Forum: F-16 Design & Construction

Salute!

John-boy! We need the series of "Technical Description" documents that GD published back in 1975 or a bit later. A specific document for FLCS is: Volume 8, F-16-060-8, 12 August 1975. These documents were distributed to many offices, as my consulting firm here at Eglin had a complete set. Maybe the GD "historical/heritage" office can help here. I am sure that all Viper feaks would love to be able to read these historic pages of the jet's early design features and innerworkings.

Remember, all you yutes, we didn't even have the official Dash Ones yet and used Xerox flight test tech orders until late 79, early 1980. As I was setting up the academics shop, I had to use whatever I could get. Both Pratt and GD tech reps did an awesome job providing stuff for us to use.

I'll use an Excel sheet to plot the no sierra pitch and roll curves for the FLCS. Then I'll put'em on a PhotoBucket URL for all to see. My sheets are really neat, as they have the analog functions beside the plots. Not sure if they are la place transforms or fourier functions or what!!!!! Gotta remember these functions were hard-wired with capacitors, resistors and inductors. Pretty neat, as they were "instantaneous", smooth and relatively immune from EMP.

loggin'

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Gums,
Back in about June of '79, my boss came to me one day and said I was now responsible for the External Stores Limitations Chart of the -1 and it had to be ready for the Tech Pubs team by Sept 1. So I had to go to all the groups with any input to stores limits (Flying Qualities, Weapon Separation, Flutter, Structural Loads (me), SMS, Safety, etc, and get all their limits for all the takeoff loadings and all possible downloadings. Then I had to somehow construct a chart to show all those limits in a reasonably concise way. Because there were air to air, air to ground loadings, take off loadings, maneuver limits, separation limits, emergency limits, speed limits, AOA limits, and limits for after the stores were separated, I had a really bad time of it. They gave me sample sheets from A-10, F-5, and F-15, but they had relatively simple charts because they were mostly single purpose airplanes, while F-16 was do everything. Somehow it came together on time. But as you say, it took more months for Tech Pubs to get the information to Hill.

I was never totally satisfied with the result, but after it got into the field we got a lot of feedback on how to improve it. I went to -1 user's conferences at Hill, McDill, and Brussels, so if you were at Hill in mid '80, we were probably in the same meetings.

Correct jownhill!! Doh

Quote:

This isn't correct, but it's going the right way. The horiz. tail moves as the airplane is taxiing because the pitch rate sensor gyro senses ACTUAL NOSE MOVEMENT up and down and directs the tail to correct for it. That movement comes from the nosewheel riding up and down imperfections in the pavement.

I think thats exactly what i meant Six viper Cheers

Raptor claw, as I said to Gums, I might have been remembering the roll command max stick force when I said 17 lb. There is no difference in the max stick force for air to ground or air to air, as there is no air to ground g limiter other than 9g used for air to air. A pilot can pull 9g any time he wants to with a/g stores, so long as his airspeed is enough to keep him under 15 deg AOA and he is willing to risk tearing up the airplane.

True story about the pylon and wing connection. When preliminary design loads were developed, the load passed into the wing from the pylons was used to design both sides of the connection. When refined loads (more accurate) loads were developed they were smaller, so the wing was redesigned to save weight. Pylon weight was not as important, so to save the taxpayers money, the pylon was not redesigned to the lower loads. Fine, strength was adequate for both pylon and wing. But wait (as they say on TV), if there was an unexpected high load condition, which broke first, pylon or wing? Wing of course, since it was now designed for lower loads. So which would a pilot want to fail first, pylon or wing? During FSD flight test, loads were verified and everyone realized the absurdity of the wing design, so for Block 15, the wing hardpoint strength was increased enough for the pylon to fail first.

Salute!

OK, I plotted the chart from my Jurassic document for the pitch gradient.

Here it is:

Remember that the FLCS assumed 1 gee as the baseline normal gee, so you only see a 8 gee max command, but look at the negative gee (it's really 3 gee neg gees).

I'll get the roll command chart up soon.

Gums sends .....

Gums wrote:

OK, I plotted the chart from my Jurassic document for the pitch gradient...

I found some SSC info in a Sept. 1979 FQ report from FSD....

The above chart does date back to the 'fixed' stick design (i.e. from YF and the beginning of FSD). That design moved a whopping 0.032" aft (@31.2 lbs) and 0.045" laterally (@17.0 lbs).

The current 'moveable' stick design was developed during FSD (1976-1979). With the incorporation of the stick movement, the gradient forces were reduced by 20%. So, the max forces were reduced to 24.8 lbs aft (at 0.198") and 13.6 lbs lateral (at 0.127") Also it was during this study that the stick was re-orientated to a 12 degree skew (the pitch/lateral axes were rotated).
I did double-check, and the current FLCS gradient gives almost exactly 8 g's at 23.05 lbs (24.8-1.75). So that checks. I also found that there is no additional 'mechanical' breakout in the force sensor, the 1.75 software breakout is all there is.

johnwill wrote:

I might have been remembering the roll command max stick force when I said 17 lb. There is no difference in the max stick force for air to ground or air to air, as there is no air to ground g limiter other than 9g used for air to air.

Your explanation (the roll force) does seem logical. I was just hypothesizing that 17 might have been a number you tossed around with pilots when discussing what stick forces they should expect for a 5g test point - which I figured would be most common with stores.

Seems we have a good handle on the stick forces now, thanks to Gums and Raptor claw. Interesting you mention rotation of the axes to a 12 degree skew. During YF-16 flight test, it was found the pilots had a tendancy to apply a little roll command when trying to apply pure pitch and vice versa. The stick was of course offset to the right (hence the term "side stick") so when the pilot pulled back he inadvertantly also pulled slightly inboard. After some analysis of the data, it was found that by rotating the stick pitch and roll axes, that cross talk could be greatly reduced. The rotation could have been mechanical or mathematical, but I can't remember which way they did it.

Gums, I talked to my friend still slaving away at what is still locally called "the bomber plant" (B-24, B-36, B-58) and he will check with the library tomorrow about the tech description docs.

Salute!

Tnx, "claw". And you too, John-boy.

Remember, we're talking ancient history (earth was still cooling, and I had to watch out for the "raptors", heh heh).

OTOH, this kinda stuff is what a lot of the yutes patrolling these forums want to see/need to see.

***************

Our first 20-30 jets didn't have any discernible movement in the stick. The small amount that "claw" notes was prolly the transducer limits. Also, I think the stick had been rotated BEFORE they gave us the small amount of movement to "tell" us we had pulled as hard as the system would recognize. No matter. Biggest thing we noted on the BK1A/BK 5 was it seemed smoother in close formation. The pilots still pulled 100 pounds aft in a fight, but whatthehell.

Funny, but the SLUF stick had similar transducers in its stick grip. They were activated when we had "control aug" engaged. So an old roomie of mine who was at Edwards in early 70's told me that the SLUF flew "fly-by-wire" more than most folks realized. The system used forces on the stick to command pitch and roll without having to move the whole control column at all. In fact, after he told me that, I held the actual control column with one hand and used the other to "twist" the grip. Sure enough, the sucker would roll and change pitch without the column moving.

And remember, I had flown the VooDoo, which had two "limiters" to help us from departing. No transducers in the stick grip, but mechanical doofers to limit commanded AoA and pitch rate. We also had a super ARI to help with adverse yaw, as the ailerons were the size of your bathroom doors and we could roll really fast. Of course, we better pilots always unloaded that beast when rolling fast and didn't use the "rudder roll technique" that the Double Ugly folks had to. Hell, we'd depart in an instant if rolling when close to the AoA limiter.

Great thread, and I'll post the original "roll gradient" soon as I get it into Excel.

Gums sends .....

Gums--The Thud also had a force switch assembly that made up the control column. Memory starts getting foggy here, but I think the four switches (two pitch, two roll) actually turned off the Stab Aug system while maneuvering. They would activate whenever the pilot moved the stick grip.

The first fighter sim I ever flew was a VooDoo sim--crashed it so hard it broke!! I got a little better over the years...

Salute!

OK, here's the roll cmd plot from original Vipers.

later,

Gums sends

Is the F-16's FBW analog or digital and does it come with double, triple or quadruple redundancy in case the main unit fails?

The Sukhoi Su-37 Terminator has a digital quadruple redundancy FBW system.

Actually, the computers tend to move the surfaces in order to have stability.Pilots movements are filtered when the jet is in the air.Only when the jet is on the ground the exact movements of the pilot are transimitted to the surfaces as they are.When during taxi the jet bumps up and down the computer thinks that the jet pitches up or down and so it tries to offset this undesired movement by moving the surfaces up and down. Cheers

Yeah Joe I forgot that one about the pulse.
I think that Gayle Itomitsu showed me that one day doing a FLCS Test at MJ.
Or was it you showing me that at Clark one day when I had been partying all night with Leigh?

Viper,
It also depends on what surfaces you are looking at. and Yes you can see them in level flight.
I was on a KC-135 taking pix here at MacDill many many years ago, When we had vipers slip in and around you could see the the rudder, stabs and flaperons all moving to position the birds. How much they move is controlled by several of the above mentioned "Rules" And yes small movements are the norm for level flight...

HTH William G

skyhigh wrote:

Is the F-16's FBW analog or digital and does it come with double, triple or quadruple redundancy in case the main unit fails?

The Sukhoi Su-37 Terminator has a digital quadruple redundancy FBW system.

Skyhgh,

The F-16 FBW is analog in the A, B and the Block 25, 30 and 32 C's and D's

Block 40 and onward were Digital.

All have 4 channels for redundancy...

William G

Forum: F-16 Design & Construction

Fly-by-Wire