Help with Military Fast-Plane Question

[Rustic23]

Spin scenario.

I don't see it. You have two people in the AC. One qualified in the AC the other never been in it before. The probability of the old geezer knowing the characteristic of the 'Space Plane' well enough to talk a pilot out of a spin, IMHO, is slim and none. All Air Force, and Navy pilots are trained in spin prevention and recovery in flight school. All are trained in acrobatics. This part of your story, for me, is like the teenage private that knows more then the forty year old Officer that has been doing it for twenty years.

If the old geezer is an engineer that developed the electrical system of the space plane and has indepth knowledge of some specific part, maybe.

Another thing about a spin, is it is very violent, and happens real quick. Loss of altitude is very rapid. Ejection is recommended passing through 15,000 feet. This is because the altimeter in most A/C lag the actual altitude and ejecting below that altitude may not work. i.e. lower than you think, and excessive descent rate can not be overcome by the ejection seat. Also in order to spin an AC you have to stall the AC. There is little reason to slow an AC to the stall speed at altitude cruising from point A to B. In most modern AC you have to work to put them into a spin. The fly by wire systems work to prevent this. A glitch in the fly by wire could result in a spin, but then you have another emergency to recover from.

[Walt34]

Quote:

Originally Posted by Rustic23 Spin scenario. I don't see it.

I agree. I could better believe the sextant being needed and lots of practice in pilotage because most pilots now are "raised on radios" and have either minimal or no actual pilotage skills. Turn off the electricity and those guys are lost.

A friend of mine is flying from MD to CA next month in an airplane that has one engine and no radio. Except for being 60 instead of 90 he'd be your "character"!

[Rustic23]

I am 71, and I spent most of my Air Force time as a FAC (Forward Air Controller) We used almost no electronic navaids, and used maps. In order to get through the program you had to find the right outhouse behind a house! We navigated on 1 to 50,000 maps in the target area. Give a FAC a map and he can navigate. I really don't think a sextant is necessary. An old geezer with a map would do.

[samclem]

Quote:

Originally Posted by Rustic23 Spin scenario. I don't see it. . . . There is little reason to slow an AC to the stall speed at altitude cruising from point A to B. In most modern AC you have to work to put them into a spin. The fly by wire systems work to prevent this. A glitch in the fly by wire could result in a spin, but then you have another emergency to recover from.

FWIW, I agree. But, if the spin scenario is essential (doesn't sound like it is), it might be possible to get there if our spaceplane is operating well above normal altitude in order to make that radio call we discussed earlier. With very low effective thrust and very low air density (rho, in our lift equation), the stall speed starts to get very close to the cruising speed. The U-2 operates in that regime--just a few knots difference between "as fast as she can go at this altitude" and stalling.
But stalling ain't spinning. And if the plane can be recovered, then the guy flying it knows a lot more about it than Salty does.

I'm afraid it's hard to think of a situation where Salty is an asset. I have thought, however, that a proficient stick-and-rudder pilot or even a run-of-the-mill transport pilot with a good crosscheck and good aeronautical instincts and a basic understanding of the plane would have done a better job of flying an Airbus than did the Air France Flight 447 crew.

Quote:

Originally Posted by TromboneAl So, in 1947 they still used sextants for navigating for transatlantic flights? It makes sense, but I never considered that. Does that mean that all transatlantic aircraft included astrodomes?

Most of the larger USAF aircraft used sextants until fairly recently, and had navigators trained to use them. Typically they use a sextant port--just a small hole (maybe 1.5" diameter) that has a cover to help retain the pressure in the plane. To take a sextant reading the device is poked through the sextant port during the time needed to "shoot" the reading, then the sextant is brought back in and the little door closes. Trivia bit: Some planes have a hose the hooks up to the sextant part and this is used to vacuum out the flight deck. The difference in the pressure inside the plane and the pressure outside does the trick.

[TromboneAl]

Okay, the spin scenario is probably out.

I can get the plane into a tumble or spin, because the alien craft shows up, and screws with the spaceplane's electronics, or otherwise throws it out of control. But I agree that having Salty tell the pilot what to do is a bit of a stretch.

Quote:

In order to get through the program you had to find the right outhouse behind a house! We navigated on 1 to 50,000 maps in the target area. Give a FAC a map and he can navigate.

This will be a moonless night with cloud cover. The plane is above the clouds, and traveling from California to DC. They'll need the sextant in this situation, right?



Current scenario: Plane is using dead reckoning from, say, Kansas on. An encounter with the alien spacecraft messes even that up. But a sextant sight gets them in the right ballpark. Ground mapping radar is broken. They drop below the clouds when they get close, and Salty recognizes the terrain, or they use a map.

[TromboneAl]

Quote:

Originally Posted by samclem Most of the larger USAF aircraft used sextants until fairly recently, and had navigators trained to use them. Typically they use a sextant port--just a small hole (maybe 1.5" diameter) that has a cover to help retain the pressure in the plane. To take a sextant reading the device is poked through the sextant port during the time needed to "shoot" the reading, then the sextant is brought back in and the little door closes. Trivia bit: Some planes have a hose the hooks up to the sextant part and this is used to vacuum out the flight deck. The difference in the pressure inside the plane and the pressure outside does the trick.

Interesting. I had pictured this:





But I now see that it was like this:



I'm figuring that even the first type of sextant can be used in cockpit like this:

[Rustic23]

Al, I don't know about the current generation of fighters, but again the F-111 had an inertial nav system. No external nav/radio required. Set in where you wanted to go and the system took you there. This site http://www.af.mil/AboutUs/FactSheets...-15-eagle.aspx says the F-15 has inertial nav also. It would also be shielded from EMP. F-16 also. When these are running they can take you within feet of where you want to go.

[kombat]

Quote:

Originally Posted by Rustic23 Another thing about a spin, is it is very violent, and happens real quick. Loss of altitude is very rapid. Ejection is recommended passing through 15,000 feet. This is because the altimeter in most A/C lag the actual altitude and ejecting below that altitude may not work. i.e. lower than you think, and excessive descent rate can not be overcome by the ejection seat.

Just to correct some minor inaccuracies here, the loss of altitude is not actually that rapid. It's slower than a free-fall. A spiral dive is a MUCH faster rate of descent. So from 15,000 feet, in a spin, you'd still have well over a minute before you hit the ground. Also, the altimeter does not lag the actual altitude - it is extremely accurate. You may be thinking of the VSI (Vertical Speed Indicator) which does indeed lag your actual rate of climb/descent. Pilots are taught to watch the needle on their altimeter when starting/stopping a climb/descent, and to only use the VSI to gauge the rate during a long, steady climb/descent.

Quote:

Originally Posted by Rustic23 Also in order to spin an AC you have to stall the AC. There is little reason to slow an AC to the stall speed at altitude cruising from point A to B. In most modern AC you have to work to put them into a spin. The fly by wire systems work to prevent this. A glitch in the fly by wire could result in a spin, but then you have another emergency to recover from.

This is mostly accurate, but an aircraft's stall speed is not constant. You can trigger a stall by rapidly changing the angle of attack. Also, if you're looking to contrive a scenario where a plane in a cruise went into a stall, there are some real life examples where an instrument failure confused the flight computer and caused the pilots to inadvertently stall the airplane. Specifically, if the pitot tube becomes blocked (eg., by ice, common at high altitudes if the pilots forgot to turn on the pitot tube heater), then the airspeed indicator essentially turns into an altimeter. So if the plane climbs slightly, the pilot will see the airspeed increase. Without a visual reference (such as at night over a featureless landscape (ocean, desert, prairies), or in cloud), the pilot can think he's actually accidentally aimed the nose downward (as would normally be the explanation for an increase in airspeed if you left the throttles constant). This instinctively causes him to pull up, in an attempt to pull out of the perceived dive and get the airspeed to drop back down. But of course, with the pitot blocked and the airspeed indicator acting as an altimeter, this will simply cause the airspeed needle to climb even higher, giving the illusion that he's speeding up even more, creating a self-reinforcing feedback loop until the nose is so high that the plane stalls. This is exactly what happened to Air France flight 447 over the Atlantic ocean.

And while modern electronics do indeed have numerous protections and measures to prevent the pilots from getting into a stall, it's still quite hard to recover from one once you're in it, particularly in large commercial planes, or tempermental military fighter jets.

[TromboneAl]

Quote:

Originally Posted by Rustic23 Al, I don't know about the current generation of fighters, but again the F-111 had an inertial nav system. No external nav/radio required. Set in where you wanted to go and the system took you there. This site http://www.af.mil/AboutUs/FactSheets...-15-eagle.aspx says the F-15 has inertial nav also. It would also be shielded from EMP. F-16 also. When these are running they can take you within feet of where you want to go.

Well, that's quite a monkey wrench, I'm glad you caught that. I will have to get that disabled. Damn prototypes--things are always breaking.

[Rustic23]

Kombat, you missed my point. In an out of control situation, which a spin is, eject passing through 10,000 feet! Period, end of statement. This is standard Air Force doctrine. It is based on the lag of the instruments. I flew in and piloted the T-38, F-111, F-100, F-105, and it was the same for all of them in their Dash-1 (primary flight Manual) I do not remember the T-37 as we trained spins and I don't remember the min ejection altitude. Maybe Rewahoo might. In the OV-10, It was 5,000 if I remember correctly. Here again we seldom went above 8,000 and spin avoidance not spin recovery was taught. Getting out of a spin depends largely on the aircraft. The T-37, and OV-10, no problem. The fighters a different world. I can only speak for the F-111. It does not recover! In the spin test at Edwards, the air craft was fitted with a drag chute to aid in spin recovery. During the test, the air craft did not recover. The chute was deployed, it quickly departed from the aircraft and the crew ejected passing, you guessed it 10,000 ft.

Correction: As it has been several years since I flew fighters, like more than 20, I had to do some research. It appears the altitude is 10,000 ft, not 15,000 ft.

For the F-102 it is 12,000 Dash 1 page - http://books.google.com/books?id=v9N...titude&f=false

[TromboneAl]

Okay, here's what I've got so far. This is a very rough draft, and I know it's over the top, but here are pilot Frank Cobb and the old sextant-guy, Salty, recounting their adventure at a breakfast:

“It happened over the midwest. We had a radar contact on our six, less than one hundred feet back.” Salty held his hands three feet apart.

“Right,” said Cobb. “We’re going Mach 3.5. There’s no way a normal aircraft could occupy that position. I switch on the rear-view camera, and sure enough, it’s the sphere. I slow down to subsonic, and try some evasive maneuvers, but I can’t shake it. It’s as if it’s connected to the Peregrine by a rigid rod.”

“Then it just disappears.” Salty snapped is fingers, and made like he was looking around for something. “Not flies away, not stops and lets us fly away, it just disappears from the radar. The camera shows it hasn’t moved. Then it comes closer and closer. I say ‘Ah, Frank,’ and it’s just off the horizontal stabilizer. My neck isn’t what it used to be, folks, and it was hard to turn enough to see it, but it was there. Almost touching us. Now, are you guys ready for the piece of resistance?” Salty took a big bite of sausage.

Major Cobb sat back and smiled, knowing what was coming.

Salty finished his bite, and swallowed. “Damned if that sphere didn’t move right over my head, and, I’m not making this up, it starts tapping on the canopy. Tap, tap, tap. Just like that.” Salty mimed straining to look straight up, and tapped his fork on his forehead.

Cobb took over the narrative. “I’m subsonic now, but the sphere is just totally messing with the aerodynamics. I’d figure out how to compensate for this thing, or, I should say that the computer would figure it out, and then it would move. It’s like we had this huge beach ball glued to the plane. Alarms sounding all over the place.”

“So far,” said Salty, “everything was nice, nice. Just a little friendly ‘Hello there, Earthlings, isn’t this fun” tapping. But then—”

Cobb slapped the table. “Then all hell breaks loose. The electronics go out for about one second, and I find out how well this plane flies without the computer.”

“And the answer is …” Salty made a wrong-answer-buzzer sound. “It doesn’t.”

“Right, we had a flameout and I had no control over the plane. We start descending. The manual says ‘Do not delay ejection if the aircraft is in an uncontrolled condition,’ and I tell Salty to get ready to eject. But I’ve got to hand it to the programmers, the engines restarted like clockwork, and we were soon straight and level. I didn’t do a thing. I’m going to kiss those guys if I ever find them.”

“But we weren’t out of the woods yet,” said Salty. “Our little adventure kind of shook things loose.”

“Right.” Cobb nodded. “We had about five systems down, and the most important one was the inertial guidance. According to that, we were somewhere over South America.”

[Rustic23]

You are spot on as far as dumping the inertial nav. It will spin off several thousand miles in a heart beat.

[samclem]

Nitpicking:
I don't know if Salty would say "horizontal stabilizer". A guy who'll say "piece of resistance' will probably say "H-stab", "stab" or, more likely, "the tail".
And, modern very fast planes don't have radar that can look directly aft (there's fuselage and engines in the way)--but this is a made-up plane, so anything is game.
Looks like a lot of fun.

[TromboneAl]

Quote:

Originally Posted by Rustic23 You are spot on as far as dumping the inertial nav. It will spin off several thousand miles in a heart beat.

That was just dumb luck, then.

Quote:

I don't know if Salty would say "horizontal stabilizer". A guy who'll say "piece of resistance' will probably say "H-stab", "stab" or, more likely, "the tail".

Good, thanks.

Quote:

And, modern very fast planes don't have radar that can look directly aft (there's fuselage and engines in the way)--but this is a made-up plane, so anything is game. Looks like a lot of fun.

Actually, maybe it will be better if it just shows up on the tail.

[Walt34]

Agreed with the others. And this book is gonna be an entertaining read.