Discussion: F-14, F-15 Hybrid Idea

[KJ_Lesnick]

Actually, the F-15 has it's gear attaching to full width fuselage frames rather than to just frames around the inlet; putting the gear into the inlet/engine pods would've required strengthened frames there as well as some enlarging of the contours to stow the gear.

Couldn't the fuselage frames then merge with a support member (spar or something) used on the pancake?  So you essentially have a frame that covers the whole fuselage and inlet duct?  I don't know if that would work, but deliberately having fuselage frames connect with a spar I've heard is a good way to improve fuselage strength.

I can't prove it, but I rather would expect the difference between the main gear on the F-15 and the proposed navalized F-15 to be similar to that between the proposed F-18L and the production F'A-18; i.e. the carrier version in each case would be a trailing beam gear while the strictly land-based version suffices with a much simpler design.

You may very well be right.  I'm just telling you what I saw in the drawings...

[quoteI suspect the navalized F-15 may well have an extendable nose gear for launch, much as the F-4K did.  I'd say that the F-14's gear was as reasonably light as it could be and still meet the strength and life requirements.[/quote]

Well that's good...

The design philosophy I mentioned MTBF components was somewhat possible to do back when the F-14 was designed, though it would've required several detailed mockups before it could get to the level that CAD allows you today.

Did Grumman have the money or time to do several detailed mock-ups?

I'd hazard a guess that Grumman did the best they could with the tools available at the time.  I'm in a situation now where I'm working with everything from ink-on-mylar drawings to the latest CAD models and it's quite an "interesting" experience.

Yeah, some of the old and some of the new.  Sounds like a very interesting experience.


KJ Lesnick

[elmayerle]

Well, it's likely the frames around the inlet merged into frames of the "pancake" anyway, but you'd need much larger frames to handle the loads being transmitted from the landing gear into the structure.   I'm not saying it'd be impossible, just that the approach Grumman took was both reasonable and prudent.  I rather suspect that the frames around where the drop tanks attach are beefed up for that reason so it wouldn't be impossible.  I think it's a trade, if you put the main gear on the fuselage, you'd have to have drop tank provisions where the gear formerly was, I don't think you could have both drop tanks and gear on the inlet/engine "pods".

[KJ_Lesnick]

I got a question. 

If you had a strake over the inlet duct (Think F-18E/F) does that reduce or enhance the efficiency of the duct (compared to a duct-design without a strake over it, like the F-14 and F-15)?  Or does it make no difference?


KJ Lesnick

[elmayerle]

If you had a strake over the inlet duct (Think F-18E/F) does that reduce or enhance the efficiency of the duct (compared to a duct-design without a strake over it, like the F-14 and F-15)?  Or does it make no difference?

Well, not at normal angles of attack but it definitely would at high angles of attack.  That's one of the virtues of the configuration of the Su-27 and MiG-29.  While I'm mentioning the Su-27, note that this aircraft is reasonably comparable in configuration and size to the F-14 and has a similar landing gear configuration; I'd say some commonality in reasoning led to this.

[KJ_Lesnick]

Mr. Mayerle,

Well, not at normal angles of attack but it definitely would at high angles of attack.  That's one of the virtues of the configuration of the Su-27 and MiG-29.  While I'm mentioning the Su-27, note that this aircraft is reasonably comparable in configuration and size to the F-14 and has a similar landing gear configuration; I'd say some commonality in reasoning led to this.

Okay, so it would have a benefit at high-alphas, but none at low right?  This applies to both subsonic and supersonic speeds (well, I don't think you'd be doing high-alphas at supersonic-speed -- I'm talking about level flight and moderate maneuvers), or just subsonic?  In other words, would the interference-effects from the chine/strake adversely affect the inlet (would it have any benefit) while racing along at high supersonic-speed (even on a very fast design like say the F-15 and MiG-25)?


BTW:  Would the F-15's inlet be better in the fact that it can increase it's capture-area in addition to decrease the throat-area than an inlet like this one (which could not increase it's capture area because the upper part of the inlet couldn't flip up like the F-15's inlet could with the strake above it in the way, and the only other way to increase capture would be to rotate the bottom part of the duct down, which would actually lower the pressure along the bottom of the airplane reducing lift rather than the F-15's design who's ramp deflecting up increases lift by producing pressure under the ramp, and produces a concave-shape on the top side of the plane due to the ramp being angled up, which does produce a lower pressure on the bottom)

[elmayerle]

Well, even at low-alpha you'd get some flow straightening from the strake over and ahead of the inlet and that shouldn't hurt inlet efficiency.  With some careful geometry and shaping, you should be able to avoid any adverse interference effects from the chine/strake at supersonic speed.  Regarding the F-15 inlet vs. the more basic 2-D inlet used by the F-14, Su-27, et al., I'd hazard a guess that careful geometry and shaping would likely make the F-14-style inlet more than adequate (assuming you're going to be going up into the speed regime where a fully-variable inlet is required).

[KJ_Lesnick]

Mr. Mayerle,

Well, even at low-alpha you'd get some flow straightening from the strake over and ahead of the inlet and that shouldn't hurt inlet efficiency.  With some careful geometry and shaping, you should be able to avoid any adverse interference effects from the chine/strake at supersonic speed.  Regarding the F-15 inlet vs. the more basic 2-D inlet used by the F-14, Su-27, et al., I'd hazard a guess that careful geometry and shaping would likely make the F-14-style inlet more than adequate (assuming you're going to be going up into the speed regime where a fully-variable inlet is required).

So the design would be just as good as the F-15's design at the F-15's speed?


KJ Lesnick

[elmayerle]

With the strake over and ahead of the inlet, as on the Su-27?  I'd call it just as efficient as the more variable F-15 inlet at the F-15's high-end speeds.

[KJ_Lesnick]

Mr. Mayerle,

Understood...

By the way, do you think a design like this with larger wings, slightly smaller strake, and a small pancake (MiG-29 like), and tailfins positioned further rearward would be a good design?

(drawing courtesy of LEGO -- a Chinese fan-artist)

Would the strakes/chines interfere with the radar (I assume it could be fine tuned, but I'm not sure how long that would take)?


KJ Lesnick

[elmayerle]

Well, I'd think that the vertical fins need to be moved aft a bit (the basic planform looks like a cross between a scaled-down F-22 (especially the wing planform) and much of the F-35's basic configuration.  I think that an enlarged version with larger wings, aft-moved verticals, and a Mig-29-like pancake would do well.  Judging by where the strakes end, it appears they're clear of the radome, esp. if you're using an AESA-type radar

[KJ_Lesnick]

Mr. Mayerle,

Is an AESA Required for that design to work?

[Sauragnmon]

If you aren't using an AESA radar, you're not going to have the good engagement capacity.  PESA radars are nothing beside a good, powerful AESA, because they can operate on more than one band, and switch bands very quickly.  Not to mention you'd lose the ability to operate the Phoenix missile - granted it's only really good as a bomber-killer but it's still a powerful, purposeful missile.

[elmayerle]

No, it's not required, but it makes a lot of things easier and your overall reliability goes up considerably compared to a standard, mechanically-scanned, radar.  For instance, the F-35's radar is an AESA unit and takes up less volume than less-capable radars in the F-16 while being able to 'fail softly", by virtue of having multiple transmit/receive modules, rather than all at once.

The main point is to end the strakes at or behind the bulkhead the radar antenna is mounted to, so that your structure doesn't interfere with your scan.

[KJ_Lesnick]

Sauragnmon,

I don't think AESA's existed from 1967 to 1970 (The timeframe from when the F-14's development started, Grumman was selected, and the F-14 first flew) ...


Mr. Mayerle

How do you know where the bulkhead where the radar antenna is mounted to? 

Would mounting a radar inside a nose like the XF8U-3 Super Crusader or YF-23 (it's nose kind of flares down to a much smaller diameter at the tip then where the nose starts in front of the cockpit, which seems to have aerodynamic benefits -- sharper nose for one) cause any problems with the radar?


Kendra Lesnick

[elmayerle]

Mr. Mayerle

How do you know where the bulkhead where the radar antenna is mounted to? 

Would mounting a radar inside a nose like the XF8U-3 Super Crusader or YF-23 (it's nose kind of flares down to a much smaller diameter at the tip then where the nose starts in front of the cockpit, which seems to have aerodynamic benefits -- sharper nose for one) cause any problems with the radar?

Well, as a general rule, it's also usually the bulkhead that the radome attaches to since it would of necessity be the farthest forward bulkhead in the airframe.  With proper tailoring of materials and shapes, I don't think such a radome would cause any problems (consider the "sharknose" radome flown on the last couple F-20's). though I'm not certain what, if any, radar was fitted to the YF-23 (I was at Northrop at the time but on other programs).