Hornet - underpowered at high altitude?

[datafuser]

AIR SUPREMACY AND AIRLAND OPERATIONS, a thesis by a USAF major at the U.S. Army Command and General Staff College in 1992, pointed out the following as the F/A-18 Hornet's weakness.

WEAKNESSES: The engine design of the Hornet leaves it under powered in the high altitude environment. Moderate weapons loads reduce the low altitude maneuverability considerably.

Exactly what aspect of the F404 engine design made the Hornet underpowered at high altitude?

 

[datafuser]

Any idea what features of the F404 engine design make the Hornet underpowered at high altitude?

 

[GeorgeA]

I'm guessing this was one of the things they tried to address with the F-18E/F.

 

[sferrin]

I'm going to go out on a limb and suggest it has something to do with their engines bypass ratios. Lower bypass engines tend to do better at higher altitudes. Apparently the M53 is even more powerful than early versions of the F100 at high altitude. This might also explain why most later model F-15s have gone with the F100-229 instead of the F110 despite the common engine bay that would allow them to go with the F110. The F100 has a lower bypass ratio and higher exhaust velocity than the F110. This would allow the F-15 to have more power at high altitudes than if they went with the F110.

 

[Sundog]

I'm going to guess it doesn't have as much to do with the F404 as it does the weight of the F/A-18 to begin with. It isn't about thrust, it's about T/W and T/D ratios. I would like to know what the F404's T/W ratio is as the F414, developed from the F404, has the highest T/W ratio of any engine in production. I also say this because the drawback I've read about with the original JAS-39 as well was it's T/W ratio with the F404. A drawback the F-20 didn't seem to suffer from.

 

[sferrin]

I'm going to guess it doesn't have as much to do with the F404 as it does the weight of the F/A-18 to begin with. It isn't about thrust, it's about T/W and T/D ratios. I would like to know what the F404's T/W ratio is as the F414, developed from the F404, has the highest T/W ratio of any engine in production. I also say this because the drawback I've read about with the original JAS-39 as well was it's T/W ratio with the F404. A drawback the F-20 didn't seem to suffer from.

Heh, good point. However, where they mention "at high altitude" the engine's cycle is definitely going to be a factor. They didn't claim "underpowered at ALL altitudes".

 

[F-14D]

I'm going to go out on a limb and suggest it has something to do with their engines bypass ratios. Lower bypass engines tend to do better at higher altitudes. Apparently the M53 is even more powerful than early versions of the F100 at high altitude. This might also explain why most later model F-15s have gone with the F100-229 instead of the F110 despite the common engine bay that would allow them to go with the F110. The F100 has a lower bypass ratio and higher exhaust velocity than the F110. This would allow the F-15 to have more power at high altitudes than if they went with the F110.

USAF stayed with the F100 because once the F110 was availalbe, Pratt fixed the reliability and perfromance issues of the F100. USAF didn't have that many more F-15s left to buy by then so probably thought they didn't want a 2nd engine in the aircraft that might raise some logistics costs for such a limited number of aircraft. Back in the '90s there were proposals to re-engine existing F-15s with F100s that performed up to or exceeded original spec or maybe F110s (then there would be a big USAF market) but that got limited to F-15Es and F-15C/Ds that would be in support of NATO operations in Europe.

Once it became available, most export customers for the F-15 chose the F110, Saudi Arabia even going to the trouble of exchanging F100s in its existing F-15s for F110s (mostly because the F110 handled the desert environment better).

 

[F-14D]

I'm guessing this was one of the things they tried to address with the F-18E/F.

The F/A-18E/F needed higher thrust because of the greater weight and size it had to lift. Reportedly the E/F does not accelerate as fast or is as agile, except for its phenomenal high AoA abilities, as the earlier Hornets. There have been proposals to address this with the F414 EPE, but USN has shown little interest in the EPE,

 

[Trident]

I'm going to guess it doesn't have as much to do with the F404 as it does the weight of the F/A-18 to begin with. It isn't about thrust, it's about T/W and T/D ratios. I would like to know what the F404's T/W ratio is as the F414, developed from the F404, has the highest T/W ratio of any engine in production. I also say this because the drawback I've read about with the original JAS-39 as well was it's T/W ratio with the F404. A drawback the F-20 didn't seem to suffer from.

Agree. The F404 and M53 both have as near as makes no difference the same, very low bypass ratio and uninstalled thrust to weight ratios are not that different either (if anything, this favours the Hornet). Depending on what Mach number range the author was referring to the Mirage has the advantage of variable intakes, but IMHO wing loading may be the answer - the M2000 is way better in this respect (much like the F-15)!

 

[datafuser]

I'm going to go out on a limb and suggest it has something to do with their engines bypass ratios. Lower bypass engines tend to do better at higher altitudes. Apparently the M53 is even more powerful than early versions of the F100 at high altitude. This might also explain why most later model F-15s have gone with the F100-229 instead of the F110 despite the common engine bay that would allow them to go with the F110. The F100 has a lower bypass ratio and higher exhaust velocity than the F110. This would allow the F-15 to have more power at high altitudes than if they went with the F110.

It seems the M53 has a higher bypass ratio than the F404. SNECMA's product info on the M53 says it has a bypass ratio of 0.36, while Wiki says the F404's bypass ratio is 0.34 (GE and MTU websites say nothing about the F404's bypass ratio).

F414: 0.25 http://www.mtu.de/en/products_services/military_business/programs/f414/index.html

M88: 0.3 http://www.snecma.com/IMG/pdf/M88-2_ang-2.pdf

RM12 (F404 derivative): 0.31 http://www.volvoaero.com/volvoaero/global/en-gb/products/Aircraft%20engines/RM12/Pages/technical_data.aspx

M53: 0.36 http://www.snecma.com/IMG/pdf/M53-P2_ang-2.pdf

F100: 0.36 http://www.pw.utc.com/products/military/f100.asp

EJ200: 0.4 http://www.mtu.de/en/products_services/military_business/programs/ej200/index.html

F135: 0.57 http://www.pw.utc.com/products/military/f135.asp

F110: 0.76 http://www.mtu.de/en/products_services/military_business/programs/f110/index.html

RB199: 1.3 http://www.mtu.de/en/products_services/military_business/programs/rb199/index.html

 

[Archibald]

There were specific details about the M53 in Le Fana articles about the ACF and Mirage 4000.
The M53 was build without compromises, for high-speed interceptors of the mid-60's that never materialized. It was essentially build for Mach 2.5+ speeds, and I don't think the F-404 ever was. Perhaps that explains its superiority at high heights and speeds - by its very origins.