Two J85s were lighter than one Adour (both reheated versions) by 200 kg/450 lbs; single non-reheated Adour weighted almost as much as two reheated J85s. One old-tech Avon weighted 300 kg less than the two Adours, while making same thrust as these two combined.Is it?
If it is, then it's likely because it's a scaled down version of the original RB.172 which was closer to RB.153 or RB.199 or M.45 in size.
The Adour was initially designed well within the limits of technology available when its specification was formulated. The aim was to produce a relatively simple and rugged design, with modest operating temperatures, capable of performing reliably under the demanding conditions required for training and for the low level strike role.
[..]
The Adour engine cycle was chosen to meet the demanding requirements of ground attack and advanced training. A low bypass ratio of 0.75 to 1 was chosen to combine a small frontal area with the good fuel economy of the turbofan, and to provide the capability for substantial thrust increases through afterburning. Also, the traditional turbofan thrust lapse rate with altitude is minimized at this bypass ratio, providing good climb performance. Moderate operating temperatures and pressures were specified and combined with rugged construction to provide good reliability, high resistance to FOD, and considerable potential for thrust growth. Substantial improvements in maintainability were provided by grouping all major accessories on the underside to provide easy access, and by adopting modular construction.
Turbofans are always going to be heavier than turbojets. The benefit is increased fuel efficiency.
J85 was designed for light weight and initially short duration disposable use. It had high thrust to weight but also high specific fuel consumption. Orpheus was somewhat similar.
J85 reached 8:1 T/W ratio with later versions but was a very different engine.
The Adour was initially designed well within the limits of technology available when its specification was formulated. The aim was to produce a relatively simple and rugged design, with modest operating temperatures, capable of performing reliably under the demanding conditions required for training and for the low level strike role.
[..]
The Adour engine cycle was chosen to meet the demanding requirements of ground attack and advanced training. A low bypass ratio of 0.75 to 1 was chosen to combine a small frontal area with the good fuel economy of the turbofan, and to provide the capability for substantial thrust increases through afterburning. Also, the traditional turbofan thrust lapse rate with altitude is minimized at this bypass ratio, providing good climb performance. Moderate operating temperatures and pressures were specified and combined with rugged construction to provide good reliability, high resistance to FOD, and considerable potential for thrust growth. Substantial improvements in maintainability were provided by grouping all major accessories on the underside to provide easy access, and by adopting modular construction.
So more than enough time for any competant engineering team to have noticed that they were complete idiots in wanting to use a new turbofan - or it actually provided them with benefits to validate using it?The J85s powering manned aircraft were produced for 'normal' service lives, and still were very light.
J85-GE-13, that powered the F-5A, was making 4080 lb of thrust at A/B, weighting 579 lbs; T/W ratio of 7:1. 1st flight of the F-5A happened 9 years before Jaguar's 1st flight.
Yes, turbofans will have better fuel efficiency. Unfortunately, heavier engines will drive up the weight and size of aircraft designed around them, weight and size tend to eat up the fuel savings provided by engine type. Growth in size and weight also increases the price of an aircraft, not a good thing when commercial success means a lot. Take-off runs are also increased.
If a small jurbojet and airframe really was obvious an advantage of a design path 9 years is more than enough time for Rolls Royce, Turbomeca, Breguet and BAC to have taken notice and develop their engine and airframe concepts accordingly. The fact that their design was thrust into a role it was never really designed for as its primary mission is another story all together.
If a small jurbojet and airframe really was obvious an advantage of a design path 9 years is more than enough time for Rolls Royce, Turbomeca, Breguet and BAC to have taken notice and develop their engine and airframe concepts accordingly.
The fact that their design was thrust into a role it was never really designed for as its primary mission is another story all together.
Hency why I stated "primary mission". A armed trainer is very different in requirement to a dedicated strike platform which the jaguar became upon entering service. Look at the Hawk. Good combat trainer with tactical support capability, in no way a dedicated strike platform. Poor comparison in terms of size and power yes, but combat trainer usually means comparatively light loads - not lots of large heavy bombs and tanks on long missions with lots of extra ECM toys to try and protect you. The latter will always be a compromise if starting with an advanced jet trainer as your primary mission.By French in the early 1960s it was designated for the roles of "École de Combat et d'Appui Tactique", or literary "Trainer for combat and for tactical support". Lugging bombs, rockets and guns was in it's description.
Poor comparison in terms of size and power yes, but combat trainer usually means comparatively light loads - not lots of large heavy bombs and tanks on long missions with lots of extra ECM toys to try and protect you. The latter will always be a compromise if starting with an advanced jet trainer as your primary mission.
Most armed trainers can provide tactical support if required. Both the Hawk and Alpha Jet were designed with such a secondary mission if Europe had to go to war. Unless the actual requirements were comparable to those of a dedicated strike platform (which I highly doubt given how the program evolved but do correct me if I'm wrong) a trainer with weapons capability would have surficed for that role.Please note the "d'Appui Tactique" (tactical support) half of the job description.
A case could be make that when the AFVG was screwed, Jaguar could have had one RB.172 instead of two Adours. But it was too far long.
J85 reached 8:1 T/W ratio with later versions but was a very different engine.
The J85s powering manned aircraft were produced for 'normal' service lives, and still were very light.
J85-GE-13, that powered the F-5A, was making 4080 lb of thrust at A/B, weighting 579 lbs; T/W ratio of 7:1. 1st flight of the F-5A happened 9 years before Jaguar's 1st flight.
2 x J85-13 weighed 1,195lb and produced 8,160lb thrust in afterburning, which is 6.8 thrust/weight ratio, with SFC 1.26 in dry thrust
1 x Adour Mk 102 weighed 1,552lb and produced 7305lb thrust in afterburning, which is 4.7 t/w ratio, with SFC 0.75 in dry thrust
1 x Adour Mk 104 weighed 1572lb and produced 8040lb thrust in afterburning, which is 5.1 t/w ratio, with SFC 0.75 in dry thrust
So for 377 extra pounds, you get similar maximum thrust, but your dry SFC is so much lower that it will make a big difference for range in a strike aircraft mission. You'll actually save weight on the fuel needed for the mission.
For a short range lightweight air-air fighter, the J85 is a better option.
For Jaguar, the Adour is a better option.
Guess the trade space was filled where weight vs SFC was concerned....did size go into the calculus of the design?Two J85s were lighter than one Adour (both reheated versions) by 200 kg/450 lbs; single non-reheated Adour weighted almost as much as two reheated J85s. One old-tech Avon weighted 300 kg less than the two Adours, while making same thrust as these two combined.Is it?
If it is, then it's likely because it's a scaled down version of the original RB.172 which was closer to RB.153 or RB.199 or M.45 in size.
Yes, I'm comparing turbofans vs. turbojets, here, but anyway the weight/thrust discrepancy is amazing.
We can take a look at the RB.199, too. Weighted 20% more than the reheated Adour (976 vs. 810 kg) while making 80-100% more on reheat and 35-50 % 'dry'.
The old Bristol Orpheus also had an amazing thrust to weight ratio, perhaps it is too bad it wasn't developed into at a 'leaky turbojet' version? Development of the Pegasus shows the untapped potential of the Orpheus IMO.
Am going to make an overt edit....correction to the above turbomecca adour is over all 5 cm longer, but dry thrust 6,000 lbs vs j85 3,600 lbsGuess the trade space was filled where weight vs SFC was concerned....did size go into the calculus of the design? Yes, while heavier, they are not much larger in diameter ~5-6 cm and a good deal shorter with afterburner. Looking at the SFC, Adour is .8 something and J-85 is 1.2 something. That is what approx 33% more efficient?!.Two J85s were lighter than one Adour (both reheated versions) by 200 kg/450 lbs; single non-reheated Adour weighted almost as much as two reheated J85s. One old-tech Avon weighted 300 kg less than the two Adours, while making same thrust as these two combined.Is it?
If it is, then it's likely because it's a scaled down version of the original RB.172 which was closer to RB.153 or RB.199 or M.45 in size.
Yes, I'm comparing turbofans vs. turbojets, here, but anyway the weight/thrust discrepancy is amazing.
We can take a look at the RB.199, too. Weighted 20% more than the reheated Adour (976 vs. 810 kg) while making 80-100% more on reheat and 35-50 % 'dry'.
The old Bristol Orpheus also had an amazing thrust to weight ratio, perhaps it is too bad it wasn't developed into at a 'leaky turbojet' version? Development of the Pegasus shows the untapped potential of the Orpheus IMO.
Tthings are never as simple as 'armchair analysis' suggests.
Except that while the Jaguar carries 64% more fuel internally* (4200 liters versus 2560) it has almost four times the combat radius on that fuel load (440nm versus 120nm hi-lo-hi, no tanks). The greater weight and drag of the Jaguar sure seems like it mattered a lot less in the range department compared to the Adour's far lower fuel consumption.This is why I've brought out the aircraft's weight, size and drag - those are of interest for anyone making an analysis. A bigger and heavier engine will drive these up, and it will drive up the fuel spent for a mile traveled.
Except that while the Jaguar carries 64% more fuel internally* (4200 liters versus 2560) it has almost four times the combat radius on that fuel load (440nm versus 120nm hi-lo-hi, no tanks).
The balance of secondary sources point to the ferry range being the incorrect number: AirVectors backs up the combat radius, as do multiple other online sources, and this gives the ferry range as 3524 kilometers.What would be the loads for these radii?
If we're already going by Wikipedia, for the Jaguar the ferry range with 3 drop tanks was supposed to be 1027 nmi "with full internal and external tanks", while the combat radius with external fuel is 760 nmi? Making the aircraft go 760 nmi in one distance, reduce the altitude, drop the bombs, climb while returning to base for another 760 nmi for total of 1520 nmi?? Almost 500 nmi greater distance covered while making a combat sortie than it is the ferry distance.
The balance of secondary sources point to the ferry range being the incorrect number: AirVectors backs up the combat radius, as do multiple other online sources, and this gives the ferry range as 3524 kilometers.
As for loads, again based on AirVectors information the most likely load Jaguar would be carrying two AS.30L missiles, an Atlis II sensor pod, and two chaff pods, for a total warload of approximately 3000 pounds. All other loadouts show use of fuel tanks.
Which, yes, is a fair bit less than the listed warload for the F-5, but not so much to account for the entire massive difference in range.
So the trade space(s) is/are full, up and down the ladder....did we include politics? : )One other issue that hasn't been addressed is that there may be significant differences in the two engines resistance to things like birdstrikes, which would be a very real issue in the low-level operations the Jaguar was frequently tasked with, and FOD, especially from operating off ill-prepared runways. I do not know how these engines compare, and without access to actual test and service data, it may not be possible to make the comparison.
Do you actually have an answer to the question?So the trade space(s) is/are full, up and down the ladder....did we include politics? : )One other issue that hasn't been addressed is that there may be significant differences in the two engines resistance to things like birdstrikes, which would be a very real issue in the low-level operations the Jaguar was frequently tasked with, and FOD, especially from operating off ill-prepared runways. I do not know how these engines compare, and without access to actual test and service data, it may not be possible to make the comparison.
I think experience showed that the Jaguar needed both Adours when cruising at altitude… during air-to-air refueling it was not uncommon to have to light up partial reheat on one engine to offset the drag at high incidence!Jets like Jaguar didnt need both Adours for the whole mission.
It is not about simply having a more efficient motor. Liquid fuels have high energy density. You want to be able to convert that fuel to energy quickly. At other times you want to use the bare minimum. Turbofans are fuel efficient compared to turbojets when similarly sized, but turbojets generally convert fuel to energy faster for similar sized motors. Turbofans used like turbojets isnt ideal because of the high drag. Turbojets cannot typically offer anywhere near the turbofans efficiency even though they have lower drag.
They've had liftjets in the 20+ twr range for 5 decades. I'm surprised they couldnt find a way to run a turbofan in cruise mode while liftjet type engines are concealed. When high speeds are needed you flip out the liftjets and run the turbofan with a simpler, less fuel hungry afterburner.
Jets like Jaguar didnt need both Adours for the whole mission. One motor slightly larger than the Adour and the liftjet style motors could have allowed a higher fineness ratio overall, using only one motor running at a better power rating for the bulk of flight. Takeoffs and combat then would depend on high twr motors to maximum burn fuel at the right time. While these motors may be deadweight when not in use, some of these motors were only around 200 pounds in weight putting out thrust comparable to the J85 wet thrust.
It is not about simply having a more efficient motor. Liquid fuels have high energy density. You want to be able to convert that fuel to energy quickly. At other times you want to use the bare minimum. Turbofans are fuel efficient compared to turbojets when similarly sized, but turbojets generally convert fuel to energy faster for similar sized motors. Turbofans used like turbojets isnt ideal because of the high drag. Turbojets cannot typically offer anywhere near the turbofans efficiency even though they have lower drag.
They've had liftjets in the 20+ twr range for 5 decades. I'm surprised they couldnt find a way to run a turbofan in cruise mode while liftjet type engines are concealed. When high speeds are needed you flip out the liftjets and run the turbofan with a simpler, less fuel hungry afterburner.
Jets like Jaguar didnt need both Adours for the whole mission. One motor slightly larger than the Adour and the liftjet style motors could have allowed a higher fineness ratio overall, using only one motor running at a better power rating for the bulk of flight. Takeoffs and combat then would depend on high twr motors to maximum burn fuel at the right time. While these motors may be deadweight when not in use, some of these motors were only around 200 pounds in weight putting out thrust comparable to the J85 wet thrust.
This has been done in the civil sector, namely the Trident 3B airliner which had a extra jet in the tail for take off / climb in certain hot/high conditions. It used a modified lift engine jet - from Wikipedia
"Trident 3B, used, in addition to its three Rolls-Royce Spey turbofan engines, a centrally mounted RB.162-86 which was used for takeoff and climb in the hot prevailing conditions of the Mediterranean area. The 'boost' engine was shut down for cruising flight. Some conversion was needed for the change from vertical to horizontal installation. With the RB.162 fitted the Trident 3B had a 15% increase in thrust over the earlier variants for an engine weight penalty of only 5%"
In 1966 British European Airways (BEA) had a requirement for an extended range aircraft to serve Mediterranean destinations. After a plan to operate a mixed fleet of Boeing 727 and 737 aircraft was not approved by the British Government[4] Hawker Siddeley offered BEA a stretched and improved performance version of the Trident that they were already operating. This variant, the Trident 3B, used, in addition to its three Rolls-Royce Spey turbofan engines, a centrally mounted RB.162-86 which was used for takeoff and climb in the hot prevailing conditions of the Mediterranean area. The 'boost' engine was shut down for cruising flight. Some conversion was needed for the change from vertical to horizontal installation. With the RB.162 fitted the Trident 3B had a 15% increase in thrust over the earlier variants for an engine weight penalty of only 5%.