Discussion: F-14, F-15 Hybrid Idea

[KJ_Lesnick]

I was thinking of some kind of USN F-14 and F-15 hybrid as a drawing-request... But I'm still kind of thinking up the idea, and I could use some guidance... (Most of the stuff I mention is what it looks like -- however I did list somethings it would be able to do as well as it's kind of a concept -- one can fantasize right?)

Here's my idea

F-15-Esque Characteristics: 
1.) Overall similar shape
-Explanation:  I like the F-15 design more than I like the F-14 design
2.) Wing-shape like the F-15U design (more sweep, and more area) but thickness should be between the regular F-15A and the F-15U
-Explanation:  The higher sweep angle would yield more area for the same span and could potentially allow faster speeds, as long as it wasn't proportionately thick like the F-15U's design, but instead a wing with the F-15A's thickness or just a tiny bit more, with the higher sweep helps yielding a low t/c ratio.  This would be better for high-speed in an interceptor role, in addition to provide extra fuel for the aircraft.  The extra wing-area would probably help offset the higher sweep-angle.
3.) The inboard wing right next to the wing-body fairing could be sort of blended with the wing/body fairing by a sweep-increase adding a chine like effect to the normal wing/body fairing
-Explanation:  Blending helps reduce drag, good for high-speed, the modification would add area to the wing-body fairing helping improve maneuverability, shape would probably help provide improve vortex-generating effects as well which are useful at low-speed. 
4.) The variable-geometry lip
-Explanation:  The inlet design was very clever, using a combination of ramps AND the moving ramp works really nicely for increasing capture area while tightening down the throat.  The variable-geometry lip also provides a camber like effect at low-speeds which are beneficial.
5.) Similar gun position
-Explanation:  Mounted right in the chine, it seems to be better blended in with the frame and doesn't require a special blister for the gun to be mounted elsewhere on the frame.
6.) Better flaps (possibly multiple-position)
-Explanation:  The design's lower speed characteristics probably would at BEST be as good as a regular F-15, and most likely would not be quite as good as the regular F-15, it's t/c ratio is lower, albeit possessing significantly more area.  While the F-15's approach speeds are quite low, this plane would probably be a bit heavier, and would probably require even lower speeds yet.  The F-15's flaps are not that brilliant a design, they're very simple in design and do not appear to provide as good an increase in lift as those used on other fighters (could be wrong), a better flap design with a better L/D ratio would be preferred, and variable-position flaps would probably provide more versatility in terms of flight characteristics, especially since the airplane would also have to be able to hold station a long-time, the ability to use very, very small flap deflections could help L/D ratios at subsonic cruise
7.) Leading-edge devices (droops I'd say, like the F-18)
-Explanation:  The plane would have to operate off carriers, and the ability to takeoff and land at slower speeds are very useful.  Plus, the wing would have a lower t/c ratio over the regular F-15, and would possess a sharper leading-edge which would make stalls easier -- The wing-body fairing does shed a vortex, and the leading-edge/chine mod would probably help that area a bit, but a leading edge device would definetly be helpful.  They could also be used in very small settings at subsonic speed when holding station.


F-14 Esque:
1.) Nose diameter to be able to accomodate the AWG-9 radar
-Explanation:  The F-14 uses the AWG-9, which has a much longer range than the F-15's radar, and is essential for its intercepting capability.
2.) Two-man crew
-Explanation:  The F-14 has a twin-man crew, and the USN generally preferred the twin-man layout over the single-man layout used by the USAF. 
3.) Pallets to mount the AIM-54 Phoenix in streamline fit
-Explanation:  The pallets reduced drag vs just the phoenix missile itself hanging down under the plane
4.) Gun-Cam (However mounted in the opposite chine as the gun)
-Explanation:  The F-14's design is a big clunky design and while it is in a low drag area of the plane, having a nice streamline set-up would be better... plus the ability to visually ID targets from a distance is a good idea in case some idiot like McNamara ever says he wants a visual ID before taking the enemy out. 


Other Conceptual Ideas: 
1.) Single large vertical tail (Like the A-3J/A-5A, F-108A, XB-70)
-Explanation:  I figure if the tail is nearly all moving you could achieve satisfactory directional control with just one vertical surface instead of two (although I'm not sure how that would work with the fin in the neutral-position compared to two fins), plus a higher leading-edge sweep on the vertical tail could be allowed (still significantly tapered at the tip).  The obstacles I would see with such a design is it could add excess weight (the aft area of the wing-body fairings mount the stabilators and the vertical-fins... for all I know they may have been sturdy enough to mount the vertical and horizontal stab without extra strengthening over just mounting the vertical-stab...  if the vertical was added in the middle, that would require more support structure...) would get in the way of the speed-brake requiring a newer design (Perhaps a design that fans out at 45-degree angles to the centerline or something could work, but that might add more weight than worth it).  Also there's an area between the two engines which in addition to providing protection in the event of one engine blowing up, also houses an APU... if the tail was moved to the center this might not work... also the F-15 has two antennae on the top of the fins... that could pose a problem too.
2.) Side-stick
-Explanation:  You don't need FBW to use a sidestick... in fact if you have a device that has enough throw, it works.  A simple idea is a rod that you can push in and out which produces pitch change, and the ability to twist the stick left or right should be able to do the job just fine.  And the pilot could fly much better with his right hand on the stick, the left hand on the throttles.  I don't know if that would eliminate the need for a RIO, or would just make the pilots able to fight-better.  The airplane could use a CAS type system, which is a simple FBW, and have mechanical back-up. 


KJ_Lesnick

[KJ_Lesnick]

there might be a couple of people who will remember me "defending" McNamara but he wasn't all failure .

Oh, I know that... He did have a bunch of good ideas (Rejecting the JCS plan for Operation Northwoods, Having the USN and USAF use the same designation system, Having the same company that makes the uniforms for the Army, make uniforms for the USAF and USN, and USMC -- to their own specifications, but the same company, His actions during the Cuban missile crisis probably helped avert a major nuclear war) but a whole lot more bad ideas (Cancellation of the B-70, obsession with ICBM only approach, the TFX program, and particularly ramming it down the USN's throat, rejecting the F-12B over an interceptor F-111 and F-106X of which neither flew, and trashed all the Blackbird-hardware, failure to listen to military leadership, LOADS of screw-ups in Vietnam and probably a whole lot more)

As for visual identification , the Sparrow's kill ratio might well climb into double digits if the Americans shot down by it were factored in .

Yikes... I knew the Sparrow was not particularly accurate (It was designed to take out bombers predominantly), but I didn't know it accounted for so many friendly-fire deaths. 

The very first kill of a Mig around there wouldn't have happened if the USN pilot Murphy's "wingman" had fired about 3 seconds earlier as the own goal would have broken the missile guidance and the Chinese Mig have gone back to Hainan...

I did not know that...

the undernose position allows more flexibility , I would say.

How so?  Improved visibility, or more versatility in being able to mount different types of cameras under the nose than in the wing-body fairing?


Kendra Lesnick
BTW:  What is your overall opinion about this concept design in general (I want the concept to something that will look good and realistic) what ideas do you like, and which do you dislike? (I already noted your opinion of the camera placement)

[tinlail]

It's cause the f-14 is a much prettier plane to start with.

As a point. I think that having the gun cam in the wing chime is not a bad idea. The nose mounted cameras change on the f_14D need a fair amount wind tunnel time, because a fear interaction with the engine air intakes. A single tail also helps this being less troublesome.

[KJ_Lesnick]

tintail,

It's cause the f-14 is a much prettier plane to start with.

I'm not saying this as a personal attack against the F-14 or anything.  it's a nice looking plane too.  Appearance wise, I like both designs -- performance wise, I like the F-15 better, missile and radar wise, I like the F-14 better! 

As a point.  I think that having the gun cam in the wing chime is not a bad idea.  The nose mounted cameras change on the f_14D nead a fair amount wind tunnel time, because a fear interaction with the engine air intakes. A single-tail also helps this being less troublesome.

The gun-cam in the chine would be the most aerodynamically clean set-up (which is why I considered it... plus with the gun in one chine, putting the camera in the other seems logical, right?).  The only thing I'm wondering is if it would take up too much space to accomodate the probe (for the USN's drogue and chute refuelling system -- in this case the extended receptacle). 

I don't know how a single tail avoids an adverse engine-intake interaction though... although it sounds like it would be lighter structurally.  Interestingly, I read something not too long ago (meaning today) that was quite fascinating about the F-15...

URL:  http://forum.keypublishing.co.uk/showthread.php?t=16595  (Mad Dog's first post in the thread)

The original F-15 did not have a "dog tooth" leading edge (aka "snag"), nor did it need one from a pure control power standpoint. However, in the course of flight testing, an undesirable aeroelastic interaction of the tail surfaces (horizontal and vertical) was found, due to the fact that they are both attached to a boom instead of a (very stiff) fuselage proper. The final solution was to change the structural/mass properties of the stabilators by removing a chunk of leading edge, creating the snag. Any aero benefit was gravy. Don't ask me how they figured that one out in 1972-ish.

Assuming this is true (I also have heard also that the large-wing had turbulence problems at certain speeds early on and the modified wingtips from the YF-15 to the F-15 were added, and there's a possibilty that the dog-tooth may have been added for that reason as well), a single tail though would have avoided having to mount the vertical tail booms, and would have avoided the aerodynamic interactions and avoided the need for the dog-tooth, which makes things simpler.

Regarding the side-stick idea I mentioned -- Sound like a good idea?  If so, would such a set-up eliminate the need for the RIO, or would it still be practical as a twin-seater, (As it might be considered more HOTAS like although it would be using the same basic radar and electronics as the F-14) or would the workload still be too high to be practical with a one-man crew and still require the two-man set-up? 


Any interesting ideas, I'd love to hear as I plan to ultimately make a profile-drawing or CGI request out of it...


Kendra_Lesnick

[KJ_Lesnick]

r16,

ı was thinking of putting a laser ranger in there , which could also pick up spotted targets on the ground on both sides of the nose . There are targetting pods but ...

I didn't realize that the ability to spot targets on either side of the nose could be an obstacle with such a set-up.  At distances beyond a few dozen feet you'd be able to see past the nose, and at a few hundred feet or a few hundred yards you can see well on either side, let alone 30-miles.  But that's actually a very good point. 

Plus I think the gun-cam used on the F-14 was larger than the M-61 gun-mount (in the F-15's chine) as well. 

Due to the particulars of the F-14's design and the fact that it did not have to be as fast as an F-15 or MiG-25, the simple camera mount was okay (big clunky thing mounted on a relatively low-drag area of the plane)... for the idea I'm thinking of (as fast as an F-15 or MiG-25), a blister-type streamlined-pod might be better, (modular-type that  can be attached and be removed) as the drag difference can become more extreme at higher speeds.


On a different topic, I was thinking about the single tailfin idea (which I actually like a lot):  Wouldn't the engines require a little bit of extra spacing between them because of area ruling requirements (the engine-"bumps" interacting with a tail in between them which is not there on the F-15)?  I'm also thinking, could the booms (the horizontal stabilizers are mounted on them) be reshaped as the stabilator is actually mounted low on the booms and without vertical stabs mounted on either one could be flattened a little bit over the top? 


Opinions?


Kendra Lesnick

[tinlail]

I don't know how a single tail avoids an adverse engine-intake interaction though... although it sounds like it would be lighter structurally.  Interestingly, I read something not too long ago (meaning today) that was quite fascinating about the F-15...

I believe that a single tail would help avoid interaction with the cameras on the tail. where as twin tail designs have to worry about air flow off the chimes at higher AoAs, interacting with the tails.

URL:  http://forum.keypublishing.co.uk/showthread.php?t=16595  (Mad Dog's first post in the thread)

The original F-15 did not have a "dog tooth" leading edge (aka "snag"), nor did it need one from a pure control power standpoint. However, in the course of flight testing, an undesirable aeroelastic interaction of the tail surfaces (horizontal and vertical) was found, due to the fact that they are both attached to a boom instead of a (very stiff) fuselage proper. The final solution was to change the structural/mass properties of the stabilators by removing a chunk of leading edge, creating the snag. Any aero benefit was gravy. Don't ask me how they figured that one out in 1972-ish.

Assuming this is true (I also have heard also that the large-wing had turbulence problems at certain speeds early on and the modified wingtips from the YF-15 to the F-15 were added, and there's a possibilty that the dog-tooth may have been added for that reason as well), a single tail though would have avoided having to mount the vertical tail booms, and would have avoided the aerodynamic interactions and avoided the need for the dog-tooth, which makes things simpler.

I have also heard that dogtooth, restart the wing airflow, in that the leading point acts as a new wing root. I think that dog tooth and wing fences are kudges that come in late in the design process, and never show up in early versions of a design. I think for a whif there is no wrong answer just wave you hands and say "In testing they found ...."

Regarding the side-stick idea I mentioned -- Sound like a good idea?  If so, would such a set-up eliminate the need for the RIO, or would it still be practical as a twin-seater, (As it might be considered more HOTAS like although it would be using the same basic radar and electronics as the F-14) or would the workload still be too high to be practical with a one-man crew and still require the two-man set-up? 

I don't know much about side sticks vs center sticks, in general it seems that the pilots job has remained mostly the same and the RIO job  is varied by the amount of automation possible. Changing the pilots control around hasn't changed his work load, which is fly the plane to it's limits. A side stick might change those limits, but I doubt it will allow him to do other complex jobs.

[KJ_Lesnick]

I believe that a single tail would help avoid interaction with the cameras on the tail. where as twin tail designs have to worry about air flow off the chimes at higher AoAs, interacting with the tails.

Cameras on the tail???  What cameras? 

How would the airflow off the chines pose a serious problem to the tail?  Those chines produce fairly decent vortices, you'd figure that would improve the tail's effectiveness, no?

I have also heard that dogtooth, restart the wing airflow, in that the leading point acts as a new wing root. I think that dog tooth and wing fences are kudges that come in late in the design process, and never show up in early versions of a design. I think for a whif there is no wrong answer just wave you hands and say "In testing they found ...."

Still, I kind of wonder what kind of aerodynamic interactions occurred between the booms, the horizontal and vertical stabs, though...

I don't know much about side sticks vs center sticks, in general it seems that the pilots job has remained mostly the same and the RIO job  is varied by the amount of automation possible. Changing the pilots control around hasn't changed his work load, which is fly the plane to it's limits. A side stick might change those limits, but I doubt it will allow him to do other complex jobs.

I just was wondering because one of the things that enabled the F-15 to ditch the GIB was because the stick and throttle had all sorts of buttons on them allowing the pilot to work the radar, lock onto stuff, do this, and that, without having to take his hands off the stick or throttle most of the time.  I think the electronic systems also helped in that all the data was displayed right in front of him on an easy to read display... but I'm not sure how much the HOTAS (not a side-stick, just having lots of buttons on the throttle and stick to enable the pilot to work the radar and equipment without having to take his hands off the throttle) played in the part.


Kendra Lesnick

[tinlail]

I believe that a single tail would help avoid interaction with the cameras on the tail. where as twin tail designs have to worry about air flow off the chimes at higher AoAs, interacting with the tails.

Cameras on the tail???  What cameras? 

How would the airflow off the chines pose a serious problem to the tail?  Those chines produce fairly decent vortices, you'd figure that would improve the tail's effectiveness, no?

Poorly worded, on my part. Air flow off the camera, might cause interaction with the tails. The F-18 had to have stiffeners retrofitted to the tails because the vortex from the LEX buffeted the tail too much.

I would say if you have twin tails then stuff in the wing root is problematic, because you can't upgrade it without a lot of wind tunnel work. But with a single tail the issue isn't as big.

I just was wondering because one of the things that enabled the F-15 to ditch the GIB was because the stick and throttle had all sorts of buttons on them allowing the pilot to work the radar, lock onto stuff, do this, and that, without having to take his hands off the stick or throttle most of the time.  I think the electronic systems also helped in that all the data was displayed right in front of him on an easy to read display... but I'm not sure how much the HOTAS (not a side-stick, just having lots of buttons on the throttle and stick to enable the pilot to work the radar and equipment without having to take his hands off the throttle) played in the part.

I think part of it is that the sparrow is a significantly simple missile to operate. The Phoenix has various attack modes, in addition I think the operator can target and launch missiles in parallel, where as the F-15 and Sparrow, are forced in the a serial mode of select target, and launch for each missile fired.

[KJ_Lesnick]

Poorly worded, on my part. Air flow off the camera, might cause interaction with the tails. The F-18 had to have stiffeners retrofitted to the tails because the vortex from the LEX buffeted the tail too much.

You mean the camera mounted in the chine idea right?  From what I saw in diagrams, the F-14's VID/Gun-Cam is bigger in diameter than the M-61 mount (which is on the left chine), making it impractical to mount on the right.  The only way for it to work would be for a large portion of the chine to be an aerodynamically-shaped transparency which can get dust on it and stuff, and the camera would have to be recessed a bit back in the chine and would take up too much space for a refuelling probe that USN planes use.

I think the best way would be to mount it on the bottom like the F-14, but use a streamlined, yet modular, mounting to produce less drag than the F-14 (which actually does reduce the F-14's speed a bit) to allow speeds faster than the F-14 and ideally as fast as the F-15/MiG-25.

[quoteI think part of it is that the sparrow is a significantly simple missile to operate. The Phoenix has various attack modes, in addition I think the operator can target and launch missiles in parallel, where as the F-15 and Sparrow, are forced in the a serial mode of select target, and launch for each missile fired.
[/quote]

I don't know about that -- an F-15 did (in an experimental setting) fired an AIM-54 at least once.


Kendra Lesnick

[KJ_Lesnick]

ı think F-15 had HOTAS to be a single seater . I believe there were many in USAF that felt that the F-4 over Vietnam was not good . The need was for for a clean start and by the time it was serious , the Eagle answered the call . F-14 was for endurance , semi autonomous operations and a likely scenario where jamming was to be severe . On the other hand F-15 could rely on for more concentrated support .It would either defend with the ground control help or attack in highly capable packages .

So, HOTAS was a highly important factor in allowing a single-seater, but was it the only factor that allowed it to be done?  (In other words, were the computer displays, with lots of information presented to the pilot in easily understood displays also important, and was it also necessary for a single-seater, or just the HOTAS)

When you say ground-control, do you mean SAGE?  Or did it just use the ground controller telling them which way to go? 

In that case it made sense to omit the second seat for economic and performance issues but there was still the potential to become a two seater if needed .All the sectional drawings I have seen of the Eagle shows the place for a second seat is kept empty in single seater .It appears to me , but only as an hunch that the F-15 force would quickly become an entirely twin seater community if HOTAS had proved to be too difficult to master .

Would a side-stick system I was mentioning earlier, by necessity, or for practical purposes for a plane with interceptor performance a'la the F-14 and dogfighting performance like the F-15, result in a HOTAS set-up (with various buttons being mounted on the throttle and stick to allow the pilot to avoid having to take his hands off the throttle/stick) or not? 

If so, would it be enough to eliminate the RIO, or would the F-14 with it's particularly complex long-range radar still have a high-enough workload to require two crew?   


Kendra Lesnick

[Hobbes]

I thing having one or two seats was more a matter of preference. The US Navy likes having twoseaters, maybe because they need to make the most of their limited number of aircraft. The USAF can easily send two aircraft to do one job.
HOTAS is nice, but aircraft like the EE Lightning did without (?). Cockpit automation as a whole needs to be considered. The F-15 and F-14 came at a bad time: computers were powerful enough to perform complex tasks, but user interface design and hardware (needed to present the information in a logical and simple way) lagged behind. Aircraft like Typhoon are designed to be simple to operate, I'd expect the workload in a Typhoon to be lower than in an F-14, despite being more capable.

[KJ_Lesnick]

So basically the consensus seems to be that even if the sidestick/HOTAS idea was used on this F-14/F-15 hybrid, would have still been a twin-seater, correct?

Okay, my next question is since the single-tail idea seems to be more popular among members here and I like the idea myself.  Should it have the same basic shape as the F-15's verticals, or should it have a different sweep and taper? 

Ideas?


Kendra Lesnick

[Weaver]

HOTAS + UFC are primarily dogfighting aids: they prevent the pilot having to look down and fiddle with switches at a time when he really, REALLY wants his eyes pointing outside 100% of the time. Any fighter would benefit from HOTAS whether it had a GIB or not.

The reason why an F-14 needs a GIB and the F-15 (arguably*) doesn't is that the AWG-9/AIM-54 allows the former to fight an engagement across a VERY large volume of airspace, with potentially so many contacts/targets in it that managing the battle is a full-time job, particularly since several could be engaged simutaneously. The F-15's more limited "battlespace horizon" (God I hate these buzzwords) means that, with a reasonably user-freindly radar, the single pilot can manage a series of sequential engagements on his own.

* The RAF wouldn't have agreed at the time, which is why the Tornado F.3 had a GIB, despite only being armed with the Sparrow-ranged Skyflash.

[KJ_Lesnick]

wouldn't a single F-15 tail too high ? It would be more like a Phantom fin I think.

Not to be contradictory, but I think the height of the tail is perfectly acceptable -- the tail has to be able to be large enough to provide adequate directional stability and adequate yaw-control to work.  Since there will only be one vertical tail, I think the area might need to be a little higher -- I'm thinking a tail like the F-108A Rapier design.  It has a little bit more area than one F-15 tailfin, and because of it's higher-sweep has greater area, and can avoid effects due to extreme sideslip without fin-stall (if even applicable), and the F-108A's tail is virtually all-moving which should provide any extra yaw-control needed (and since the engines might have to be spaced a little bit further apart to deal with area-rule requirements, a little extra control power probabily will be needed)!

HOTAS + UFC are primarily dogfighting aids: they prevent the pilot having to look down and fiddle with switches at a time when he really, REALLY wants his eyes pointing outside 100% of the time. Any fighter would benefit from HOTAS whether it had a GIB or not.

The reason why an F-14 needs a GIB and the F-15 (arguably*) doesn't is that the AWG-9/AIM-54 allows the former to fight an engagement across a VERY large volume of airspace, with potentially so many contacts/targets in it that managing the battle is a full-time job, particularly since several could be engaged simutaneously. The F-15's more limited "battlespace horizon" (God I hate these buzzwords) means that, with a reasonably user-freindly radar, the single pilot can manage a series of sequential engagements on his own.

I see your point -- one of the roles of the F-14 was to deal with waves and waves of bombers in addition to an air-superiority role.  Still, I thought the F-15 had a limited interceptor role?


BTW: What's a UFC?  And did the USN or Grumman ever consider during the F-14's development, a single-seat variant?     
Kendra Lesnick

[Weaver]

HOTAS + UFC are primarily dogfighting aids: they prevent the pilot having to look down and fiddle with switches at a time when he really, REALLY wants his eyes pointing outside 100% of the time. Any fighter would benefit from HOTAS whether it had a GIB or not.

The reason why an F-14 needs a GIB and the F-15 (arguably*) doesn't is that the AWG-9/AIM-54 allows the former to fight an engagement across a VERY large volume of airspace, with potentially so many contacts/targets in it that managing the battle is a full-time job, particularly since several could be engaged simutaneously. The F-15's more limited "battlespace horizon" (God I hate these buzzwords) means that, with a reasonably user-freindly radar, the single pilot can manage a series of sequential engagements on his own.

I see your point -- one of the roles of the F-14 was to deal with waves and waves of bombers in addition to an air-superiority role.  Still, I thought the F-15 had a limited interceptor role?


BTW: What's a UFC?  And did the USN or Grumman ever consider during the F-14's development, a single-seat variant?     
Kendra Lesnick

Well the F-15 does have an interceptor role, but as soon as you decide it's biggest missile is going to be Sparrow, then it's engagement range is automatically limited to about 30 miles. The radar can see MUCH further, but once combat's joined, the pilot really only has to concentrate on:

First: shooting Sparrows at a rapidly closing set of targets at less than 30 miles,

Next: dogfighting with Sidewinders and Gun.


UFC = Up Front Control. Basically, it's a small panel on the front of the HUD that gathers together a bunch of dogfight-relevent switches and knobs, that there either isn't room for on the throttle and stick, or which need to be looked at when they're operated. It's not quite as good as HOTAS since the pilot still has to take his hands off the stick or throttle to work it, but being right underneath the HUD, the degree of look-down is minimal.

Grumman certainly did R&D on single-seat F-14s: there are several models illustrated (IIRC) in Tony Buttler's ASP - Fighters.