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Why No Slats On The F15?  
User currently offlineMax Q From United States of America, joined May 2001, 4751 posts, RR: 18
Posted (5 years 2 months 1 week 2 days 16 hours ago) and read 9179 times:

Always found this a bit odd, all the other 'teen' fighters have them, as do most if not all since then. I have no doubt it's low speed performance and manoeuvering capability is excellent but Slats usually give you a lot more lift, could it not be even better ?


The best contribution to safety is a competent Pilot.
27 replies: All unread, showing first 25:
 
User currently offlineKC135TopBoom From United States of America, joined Jan 2005, 12173 posts, RR: 51
Reply 1, posted (5 years 2 months 1 week 2 days 11 hours ago) and read 9146 times:

The F-15 also has a flat bottom fuselage, which also adds to lift. That is what saved the IDF F-15C when it lost its right wing in a mid-air collision years ago. So, I don't think it needs leading edge slats.

User currently offlineDragon6172 From United States of America, joined Jul 2007, 1203 posts, RR: 0
Reply 2, posted (5 years 2 months 1 week 1 day 4 hours ago) and read 8856 times:

Could come down to the amount of lift gained does not offset the weight and space that it would take.


Phrogs Phorever
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 3, posted (5 years 2 months 1 week 1 day 3 hours ago) and read 8856 times:

Not 100% sure but it's more than likey that the Mach 2.5 requirement had a lot to do with it. The leading edge of the wing has to be specifically designed for that speed.

In any case the F15 carries a lot of wing with a shed load of power, it has a very low wing loading with loads of excess power (for the time). Just look at its lifting ability or the quoted landing speed, its the same as an F14 or F18 (134 kts IIRC) with all their aero aids. It probably just doen't need them for the task it's designed for.
I believe that low and slow was not the F15s forte (I think it was inferior to the other teen fighters in this corner of ACE chart) but tactics were more than enough to counter this.


User currently offlineEBJ1248650 From United States of America, joined Jun 2005, 1932 posts, RR: 1
Reply 4, posted (5 years 2 months 1 week 11 hours ago) and read 8716 times:



Quoting Spudh (Reply 3):
I believe that low and slow was not the F15s forte (I think it was inferior to the other teen fighters in this corner of ACE chart) but tactics were more than enough to counter this.

Not too sure about this. The F-15 has enough power to allow it to fly slow and still be able to manuever admirably. I'm more inclined to believe the airplane didn't get slats for the simple reason it just didn't need them.



Dare to dream; dream big!
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 5, posted (5 years 2 months 1 week 10 hours ago) and read 8693 times:



Quoting EBJ1248650 (Reply 4):
Not too sure about this. The F-15 has enough power to allow it to fly slow and still be able to manuever admirably. I'm more inclined to believe the airplane didn't get slats for the simple reason it just didn't need them.

I probably worded that badly, this is the F15 we're talking about! Its like saying that a McLaren F1 was harder to park than a Corvette LS1. The F15 was top dog in almost the rest of any ACE chart. I didn't mean it was bad, low wing loading + Power meant its very good indeed, just that its the only area that it gives ground to the other slat equiped teen tighters. Even without slats It was still superior to all the threat aircraft in that small area of a manoueverability chart until the Mig 29/Su 27 came along and then they just adapted their tactics to try and avoid bleeding energy.

As you said, it probably simply didn't need them.

I find the whole area of wing design fascinating. I thought the swing wing, for all its aerodynamic advantages, was gone as a design solution (presumaby for weight/complexity reasons) until I saw AirRyans impression of a swing wing NATF. I wonder how the variable geometry affects stealth, probably doesn't help there either. Maybe with all the advaces in composites they might be able to solve some of downsides of VG.


User currently offlineMax Q From United States of America, joined May 2001, 4751 posts, RR: 18
Reply 6, posted (5 years 2 months 4 days 15 hours ago) and read 8466 times:

No question the F15 is a superb machine, there are more than a few accounts, however of the F14D's ability to be able to out manoeuvre it close in.


With the huge increase in power of the GE engines and the massive lift of the swing wing it's not surprising.



The best contribution to safety is a competent Pilot.
User currently offline747classic From Netherlands, joined Aug 2009, 2198 posts, RR: 14
Reply 7, posted (5 years 2 months 4 days 12 hours ago) and read 8451 times:



Quoting Max Q (Reply 6):
With the huge increase in power of the GE engines and the massive lift of the swing wing it's not surprising

I still think the F14D was retired to early, but that's another topic.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 8, posted (5 years 2 months 4 days 9 hours ago) and read 8422 times:



Quoting 747classic (Reply 7):
I still think the F14D was retired to early, but that's another topic

I've just given the last couple of hours reading through a lot of the old F18/F14 threads. I wish I was a member back when those discussions were hot. I probably have the best library of F14 books this side of the Atlantic! You almost have to apologise these days if you want to talk about the F14.  Sad

I've no doubt that the F-14D finally put to bed all the arguments about the F15/F14 debate because all the USAF guys suddenly switched to putting forward the F16 when the debates opened up about dogfighting.

Thats what I find interesting about current wing design. The VG wing was a cure all but seems to have carried too big a weight penalty for anything but a big twin 25,000 lb plus engined aircraft. Everyone that has tried it has replaced their VG with a conventional(ish) winged craft:
Mig 23-27/Su-24 - Su 27-3x
Tornado - Typhoon/JSF
F-14 - F18
F111 - F15/JSF

In each case except Russian the replacement plane appears on the surface to have some inferior airframe characteristics:
Tornado/F111 have better load carrying and/or low level flying ability than their replacements (and I include the mighty F15E in that statement). Admittedly their replacements are several orders of magnitude better at Air to Air.
The F14 outperforms the F18 in almost every aspect but electronically and in the hangar.
I believe for all it other failings the mig 27 was very good on the deck, better than its ground attack replacement anyway.
How have they solved the low level ride comfort issues with the likes of the Rafale and Eurofighter, even the JSF for that matter, I didn't think there was much you could do with a low wing loaded aircraft when it came to gust response (another area I believe the F15 was inferior to F14 and where F111 and Tornado were kings)?

How come the NATF is the only VG on the drawing board?


User currently offline747classic From Netherlands, joined Aug 2009, 2198 posts, RR: 14
Reply 9, posted (5 years 2 months 4 days 7 hours ago) and read 8408 times:



Quoting Spudh (Reply 8):
You almost have to apologise these days if you want to talk about the F14.

It wasn't the fault of the F14 and F111 airframes, both with variable geometry wings, that they were retired relative early.
The thing that caused all the problems on both airframes, was the PW TF30 engine, in aviation literature described as one of the most ill designed engines. The weight/thrust ratio of that engine was awful, also the flight envelope was severely restricted by operating to close to the stall limit. In fact it was a nightmare, the problems were never resolved completely.
After re-engining with the General Electric F110-400 the F14 was reborn and in the final F14D variant with the digital update and the new AN/APG 71 radar it was IMO a formidable aircraft.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 10, posted (5 years 2 months 4 days 7 hours ago) and read 8394 times:



Quoting 747classic (Reply 9):
The thing that caused all the problems on both airframes, was the PW TF30 engine, in aviation literature described as one of the most ill designed engines

In Paul T Gilchrist's book he rails against the 'band aid' fixes for the TF 30. He reckoned that for the money they spent 'fixing' the PW engine they would have funded development of the GE Engine almost a decade earlier. I still find it astounding that PW got away with a containment ring for the compressor shedding blades instead of actually successfully fixing them- and got PAID for it!!!!

Imagine that the F14A had the latent ability of the F14B in 1972!! As it was the A was nearly as big a jump compared to the F4 as the F22 is to the F15. In one of my early books (written before the TF-30 engine problems were widely reported) they reported that 2 F-14A were more than a match for 8 F4J's. Put in the GE engines and you'll get figures approaching the F22 level of superiority over all comers at the time.


User currently offline747classic From Netherlands, joined Aug 2009, 2198 posts, RR: 14
Reply 11, posted (5 years 2 months 4 days 6 hours ago) and read 8382 times:

Quoting Spudh (Reply 10):
I still find it astounding that PW got away with a containment ring for the compressor shedding blades instead of actually successfully fixing them- and got PAID for it!!!!

I think nothing is learned, the story repeats itself with the PW F135 on the JSF. IMO, it will be wise to raise some funds to have the alternative engine, the GE/RR F136 on standby.
Two competing engines for the same application will lead in the end to better results for the buyer, see the competition between PW and GE on the F16.

[Edited 2009-09-25 12:21:19]

[Edited 2009-09-25 12:22:10]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineMax Q From United States of America, joined May 2001, 4751 posts, RR: 18
Reply 12, posted (5 years 2 months 3 days 18 hours ago) and read 8296 times:

Very good points and I agree the F14D was retired too early. The D version was really something and the proposed 'super Tomcat' would have been even more so.


I have only one book on the F14 but as concerns the 'A' model one of its Pilots liked to say:


'If it says Pratt & Whitney on the side it better say Martin Baker on the seat..



The best contribution to safety is a competent Pilot.
User currently offline747classic From Netherlands, joined Aug 2009, 2198 posts, RR: 14
Reply 13, posted (5 years 2 months 3 days 14 hours ago) and read 8270 times:

Even in the magnificent movie "TOP GUN" (sponsored by the USN) both TF-30 engines of the Tomcat (F14A) stalled several times and the aircraft came down in a flat spin.
For the real F14 lovers, it's released on Blue-ray now !!!! High resolution, like in the cinema.
What a sound (Digital HD), when they Take Off with full AB.

P.S. F14D's didn't need afterburners, when departing from an aircraft carrier.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 14, posted (5 years 2 months 3 days 4 hours ago) and read 8199 times:

I have some stats somewhere (probably in Gilchrist's book) on the number of F14s actually lost to compressor stalls, IIRC its a big percentage of the total attrition.

I've read lots of posts about the irrelevance of quoting top speeds of fighter aircraft as they're mostly clean, but an interesting piece of trivia is that the Mach 2.34 for the F-14 is with 4 sparrow missiles IIRC. I've also read that the F14D could 'supercruise' albeit at 1.05M.


User currently offlineMax Q From United States of America, joined May 2001, 4751 posts, RR: 18
Reply 15, posted (5 years 2 months 3 days 2 hours ago) and read 8179 times:

Yes I think that top speed is irrelevant....until you need it !


The best contribution to safety is a competent Pilot.
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 16, posted (5 years 2 months 2 days 8 hours ago) and read 8110 times:



Quoting Max Q (Reply 15):
Yes I think that top speed is irrelevant....until you need it !

There is an interesting topic on www.ausairpower.net where they compare the F18 SH to the threat SU 30 and one of the points it makes is that the SH is significantly slower and carries less fuel than the SU. Therefore it has to win any fight it gets into quickly as it can't get away if it tries to disengage or outlast them in a fight.

BTW I just found some more info, the F14 could break Mach 2 with 4 phoenix, 2 sparrow, 2 sidewinder. Now thats speed!


User currently offlineBMI727 From United States of America, joined Feb 2009, 15812 posts, RR: 27
Reply 17, posted (5 years 2 months 2 days 5 hours ago) and read 8094 times:



Quoting Spudh (Reply 16):
BTW I just found some more info, the F14 could break Mach 2 with 4 phoenix, 2 sparrow, 2 sidewinder. Now thats speed!

The top speeds we see are not the actual top speeds. There are a lot of round numbers in the specs sheets.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 18, posted (5 years 2 months 2 days 3 hours ago) and read 8080 times:

Yeah, I understand that, F14D is quoted in Janes as having Mach 1.88 top speed but I know that was an operational top speed based on flying with external fuel tanks, even the quoted 2.34 for the A was actually operational limitation (I think radome integrity was the reason). The prototype A had been beyond 2.4 and still accelerating when they stopped the test due to RFP requirements being met, You would expect the B/D with 20% more power to be obviously faster again.

User currently offlineMax Q From United States of America, joined May 2001, 4751 posts, RR: 18
Reply 19, posted (5 years 2 months 1 day 2 hours ago) and read 7978 times:



Quoting Spudh (Reply 16):

BTW I just found some more info, the F14 could break Mach 2 with 4 phoenix, 2 sparrow, 2 sidewinder. Now thats speed!

What a machine! the Navy grounded the best Fighter they ever had.



The best contribution to safety is a competent Pilot.
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 20, posted (5 years 2 months 15 hours ago) and read 7901 times:



Quoting 747classic (Reply 11):
I think nothing is learned, the story repeats itself with the PW F135 on the JSF. IMO, it will be wise to raise some funds to have the alternative engine, the GE/RR F136 on standby

Just pulled some figures out of Gilchrists book, printed in 1994 so well out of date considering it flew another 10 years after that. He states that over 40 airplanes were lost due to compressor stall related crashes at a then cost of roughly 1 billion euro, on top of the 0.25 billion spent on 'band aid' fixes for the engine. I don't have the full attrition figures for the F14 but I bet that this is a significant, maybe 25%, portion of attrition which won't be the case with the F14B/D.
Navy participation in the TF-100 engine (F-15 engine) was cancelled (among other items) and the build run dramatically reduced in 1971 as the complete F14 programme was $400 million in the red.
You're bang on 747Classic, theres a stark lesson in those figures when you look at what's going on with the JSF engine programme. A short term budget gain cost the F14 dearly in the long run and may have proved pivotal if the F14 had been used in cold war anger. At least the F14 was an order of magnitude better than threat fighters air to air which the F35 is clearly not.

It would be interesting to find out how many F16A's were lost due to engine failures since its a single engined comparison to the F35


User currently offline747classic From Netherlands, joined Aug 2009, 2198 posts, RR: 14
Reply 21, posted (5 years 2 months 9 hours ago) and read 7865 times:

From the book (ISBN 1 85260 586 3)
"The Development of Jet and Turbine Aero Engines" by Bill Gunston (second edition) :

Quote 1 :
Even the carefully designed TF30 proved to have compressors which were aerodynamically much too close to the stall line, so that taken in conjunction with the short curving inlets the stall tendency was unacceptable. Even the basic specification was unimpressive".

Quote 2 :
If anything , the TF30 caused even more problems in the F14 than in the F111, and certainly led to more aircraft losses. Navy Secretaries and Admirals called this "the worst engine/airplane mismatch in history". It led via the TF30-412 to the -414 and ultimately to the -414A, in which in a desperate measure to contain fan blades the casing was surrounded by steel, increasing weight from 3,992 to 4,201 lb.

Quote 3 :
The new standard Tomcat engine (F110-400) has dry and after burning thrusts of 16.000 and 27.000 lb. This dramatically improves flight performance, also brings safety and reliability, as well as a new ability to do anything the pilot wishes with the power levers, no matter what the altitude,airspeed, AOA, or yaw.

Quote 4 :
More over , it was found, with the F110 installed, afterburner was no longer needed for catapult launch, and while time-to-climb was reduced by 61 per cent, mission range was extended by 62 per cent! Seldom has a fighter been so improved.


IMO, above mentioned Quotes by Bill Gunston, an authority regarding engine design, speak for them self. But the USN decided otherwise.


View Large View Medium
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Photo © Glenn Beasley - Global Aviation Resource
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Photo © Ashley Wallace




Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineSpudh From Ireland, joined Jul 2009, 301 posts, RR: 1
Reply 22, posted (5 years 2 months 7 hours ago) and read 7844 times:

Great shots!!
Shame about the AMARC one, looks like an F14D CAG bird in the foreground, at least it hasn't been canned yet, are they going to keep a certain percentage as a war reserve or are the whole lot being shredded to keep the Iranian hands off?

I bet the fleet guys gave those planes some wringing, flew them to within an inch of their lives, in the last weeks before they decommisioned. I know I would rules or no rules  Smile


User currently offlineHaveBlue From United States of America, joined Jan 2004, 2121 posts, RR: 1
Reply 23, posted (5 years 2 months 5 hours ago) and read 7829 times:



Quoting Spudh (Reply 22):
I bet the fleet guys gave those planes some wringing, flew them to within an inch of their lives, in the last weeks before they decommisioned. I know I would rules or no rules

Dale Snodgrass sure did, a bunch of times. And I was lucky enough to catch some of his demos, and still get to see him fly his F-86 on the airshow circuit.



Here Here for Severe Clear!
User currently offline747classic From Netherlands, joined Aug 2009, 2198 posts, RR: 14
Reply 24, posted (5 years 1 month 3 weeks 3 days 17 hours ago) and read 7545 times:



Quoting 747classic (Reply 13):
Even in the magnificent movie "TOP GUN" (sponsored by the USN) both TF-30 engines of the Tomcat (F14A) stalled several times and the aircraft came down in a flat spin.

I found this movie shot of an actual F14 flat spin, during testing in 1979.
http://www.youtube.com/watch?v=z7VS9_Ce0sg



Operating a twin over the ocean, you're always one engine failure from a total emergency.
25 Post contains images HaveBlue : " target=_blank>http://www.youtube.com/watch?v=z7VS9...Ce0sg Seen that before on TV but now I have a link of my own! Sad to see such a great aircraft
26 Post contains links 747classic : I was surfing the net for some details of the F-14D and came along this comparison of the Tomcat F-14D with the Super Hornet F/A-18/E/F. Very interest
27 Spudh : Good article, 747Classic, thanks for posting it. I read somewhere else on here that the engine pods of the F14 were the right size to take an F119/F12
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