THE OVERHEAD PATTERN FOR LANDING

Landing the F-4 was a new experience for all early flyers because the F-4 was not 'flared' like every other Century series fighter the Air Force flew.  Almost all Air Force airplanes, at the time of the F-4 introduction, were pointed at a point short of the touchdown point, and when about 40' above the runway, the power would be reduced and the airplane 'held off' or flared until it sank and touched down.  Even in the old T-33, you would aim the nose at a point 500' to 800' before the touch-down point in the overrun, pull the power back and level off at that point and float forever until it touched down.

But the F-4 was very different.  It had BLC - Boundary Layer Control.  Hot air from the 17th stage of the compressor was pumped through the flaps and out 3 mm slits at the back of the leading edge flaps and at the front of the trailing edge flaps.  This fast hot air made the flaps seem much bigger and provided a much lower (10 -15 kts) landing speed then without BLC..  The BLC was totally dependent on the engines rotation pretty fast - 83% RPM or so.  Bring the power back below 80%, certainly below 78%, and the BLC effectively quit and the wing was suddenly a different shape.  And it quit flying at the given IAS (Indicated Air Speed).  And down she went.  So early pilots who made that mistake would try to save it by quick aft stick - and drag the stabilator.  

So in the F-4, when rolling out of the base turn onto final, about 800' above the ground and 2,500' to 3,000' from touchdown, you picked up "on speed" AOA (angle of attack) and kept it there all the way to tires in contact with the payment.  'On Speed' AOA was 19.2 units - an arbitrary number but it equaled base airspeed of 132 kts plus 2 kts IAS for every 1,000 pounds of fuel on board.  (Base airspeed would change for configuration and all the TCOTs with "negligible weight effect".  Real base airspeed in the RF-4C was closer to 134 kts.)  Once you rolled final and picked up 'on-speed' and a donut on the AOA indexer lights, the nose was up about 12 - 13 degrees.  And you kept it there all the way to touch-down.   It was like a line from where you were when you picked up 'on-speed' straight to the touch-down point.  And you just kept it there.

Eight-three percent RPM was also a magic number.  Eight-three percent would give you 300 kts IAS on initial, and "on-speed" on final.  In fact, you did not need to move the throttles much at all if you flew the pattern right.  Leave the power at 83% in the break, but put the speed brakes out and hold 60 degrees of bank (a 2g turn) which would drop your speed from 300 to about 245 as you rolled out on downwind.  Drop the gear and the hold level flight and the speed would continue to fall off.  As you approached the start of the base turn, the speed should be about 180, and put full flaps down and as soon as they were green, drop the nose and start the descending base turn (you were at 1,500' above the ground for the break and downwind.)  Continue to let the speed decay in the turn and it should hit 'on-speed' as you roll wings level for final.  Power is still at 83%.  Now if you got the distance right, you don't have to do anything with the power, just enjoy following the VASI down the glide slope. 

If there was any flare in the F-4, it was the effect of the "ground effect" bubble of air under the airplane.  As you got to about 40' to 50' above the runway, the nose would start to drop because of the change in pitch fulcrum cause by the ground effect.  Just hold the nose in the same attitude as it was at initial "on-speed' by smoothly bringing the stick aft to hold the nose up.  If you did it right, just as the stick hit the aft stop, the tires would hit the payment and spin up with no or almost no smoke.   A grease job.  

It was fun!

Some time later, after I stopped flying the RF-4C (nine and a half years), the trailing edge flaps were changed to only one position, 30 degrees, which we called half flaps.  The full flaps of 60 degrees was eliminated and the base landing speed was increased by 15 kts - 145kts - way to fast!.  I think that was for the guard.  The only time I ever flew half flaps was for an engine out and I only had one of those.  Half flaps were also flown for hydraulic failure when you had to blow them down.  I had about six of those - all barrier engagements.

THE FUNCTIONAL CHECK FLIGHT - MACH RUN

The General Electric J-79 engine was the heart of the F-4.  The J-79 was the greatest engine made. 

I flew the RF-4C for nine and a half years (2,207 hrs on my Form 5 or 2,261 hrs in my records) and never saw an over-temp or anything on the gauges except green.  I had to shut down one once when an afterburner actuator line broke (engine oil operates the afterburner actuators).  I was flying tactical wing over Scotland and was puzzled that I was falling behind with the throttles at mil (Military power = 100%.)   I glanced down and saw the number 2 oil pressure at ZERO, so I told the GIB, verified I had my hand on the correct engine throttle and shut it down.  I did not want it to seize up and act like a barn door.  The lead slowed down so I could join and we went on back to Alconbury.  Discovered the highest I could get on one engine was 17,000 feet. 

I flew about 152 FCF flights (Functional Check Flight - a test flight after an engine change (or major hydraulic work) to push the airplane to the edge of the operating envelope to see it was "going to hang together".)  Sixty-five were good Mach Two runs and good FCFs. 

FCFs were not really Mach Two runs but actually Vmax (velocity maximum) runs as Vmax may very between 1.97 and 2.15 depending on the temperature at a true altitude of 40,000 feet.  About 45 of those had compressor stalls at or near Vmax, because the variable stator vanes (first six stages of the compressor) were miss-rigged.  Usually they are re-rigged that afternoon and then worked good the next day.  The neatest thing about flying FCFs was flying a clean airplane.  Only the inboard pylons were left on.

The FCF profile called for a normal take-off, level off at 10,000' and run a controllability check that everything was moving the way it was supposed to, then a Mil climb to FL 400 and cruise at .95 Mach to the published supersonic corridor.  Report to ATC that you were taking the '"block" - you were cleared to operate between FL400 and FL480.  Punch the stop watch and pop the throttles outboard past the detent and into full AB.  (Above about 35,000' the afterburners only had two stages, the inner two, instead of four, to keep from overheating the tail pipe.) 

Every tenth of a Mach I would call out the fuel, engine and pressure gauges for the GIB to record.  At 1.6 Mach alert the GIB to verify the ramps were starting to open and opening at the same rate (they did not always work together.)  If everything was working right, exactly four minutes and thirty seconds after the AB was lit, we should reach calculated Vmax.  (I think the F-4C/D took about seven minutes - they were dogs compared to the RF-4C.)

If the sun was just right, you could watch the shock wave walk back across the canopy.  Just a shimmer of disturbed light (refraction) about a quarter of an inch wide.  At 1.6 Mach would be about the time it would reach the face of the engine.  That is when the variable ramps would start to open and bend the shock wave obliquely forward to keep the shock wave off the engine.  The faster you went the wider they opened until they were full open, about 4", at Vmax. 

Turbojet engines of the day could not digest supersonic air.  (Not true now with the F-22)  All the air behind the shock wave is still subsonic so the engine kept going as long as the ramps kept doing their thing.  The F-104 and A-12/SR-71 had inlet 'spikes'.  The F-14 and f-15 ramps come down from the top (I think).  If you did not have a spike or ramp, the limiting speed was 1.6 or maybe as high as 1.8 (the F-16), even though the engine was capable of pushing the aircraft faster. 

During the Mach run, watch the fuel really close.  You should have about 3,500 lbs remaining at the end of the Mach run.  You started the engines with 12,800 internal fuel and started the Mach run with about 8,200 - 7,800 lbs of fuel..  At Vmax pull the throttles out of afterburner.  At this point, you will lean forward in the shoulder harness because of the rate of deceleration.  Clime to FL480 and check the cabin pressure at 18,000.  The cockpit was kept at a 5 pound differential.   Watch how fast you climb to 48,000 or you might see something well above that.  Question:  What is the boiling point of water at 52,000 feet?

Now you are at 48,000 and about 150 miles away from base and starting to suck fumes and still had five pages of FCF check list to do.  So ask the ATC center for a clearance back to base (Bergstrom in this case), out of the block and below the APC (below 18,000 feet so you can cancel the IFR clearance and fly VFR the rest of the FCF.)  If you were doing the west supersonic corridor, you were now very close to Waco, TX.  Center would always give you a turn to the west to Stockton TACAN, away from Bergstrom.  You would tell center you don't have the fuel to go to the west and they would reply they cannot give you a southeast vector direct to Bergstrom because of traffic on the airways.  So I would then ask if I could have a "clearance below the APC maintaining a half mile radius my present position."  When they would say OK, I would drop the nose about 30 degrees, roll into a 70 degree bank, put on 5 g, and let the nose continue to drop to about 70 degrees down.  Soon we would be going down at about 84,000 feet per minute.  So it is going to take about 30 to 35 seconds to get below the APC.   Weeee!   The center loved it because for those 30 seconds the return stopped going forward on their displays.  They could read the altitude decreasing from the SIF.  Call cancelling your IFR clearance passing FL180.

Now as for compressor stalls.  If the compressor stalls, either from being miss-rigged or because the ramps don't open, you hear a very loud bang, the aircraft goes sideways, even with engines so close together.  Just slowing down a little bit will clear the stall.  You can hear the bang even through the microphone which is inside the oxygen mask.  There is at least one case of a flight surgeon riding in the back seat on an FCF defecating his pants at a compressor stall.

The compressor stall is basically a backfire.  If it were dark you would see the flame come out front.   A turbojet engine gets it's power from the weight of the air it can pushed out the back. Throw a pound of air out the back and you get a pound of push forward (thrust).   (At takeoff the intakes are sucking 160 pounds of air a second.)  (The burning fuel just adds the energy to turn the turbine which turns the compressor.)   As long as the pressure at the front of the combustion cans is greater then at the back of the combustion cans, the flow is through the engine and away you go.

Now there are a lot of pilots that would climb to 48,000 first and then descend to reach Vmax.  Maybe you had to do it in the F-4C/D just to get to Vmax, but I was more interested in total performance.  Did it take more the 4 minutes, 30 seconds - then you have a problem.  Could be the a lot of the 12,000 holes in the variable ramps were too dirty. 

We flew the Mach run (Vmax) at 40,000 because if you have a compressor stall it is just a big bang.  If you were trying to run in combat at Vmax at sea level, 715 kts CAS or about Mach 1.1 and you had a compressor stall, the overpressure might blow the tail pipe off the aircraft.  The "Q" or dynamic pressure at sea level is twice as much as it is a 40,000 feet.

Anyway, there is more to do on the FCF like pulling 8 gs and testing all the systems.  I always ended with a FOD check.  (FOD - Foreign Object Damage - an acronym used as a noun which the Air Force has turned into a verb, adjective, and adverb.)   To do a FOD check I did a 1 negative g push over causing all the large pieces of FOD to slam against the canopy.  You can see them in the rear view mirrors.  Then just a tad of positive g causes them to slam against the instrument panel and grab the big ones as they go by with your left hand.  I have a whole bag of light bulbs, pieces of Plexiglas, parts of instrument panels, nuts, bolts, labels, even several screw drivers. 

The last part of the FCF is the landing and the check of the fuel level low light.  The fuel level low light will light (and light the Master Caution light) at 1,800 pounds of fuel remaining in the number one feed cell.  If you did it right the light should come on during the base turn or while on final.  Normal operations called for landing with at least 3,500 pounds.  If you had to 'go-around' (abort the landing at the direction of the tower), when planning to land with 3,500 pounds on the ground, you would have the 13 to 18 minutes of flying time to try it again.  With 1,800 of fuel, if you had to go-around, you might have 6 minutes.  Better keep the pattern really tight. 

Exciting things that have happened on FCFs is for another day.

Question:  What is the boiling point of water at 52,000 feet?  Answer:  37 degrees Celsius or 98.6 F.