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YF-17 Design Philosophy, LWF and Boyd

Sundog

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FighterJock said:
Yes I remember the YF-17, the loosing competitor to the F-16. Having seen it in aviation books back in the 1980s when I ordered them out the local library. A great pity it was not chosen because I am sure that it would have made a great fighter for the USAF, apparently there was not that much to separate the YF-17 from the F-16 in the fly off.

There is what SFerrin posted above, which is completely true, but there is more to it than just that. The YF-17 was actually being developed to a European specification, most likely West German. I base that on the fact that they never bought the F-16 and when the LWF competition was won by GD, Dornier started work on the TKF-90, of which the early versions looked like the YF-17. Northrop never said who their "European" customer was driving the design, to the best of my knowledge. As such, the YF-17 wasn't actually designed for the LWF program, though it did influence it's creation.

There was a version of it with a single F-100 engine and I've read various reasons as to why they went with the twin engine; From the USAF wanted a single and twin to compete against each other, since they didn't want two aircraft too similar in the competition, to their "European" customer not wanting a single engine aircraft. I lean towards the latter, though both may be true, as it helps explain further why West Germany never bought the F-16.

As such, I've always felt the YF-17 was somewhat handicapped in the competition as the F-16 was more tailored for the requirements. You also have to consider the YF-17 was more "multi-role" than the YF-16, which was a pure daylight A2A fighter. Of course, after it won the USAF added a whole lot of weight to the F-16 and didn't touch the wing area. It was still a good aircraft but lacking when compared to the YF-16, at least in terms of maneuverability. I think this was partly to keep the F-15 the star of the show. But I also think it was pragmatic, in that if they had increased the wing area at the time they would have greatly increased the cost as well. Which was due to all of the new testing that would have had to been done and the costs of the bigger wing itself.

Having said all of that, if Northrop had entered the single engine YF-17 in the competition, I still think the YF-16 would have won. I base this on the YF-16's FBW FCS and the incredible fuel fraction it has, assuming the flight performance of both aircraft would have been very close.
 

Stargazer2006

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Very, very interesting contribution, Sundog, thanks for this.

Sundog said:
I lean towards the latter, though both may be true, as it helps explain further why West Germany never bought the F-16.

The unparalleled death toll of the single-engined, small-winged F-104 in Germany may have played a decisive part in that respect.
 

overscan (PaulMM)

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Sundog said:
There is what SFerrin posted above, which is completely true, but there is more to it than just that. The YF-17 was actually being developed to a European specification, most likely West German. I base that on the fact that they never bought the F-16 and when the LWF competition was won by GD, Dornier started work on the TKF-90, of which the early versions looked like the YF-17. Northrop never said who their "European" customer was driving the design, to the best of my knowledge. As such, the YF-17 wasn't actually designed for the LWF program, though it did influence it's creation.


Quite incorrect. The YF-17 was designed for the LWF program, based on work done on the existing P-530 Cobra. P-530 was designed in 1966-1969 as a successor to the F-5A/B evolving into a higher-end design for e.g. the F-104 replacement market. Intended customers included existing F-5 users, West Germany, Italy, the Netherlands (who all purchased F-104) and Iran. There was no specific customer.


P-530 was an all-weather fighter design more in the F-18 class. YF-17 was a barebones demonstrator reusing the P-530 design.
 

FighterJock

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Yes and more can be found about the P-530 and the other designs of the naval project that led to the F-18 can be found in the American Secret Projects Book Fighters and Interceptors by Tony Buttler.
 

Sundog

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You can also find more in the book on the YF-17 as well.

However, I stand by my earlier comments as the YF-17 wasn't actually that different from the final Cobra designs, which were completed before the LWF program began. As I said in my previous post, though it would have been more accurate to say the Cobra, rather than the YF-17, partly lead to the creation of the LWF program. Although I'm sure, as most of these things are, it was a combination result of the USAF people, not just Boyd, who thought there should be a LWF, and Northrop actively having that in their mind as well as the Cobra was developed. I'll have to go back and find Lee Begin's interview by Braybrook from Air International to see if there was more information in there.

Though, to that end, I've never seen/read any definitive information on why they went with the twin engined design as opposed to the F-100 powered variant. Also, I haven't seen any definitive info that they used Boyd's work in the development of the YF-17. I'm not saying they didn't, but you always read about the connections between Boyd and Widmer, bot not Begin/Fellers. I'm not saying they not out there, but if you guys have some references I would like to see them. It seems to me that Northrop used high AOA more as a design criterion than Ps.
 

Sundog

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Stargazer2006 said:
The unparalleled death toll of the single-engined, small-winged F-104 in Germany may have played a decisive part in that respect.

The only reason I don't think that would be the premise is that, it's my understanding that most of the F-104 crashes were due to the pilots lack of experience in very high performance aircraft, especially one as demanding as the F-104. I don't recall engine problems being the cause of most of those crashes. Also, did Italy or any of the other NATO operators have the same problems that W. Germany did with them? Was it just because the W. Germans were using them in the strike role more so than any others? I know Canada used them in that role as well. These are just questions I'm asking as I don't have the stats, but it's something to think about.

Of course, I don't know the exact mission the W. Germans were looking for either, as I would be quick to harp on. Didn't they start flying their Phantoms around 1980? Maybe because of Europe's weather they preferred twin engines? Now I'll have to go back and dig up the info on the original F-4F requirements. ;)
 

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I always thought that it was the general design of the F-104 that caused them to crash, being far to sleek for air to ground, the F-104 was supposed to be just for use as a high speed fighter.
 

Stargazer2006

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Sundog said:
The only reason I don't think that would be the premise is that, it's my understanding that most of the F-104 crashes were due to the pilots lack of experience in very high performance aircraft, especially one as demanding as the F-104.

Might have been one factor, but we're talking here about the loss of about 200 aircraft and 93 pilots, if memory serves. 93 PILOTS!

Some very interesting leads here: http://yarchive.net/mil/german_f104_losses.html
 

GTX

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The high Luftwaffe F-104 accident rate was not the aircraft but poor training for pilots on that particular aircraft. This was addressed under Johannes "Macky" Steinhoff with an intensive training regime and the accident rate dropped dramatically.
 

overscan (PaulMM)

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Sundog said:
You can also find more in the book on the YF-17 as well.

However, I stand by my earlier comments as the YF-17 wasn't actually that different from the final Cobra designs, which were completed before the LWF program began. As I said in my previous post, though it would have been more accurate to say the Cobra, rather than the YF-17, partly lead to the creation of the LWF program. Although I'm sure, as most of these things are, it was a combination result of the USAF people, not just Boyd, who thought there should be a LWF, and Northrop actively having that in their mind as well as the Cobra was developed. I'll have to go back and find Lee Begin's interview by Braybrook from Air International to see if there was more information in there.

Though, to that end, I've never seen/read any definitive information on why they went with the twin engined design as opposed to the F-100 powered variant. Also, I haven't seen any definitive info that they used Boyd's work in the development of the YF-17. I'm not saying they didn't, but you always read about the connections between Boyd and Widmer, bot not Begin/Fellers. I'm not saying they not out there, but if you guys have some references I would like to see them. It seems to me that Northrop used high AOA more as a design criterion than Ps.


While the F-X requirement was slimmed down under Boyd's influence from a tubby 60,000lb to 40,000lb, Sprey & Boyd were convinced it was still too large and that their studies showed a design under 25,000lb to be optimal - which they dubbed F-XX or "FX squared". Sprey validated his analysis with Northrop and General Dynamics. Northrop were already well advanced on the design of the P-530 while General Dynamics had worked on single engine and smaller size F-X designs. By late 1968, both companies had validated the F-XX concept. In June 1969, Sprey's paper "F-XX and VF-XX - Feasible High Performance Low Cost Fighter Alternatives" used the Northrop N-700 P-530 variant [perhaps N310 / P700?] and General Dynamics FX-404 designs to substantiate their work. Riccioni's "Falcon Brief" in 1971 used the Boeing 909-618, Northrop N314-2 (another P-530 version), and a General Dynamics 401(?) design [Stevenson gives FW71-274-VG1369 which is a drawing number not a model number] to illustrate his concepts. So Northrop were on board from the very beginning of LWF.

The P-530 started life as N-300, an advanced F-5 design, with twin engines. It was aimed as an F-5 and F-104 replacement. As the design evolved through N-300 versions, P-530, P-530-2, P-530-3, its size increased, these twinengines were single spool, high T/W J97(GE1/J1A1) turbojets (8,000lb), then its development the GE1/J1A2 (10,000lb), then this was replaced by the GE15/J1A5 (initally 13,000lb, then 14,300lb) twin spool "leaky turbojet", which become the J101. Northrop were convinced they could sell P-530 as an F-104 replacement to various NATO countries including West Germany and the Netherlands.

The LWF program represented a great chance for Northrop to build a demonstrator for their P-530 design. Unfortunately for Northrop, as LWF finalised a consensus was developing around 20,000lb and a single F100 (e.g. General Dynamics, Boeing, LTV). P-530 was larger, 25,000-27,000lb. Northrop still had its eye firmly on the NATO nations and felt P-530's larger size and twin engines were right for this market. Neither Northrop nor General Dynamics had the benefit of hindsight to know they were in fact playing for a huge USAF acquisition as well as foreign sales, so the engine commonality factor was not a big consideration - noone minded buying J85 engines for their F-5s. The J101 engine bypass ratio was also more optimal for an air-air fighter mission and it was simpler and less challenging in terms of pressure ratio than F100. Also Northrop & GE had close relationships from F-5 days and had worked long and hard on matching the airframe, intakes and engines, work that would be lost by switching to F100. The P-610 was Northrop's attempt to leverage the P-530 work into a lighter weight F100 powered design, but its designer Bill Roth died of a heart attack before finalising it, and it was never accorded the same importance as the P-530 derived P-600. It threatened to invalidate the years of work put into the P-530. Apparently P-610 was submitted mostly at the insistence of Sprey & Boyd.
 

overscan (PaulMM)

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Regarding the West German connection, lack of F-16 orders, and TKF-90:

In 1968 West Germany, the Netherlands, Belgium, Italy and Canada formed a working group to examine replacements for the Lockheed F-104 Starfighter initially called the Multi Role Aircraft (MRA), later renamed as the Multi Role Combat Aircraft (MRCA). Britain joined, Canada, Belgium and the Netherland exited, and in 1969 Britain, Italy & Germany launched what became the Panavia Tornado. Italy & Germany were supposed to get a single seat fighter (Panavia 100) with Britain getting a twin seat strike version (Panavia 200). Everyone ended up with a strike optimised design. Germany bought interim F-4Fs for the fighter mission instead and began planning to replace them eventually, which led to the TKF-90 (and a determination to not let the Brits turn that into another strike aircraft :))
 

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PaulMM (Overscan) said:
Regarding the West German connection, lack of F-16 orders, and TKF-90:

In 1968 West Germany, the Netherlands, Belgium, Italy and Canada formed a working group to examine replacements for the Lockheed F-104 Starfighter initially called the Multi Role Aircraft (MRA), later renamed as the Multi Role Combat Aircraft (MRCA). Britain joined, Canada, Belgium and the Netherland exited, and in 1969 Britain, Italy & Germany launched what became the Panavia Tornado. Italy & Germany were supposed to get a single seat fighter (Panavia 100) with Britain getting a twin seat strike version (Panavia 200). Everyone ended up with a strike optimised design. Germany bought interim F-4Fs for the fighter mission instead and began planning to replace them eventually, which led to the TKF-90 (and a determination to not let the Brits turn that into another strike aircraft :) )


And what happened to the TFK-90? The West Germans (at that time) joined the European Fighter Program (Eurofighter) and scrapped TFK-90, then wanted over 90% control over the production of the Typhoon program which then ended up being a multi-role fighter.
 

Sundog

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Thanks Paul! That's exactly the information I was looking for with regard to the LWF's development.
 

BillRo

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During this period Northrop strongly believed that fighters should have two engines. Similar to the US Navy philosophy, they felt that the survivability aspect was too important to ignore. The P610 would only have been proposed at the insistence of the customer. Although I have no direct knowledge, I would not expect the single engine design proposal would have received the same level of attention as what became the YF-17. It was unfortunate that the advantage of having a common engine for both the LWF and the F-15 was too large to overcome.

Another basic Northrop tenet was that the aircraft should take care of itself without the pilot having to worry about it, allowing the crew to concentrate on situational awareness and the mission. They had excellent Aero and Flight Controls groups to make sure that happened.

After his Air Force career, Col. Riccioni found a home at Northrop and every few months gave presentations to Advanced Design people on his philosophies, using his characteristic arrow as a pointer. Walt Fellers continued his connections with Germany and Dornier with his ND 102.

BillRo
 

overscan (PaulMM)

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Indeed. Lee Begin even told Roy Braybrook in an Air International interview that a twin engined aircraft was actually lighter than an single engined one.
 

robunos

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Braybrook/Begin interview can be found in 'Air International,January 1971, pp.15-26...

cheers,
Robin.
 

LowObservable

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The J85 had excellent thrust/weight ratio, and I believe the J101 promised more of the same. Getting comparable T/W out of a larger engine required far more time and money than requested, considering that the F100's early problems stayed unfixed until the mid-1980s. Other things being equal, too, a twin can be shorter. On the other hand, the F-17/18 shape is complex and has been bedevilled by excess drag in all its incarnations.
 
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Just to elaborate on the YF-17 evolution...
The design process started with the N-300 in c.1966 which was essentially an evolution of the F-5 design.

This evolution continued through P530, P530-1 (introduced twin tails & longer LERX), P530-2 (tails moved forward, more LERX), and the larger P530-3 Cobra.

The two designs Northrop pitched to the initial LWF RFI were the P600 twin engine and P610 single-engine concepts, both of which were lighter than the P530-3, and these went up against GD's 401 design, the LTV V-1100, Lockheed CL-1200, and the Boeing 908-909.

After being shortlisted along with GD, the P600 was designated the YF-17 for the LWF/ACF competitions.
 

overscan (PaulMM)

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Braybrook/Begin interview can be found in 'Air International,January 1971, pp.15-26...

cheers,
Robin.

Air International January 1971 doesn't exist, as far as I know. June 1971 was the first issue and it was called Air Enthusiast then.
 

AeroFranz

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The correct issue is January 1976, the article is titled "Fighter Design philosophy".;)
 

robunos

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I've checked, AeroFranz is correct, 'Air International', January 1976, pp.15-21.

cheers,
Robin.
 

Sundog

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Thanks - I'll check it out.

I think I may have already sent that to you. If not, I'll check tomorrow, as I definitely have that article scanned to my PC.

Hi Paul, it's in the zips titled "Begin vs. Braybrook" Let me know if you have them.
 
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AeroFranz

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that was an excellent article...btw, if you can think of other similar articles, i'd be interested to find out. I have inherited a stack of AI but have not gone through all of them - it's kind of daunting!
 

Sundog

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that was an excellent article...btw, if you can think of other similar articles, i'd be interested to find out. I have inherited a stack of AI but have not gone through all of them - it's kind of daunting!

Read anything by Roy Braybrook. His opinion pieces are hilarious. "How they ever got to the moon?" is excellent. I'm not sure that's the exact title, but it's something similar.
 
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