F-14 Questions Answered - Ask Away

[billt460]

Astro,

In a past post you mentioned landing an F-14 successfully with a massive fuel leak. Did you ever find out what failed that caused the leak? And how close did it come to causing an in flight fire?

 

[Astro14]

Originally Posted by billt460
Astro,

In a past post you mentioned landing an F-14 successfully with a massive fuel leak. Did you ever find out what failed that caused the leak? And how close did it come to causing an in flight fire?


Well, I can't really speak to how close it came to causing an in flight fire, because, well, it didn't...though with all the fuel leaking, that was a strong possibility. I think that I mentioned this in the story; I calculated the leak to be 1,500#/minute. So, about 250 gallons of jet fuel per minute in the aft fuselage... Fortunately, it was in the aft fuselage - so, behind a lot of things, like engine generators and electric components that could've caused a spark. So, even though it was impinging on the engines, which are hot, the high altitude and cold kept it from lighting off.

The root cause was a fuel management computer. A circuit board, really, that controlled the engine crossfeed valve, motive flow isolation valve, motive flow shutoff valves and sump tank interconnect valve. The idea was that the fuel system operation was all automatic, so that the pilot didn't have to manage it. It usually worked great. There was a switch in the cockpit, on the left side, forward, that allowed you to feed engines from one side or the other. But we rarely used it.

But on that night, the short in the computer led it to feed both engines from the right/front side and to send motive flow fuel to the aft/left side.

The fuel system was split into a left/right configuration, and normally, the engines fed from their respective side. Now, there were some tanks fore and aft inside the fuselage, so the forward tanks were paired with the right side, and the aft tanks were paired with the left side. Wing tanks were fed to their respective side. Equal fuel quantity available to each engine.

Motive flow was fuel that was sent by a high pressure pump to venturi pumps in various tanks throughout the airplane. The venturi pumps picked up the fuel and fed the engines. This reduced the number of pumps in the system. There were 8 tanks in the fuselage and wings. Small, numerous tanks for resistance to combat damage and ease of repair would mean lots of fuel pumps (which is lots of weight, and lots of repair points, and lots of pumps to turn on/off), so simple motive flow/venturi pumps with no moving parts and no control required were used in most tanks.

Motive flow and the scavenged fuel was delivered to a sump tank that fed the engines. The engine fuel pickup (which was flexible, and would swing around under negative G to stay submerged in the fuel) was in that sump tank.

The engine feed was about 100# per minute, and in the case of this failure, all of that draining the right/front tank set.

But motive flow was about 1,500# per minute. It takes a lot of fuel to venturi the fuel out of a tank via multiple pumps.

When the motive flow fuel arrived in the already full sump tank for the left side, it cascaded into the rest of the tanks - eventually rupturing the vent tank, where excess fuel from the system was sent. It was designed to handle fuel expansion, not 250 gallons a minute...

When I pulled the CB (RD2), I killed power to that computer. The system was designed to go back to a "safe mode" when power was lost, in which the isolation valves closed, and each engine fed only from its respective side.

The airplane flew the next day with a new fuel management computer and a new vent tank.

 

[billt460]

Thank you for all of that. Unbelievable they were able to diagnose all of that, and had it flying the very next day. Imagine if they had guys like that working at car dealerships!

 

[Astro14]

Originally Posted by billt460
Thank you for all of that. Unbelievable they were able to diagnose all of that, and had it flying the very next day. Imagine if they had guys like that working at car dealerships!


I give tremendous credit to the kids we had fixing airplanes.

They're amazing.

The average age was something like 21 years old in our squadron. They really worked hard. This airplane was no different - there were kids crawling all over it from that night until the next morning to make it fly.

 

[billt460]

Astro,

If you were to take an F-14 off with the heaviest fuel load it could carry, how long would it take to get rid of all of it, if you ran at the highest power settings without overheating or damaging anything in the engines? I ask because a while back I had read an interesting article about the old F-104 Starfighter. They said a pilot could get rid of all the gas that plane could carry in less than 9 minutes in full burner. I believe it had a General Electric J-79 engine.

 

[Astro14]

It's about the same, Bill.

The airplane held 16,200 lbs internal fuel. Two drop tanks of 2,000 each could be installed. So, 20,000 lbs of fuel was a max load.

The rule of thumb for fuel use in AB was 2,000lbs/minute. That varied with altitude (lower increases fuel burn) and airspeed (faster increases fuel burn) and engines (GE F110-400 used more than the TF-30) but close enough.

10 minutes.

Give or take.

If you climbed while using full AB, then it would last longer. The best rate of climb would have you getting above 35,000 feet and supersonic in about 3 minutes, at which point your fuel flow is a lot lower, because of the altitude. I don't remember the numbers, but you could go a long way once up high, even in full AB.

I once flew from Pensacola to Key West and was supersonic, in mid-range AB, the entire way. About a 30 minute flight. With a clean (16,200# capacity) airplane.

It's not the engines that would have trouble being at sea level at max AB for that long. Assuming they were tuned properly (TF-30 mechanical fuel control fuel trim level), the engines would run OK. It's actually a matter of total temperature on the airplane. You would exceed the external tank airspeed limit pretty quickly (620KIAS) as the airplane would stabilize a bit above that and supersonic at sea level. That's a lot of heat in the air itself. Ram pressure, temperature rise from friction, etc.

Total air temperature - Wikipedia

en.wikipedia.org

So, one day, I launched late from the carrier. Last airplane airborne for a fly-off. Airspace constraints kept me down low (I stayed at 500 feet, just to be safe) but I had a flight of 8 other airplanes to catch on a short flight (200 miles) to Oceana. I stayed in full AB after takeoff, and at 620 KIAS, throttled back to mid AB, and on a hot, humid day, about 8-10 minutes after takeoff, at 500 feet and still at 620 KIAS (barely subsonic) I got a bleed duct overheat warning.

The bleed duct was the inlet to the pressurization/AC system. Where the engine bleed air entered the expansion turbine, from which it was cooled and sent to cockpit and avionics. It was a serious emergency, as a bleed duct leak could lead to fire. Bleed duct warnings had preceded several F-14 in flight fires that led to aircraft losses.

Long story short, I had simply overheated the airplane's pneumatic systems. The total air temp was hot enough that the heat exchangers couldn't keep up and the whole pneumatic system got hot, triggering the warning.

 

[billt460]

That's a lot of fuel! At 6.8 pounds per U.S. gallon, that equals 294 gallons per minute. Or over 5, 55 gallon drums per minute. It's hard to imagine a nozzle capable of flowing at that high of a rate. It divides out to just under 5 gallons per second. Performance comes with a price, that's for sure.

 

[claluja]

Ever fly under the SF Bay Bridge?

Old friend (since passed) used to tell me about doing that, iron hand missions flying point, etc. Great stuff.

 

[Astro14]

Originally Posted by claluja
Ever fly under the SF Bay Bridge?

Old friend (since passed) used to tell me about doing that, iron hand missions flying point, etc. Great stuff.


Only in the simulator...

 

[billt460]

Astro,

When you find yourself landing an F-14 on a runway instead of a carrier, do you approach it differently? By that I mean do you allow yourself the luxury of using up a couple thousand feet to, "grease it on", or do you fly the same type of approach as you would landing on a deck aiming for a wire?

 

[y_p_w]

Originally Posted by billt460
Astro,

When you find yourself landing an F-14 on a runway instead of a carrier, do you approach it differently? By that I mean do you allow yourself the luxury of using up a couple thousand feet to, "grease it on", or do you fly the same type of approach as you would landing on a deck aiming for a wire?

I really doubt they slam into a runway unless they really have to. However, I found this footage of the last time an F-14 ever landed before they were all made non-airworthy (to keep parts from possibly being smuggled to Iran). I think this was where Grumman used to be headquartered years ago. I guess this landing was taken really hard as a sendoff.

 

[ArrestMeRedZ]

I'm not sure how Astro does it, but you could almost hear an audible groan from the concrete runway at Nellis AFB whenever there was a Navy fighter on final approach. I have been assured there is no truth to the rumor the Air Force sends a sweeper out after every Marine jet lands. It's after every other one.

In truth, greasing a modern fighter onto the runway looks good, but it's harder on the tires than a firm landing. Of course, a Navy firm landing and an Air Force firm landing are two different animals, each appropriate to the conditions they face.

 

[Astro14]

A carrier landing was a normal landing in the F-14. Constant sink rate (700-800 FPM) until touchdown.

At every Naval Air Station, there was an FLOLS, a Fresnel Lens, the "meatball".

So, every landing at an NAS was a chance to practice a normal carrier landing with the same visual cues.

If everything was normal, I would do a normal landing. A carrier-style landing. Even at an Air Force base. It didn't hurt the airplane. It allowed you to dissipate energy on landing, which was really important in a fighter landing in the rain, or on a short runway.

Now, if the airplane was over normal landing weight, or I had something structurally wrong, I would land it gently. But I would also choose the longest runway in that case. 12,000 feet at Oceana. Most fighters aren't really built to stop...with the notable exception of airplanes built by SAAB, of course...

As a data point, a friend of mine couldn't get the flaps down when coming back to Oceana during a rainstorm. So, he landed without flaps, which added a good 20+ knots to your approach speed. He chose the shorter runway at the request of Tower (note to the wise: never listen to Air Traffic Control when making decisions).

He touched down, hydroplaned, and 7,000 feet later, slid off the end of the runway about 200 yards into the dirt.

First, he should've taken the longer runway, and next, a normal landing that dissipates energy would've helped him.

 

[The_Eric]

Astro- thank you for playing Q&A with us! Your depth of knowledge is really quite amazing, as is your willingness to so thoroughly explain it to us!

As an aside, I saw earlier in the thread that you are/were considering building an RV8. I urge you to get in touch with Cleveland Aircraft Tool - they're great folks to deal with who have lots of tools, equipment and odds and ends to build planes, especially RVs. In fact the plane that spurred starting the business was an RV4 (N50036) They built it without the aid of all the tools (or made them as they went) and took it to Oshkosh and won grand champion with it!

 

[Astro14]

Thank you! Glad you're enjoying it. That was my hope.

I've got a good friend building an RV-14. He's been a great source.

I will definitely check out Cleaveland Aircraft Tool. I appreciate the recommendation.

Cheers,
Astro

 

[billt460]

Astro,

When you found yourself training right from the get go exclusively in turbine powered aircraft, was it difficult to adjust to flying piston powered airplanes, when you finally got the chance? In turbines, (both prop and jet), you have far more power available, which translates into greater speed, rate of climb capability, and overall higher performance. Also, turbine drivers have to concern themselves with things like N1, TOT, EGT, along with hot starts, spool up time when power is added, etc.

While piston pilots need to concentrate on fuel mixture settings, manifold pressure, along with other things turbines don't have. There are also things like constant speed props, as opposed to some turboprops that start with the props feathered, etc. All of it results in important differences.

And when you look at all the difference, it would seem to add up. And not be something you could just "do" without additional training. Was doing it the opposite, (turbine first, piston later), easier than going from piston to turbine, like most pilots do? I can understand why the Navy does it this way, seeing as they have so few, (if in fact any), piston powered aircraft in our current inventory. Why would they waste their time, and the taxpayers money, training their pilots for aircraft they will never fly, as long as they wear the uniform while doing it?

 

[Astro14]

Bill - The Navy starts us out on an airplane that gets us to the next step as quickly as possible. Flight training costs millions per pilot, so adding a simpler airplane would add cost without really adding benefit. There wasn't really a need to fly a piston airplane. As you said, I would never see a piston airplane in the fleet, so, what's the point of learning about mixture, etc.?

The USAF, by contrast, used to send pilot trainees who did not have a private license down to Hondo, TX and have them fly 172s for six weeks. Navy didn't bother with that.

I went through 3 airplanes in flight training:

1. 450HP turboprop, retractable, aerobatic.
2. twin engine jet, aerobatic, carrier capable
3. single engine jet, aerobatic, weapons capable, carrier capable.

Now there are two:

1. 1600HP turboprop, retractable, aerobatic, ejection seat
2. single engine jet, aerobatic, weapons capable, carrier capable.

First time that I flew a piston, it was a piece of cake. It was so slow, so docile, so simple (fixed gear, for example). It couldn't get out of a situation like a jet, but I wasn't dumb enough to place it in a bad position in the first place. Dealing with the mixture and other peculiarities of a piston engine wasn't hard for a kid that grew up working on cars or fixing his own motorcycles. Getting a piston engine airplane started is a lot like starting the Packard, only with a more reliable ignition system...not hard for me to understand or learn. Maybe pilots who weren't gearheads to begin with would struggle going from turbine to piston the first time, but most pilots I've met are car folks, who own and understand piston powered vehicles...

Trim is trim. Performance instruments are performance instruments. P-factor exists with any prop. Constant speed props are rare in the piston world, but having flown a feathering turboprop, that wasn't hard. I've flown a Cherokee, Cirrus SR-22, 172, turbo 182, Seminole, among others. Every single one of them was a piece of cake.

I flew the Seminole as part of my ATP check ride. Twin, retractable, IFR. It was easy. Hard part was the fixed RMI card when flying ADF holding and an ADF approach with 40+ knots of wind aloft. The airplane only went about 90 knots, so a bit of quick math yields some huge crab angles for the crosswind...

Landing an airplane at 70 knots and 4 feet above the runway requires a different sight picture than a 140 knot airplane that sits much higher, but by the time I flew anything with a piston, it wasn't hard, it just took a few laps around the pattern with an instructor to get the feel for that airplane.

If you drove Formula 1, getting in a rental car doesn't pose a big challenge...

 

[billt460]

Originally Posted by Astro14
.....If you drove Formula 1, getting in a rental car doesn't pose a big challenge...

That's a really good way of putting it.

 

[Fastzntn]

Thank you for taking time out of your day to do some Q&A about such an iconic fighter! I'm just coming off of a trip to the National Museum of Naval Aviation- what a great place.

Two things I'm curious about-
1- are the cockpit controls configurable differently in any way for left handed pilots?

2- was there any specific watch or timepiece F-14 pilots were issued to wear when flying, and if so are you able to talk about it? I'm interested in watches, and seeing the last Omega "moon watch" worn on the moon at the museum was neat. Plus the Breitling Emergency line is an interesting concept, both the first gen in 121.5mhz and the newer gen with dual 121.5/406.040mhz.

 

[y_p_w]

Originally Posted by Astro14
If you drove Formula 1, getting in a rental car doesn't pose a big challenge...

A lot of race car drivers have gotten speeding tickets. I heard of a NASCAR driver who had his driver license suspended for going 120 MPH in a school zone. So the challenge is driving like the rest of us. And a driver can't toss around a street car like an open wheel car. Strangely enough, Formula 1 requires that all drivers have a valid road license. Not sure how that might work if someone had a license suspended and tried to get a license in another jurisdiction.

Quote
https://www.formula1.com/en/champio...iver_changes_and_additional_drivers.html

As well as securing enough points, drivers will have also have to have spent at least two years in junior single-seater categories, hold a valid road driver's licence and pass a test on the Formula 1 sporting regulations.


However, I remember playing some racing video game and then getting back in my own car. Felt kind of strange for a minute.