the CAR 4B Rules, which required redundancy in critical aircraft systems, but not to the extent of requiring fail-safe operation of these critical systems as currently defined by the FAA, the fail-safe level being defined in "Part 25" of the Rules. Substantial modifications to the 727's systems invoke Part 25 of the Rules, which require conversion of those critical systems to a fail-safe level of operation - extremely expensive.
All glass cockpit solutions, involving software associated with the CRTs, required FAA oversight under Part 25 of the Rules, requiring the certification applicant to prove fail-safe operation of all software to a determined level of probability. In short, unless the majority of the supplemental type certificate (STC) observation and documentation procedures could be conducted under CAR-4B rules, the unit costs associated with aircraft modification are driven up to the point that the investment in the supplemental type certificate (STC) for the Boeing 727 cannot be returned. So they set out to make a CAR-4B conversion.
They relocated instrument controls from the flight engineer's instrument panel to positions in the cockpit closer to the remaining two pilot air crew, so the relocated instruments were accessible for monitoring and operation by the two pilot air crew. Although they make use of stored programme computers, they did not involve a "glass cockpit" type of conversion with CRT-based displays, thus avoiding the significant costs involved in the creation of the substantial software required to achieve the reading and conversion of analog control inputs/outputs for display on the CRT screens. Since no existing aircraft systems were changed, the STC could be under the CAR-4B rules of certification.
The installation of the conversion was claimed to be doable in less time than a week. The flight engineer's control panels were relocated to an extended overhead panel added between and over the captain's seat and the first officer's seat, and to a first officer's auxiliary panel mounted to the cockpit bulkhead adjacent the first officer's seat. All relocation of flight engineer instrument panel instruments was done without modification to the aircraft systems except to the fuel panel, the electrical panel, and the environmental control systems panel. The fuel panel, electrical panel and environmental control systems panel were modified to be more compact and include partial automation of these systems to reduce crew member workload. A master caution system was installed in the cockpit to monitor irregular and critical warning indicators out of the direct line of sight of the two crew members. In order that the two crew members not leave their seats during a landing gear extension failure, a mechanism provided gear extension capability from a seated captain or first officer's position.
