YF-17

[KJ_Lesnick]

I was thinking about the YF-17 and I'm curious about something fairly simple: Why did the design end up inferior to the YF-16 in almost every parameter? 

Northrop was a good aircraft designer, they were highly innovative, and already had a large basis of knowledge available on the F-5

[Alvis 3.14159]

You'd have to look at the whole story of how the F-16 concept came about to get an idea of why the F-17 didn't make the cut. While part of the F-17 came out of inhouse Northrop ideas for an F-5 replacement, the F-16 came out of the rejection of the upward spiralling cost/size/complexity mentality in the USAF/Pentagon. Several USAF officers were driving the rquirements for a new, lightweight plane, and they helped create the F-16 by such demands. General Dynamics was able to take the ideas and come up with something new, several other companies merely dragged out updated older designs.

Part of the procurement process dictated there should be two planes to choose from, and the idea of a single engined plane also didn't fly with everyone, so the F-17/P-350 Cobra design entered the fray as the alternative to the single engined F-16. Apparently, there were people at Northrop who wanted to field a single engine variant, but were over ruled.

From what I recall reading, the F-17 design wasn't that bad, it's just that the F-16 was that much better. Range was an issue, and the F-16 had a really incredibly good fuel fraction, and had a range far outstripping most other planes of the day. Realising that their F-16 had to be leaps and bounds above what else existed, the designers at GD were likely pressed to do more freash new approaches, rather than merely improving something already underway. A fresh sheet of paper will often yield better results.

If I recall correctly. I'm sure others here have more accurate info.

Alvis Pi

[KJ_Lesnick]

You'd have to look at the whole story of how the F-16 concept came about to get an idea of why the F-17 didn't make the cut. While part of the F-17 came out of inhouse Northrop ideas for an F-5 replacement, the F-16 came out of the rejection of the upward spiralling cost/size/complexity mentality in the USAF/Pentagon.

That I know, but still the aim was essentially the same: A small, low-cost, extremely agile, air-to-air fighter...

General Dynamics was able to take the ideas and come up with something new, several other companies merely dragged out updated older designs.

Why did GD use a completely new design while the others didn't?  Also, though the F-17 was inspired by the F-5, the designs were fundamentally different in a number of ways.

Part of the procurement process dictated there should be two planes to choose from, and the idea of a single engined plane also didn't fly with everyone, so the F-17/P-350 Cobra design entered the fray as the alternative to the single engined F-16.

I understand the idea of having a fly-off between two aircraft, but why did the USAF want the YF-17 to have a twin-engined set-up?  Some people said that it was for experimental purposes to evaluate single and twins, but a book on Col Boyd stated that Boyd wanted both designs to be single-engined but a General overruled him because he couldn't imagine a single-engined fighter (makes no sense to me, but hey)

Range was an issue, and the F-16 had a really incredibly good fuel fraction, and had a range far outstripping most other planes of the day.

I thought both airplanes had fuel fractions over 30%...

[bearmatt]

I'm currently building a yf-16 and I read about the lwfighter story.

One reason, why the F-16 was chosen, was also because of the engine-type. It has the same as the F-15. And this was a very important advantage for the air force as far as logistics, maintenance and costs goes.
Of course, GD checked twin engine concepts. But by then, the engines had become so reliable, that the risk was negligible.
Especially in comparison of what their weight and cost saving would be, if they went for a single engine concept.

I have to check out, what else there was in this book. But they also stated the exceptional low fuel consumption of the F-16.

[KJ_Lesnick]

One reason, why the F-16 was chosen, was also because of the engine-type.

That I know, and it really baffles me why the USAF wanted a single and twin design.  Admittedly for technology demonstrators (they were made to appear as tech-demonstrators so there'd be little resistance to them so the proponents could get the foot in the door) having variants that have 1 and 2 engines does make sense, but I'm not sure if that was the critical decision.  

Regardless for a cheap lightweight fighter, only one engine is really needed.

[The Rat]

...so the F-17/P-350 Cobra...

Alvis Pi

P-530 actually[/pedantic_rat_strikes_again]

[Alvis 3.14159]

...so the F-17/P-350 Cobra...

Alvis Pi

P-530 actually[/pedantic_rat_strikes_again]

Dyslexic Alvis strikes again!

One rationale behind a twin engined design being requested was that the idea of a single engined plane gave (and still gives) some people the heebie jeebies. Twin engined, in some circles, means more reliability. In the case of the LWF program, twin engined would also mean more maintenance, so that may have been a factor in the favour of the F-16.

One reason GD may have gone with a clean sheet of paper was that they didn't already have anything in a fighter design in service. Also, after the drubbing they received over the F-111 program, they wanted/needed to prove they could make something affordable, simple, and reliable.

While Boyd and his acolytes were pushing for a truly Light Weight Fighter, many opposed him and his ideas. Procurement would have been a factor in the whole program, and according to what Boyd said, there were several warmed over old designs submitted that didn't meet his criteria, but those companies had the ear of important people in the procurement system. Thus, the whole "Technology demonstrator" dance, just so they planes wouldn't be axed before they got a chance to prove their mettle.

Ironically, Northrop had tried to sell the USAF on a lightweight fighter when they began their F-5/T-38 series of planes, but higher ups never caught onto the idea. The idea of bigger/faster/larger/longer range/faster/more expensive seemed very entrenched, and the company that had been known for big expensive planes, General Dynamics, wound up creating the F-16 still perplexes me. As far as I know, the F-17 didn't borrow much from the F-5, but was the next logical step by the Northrop designers. I guess you could say it was evolutionary, whereas the F-16 was revolutionary.

I'm not certain of the actual range capability of the F-17, but the F-18, while a very different airplane, was heavily criticised when it was first being evaluated as having poor range.

Alvis Pi

[KJ_Lesnick]

Dyslexic Alvis strikes again!

One rationale behind a twin engined design being requested was that the idea of a single engined plane gave (and still gives) some people the heebie jeebies. Twin engined, in some circles, means more reliability.

I suppose you're right, but there have been a lot of fighters historically that only had one engine.  For the most part, every single fighter prior to the P-38 seemed to be twin-engined, the P-80/F-80, F-84, F-86, XF-91 and XF-92, F-94, F-100, F-102, F-104, F-105, and F-106 were all single-engined designs.

Ironically, Northrop had tried to sell the USAF on a lightweight fighter when they began their F-5/T-38 series of planes, but higher ups never caught onto the idea.

Which was a real shame because the F-5 was an amazing performer

I'm not certain of the actual range capability of the F-17, but the F-18, while a very different airplane, was heavily criticised when it was first being evaluated as having poor range.

The F-18 might have been based on the F-17, but they had little in common by the time they were finished.

[PR19_Kit]

For the most part, every single fighter prior to the P-38 seemed to be twin-engined

Eh? Surely a misprint?

I can't find a SINGLE twin engined USAAC fighter prior to the P-38.............

[kerick]

[/quote]


Dyslexic Alvis strikes again!

One rationale behind a twin engined design being requested was that the idea of a single engined plane gave (and still gives) some people the heebie jeebies. Twin engined, in some circles, means more reliability. In the case of the LWF program, twin engined would also mean more maintenance, so that may have been a factor in the favour of the F-16.

[/quote]
Two engines means twice as much stuff to go wrong! (IMHO)

[PR19_Kit]

Two engines means twice as much stuff to go wrong! (IMHO)

That's actually true.

When I used to work out reliability figures the MTBF (Mean Time Between Falures) was divided by the number of the components I was considering in the study. So if an engine had an MTBF of 400 hours, two of them had an MTBF of only 200 hrs, and thus the pair of them were more likely to go wrong in theory.

Having said that I've never found that it worked like that in the real world, and these days I'll bet they use some uber-sophisticated PC based software that takes all these things into account, not to mention the time of High Tide and London Bridge, to come up with a more accurate answer.

[kerick]

The Navy may use the term reliability but the real issue was being able to limp back to the ship/base over many miles of open water instead of being lost in the ocean. This would include combat damage as well as part failure. So I do see the Navy's point about two engines on their aircraft. It can be a comprimise between getting back home and extra complexity.

[rickshaw]

The Navy may use the term reliability but the real issue was being able to limp back to the ship/base over many miles of open water instead of being lost in the ocean. This would include combat damage as well as part failure. So I do see the Navy's point about two engines on their aircraft. It can be a comprimise between getting back home and extra complexity.

However, as experience with the F-16 has shown, this belief about reliability has been shown to be false.  The Norwegian Air Force operates F-16s on long, over-ocean flights and hasn't lost one IIRC to a failed engine.   Engine reliability, particularly Jet engine reliability has increased considerably since the 1950s when that view came into vogue.    With the F-35, the Navy has finally recognised that (along with the difficulties of making a VTOL aircraft with two engines) and decided to accept the compromises that a single-engine configuration brings.

[kerick]

I'm sure you are right but I can still hear the old timer pilots grumbling about the designers not being the ones getting wet!

[jcf]

The current level of turbine engine reliability has far more to do with civil air transport
requirements than it does with any military aircraft. The military products have been
the beneficiary of the commercially driven improvements.

Twin engine airliners regularly fly routes that, at one time, would have been considered
unthinkable. Currently the 777 family is type-approved up to ETOPS-330, that is 330 minutes
flight with a full load on only one engine. Airbus has indicated plans to certify the A350XWB to 350
minutes.

There is no truth to the rumour that ETOPS actually stands for Engines Turning Or People Swimming.