McDonnell-Douglas F-15N "Sea Eagle"

F-15(N) and F-15(N-PHX)

McAir spent considerable time and effort from 1970 to 1974 to define several versions of the F-15 for naval service. An unofficial (and per­haps, unwelcome) title of 'Seagle' was applied by various organizations involved. The first pre­sentation to the Navy occurred in July 1971. McAir's position was that due to its excellent thrust-to-weight ratio and good visibility, the F- 15 could easily be adapted for carrier opera­tions. The only modifications required to enable it to operate off of CVA-19 class (or larg­er) carriers were: strengthened landing gear; an extendible front landing gear strut to pro­duce the proper angle of attack upon catapult launch; installation of a nose-tow catapult sys­tem; folding wings; and a beefed-up arresting hook and associated structure. Both the nose and main landing gear wells would have to be enlarged to accommodate the increased stroke of the new gear. These modifications would add approximately 2,300 pounds to the basic F-15A.

The Navy was not overly impressed with this proposal, so McAir further modified the design. Two McAir models (199-A-11 and 199-A-12) were then presented to the Navy. Model 199-A-12 featured a bridle catapult attachment, while 199-A-11 A had a nose-tow catapult attach­ment, otherwise they were identical. The design also featured a dual nose wheel arrangement, increased fuselage structural strength, a Navy-type refueling probe, and most important, an improved high-lift system, in addition to all the originally proposed modifi­cations. The high-lift system was composed of full-span leading edge flaps, BLC trailing edge flaps, and a slotted aileron, all of which con­tributed 632 pounds to the projected 3,055 pound increase (to 42,824 pounds) over the USAF F-15A. An additional 71.9 pounds would be added for Navy avionics, including: AN/APN-15(V) radar beacon set; AN/ASW-27B digital data communications set; AN/ALQ-91A countermeasures set; AN/ASN-54(V) approach power compensator set; AN/ ALQ-100 decep­tive countermeasures set; AN/ARA-63 receiver decoding group; and an AN/APN-194 radar altimeter. The standard TEWS ECM system would be deleted.

These versions of the F-15(N) were still armed the same as the USAF F-15A (M61A1, AIM-7, and AIM-9), and were deemed roughly equal to the F-14B in overall performance, except for range. The radius of action in a fight­er-escort configuration was 271 nm on internal fuel, compared to 481 nm for the F-14B and 319 for the F-4J. With external tanks, this increased to 516 nm versus 685 for the F-14B and 485 for the F-4J. No data was generated for FAST Pack equipped aircraft. A total of $403.5 million was projected for non-recurring engineering costs, with a flyaway price of $7.6 million based on a 313 aircraft production run.

The F-15N then became the focus of Navy Fighter Study Group Ill. This group disregard­ed the McAir data, enlarged the nose to carry the AN/AWG-9 radar, and added Phoenix mis­siles, resulting in an aircraft that weighed 10,000 pounds more than the basic F-15A. This weight increase, along with the associated drag, greatly decreased the performance of the F-15, negating any advantage it had over the F- 14A. There was also considerable concern over the 12° angle-of-attack used by the F-15 (compared to 10.2° for the F-14A) during approaches, and the relatively narrow landing gear track.

McAir and Hughes countered the study group's criticisms with a further modified ver­sion known as F-15(N-PHX), which added a rudimentary AIM-54 Phoenix missile capability. This version (model 199-A-19B) took the model 199-A-11A and modified the AN/APG-63 radar set into an AN/APG-64. These modifications involved increasing the transmit power to 7 kW (compared to 10 kW in the AN/AWG-9 and 5.2 kW in the AN/APG-63), a command link, a track-while-scan capability, and a Phoenix test feature. The radar antenna was also modified to effect a slight frequency shift. The central computer had its load changed to support the new track-while-scan modes, as well as adding additional memory and Phoenix unique soft­ware. Some cockpit controls and displays were also modified. The aircraft could carry up to eight AIM-54s: one on each fuselage AIM-7 sta­tion, one on each inboard wing pylon, and two (in tandem) on a special centerline pylon. The appropriate missile cooling systems were added to each station. Take-off gross weight was up to 46,009 pounds. The high-lift devices were changed to include full-span Krueger leading edge flaps, BLC trailing edge flaps, and single-slotted ailerons. Approach speed to a carrier was estimated at 136 knots.

Another proposal was also presented, one essentially echoing the results of Navy Fighter Study Group Ill. The aircraft was equipped with the Hughes AN/AWG-9 weapons system from the F-14A, but otherwise resembled the earlier F-15(N-PHX). Estimated non-recurring R&D costs were $1.173 billion in FY72 dollars. Based on a313 unit production run, the flyaway cost was $11.5 million per aircraft.

On 30th March 1973, the Senate Armed Ser­vices Committee's ad hoc Tactical Air Power subcommittee started new discussions on the possibilities of modifying the F-15 for the Navy mission. At this point the F-14 program was having difficulties, and the subcommittee want­ed to look at possible alternatives, namely lower-cost (stripped) F-14s, F-15Ns, and improved F-4s. There were even proposals by Senator Eagleton for a 'fly-off' between the F-14 and F-15, but this never transpired. These dis­cussions, along with some other considera­tions, led to the forming of Navy Fighter Study Group IV, out of which the aircraft ultimately known as the F/A-18A was born.

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BLC trailing edge flaps

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marauder2048 said:

BLC trailing edge flaps

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The Navy's historical and continued aversion to blown flaps and active flow control in general remains as baffling as ever.

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sferrin said:

marauder2048 said:

BLC trailing edge flaps

Click to expand...

The Navy's historical and continued aversion to blown flaps and active flow control in general remains as baffling as ever.

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The F-4 had it:

"F-4A (F4H-1F) changes were a leading edge flap boundary layer air control system first used on the 5th preproduction aircraft and blown flaps introduced on the 7th preproduction aircraft.11 The wing leading edges and trailing edge flaps were blown by high-pressure bleed air from the engine compressors, which produced a thin layer of air which helped keep airflow attached at high angles of attack."

So did the A-5 Vigilante:

"At the time of its introduction, the Vigilante was one of the largest and by far the most complex aircraft to operate from a United States Navy aircraft carrier. It had a high-mounted swept wing with a boundary-layer control system (blown flaps) to improve low-speed lift.[4] "

Maybe the USN learned not to like it. (More trouble than it was worth maybe?)

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overscan (PaulMM) said:

To counteract some bad/incomplete information on the F-15N "Sea Eagle" on the internet, here's a really good account from Dennis R. Jenkin's fine Aerofax on the F-15.

F-15(N) and F-15(N-PHX)

McAir spent considerable time and effort from 1970 to 1974 to define several versions of the F-15 for naval service. An unofficial (and perhaps, unwelcome) title of 'Seagle' was applied by various organizations involved. The first presentation to the Navy occurred in July 1971. McAir's position was that due to its excellent thrust-to-weight ratio and good visibility, the F- 15 could easily be adapted for carrier operations. The only modifications required to enable it to operate off of CVA-19 class (or larger) carriers were: strengthened landing gear; an extendible front landing gear strut to produce the proper angle of attack upon catapult launch; installation of a nose-tow catapult system; folding wings; and a beefed-up arresting hook and associated structure. Both the nose and main landing gear wells would have to be enlarged to accommodate the increased stroke of the new gear. These modifications would add approximately 2,300 pounds to the basic F-15A.

The Navy was not overly impressed with this proposal, so McAir further modified the design. Two McAir models (199-A-11 and 199-A-12) were then presented to the Navy. Model 199-A-12 featured a bridle catapult attachment, while 199-A-11 A had a nose-tow catapult attachment, otherwise they were identical. The design also featured a dual nose wheel arrangement, increased fuselage structural strength, a Navy-type refueling probe, and most important, an improved high-lift system, in addition to all the originally proposed modifications. The high-lift system was composed of full-span leading edge flaps, BLC trailing edge flaps, and a slotted aileron, all of which contributed 632 pounds to the projected 3,055 pound increase (to 42,824 pounds) over the USAF F-15A. An additional 71.9 pounds would be added for Navy avionics, including: AN/APN-15(V) radar beacon set; AN/ASW-27B digital data communications set; AN/ALQ-91A countermeasures set; AN/ASN-54(V) approach power compensator set; AN/ ALQ-100 deceptive countermeasures set; AN/ARA-63 receiver decoding group; and an AN/APN-194 radar altimeter. The standard TEWS ECM system would be deleted.

These versions of the F-15(N) were still armed the same as the USAF F-15A (M61A1, AIM-7, and AIM-9), and were deemed roughly equal to the F-14B in overall performance, except for range. The radius of action in a fighter-escort configuration was 271 nm on internal fuel, compared to 481 nm for the F-14B and 319 for the F-4J. With external tanks, this increased to 516 nm versus 685 for the F-14B and 485 for the F-4J. No data was generated for FAST Pack equipped aircraft. A total of $403.5 million was projected for non-recurring engineering costs, with a flyaway price of $7.6 million based on a 313 aircraft production run.

The F-15N then became the focus of Navy Fighter Study Group Ill. This group disregarded the McAir data, enlarged the nose to carry the AN/AWG-9 radar, and added Phoenix missiles, resulting in an aircraft that weighed 10,000 pounds more than the basic F-15A. This weight increase, along with the associated drag, greatly decreased the performance of the F-15, negating any advantage it had over the F- 14A. There was also considerable concern over the 12° angle-of-attack used by the F-15 (compared to 10.2° for the F-14A) during approaches, and the relatively narrow landing gear track.

McAir and Hughes countered the study group's criticisms with a further modified version known as F-15(N-PHX), which added a rudimentary AIM-54 Phoenix missile capability. This version (model 199-A-19B) took the model 199-A-11A and modified the AN/APG-63 radar set into an AN/APG-64. These modifications involved increasing the transmit power to 7 kW (compared to 10 kW in the AN/AWG-9 and 5.2 kW in the AN/APG-63), a command link, a track-while-scan capability, and a Phoenix test feature. The radar antenna was also modified to effect a slight frequency shift. The central computer had its load changed to support the new track-while-scan modes, as well as adding additional memory and Phoenix unique software. Some cockpit controls and displays were also modified. The aircraft could carry up to eight AIM-54s: one on each fuselage AIM-7 station, one on each inboard wing pylon, and two (in tandem) on a special centerline pylon. The appropriate missile cooling systems were added to each station. Take-off gross weight was up to 46,009 pounds. The high-lift devices were changed to include full-span Krueger leading edge flaps, BLC trailing edge flaps, and single-slotted ailerons. Approach speed to a carrier was estimated at 136 knots.

Another proposal was also presented, one essentially echoing the results of Navy Fighter Study Group Ill. The aircraft was equipped with the Hughes AN/AWG-9 weapons system from the F-14A, but otherwise resembled the earlier F-15(N-PHX). Estimated non-recurring R&D costs were $1.173 billion in FY72 dollars. Based on a313 unit production run, the flyaway cost was $11.5 million per aircraft.

On 30th March 1973, the Senate Armed Services Committee's ad hoc Tactical Air Power subcommittee started new discussions on the possibilities of modifying the F-15 for the Navy mission. At this point the F-14 program was having difficulties, and the subcommittee wanted to look at possible alternatives, namely lower-cost (stripped) F-14s, F-15Ns, and improved F-4s. There were even proposals by Senator Eagleton for a 'fly-off' between the F-14 and F-15, but this never transpired. These discussions, along with some other considerations, led to the forming of Navy Fighter Study Group IV, out of which the aircraft ultimately known as the F/A-18A was born.

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overscan (PaulMM) said:

The design also featured a dual nose wheel arrangement, increased fuselage structural strength, a Navy-type refueling probe,

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SSgtC said:

sferrin said:

marauder2048 said:

BLC trailing edge flaps

Click to expand...

The Navy's historical and continued aversion to blown flaps and active flow control in general remains as baffling as ever.

Click to expand...

The F-4 had it:

"F-4A (F4H-1F) changes were a leading edge flap boundary layer air control system first used on the 5th preproduction aircraft and blown flaps introduced on the 7th preproduction aircraft.11 The wing leading edges and trailing edge flaps were blown by high-pressure bleed air from the engine compressors, which produced a thin layer of air which helped keep airflow attached at high angles of attack."

So did the A-5 Vigilante:

"At the time of its introduction, the Vigilante was one of the largest and by far the most complex aircraft to operate from a United States Navy aircraft carrier. It had a high-mounted swept wing with a boundary-layer control system (blown flaps) to improve low-speed lift.[4] "

Maybe the USN learned not to like it. (More trouble than it was worth maybe?)

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The F-8 also had them in its later incarnations while the Super Crusader was designed with them from the start. My take on why they didn't become more widespread in US Naval Service is that they just weren't needed. American carriers were big enough, fast enough and had powerful enough catapults that things like BLC systems were just seen as unnecessary.

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overscan (PaulMM) said:

To counteract some bad/incomplete information on the F-15N "Sea Eagle" on the internet, here's a really good account from Dennis R. Jenkin's fine Aerofax on the F-15.

Click to expand...

overscan (PaulMM) said:

No, but this is an F-15 Interceptor model with Phoenix which emphasises the physical size. The Phoenix are mounted here on FAST packs.

I can't see really see more than 6 unless it added centrerline hardpoints.

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Firefinder said:

Likely could fit two more with the outer wing hardpoints that the F15 prototype had and every F15 got fitted for and not with.

They were to be fully set up for datalinks and a capacity of over 1000 pounds.

And apparently thise same hard points could fit a twin set of AIM120s with a quad set on the traditional inner ones.

So even the beefy AIM54 could fit.

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SSgtC said:

Maybe not on a Naval variant though. Since those outer wing panels would have to fold now. The Navy never has seemed to like putting ordinance on the outer wings of their jets

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henshao said:

The reason the F-15's outer wing hard points were never used beyond contemplation of some lightweight ECM equipment is because the F-15 was susceptible to significant lateral imbalance beyond a certain amount and those hardpoints are very far away from the CG.

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henshao said:

the best documentation on this subject I think is in the F-15E manual find the section on lateral asymmetry, after a certain point the Eagle is considered "extremely susceptible" to departure and that point would be very easy to reach with a moment arm nearly at the wingtip

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