Monday, December 14, 2015

Physics

As readers of this blog may remember, early in life I had a learning experience about Newton’s Laws of Motion, and have had a lifelong interest in the subject.  That lesson primarily covered Newton’s First Law  “An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.”  

While portions of that law apply to the story I'm about to begin, this post will focus on Newton's Second Law "Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object)."  I'll credit Aaron  for putting the thought into my head.

So....There I was*

Towards the end of my second operational assignment, flying F-4Es (the one with the gun) out of Moody AFB.  The second worst President ever has been out of office for a couple of years and flying time is abundant.  So much so, that I've got a little over a thousand hours in the F-4.  I'm a 4 ship Flight Lead, Mission Commander and Maverick and Pave Spike Instructor.  Right where I should be for this time in my career.  Life is good!




One July morning, My Flight Commander calls me into his office and says "Juvat, I've got a good deal for you."  Now, the last time he said that, I  spent 3 horrible weeks in Germany, forced to drink wine and tour towns along the Mosel River, on what was supposed to be a 4 day TDY.    So, suffice it to say, I'm going to take his words  with a grain of salt.  

"Yes, sir?"  

"We need to take a jet to Hill (AFB, Ogden Utah) for Periodic Depot Maintenance.  Wanna do it?"

Periodic Depot Maintenance is when the depot maintainers basically take a jet completely apart and fix anything and everything that's wrong with it.  They then put it back together and give it back to you.  I'd be flying one to Utah, and then turning around and flying a different one back.  So the mission is just a Cross Country flight and a generally fun, low key, see the country from 30K, go places you've never been kinda thing.  Except...

There's a reason the airplane is going to Periodic Depot Maintenance.  It's broke.

And...

No matter how much they've checked and in spite of the fact it's had a functional check flight before it's handed over to me, the fact remains, the airplane I'll be flying home, spent the better part of a couple of months with it's innards spread out in a hangar.  There's always something.

"Sure, sir, when do I leave?" 

"You and Bear (my WSO's call sign) leave Friday, return Monday."

Air Force Logistics Command (AFLC) was well known for not working on weekends.

Hill was just outside of two hop distance from Moody even with our 3 bag configuration, so we flight plan, Moody to Bergstrom, Bergstrom to Buckley, Buckley to Hill.  We'll take off at 0800 and, all things being equal, we'll arrive at Hill at 1500.  Hill has just been one of the first bases to convert from F-4s to Lawn Darts F-16s, so both Bear and I had friends there.  It was Friday and, even in Utah, there was a Stag Bar.  Our Friday Evening was set!

Bear and I brief (didn't take long, weather and NOTAMs) and step to the jet.  Fire it up and are running through the normal system checks, when I get a master caution light.  I glance down at the panel and see I've got a generator light on.  I tell the crew chief about it and ask Bear to check the circuit breaker.  

Popped Circuit Breaker is the usual cause of this malfunction, but not in this case. No big deal, I cycle the generator switch.  Light stays on.  OK, that's going to be a ground abort.  (One generator is enough to power the avionics and other devices that require electricity, such as flight control stability augmentation. Prudence would dictate not taking off with only one for a non-critical mission such as this).  We shut down the aircraft and trudge back into the squadron, thinking our good deal went bye-bye.  

Never underestimate the enthusiasm a maintenance NCOIC will have to get a hangar queen off his roster!

Around 1000, the squadron gets a call saying the jet is ready to go.  Bear and I head back out there, figuring that we should land about 1700 Hill Time, or 1900 our time (which is important as we showed up at the squadron at 0730 and we can't be airborne any later than 1930 Moody time due to Crew Duty day restrictions).  

So, it'll be tight, but we can make it, especially since Buckley to Hill is only 350 miles.  Change that leg's flight plan from .85 Mach to .95 Mach, No problem!

Start up the jet, and get through the systems checks (cycled the generators a couple of times more than the checklist calls for, just to be sure), and blast off.  

Smooth climb to the mid 30's and it's clear sailing.  Somewhere between England AFB (Alexandria LA) and our letdown point for Bergstrom, I get a Master Caution Light,  glance at the panel and see the same generator light.  The Bus Tie light is out. (That light shows the status of the switch that allows one generator to power all the avionics.  The F-4 was built with two generators and systems were divided between the two.  If the Bus Tie Switch went out, you would lose certain capabilities, but theoretically, you could safely recover the jet, it would just be more exciting.)

Bear and I run through the checklist, but nothing corrects the situation.  With the Bus Tie light out it's not an In-Flight Emergency, and the closest base is Bergstrom, so we press on in and land.  As we're coming down, I mention that we're not going to make it to Hill tonight, so when we get on the ground, I want Bear to contact Buckley and make VOQ reservations for the evening while I figure out how to get the airplane fixed.  Touchdown and landing are normal and we shutdown in Transient Parking.  Bergstrom is still an RF-4C base, so getting F-4 maintenance is not a problem.  The aircraft is fixed without too much delay (better electrician than at Moody I guess), and we're off to Buckley.  

Once at altitude, I ask Bear about quarters.  He says there were no quarters on Buckley, but he made reservations at the VOQ on Lowry AFB.  Lowry, at the time, was the USAF's Intel training base and was located pretty much in Downtown Denver.  The trip to Buckley is uneventful.  Land and coordinate with transient maintenance to only fill the internal tanks, this being July in Denver, the "Mile High City", and then catch a ride into Lowry.  Check into the VOQ and ask directions to the O Club.  Right across the street.  How convenient.  We drop off the bags and walk across to the club.  We decide that an adult recreational beverage would be refreshing after defying both death and gravity for most of the day, so walk into the bar.

You remember that scene from the original Star Wars when Luke, Obi-wan and the droids walk into the bar in Mos Eisley? 

  That was a WARM welcome in comparison.  I'm pretty sure the temperature in the main bar was approaching absolute zero when the Intel Wienies in their light blue uniforms saw us unwashed interlopers in our flight suits despoiling the sanctity of their club.  About this time, a bar waitress walks by.  I ask her if it's ok if we're in here in bags.  She said, "Yes, but you might be more comfortable in the other bar".  So we follow her to a different room.  It's a quiet place, just Bear, Me and the Bar Tender.

The next morning, we're up and call for transportation.  Well, you see, it's Saturday, we don't have anyone on Duty, but we might be able to get someone here by 10.  Ok, not optimum, but  we can make it work.  10 appears to have been an estimate.  It's almost noon by the time we get to the Base Ops.  We check the weather, and with one exception, it's not a factor.  However, outside air temperature is in the high 90's, which makes the Density Altitude much higher than we expected.  


Takeoff was from top left to bottom right


So, for the first time since Pilot Training, I actually calculate Takeoff Data for real. (The F-4 had enough excess thrust that Takeoff Data was usually, if you're on the ground and lose an engine, stay on the ground.  If you're airborne, stay airborne.) Today, given Buckley's 11000' runway and internal fuel only, shouldn't be a real problem.  Takeoff roll will be longer than usual, but less than half the runway.  

Ok, we're going.  

Walk out to the Jet and as I walk by the wing tank, I give it a rap, expecting a hollow empty sound.  Instead I get more of a thud sound.  Oh, crap!  We're three bags full.  Talk to the Transient Chief who says "oops" but defueling is not an option.  Complete the walkaround and then pull out the checklist again and redo the Takeoff data.  Looks like we should be off the ground at around 8000'.  
For min go speed, you start at the top with the runway length, drop down to the Density Ration (.7 on this day), parallel the top curve back up and left until you get to the baseline, then drop straight down to the Takeoff speed 175K, then right to the Min go speed. I figured about 138K (The runway was longer than the chart showed.)

 I calculate minimum go speed.  (The minimum speed that I can lose an engine and still take off.  )  Fortunately, we're on the right side of the curve,  minimum go speed is less than maximum abort speed (the maximum speed I can abort and stop on the runway without taking a barrier.  If they're reversed, there is a window where if you lose an engine, you can neither stop nor takeoff.  Bad juju.).  So, if I'm on the ground, I'll stay on the ground (but will put the hook down in any case), and if I'm airborne, I'll stay airborne, but my hand will be close to the jettison button.

Bear and I talk it over and decide we're going.

Fire it up, taxi out and are cleared for takeoff. I taxi onto the runway and position the jet so its tail is over the approach end of the runway, I want every inch.  Run 'em up.  Everything looks good.  Release the brakes and Newton's second law takes effect. (You wondered how that was getting worked in didn't you?)  I light the burners and watch the exhaust nozzle gauge swing open indicating a successful light.  But it feels like we're barely moving.  4000' down the runway, where we'd normally be lifting off, we're about 120 (I'd calculated TO speed to be about 175).  Halfway down the runway, we're at 150.  3000' remaining and I feel the gear leave the ground.  Gear up!  Gonna leave the flaps down for a couple.  Over the end of the runway and only about 20' between me and Colorado prairie.

About this time, I get a call from Buckley Tower switching me to Denver Center.  I've still got the burner's going, and I'm really hoping that someone doesn't have an extra high fence built anywhere along my path.  Bear switches the frequency and I contact them.

"Denver Center, Juvat 01 is with you passing 6500"  (Buckley Field elevation is 5664'.)

"Roger, Juvat, Denver Center has contact. Turn left heading 360, expedite climb to Flight Level 330."

"Denver Center, Juvat left turn 360 cleared FL330, be advised, Juvat is as expedited in his climb as he can get."

"Juvat, Denver Center, Hot out there today, Huh?"

Interesting thing I noticed on that flight.  If the throttles are in the max burner position and your left hand is on them, when you extend your index finger, the tip of it is about a half inch from the jettison button.  Nice design feature McD!

Oh and here's the video is saw on Aaron's blog that prompted the story.















*SJC

22 comments:

  1. Two zipper suited sun gods walk into an intel wienie bar? Sounds like you guys got the same looks a man would get accidently walking into the ladies room.

    Another great story Juvat, going back and reading that first link was also very entertaining.

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  2. Thanks
    Well....There are a lot of similarities between the two. Just sayin' :-)

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  3. To paraphrase Trotsky, you might not be interested in physics, but physics is interested in you!

    Except of course physical law isn't interested, it just is, and we clever apes in our colorful shoes don't get a vote.

    How would your jet have behaved if it was December and the temp was 20F?

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    1. "clever apes in our colorful shoes..."

      Oh dear, I do like that turn of phrase. Adding that to my lexicon...

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    2. How would your jet have behaved if it was December and the temp was 20F?

      I believe I'd have had a hard time getting the gear up and gear doors closed without a very steep climb. Cold air being denser enables the engine to produce more thrust as the dense air is forced through the turbines.

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    3. "It's a physics thing." is a common response when my users want to know why their computer is doing something. Course, the other response is usually "Computers have a nasty habit of doing what you tell them to do, rather than what you want them to do."

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  4. I was thinking of that Vodka Express video while I was reading this. Glad the prairie fences were short!

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  5. I loved the tower chatter on the video. Especially "I hope I have enough film to get the crash." Black humour, can't live without it in this business

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    1. I wonder what and how much of, they were carrying.

      Agree about Black Humor, but I wonder what would be said about that video if it happened today.

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    2. Juvat, when INS and Customs were separate services I had to go to Harrisburg, PA and clear the crew of one of those big Russian airplanes. I got the nickel tour of the plane and that was pretty neat. They were taking a whole bunch of American made firefighting trucks to Croatia. The "why" was beyond the scope of my job. The sole english speaking member of the crew told me the cargo deck was made from titanium. Aft of the cockpit they had some pullman style berthing for the off duty crew.

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  6. Did you really consider aborting the takeoff? I would suspect in a Phantom or any high performance jet, the decision to jam on the brakes at 120 kts and above has its own dangers.

    We have quite a few accidents over the years at the Lake Tahoe airport over 6,000 feet - - in the summer of course - with small GA planes.

    The classic is this, though...Pilot seemed oblivious to density altitude and paid the price

    https://www.youtube.com/watch?v=yDu0jYiz-v8

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    1. No, all the calculations were to prepare for the (unlikely) possibility of losing an engine. On a normal day at a lower pressure altitude, the F-4 would accelerate so fast that by the time you'd recognized you'd lost an engine, you were already airborne. That was not going to be the case that day. So I wanted an airspeed for a decision point, and that would have been max abort speed. I would have prethought the decision, below Max Abort speed, stop, above it, continue, and since, in this instance, max abort was also above minimum go, I should be able to get airborne at that point even on one engine. Had the reverse been true, I think I'd have stayed the night in Denver and made sure I had ground transportation early in the morning the next day.

      As for how to abort, the actual response would have been throttles to Idle and deploy the drag chute. The chute was functional to well above max abort and was quite effective at slowing the jet down. Finally, I've taken a few barriers in my time so, I wouldn't have hesitated, the hook would have gone down as soon as my hand was free from the drag chute handle. Wouldn't have touched the brakes till well under 100K, but you're right, an unthoughtout plan rarely ends well.

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  7. Learned to fly in a 75 hp Piper J-4 off a 7,000 ASL runway. The instructor spent six months each year as a missionary pilot in Central and South America. Density altitude, gross takeoff weight, and weight and balance instruction was part of every preflight.

    Rode in a Western Airlines 727-200 that lost two engines en-route from SLC to the old Stapleton Airport. We lost one somewhere near Meeker, CO and the other 3/4 of a mile from the runway. 95 degree day - no go around on one engine. We landed in the gravel short of 26R. Very noisy. Very stressful if you were a pilot passenger sitting in the very back where you could hear, and understand, the engine noises.. The sheeple passengers only had a few seconds of terror.

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    1. WSF, flying from Rota to Athens via some kind of four engine Navy transport with props and reciprocating engines in 1974. I was one of the sheeple sitting at the starboard wing root and looking out over the wing on takeoff climb. Shortly after the starboard inner engine blew oil all over the wing it topped that by bursting into flames. After I took that very deep breath and turned to shout, "the engine is on fire" the only thing that came out of my mouth was a squeak so high pitched that dogs for miles around were perking up their ears.
      If there had been a charcoal briquette stuck into my waste overboard sphincter, it would have been squeezed hard enough to make a diamond.
      I never really liked flying after that, and I enjoyed the quiet and safety of my enginerooms a lot more.

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    2. Similar experience in Lockheed Constellation circa 1963 from Ft Leonard Wood to Newark. Had a window seat on the wing. During the flight the cowling on #3 started shaking then came off. Guess we were in no danger but for a dumb Colorado kid in his first "big" airplane ride it was disconcerting. First "low bidder" experience.

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    3. During my time with INS I was talking to a fairly old Lufty flight engineer, he had great english and I was telling him the story. He said no big deal, there must have been a little water in the oil and during the takeoff climb it flashed into steam and blew the oil out of the engine, he said the fire was not a gasoline fire, but was merely the oil burning on the manifold. I still do not feel any better about the whole experience. I was trying to remember what type of aircraft, but the memory is not coming up with an answer. I bet that Connie you were on, and the bird I was on both had big twin row radials. Strange it was #3 in both cases, and I may have understated just how scary it was.

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  8. That's a very cool story and a great example of density altitude in the real world. Heck if it can give an F4 problems, we Cessna students need to respect the heck out of DA.

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    1. Ahh....I was successful! Course, you're not likely to have DA problems in Michigan, at least for a few months, but....you never know what with Global Warmening.

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  9. I 'think' that Il-76 takeoff was out of Perth... That set of hills looked familiar... :-) And yeah, DA can and WILL bite you in the butt!

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Just be polite... that's all I ask. (For Buck)