When exactly did the practice of reduced thrust takeoffs originate? Was it in the 1960's with the early turbojet airliners already or later? Those early jet engines were not that powerful to start with...


Faro

The simple answer is no and in fact in those early days they had to augment power by using water injection especially with P&W engines.

Faro wrote:

When exactly did the practice of reduced thrust takeoffs originate? Was it in the 1960's with the early turbojet airliners already or later? Those early jet engines were not that powerful to start with...


Faro

Probably early 70s with the introduction of the cf6, jt9 and rb211. I know our 747-200/300/SP had the performance charts for reduced thrust ops.

I seem to remember doing reduced thrust ops in the 727 with the JT-8. 2.01/2.03 seems to stick in my mind and I seem to remember that was the max reduction. However, it's been over 30 years since my last flight in the 3 holer.

yep, we did reduced thrust t/o in the 727. remember all the charts well

I recall flying on the last EI 707 on its last day in service in 1985 and the captain noted that it was a 100%-thrust take-off (DUB-NOC), which I inferred to mean that full power would not normally be used, on short sectors at any rate. This was of course a turbofan rather than turbojet aircraft.

CosmicCruiser wrote:

yep, we did reduced thrust t/o in the 727. remember all the charts well

The OP asked about Turbojets. The 727 was a Turbofan. This would be like 707-320 (without the "B"), for example.

Not sure,but I don't think reduced power or assumed temp T.O., would be possible without FADEC or EEC controllers on the repspective engines and of course these were not a part of the first generation engines. (JT3C)

Of course, you could use reduced thrust without EECs. We did on the B727 in 1978.


Gf

I remember reduced thrust EPR take off settings of 1.97 / 1.99 on the B727

You guys are missing the point. He isn't talking about low bypass turbofan's, he is talking about PURE TURBOJET's. The 727 doesn't count, the 737-100/200's don't count, anything with any bypass at all doesn't count.

Andre3K wrote:

You guys are missing the point. He isn't talking about low bypass turbofan's, he is talking about PURE TURBOJET's. The 727 doesn't count, the 737-100/200's don't count, anything with any bypass at all doesn't count.

Indeed, that was the literal question...although having the extra bit of feedback re low-bypass doesn't hurt...I just wonder with turbojets whether durability and maintainability were high on the list of operators' priorities...or whether it was a given that turbojets were going to operate at maximum thrust on a regular basis and the consequences were what they were...


Faro

CosmicCruiser wrote:

yep, we did reduced thrust t/o in the 727. remember all the charts well

indeed, where possible, it certainly was being done on the 727....

GalaxyFlyer wrote:

Of course, you could use reduced thrust without EECs. We did on the B727 in 1978.


Gf

A slight but sublle difference I believe. In one case you are using a reduced EPR or N1 where as in the other you are using a derate that is a fixed number such as 20%, or an assumed temp. The performance engineers can explain this better than I.

I understand the differences. I my time “reduced” meant a planned lower thrust set, often using an assumed temperature but all performance “redlines” were still based on rated thrust. “Derate” was like putting a different thrust on the wing and “redlines” like Vmcg and Vmca we’re now based on that rating.

GF

I think a de-rated JT3C takeoff was with no water injection.

OldAeroGuy wrote:

I think a de-rated JT3C takeoff was with no water injection.

That's what I thought but can't recall any details that far back. Besides my time in a waterway was very minal at best.

All SAA's long haul take -offs from JNB in the early days were done with water injection, from the B707's right up till our JT9-7F's on the B747 SP's, those early P&W's were very under powered.

Balerit wrote:

All SAA's long haul take -offs from JNB in the early days were done with water injection, from the B707's right up till our JT9-7F's on the B747 SP's, those early P&W's were very under powered.

Pet peeve department


The engines weren’t underpowered,the aircraft was !

Max Q wrote:

Balerit wrote:

All SAA's long haul take -offs from JNB in the early days were done with water injection, from the B707's right up till our JT9-7F's on the B747 SP's, those early P&W's were very under powered.

Pet peeve department


The engines weren’t underpowered,the aircraft was !

I'm not sure what you are getting at but our Super B's with the JT9's were rated at about 41 000 lbs of thrust. The A300 's that we received came with CF 6's, rated at 50 000 lbs.
The B747 was over engineered and over the course of their lives we spent much time on removing unwanted equipment, things like the turbine thrust reversers or the humidifier systems. Also there is so much wasted empty space above the passenger compartment ceiling.

I do not remember anyone who purposely tried to reduce the thrust of an Avon, CJ-805, JT-3 or -4 during the initial t/o. Of course, after you were off the ground you might have noise abatement to contend with. Also, in the early days of the pure-jets, everybody was going as fast as they could. It's what you did.
By the time of the embargo of '74 anyone who was still ops a pure-jet had to make some changes, but the general idea was you had to get on up to cruise altitude to reduce the burn, and slow it down some. A DL -8-30 would blast on up in the early 70's. And the 880's and 720's did not survive the embargo. TW was still ops a few -320's in the late 70's. The last one of theirs I watched t/o at TPA like the Space Shuttle.

Balerit wrote:

Max Q wrote:

Balerit wrote:

All SAA's long haul take -offs from JNB in the early days were done with water injection, from the B707's right up till our JT9-7F's on the B747 SP's, those early P&W's were very under powered.

Pet peeve department


The engines weren’t underpowered,the aircraft was !

I'm not sure what you are getting at but our Super B's with the JT9's were rated at about 41 000 lbs of thrust. The A300 's that we received came with CF 6's, rated at 50 000 lbs.
The B747 was over engineered and over the course of their lives we spent much time on removing unwanted equipment, things like the turbine thrust reversers or the humidifier systems. Also there is so much wasted empty space above the passenger compartment ceiling.

I think he meant the engine produced its design rated power, only that the aircraft should have had more powerful models. So the airframe was underpowered, not the engine itself.

I can only imagine a 747 with only 41K engines out of JNB on a hot day... that would have been a long takeoff roll. Thats not that much more thrust than the A340-300...

77west wrote:

I think he meant the engine produced its design rated power, only that the aircraft should have had more powerful models. So the airframe was underpowered, not the engine itself.

I can only imagine a 747 with only 41K engines out of JNB on a hot day... that would have been a long takeoff roll. Thats not that much more thrust than the A340-300...

The engine produced its design rated and certified power. An airliner which has received its regulatory certification is just that...certified. And a certified airliner is never legally underpowered. The airframe was underpowered from an aviation enthusiat point of view.

Taking into account wing loading and not just thrust-to-weight ratio, one must recall that many early 1960's airliners were quite overpowered like the Comet 4, Tu-104, B720, Tu-123, etc. The 720 was known as the 757 of its day...a rocket on takeoff.


Faro

If you were departing someplace like MSP on a really cold day you would see the VS pegged at 6000 fpm with now trouble at all. The 720B was as good if not better than the 757 for shear power in the climb.

We did them with the CJ-610 in the Learjet. That was a bit overpowered though.

77west wrote:

Balerit wrote:

Max Q wrote:

Pet peeve department


The engines weren’t underpowered,the aircraft was !

I'm not sure what you are getting at but our Super B's with the JT9's were rated at about 41 000 lbs of thrust. The A300 's that we received came with CF 6's, rated at 50 000 lbs.
The B747 was over engineered and over the course of their lives we spent much time on removing unwanted equipment, things like the turbine thrust reversers or the humidifier systems. Also there is so much wasted empty space above the passenger compartment ceiling.

I think he meant the engine produced its design rated power, only that the aircraft should have had more powerful models. So the airframe was underpowered, not the engine itself.

I can only imagine a 747 with only 41K engines out of JNB on a hot day... that would have been a long takeoff roll. Thats not that much more thrust than the A340-300...

It might have been it's design power but it was the strongest P&W could develop at the time and wasn't sufficient for our requirements, remember they were behind the curve ball and rushed that engine into service. They only ever got that engine right with the -7r4g2.

As a ground engineer it was nerve wracking watching them take off at 18:00 with max fuel, 162500kg, and they would just miss the approach lights at the end of the runway as they lifted off. We used to have a saying that we must 'open the gates at the end of the runway' so that they had enough distance to take off. If you had the courage, you could go to the end of the runway and watch them coming towards you and it was an awesome sight as they lifted off just above you with all four engine turbines glowing red like Nissan Skyline tail lights

Great description and I understand


My point was there’s a tendency to describe an engine as ‘underpowered’


An engine can never be underpowered, it
can have a relatively low thrust for its size
and weight but that’s only an issue if it’s bolted to an airframe that is heavier than
desired for the installed thrust



Then that aircraft is underpowered

Faro wrote:

When exactly did the practice of reduced thrust takeoffs originate? Was it in the 1960's with the early turbojet airliners already or later? Those early jet engines were not that powerful to start with...


Faro

Laker Airways pioneered them with the Spey-engined BAC 1-11. Rolls Royce used to remark on the condition of engines returned to Derby for overhaul; the practice became widespread in the industry afterwards.

Referenced too in this Wikipedia article

https://en.wikipedia.org/wiki/Laker_Airways

Max Q wrote:

Great description and I understand


My point was there’s a tendency to describe an engine as ‘underpowered’


An engine can never be underpowered, it
can have a relatively low thrust for its size
and weight but that’s only an issue if it’s bolted to an airframe that is heavier than
desired for the installed thrust



Then that aircraft is underpowered

I guess that is another way of looking at it

I had to look through my Dad's DC-8-41/43 manual to find some answers. SOPs dictated right up to the time the aircraft was retired from Air Canada in the 1970s that all take-offs were done with the thrust levers "firewalled". The Second Officer however, would check that the resulting EPR was above minimum calculated for the current conditions. One would think therefore, that it was the start of reduced thrust take-offs. Namely, if 1.77 was calculated minimum and the engines were producing 1.91 (for example), why not just take off with the thrust set at 1.77?

There are some that argue that the RR Conways of the 1961 DC-8-41 were in fact, "fan jets", they did have a very low by pass. The JT3Ds fanjets that followed a year later on the DC-8-54 did do reduced thrust takeoffs right from the start. So it might have been a certification era issue with the engines as to which could do reduced thrust and which could not, as opposed to whether they were turbojets or fanjets.

It would be interesting to find out if more advanced Conways on say the VC-10 did reduced thrust take-offs.

Interesting site: (Follow the link to blade creep)

http://code7700.com/reduced_thrust.htm