F-16XL

Unread postPosted: 18 Feb 2008, 05:32
by PeFo
So, it was politics for the most part why the XL was never put into production? I know the 15 won the contract, but if the XL has superior handling characteristics and could carry more fuel and payload why did they go with the current set up with the F-16?

Unread postPosted: 18 Feb 2008, 06:30
by TimmayMan
They wanted to keep F-15 production lines open.

But honestly the way the train and fly it would be nice to have XLs in place of the blk 40s and maybe even 50. Maybe even if the U.S. bought into CFTs we wouldn't have to waste hours and hours a week on reconfiguring jets. Or maybe we would still.

Unread postPosted: 19 Sep 2008, 21:09
by F16JOAT
The original project was CRAD funded. The delta wing has always been on the design tables as an alternate configuartion, even the F-111 had a delta wing proposal. The F-16XL just happened to come along at a time when the opportune time just happened to be during the second competition fly off for both the F-16/F-15 with new upgrades. I still would like to put a GE-132 in it , that 680 inlet will ram more air than any other inlet to make that engine produce above red-line in no time! :D :D :D

Unread postPosted: 19 Sep 2008, 22:57
by Master-of-Disaster
It's really a shame that the F-16XL project never got further than the two jets now owned by NASA.
It still is the most beautiful plane ever if you ask me.

Unread postPosted: 19 Sep 2008, 23:08
by F16JOAT
One one remains in NASA's testing. The other has gone to static display last I heard. I also had contract with crew chief a while back and I believe NASA is trying to get an engine upgrade to a current PW-229 and when who knows. :D Maybe some one in th eforum might speak up!

Unread postPosted: 20 Sep 2008, 07:17
by geogen
Concur re: GE-132 (or equivalent) rated power upgrade for F-16XL-type variant. Is my actual baseline conceptualized for a potential 'Super Viper'. Perhaps add CVV fins and CFT to this model and even 2-D (or axisymmetrical) thrust vectoring option.

Rate of climb would be phenomenal compared to Block 50 and F-15E for one thing.

Unread postPosted: 20 Sep 2008, 16:22
by JetTest
Maybe a great idea, but don't hold your breath waiting for it to happen.

Unread postPosted: 20 Sep 2008, 16:30
by FlightDreamz
If I remember correctly, General Dynamics got caught in a big scandal overbilling the U.S. Government over some contract and that played a hand in the F-16XL losing to the F-15E.

Unread postPosted: 20 Sep 2008, 17:33
by renatohm
Source: http://ausairpower.net/TE-F-15E-Strike-Eagle.html An article from the time of selection states:
"MDC's win may be attributed to several factors, firstly the mature airframe and systems of the F-15, secondly the advanced state of the F-15E/APG-63 SAR development program which ran (company funded initially) since the late seventies, thirdly the F-15's ability to carry more bombs further, and finally the 87% spares commonality with the F-15C/D."
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:

GE-132 in F-16XL

Unread postPosted: 20 Sep 2008, 22:18
by F16JOAT
geogen wrote:Concur re: GE-132 (or equivalent) rated power upgrade for F-16XL-type variant. Is my actual baseline conceptualized for a potential 'Super Viper'. Perhaps add CVV fins and CFT to this model and even 2-D (or axisymmetrical) thrust vectoring option.

Rate of climb would be phenomenal compared to Block 50 and F-15E for one thing.


The CVV (AFTI variant) wouldn't be such a good idea, delta wing aerodynamics does not lend to side slipping as some lift would be lost off the swept as the swept angle would increase beyond 73 deg and that's not good. CFT's would be a good idea, it just might help the transonic airflow boundary layer near the wing root which was a subject of one of NASA's programs ( they redesigned the wing glove on one side to a more rounded leading edge than the traditional sharp strake blended edge).

Vectoring Nozzle, well we had it tested on a standard F-16 with the GE-AVEN, but look where it went, see any planes flying with it? Lockheed ( just bought out GD when the test program started) couldn't do a good job on the sales to the customers ( NAVY and Air-Force). Navy didn't like the idea of being a sitting duck in some maneuvers where KE was lost to recovery a fast enough maneuvering speed to get out of a combat situation ( T remember that presentation clearly).

How ever, that GE-132 with the 680 inlet on the present F-16XL would be a valuable asset to that combination as it is the largest airflow inlet that any F-16 has carried.

RE: GE-132 in F-16XL

Unread postPosted: 21 Sep 2008, 00:40
by flames
I'm just putting an idea out. But what if they some how put canards on to the F-16XL??

Unread postPosted: 21 Sep 2008, 01:38
by FlightDreamz
I'm just putting an idea out. But what if they some how put canards on to the F-16XL??

Sounds like an americanized eurofighter. :roll:

Unread postPosted: 21 Sep 2008, 02:10
by flames
True. I never said it was a good idea just an idea. Besides it just might turn out better than the eurofighter :whistle:

Re: GE-132 in F-16XL

Unread postPosted: 21 Sep 2008, 04:35
by geogen
F16JOAT wrote:
geogen wrote:Concur re: GE-132 (or equivalent) rated power upgrade for F-16XL-type variant. Is my actual baseline conceptualized for a potential 'Super Viper'. Perhaps add CVV fins and CFT to this model and even 2-D (or axisymmetrical) thrust vectoring option.

Rate of climb would be phenomenal compared to Block 50 and F-15E for one thing.


The CVV (AFTI variant) wouldn't be such a good idea, delta wing aerodynamics does not lend to side slipping as some lift would be lost off the swept as the swept angle would increase beyond 73 deg and that's not good. CFT's would be a good idea, it just might help the transonic airflow boundary layer near the wing root which was a subject of one of NASA's programs ( they redesigned the wing glove on one side to a more rounded leading edge than the traditional sharp strake blended edge).

Vectoring Nozzle, well we had it tested on a standard F-16 with the GE-AVEN, but look where it went, see any planes flying with it? Lockheed ( just bought out GD when the test program started) couldn't do a good job on the sales to the customers ( NAVY and Air-Force). Navy didn't like the idea of being a sitting duck in some maneuvers where KE was lost to recovery a fast enough maneuvering speed to get out of a combat situation ( T remember that presentation clearly).

How ever, that GE-132 with the 680 inlet on the present F-16XL would be a valuable asset to that combination as it is the largest airflow inlet that any F-16 has carried.


I hear ya about 'lift' problems, interesting point. Instead of horizontal-flight flat turns however, my thinking for CVV benefit was more in line of J-turn, post-stall and helicopter maneuver enhancers (and perhaps even more stability at low level flight)? Perhaps it could further add to lower speed landings combined with Delta wing and 2-D TVC, for shorter landings??

The rate of climb with the GE-132 however could be what, north of 65k'/min?

Unread postPosted: 21 Sep 2008, 06:46
by sferrin
FlightDreamz wrote:
I'm just putting an idea out. But what if they some how put canards on to the F-16XL??

Sounds like an americanized eurofighter. :roll:


Nah, that would be one of the other "Hornet 2000" configurations that lead to the Super Hornet. Seriously, one of the concepts ditched the horizontal stab and had a canard instead.

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

Unread postPosted: 16 Mar 2009, 00:47
by darkvarkguy
Thanks, those are great! Some have said here it carried a bigger weapons load than an F-15E. I guess I can't see it visually. I mean I've seen pictures of a Strike Eagle with about a dozen Mk-20s, Aim-9s and 120s. I see the XL has a lot of hardpoints but can those stations carry multiple bomb racks too?

Unread postPosted: 16 Mar 2009, 04:00
by johnwill
The photos just posted show the XL carrying 12 Mk-82, 4 AIM-120, and 2 AIM-9. I believe that's essentially the same as what you attribute to the F-15E.

The XL did not carry multiple-bomb racks, as the single-bomb rack loadings were lighter and less draggy.

Unread postPosted: 16 Mar 2009, 04:53
by darkvarkguy
12 Mk-82s are a lot less weight and size than 12 Mk-20s (CBU-100).

Unread postPosted: 16 Mar 2009, 05:38
by geogen
darkvarkguy,

Hmmm, are you sure about that? A Wiki search notes 490 lb CBU-100? Also, there would have apparently been one heavy wet/dry station under each wing, so those could have hypothetically carried a multi-rack? And if the cranked-arrow was ever indeed constructed, perhaps an SDB twin-rack could attach to each underwing point. Otherwise, while the 15E/K could probably carry more 2k class ordnance, Johnwill pretty much summed it up: 'the XL would have more sleekly carried a similar requirement of 12 500lb class munitions + 4 + 2 AAM' (emphasizing asset of a less draggy/lower profile aircraft).

Given that, I wouldn't necessarily protest F-15Es one day turned over to NASA for a little 'crank-arrow', (possible tailless), Reverse-thrust Vectoring GE-132 surgery. That's another forum, I know :drool:

Unread postPosted: 16 Mar 2009, 09:15
by plant#4
darkvarkguy wrote:Does anybody have any pictures of an XL fully loaded out with weapons?

and another view....

Unread postPosted: 16 Mar 2009, 15:31
by johnwill
In design load analysis of Mk-20 loadings, we (General Dynamics) used approximately 500 lb, same as Mk-82.

Unread postPosted: 16 Mar 2009, 16:34
by darkvarkguy
I guess you're right. CBU-100s just seemed heavier because of their size but I then again they are hollow. The XL may have been cleaner fully loaded aerodynamically but the 'E' has twice the thrust. As you can see by my quote I am a big proponent of Strike Interdiction.

Unread postPosted: 16 Mar 2009, 17:27
by StolichnayaStrafer
Yeah- cool as the F-16XL is, it is pretty easy to see why they went with the Strike Eagle. The twin engines and the conformal tanks option from before made a real easy start for conversion from fighter to interdictor.

Did they ever compare the F-16XL to a regular F-16 in a strictly Air to air comparison before? I'm very curious to hear how the XL version performs in that aspect.

Unread postPosted: 16 Mar 2009, 18:07
by Guysmiley
I love the "which way'd he go?" camo in that first pic with the fake canopy/refueling markings/v-stab shadow!

Unread postPosted: 16 Mar 2009, 23:35
by johnwill
darkvarkguy wrote:I guess you're right. CBU-100s just seemed heavier because of their size but I then again they are hollow. The XL may have been cleaner fully loaded aerodynamically but the 'E' has twice the thrust. As you can see by my quote I am a big proponent of Strike Interdiction.


There were good reasons for choosing either airplane. But the XL could haul 12 MK-82 downtown faster and much cheaper than the F-15E. Twice the thrust means twice the fuel among other things.

StolychnnayaStrafer wrote:Did they ever compare the F-16XL to a regular F-16 in a strictly Air to air comparison before? I'm very curious to hear how the XL version performs in that aspect.


Of course. Results were mixed. XL generally had a better initial pitch rate, so could make the first turn into the target better. But, like deltas in general, it had lower sustained g capability. XL had 9g turn capability, same as F-16, but had higher rolling g capability, 7.2 vs 6 for F-16. It also had a flight control refinement which allowed the pilot to command a max roll at any g level, all the way to 9g. Roll rate was automatically reduced above 7.2g. On the F-16, max roll commands are allowed up to 6g only. The XL had a higher maximum speed than the F-16, but slower acceleration.

It was never allowed to go to its max speed at or above 50k for fear of embarrassing others. Remember the wing was based on NASA work for SST development. You know where they cruise.

Unread postPosted: 16 Mar 2009, 23:54
by StolichnayaStrafer
Very interesting- thanks for the enlightenment, johnwill! :thumb:

Unread postPosted: 17 Mar 2009, 05:09
by cywolf32
What a view!! Its just too bad we didn't buy any......

Unread postPosted: 17 Mar 2009, 07:58
by viper1234
It was never allowed to go to its max speed at or above 50k for fear of embarrassing others. Remember the wing was based on NASA work for SST development. You know where they cruise.


I'm curious if you remember its theoretical top end at high altitude. I'm sure the low altitude limits remained unchanged since the canopy and inlet appeared unchanged. I would be surprised if actual top end was much higher (in practice) than the current Vipers due to the poor high altitude performance of the inlet/engine.

Can you remember any Air-Air missile testing from the inner stations? It sure looks like there was a potential for substantial interference issues (missile exhaust to engine) from those positions assuming they were rails rather than ejectors (which I assume based on bomb clearance)

Cheers

Unread postPosted: 17 Mar 2009, 09:41
by geogen
StolichnayaStrafer wrote:Very interesting- thanks for the enlightenment, johnwill! :thumb:


Copy that..

I'd be further curious: what performance enhancements, e.g., improved sustained G and acceleration, could be estimated from say a GE-132 power upgrade? If any at all? Perhaps they would have had to put a 'max speed limiter' on it at half-throttle though?

Thus an XL-derivative would arguably be even more feasible today (ahem), Air-Air wise, than in the 80s-90s standards with regards to lower relative 'sustained' turn performance as stated., given HOBS/helmet system and better longer-range ordnance?

Imagine that... an overall superior, cheaper, higher speed, longer-ranged air-superiority fighter + superior strike. Go figure. :shock:

Unread postPosted: 17 Mar 2009, 15:37
by johnwill
viper1234 wrote:I'm curious if you remember its theoretical top end at high altitude. I'm sure the low altitude limits remained unchanged since the canopy and inlet appeared unchanged. I would be surprised if actual top end was much higher (in practice) than the current Vipers due to the poor high altitude performance of the inlet/engine.

Can you remember any Air-Air missile testing from the inner stations? It sure looks like there was a potential for substantial interference issues (missile exhaust to engine) from those positions assuming they were rails rather than ejectors (which I assume based on bomb clearance)

Cheers


I don't know of any work done to determine the max speed/altitude capability. 810 kcas/2.0 mach was the structural design limit. The airplane exceeded 2.0 at 50k and had more available. The powers that be were correctly reluctant to go much beyond what could be supported by analysis, even though everyone wanted to see what it could really do.

There was no missile launch work done from the inner stations. I have mentioned on another thread, those missiles were complete dummys, bolted in place with no launchers installed. A production XL would have had ejector launchers.

The aft missiles inadvertantly led to an inflight structural failure of the left speedbrake. The missile was mounted directly in front of the lower speedbrake panel. What no one realized was the missile blocked airflow on that panel. The speedbrake mount is designed for a maximum 60/40 distribution of load between the upper and lower panels. Wih the lower panel blocked, that ratio was more like 80/20 and the mount failed at 1.6/30k when the speedbrake was extended. That knocked out one hydraulic system too, so the airplane landed safely on one system.


geogen wrote:I'd be further curious: what performance enhancements, e.g., improved sustained G and acceleration, could be estimated from say a GE-132 power upgrade? If any at all? Perhaps they would have had to put a 'max speed limiter' on it at half-throttle though?


Sustained g can only be improved two ways, less drag or more thrust. So going to a higher thrust engine , whether GE or PW, would benefit sustained g.

Unread postPosted: 17 Mar 2009, 15:38
by darkvarkguy
The plans for an FB-22 included a design evolution that resulted in a delta wing configuration where the horizontal stabs were replaced with incorporated elevons so you would think an evolving design for the Viper would be (would have been) the XL. Woulda, coulda, shoulda.

Unread postPosted: 08 May 2009, 16:55
by vin
I am one of the XL crew chiefs at Nasa/DFRC. I have read some (not all) of the posts regarding XL. Please, let me tell you all a few things about it. The F16XL does not have a true delta wing design. The wing on XL is called a "cranked arrow" shape. XL carries 12000 lbs of fuel and it has 19 store stations. It is stretched 54 inches longer than a standard F16, and the engine bay angle is configured 3 degrees lower than a standard F16. It has LEF's but no PDU to drive them. XL2 was the F16 that tested the Laminar Glove concept. It has not flown for years and will not ever fly again. Its sitting on our ramp waiting to be ripped and stripped. The reason why Uncle Sugar never purchased XL for production is because of this: Back in the day, under contract, GD was required to produce so many of each model of F16 for FMS. Due the the cranked arrow wing desing the Gov't didnt want anyone else to have the acft. There were numerous factors driving the decision not to purchase XL models, but the main driver was the wing. To date, XL's cranked arrow wign design is the most aerodynamically efficient wing design ever. It is still so advanced in its design that (until early 2009) Boeing was considering rebuilding XL1 for its wing shape. They were going to lengthen the nose a few feet, cut the vert in half and tee-tail it, install a GE129, install an upgraded avionic system, and modify the drag chute compartment to provide an extra 10 feet off the back. Why?... Boeing is considering a new supersonic airliner concept and they wanted the XL to test this concept. Anyway when the "powers that be" sat down to calculate the $$$ involved, they decided that XL needed too many TCTO's and upgrades to make it financially worth the effort. Well, that was XL1's last chance to ever fly again folks. XL1 has not flown for approx 10 years. Last year we defueled it, repaired the engine bay fuel leaks, performed initial service of the LDG, stuffed an F15 engine in it, and ran thru hyd ops checks (no hyd leaks on the entire acft after 10 yrs sitting). Then we taxi'd the plane around Edw just to prove we could get it up and running. XL ship 1 is now a done deal. It will be end up "popsickle sticked" somewhere on Edw. Sad... its the last of a one-of-a-kind generation of acft.

Unread postPosted: 08 May 2009, 17:19
by cywolf32
Wow Vin,

Thanks for the info!! Never would have crossed my mind that the wing technology in itself would be a major kill to the XL program. Interesting indeed. Sad, sad, sad.

Unread postPosted: 08 May 2009, 18:50
by Goodwin
What it would be nice to do is to take XL-2 and transport it to the Udvar Hazy Museum where its cranked wing would be most appreciated if it were hung up in the rafters for all to see. That is a lot better than simply scrapping it.

Unread postPosted: 08 May 2009, 19:02
by Goodwin
Politics may well have been the US State Department's concerns about the range of the F-16XL as they knew the Israel Air Force would want several F-16XL squadrons vice Block 52 F-16C/D's first procured in 1986. Having those capable planes on hand would have enabled them to mount a successful air strike against the Iranian nuclear program much earlier than 2006 and to be able to do the missions whenever needed. Yes, I would have rather have the XL to nicely complement the Strike Eagle. About FMS requirements to produce sufficient numbers of each type, Congress forbade the sale of F-22's to close allies and it would not have been a problem for us to simply keep the XL for our own use.

Unread postPosted: 08 May 2009, 23:30
by johnwill
The reasons stated above for not producing rhe XL are pure speculation. I was on the program, and was told by the USAF flight test team leader that the AF liked the XL very much, but needed to keep the F-15 production line open. There was no money for both.

As far as being the most efficient wing design ever, you'd better qualify that by saying, "for supersonic cruise", as it wouldn't be true for all flight conditions.

And, to clarify the LEF drive statement, XL did not have a PDU because the LEF were far out on the wing and were driven by motors just inboard of each LEF segment.

Unread postPosted: 09 May 2009, 00:39
by whynot
Hey wassup y'all? I am not trying to start anything here and I usually just read these posts and kinda chuckle at whats being said. The one thing I've noticed though is there is always some who "Has all the answers" and always is there to correct what they think is wrong! Now mind you I'm not the smartest F-16 guy on here, 24 years worth, and maybe more so then others but thats not the point. The point is, if "You're" so smart then why you on here trying to impress us? Whats your day job? If your the "Answer Man" Then give us proof, show us evidence and make us believe!! Don't just verbally regurgetate to sound smart. I know everyone thinks they know the"Real Deal" but honestly, do they???

If that Vin guy is crewing the XL at Edwards then show us pics, if Johnwill was there on the program then cut and paste documents to show us. From what I know, based on the current aircraft I work on, the LEF statement sounds to be true. Believe me it's possible! Oh and they are PDU's (Power Drive Units)

Anyway lets just have fun, talk about the Viper and not be so uppity with each other. (You may think your the smartest guy on here but theres always someone who thinks their smarter)

Peace Out, Raptors rock!! :cheers:

Unread postPosted: 09 May 2009, 09:04
by F16guy
whynot wrote:Now mind you I'm not the smartest F-16 guy on here



Uh...Somebody call me? And are they saying I'm not smart or they are not smart? And why should I have to prove anything anyway?


Bluto: Kroger, your Delta Tau Chi name is Pinto.
Pinto: Why "Pinto"?
Bluto: [belches] Why not?

Unread postPosted: 09 May 2009, 11:33
by popcorn
I'm assuming that the XL was going to be a single-seater whereas the F-15E had 2 guys in the cockpit. I'd read somewhere that this gave the latter an edge when evaluating both designs as the workload of flying the airplane and operating the weapons systems was shared. Would the avionics at the time have allowed for effective operationof the aircraft with only a single pilot?Obviously tech has advanced significantly in the decades that followed making possible the F-35 and F-22.

Unread postPosted: 09 May 2009, 16:16
by whynot
F16guy wrote:
whynot wrote:Now mind you I'm not the smartest F-16 guy on here



Uh...Somebody call me? And are they saying I'm not smart or they are not smart? And why should I have to prove anything anyway?


Bluto: Kroger, your Delta Tau Chi name is Pinto.
Pinto: Why "Pinto"?
Bluto: [belches] Why not?


Sorry if I offended you! Remember, No blood, No foul! :wink:

Late to comment, but whathehell

Unread postPosted: 09 May 2009, 16:23
by Gums
Salute

Re-read the thread.

For life of me I can't remeber John "wolfman" 's last name. he was one of us from Hill that went down for the fly-off. Also was the guy that showed us why we had the FLCS power supply problem from uncommanded EPU start-up. He saw the green "run light" just before the plane went end over end.

We got a few briefings and were impressed with the jet as a mud-beater.

From my memories:

- The thing could sit at 600 knots on the deck using about 90% power while hauling 12 x 500 pounders. Apparently, the semi-recessed store stations really made a difference on drag.

- The internal fuel load was awesome, so range was really, really good. Once expended, you could grab alt and zoom home real fast using lots less gas than the Eagle.

- The FLCS had a feature to help from getting into the classic "delta" drag problem at high AoA. As with original Viper limiter, you could pull all you wanted, but when you got slower the AoA was more limited than the A/B models we were flying then. Initial pitch rate was better, but as you slowed down you were limited more than you would like. Having made my bones in the Deuce, I am very familiar of the delta's nose-pointing ability and the horrendous drag rise if we held the stick back too long. I don't think the XL would be as good as the A/B was back then for air-to-air.

- John-boy and others answered a question I had about the gear. We all knew that the gear had to be stronger to handle the weight. Hell, one reason we never saw a Navy Viper was the wimpy gear. Even the Hornet designers beefed up theirs from the YF-17.

+++++++++++++

I always liked neat-looking jets, and the XL fit the bill.

I always liked carrying a lot of eggs and going fast, and the XL fit the bill just fine.

I always liked not having to worry about running outta gas, and my SLUF experience was awesome. I would have felt the same way in the XL.

As with our current procurement decisions, we can't have a zillion different planes that are too specialized. And the more you can make of the same basic design, then the lower the unit cost and overall cost. Politics and a better air-to-ground radar system in the Strike Eagle made a big difference in the source selection.

The 'vark was still viable then and LO was not the "driver" in designs. We were all surprised that USAF was looking at a replacement for it at the time. Hell, I only had one joy ride in the thing down at Cannon and it was a delight to fly and could go real fast low using min gas for such a big plane. Landed the thing on first approach with all of my 2 hours of "experience" racing over New Mexico at low alt, heh heh. Sucker was like on a rail coming down final, so pilot let me land it.

Gums sends...

Unread postPosted: 09 May 2009, 16:46
by johnwill
Whynot,
Thanks for your comments. I agree we should not be "uppity", and I apologize if I sound that way. But, If I see something I don't agree with, or know for a fact is wrong, you can be sure I'll tell you my opionion. If that's "uppity", so be it. As far as people providing proof of who they are, I'll take your word and Vin's word that you are both who you say, and expect you to do the same. I don't need to give you proof, as the proof is in the answers. I'm not here to play games or impress anyone, don't need to. My "day job" is being retired from General Dynamics/Lockheed Martin following forty years as a structural flight test engineer.

popcorn,
XL number 2 was in fact a two-seater, and the production proposal included one and two seat versions.

Unread postPosted: 09 May 2009, 18:41
by plant#4
Interestingly enough, the wing jigs for the Xl were kept for over 20 years on the west lot at Fort Worth. That's not saying a lot, because they kept tooling for the F-111 for over 25 years before it was scrapped out.....

Unread postPosted: 10 May 2009, 05:21
by geogen
Salute to the XL concept, indeed... along with the -AT, the -X and the like 'woulda shoulda couldas'. With CFT, IRST, 32k class power, LOAN, AESA and 4 semi-recessed AMRAAM (among other upgrades), the interceptor role alone would have been re-invented and kept superior for decades.

Unread postPosted: 10 May 2009, 08:05
by cywolf32
Thought you all might enjoy this clip:

http://www.youtube.com/watch?v=ecM1-ISN ... annel_page

Cheers

Unread postPosted: 10 May 2009, 16:05
by popcorn
Thanks for the clarification Johnwill.

Unread postPosted: 02 Jun 2009, 18:22
by F16JOAT
Answer to the canards would be a plus. NASA did some external aero tests after they acquired the planes. Remember a few discussion to help air flow over the leading edge strake area to help with the Hi-AOA where roll off stability was hard to control.

Unread postPosted: 02 Jun 2009, 22:11
by johnwill
Canards were considered by GD during the XL design phase, but showed no improvement over the chosen design. XL had better high AoA handling characteristics than the basic F-16, even though XL did not have ventral fins.

Unread postPosted: 02 Jun 2009, 22:26
by F16JOAT
Oh right remember the ventral exercise along with the engine nozzle. Take-off and landing approach coupled with the 3 degree canted fuselage from the main landing gear aft would have resulted in grinding off about 3/4 of the effective height of the ventral. By the way, on the 4th flight Hi angle T/O the PW 220 on the #2 did scratch the turkey feathers some but not much. Made the performance guys go back to the table to double check the numbers. AFT CG issue was big factor.

Unread postPosted: 03 Jun 2009, 03:59
by geogen
Hats off to you guys, johnwill and JOAT. Thanks for your service..

My dream bird even today would be an F-16XL type, (perhaps with a later 'Finless' block and all new FCS), with CFT to possibly assist even better high AoA roll stability control characteristics, LOAN, LO inlet, 32k class power and possible CCV-type control fins for even better low altitude stability as well as improved high AoA control??

I'm pretty sure that if that bird was already developed by now as it should have been, it would be selling like hotcakes for another 10 yrs.

Unread postPosted: 03 Jun 2009, 19:38
by F16JOAT
As a matter of fact, maybe Johnwill might remember the special project where we did just that. Proposal for a tailess version of an F-16XL look alike. I think the paper proposal also added a tipped canard to the wing as oppose to the "cranked arrow design". The tips reminded me of the Rockwell X-B70 configuration.

Unread postPosted: 05 Jun 2009, 00:22
by ViperDude
whynot wrote:
If that Vin guy is crewing the XL at Edwards then show us pics, if Johnwill was there on the program then cut and paste documents to show us. From what I know, based on the current aircraft I work on, the LEF statement sounds to be true. Believe me it's possible! Oh and they are PDU's (Power Drive Units)


Okay here is my proof...I have no idea why I even have to prove myself on here.

I worked XL1 and XL2 from the summer of 1984 until day they left for NASA in late 1985. I mainly worked avionics but worked primarily Weapons and Flight Controls on them. Back then we had 2 USAF assigned personnel to the aircraft and one guys name was Bernie and the other we called Sargent Mary and she is in the 400hr photo of XL1. Every time an aircraft completed 100 flights we took a group photo. Maybe JohnWill can remember them as well. Anyway enjoy the photos and I am in them as well. The sad thing is that quite a few of the people in these photos have passed on, and one of those guys just passed away not too long ago but if you ever knew good old "Doc Blanchard", he was one great guy and a lot of laughs.

Image

Me Im standing 10 from the left, and Sgt Mary is right up front.

Image

This is the last official photo taken of Xl1 & XL2 while assigned to the F-16 CTF. They had just landed after completing the last flights together before going to NASA. I believe this is late 1985, and I am standing just to the left of XL1's pitot tube.

Image

Great shot over the water...with external fuels tanks

~Viperdude

Unread postPosted: 05 Jun 2009, 03:21
by F16JOAT
You don't need to prove anything, anyone on the forum who has worked the XL's from GD to delivery at EAFB will know who's kidding who in the forum. Especially myself. I know for fact we did not deliver XL2 to EAFB with a F100-GE-110, it had another designation and very few people especially the propulsion set will know. It was shortly removed later after a few flights to return to GE since it was not GFE but a research engine modified by GE. A GE-110 production was later installed for continued flight test.

Unread postPosted: 05 Jun 2009, 03:27
by cywolf32
Respects Vdude. I envy those who have the opportunity for these assignments. Speaks much of you character and intelligence. And thanks for the pics!! Much appreciated.

Unread postPosted: 11 Aug 2009, 21:34
by F16JOAT
Gee a GE-132 with an AVEN nozzle in a XL????

No kidding, I wonder who would like a flag ship like this that never could be beaten not even by today's new toys.

Unread postPosted: 12 Aug 2009, 06:07
by geogen
Nah, not the ANG.. they're into Hornets now.

Re: XL: Higher speed, higher rate of climb, better AoA, better range/endurance, lower RCS, higher payload...

There should be 300 at least in service by now replacing block 30s/40s (at a fraction of the cost), I'm sorry. Capable for the next 15+ yrs to match likely Mig-35/Su-30x.

Respects to those involved w/ this TIE FIGHTER program indeed, way ahead of it's time.

Unread postPosted: 02 Jul 2010, 21:16
by madrat
ViperDude, thanks for the pictures!

Unread postPosted: 03 Jul 2010, 06:16
by geogen
Oh please folks... do not bring up the F-16XL again like this. Ever. It's aruably the most historic, decisive loss to cost-effective tacair deterrence strategy planning, the USAF (and perhaps FMS) never had.. :nono:

God speed.

Unread postPosted: 03 Jul 2010, 13:29
by cywolf32
Its an open forum Geo. Many posters know how you feel regarding the XL. That does not mean that newer posters cannot opine on the subject. Obviously this poster feels the same as you. Me too infact. But it does not change the events that happened. Live and learn? In most cases not. Politics are just like taxes. No end in sight......

Respectfully

Unread postPosted: 07 Jul 2010, 21:02
by Obi_Offiah
Looking at the head-on pictures of the XL, I'm wondering if they would have retained the same stores stations and Aim-120 recesses with production aircraft. It looks like there's a possibility of stores collison with the inside station when launching an AMRAAM?

I'm also curious to know how the XL would handle various other weapon configurations. It manages well with 12 500 pounders and AMRAAM's (excluding stores collison if that is a problem?), but what about mixes of LGB's and GBU's such as the GBU-15 and AGM-130?

An F-15E with 12 MK-82's still has space for a mix of 3 2000lb GBU's or GBU's and AGM-65's

Unread postPosted: 09 Jul 2010, 07:17
by geogen
True, the F-15E class would likely still be the heavier hanger of the two (albeit at an even heavier cost to range), given twice the power and bigger airframe. The XL could probably still accomodate 2x 2k lb class stand-off load-out though, plus 12-16x mixed SDB and 500lb class load and the rear 2 AMRAAM. Perhaps up to 16x SDB or 500lb class load and possibly 18x with the twin centerline rail, could be plausible in addition to the 2x rear AMRAAM. In air-air role, there would be more load parity though, with XL seemingly capable of carrying 4x AMRAAM class, 4x heavier ESSM class, plus the two wing-tip load a centerline drop tank and IRST Shadow Pod. What would have been interesting, is if an XL-customized CFT could have been effective and feasible, both aerodynamically and in relying less on drop tank.

Off-topic, I'd be curious if F-2 could be upgraded to an XL standard as an advanced jet option (with possible follow-on new build) and to force-multiply the existing fleet in question?

Below pics pulled off the net.

Unread postPosted: 09 Jul 2010, 20:18
by Obi_Offiah
Thanks geogen, interesting comments.

The weapon station diagram is very helpful. I didn't realise that there was actually space for 8 MK-82 size weapons per wing.

What about ECM. Would pods still have been needed?

Unread postPosted: 10 Jul 2010, 02:28
by johnwill
Hi, Obi!

During my time on XL (until May, 1983) stations 2, 3A, 15A, and 16 were never loaded. Honestly, until I did some research on XL about two years ago, I did not even know they were there.

Unread postPosted: 10 Jul 2010, 05:04
by codeonemagazine
I scanned Harry Hillaker's public presentation on F-16XL he did for Lone Star Aero Club many years ago. (Admins) let me know if you want them. Bunch of jpegs. Too detailed for my site.

Unread postPosted: 10 Jul 2010, 13:19
by FlightDreamz
codeonemagazine
I scanned Harry Hillaker's public presentation on F-16XL he did for Lone Star Aero Club many years ago....Bunch of jpegs.

Ohhhh! Post them, post them! 8)

Unread postPosted: 12 Jul 2010, 19:44
by Obi_Offiah
johnwill wrote:Hi, Obi!

During my time on XL (until May, 1983) stations 2, 3A, 15A, and 16 were never loaded. Honestly, until I did some research on XL about two years ago, I did not even know they were there.


Hey John, how've ya been :) ?

Well then the rest of us can definately be excused as well, for not noticing :P
I wonder why GD didn't mount them, particularly when demonstrating the XL's carriage capability, I mean 16 bombs will alway look better than 12. Perhaps those stations weren't ready/fully integrated?

BTW what was the function of the pod like structures on the wings, the parts that gave the false impression of a folding outer wing?

What would the XL be like now if it had won the competition, one wonders?

Unread postPosted: 12 Jul 2010, 19:46
by Obi_Offiah
codeonemagazine wrote:I scanned Harry Hillaker's public presentation on F-16XL he did for Lone Star Aero Club many years ago. (Admins) let me know if you want them. Bunch of jpegs. Too detailed for my site.

Those would be a great addition to the site codeonemagazine. :thumb:

Unread postPosted: 12 Jul 2010, 20:52
by Obi_Offiah
I've just been looking over some of the XL pictures. I noticed that in the following picture stations 3A and 15A are loaded:
Image


In the following image station 16 is loaded:
Image


The following is an interesting picture because the aircraft is loaded with 4 MK-84's:
Image


This lovely over water image posted earlier, shows the aircraft carrying SUU-64/65/66 dispensers as opposed to the more common MK-82's seen in pictures. Its also illustrates how station 13F is tilted slightly upwards:
Image


There is also a picture with the aircraft carrying 6 Maverick missiles on the net.

Unread postPosted: 13 Jul 2010, 02:27
by johnwill
Obi,

I knew as soon as I said those stations were never loaded, someone would find a photo to prove me wrong. How about this - I think they were never flown. The 12 Mk-82 loading was an Air Force mission requirement, so both the XL and the F-15 Strike Eagle made many flights to demonstrate range, max speed, and safe separation of that load.

As an aside, early in the flight test, the F-15 SE carried 12 Mk-82 on wing pylons and MERs. They saw we were beating their butts on range and speed, so requested a delay in the test program. During the delay, they added six hard points on each of their conformal fuel tanks and completely transformed the airplane with much lower drag. It was very clever and done with remarkable speed. It made the range and speed capability close to the to the XL (although it used twice the fuel and ride quality sucked at low altitude). It won the competition for them - well-done, MAC!

About 13F being tilted, all the wing hardpoints followed the wing contour. That way, all the small pylons would fit at any wing hardpoint.

In your original comment about possible interference between the forward AMRAAM and the adjacent weapon, right you are. Any production XL would probably have had to move the AMRAAM inboard slightly. The pods on the wing contain the aileron actuators. Because the aileron hinge line is swept, and the actuators have to stay perpendicular to the hinge line, the actuators do not lie fore and aft, but are rotated. That is why the pods are so wide.

Unread postPosted: 13 Jul 2010, 05:18
by geogen
Fascinating, thanks. OK, I'm curious now if Obi can track down a pic out there of 4x external tanks on 2H, 16H, 4H and 14H ever being tested; or if Johnwill could offer any input on that loadout's feasibility?? One could only wonder what a strategic ferry range could look like, when hypothetically coupled w/ CFT too? You'd hardly need any tanker support?!? Talking about green fighter forces and cutting down on footprints - via not requiring the extra Tankers being launched in the first place! :mrgreen:

And perhaps a follow-up question re: the actuator pods, if known: I've been curious if there would there have been any space in the aft pointy pod section to house let's say, a towed decoy, etc? Thanks in advance..

Unread postPosted: 13 Jul 2010, 07:32
by johnwill
geogen,

No doubt, 4 tanks (plus maybe a CL tank) would give a huge ferry range. CFT frees some wing hardpoints, but for all these loadings, the problem is max gross weight. The XLs were limited to 48,000 lb, mainly due to landing gear strength and brake energy limits for refused takeoff. Certainly, a production airplane would have had a redesigned gear,

To give an idea of ferry range, an FB-111 once flew from Fort Worth to Paris unrefuelled, with six 600 gal tanks on board, plus additional tanks in the weapon bay. That's almost 5000 miles. Not saying the XL could do that, of course.

The aft half of the actuator pod was empty, just a fairing over the actuator. That may have had some function in area rule management, but I don't really know. I'm pretty sure something would have gone in there in a production airplane.

To answer your wondering about the F-2, it has a modular fuselage like the F-16, so should be capable of similar stretching and plugging. No reason it could not be developed into an F-2 XL. The F-2 JASDF mission is anti-shipping, so great range is not required, but the added weapon load capability might be worth it. As always, cost is the problem. Due to its low production, the F-2 is one very expensive airplane.

Another XL story. Looking at the posted hardpoint layout is becomes clear the aft AMRAAM was located directly in front of the speedbrake, partially blocking airflow to the lower speedbrake panel. At low airspeeds, this was not a problem. However, at 1.6 mach, 30,000 ft, it caused all kinds of problems. The speedbrake is a balanced design, meaning no more than 60% of the total load could be applied to either the upper or lower panel. When the brake was deployed, there was very little load on the lower panel, so an immediate structural failure occurred, accompanied by a loud noise and severe shock load felt by the pilot. Oddly enough, the failure was not visible to the chase pilot, so the maneuver was repeated (a very bad idea). This time the noise and shock was much stronger, followed by total hydraulic failure in either system A or B, whichever drives the brake. Fortunately the remaining system was able to bring the airplane back and get it stopped on the runway. The AMRAAM effects had been completely missed by the aerodynamics and structural engineers during design of the XL.

Unread postPosted: 13 Jul 2010, 13:00
by LinkF16SimDude
Image
How do ya tell someone that put that much work into a model that nice that they misspelled "Goddess"? :doh:

Unread postPosted: 13 Jul 2010, 13:51
by fiskerwad
LinkF16SimDude wrote:How do ya tell someone that put that much work into a model that nice that they misspelled "Goddess"? :doh:


One way would be to post it on the world wide web?
(J/K, Link. The devil made me do it!)
:-)
fisk

Unread postPosted: 14 Jul 2010, 19:31
by Obi_Offiah
johnwill wrote:Obi,

I knew as soon as I said those stations were never loaded, someone would find a photo to prove me wrong. How about this - I think they were never flown. The 12 Mk-82 loading was an Air Force mission requirement, so both the XL and the F-15 Strike Eagle made many flights to demonstrate range, max speed, and safe separation of that load.

As an aside, early in the flight test, the F-15 SE carried 12 Mk-82 on wing pylons and MERs. They saw we were beating their butts on range and speed, so requested a delay in the test program. During the delay, they added six hard points on each of their conformal fuel tanks and completely transformed the airplane with much lower drag. It was very clever and done with remarkable speed. It made the range and speed capability close to the to the XL (although it used twice the fuel and ride quality sucked at low altitude). It won the competition for them - well-done, MAC!

About 13F being tilted, all the wing hardpoints followed the wing contour. That way, all the small pylons would fit at any wing hardpoint.

In your original comment about possible interference between the forward AMRAAM and the adjacent weapon, right you are. Any production XL would probably have had to move the AMRAAM inboard slightly. The pods on the wing contain the aileron actuators. Because the aileron hinge line is swept, and the actuators have to stay perpendicular to the hinge line, the actuators do not lie fore and aft, but are rotated. That is why the pods are so wide.

As usual John thanks for the great insight to the project :thumb:

Unread postPosted: 14 Jul 2010, 20:42
by Obi_Offiah
geogen wrote:Fascinating, thanks. OK, I'm curious now if Obi can track down a pic out there of 4x external tanks on 2H, 16H, 4H and 14H ever being tested; or if Johnwill could offer any input on that loadout's feasibility?? One could only wonder what a strategic ferry range could look like, when hypothetically coupled w/ CFT too? You'd hardly need any tanker support?!? Talking about green fighter forces and cutting down on footprints - via not requiring the extra Tankers being launched in the first place! :mrgreen:

Unfortunately I haven't seen the any pics of the XL configured with 4 tanks geogen. If it had entered production I wonder if it could have been cleared to carry the 600gal tanks. Imagine four of those, a centreline tank and CFTs :shock: :shock: :shock: . Excluding the CFTs you'd be looking at an external fuel capacity of 18500lbs and an external load thats over 20000lbs. johnwill has already stated the gear limitations for the prototypes, but if the gear could be made robust enough the unrefueled could be immense.

In terms of required space I can't see why it couldn't carry 8 MK-84's leaving the centreline for an ECM pod or tank. Another possibility would be for 2 wing tanks, 6 MK-84's and a centreline tank or pod. Both of those would be serious stores loads, very impressive.

Unread postPosted: 14 Jul 2010, 20:47
by Obi_Offiah
johnwill wrote:Another XL story. Looking at the posted hardpoint layout is becomes clear the aft AMRAAM was located directly in front of the speedbrake, partially blocking airflow to the lower speedbrake panel. At low airspeeds, this was not a problem. However, at 1.6 mach, 30,000 ft, it caused all kinds of problems. The speedbrake is a balanced design, meaning no more than 60% of the total load could be applied to either the upper or lower panel. When the brake was deployed, there was very little load on the lower panel, so an immediate structural failure occurred, accompanied by a loud noise and severe shock load felt by the pilot. Oddly enough, the failure was not visible to the chase pilot, so the maneuver was repeated (a very bad idea). This time the noise and shock was much stronger, followed by total hydraulic failure in either system A or B, whichever drives the brake. Fortunately the remaining system was able to bring the airplane back and get it stopped on the runway. The AMRAAM effects had been completely missed by the aerodynamics and structural engineers during design of the XL.

Was this problem ever cured or had McD won the competition bt that time?

Unread postPosted: 14 Jul 2010, 20:52
by johnwill
No attempt was made to cure the problem on the XL demonstrators. A flight limitation was issued to prohibit speedbrake extension above some airspeed, 500 kt, I think.

Does anyone else on F-16.net remember Spy vs. Spy in Mad Magazine? That photo of the Godess Air Force looks like a perfect airplane for Spy vs. Spy.

One other point, only four MK-84 or similar 2000 lb. store could be carried. They are mounted on "H" hardpoints, 2H, 4H, 14H, and 16H.

Unread postPosted: 14 Jul 2010, 23:37
by outlaw162
"What, me worry?"

--- .-..

:D

Unread postPosted: 15 Jul 2010, 03:19
by Obi_Offiah
johnwill wrote:One other point, only four MK-84 or similar 2000 lb. store could be carried. They are mounted on "H" hardpoints, 2H, 4H, 14H, and 16H.

The reason I thought 8 MK-84's may be possible, was because in the image below the aircraft seems to be fitted with 2 special pylons on the left and right wing, that occupies stations 5A, 5C, 5F on the left wing & 13A, 13C, 13F on the right wing, each holding two MK-84's. This leaves stations 2H and 4H on the left wing and 14H and 16H each free to carry a single MK-84?
It would be one hell of a loadout if it were possible, shame.
Image

Unread postPosted: 15 Jul 2010, 03:31
by Obi_Offiah
Double post.

Unread postPosted: 15 Jul 2010, 05:49
by johnwill
Although there was enough length for tandem Mk-84 at the inboard station, clearance with 4H and 14H might have been a problem. Interference aerodynamic drag with closely spaced stores can be a problem even if there is physical clearance. Separation is an entirely different problem, sometimes adversely affected by closely spaced stores (as with F/A-18 E/F).

There is something visible in your latest photo you may not have noticed. If you look carefully, you can see the lower surface of th forward fuselage is painted black with a white disk on it. There is also more black paint and another white disk on the lower surface of the inlet. Taken together, the idea was to make the lower view of the airplane look like the upper surface from an enemy viewpoint. Why? To possibly confuse the enemy as to which way the XL might maneuver. A similar scheme was tried on some F/A-18s.

Unread postPosted: 15 Jul 2010, 06:09
by fiskerwad
johnwill wrote:There is something visible in your latest photo you may not have noticed. If you look carefully, you can see the lower surface of th forward fuselage is painted black with a white disk on it. There is also more black paint and another white disk on the lower surface of the inlet. Taken together, the idea was to make the lower view of the airplane look like the upper surface from an enemy viewpoint. Why? To possibly confuse the enemy as to which way the XL might maneuver. A similar scheme was tried on some F/A-18s.


Same idea was used on a few A-10s, John. They painted a canopy lookalike on the bottom of the fuselage to confuse the bad guys.
fisk

Unread postPosted: 15 Jul 2010, 06:34
by Prinz_Eugn
Canadians still have the false canopy, they even painted one on the airshow demo jet (but had the color fit in with the scheme). I saw it at an airshow, it was kinda funny looking, I'm sure a few people were confused.

Unread postPosted: 15 Jul 2010, 14:12
by ViperDude
There was an F-16XL reunion over the 4th of July weekend in Ft Worth, TX, and it might make some of you happy to know that
XL-1 may be in the skies again very soon!! Stay tuned.

ViperDude

Unread postPosted: 15 Jul 2010, 15:59
by Obi_Offiah
johnwill wrote:Although there was enough length for tandem Mk-84 at the inboard station, clearance with 4H and 14H might have been a problem. Interference aerodynamic drag with closely spaced stores can be a problem even if there is physical clearance. Separation is an entirely different problem, sometimes adversely affected by closely spaced stores (as with F/A-18 E/F).

That's a very good point.

johnwill wrote:There is something visible in your latest photo you may not have noticed. If you look carefully, you can see the lower surface of th forward fuselage is painted black with a white disk on it. There is also more black paint and another white disk on the lower surface of the inlet. Taken together, the idea was to make the lower view of the airplane look like the upper surface from an enemy viewpoint. Why? To possibly confuse the enemy as to which way the XL might maneuver. A similar scheme was tried on some F/A-18s.
I can understand the black paint mimicking the canopy, but what is the purpose of the white circles, it had to simulate reflections?

Unread postPosted: 15 Jul 2010, 16:00
by Obi_Offiah
ViperDude wrote:There was an F-16XL reunion over the 4th of July weekend in Ft Worth, TX, and it might make some of you happy to know that
XL-1 may be in the skies again very soon!! Stay tuned.

ViperDude

:cheers: fingers crossed.

Unread postPosted: 15 Jul 2010, 18:09
by johnwill
The white disks represented helmets.

Unread postPosted: 15 Jul 2010, 20:01
by Obi_Offiah
johnwill wrote:The white disks represented helmets.

Thanks John. :cheers:

Unread postPosted: 15 Jul 2010, 23:53
by lampshade111
While I love the F-15E, the F-16XL is still an amazing design in my opinion. Yet the lack of stealth means it is pretty much a dead end these days.

However there must have been some disadvantages to the cranked arrow wing design. If not, why wouldn't such a wing have been used on the F-35 or later designs?

Also, was the top speed of the F-16XL any higher than that of a normal F-16?

Unread postPosted: 16 Jul 2010, 01:41
by johnwill
The XL wing, like any delta wing, has a flatter lift coefficient curve than a wing with lower sweep angle. So for a given wing area, it takes more angle of attack to produce a given amount of lift. More AoA in itself is not a bad thing, but along with more AoA comes more drag increase. Deltas also tend to have higher takeoff landing speeds (no flaps). Canards can be added to help reduce some of the disadvantages. Deltas are best suited for high speed cruise (Concorde, SR-71, B-70, B-58) and interceptors (F-102, F-106).

The top speed of XL was higher than the F-16, but by how much, we'll never know. At high altitude, high mach the climb rate and acceleration was excellent, but airplane was limited to 2.05 mach since analysis and testing had not been done to support higher speeds.

XL photos

Unread postPosted: 17 Jul 2010, 04:02
by codeonemagazine
New Code One site just posted about twenty XL photos in high-res. Have more, but need to scan them first. Some show aircraft under construction.

Re: XL photos

Unread postPosted: 17 Jul 2010, 05:41
by geogen
codeonemagazine wrote:New Code One site just posted about twenty XL photos in high-res. Have more, but need to scan them first. Some show aircraft under construction.


Thank's for the head's up. Two pretty dynamic images in particular, if I can list them here:

Image

Image

RE: Re: XL photos

Unread postPosted: 18 Jul 2010, 15:43
by strykerxo
Shot this video @ Edwards AFB 2009 Test Nation airshow

The F-16XL video is at the 1:45 mark, she is a beauty.

http://www.youtube.com/watch?v=NM5swD4iHlE

Unread postPosted: 19 Dec 2010, 14:42
by mlk32170
The XL required considerably more development and cost. Canards on any 16 would require a redesign of the forward fuselage. Space for actuators doesn't exist on the present configuration. The structure of the nose section would could not handle the loads, forcing more redesign.

Unread postPosted: 19 Dec 2010, 16:43
by johnwill
Canards were considered and rejected for a production version of the XL, but you are correct about more development and cost. The winning F-15E also required considerable redesign, development, and cost.

Unread postPosted: 19 Dec 2010, 21:07
by F16VIPER
The -XL was suposed to be a supersonic cruise aircraft. Did it ever achieve it and what was the maximum speed, and if not, what was the issue.

Unread postPosted: 20 Dec 2010, 01:50
by johnwill
It had no significant supercruise capability in mil power, about like any other F-16. However, max speed was never reached, due to political considerations and lack of analytical and wind tunnel support for those speeds. It was not allowed to exceed 2.05 mach. Let us say that at 2.05 there was lots of climb rate and acceleration available.

Flight control, flutter, loads, propulsion, and heating could have been problems, because no analysis or testing had been done to support anything above 2.0.

Unread postPosted: 20 Dec 2010, 02:04
by johnwill
mlk32170 wrote:The XL required considerably more development and cost. Canards on any 16 would require a redesign of the forward fuselage. Space for actuators doesn't exist on the present configuration. The structure of the nose section would could not handle the loads, forcing more redesign.


Another comment is that finding space for canard actuators and strength for canard loads was not a big problem for the CCV YF-16 nor for the AFTI F-16. So if canards had been beneficial, you can be sure our designers and engineers could have made it work.

For example, the leading edge extensions were totally empty and could have easily accommodated canard actuators and loads. In addition, there was a 26 inch plug between the wing front spar and the cockpit. That area could also have acted as canard mounts if needed.

Unread postPosted: 20 Dec 2010, 04:08
by F16VIPER
It had no significant supercruise capability in mil power, about like any other F-16. However, max speed was never reached, due to political considerations and lack of analytical and wind tunnel support for those speeds. It was not allowed to exceed 2.05 mach. Let us say that at 2.05 there was lots of climb rate and acceleration available.

Flight control, flutter, loads, propulsion, and heating could have been problems, because no analysis or testing had been done to support anything above 2.0.


Thanks John. Does it mean that the "S" side of SCAMP was just wishful thinking or aerodynamic impediments were discovered. What was the main impediment for supercrise not being possible with this plane given its more efficient ? aerodynamic shape.
Re max speed: would you please elaborate what the political aspects were.

Unread postPosted: 20 Dec 2010, 11:41
by geogen
Hey, it's great to see this thread pop back up from time to time!

Instead of traditional canards, I've wondered if the front AMRAAM pair could have been set back 2 feet or so, in order to allow for LCA Tejas-Naval style LEVCON controls above from where the front AMRAAM pair poke out their noses? Or would that have obstructed w/ the landing gear? If the case, maybe AF could have just accepted writing off the two front points altogether and make them up elsewhere in an air defense/Intercept sortie loadout. Perhaps in place, a couple 6' - 9', conformal EW arrays (or some other component/system) of similar width to the AMRAAM but set back allowing an effective LEVCON type control? (w/ controls possibly enabling lower approach speeds, faster low-level speeds and better instantaneous pitch/higher AoA?)

And great observation, johnwill, about F-15E requiring substantial development work too prior to becoming operational! Wise guy, lol :wink:

Anyhow, an F-16XL concept could have been just the starting point with so many plausible spiral developments and growth - possible in later blocks - as requirements became justified and the airframe/systems technology available.

One could continue w/ some conceptual ideas on that, but to save the boredom and in the interest of not conjecturing on various sensitive areas of discussion, I'll leave it here. Although one final point... I'm almost certain that someday LM will be kicking themselves they didn't partner up around the time block 60 was being studied and separately develop the XL which could have been available today at a discount to the still kicking F-15E class. Surely Congress would be having a field day with it at least - taking into account today's mode for contingencies...

If I could have the honor then to propose an hypothetical name for the woulda been operational example, I'd vote for: F-16 6G Strategic Falcon. imho.. :thumb:

Unread postPosted: 20 Dec 2010, 15:25
by johnwill
F16VIPER wrote:
It had no significant supercruise capability in mil power, about like any other F-16. However, max speed was never reached, due to political considerations and lack of analytical and wind tunnel support for those speeds. It was not allowed to exceed 2.05 mach. Let us say that at 2.05 there was lots of climb rate and acceleration available.

Flight control, flutter, loads, propulsion, and heating could have been problems, because no analysis or testing had been done to support anything above 2.0.


Thanks John. Does it mean that the "S" side of SCAMP was just wishful thinking or aerodynamic impediments were discovered. What was the main impediment for supercrise not being possible with this plane given its more efficient ? aerodynamic shape.
Re max speed: would you please elaborate what the political aspects were.


SCAMP was a clever name, but I don't think anyone expected XL to truly supercruise given the engines of the day. The wing didn't really start to show its capabilities until higher machs were reached. Today might be different with the latest F-16 engines and possibly TV for better trim. It did not help pitch trim for the 30 inch longer aft fuselage (and engine of course) to be tilted up 3 degrees for runway clearance.

I can only give you an opinion, that of a mid-level engineer, not a manager type. It seemed to many people that the AF was dead set on the F-15E winning the competition, mainly to preserve the production line. The F-16 line was assured for many more years, but F-15 was nearing it's end. That was understood and accepted. We knew we had to be a lot better to win. A dramatic increase in XL top speed, while tactically useless, could be embarrassing.

geogen,

The XL AMRAAMs were total dummies, scabbed on to the lower wing and fuselage surface, with no troughs. So there were lots of possibilities for production mounting.

My proposed solution for the pitch control problem was to ditch the elevons and replace them with standard horizontal tails, nested well into the wing planform, similar to the F-22. More area, plus no aeroelastic loss from wing twist. The elephants weren't interested in a flight control proposal from a structures engineer.

I've mentioned before how the aft AMRAAMs almost caused us to lose one of the airplane. They were mounted directly in front of the lower speedbrake panels and shielded them from much of their normal airflow. That was not a problem at lower speeds, but at the first really high speed usage (1.6/30k), the upper door had its normal load, while the lower door had about half of its. That caused an big imbalance and the door mount structure failed. The door mount structure was also the hydraulic actuator, on system B I think. The pilot, hearing and feeling the the failure, retracted the brake. Chase couldn't see any problem, so the operation was rather unwisely repeated. This time the pilot felt and heard another failure, then saw the master caution and system B lights come on. A safe landing was made, but the failure was not our proudest moment.

Unread postPosted: 20 Dec 2010, 15:49
by ViperDude
JohnWill,

As I remember the XL AMRAAMS were made out of wood? I also remember the first time I ran a flight control bit and was surprised to see L, E, A, F lights in the cockpit instead of P, R, and Y lights. I will say that the flight control troubleshooting tester for the XL was very cool because it hooked up down below as I remember and I think you could use it with engines running. (I can't remember anymore..lol)

Cheers,

ViperDude

Unread postPosted: 20 Dec 2010, 16:05
by johnwill
Yes, wooden AMRAAMs, with sheet metal nosecones and fins.

Looking back, I see I've told that speedbrake story more than once. Forgive me. My wife is probably right. She says I'm getting senile.

Unread postPosted: 20 Dec 2010, 17:38
by madrat
johnwill-

Can you give a rough drawing of your standard horizontal tails idea and missile mounting ideas? They sound interesting. And who in the hierarchy is an elephant? I am not familiar with that term.

Like this?

Unread postPosted: 20 Dec 2010, 19:14
by johnwill
Your drawing is exactly what I proposed. I don't have any insight for missile mounting. What they had could probably have been made to work.

Elephants were just our term for any heavy weight manager. Big Dog, Honcho, whatever. The rest of us had to be careful not to get stepped on by an elephant, even inadvertently. Elephants don't always see where they step.

Unread postPosted: 21 Dec 2010, 04:46
by geogen
Thanks for reply and fascinating 'structure oriented' inputs as always, johnwill. And no, you're not getting senile in re-posting your thoughts on these repeating subject matters, you're just a nice, polite guy :) Just keep telling your wife that too, she'll eventually hear you..

Re: the airbrakes being affected by the rear AMRAAM placement, I'm curious if the Gripen style Airbrake concept could have applied for a production XL design instead (i.e., 2x brakes at upward 45 degree, one on each side, towards the rear of the engine fuselage just before the nozzle)?

Best regards,

Unread postPosted: 21 Dec 2010, 07:47
by johnwill
I suspect a better way would be to use ailerons and elevons simultaneously, as in F-22, F-35, possibly others I don't know about.

My wife and I (married 48 years) have a great time growing older together and are constantly kidding each other about how old, senile, forgetful, etc. the other is. I wish for everyone to be so blessed with a mate as I am.

Unread postPosted: 21 Dec 2010, 12:10
by FlightDreamz
johnwill
I can only give you an opinion, that of a mid-level engineer, not a manager type. It seemed to many people that the AF was dead set on the F-15E winning the competition, mainly to preserve the production line. The F-16 line was assured for many more years, but F-15 was nearing it's end. That was understood and accepted. We knew we had to be a lot better to win.

If you don't mind me throwing in my :2c: I also remember that at the time General Dynamics (who was still building the F-16 before they sold off the design and production line) got caught "with it's hand in the cookie jar" overbilling Uncle Sam for something or other and there was a big controversy over that. Might have skewered some viewpoints. I'm sure that's been covered on f-16.net and elsewere but I don't have links at present (too early in the morning - the caffeine from my coffee has only just started to hit the system)! :shrug:

Unread postPosted: 21 Dec 2010, 17:25
by johnwill
Right you are. With so many thousands of employees at ALL defense contractors, there will always be some individual or small group of individuals willing to bend the rules. Name a contractor who has not been there. However, very rarely is the infraction a result of contractor policy, as no contractor is foolish enough to do that. Recall also, that for every $300 hammer charged to the government, some civil servant approved the payment.

That of course does not excuse the overcharge, but goes to show that mis-deeds abound everywhere. Remember what Pogo said, "we have met the enemy and he is us".

Unread postPosted: 23 Dec 2010, 04:59
by FlightDreamz
Point taken, it's true that pretty much every defense contractor has been charged with overbilling something, somewhere. I like you point about the civil servants approving it as well. Will try to dig up some concrete data on why the U.S. govt was upset with General Dynamics this weekend after the holiday rush and keeping the F-15 line open was almost certainly a factor as stated earlier in the post.
FlightDreamz
If I remember correctly, General Dynamics got caught in a big scandal overbilling the U.S. Government over some contract and that played a hand in the F-16XL losing to the F-15E.

Whoops! Looks like I'm repeating myself! I've already mentioned it way back in 2008, on the first page of this thread :doh: I must be getting senile!

Unread postPosted: 23 Dec 2010, 15:49
by johnwill
Welcome to the club. :cheers:

Unread postPosted: 23 Dec 2010, 16:53
by fiskerwad
johnwill wrote: Recall also, that for every $300 hammer charged to the government, some civil servant approved the payment.



I remember the hammers as costing $750 but that probably included the civil servant's cut.

Some of the time, tools that were "local procurement" were ordered from GD instead so the customer wasn't liable for damage caused by using the wrong tool. Since GD was required to re-QA and then store and inventory those tools, $15 hammers quickly become $300 hammers.

fisk