Forum: F-16 Design & Construction

Salute

Gee, Sky knows all about the Russian system, huh.

In summary for Sky:

- Viper FLCS was analog FBW from day one to the later block aircraft. In those days egineers did not trust the digital stuff due to misplaced "bytes" and inability to do time-proven fault analysis. The hardwired analog capacitors, resistors and inductors for the FLCS functions were very easy to troubleshoot and test.

- Due to the FBW concept, the aero folks could move the center of gravity further back than for the "traditional" designs. So pitch rate went up, trim drag went down, AoA and gee limiters kept Joebaggodonuts from overstressing the jet, etc.

- The system did not have a "primary" computer, nor did it "vote" or "average". The thing used three channels until one failed, then it picked up the fourth channel. The output to the control surfaces was the "most benign", meaning the lowest value. This came back to bite us when we had the power supply problem, as the "most benign" output was "zero".

- The stick forces were "standard" for pitch - close to 4 pounds per gee. In older planes we had springs and "shock absorbers" and even "bellows" that restricted stick inputs depending on how fast you were flying. All of these were mechanical doofers.

- The older jets used control stick MOVEMENT for the most part to command flight control surface movement. The SLUF had transducers in the stick that became active if you had "control aug" enabled. So we could actually hold the control column steady with one hand, and exert force on the handgrip to get control surface movement. So the SLUF had a portion of it's system FBW.

- You don't need superhuman strength to fly around pulling 9 gees. The force for 9 gees in the Viper was about 30 pounds originally, and that ain't a lot. it also met the existing USAF spec for gees per pounds of force. What you DO need is to be in shape so you don't blackout. Talk with SnakeHandler about this.

- The early Migs had more direct mechanical connections to the contol surfaces. So a few Viper pilots delivered the first Pakistani Vipers and got to fly in Mig-19's or -17's. They said that at 400 knots IAS they could not pull hard enough to increase pitch. They had to slow down to get any turn rate at all. Back long ago, the WW2 planes had the same problem, and they had no hydraulic boost.

Anymore questions, Sky?

Gums sends...

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Forum Veteran Joined: Jul 01, 2007 - 07:22 PM Posts: 620

I'm curious to know just how much force I'm putting on the controls when flying BFM. Sometimes it seems like I'm going to separate the SSC from the jet.

Seems like that very thing happened to an Eglin sedan a number of years ago. Dunno what they were doin' but the front seat SSC came off in the guy's hand. The GIB had to land it. He was a Flight Test Engineer (not fighter qual'd) and had to be talked thru it by the GIF. Never did hear the reason for the failure.

I've had to replace the SSC grip in the sim once or twice (we used actual flight hardware) and the locking ring had loads of threads on it. Took quite a few turns to secure it so unless the collar on the transducer housing was compromised, it could take whatever you could dish out.

Pull on the stick, pull hard

Yeah, Snake, folks pull damned hard on the stick.

One reason they gave us for putting in a bit of movement in the stick starting in Block 5 was to let folks know they were commanding max gee/roll.

Rumor back then had it that GD had measured over a hundred pounds of "pull" on occassion. Guess that's an urban legend, but I believe it. Seems I could tell I was pulling hard enuf when the nose wasn't moving any faster, heh heh.

Gums

Elite 1K Joined: May 26, 2005 - 08:39 PM Posts: 1496

So are Viper pilots' forearms lopsided from all that right handed stick pulling? Very Happy

Forum Veteran Joined: Jul 01, 2007 - 07:22 PM Posts: 620

Along these same lines, I've heard urban legends of the early Aggressor dudes opening the AR door to get more nose authority at low speeds with T&L gains. Can you confirm this Gums? Could be a good trick to pull on someone unsuspecting these days.

SnakeHandler,

Do not, I repeat Do not try that trick! I know you wouldn't but ... Don't do it.

Have you gone to Kirtland? If you do you'll get to see what is left of Viper that did that. It was done at highspeed but no need to go trying that while flying slow either.
You don't need any tricks to beat someone in BFM.

Forum Veteran Joined: Jul 01, 2007 - 07:22 PM Posts: 620

I know, I just wanted to know if it was truely an urban legend or not. I guess not. Did that guy get out?

Nope.

The Viper pilots may have RSI, or repetitive strain injury on their right forearms and hands.

Forum Veteran Joined: Jul 01, 2007 - 07:22 PM Posts: 620

Your posts are giving us repetitive brain injury.

Gums & Snakehandler,

Say you look over the shoulder and see a guy on the perch (3000' or so)inside your circle. What effect would throwing the MPO switch and pulling like hell have? Would it allow you enough pitch authority to force an overshoot? Just curious.

Forum Veteran Joined: Jul 01, 2007 - 07:22 PM Posts: 620

Before or after the jet broke in half and you blacked out?

F16guy wrote:

Have you gone to Kirtland? If you do you'll get to see what is left of Viper that did that. It was done at highspeed but no need to go trying that while flying slow either.

Scary, learn something new everyday ... when you open the IFR door the fuel system depressurizes and the centerline stops feeding because you’re supposed to be taking on gas. That can't be good whilst BFMing.
I don’t know how much gas you guys have left in the centerline when you engage, but if its not feeding but internal load is still feeding by gravity, that’s got to upset the jets flying characteristics!

For you folks that don't know, exteral fuel always feeds internal fuel on any jet ... thats why its critical to monitor your external fuel. Can you imagine a viper with a 600 gallon wing tank thats not feeding? Well I guess thats why they are carted!!!

Good reading on the MPO from a legend!

http://www.codeonemagazine.com/archives ... index.html

Snakehandler,

Understood, let the limiters do their thing. Holding the MPO to gain angles is not recommended.

VarkVet, thx for JB's write-up on the flicks. I recall a similar article in the old TAC Attack magazine of yester year I just dug up off my book shelf also written by Joe Bill in the Nov 1991 issue titled 'No Excuses'.

Forum: F-16 Design & Construction

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