Discussion: Grumman VFX Concept/WHIF (Alternate F-14 Design)

[KJ_Lesnick]

I had previously titled a post "Discussion: F-14, F-15 Hybrid Idea" ( URL = http://www.whatifmodelers.com/index.php/topic,19861.0.html ) however after talking with a number of people, my concept evolved so much to the point that the design really isn't an F-14/F-15 Hybrid anymore and is pretty much an entirely different concept in its own right.

As a result, I have decided to start a new thread revolving around the new concept that I have. 
(Feedback and Opinions would be appreciated.) 

The idea more or less first revolves around an alternative history where Grumman's VFX design either during the TFX Phase (The Defense Department asked Grumman and General Dynamics to submit alternative designs to the TFX) or during the VFX-Phase took shape rather than a swing-wing design with widely spaced engines with a huge pancake, instead took shape as a tailed clipped delta with variable-camber wings, a strake, and a smaller MiG-29-esque tunnel.  The idea would be to produce a design that could do with a fixed-wing what the F-14 required with a swing-wing, using technology of the era, and meeting all the USN's requirements.


So far, the idea I have revolves around the following

Length of up to 67.5 feet
Reason:  Some of the design is still based on the F-15, and F-15U design.  Since I never really was a fan of the dogtooth used on the F-15 (especially if it could be avoided on this design), I would want to use a design more true to the original if it was workable (on this particular design).  With the F-15U's wing there would be no spacing between the leading edge root of the tail-plane and the trailing edge of the wing.  I figure another 3 or 3-1/2 feet would probably be needed to make it all fit.  I should also note that the fuel capacity might not be as high as the F-14's as it has a smaller pancake and a different wing.  This could potentially free up a little extra space inside the design for extra fuel.

Twin-Man Crew, Canopy Shape similar to an F-18B/C
Reason:  The F-14 design requires a twin-man crew, plus two pairs of eyes are generally a good thing.  The F/A-18B/D's cockpit seems more aerodynamic than the F-14's design.

Nose configuration based around the F-15
Reason:  It appears to be pointier, and more efficient aerodynamically than the F-14, and I've been told the AWG-9 could fit within it's contours

A large-wing with approximately the same area as the F-15U, not counting the strake or pancake-area, with wing leading-edge sweep to be 50-degrees, thickness to be somewhere between the F-15U and the F-15A
Reason:  The airplane is going to have to land at lower speeds than the F-15, will have to cruise on station and loiter for longer periods, and will almost certainly weigh more.  Extra wing-area is a good way to resolve this problem.  The higher sweep-angles would produce better high-speed performance in principle and probably a touch less trim-drag.  The thickness of the F-15U's wing I was told made the design slower than earlier F-15's design however, so using a wing of the same physical thickness of the earlier F-15's or somewhere between the F-15U and earlier F-15 designs should, with the higher sweep allow the higher speeds.  Additionally, light-wing loading is excellent for sustained high-g maneuvers. 

Wings to feature leading-edge devices (droops = like the F-104, F-16, and F/A-18) and multiple-position slotted-flaps, slotted-flaperons with flap/flaperon-shrouds.
Reason:  While the F-15's wing worked well without leading-edge devices, this design will have to takeoff and land at lower-speeds so having a drooping leading-edge, and a full-span drooping trailing-edge is a good idea.  The slotted flap/flaperon set-up, and flap/flaperon-shrouds further increase low-speed handling down as well.  The droops and flaps (no slot would open between the flap and wing under such conditions) would work in small amounts like how the F/A-18 does as a variable-camber mechanism which improves L/D ratios while cruising and loitering on station.

Trailing edge sweep to be zero-degrees for roughly the outboard 60% to 67% of the span, with the roughly inboard 33% to 40% of the wing having an aft-sweep about the same as the leading-edge if not a little less producing a notched out appearance similar to the English-Electric Lightning
Reason:  The clipped delta shape of the F-15U appears to at least be partially shaped for stealth.  The VFX did not require the same stealth requirements.  Additionally looking at some of the fixed-wing Grumman designs, a wing-shape like the one I described probably would work better.

Long strake not entirely unlike the F/A-18's design extending (assuming the design can be made stable) all the way to the bulkhead the radar is mounted on
Reason:  Strake adds wing area under pretty much all conditions, it produces powerful vortices allowing high-alpha maneuvers.  It also can reduce trim-drag at supersonic speeds which means more control-power is available for maneuvering.  The whole idea is to be able to achieve the same alpha capability the F-14 can, the same high-speed maneuverability the F-14 can, possibly fly a little faster (the target goal is a speed as fast as the F-15 or the MiG-25).
 
Thinner booms more like that of the F-16 instead of the F-15
Reason:  First of all the booms are basically aft of the chine/strake used on the F-15 and F-16 which are attached to the sides of the fuselage and form the wing-body fairings, and extend all the way to the tails.  On the F-15 the vertical and horizontal stabs are mounted to them, on the F-16 the horizontal stabs are attached only, and on the F-16 on the back of these booms are a pair of speed-brakes.  Second, the design I'm proposing is going to have a pancake, which the F-15 does not have -- the design would be too fat with both, so my solution is to reduce the size of the booms.  Even with the thinner booms and the pancake you'd probably get a significant benefit over just the pancake, or the larger booms of the F-15.

Variable-Geometry Engine Intakes
Reason:  To produce high performance at high-speeds an automatically-controlled variable geometry multi-shock inlet with porous-ramps and a bypass door is generally a good idea.  Design should be able to keep up with a MiG-25.

Engine intakes to be spaced apart about the same distance as the F-14 and F-15 designs, probably a box or trapezoidal shape (Possibly the inlets might need to be canted out a little bit -- ie, the bottom of the duct is further outboard then the top of the duct)
Reason:  First, both the F-14 and F-15 have about the same spacing between the inlet duct.  Second the design has a strake/LEX, and I don't think it would be easy to keep the intake under it if they were spaced any further out.  As for canting the ducts, part of it is that the F-14 has them, and there's probably a reason for it, and for this tunnel to work you might need the area from the where the intakes form at the start of the tunnel to be wider than where the engines are located at the back of the tunnel for reasonably low drag, especially when carrying stuff under 'em  (I could be wrong), canting the inlets would provide a wider area in the front, and keep the inlets under the LEX (at least the top of the inlet).

Engine spacing (rear) to be spaced about as far apart as the MiG-29 with (assumingly) aerodynamic tunnel/pancake tunnel of similar width.
Reason:  The larger pancake has the effect of reducing roll-rate.  Roll rate is actually quite important in a dog fight as it allows you to switch/reverse maneuvers faster, and allows you to set yourself up for a high-g maneuver.  The faster you can bank, the earlier you can yank (yank as in yank back on the stick).  One area where the F-14 had shortcomings in (well, that might be an exaggeration, but it wasn't spectacular) was roll-rate.  As long as the pancake set-up doesn't produce too much drag it sounds to be a much better idea.  I'm not entirely sure how well the closer pancake works at high-speeds (interference effects and such -- could be worse than the F-14 or it could be less extreme, I'm not sure)

Palleted mounting for Phoenixes
Reason:  Reduces drag, allows a flush set up for Sparrows

Reasonably Light Weight
Reason:  The whole idea of such a design is to get the same job done that the F-14 did but at a lighter weight.  It would obviously be wise to come up with a design that is sturdy and yet reasonably light weight.  I assume most Naval Aircraft designers would know how to do this.  I'm not entirely sure what a reasonable empty weight, fuel-weight, gross weight, and fully loaded weight would amount to.

Speedbrakes / Spoilers
Reason:  The ability to slow down in a hurry can be useful (although I doubt they'd be used often in a dogfight except if you're "Maverick").  The idea I was thinking of was more or less having spoilers on the wing and a center brake on the top fuselage.  To the best of my knowledge, one of the more useful qualities the F-14 had was it used a direct-lift control system which modulated the spoilers during approach to allow excellent control over the descent.  Even with ailerons and differential tailplane movement, asymmetric use of spoilers can be useful for enhancing roll-control.

Reusable Holdback
Reason:  From what I remember older carrier aircraft, the holdback fittings ended up broken after each cat-shot.  The F-14 was the first that could be reused.  That's a good feature

Wing-Folding Capability
Reason:  Wingspans greater than either 27 or 36 feet require a wing-folding mechanism on a carrier

Tailhook
Reason:  Tailhook needed for carrier landing


So far, the performance goals revolve around the following

Same or similar landing speeds to the actual F-14 design
Reason:  One of the reasons Grumman went with a swing-wing was because they couldn't get the landing-speeds down to satisfactory levels without them especially with the bring-back requirements.

Same subsonic range and loitering capability as the actual F-14
Reason:  Grumman went with a swing-wing at least partially because they had trouble meeting the loitering requirements without them.

Same bring-back capability as the actual F-14
Reason:  It was one of the requirements for the VFX-program. 

Same or similar high-alpha capability as the actual F-14
Reason:  The actual F-14 had absolutely remarkable high-alpha capability which actually even had the F-15 beat -- it was one of it's finer qualities.

Same or similar instantaneous-G and turning capabilities as the actual F-14 at low-airspeeds
Reason:  One of the actual F-14's finer qualities -- The F-14's instantaneous-G capability was actually better than the F-15 at low-speeds, and (from what I remember hearing) at least under some conditions actually was rivalable to the F-16.

Improved sustained-G and turning capabilities at high-subsonic, intermediate-airspeed (closer to the F-15)
Reason:  The F-14 was somewhat poorer in that range as the F-15.  I'm not sure achieving the same sustained turning ability is possible, but I'd like to at least get it closer to the F-15

Same or similar supersonic-agility as either the F-14 or F-15
Reason:  The F-14 was one of the most agile fighters in the world at supersonic speed; the F-15 had pretty good tactical maneuvering capability at high speeds as well.  Ideally I would want to achieve maneuverability figures similar to the F-14 but the F-15 would do fine.

Superior thrust/weight-ratio to the actual F-14
Reason:  One of the entire reasons for my WHIF having a fixed-wing is that it is significantly lighter than a swing-wing which would naturally bump up it's thrust to weight ratios.  Even if the wings are almost as good at a majority of the speeds the F-14 flew at with the higher thrust to weigh ratio, the plane would be a substantially better energy/maneuvering-wise.

Same top-end speed as a MiG-25 or an F-15
Reason:  The MiG-25 and F-15 are faster than the F-14.  High top-end speed is more important for an interceptor than an air-superiority fighter, plus the MiG-25 was considered one of the threats the F-14 would face as well.

Same or similar roll-rate to the A-4 / F/A-18
Reason:  One of the areas the F-14 came up short in comparison to the F-15 was it's roll-rate.  Roll-rate can actually be quite useful in regards to being able to switch back and forth from one maneuver to another.  I think with a large wing, big ailerons, differential flap or differential spoiler use such a roll-rate might be possible.


KJ Lesnick

[KJ_Lesnick]

I have a couple of technical questions which I could use answers for

The first question pertains to the shape of the engine-ducts.  The F-15 uses boxy intakes which only round out into cylindrical shapes where the engines are, the F-14's inlets round out into cylindrical shapes further away from the engines.  I'm kind of curious as to which shape works better. 

The second question is in regards to the pancake, I'm not sure exactly how much blending or thickness the pancake should have.  The F-15 does have a small gap between the engine ducts and that area is very thick; the F-14's pancake is fairly thin.  Since my design is somewhere in the middle, should the thickness be somewhere in between?

The third question pertains to the missile mounting and set-up.  The F-14 carried four AIM-54's under it's tunnel/pancake and two missiles under the glove.  The WHIF I'm coming up with has a narrower aerodynamic tunnel/pancake than the actual F-14 has and I'm actually not sure if the spacing is sufficient for being able to carry four AIM-54's under it.  Normally I would try and find a picture of a MiG-29 carrying a Vympel R-33/AA-9 Amos and look at the two, but I cannot seem to find a single picture of a MiG-29 carrying them.  Anyone got some answers?

The fourth question pertains to the engine that was to power the plane, the F401.  Because of it's higher bypass ratio (which can have significant effects at high supersonic flight I've been told), I have doubts as to it's ability to propel an airplane to the same top-speed as the F-15 or MiG-25.  I could be wrong, but I was thinking of a Whiffed-up version of the F401 that would either have a re-positioned or split IGV (Inlet Guide Vane).  The idea is to use such a redesigned IGV to lower the core pressure-ratio as normal (the guide vane adjusts, lowering the blade's AoA) without lowering the fan-duct pressure (due to the IGV being either moved further inboard, not fully affecting the fan duct, or due to the IGV being split -- in which the inner section adjusts to lower core pressure ratio with the outer section of the guide vane maintains normal AoA through the fan duct) to squeeze more power out of the afterburners.  Sound like a good idea?


KJ Lesnick

[Shasper]

Regarding the MiG-29 reference, the Fulcrum cannot carry the Amos. . . that missile was designed for use with the fire-control system mounted in the MiG-31 Foxhound, which has a similar under fuselage as the F-15 with recesses for 4 () AA-9s.

Shas

[KJ_Lesnick]

Shasper,

I did not know that actually -- I thought the Su-27 and MiG-29 could carry them too.  You learn something new every day.


KJ Lesnick

[KJ_Lesnick]

I've looked at some VFX concepts that were drawn up.  I don't think a plane with a pancake as thin as a MiG-29 could accommodate 2 rows of paired (2 x AIM-54's in the front, 2 x AIM-54's in the rear) AIM-54's under it.  There just isn't quite enough room and I don't recall Hughes ever considering a variant with folding fins.

2 x 2 AIM-54's at the front of the pancake will fit, I know at least one other AIM-54 could be fitted aft of that whether two could (single file) I'm not sure as there needs to be room for the arrestor-hook. 

Honestly I'm thinking of incorporating one of the following solutions

Solution 1: Enlarge the pancake so 2 rows of paired AIM-54's could fit under it
Advantage:  Everything fits!
Problem:  Wider pancake will affect roll-rate I've been told (I'm trying to get a roll-rate on par with an F-15 at the very least)

Solution 2a:  Only put the AIM-54's single file in the pancake and put two AIM-54 pylons under each wing
Advantage:  Six AIM-54's retained
Problem:  Drag levels would probably be significantly higher affecting combat-radius, loitering capability and top-end speed than the conventional configuration

Solution 2b:  Same as 2a but using modular pallets as wing-pylons to reduce drag a bit
Advantage:  Lower drag
Problem:  Would weigh 400 lbs more than the mounting used by the extra two pallets (there are only 4 on the actual F-14, there would be six on this).  The pallets only went over to my knowledge because they allowed a flush sparrow set up and to the best of my knowledge, flush-mounts don't work all that well on wings.  I don't think having modular pylons/pallets (meaning every time you wanted to carry a sparrow you'd have to swap the pallet off and put on a pylon, and vice versa when switching back to carrying AIM-54's) would go over well, though it might drastically improve air-to-ground versatility (The original capabilities for the F-14 did allow for air to ground -- Congress ordered it deleted but the project was already in motion then)

Solution 3a:  Put three AIM-54's under the pancake, 2 side by side at the front, and another in the back, then carry four AIM-54's under the wings
Advantage:  It would allow 7 Phoenix's
Problem:  More drag than Solution 2a, and it might require further fuselage strengthening

Solution 3b:  Same as 2b but with the Extra Phoenix of Solution 3a
Advantage:  Seven phoenixes and less drag than Solution-3a
Problem:  Same as 2b, but a little worse, it also might require strengthening to the plane.

Opinions?


KJ Lesnick

[KJ_Lesnick]

I think a lot of members would be happy to see this one:  I actually found the RFP for the VFX... I don't know how accurate this is so I could use to know if there were changes

- Two-man crew (tandem-seating)
- Two-engines (Pratt &Whitney TF-30 P-412 to be used as interim)
- Incorporate AWG-9 and AIM-54 Phoenix weapon system
- Carry up to 6 x AIM-54 Phoenix, or 6 x AIM-7 Sparrow, and/or 4 x AIM-9 Sidewinder missiles plus one internal M61-A1 Vulcan-cannon.
- Be designed to endure high fighter loads exceeding those of the F-4J loaded with AIM-7 Sparrow or AIM-54 Phoenix missiles
- Carrier suitability:  Landing strengths for 6 x AIM-54 Phoenix missiles and 4,000 lbs of fuel.  Landing speeds and weights of VFX are suitable for operations from the Hancock-Class CVA's.


I don't know if this meant that the USN didn't want any fixed wing designs or was seriously dubious as to their performance, but USN disagreed with the performance claims that NAA made.  A NASA review also stated more or less the same thing -- I'm not sure if the NASA review came after the USN disagreed with it's capabilities or not (Anybody got any further data here?)


KJ Lesnick

[KJ_Lesnick]

Does anybody know how McDonnell Douglas planned to mount Phoenixes on their Model-225 -- their VFX-Design (i.e. Flush mounts, Palleted mounts, etc)

KJ Lesnick

[Talos]

Looking at pictures of a model of the 225 in "American Secret Projects: Fighters and Interceptors 1945-1978", they're flush-mounted just like the Sparrows.

[KJ_Lesnick]

Talos,

Thank you

[Talos]

No prob, KJ. Big Tomcat fan here and I've been researching the TFX designs to do some profile drawings of them anyway.

[KJ_Lesnick]

Talos,

Big Tomcat fan here and I've been researching the TFX designs to do some profile drawings of them anyway.

That I'd love to see


KJ Lesnick

[KJ_Lesnick]

I've looked at some VFX concepts that were drawn up.  I don't think a plane with a pancake as thin as a MiG-29 could accommodate 2 rows of paired (2 x AIM-54's in the front, 2 x AIM-54's in the rear) AIM-54's under it.  There just isn't quite enough room and I don't recall Hughes ever considering a variant with folding fins.

2 x 2 AIM-54's at the front of the pancake will fit, I know at least one other AIM-54 could be fitted aft of that whether two could (single file) I'm not sure as there needs to be room for the arrestor-hook.

Was it considered an important requirement for 4 AIM-54's to be carried under the main fuselage?  Or was it not a serious criteria? 


Honestly I'm thinking of incorporating one of the following solutions

Solution 1: Enlarge the pancake so 2 rows of paired AIM-54's could fit under it
Advantage:  Everything fits!
Problem:  Wider pancake will affect roll-rate I've been told (I'm trying to get a roll-rate on par with an F-15 at the very least)

Solution 2a:  Only put the AIM-54's single file in the pancake and put two AIM-54 pylons under each wing
Advantage:  Six AIM-54's retained
Problem:  Drag levels would probably be significantly higher affecting combat-radius, loitering capability and top-end speed than the conventional configuration

Solution 2b:  Same as 2a but using modular pallets as wing-pylons to reduce drag a bit
Advantage:  Lower drag
Problem:  Would weigh 400 lbs more than the mounting used by the extra two pallets (there are only 4 on the actual F-14, there would be six on this).  The pallets only went over to my knowledge because they allowed a flush sparrow set up and to the best of my knowledge, flush-mounts don't work all that well on wings.  I don't think having modular pylons/pallets (meaning every time you wanted to carry a sparrow you'd have to swap the pallet off and put on a pylon, and vice versa when switching back to carrying AIM-54's) would go over well, though it might drastically improve air-to-ground versatility (The original capabilities for the F-14 did allow for air to ground -- Congress ordered it deleted but the project was already in motion then)

Solution 3a:  Put three AIM-54's under the pancake, 2 side by side at the front, and another in the back, then carry four AIM-54's under the wings
Advantage:  It would allow 7 Phoenix's
Problem:  More drag than Solution 2a, and it might require further fuselage strengthening

Solution 3b:  Same as 2b but with the Extra Phoenix of Solution 3a
Advantage:  Seven phoenixes and less drag than Solution-3a
Problem:  Same as 2b, but a little worse, it also might require strengthening to the plane.

Opinions?


KJ Lesnick

[sotoolslinger]

Hey KJ , you have a lot more knowledge of aerodynamics than I do but reading your specs and requirements and knowing the time frame you are working in I thought you might like to look at this
http://www.whatifmodelers.com/index.php/topic,23131.msg334678.html#msg334678
While considerably smaller than you seem to be considering it will have the capability to carry 4 Phoenix type missiles as well as shorter range stuff.

[KJ_Lesnick]

sotoolslinger,

I looked at your design.  I think it's a pretty impressive work you've engaged in, and way beyond the modeling skills I have.

You're right though, the design is smaller than the specifications I'm looking for.   


KJ Lesnick

[sotoolslinger]

Thanks for looking KJ I really enjoy reading your threads. Lots o great ideas. I'll let you know when I start the VG Flanker