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July, 2003 Archive Story

LIGHTNING v F-15

Quite where to start with comparisons between the Lightning and the F-15 Eagle is extremely difficult, as they are two high performance aircraft but from differing eras. The Lightning concept dates back to a period just after the end of WWII, although it was not until 1947 that an experimental study contract was approved, and another two years before a contract was given for two prototypes and an airframe to be used for static tests. As we all know, the P1 finally took to the air on 4 August 1954. With that in mind, it must be appreciated that a gap of some 18 years separates the development of the two aircraft, so some of the differences are bound to be significant. The F-15 Eagle was barely on the drawing boards in 1967, though by 1974 it was challenging the MiG-25 Foxbat for various climb-to-height records and also the absolute altitude record for this type of aircraft. Possibly a little more of that later on.

How, then, do the two aircraft compare from the pilot's seat? Bearing in mind my limited experience of the Eagle compared to many years flying the Lightning, I may miss out on a few pertinent aspects. Nevertheless I will attempt to be as objective as possible. No doubt any Eagle pilots who read this article will have different views.


F-15 (Image courtesy of U.S.A.F.)

The F-15C Eagle is a single-seat, high-performance, supersonic, all-weather air-superiority fighter built by McDonnell Douglas Aerospace. It relies on its excellent design features as well as state of the art avionics to keep it at the pinnacle of world-wide fighter capabilities. The Eagle was designed to fix all of the problems that were discovered in building the F-4 Phantom. The Eagle is a high-mounted, swept wing fighter with twin vertical stabilisers. The wing design and twin tails give the Eagle excellent flying qualities throughout the entire flight envelope.

My first impression of the Eagle was its size. It’s a large aircraft, bigger than the Lightning in every aspect, especially inside the cockpit. There's so much room that one could nearly walk around, compared to the glove-like fit of the Lightning. Even so, everything came to hand without having to stretch; in fact, all essential control functions could be accessed either from the stick or the throttle. In all there are 15 multi-functional buttons and switches. Having said that, the Lightning too was well supplied with such facilities, though they were spread a little wider. There were more of them as well, at least 22 primary ones and several others scattered around various parts of the cockpit. In consequence, there was a certain amount of rapid hand work needed from time to time, and considerable dexterity was needed to ensure hitting the correct switch. It would be embarrassing if one were to switch the radar off at the critical moment, but fortunately I never did.

Starting systems on both aircraft were straightforward. Taxiing out needed some braking since they would both gently accelerate if not held in check. Now onto the runway for take-off. Acceleration in both was impressive; you have all seen the Lightning leap away once brakes are released, the Eagle was almost as good, and climb speed was rapidly achieved. Take-off roll is between 2,000 & 3,000 feet, depending upon military or maximum afterburner-powered take-off. The Lightning was quicker off the ground, reaching 50 feet height in a horizontal distance of 1,630 feet, and a climb speed of 450kts in 61.8 seconds. The Streak Eagle set the time to climb record in 1975 of 207.8 seconds from brake release to 30,000M (98,425ft). The Streak Eagle also beat the Apollo Moon-shot rocket up to about 50,000ft! Keep in mind that that was a modified Eagle on the coldest day they could find, and a precise profile was flown, but it gets across the capability of the F-15.

The range proficiency of the F-15 is impressive. With three external tanks it can cover about 2,500 nautical miles. Compare that to the Lightning’s figures on standard internal tanks, where the maximum attainable range was (and this was stretching things a bit) 900 miles. Even this required a cruise let-down to conserve the juice. If nothing else, it emphasises the shortage of fuel that British fighters have always suffered. Filling the over-wing tanks prior to take-off gave no advantage, the extra weight burned off so much fuel that it was never practised unless a low level only trip was planned, otherwise in-flight refuelling was the norm.

My first flight involved a formation take off, and here I discovered the first difference. The Pratt & Whitney engines (turbofans) were slow to react to throttle movement, so maintaining a steady position on the wing of my lead aircraft took a few moments to sort out. Otherwise it presented no difficulties, and I was soon relaxed and enjoying the flight.

The controls are beautifully balanced and very responsive, although this applies to both aircraft. I might add here that the latest F-15s have Pratt & Whitney F-100 (-220) engines. These are turbofans with a 5 stage afterburner capable of burning fuel in excess of 100,000pph (lbs per hour). The newest motors (-220) have a Digital Electronic Engine Control (DEEC) that gives the engines faster response times to throttle demands. Each motor produces about 20,000lbs of thrust for a total of about 40,000lbs. This compares with the Lightning, which produced 32,600lbs of thrust in full burner (22,200 in cold power).

For the F-15, typical training configuration weights are around 45,000lbs, with a combat load closer to 55,000lbs. This compares with Lightning figures nearer to 41,700lbs maximum take-off weight with full combat load.

The brief for this sortie was a 1 v 1 radar interception profile, followed by 1 v 1 Air Combat Manoeuvres (ACM). I now experienced a whole new word of avionics. This is where the Eagle is head and shoulders above its peers. The Eagle avionics are centred around the APG-63 Pulse-Doppler Radar. This is the eyes of the Eagle. The Radar is interleaved with High and Medium PRFs which aid in its detection and allow it to still be the best air-to-air radar in the world today. The Eagle also has a Radar Warning Receiver which alerts the pilot to enemy radars in various modes. On the defensive side, the Eagle has a Counter Measures Dispenser which allows it to deploy both chaff and flares for its own protection.

The Lightning’s on-board radar was, to say the very least, basic, and hard work to operate - the phrase ‘a one-armed paper hanger’ comes to mind. The Lightning had no defensive counter measures, something that we would have much appreciated. By comparison the F-15’s kit was simplicity itself to use. All the requisite information to carry out an interception was displayed on the HUD. Details such as the target's speed and height were digitally shown, along with its heading. Should the target throw a turn, the display informed you of the direction of turn, also the amount of ‘g’ he was pulling. Pick-up range was far in excess of the Lightning’s AI, and in the lower levels, ground returns were virtually non existent, making interceptions a more viable proposition.

As far as weaponry is concerned, the Eagle can carry 8 air-to-air missiles and has its own internal 20mm cannon. The gun carries 940 rounds and fires at a rate of 100 rounds per second. The short range missile that the Eagle carries is the AIM-9M Sidewinder. This is an IR homing missile and is used for close-in combat, as it has a short range. The Eagle can carry up to 4 of these on the wing pylons.

The long range missiles for the Eagle are the AIM-7M Sparrow and the AIM-120 AMRAAM. These missiles allow the Eagle to reach out and touch the bandits at longer ranges. The Eagle can carry up to 4 AIM-7Ms on the fuselage and up to 8 AIM-120s on the fuselage and wing pylons. A typical combat load is 4xAIM-120, 2xAIM-7, 2xAIM-9, and 940 rounds of 20mm. By comparison, the Lightning was poorly armed, carrying only 2 missiles and two 30mm cannon. The F-53’s could also fit bombs and rockets, but basically its weapons load was no match for the F-15.

Manoeuvrability in the F-15 during the 1 v 1 was outstanding throughout the entire flight envelope, from <100 knots in a BFM engagement, to >2.0M interceptions, and I have no doubt that the Eagle would be more than a match for the Lightning. With so much thrust, optimum manoeuvring speed was easily maintained, with little if any need to unload in order to maintain it.

On completion of the air exercise we recovered as individuals, thus giving me the opportunity to get a feel of the aircraft without having to concentrate on the leader. Although this was my first trip, I felt completely at home with it. It was simply a splendid aircraft to fly; like the Lightning, a pilot's machine.

The recovery was uneventful, electing for a instrument approach using the ILS system. In the same way as the Lightning, the Eagle was easy to trim for the approach and descent. Once trimmed, it rode the rails like a thoroughbred, which indeed they both are. Landing was straightforward, the aircraft settling easily onto the tarmac, slowing well with aerodynamic braking, a procedure not generally employed in the Lighting. Both aircraft have brake-chutes, which as we all know are most effective.

The overall impression was that both aircraft had very similar performance and handling characteristics, both were joy to fly.

Considering the age difference, the Lightning’s performance was totally outstanding when introduced into service, and when it finally bowed out it could still out-climb most of its successors. Its initial rate of climb was 50,000 ft per minute. The Mirage 111E climbed initially at 30,000 ft per minute; the Phantom-4M managed 32,000 ft per minute; the MiG-21 could only manage 36,090 ft per minute; the initial rate of the F-16A was 40,000 ft per minute, and the Tornado F-3 43,000 ft per minute, so the Lightning reigned supreme. Only now has it been surpassed; the F-15 Eagle, and the MiG-25 both have initial climb rates as good or better. The Lightning’s time to FL 360 in re-heat was 2.5 minutes. In this respect, the Eagle produced a similar figure, though this could vary depending upon its configuration

My conclusion has to be that, given the choice between the two, I would have been mad not to take the Eagle, but only because it has such superb avionics and weaponry. However, for the pure joy of flying, the Lightning still heads the list. It was, and indeed still is, a magnificent aircraft, and a credit to the designers and test pilots who developed and brought it into service for people like me to enjoy.

Data Comparisons:-

Span: Lightning, 34.83ft   F-15, 42.75ft    

Length: Lightning, 55.25ft   F-15, 63.75ft    

Height: Lightning, 19.58ft   F-15, 18.42ft    

Armament: Lightning 2 missiles & 44 2-inch rockets, 2 x 30mm Aden cannon with 120 rounds each
Lightning Ground-attack 2 x 30mm cannon with 120 rounds each, 36x68mm SNEB rockets, 2 x 1,000 HE bombs
Reconnaissance: 5 x 70mm cameras   F-15 Standard Load - 4xAIM-120, 2xAIM-7M, 2xAIM-9M, 940 rounds of 20mm    

Weight: Lightning, 41,700lbs full combat load   F-15 Max T/O - 68,000lbs = 30,844kg    

Engines: Lightning, 2xRolls Royce Avon   F-15, 2xPratt & Whitney F-100 or F-100-220 (with the digital modification)    

Thrust: Lightning, 11,100 cold & 16,300 Max re-heat   F-15, Combat thrust to weight ratio + 1.3:1    

Fuel Capacity: Lightning, 10,600 internal + 2 x over-wing tanks with 2,000lbs each   F-15, 13,455 (internal), with full external 25,755lb    

Oxygen: Lightning LOX (Liquid Oxygen) 3.5 litres capacity   F-15, 5 litres of LOX    

Radar: Lightning, Approach & Attack computers, Search & Attack display unit (CRT), Visual display cine recorder, Light fighter sight   F-15, APG-63 multi-mode pulse Doppler radar.    

Nav Aids: Lightning, Compass, TACAN with off-set computer, UHF homing & IFF with SIF   F-15, TACAN, ILS, Laser Ring Gyro INS    

Radio: Lightning, 1,750 channel combined UHF/VHF, TX & RX, UHF standby set, Telebriefing for ground communications   F-15, 2 UHF radios

Having made an attempt to compare the Lightning and the F-15 Eagle, and to give my personal impressions, and having also mentioned the MiG-25 earlier, a few words about that aircraft may interest readers. It was and still is quite some machine.

The MiG-25 has a very similar profile to the F15, but it was around and flying in June of 1967 - in fact, the Russians had four prototypes, or pre-production models, by June 9 of that year. Even earlier, there were reports in 1965 of what was designated the Ye-266 which was snatching every known record of speed, time to height and absolute altitude. The Ye-266 was in fact a stripped-down MiG-25 fighter prototype, and at that time no one knew what they were.

Referring to the 1967 appearance of the MiG-25, it was on the scene when the F-15 was barely on the drawing board. It was engined by the R-31 Turmansk turbojet, initially producing 25,000 lbs of thrust, later increased to 30,000 lbs. The tail pipe diameter of each engine was 4 ft 9 inches, seriously large. By late 1969 it went into production, and by 1972 there were three versions in operation, the Fighter-Bomber, the Interceptor and the Reconnaissance, all fully operational.

Around that time, the Israeli radar tracked high-flying MiG-25's on Egyptian-sponsored snooping missions over the Sinai peninsula cruising at Mach 2.8 and on one occasion at Mach 3.2. Neither the Israelis nor the Americans had anything at that time to touch them.

Two years later, an F-15 managed to wrest the Foxbat's time to height records, but not for long, as the Ye-266 with the up-rated engines led the field again. A pilot by the name of Aleksandr Fedotov reached 114,800 feet in 4 minutes 11.7 seconds. That was on 22 July 1997, and five weeks later he zoomed to a new absolute height record of 37,650 metres. The article says that the Russian record still stands, but they could be wrong.

I think the “Streak Eagle” has matched this. It certainly achieved 100,250 feet. The surprising thing is that the engines remained alight at such a height, as there is virtually no oxygen and very limited airflow to keep things going. I once had an F-53 Lightning up to 87,300 feet over Saudi and it was really on a knife edge. Both engines remained alight, but were very touchy, and getting down to a more reasonable and sane altitude needed delicate handling. Earth curvature was visible and the sky was quite dark. So, another 37,000 feet is quite something.

Endurance and combat radius were quite a problem for the MiG-25, something in the order of 750 miles in cold power and a combat radius of only 350 miles. If and when they pushed to 3.2 Mach, the engines were shot. Their usual briefed limit was 2.5,which could be achieved with a full weapons load. Going any faster risked the engines accelerating out of control until they cooked, so I guess discretion was the buzz word. With high wing loading the aircraft was limited to around 5g and only 3.5g with full tanks, and when subsonic any other fighter could out-turn it. This was a severe limitation for a fighter, and must have been good news for the West when they were made aware of the various limitations.

All the performance data etc. were revealed when the Russian Victor Belenko defected with his MiG-25 to Japan on 6 September 1976. It was, as you probably know, stripped down, examined and then put back together before being returned to the Russians. The crude build came as no surprise, and the avionics were hardly state of the art. The aircraft skin was primarily a steel alloy, which imposed a severe weight penalty but was done to save on costs. Titanium skinning was only used in areas subject to high friction. A lot of spot welding was employed, as there was a shortage of skilled riveters. Where rivets were used, they left the heads protruding for added strength.

Another of the problems they encountered was sourcing suitable canopies, seals, hydraulic fluids, tyres etc. that could withstand high temperatures of up to 300°C. Alcohol cooling was used, stored in a 500 litre tank, which gave the MiG-25 the nickname of the ‘Flying Restaurant’. Apparently the alcohol used was purer than the vodka on the base.

They also developed a powerful air conditioning system to keep the pilots cool. Semi-conductors would not work above 65°C, so they stuck to using vacuum-tube avionics, even for the radar. It was a monster item of equipment, weighing in at slightly over half a ton. Its pulse-Doppler search and track were basic, but
the valve technology and its awesome power gave it unmatched power to burn through the thickest electronic jamming to a range of fifty miles. It would kill a rabbit at one kilometre if activated on the ground!

Brian Carroll

This is an article I published in the Lightning Review, written by a good friend, Brian Carroll, a former RAF Lightning pilot, ex-Lightning Chief Examiner - Strike Command and Fighter Combat Leader, QFI & CIRECFI, Royal Saudi Air Force.
Charles

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