F-14 Questions Answered - Ask Away

There is absolutely a coffin corner on airliners.

For example, the FMC in a Boeing 757 calculates max altitude (at which the airliner can only climb 300 FPM when wings level, or at which it can only maintain 1.2 x stall speed). That altitude depends on gross weight, the speed at which the airplane is intended to be flown*, air temperature, and a few other things...

Indicated airspeed is a measure of dynamic pressure, so, with fewer air molecules hitting the airplane, it has to be going a lot faster through the air to get the same dynamic pressure. True airspeed is a measure of pure velocity through the air.

So, at sea level, if you see 230 KIAS, you're going about 230 KTAS (True Air Speed). 230 KIAS is often the clean maneuvering speed for a 757 with flaps up at high gross weight. The plane can be banked up to 30 degrees and flown well, but there isn't a ton of maneuverability at clean maneuvering.

Now, look at 230 KIAS when up at FL 370, and you'll see the TAS up around 500 KTS...mach number about .80...so, you're near the airplane's max speed, but without a lot of dynamic pressure (created by Indicated Air Speed) to create lift/forces over the wings and flying surfaces.

Airliners tend to be thrust limited. You simply can't get any higher...and the difference between stall buffet and mach buffet gets quite narrow at high altitude. For the U-2, for example, it's 4 Knots of Indicated airspeed. For a 757, I've seen about 30 KIAS between stall and max...not comfortable if you hit turbulence that could push the airspeed to either buffet regime.

You don't want either form of buffet.

"Nervous about buffet"...yeah, in the same way that we are "nervous about sliding sideways on black ice as we drive to the airport"...it's something you really, really try to avoid. Mach buffet will overstress some airplanes. Stall buffet leads to a control loss. For some folks, that's solved with a giant altitude loss...for some folks, it's worse...

Air France 447 experienced a high altitude stall...didn't work out well for them.

In a high altitude stall, you don't have the thrust to recover. Those HBPR fans make less power at high speed and less power at low air density...making high altitude a real challenge as the engines aren't making much net thrust. You have to accept a massive altitude loss to recover from a fully developed stall at high altitude, you're not going to power out of it.

For all airplanes flying up high, the behavior changes. The airplane is a body moving through space, acted on by the forces of wings, engines, control surfaces.

At high altitude, those forces are reduced because the air density is reduced. However, the airplane still follows Newton's laws and it is flying much faster. So, more inertia, but less force available to act on that body.

Turn radius then, is huge at high altitude, because the airplane is going much faster, and is acted upon by much smaller forces.

I know of pilots (who get extra training and this discussion in greater detail) who have tried to push an airplane higher than the FMC calculated max...and then hit stall buffet...which led to a huge altitude loss...and a potential loss of separation with other traffic. That loss of separation can lead to certificate action...like a traffic ticket for pilots...if traffic tickets came with a $10,000 fine and the permanent loss of your job.

The 757 is a good, honest jet. Handles well. Has good power. But at altitude it, like all other airliners, has to be flown gently. There isn't a performance margin to maneuver it aggressively. The autopilot imposes bank and pitch limits on the airplane up there...and the thoughtful pilot who is hand-flying does the same thing.

*Expressed as a mach number based on a parameter know as cost index. Higher CI = faster cruise speed, and sometimes, a lower max altitude.
 
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Thanks for that great explanation.

Let's talk about a hypothetical situation. An unscrupulous 757 captain and FO are ferrying a 757 and decide to max the airplane out. Ignoring warnings and, either unaware of the fact that the aircraft is thrust-limited from climbing any higher, or just choosing to ignore that fact, they stall it.

At that moment, does the elevator have enough control authority to push the nose down and get the jet flying again, or is it just going to start falling in a flat attitude? As it loses altitude, will it naturally correct, and start flying again?

I've read about T-tail aircraft, like the DC-9 and its descendants, and the 727, etc, having a tendency to lose elevator authority at high angle-of-attack stalls, due to turbulent airflow from the wings washing over the empennage (I know they also have stick pushers to prevent that).
 
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If you stall an airliner at altitude, the elevator authority usually is sufficient to overcome any pitching moment created by the engine thrust. The engines are weak up there...

This has happened. With passengers on board, not because the crew was unscrupulous, but because they were incompetent. Those crews are quite rare.

Now, in the case of Air France 447, they stayed stalled long enough to trim the horizontal stabilizer to the point where the elevator wasn't effective in overcoming engine thrust. To recover that airplane would have taken about 30 seconds of forward stick, during which time the stabilizer would have slowly re-trimmed to nose down and allowed the airplane to recover...
 
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I would like to hear what some of the fuel consumption rates are on 757's and even F14, If in pounds are you using 6.5 pounds for a gallon.
 
Originally Posted By: Exhaustgases
I would like to hear what some of the fuel consumption rates are on 757's and even F14, If in pounds are you using 6.5 pounds for a gallon.


Consumption rates are measured in pounds. Fuel density varies, but 6.6 - 6.7 lbs/gallon is close. On big airplanes (747), the density, as well as the freeze point was part of the upload information. The tanks, after all, are sized in gallons, but aircraft performance depends on weight.

So, fuel flow depends on the mass of air moving through the engine on the use of afterburner. Slower speed = less mass = lower fuel flow. Higher speed = more mass = more fuel flow. Higher altitude = less dense air = less mass = lower fuel flow

F-14 at idle, on the ground, uses about 1100#/hr for each engine. Worst case, high speed, low altitude, would get you about 12,000 #/hr per engine.

Light the AB, and it's a whole different ballgame...in full AB, fuel flow at low altitude, and high speed, was between 2,000 -2,500 # per minute (for both engines). That's roughly 60,000#/hr for each engine. Or, back to gallons, about 10,000 gallons per hour per engine. That took big pumps, and big fuel pipes, to feed the AB.

But in cruise, at altitude, the F-14 was quite efficient - about 2,400#/hr per engine loitering. At 3,000#/hr/engine - the airplane would cruise at .85 IMN.

Airliners, with high bypass turbofans, are very efficient at moving air...but at high speed, they're limited in the amount of air (mass) that they can move...

For example, 757 at idle on the ground uses about 1,000#/hr per engine. About 3,500#/hr per engine in cruise. So, on roughly 1000 gallons, the airplane is moving 200 people 550 miles. About 100 MPG/person.

At ten times the speed that you're driving on the highway...

Newer airplanes, like the 787, are far more efficient. Even the Airbus 320, a 30 year old design, uses about 2,500#/hr/engine in cruise, and is moving nearly as many people as the 757. The 757 is a great airplane for performance. Power/weight. Climb. Short field performance, it's just a high performance airliner...a muscle car, when the industry is moving to economy cars...
 
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Originally Posted By: john_pifer
Astro, did you ever consider becoming an astronaut?


Of course. I majored in Astrophsyics in college. My goal was Navy fighter pilot.

But military pilot was a common first step in the road to astronaut. Test pilot was the next step. I applied to Navy Test Pilot School (TPS) twice but wasn't successful. They only took one F-14 pilot those years (it was an annual board). The next year, when I didn't apply (because it would have potentially thrown off my career timing), they took six F-14 pilots to supply the F-14 air-ground mission integration testing that was upcoming at that time. I heard, through the grapevine, that the board was looking for my application.

But by then, I was an instructor and was going back to sea as Wing LSO.

C'est la Vie.

A good friend of mine from Aviation Officer Candidate School, Barry Wilmore, CAPT, USN is an astronaut. Flew the Space Shuttle. Commanded the ISS. Had lunch with him at the Quantico O'Club last year - a reunion of sorts, with my son's godfather, a Marine, and Barry. The three of us were neighbors and friends as we went through jet training in Meridian, Mississippi 28 years ago.

But as we took a few photos at the club, I thought it was remarkable that we don't look any older now...
 
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Originally Posted By: Astro14

But as we took a few photos at the club, I thought it was remarkable that we don't look any older now...


Moving fast and being in space saves a bit of time compared to us earthlings, no?

I guess the compromise is radiation load...
 
or deteriorating eyesight
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Awesome read...two of my friends fly F-16's currently. One just flew the F-35 simulator. His comparison to his F-16 was interesting...let's just say his car comparison was a Ferrari vs a school bus. I am sure you can all figure out which is which.
 
I wish we were keeping the Ferraris...

The minivan, I mean, F-35, has sweet Bluetooth and "infotainment", and the DVD player for the kids, and lots of seats...but it's a pig. It's slow. It's ugly. It's got "issues".. But it's too big to fail, so we will buy this thing...even though it isn't worth what we are paying...
 
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Originally Posted By: Jetronic
or deteriorating eyesight
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The only eyesight deterioration noticed was the moment when the check came...
 
Originally Posted By: Astro14
I wish we were keeping the Ferraris...

The minivan, I mean, F-35, has sweet Bluetooth and "infotainment", and the DVD player for the kids, and lots of seats...but it's a pig. It's slow. It's ugly. It's got "issues".. But it's too big to fail, so we will buy this thing...even though it isn't worth what we are paying...


The sad part is it looks like our government will buy the F-35 aswell to replace the F-16.

How would the F-35 compare to a Eurofighter or Rafale or even a SAAB? Pricewise it's no contest, I'm sure...
 
Originally Posted By: Astro14
I wish we were keeping the Ferraris...

The minivan, I mean, F-35, has sweet Bluetooth and "infotainment", and the DVD player for the kids, and lots of seats...but it's a pig. It's slow. It's ugly. It's got "issues".. But it's too big to fail, so we will buy this thing...even though it isn't worth what we are paying...
Bathrooms? I am at that age
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So an old Constellation flew from California to Washington DC. at an average of 331 miles per hour, in about 7 hours. They could carry up to 109 passengers.
Imagine what a decent aerodynamic airframe and diesel piston engines could do. As far as economy jets would be obsolete.
A geo metro would get 200 mpg per person with 4 people on board right?
 
Originally Posted By: Exhaustgases
So an old Constellation flew from California to Washington DC. at an average of 331 miles per hour, in about 7 hours. They could carry up to 109 passengers.
Imagine what a decent aerodynamic airframe and diesel piston engines could do. As far as economy jets would be obsolete.
A geo metro would get 200 mpg per person with 4 people on board right?
Turbine engines have much lower maintenance per hour of use.
 
What will be very interesting to see is how well the propfans do when they eventually enter service.

I have no doubt that the fuel savings will never be passed along to the customer, but it could really change the way the airlines are run.
 
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The Fulcrum is a very simple jet that was designed to fit in the Soviet model of tactical aviation. That means the pilot was an extension of the ground controller. As many have read, innovative tactics and autonomous operations were not approved solutions in the Warsaw Pact countries. The cockpit switchology is not up to western standards and the sensors are not tools used to enhance pilot situation awareness, rather they are only used as tools to aid in the launch of weapons.The jet is very reliable and fairly simple to maintain. I could service the fuel, oil, hydraulics and pneumatics and had to demonstrate proficiency in these areas before I could take a jet off-station. Its handling qualities are mediocre at best. The flight control system is a little sloppy and not very responsive. This does not mean the jet isn't very maneuverable. It is. I put it between the F-15C and the F-16. The pilot just has to work harder to get the jet to respond the way he wants.

The Fulcrum also has a lot of ponies under the hood. I rack-and-stack it in the same order as above as far as thrust-to-weight. The only real side-by-side performance comparison was with an F-15C. I was carrying a centerline fuel tank and the Eagle had no external stores except for the wing pylons and missile launch rails. The mission was BFM but the MiG-29's centerline tank is limited to 4 g until empty. The performance comparison put me 3000 feet line abreast with the F-15 at 10,000 feet and 300 knots indicated airspeed. At the F-15 pilot's call we each selected full afterburner and I matched his pitch rate until we got to 70° nose high. The first one to reach 100 knots would call terminate and we'd see how it played out. When the F-15 pilot hit 100 knots I still had 170 knots and was well above him.

Another common performance comparison that doesn't require any side-by-side look is over-top-top airspeed – the speed required to complete a loop. The Viper requires about 250 knots to get over the top. I could horse the MiG-29 over the top at 150 knots. While the GE-powered F-16 does have a thrust-to-weight advantage over the MiG-29, the Viper will get to its angle-of-attack limit if it started a loop at such a slow speed and the pilot can't pull the nose through the vertical. Although the Fulcrum has the same angle-of-attack limit as the F-16 (26°), the Fulcrum pilot can override the limiter and get to 45° to 50° angle-of-attack. The only caution when doing this with the MiG is that it loses some directional stability above the angle-of-attack limit.


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From BVR (beyond visual range), the MiG-29 is totally outclassed by western fighters. Lack of situation awareness and the short range of the AA-10A missile compared to the AMRAAM means the NATO fighter is going to have to be having a really bad day for the Fulcrum pilot to be successful.

In the WVR (within visual range) arena, a skilled MiG-29 pilot can give and Eagle or Viper driver all he/she wants. When I was flying the MiG-29, the way I prosecuted the visual arena depended on the scenario. If it was 1 v 1 BFM and we only called kills with a gun shot, I flew the jet differently than if missiles and guns were in play. If the BFM scenario was guns-only, I flew the jet more like an F-16, knowing I had a lot more angle-of-attack (than an F-16) available if required. If missile shots were in play then I would pull as hard as I could to place the other guy in Archer parameters as quickly as I could and make him at least feel threatened by my nose position; hopefully, forcing him into making a mistake. In a many versus many scenario in which missile shots were generally counted for kills, I was hesitant in bleeding off all my airspeed to get the quick Archer shot since I probably needed the energy to maneuver against other aircraft in follow-on engagements.


No bluetooth and infotainment or dvd player, but I suppose this is going off the other end...

The newer versions (Mig-35) are fly-by-wire vs hydraulic for the MiG-29A so the sluggish controls are likely gone... I wonder if they can still carry and shoot AIM-9 instead of AA-2
 
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