Discussion: F-14, F-15 Hybrid Idea

[elmayerle]

Well, since the F-14 was a few years ahead of the F-15, I imagine that a hypothetical fixed-wing design, if it had the flexibility to meet all the Navy's requirements would be no more likely to be cancelled in favor of the F-15N than the F-14 actually was.

[KJ_Lesnick]

Evan,

Well, since the F-14 was a few years ahead of the F-15, I imagine that a hypothetical fixed-wing design, if it had the flexibility to meet all the Navy's requirements would be no more likely to be cancelled in favor of the F-15N than the F-14 actually was.

Understood...

Regarding my concept -- I have two designs which I'm kind of unsure which one to go with...  (This is a lot of information, but I could use some advice here)

The first one incorporates elements of these two designs here...



The first one depicted is the F-15U and the second one depicted is one of Boeing's tailed X-32 designs. 

The idea I'm thinking of is the large wing the F-15U has and it's higher-sweep, although the X-32 wing is simper in design and has larger flaps and aileron surfaces.  I was thinking for this idea of incorporating elements of both wing designs.  I would probably prefer to use the F-15A/B/C/D/E's (not F-15U's) wing-thickness maybe a little more, but definitely not as much as the F-15U's.  Unlike the F-15 I'd want to use multiple position flaps as I've mentioned before innumerable times and LED's which can be used even at subsonic cruising speed to provide good L/D ratios in lieu of having to resort to an ungodly-heavy swing-wing design. 

As for the wing-body fairings - I'm thinking of rather than using smaller chines which the F-15U did, of using flatter chines instead and re shaping some of the inverse camber inboard surface.  Not sure exactly how this would work, but it seems to me you could get more lift out of the chine by flattening it a bit.  With the inverse camber retained I figure you could still retain some high speed aspects. 

Also, the proposal I was thinking of was to incorporate a lifting-surface/tunnel/pancake in between the wings approximately the spacing of that in the MiG-29, with the lifting-surfaces produced by the wing-body fairing/twin-boom could have characteristics of both the X-32 and F-15, with a triangular shaped tail cone (F-23 like shaped from over head, though more cone-like if looked at from the rear)

I was also thinking of using a nose more like the XF8U-3 or YF-23 with that flared ramp.  It would cut drag a bit probably.  I don't know how much the overall nose size would have to change to accomodate the AWG-9 over a standard F-15's nose, but a twin-crew would be used with a cockpit featuring F-15B/D/E and F-14 characteristics. 

The inlet would be basically the same as before...



The Second Concept here...


Depicts a 3D art concept from a Chinese guy nicknamed "Lego". 

I like the design in that it's chine looks like it would have huge high-alpha potential and good airflow-stability to the engines.  It would probably help produce low-trim drag, possibly better than the F-15 chines set-up.  Inlet performance you said looks rivalable to the F-15's set-up.  The wing-sweep could be increased and area enlarged and tailfins moved aft.  I was thinking of having a lifting device between the two engines like the MiG-29 with a tail-cone between them (YF-23 like). 

The design I would probably want to use multi position flaps and variable-position leading-edge devices, even to be used at low deflections for cruise.

I'm not sure if the chines would be too far forward and could interfere with the radar... I don't know how a YF-23 style nose would work on it.


Comparison Wise:
Yes I know when the two are compared with all the additions I added, they would actually look largely similar with the major difference would be the size of the chines and thickness of them, and how far forward they go.  I'm not sure which would work best.


Other ideas I was thinking of was...
1.)  In addition to having ailerons, having asymmetric spoilers to assist roll-control:  It would provide an improved roll-rate which could be useful in a fight (getting onto your side quick with a rapid roll allows you to get into position for taking the plane into a sharp turn).
2.)  Stabilators with geared tabs (Think FJ-4 Fury:  When the stick is pulled back, the geared tabs deflect up in addition to the stabilator moving which provides more control power and/or less stabilator movement for the same pitch/roll level achieved as they would be used for roll as well)

[elmayerle]

Pardon me, there's a lot to digest here.  I rather like your first approach and, actually, I think something like the F-15U wing would fit nicely with the existing F-14 fuselage.  I seem to remember that the F-15N proposal did add LEDs to the basic F-15 wing and you might check that for some ideas.  As to asymmetric spoilers, take a look at the spoiler installation on the Vigilante, that might give you some conceptual help.  I don't know that an aircraft designed in the 1960s would have too much of the LO shaping that the YF-23 radome has, that benefitted a lot from both knowledge growth and computing power growth between when Northrop first started looking into low observables (just after they finished the flight testing on the Snark as they found it rather difficult to track at times and there's also the difficult ground-based radars had tracking the original Flying Wing bombers).  I'm not sure, either, how much the F-15 airframe would have to be mod'd to accomdate the AWG-9 system, but I'm not sure that's necessary as Hughes at least did the preliminary development on the AN/APG-64 derivative of the F-15's AN/APG-63 that included the ability to work with Phoenix missiles as part of the F-15N proposal (since they'd build both the radar and the missiles, it should, in theory, be fairly easy for them to ensure compatibility).

The chines on that Chinese illustration look to go about as far forward as you could (though that nose looks on the small side to me - then again, it might work for an AESA radar rather than a mechanically-scanned one).  Personally, I'd take a look at tweaking the front of the radome along the lines of what was done with the late-model F-5E/F/N and the later couple F-20 prototypes to tailor the radome shape for better alpha performance (some of the same folk who did the LERX on the F-18).

[KJ_Lesnick]

Evan,

Pardon me, there's a lot to digest here.

Yeah, I know what you mean.  I wasn't kidding when I said it was a lot of data!

I rather like your first approach and, actually, I think something like the F-15U wing would fit nicely with the existing F-14 fuselage.

I'm surprised that wing-type would work so well.  Regardless, it would produce a very light wing-loading which is highly desirable (especially considering the plane would have to do with a fixed wing what the actual F-14 did with a swing-wing, and it would be powered by underpowered engines for awhile) 

I seem to remember that the F-15N proposal did add LEDs to the basic F-15 wing and you might check that for some ideas.

Really?  I did not know that.

As to asymmetric spoilers, take a look at the spoiler installation on the Vigilante, that might give you some conceptual help.

Most of my knowledge of asymmetrical spoiler use comes from commercial aircraft, however I have seen it implemented on fighters.  Looking at the A3J/A-5, and F4H/F-4, placing the spoilers in front of and above the flap seems to be the typical set-up. 

I don't know that an aircraft designed in the 1960s would have too much of the LO shaping that the YF-23 radome has

The radome shape I'm thinking of (XF8U-3/YF-23 like) isn't due to concerns with radar cross-section; it has to do with the fact that the particular shape does appear to be useful for low drag, and it blends the cockpit and nose together quite well.

I'm not sure, either, how much the F-15 airframe would have to be mod'd to accomdate the AWG-9 system, but I'm not sure that's necessary as Hughes at least did the preliminary development on the AN/APG-64 derivative of the F-15's AN/APG-63 that included the ability to work with Phoenix missiles as part of the F-15N proposal (since they'd build both the radar and the missiles, it should, in theory, be fairly easy for them to ensure compatibility).

Did the APG-64 have as good a range (or greater) as the AWG-9?  I would assume the APG-64 would be like the APG-63 and would be workable with a single crew-member?

The chines on that Chinese illustration look to go about as far forward as you could (though that nose looks on the small side to me - then again, it might work for an AESA radar rather than a mechanically-scanned one).

You think the chines wouldn't get in the way of an AESA Radar, or the AWG-9 (or APG-64)?  Regarding the noses size, I assume you're talking about diameter correct?   

Personally, I'd take a look at tweaking the front of the radome along the lines of what was done with the late-model F-5E/F/N and the later couple F-20 prototypes to tailor the radome shape for better alpha performance (some of the same folk who did the LERX on the F-18).

The F-20's nose looks longer to me and flatter at the front, is that what you mean?


K.J.  Lesnick

[elmayerle]

I honestly don't know how the AN/APG-64 compares with the AWG-9 with regard to range and I suspect it was indeed set up for sinlge-crew operation.  For a two-seat variant, it could, of course, be optimized much as the AN/APG-70 and -71 were.

The chines on that chinese design won't get in the way of the radar simply because they appear to end about where the bulkhead mounting the radar has to be for that configuration, right in front of the cockpit (if anything, I suspect that concept doesn't allow enough room up front between the cockpit and radar).  The diameter looks to be on the small side for a mechanically scanned system where you have to allow for the moving antenna.  An AESA system doesn't need that room (that's one reason the F-35's radome is so pointed).

If you look at the later F-20 radomes, they've had the planview modified to give something of a strake effect at the nose, much like what was done on later F-5E/F aircraft (compare an early one with the ones the Swiss, for example, have now).  This does add to the maneuverability.

Radome shaping is driven pretty much by a compromise between aerodynamics and radar performance, sometimes resulting in some radio-transparent structural developments to meet both requirements (IMHO, it's still very much an art form).  I'd go for the simplest shape the aerodynamics can work with, but that's just my take.

[KJ_Lesnick]

Evan,

I honestly don't know how the AN/APG-64 compares with the AWG-9 with regard to range and I suspect it was indeed set up for sinlge-crew operation.  For a two-seat variant, it could, of course, be optimized much as the AN/APG-70 and -71 were.

Makes sense, the F-15 was a single seater.

As an interesting point, would it have been more expensive to simply put the APG-64 in an F-14?  Or would that have made it worse?

The chines on that chinese design won't get in the way of the radar simply because they appear to end about where the bulkhead mounting the radar has to be for that configuration, right in front of the cockpit (if anything, I suspect that concept doesn't allow enough room up front between the cockpit and radar).

Is there any way to make a design with a chine like that stable enough to fly before the era of digital fly-by-wire (a-la the F-16)?

The diameter looks to be on the small side for a mechanically scanned system where you have to allow for the moving antenna.  An AESA system doesn't need that room (that's one reason the F-35's radome is so pointed).

Regarding the size/diameter of the nose -- Are you sure?  I'm looking at the F-15U in the rendering and the two designs (Chinese design and F-15U) don't look too much different in terms of nose-length or nose-width (Maybe the F-15's nose is 'taller', but they appear to me at least be about the same width:  could be wrong though) considering the relative-spacing between the cockpit and nose and the size difference between the two (The F-15 is 63.75 feet and the Chinese design looks to be smaller).

Regarding the F-15... (I'm not sure I asked this before -- my memory hasn't been doing so good lately) was it's radome big enough to accommodate an AWG-9 antenna (assuming the radar was mounted further aft in the nose like how it's mounted on the F-14, like if you look at the cut-away drawings)? 

If you look at the later F-20 radomes, they've had the planview modified to give something of a strake effect at the nose, much like what was done on later F-5E/F aircraft (compare an early one with the ones the Swiss, for example, have now).  This does add to the maneuverability.

Yeah, it sort of makes the nose into a shape that actually produces lift.  The F-5 appears to have a REALLY long nose though even compared to the F-14 or F-15 (could be an illusion scale wise)

Radome shaping is driven pretty much by a compromise between aerodynamics and radar performance, sometimes resulting in some radio-transparent structural developments to meet both requirements (IMHO, it's still very much an art form).  I'd go for the simplest shape the aerodynamics can work with, but that's just my take.

During the timeframe the F-14 was developed, could an F-20 (or new F-5) style nose have been created with the technology then available?


KJ Lesnick

[elmayerle]

Taking your questions in order:
- Replacing the AWG-9 with the AN/APG-64 in the F-14 likely would've incurred a fair bit of redesign expense to fit the different antenna and boxes; additionally, since the AWG-9 was already well developed (it was originally supposed to be fitted to the F-111B), it would've taken a lot longer to field the AN/APG-64 which wasn't even started 'til rising F-14 costs brought consideration of a navalized F-15.  This doesn't even consider whether you'd refit the entire F-14 fleet or have to deal with the enlarged logistics footprtint of two separate radar and fire control systems.
- Considering that the maneuvering vanes on the F-14 have much the same effect at low speed as the chines, I wouldn't call it impossible for such a design to be stable enough to fly using the tech level of the F-14
- Going by cockpit/pilot size, that Chinese design looks closer in size to a F-18 or, possibly, a Chung-Kuo than a F-15
- Just going by a comparison of radomes in 1/72, I'd say the F-15 could accomodate the antenna of the AWG-9; fitting all the boxes for it might be a problem depending on how their number and size compare with equivalent values for the An/APG-63 as extra volume is always at a premium in combat aircraft
- The F-5 nose just appears to be longer 'cause it's a smaller aircraft and they do have a fair bit of equipment to fit in front of the pilot
- I don't think they could've done quite as much CFD as the late-version F-5/F-20 radome did, or at least not as fast, but wind tunnel testing would've still worked as long as the basic idea and they could've taken it from there

[KJ_Lesnick]

Evan,

I'm responding in order, with appropriate responses and questions:

- Replacing the AWG-9 with the AN/APG-64 in the F-14 likely would've incurred a fair bit of redesign expense to fit the different antenna and boxes; additionally, since the AWG-9 was already well developed (it was originally supposed to be fitted to the F-111B), it would've taken a lot longer to field the AN/APG-64 which wasn't even started 'til rising F-14 costs brought consideration of a navalized F-15.  This doesn't even consider whether you'd refit the entire F-14 fleet or have to deal with the enlarged logistics footprtint of two separate radar and fire control systems.

Good point.  What caused the costs of the F-14 to go up so much?  Was it predominantly the F-401, or other problems?

- Considering that the maneuvering vanes on the F-14 have much the same effect at low speed as the chines, I wouldn't call it impossible for such a design to be stable enough to fly using the tech level of the F-14

Maneuvering vanes?  You mean the glove-vanes?

Going by cockpit/pilot size, that Chinese design looks closer in size to a F-18 or, possibly, a Chung-Kuo than a F-15

Yeah, it doesn't look quite as big.  Regardless I made an error by stating that it's nose was similar in length and width as the F-15's.  It's width might be close if not the same, but it's length is not.  Whoops!

- Just going by a comparison of radomes in 1/72, I'd say the F-15 could accomodate the antenna of the AWG-9; fitting all the boxes for it might be a problem depending on how their number and size compare with equivalent values for the An/APG-63 as extra volume is always at a premium in combat aircraft

So the nose is wide enough (as well as deep enough) to accomodate the AWG-9 antenna (and the range of travel the antenna will move)?

Looking at that cut-away of the F-14, it does look like those boxes take up quite a bit of space... 

- The F-5 nose just appears to be longer 'cause it's a smaller aircraft and they do have a fair bit of equipment to fit in front of the pilot

Good point...

I don't think they could've done quite as much CFD as the late-version F-5/F-20 radome did, or at least not as fast, but wind tunnel testing would've still worked as long as the basic idea and they could've taken it from there

So if they thought up the basic concept, they could have come up with a shape that would have eventually worked with a wind-tunnel?


KJ Lesnick

[KJ_Lesnick]

I have been told that the F-14 had excellent high-speed maneuverability which was far in excess of any fighter of the day -- did this factor in the F-15? 

Assuming it did not - was the F-14's excellent high-speed maneuverability a requirement; or was it just a virtue of the F-14's design? 


KJ Lesnick
BTW:  How did the McDonnell Douglas competing designs fare in this area?

[elmayerle]

I think part of the reason the F-14 costs went up was the first oil crunch causing inflation as well as a reduction in purchased numbers (the USMC not buying it); certainly the costs of the F401 program had some effect but I'm not sure how much (of course, continuing the F401 program would've meant running into the same problems with it in the mid-1970s that the F100 did).  Yeah, I meant glove-vanes, I use 'Maneuvering vanes" 'cause they were there to enhance maneuvering in certain parts of the envelope).

As far as I can tell, the F-15 radome is roomy enough to accomodate the AWG-9 antenna and its full range of movement.

I think that, if they'd come up with the basic shape, they could've easily refined it in wind tunnel and flow tunnel testing.

The F-14's maneuverability is, I believe, part of the requirements of the VFX Request for Proposal; these evolved out of the F-111B not being particularly maneuverable.  The F-15 was always intended as an air superiority fighter and the lessons of Viet Nam ensured that the USAF wanted a very maneuverable aircraft.  The closest the two programs came was probably in NAA's entries as both share a distinct family resemblance and there's clearly a lot of the same approaches used later on the B-1A.

[KJ_Lesnick]

Evan,

I think part of the reason the F-14 costs went up was the first oil crunch causing inflation as well as a reduction in purchased numbers (the USMC not buying it)

The USMC cancelled it because it was stripped of it's Air-to-Ground capability right?

certainly the costs of the F401 program had some effect but I'm not sure how much (of course, continuing the F401 program would've meant running into the same problems with it in the mid-1970s that the F100 did).

The problems the F-100 ran into was surging problems at low airspeeds at high altitudes right? 

I assume this problem wasn't anywhere near as bad as the TF-30, but how bad was it exactly?

Yeah, I meant glove-vanes, I use 'Maneuvering vanes" 'cause they were there to enhance maneuvering in certain parts of the envelope).

What speeds exactly were the glove-vanes used at?  From what I remember they were used at transonic speed and low supersonic speed, I don't recall them being used at low speeds (though I could be wrong)

As far as I can tell, the F-15 radome is roomy enough to accomodate the AWG-9 antenna and its full range of movement.

If so that's good.  I prefer the nose design of the F-15 better -- looks more aerodynamic to me.

I think that, if they'd come up with the basic shape, they could've easily refined it in wind tunnel and flow tunnel testing.

Makes sense to me.

The F-14's maneuverability is, I believe, part of the requirements of the VFX Request for Proposal; these evolved out of the F-111B not being particularly maneuverable.

I know that overall maneuverability for dogfighting purposes was a requirement...

What I was specifically asking had to do with supersonic maneuverability.  Airplanes generally appear not to be able to maneuver quite as well at supersonic speeds due to the center of pressure shifting rearwards.  I was told that the supersonic maneuverability of the F-14 was nothing short of extraordinary -- was that particular aspect of the plane's performance a requirement (I think I remember hearing it's supersonic maneuverability was even better than the F-15's)?


K.J. Lesnick

[elmayerle]

I would certainly think that one reason the USMC cancelled the F-14 was if the Air-to-Ground side of the aircraft, as demostrated on prototype  12 carrying 12 500-lb bombs in the center tunnel, was either stripped or not completely developed.  The Marines have generally gone for multi-role aircraft since their first priority is to support the shooters on the ground.

The F100 had some surging problems and also had a problem with dealing with the maneuvering loads since what the aircraft was actually doing was rather more than expected by the folks who wrote the spec. the engine was developed to.  By the time they got it sorted out, GE had scaled up the fan and afterburner/nozzle sections of the F404 to mate with the F101 core and produce the F101DFE/F110.  A very flexible core, being used in the CFM56 as well as the F118 (B-2A and U-2S).

Not having any references handy, I can't say at what speeds the glove vanes are used though I'd hazard a guess that they'd be used in the high-subsonic to low-supersonic range.

I don't know what the exact requirement was, but I rather suspect that Grumman did a lot of work to refine the design to be quite maneuverable throughout its speed range as a reation to the problems they had with the F111B.  I doubt

[KJ_Lesnick]

Evan,

The F100 had some surging problems and also had a problem with dealing with the maneuvering loads since what the aircraft was actually doing was rather more than expected by the folks who wrote the spec. the engine was developed to.

So, the airplane was too maneuverable for it's own good? 

By the time they got it sorted out, GE had scaled up the fan and afterburner/nozzle sections of the F404 to mate with the F101 core and produce the F101DFE/F110.  A very flexible core, being used in the CFM56 as well as the F118 (B-2A and U-2S).

If I may ask:  Were the maximum-mach limits of the F-110 equal to, less than or superior to the F-100 or F-401?

Not having any references handy, I can't say at what speeds the glove vanes are used though I'd hazard a guess that they'd be used in the high-subsonic to low-supersonic range.

Well, if you could find that out it could be quite helpful (in either case I'm looking around as well)

I don't know what the exact requirement was, but I rather suspect that Grumman did a lot of work to refine the design to be quite maneuverable throughout its speed range as a reation to the problems they had with the F111B.

I guess I couldn't blame them there, the F-111B was a complete disaster.


KJ Lesnick
BTW:  I'm wondering about a few things pertaining to my concept and can use some answers pertaining to this

- My concept calls for a pancake/tunnel not unlike that used on the MiG-29 Fulcrum in terms of approximate width and such which is obviously thinner than the F-14's.  Earlier when I thought of adding a pancake to my WHIF-concept.  I was under the impression that it would all work, however now that I think about it, especially considering the F-14 carries a lot of weaponry under its tunnel -- up to 4 x AIM-54 Phoenix's which are not exactly small.   Do you have any idea if 4 x AIM-54 Phoenixes could actually fit inside the thinner MiG-29-like tunnel and be carried with a relatively low drag-penalty comparable to the actual F-14?

- Even though I prefer the aerodynamics of the F-15's nose over the F-14:  I'm wondering if the nose and fuselage underside should be flatter as it's shape seems as if it would blend in better with the pancake.  I am basing this on the fact that the underside of the F-14's nose and fuselage underside is flatter and it appears to merge well with the pancake.

- Since the USN wanted to remove the engines out of the bottom of the fuselage would that make the diameter of the engine bay larger?  This is not to sound silly -- the areas where the F-14's engines are housed in are kind of fat relative to the diameter of the engine location on the F-15.  From what I remember the diameter of the F-100 and F-401 were just a few inches apart...

[KJ_Lesnick]

I got a good question, I'd really like it if anybody has an answer...

From what I have read in the book "F-15 Eagle Engaged", it would appear that McDonnell-Douglas was initially more pre-occupied with winning the Navy VFX program (As McDonnell, and Douglas for that matter, both, had a lengthly history of building aircraft for the US Navy) than they were with winning the F-X program. 

According to what was written in the book, when McDonnell Douglas lost, they funneled much of what they learned in the VFX program into the FX-Development. 

I'm wondering during such design competitions:

1.)  Are the competitors aware of their opponents designs.  If so, how intimately?
2.)  Is it common practice for a competitor to sometimes copy various design concepts off of each other?


K.J. Lesnick
BTW:  If Grumman's design took shape as a fixed wing design with potentially large strakes such as the WHIF concept I described, especially considering how McDonnell Douglas spent a lot of effort on the VFX program, would McDonnell-Douglas have significantly altered their design as a result?

[GTX]

1.)  Are the competitors aware of their opponents designs.  If so, how intimately?

Sometimes, but not in any great detail.  They are usually focussed on their own product. To be to intimate, they risk wasting valuable effort, not to mention, being accused of industrial espionage.

2.)  Is it common practice for a competitor to sometimes copy various design concepts off of each other?

Generally not - they usually believe they have the best concept/design themselves.  They may however 'copy' (using this term very carefully) some aspects - something along the lines of "gee that's a good idea, we may do something similar".

Regards,

Greg