Tumansky R11F-300 vs. General Electric J79 - worlds apart. 🧵
The MiG-21 & F-4 have very different layouts, & their engines are no less dissimilar. Although both engines seem alike, the R11 and J79 were designed with different priorities in mind.
The mid 1950s is, for me, one of the most interesting periods in jet engine design. Every desig team was using its own distinct solution of increasing compressor pressure ratio (PR).
Rolls-Royce was using variable inlet guide vanes (VIGVs) & air bleed valves obtaining a PR of 9.1 - 10 with 16 stages in the Avon Mk.301R (Volvo RM6C).
Note: the picture is of a Avon RA.29/1 Mk.524 from the Comet 4, and has a 3-stage turbine, unlike the Mk.301R with 2.
SNECMA, who wanted simplicity, was getting a PR of only 5.50 in their Atar 9B/C with 9 stages.
OKB-165 Lyulka was using casing treatment, air bleed strip valve & a single VSV stage to get a PR of 9-9.5 out of a 9-stage supersonic compressor in their AL-7F-1.
OKB-300 Tumansky, in their R11F-300, was getting a PR of 8.9 using a supersonic twin spool with 3+3 stages. Later, the R13/25-300 went to PR=9.25/9.55, using 3+5 stages & casing treatment.
Pratt & Whitney was using twin spools in the J57-P-20, getting PR=12.5 out of 9+7 stages, & for the J75-P-19W PR=12.0 out of 8+7 stages.
And General Electric was using VIGVs & variable stator vanes (VSV) in the first 6 stages to get a PR of 12.1 to 13.5 out of 17 stages in the J79-GE-5 to J79-GE-17 respectively.
Out of all of these, I find the R11 and J79 to be almost diametrically opposed in compressor design. The R11F-300 series engines use just 6 stages to obtain a maximum PR of 8.9. A remarkably high loading per stage of 1.48, which is roughly double that of the J79's 0.72-0.79.
How does it achieve this? Well the R11F-300 compressor, in addition to using an air bleed valve and and twin spool design, is also supersonic (first 4 stages only). This means that the relative velocity between the air and rotor blade is supersonic (1st stage blade tip Mach...
...is 1.36), not that the compressor receives supersonic air from the inlet. The advantage is obvious, the R11 is able to obtain a high PR with a relatively light compressor, contributing to it having the best thrust/weight of its generation (T/W=5.40, 5.98 for later R11F2-300).
Compare this with the T/W of the others:
AL-7F-1 at 4.78
RM6C at 4.38
J75-P-17 at 4.17
J79-GE-5B at 4.29
J79-GE-8 at 4.71
Atar 9B at 4.44
Atar 9C at 4.25
But there is one major drawback to the R11's compressor design choice.
Although it gives you excellent T/W, the supersonic compressor also yields quite poor specific fuel consumption (SFC). Its minimum SFC is about 0.91 to 0.89 kg/kgf/h.
SFC values for the AL-7F-1 & Atar 9B/C, suggest that they're pretty close, but the Avon is likely a bit better.
There is no doubt however that the J79 is the most fuel efficient of them all, with its minimum SFC being about 0.78 for the J79-GE-8/11/15, to 0.76 in the J79-GE-10/17/19.
Note: the J75 likely has an SFC that's pretty good too.
The J79 needs 17 stages to obtain its excellent PR, which makes the compressor heavy, but since the stages are subsonic & PR is high, this gives good SFC. Here we can clearly see how the two engines perfectly reflect the intended roles of the aircraft that they power.
The MiG-21's primary requirement was always speed, altitude, rate of climb, range not being particularly important. The J79's development is however intrinsically linked to that of the Convair B-58A, so range was also important.
This difference in priorities is also made evident in the choice exhaust nozzle design. The R11F-300/MiG-21 nozzles is made to be simple & light (the actuator ring isn't even connected to the nozzle flaps!) likely with some efficiency loses while subsonic.
The J79-GE-5 of the B-58 is the exact opposite, complex, with many parts, but to reduce drag (low base drag nozzle) & be efficient in a wide range of conditions. Early J79s in the F-104 & F-4 had a less complex nozzle than the B-58, though in the later models this would change.
Of course, there are other aspects to consider. For example, turbine inlet temperature seems to be roughly the same for these engines though. About 877-924 °C in early models. But that's enough for now.
End.
VSXE = variable stator experimental engine with 14 stages (first 5 with VSV & VIGV), variable stator technology demonstrator for the J79.
I read a few years back a YouTube comment by a former GE employee, who said they joked about "VSXE" actually standing for "Very Sеху".
J79-GE-2 cutaway drawing, 1958.
Pratt & Whitney J57 cutaway drawing.
R11F-300 slow spool-up.
One weakness of all MiG-21 engines, from R11F to R25-300 is long spool-up time, as found by US HAVE DOUGHNUT evaluation of an MiG-21F-13 (R11F-300).
This weakness is well noted in the aircraft's manual and engine's operating handbook:
One might be tempted to conclude that the slow spool-up is the result of compressor design (as I used to assume). But this not true. The culprit is the variable exhaust nozzle control system design, according to a Hungarian Air Force pilot.
Czech Su-25 pilot, Leoš Liška said about the R-95Sh (basically R13-300 without variable exhaust nozzles):
"It was basically a stripped-down version of the MiG-21 engine. It had better acceleration than the original MiG-21 engine, 5.5 to 7.5 seconds, if I remember correctly."
Since now I have Avon Mk. 302 info, here's a comparison of the Mach 2 fighter engines of the early 60s. The stats are the best that I could find for each.
Tumansky R11F-300 vs. General Electric J79 - worlds apart. 🧵
The MiG-21 & F-4 have very different layouts, & their engines are no less dissimilar. Although both engines seem alike, the R11 and J79 were designed with different priorities in mind.The mid 1950s is, for me, one of the most interesting periods in jet engine design. Every desig team was using its own distinct solution of increasing compressor pressure ratio (PR).Rolls-Royce was using variable inlet guide vanes (VIGVs) & air bleed valves obtaining a PR of 9.1 - 10 with 16 stages in the Avon Mk.301R (Volvo RM6C).
Note: the picture is of a Avon RA.29/1 Mk.524 from the Comet 4, and has a 3-stage turbine, unlike the Mk.301R with 2.SNECMA, who wanted simplicity, was getting a PR of only 5.50 in their Atar 9B/C with 9 stages.OKB-165 Lyulka was using casing treatment, air bleed strip valve & a single VSV stage to get a PR of 9-9.5 out of a 9-stage supersonic compressor in their AL-7F-1.OKB-300 Tumansky, in their R11F-300, was getting a PR of 8.9 using a supersonic twin spool with 3+3 stages. Later, the R13/25-300 went to PR=9.25/9.55, using 3+5 stages & casing treatment.Pratt & Whitney was using twin spools in the J57-P-20, getting PR=12.5 out of 9+7 stages, & for the J75-P-19W PR=12.0 out of 8+7 stages.And General Electric was using VIGVs & variable stator vanes (VSV) in the first 6 stages to get a PR of 12.1 to 13.5 out of 17 stages in the J79-GE-5 to J79-GE-17 respectively.Out of all of these, I find the R11 and J79 to be almost diametrically opposed in compressor design. The R11F-300 series engines use just 6 stages to obtain a maximum PR of 8.9. A remarkably high loading per stage of 1.48, which is roughly double that of the J79's 0.72-0.79.How does it achieve this? Well the R11F-300 compressor, in addition to using an air bleed valve and and twin spool design, is also supersonic (first 4 stages only). This means that the relative velocity between the air and rotor blade is supersonic (1st stage blade tip Mach......is 1.36), not that the compressor receives supersonic air from the inlet. The advantage is obvious, the R11 is able to obtain a high PR with a relatively light compressor, contributing to it having the best thrust/weight of its generation (T/W=5.40, 5.98 for later R11F2-300).Compare this with the T/W of the others:
AL-7F-1 at 4.78
RM6C at 4.38
J75-P-17 at 4.17
J79-GE-5B at 4.29
J79-GE-8 at 4.71
Atar 9B at 4.44
Atar 9C at 4.25
But there is one major drawback to the R11's compressor design choice.Although it gives you excellent T/W, the supersonic compressor also yields quite poor specific fuel consumption (SFC). Its minimum SFC is about 0.91 to 0.89 kg/kgf/h.
SFC values for the AL-7F-1 & Atar 9B/C, suggest that they're pretty close, but the Avon is likely a bit better.There is no doubt however that the J79 is the most fuel efficient of them all, with its minimum SFC being about 0.78 for the J79-GE-8/11/15, to 0.76 in the J79-GE-10/17/19.
Note: the J75 likely has an SFC that's pretty good too.The J79 needs 17 stages to obtain its excellent PR, which makes the compressor heavy, but since the stages are subsonic & PR is high, this gives good SFC. Here we can clearly see how the two engines perfectly reflect the intended roles of the aircraft that they power.The MiG-21's primary requirement was always speed, altitude, rate of climb, range not being particularly important. The J79's development is however intrinsically linked to that of the Convair B-58A, so range was also important.This difference in priorities is also made evident in the choice exhaust nozzle design. The R11F-300/MiG-21 nozzles is made to be simple & light (the actuator ring isn't even connected to the nozzle flaps!) likely with some efficiency loses while subsonic.The J79-GE-5 of the B-58 is the exact opposite, complex, with many parts, but to reduce drag (low base drag nozzle) & be efficient in a wide range of conditions. Early J79s in the F-104 & F-4 had a less complex nozzle than the B-58, though in the later models this would change.Of course, there are other aspects to consider. For example, turbine inlet temperature seems to be roughly the same for these engines though. About 877-924 °C in early models. But that's enough for now.
End.VSXE = variable stator experimental engine with 14 stages (first 5 with VSV & VIGV), variable stator technology demonstrator for the J79.
I read a few years back a YouTube comment by a former GE employee, who said they joked about "VSXE" actually standing for "Very Sеху".J79-GE-2 cutaway drawing, 1958.Pratt & Whitney J57 cutaway drawing.R11F-300 slow spool-up.
One weakness of all MiG-21 engines, from R11F to R25-300 is long spool-up time, as found by US HAVE DOUGHNUT evaluation of an MiG-21F-13 (R11F-300).This weakness is well noted in the aircraft's manual and engine's operating handbook:One might be tempted to conclude that the slow spool-up is the result of compressor design (as I used to assume). But this not true. The culprit is the variable exhaust nozzle control system design, according to a Hungarian Air Force pilot.Czech Su-25 pilot, Leoš Liška said about the R-95Sh (basically R13-300 without variable exhaust nozzles):
"It was basically a stripped-down version of the MiG-21 engine. It had better acceleration than the original MiG-21 engine, 5.5 to 7.5 seconds, if I remember correctly."Since now I have Avon Mk. 302 info, here's a comparison of the Mach 2 fighter engines of the early 60s. The stats are the best that I could find for each.
yes
Tumansky R11F-300 vs. General Electric J79 - worlds apart. 🧵
The MiG-21 & F-4 have very different layouts, & their engines are no less dissimilar. Although both engines seem alike, the R11 and J79 were designed with different priorities in mind. ... The mid 1950s is, for me, one of the most interesting periods in jet engine design. Every desig team was using its own distinct solution of increasing compressor pressure ratio (PR). ... Rolls-Royce was using variable inlet guide vanes (VIGVs) & air bleed valves obtaining a PR of 9.1 - 10 with 16 stages in the Avon Mk.301R (Volvo RM6C).
Note: the picture is of a Avon RA.29/1 Mk.524 from the Comet 4, and has a 3-stage turbine, unlike the Mk.301R with 2. ... SNECMA, who wanted simplicity, was getting a PR of only 5.50 in their Atar 9B/C with 9 stages. ... OKB-165 Lyulka was using casing treatment, air bleed strip valve & a single VSV stage to get a PR of 9-9.5 out of a 9-stage supersonic compressor in their AL-7F-1. ... OKB-300 Tumansky, in their R11F-300, was getting a PR of 8.9 using a supersonic twin spool with 3+3 stages. Later, the R13/25-300 went to PR=9.25/9.55, using 3+5 stages & casing treatment. ... Pratt & Whitney was using twin spools in the J57-P-20, getting PR=12.5 out of 9+7 stages, & for the J75-P-19W PR=12.0 out of 8+7 stages. ... And General Electric was using VIGVs & variable stator vanes (VSV) in the first 6 stages to get a PR of 12.1 to 13.5 out of 17 stages in the J79-GE-5 to J79-GE-17 respectively. ... Out of all of these, I find the R11 and J79 to be almost diametrically opposed in compressor design. The R11F-300 series engines use just 6 stages to obtain a maximum PR of 8.9. A remarkably high loading per stage of 1.48, which is roughly double that of the J79's 0.72-0.79. ... How does it achieve this? Well the R11F-300 compressor, in addition to using an air bleed valve and and twin spool design, is also supersonic (first 4 stages only). This means that the relative velocity between the air and rotor blade is supersonic (1st stage blade tip Mach... ... ...is 1.36), not that the compressor receives supersonic air from the inlet. The advantage is obvious, the R11 is able to obtain a high PR with a relatively light compressor, contributing to it having the best thrust/weight of its generation (T/W=5.40, 5.98 for later R11F2-300). ... Compare this with the T/W of the others:
AL-7F-1 at 4.78
RM6C at 4.38
J75-P-17 at 4.17
J79-GE-5B at 4.29
J79-GE-8 at 4.71
Atar 9B at 4.44
Atar 9C at 4.25
But there is one major drawback to the R11's compressor design choice. ... Although it gives you excellent T/W, the supersonic compressor also yields quite poor specific fuel consumption (SFC). Its minimum SFC is about 0.91 to 0.89 kg/kgf/h.
SFC values for the AL-7F-1 & Atar 9B/C, suggest that they're pretty close, but the Avon is likely a bit better. ... There is no doubt however that the J79 is the most fuel efficient of them all, with its minimum SFC being about 0.78 for the J79-GE-8/11/15, to 0.76 in the J79-GE-10/17/19.
Note: the J75 likely has an SFC that's pretty good too. ... The J79 needs 17 stages to obtain its excellent PR, which makes the compressor heavy, but since the stages are subsonic & PR is high, this gives good SFC. Here we can clearly see how the two engines perfectly reflect the intended roles of the aircraft that they power. ... The MiG-21's primary requirement was always speed, altitude, rate of climb, range not being particularly important. The J79's development is however intrinsically linked to that of the Convair B-58A, so range was also important. ... This difference in priorities is also made evident in the choice exhaust nozzle design. The R11F-300/MiG-21 nozzles is made to be simple & light (the actuator ring isn't even connected to the nozzle flaps!) likely with some efficiency loses while subsonic. ... The J79-GE-5 of the B-58 is the exact opposite, complex, with many parts, but to reduce drag (low base drag nozzle) & be efficient in a wide range of conditions. Early J79s in the F-104 & F-4 had a less complex nozzle than the B-58, though in the later models this would change. ... Of course, there are other aspects to consider. For example, turbine inlet temperature seems to be roughly the same for these engines though. About 877-924 °C in early models. But that's enough for now.
End. ... VSXE = variable stator experimental engine with 14 stages (first 5 with VSV & VIGV), variable stator technology demonstrator for the J79.
I read a few years back a YouTube comment by a former GE employee, who said they joked about "VSXE" actually standing for "Very Sеху". ... J79-GE-2 cutaway drawing, 1958. ... ... Pratt & Whitney J57 cutaway drawing. ... R11F-300 slow spool-up.
One weakness of all MiG-21 engines, from R11F to R25-300 is long spool-up time, as found by US HAVE DOUGHNUT evaluation of an MiG-21F-13 (R11F-300). ... This weakness is well noted in the aircraft's manual and engine's operating handbook: ... One might be tempted to conclude that the slow spool-up is the result of compressor design (as I used to assume). But this not true. The culprit is the variable exhaust nozzle control system design, according to a Hungarian Air Force pilot. ... Czech Su-25 pilot, Leoš Liška said about the R-95Sh (basically R13-300 without variable exhaust nozzles):
"It was basically a stripped-down version of the MiG-21 engine. It had better acceleration than the original MiG-21 engine, 5.5 to 7.5 seconds, if I remember correctly." ... Since now I have Avon Mk. 302 info, here's a comparison of the Mach 2 fighter engines of the early 60s. The stats are the best that I could find for each.
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