Avon engines

[Yankee_Aviator]

My understanding is that SNECMA was weak at combustion chambers and other "hots" parts, and the solution was their partnership with General Electric over the CFM56. That way they snatched the F101 core, and it probably helped a lot when making the M88.

This is an impression I've had for awhile based on the ATAR's mediocre performance, always wondered if there was any truth to it, or just an opinion formed based on casual observations. Anyways, I wonder if a partnership with another engine company earlier on (say RR or MTU) could have helped squeeze more power out of the ATAR without increasing its weight. Again, at this point I just want to know if there is some design or materials change SNECMA could have hypothetically made to improve the ATAR 9 family's T/W (and thus the Mirage III's T/W)

 

[Archibald]

You've been told repeatedly ATAR performance was NOT mediocre...

 

[GTX]

You've been told repeatedly ATAR performance was NOT mediocre...

Indeed, with only 3600+ produced...

 

[kaiserbill]

The American engines would have required much redesign of the rear fuselage; the Aussies' opinion of them was not overly high in other respects.

I'm aware that the Kfir suffered from stability (aft CG) issues due to the J79 being shorter and heavier (more weight positioned further aft in the fuselage) and the additional cooling equipment required for it ate into the performance advantages the J79 offered. At this point I just want to know if there's anything SNECMA could have done to improve the ATAR's thrust output without increasing its weight, I want to know if they could have done anything to improve the Mirage III/F1's thrust to weight ratio.

South Africa did work on an improved ATAR 9k50.
The two major goals were:
1. Increased thrust.
2. Weight reduction.

From what has been intimated, an increase in thrust was achievable ( about 10%), but the weight reduction goals (not stated) were not achieved, at least when the project was shelved.

At that stage (late 80's), a low bypass turbofan was the better solution.

 

[BlackBat242]

I suppose I had failed to take into account another well-known possible issue with the Avon...

Taking a second look at the engine stats I have, I see that the series 300 Avons had an airflow-mass requirement of 170-175 lb/sec... while the ATAR 9C had only a 150 lb/sec requirement.

As the Mirage III's intakes were sized to provide the proper airflow-mass for the ATAR 9C, and having them unnecessarily large would increase drag... perhaps the Avon's disappointing performance could be simply due to the test aircraft's intakes having NOT been enlarged in cross-section, thus slightly starving the Avon of needed airflow-mass? Or if they were enlarged, did that significantly increase the drag?


It was the need to enlarge the intakes on the British Phantoms to satisfy the higher airflow-mass requirements of the Spey (200-210 lb/sec vs 170 lb/sec for the J79) that increased the airframe drag of the Queen's Phantoms so significantly, after all.

 

[steelpillow]

As the Mirage III's intakes were sized to provide the proper airflow-mass for the ATAR 9C, and having them unnecessarily large would increase drag... perhaps the Avon's disappointing performance could be simply due to the test aircraft's intakes having NOT been enlarged in cross-section, thus slightly starving the Avon of needed airflow-mass? Or if they were enlarged, did that significantly increase the drag?

It was the need to enlarge the intakes on the British Phantoms to satisfy the higher airflow-mass requirements of the Spey (200-210 lb/sec vs 170 lb/sec for the J79) that increased the airframe drag of the Queen's Phantoms so significantly, after all.

You would have to dig out the Dassault archives to find out if they modified the intake geometry for the Avon. It had moveable shock cones, so maybe they just adjusted the positioning. Then again, you would have to compare the altitudes, temperatures and airspeeds for which the airflow numbers were given. I am sure that R-R and the Aussies would have been aware of any such issue and would have taken it all into account.

My understanding of the RN Phantoms was that the Speys hung down at the back, and this was what stuffed the area ruling. But maybe it was a double-whammy.

 

[Archibald]

I suppose I had failed to take into account another well-known possible issue with the Avon...

Taking a second look at the engine stats I have, I see that the series 300 Avons had an airflow-mass requirement of 170-175 lb/sec... while the ATAR 9C had only a 150 lb/sec requirement.

As the Mirage III's intakes were sized to provide the proper airflow-mass for the ATAR 9C, and having them unnecessarily large would increase drag... perhaps the Avon's disappointing performance could be simply due to the test aircraft's intakes having NOT been enlarged in cross-section, thus slightly starving the Avon of needed airflow-mass? Or if they were enlarged, did that significantly increase the drag?


It was the need to enlarge the intakes on the British Phantoms to satisfy the higher airflow-mass requirements of the Spey (200-210 lb/sec vs 170 lb/sec for the J79) that increased the airframe drag of the Queen's Phantoms so significantly, after all.

Well if you are looking at a F-4K-like, "bloated by a big turbofan" Mirage III - try the III-T. It swallowed a Pratt JTF-10 / TF104 / TF106 but paid the price to it.

Another example is the Kfir. Digesting a J79 was a bit more easier but still caused a lot of issues.

Compared to the two above, never heard the Avon III-O suffered similar miseries.

A good case could be made the Mirage III / V / F1 engine bay upper growth limit is somewhere between Avon and J79.
- M53-2 was specifically designed to fit an Atar engine bay
- Avon fits barely
- J79 busted at the seams
- TF104 / 106 were clearly oversized
Asides from the specially designed M53, most of the 1960's era early tubofans (Spey, TF10/30) also busted that limit. A F404, M88 or EJ200 probably would not, but the Mirage III by this point of time was old stuff. The F1 could have benefited from them, however. But it missed the M53 train and scorned the M45 one.

 

[BlackBat242]

Its less about the size of the engine and more about the size of the intake.

Enlarging the intake cross-section to provide the greater airflow-mass changes the aerodynamics of the airframe along the whole fuselage between the intake mouth and the engine face.

The F404 and the F414 have the same engine body & afterburner diameter... but the diameter of the opening in the engine faces are different: the F404's is 27.7" and the F414's is 30.6".

The intake ducting all the way along is similarly larger for the Superhornet than for the Hornet, affecting the fuselage aerodynamic shaping.

F404 airflow-mass 142-146 lb/sec
F414 airflow-mass 169 lb/sec.

 

[steelpillow]

Its less about the size of the engine and more about the size of the intake.

and of course the intake is sized not just for the engine but for the speed and altitude at which the engine power is to be optimised. A low-altitude attack plane will have a smaller intake than a high-altitude interceptor, even with the same engine. This is the wonder of variable-geometry intakes, as standard on the Dassault Mirage.

 

[BlackBat242]

Its less about the size of the engine and more about the size of the intake.

and of course the intake is sized not just for the engine but for the speed and altitude at which the engine power is to be optimised. A low-altitude attack plane will have a smaller intake than a high-altitude interceptor, even with the same engine. This is the wonder of variable-geometry intakes, as standard on the Dassault Mirage.

The primary function of a variable-geometry intake is to slow the incoming air to subsonic speeds before it reaches the first row of turbine blades, as supersonic air does not work well entering a turbine.

Yes, most variable-geometry intakes do restrict the size of the opening to reduce the incoming airflow-mass at lower altitudes/speeds as well - but the intake itself must be sized to allow the proper amount of total airflow-mass to enter and pass through... having a variable-geometry intake will not magically compensate for a too-small intake cross-section.

 

[steelpillow]

having a variable-geometry intake will not magically compensate for a too-small intake cross-section.

I think we would all like to see the comparative figures used by Dassault in designing their conversion job. However, I am inclined to follow the Australian view that they knew what they were doing. Do you have any evidential basis for questioning their competence?

 

[BlackBat242]

Nowhere in any of my posts was there any claim - or insinuation - of any sort of "lack of competence" in regards to the Dassault engineers working on the Aussie Mirage project.

What I openly state is my suspicion that this was an early case of what later became a standard modus operandi for Marcel Dassault and his company... doing whatever it took to insure the maximum French (preferably Dassault-French) content and work-load of any putative "multi-national" project Dassault was mixed up in.

Just as the USAAF in the early 1940s had a habit of deciding at a glance that they didn't like a design proposal, then allotting only a much weaker engine than the design called for to use in the prototypes, then rejecting the design because" it failed to meet the promised performance" - said unreached performance being the numbers expected from the design with the more-powerful engine... so too I suspect the engineers at Dassault deliberately did not do their best to get the best performance from the Avon in the M-III - at the direction of MD, so that the ATAR looked "just as good" by comparison.

 

[BlackBat242]

The Aussies trusted Dassault "to know what they were doing" (and they did know)... but they (and much of the world) had not yet experienced Marcel Dassault's way of "adjusting" the outcome of things to favor French equipment and workshare.

 

[Archibald]

A private company in 1950's France, Dassault had to tread lightly between the French Gvt and the state owned SNECMA too. They also learned quickly...
Note that Australia was one of Dassault earliest competitions and sales pitch.

 

[steelpillow]

Nowhere in any of my posts was there any claim - or insinuation - of any sort of "lack of competence" in regards to the Dassault engineers working on the Aussie Mirage project.

What I openly state is my suspicion that this was an early case of what later became a standard modus operandi for Marcel Dassault and his company... doing whatever it took to insure the maximum French (preferably Dassault-French) content and work-load of any putative "multi-national" project Dassault was mixed up in.

You glibly swap deliberate subterfuge for incompetence - same difference, same need for verifiable sources. You still offer none, except equally wrong-headed imaginings:

Just as the USAAF in the early 1940s had a habit of deciding at a glance that they didn't like a design proposal, then allotting only a much weaker engine than the design called for to use in the prototypes, then rejecting the design because" it failed to meet the promised performance" - said unreached performance being the numbers expected from the design with the more-powerful engine... so too I suspect the engineers at Dassault deliberately did not do their best to get the best performance from the Avon in the M-III - at the direction of MD, so that the ATAR looked "just as good" by comparison.

R-R were closely involved in the project. If Dassault had tried any technical monkey business, R-R would have not hesitated to blow the whistle with vigour. The records show that R-R felt no such need. Your suspicions are no more than malicious gossip.

The Aussies trusted Dassault "to know what they were doing" (and they did know)... but they (and much of the world) had not yet experienced Marcel Dassault's way of "adjusting" the outcome of things to favor French equipment and workshare.

The Aussies trusted nobody. Not the Americans, not the British, not the French. "You do not sell to Australia, we buy"; that was precisely why they demanded the flyoff! And the results of that unequivocally give the lie to your nonsense. This has already been covered here in direct quotes from source documents.

In short, you keep ignoring and contradicting the evidence and in return offering only weasel words, unjustified "suspicions" and outright falsehoods. I think I have exposed enough of it now, for our fellow readers to make up their minds for themselves.

 

[zen]

To be fair....
I'm not sure how invested RR was in Etendard or Mirage III engine options.
And equally we know McDD and RR had to revise the F4K for inlets and back end to much increases in cost.

At the time the chief UK option tendered was a Lightning variant to the RAAF (with 2 RR Avons) and the Indian purchase of Etendard looked like very small numbers. So RR was probably not that invested in the outcome.
The big occupation for Avon sales was I think Comet, Hunter and Lightning. The future was first Thames and then Medway (and scaled down variant Spey). While the small engine market looked like blooming with the advent of VTOL aircraft.

Irony here is maybe had Dassault approached Armstrong Siddeley instead, Sapphire powered versions might have gained for investment from AS.
And we know Dassault had a Bristol Orpheus option. But sadly Bristol had no competitor to the Avon and Sapphire.

And again had DH been approached instead, Gyron Junior might have actually got it's issues fixed.

 

[Archibald]

Both Dassault and the French Gvt were trapped with SNECMA and Atar, whatever their flaws and weaknesses. The temptation of using foreign engines to please the customer and get better performance was quite strong, but the options were limited.

 

[steelpillow]

To be fair....
I'm not sure how invested RR was in Etendard or Mirage III engine options.

So you are suggesting it was the RR engineers not the Dassault ones who were incompetent in overseeing adequate installation of their own engine? And the Aussies were incompetent to recognise a mismatch when presented with one? Your documentary evidence for this handwaving is...?

I do wonder whether Dassault secretly recalibrated the airspeed indicators to make the Atar appear faster. Or perhaps the Avons were time-expired prototypes that RR were glad to see the back of. More likely, the gremlins sabotaged the Avons in-flight, to get even with R-R for not believing in them; Dassault probably made a secret deal with the gremlins (gotta be a French word, right?) and paid for it out of their slush funds. Sheesh guys, I have as much evidence for these theories as you have for yours.

"To be fair", we should consider the objective evidence, not return constantly to a lost cause. Face it. The Avon was beaten by the Atar fair and square on a level playing field. There really were no molehills for you guys to imagine up into mountains.

 

[zen]

So you are suggesting it was the RR engineers not the Dassault ones who were incompetent in overseeing adequate installation of their own engine?

I don't reccal putting words in your mouth, so try to not return a favour ungiven.

More likely, the gremlins sabotaged the Avons in-flight, to get even with R-R for not believing in them

If by gremlins you mean the umpteen potential pitfalls associated with installing jet engines into an airframe, then you may be right.
As I've suggested RR had bigger fish to fry, and it would need accounts of those involved to gage how invested in the effort RR staff were.

Which is not to say Atar won by underhand means. But is to say things are never quite as simple as sales brochures and even prototypes.

 

[steelpillow]

<snip>

Asking what you meant is not putting words in your mouth, there's no need to get personal.

I parodied your and BlackBat's unfounded speculations which conflict with the Australian account, because that is all they are.

 

[zen]

I parodied your and BlackBat's unfounded speculations which conflict with the Australian account, because that is all they are.

The Australian account is just the Australian account.
Not that of Dassault's staff or RR's.

One side of a story

 

[H_K]

There is no evidence that Dassault particularly favored Snecma engines. If anything it’s the opposite… there was a constant search for foreign engines:

Avon on MD550, Super Mystère B1, Etendard IVB and Mirage IIIO
Orpheus on Etendard VI
Spey on Mirage IVK and Mirage G4 (study)
JTF10 on Mirage IV (study)
TF30/TF306 on Mirage V, Mirage G and Mirage F2/F3
J79 on Mirage G (study)
J52 on Super Etendard (study)

… presumably this wasn’t just hand waving and Dassault were somewhat serious about investing time & money into these efforts.

 

[kaiserbill]

To answer some questions earlier in the thread, the 1310kg weight and 3200mm length for the afterburning Avon 300R as given on wiki is incorrect.

It's long been obvious to me that these specs are for the engine without afterburner.
Below is a placard for the RM6C which gives a more accurate reflection.

Weight without afterburner: 1300kg
Weight with afterburner: 1770kg
Length: 8.14m
Diameter: 1.18m
Dry thrust: 5845kg
Wet thrust: 7880kg
Airflow: 78kg/s
Compression ratio: 8.25

It's actually a very long engine.
In fact, I cannot think of a single jet engine fitted to an operational combat aircraft that is longer.

 

[kaiserbill]

Another pic of the RM6C, showing its length.
Did the Swedes develop their own afterburner or aft section?
What was the engine on the EE Lightning like?
I'm struggling to find illustrations of the Avon 301 and 302 as fitted to the Lightning.

Looking at the fact that they fitted an afterburning Avon into the Mirage III in Australia, it's clear that there must have been shorter aft sections/afterburners than found in the RM6C.
No way that they could have fitted an engine over 2 meters longer in the Mirage airframe.
Was the engine middle portion shorter?

EDIT: The EBK67 was indeed a Swedish designed afterburner.
I suspect the extension section in the middle between the front core Avon engine and EBK67 afterburner was put there to fit into the Draken within CG limits.
Thus, the afterburning Avon as fitted to the Mirage III probably was considerably shorter.

 

[Arjen]

Did the Swedes develop their own afterburner or aft section?

In SAAB aircraft since 1937 by Hans G Andersson, Putnam 1997, in the description of the RM 6B:

The afterburner was completely designed and developed in Sweden.

 

[kaiserbill]

In SAAB aircraft since 1937 by Hans G Andersson, Putnam 1997, in the description of the RM 6B:

Snap!
After digging around, I had edited my post around the same time as your post.
Thanks.

 

[red admiral]

There's a duct between the turbine and the afterburner which is dependent on the installation: engine is in a fixed location and the exhaust needs to be at the back. The actual reheat section and nozzle itself (the wider bit) is about 3-4 diameters long which is pretty normal.

 

[BlackBat242]

The Avon as fitted in the Lightning shows this well - the front (lower) engine had a much longer exhaust duct between the engine and the afterburner than did the rear (upper) engine.

Note that both afterburner modules are at the extreme end of the aircraft.

 

[H_K]

Below is a placard for the RM6C which gives a more accurate reflection.

Weight without afterburner: 1300kg
Weight with afterburner: 1770kg
Length: 8.14m
Diameter: 1.18m
Dry thrust: 5845kg
Wet thrust: 7880kg
Airflow: 78kg/s
Compression ratio: 8.25

I found the RM6B specs (Avon 200 series)...

Diameter: 920 mm (36.2 in)
Engine length: 3.552 m (139.9 in)
Total length with reheat (Type 66): 8.046m (316.8)
Dry thrust: 4,750 kgp (10,472 lb) at 8,000rpm
Wet thrust (Type 66): 6,340 kgp (13,980 lb) at 8000 rpm
Compressor, pressure ratio: Approx. 7.5:1 at 8,000 rpm
Exhaust gas temperature: approx. 700 degrees Celcius (1,292 degrees Fahrenheit)
Weight: 1,350 kg (2,976 lb)
Weight with Afterburner (Type 66): 1,720 kg (3,792 lb)

https://web.archive.org/web/2014031...Motorhistorik/EngineAndComponents/ARM_rm6.htm
https://web.archive.org/web/2010081...botmuseum.se/Mappar/Motorhistorik/ARM_rm6.htm

 

[H_K]

Also here's a nice compilation of RM6 data from various sources here:

RM6 (LeteckeMotory.cz)

BASIC CHARACTERISTICS OF RM6 ENGINES​

Version	-	RM6A	RM6B	RM6C	RM6C	RM6C
Maximum thrust	kN	47.46	46.58	58.35	54.92	55.4
Thrust with afterburner	kN	63.94	62.17	76.05	75.51	76
Total compression after the compressor	-				8.25
Maximum speed	min -1	8000	8000	8100	8100
Air flow rate	kg.s -1	70.5	70.5	78	78
Diameter	mm		920			1118
Length	mm		3552
Length with afterburner	mm		8046			8140
Weight	kg		1350
Weight with afterburner	kg	1675	1720	1770	1900	1770
Source	-	[volvo]	[volvo] [robot museum]	[volvo]	[angelholm]	[aerofax]

RM6B dry thrust is given as 46.58 kN or 50.01 kN.
RM6B thrust with afterburner is given as 62.17 kN or 67.56 kN.
RM6C dry thrust is given as 54.92 kN [angelholm] to 58.35 kN [volvo] (a difference of over 6%). The source [manual] gives 56.49 kN.
RM6C thrust with afterburner is given as 74.73 kN [flight] to 77.28 kN [volvo] (a difference of over 3%). The source [manual] gives 76.73 kN.
The specific consumption of the RM6C is apparently close to the values of 95 and 189 kg/kN/hr

RM6B OPERATING LIMITATIONS [flight manual]​

Regime	Mission time limit	Speed	Outlet gas temperature
Maximum dry thrust or reheat	10 minutes	100-98% (1)	750°C (2)
Climb (with/without pre-flight)	30 minutes	97.5-95.5%	720°C
Maximum continuous		up to 95%	680°C
Idling in flight		56 +2.5%	525°C
Idling on the ground		32 +2% (3)	650°C

(1) Speeds above 100% should, if possible, be reduced to 100% or lower by moving the POM.
(2) During afterburner ignition, the temperature can rise to 800°C
(3) When the engine is cold, the maximum speed is 37%.

RM6C OPERATING LIMITATIONS [flight manual]​

Regime	Mission time limit	Speed	Outlet gas temperature
Maximum dry thrust or reheat	25% of flight time, but no more than 15 minutes	100.5-101.5%	max 770°C, min 600°C tensile
Climb	75% of flight time, but no more than 45 minutes	max 97.5%	max 730°C
Maximum continuous		up to 95%	max 700°C
Idling in flight		65-67.5%	max 525°C
Idling on the ground		36-42% (cold engine max 45%)	max 700°C

During engine acceleration and afterburner activation, the temperature can briefly reach 800°C.
During climb, the speed can increase to a maximum of 104% (at altitudes above 13 km).
During takeoff at high ambient temperatures, the maximum speed is reduced to 96%.
During fast flight at low altitudes, the maximum speed is reduced to 97.5%.

 

[kaiserbill]

On the subject of the length of the Avon in different applications, this was in the F-104 projects topic.
An RA-24R Avon powered F-104 proposal.
J79-3 is 205 inches long, or 5,2 meters.
Avon is 229,7 inches long, or 5,8 meters.
This is a full 2,2 meters shorter than the Draken installation, and does not appear to need the mid engine extension found in the Avon installation in the Draken or Lightning.

It's worth pointing out that this is an Avon 200 series, whilst the later Drakens and Lightning used the 300 series.
Not sure whether that would hugely affect length though.

 

[kaiserbill]

An interesting archived report concerning the Avon 67 powered Mirage IIIC vs the Atar 09C.

View Digital Image

recordsearch.naa.gov.au

 

[H_K]

An interesting archived report concerning the Avon 67 powered Mirage IIIC vs the Atar 09C.

View Digital Image

recordsearch.naa.gov.au

Do I read that correctly (page 8) that the Avon Mirage was expected to super cruise at Mach 1.35!?

“11. Speed without Reheat. The Avon Mirage has a higher Mach number throughout the entire flight envelope, for example, the Avon Mirage achieves a maximum altitude of 51,000ft and a maximum Mach number of 1.35 compared with the Atar Mirage which achieves an altitude of 48,000ft and a maximum Mach number of 1.07.”