Discussion: F-14, F-15 Hybrid Idea

[GTX]

the inability to land with full weapon load was just an excuse to get rid of the Tomcat .

The F-14 was extremely maintenance intensive compared to other more modern types - I don't have the exact figures at hand right now, but they were high.  This was also a large contributor to the decision.

Regards,

Greg

[KJ_Lesnick]

So, the original requirement specified all you'd have to be able to do is be able to bring back two Phoenix's to the carrier?

KJ Lesnick
BTW:  If so that WHIF idea I was thinking of could work...  the larger wing, droops, and multi-position flaps theoretically could produce enough lift to equal the F-14's landing speed under those conditions... don't know how seriously it's speed would take a hit, but the F-14 also lost serious speed too.

[elmayerle]

Out of curiousity, why did they get rid of the F-15's originally intended air to ground capability and adopt the "not a pound for air to ground" -- was it just weight?  Or was it the worry of taking an expensive plane down into the weeds to do air to ground missions? 

ISTR that this was a mandate fro Congress and, really, all it meant is that some of the air-to-ground hardware that was tested on the prototypes wasn't taken up for production (there are pics of one of the prototypes carrying 12 x 500 lb bombs between the inlet trunks in four columns of three bombs each on palletized racks that appear to share aerodynamics with the Phoenix pallets).   I beliedve this insistence was one reason the USMC did not take up the F-14 to replace at least some of their F-4s.

[KJ_Lesnick]

To R16,

What made the F-14 so maintenance intensive?  Was it just the swing wings, or the particulars of it's electronics?


To ElMayerle,

ISTR that this was a mandate fro Congress and, really, all it meant is that some of the air-to-ground hardware that was tested on the prototypes wasn't taken up for production (there are pics of one of the prototypes carrying 12 x 500 lb bombs between the inlet trunks in four columns of three bombs each on palletized racks that appear to share aerodynamics with the Phoenix pallets).   I beliedve this insistence was one reason the USMC did not take up the F-14 to replace at least some of their F-4s.

What does ISTR mean?   And why did Congress mandate them taking away the Air To Ground capability?  Why didn't they take up the Air-to-Ground hardware on the design for production?

Did this mandate cover both the F-14 and F-15?


KJ Lesnick

[elmayerle]

ISTR = I Seem To Recall

As I remember, Congress felt it was so expensive an aircraft that they didn't want it "risked" on air-to-ground missions and thus the special bomb-carrying pallets, that mounted the same as tje Phoenix pallets, were not produced past those used on the prototypes.

Oh, going back a bit, the twin tails instead of a single tail are a function of maneuvering aerodynamics were there are cases where a single tail could get rendered ineffective by airflow but the twin tails will have at least one vertical still effective.  Too, in the F-14's case, it makes for smaller vertical fins as well as ventral fins (take a look at the mockup photos available in several books of the final single-vertical mockup with it's huge folding ventral fins).  Going back farther, NAA-Columbus had originally proposed, and mocked up, the A3J-1 with twin verticals but the USN insisted on a single, large one, which required an extra fold at the tip to clear the hanger deck overhead.

[KJ_Lesnick]

elmayerle,

ISTR = I Seem To Recall

Okay, I got what you're talking about.

As I remember, Congress felt it was so expensive an aircraft that they didn't want it "risked" on air-to-ground missions and thus the special bomb-carrying pallets, that mounted the same as tje Phoenix pallets, were not produced past those used on the prototypes.

I assume you're talking about the F-14 now, as the F-15 to the best of my knowledge did not have capacity for Phoenixes? 

It's kind of silly what they're thinking -- that's what military planes are meant to do... fly into harms way, ideally coming out alive.  The best plane tends to be able to do this with the lowest odds of loss.  Why didn't they just have the plane fitted with provision for air-to-ground, and then use a bunch of smaller cheaper fighters to normally do the role, but if you really need the extra performance you can fit the plane with Air to Ground?
 

Oh, going back a bit, the twin tails instead of a single tail are a function of maneuvering aerodynamics were there are cases where a single tail could get rendered ineffective by airflow but the twin tails will have at least one vertical still effective.

Does that always happen?  One tail rendered ineffective?  Or is that only with certain designs?

Too, in the F-14's case, it makes for smaller vertical fins as well as ventral fins (take a look at the mockup photos available in several books of the final single-vertical mockup with it's huge folding ventral fins).  Going back farther, NAA-Columbus had originally proposed, and mocked up, the A3J-1 with twin verticals but the USN insisted on a single, large one, which required an extra fold at the tip to clear the hanger deck overhead.

The A3J/A-5A required a folding tip atop the vertical fin?  I don't ever remember hearing or seeing that?  Were later models modified to eliminate the need for it?


KJ

[elmayerle]

Actually, all Vigilantes have folding vertical tail tips, it's needed for hanger deck clearance. 

The twin tails are as much to take advantage of air flow as to prevent the blanking that a single vertical would encounter; granted, two widely spaced verticals have less chance of either encountering such flow, but it also greatly reduces the chances of both encountering it at the same time.  Bsides, I seem to remember a USAF/USN/NAS extensive wind tunnel study in the late 1960s on fighter afterbody design that found that twin tails, properly done, had a touch less drag, too.  The study did appear to have valid results in that the original aft end design for the F-111 appears to have had 'bout every feature known to increase aftbody drag and they did have to do a fair bit of redeisgn there to deal with ijust that problem.  If you look at pictures of the final single-tail F-14 mockup in the old Salamander large-size book, you'll see that it has folding vetral fins, folding outboard from under each engine nacelle, much like the MiG-23/23 family; going to twin verticals allow smaller fixed ventral fins.  Mind you, I've got one of the old and inaccurate Mongram/Mattel 1/72 F-14A kits that's based on that mockup and I'm sorely tempted to rework it back to single-tail configuration and I might utilize the ventral fins from a couple MiG-23s as starting points for those ventrals.

[elmayerle]

Well, yes, I'm reasonably familiar, or at least was since it was 30 years ago, with the F401 engine. *wry smile* Don't get me started about who led the fight for its cancellation or what I think of that person; it's not pretty.

Seriously, the maintenance "footprint" of an aircraft is something that started getting real attention only after the F-14 was designed.  These days, and for at least the last 20-25 years, the "-ilities" (i.e. reliability, servicability, maintainability, manufactureability etc.) have become a much more important part of the design and development process rather than the old design paradigm of design it and then "throw it over the wall" for the other disciplines to worry about.  Mind you, I learned better long ago and it's helped me along the way.

[KJ_Lesnick]

elmayerle,

The twin tails are as much to take advantage of air flow as to prevent the blanking that a single vertical would encounter; granted, two widely spaced verticals have less chance of either encountering such flow, but it also greatly reduces the chances of both encountering it at the same time.  Bsides, I seem to remember a USAF/USN/NAS extensive wind tunnel study in the late 1960s on fighter afterbody design that found that twin tails, properly done, had a touch less drag, too.

Does this always apply (That 1 single tail ideally set up will produce less drag than a twin-tail ideally set-up)?  How does one tail produce more drag than two (Is this only at subsonic, or both subsonic and supersonic)?


BTW:  Did the USAF and USN operate always under the opinion that a twin-tailed design was better than one, or did they evaluate each proposal individually as well 


R16

at the time of SuperHornet selection , there was an article that showed there were many types of screws that didn't match on the Tomcat , you would need the whole set of screwdrivers , while I got the impression that one or two would be enough on the '18. The F-14 had many diverse systems and it would still need lots of care , but I get the impression at least when it was new , it demanded less than a naval Phantom , which should be similar in electronics .

So, the F-14 when it was new, electronics wise was no more difficult maintenance wise than an F-4?  I would guess the problem was the mechanical stuff, the swing-wings and that sort of thing then (I thought the F-4's electronics were fairly easy to maintain?)?


KJ

[dy031101]

It's kind of silly what they're thinking -- that's what military planes are meant to do... fly into harms way, ideally coming out alive.  The best plane tends to be able to do this with the lowest odds of loss.  Why didn't they just have the plane fitted with provision for air-to-ground, and then use a bunch of smaller cheaper fighters to normally do the role, but if you really need the extra performance you can fit the plane with Air to Ground?

Because the bunch of smaller cheaper fighters are there to do the job.

Bean counters don't spend money "just in case".

[KJ_Lesnick]

Because the bunch of smaller cheaper fighters are there to do the job.

Bean counters don't spend money "just in case".

So all the politicians were bean-counters?  There were no politicans back then who were war-hawks? 

I mean there are so many now...

[elmayerle]

elmayerle,

The twin tails are as much to take advantage of air flow as to prevent the blanking that a single vertical would encounter; granted, two widely spaced verticals have less chance of either encountering such flow, but it also greatly reduces the chances of both encountering it at the same time.  Bsides, I seem to remember a USAF/USN/NAS extensive wind tunnel study in the late 1960s on fighter afterbody design that found that twin tails, properly done, had a touch less drag, too.

Does this always apply (That 1 single tail ideally set up will produce less drag than a twin-tail ideally set-up)?  How does one tail produce more drag than two (Is this only at subsonic, or both subsonic and supersonic)?


BTW:  Did the USAF and USN operate always under the opinion that a twin-tailed design was better than one, or did they evaluate each proposal individually as well 

Well, twin tails for twin-engined aircraft with the engines in the fuselage tend to have less drag than a single tail due to the chances of interference drag and the need for a larger single vertical (again, compare the verticals of the twin-finned mockup and the single-finned produced Vigilante).  Again, there are a lot of other aspects that were studied in that exhaustive wind tunnel test program, but these were among the findings.

[KJ_Lesnick]

Well, twin tails for twin-engined aircraft with the engines in the fuselage tend to have less drag than a single tail due to the chances of interference drag and the need for a larger single vertical (again, compare the verticals of the twin-finned mockup and the single-finned produced Vigilante).  Again, there are a lot of other aspects that were studied in that exhaustive wind tunnel test program, but these were among the findings.

How would two tails produce less interference effects over one tail?  If anything it looks like two tails would produce more interference effects (at least supersonically)...

Regarding the fact that you'd need a larger vertical fin for a single-fin set-up, that does make sense. 


KJ

[elmayerle]

I think it depends on the structure supporting the tail assembly and around the engines as much as anything.  On the F-111, GD improperly reduced their wind tunnel data (as I understand it) and the original design had just about every afterbody drag increasing feature noted in the subsequent extensive wind tunnel studies.  You can have a low-drag single vertical tail, but it still ends up being tallerthan twin verticals and it's more susceptible to blanking in maneuvering flight (like dogfights); this is not good when you really need full control authority.

[KJ_Lesnick]

Elmaylerle,

I suppose you make a good point.  What caused them to reduce their data wrong out of curiousity?

Regarding the twin-tail issue, you make a good point.  Although, there are exceptions (The Eurofighter Typhoon for example) which seems able to function even in high alpha maneuvers even with only one tail and no control-loss (whether it would meet the clearance requirements for a carrier I got no idea, although rather than using two tails with rudders on them you could use an all moving tail which could provide enough control power, dunno how heavy that would be however)


KJ_Lesnick