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Unread postPosted: 22 Sep 2008, 08:31
by johnwill
XL did not need a canard, as it already possessed superior nose pointing capability, significantly better than the F-16. A canard was studied but proved to be of no significant benefit anywhere in the flight envelope.

CFT on XL? The wing itself is a CFT, nearly doubling the F-16 internal fuel capacity.

Why was the F-15E selected? Very simple - it was good enough and it preserved the F-15 production line. During the competitive fly-off with XL, the E lagged behind in the ability to lug 12 Mk-82 at high speed, low altitude conditions (range and speed), because it carried the bombs on underwing pylons. When the XL semi-conformal underwing carriage proved to be so successful, Mac quickly adapted their conformal tanks to mount the bombs. All credit to Mac for adopting the XL low drag carrige to the E. Without that, they probably would have lost the competition.

Unread postPosted: 22 Sep 2008, 10:05
by geogen
johnwill wrote:CFT on XL? The wing itself is a CFT, nearly doubling the F-16 internal fuel capacity.


Good point jw. But perhaps the CFT would allow that wet/dry station to hold some 'dry' such as a JASSM or 3,000lb GBU, or...??

Obvious plus is: hard to go wrong with more rcs/drag-reducing efficiencies, while adding extra endurance.

Unread postPosted: 22 Sep 2008, 19:39
by ViperDude
renatohm wrote:If there were politics involved also, e.g., keep the F-15 production line open, GD scandal, etc., we will never know unless someone directly involved in the decision telling it.
EDIT: mispelling :oops:


Well I worked both F-16XL's out at EAFB from the summer of 1984 (I was the Avionics Specialist) until the last flight before going to NASA. Politics were involved, and keeping the F-15 line open was one of the issues, and as I remember it the XL had a much better range and payload then the F-15E did. Heck we had 17 Hardpoints with 29 stations for external storage.

As far as engines I remember at one point have a J-79 engine in there that caught fire when the fuel spray bar came loose and melted 3/4 of the turkey feathers on the engine...we almost lost an XL that day.

Cheers,

ViperDude

Unread postPosted: 23 Sep 2008, 03:49
by johnwill
geogen,

With the XL fuselage stretch, bigger wing, more fuel, more weapons, etc, the gross weight of the XL reached as much as 48,000 lb. That really pushed the capability of the landing gear to handle all the extra weight. We used some Isreali F-16 gear components to increase capability, but any production XL would have required a full redesign of the gear and fuselage substructure. Add in CFT and the problems are compounded. Of course, they could be made to work, but there is a point beyond which little is gained by adding more fuel and weapons.

ViperDude,

I was structural flight test leader for GD on XL at Eddy in 1982, so maybe I ran into you then. I did the same job on AFTI at NASA Dryden in '84 and '85.

My memory of the J-79 differs from yours. As I recall, the J-79 F-16 was F-16B No. 2, not either of the XLs.

Unread postPosted: 23 Sep 2008, 06:50
by geogen
johnwill,

I salute your service to the XL. (my favorite prototype and one which I'd still support as influence for a next-gen Viper). I'd be curious then, as to your opinions about the plausibility and requirements necessary for a flying F-16X type tailless model someday?

I totally understand your point about a production model needing more structural redesign from the prototype model. That would be expected with F-22 or F-35 program as well.

Unread postPosted: 23 Sep 2008, 07:00
by TC
IIRC, the powers that be also saw the Strike Eagle as less a departure from its original design than the XL. The XL was deemed "radical" by some, whereas the Strike Eagle was seen as simply a modified D model. This also played a role in the decision-making process.

Unread postPosted: 23 Sep 2008, 14:26
by ViperDude
johnwill wrote:My memory of the J-79 differs from yours. As I recall, the J-79 F-16 was F-16B No. 2, not either of the XLs.


You know what? your right...It was B-2 with the J-79. Hey I'm getting a little fuzzy after 25 years..lol. There is a famous photo of the XL shooting an AGM-65 off and I was the one who wired that to work. The station we fired off of had wiring that was messed up from a fire at one point? and so I had to use the wiring from a the next station over for the AGM-65 to come off.

I was out at EAFB from 1984 to 1993 and except for the 1st couple years I ended up being a flight test engineer and conducted over 575 missions out there. I'm sure we crossed paths out there at some point. When I got there Floyd Finberg (a Korean War Ace) was the Chief of Flight Test and then replaced by Toby Bensinger. I am still in touch with one of the original designers of the F-16 Flight Controls Bill Clark, not sure if you knew any of them.

I also have quite a few crew pictures from my days on the XL including a picture of the last flight before both XL's went to NASA (I think I have previously uploaded it here on this website.) Thanks for jogging my memory.

Cheers,

ViperDude

Unread postPosted: 23 Sep 2008, 15:54
by johnwill
ViperDude,

All the guys you mention were good friends. Floyd was so easy-going, I never realized he was a fighter pilot. Toby and I came out from Fort Worth at the same time for XL, liked the area and the work so much, he decided to stay for about 15 years before he went to Japan as Lockheed chief engineer on F-2.

geogen,

With elevons and ailerons on the XL wing, XL could be a good starting point for a tailless prototype. As you know, XL already lost the ventrals, so maybe they could lose the vertical too. A 3D TV nozzle might help too.

Unread postPosted: 23 Sep 2008, 16:03
by ViperDude
johnwill wrote:ViperDude,

All the guys you mention were good friends. Floyd was so easy-going, I never realized he was a fighter pilot. Toby and I came out from Fort Worth at the same time for XL, liked the area and the work so much, he decided to stay for about 15 years before he went to Japan as Lockheed chief engineer on F-2.


Last time I saw Floyd he was rollerblading down the street in Lancaster..lol and Toby is retired and living in Washington State, I spoke to him about a year ago.

Cheers,

ViperDude

Unread postPosted: 25 Sep 2008, 04:23
by johnwill
Last time I saw Toby (1986), he was raising donkeys in Quartz Hill and loving it. I knew he retired to a place southeast of Seattle, but not sure where. When we moved to Lancaster in 1984, he and Irene were away for a few weeks on a wind tunnel trip to Langley, so he let us live in his house until our apartment (Park Somerset) was ready. I missed him in Japan, as he left there before I came. Good news about Floyd, as I did not know anything about him since '86. Thanks for the update.

Unread postPosted: 25 Sep 2008, 05:39
by geogen
johnwill,

Just curious if you have any info of F-2 requiring major redesign of the gear since it has about the same max take-off weight as the F-16XL and maybe 500lbs less empty weight vs XL?

I researched the basics on F-2s frame strengthening. And yes, I would support a future F-16X type (or XL) variant perhaps, integrating critical F-2 program data to assist development, as a supplement to F-35 program for US and worldwide FMS.

I'd propose a joint R&D plan between Japan, AUS, US, and perhaps Korea and even India. Maybe a 3 year $7-10 billion total development? Production by 2012? Nothing wrong with competition, you know what I'm talking about? :)

Unread postPosted: 25 Sep 2008, 07:46
by johnwill
Well, I spent a year and a half working in Japan at Gifu AB on structural flight test, but never had occasion to be curious about the gear re-design. The F-2 did not require additional flight test to verify gear loads, so I did not worry about it. I also don't recall the max TOGW of the F-2 or how it compared to XL. I suspect the F-2 used an Israeli F-16 gear design, since those GW are similar.

As far as F-2 providing input to an advanced F-16, I don't see much benefit there, but remember I am a structures guy and know little about other systems. The F-2 structure was supposed to show some advancements, but it did not work out that way. The co-cured wing for example was no better than the aluminum F-16 wing and in some ways it was worse.

The F-2 primary mission (anti-shipping, keep the sea-lanes open) is also quite different from XL. Don't get me wrong, I'd love to see a fully developed XL, but have no hope it will ever happen. :cry:

Unread postPosted: 26 Sep 2008, 07:29
by ViperEnforcer
johnwill wrote:geogen,

With the XL fuselage stretch, bigger wing, more fuel, more weapons, etc, the gross weight of the XL reached as much as 48,000 lb. That really pushed the capability of the landing gear to handle all the extra weight. We used some Isreali F-16 gear components to increase capability, but any production XL would have required a full redesign of the gear and fuselage substructure. Add in CFT and the problems are compounded. Of course, they could be made to work, but there is a point beyond which little is gained by adding more fuel and weapons.



I believe the XL was what the initial implementation of the heavy weight gear. The IAF Block 30 F-16Cs, which were the first production F-16s to get the heavy weight landing gear, were not built until the mid 80s. Ship 1 XL was retrofitted with the heavy weight gear in early 83 and ship 2 a few months later. The XLs were the first F-16s of any type to receive the heavy weight gear.

From reading over some of the program details as well as looking at many photo archives, the XLs rolled out with the light weight gear. The heavy weight gear was not ready at that point, though both jets did have the bulged MLG doors on roll out.

Mike V

Unread postPosted: 15 Mar 2009, 18:41
by darkvarkguy
Does anybody have any pictures of an XL fully loaded out with weapons?

Unread postPosted: 15 Mar 2009, 20:21
by cywolf32
Here are some I found. :D