Forum: Technology

Hello everyone, I'm just a curious newcomer.

After I read about the roll posts that the F-35 uses to mantain control in the roll axis when landing vertically, I eventually wondered about how similar control posts could be used for in-flight maneuvering.

Let's imagine an aircraft that has a duct similar to the ducts in the F-35 that lead to the roll posts. Instead of leading to the wings as in the F-35, this aircraft has a duct that leads to an exhaust nozzle under the nose or the cockpit. The purpose of the duct is to vent gases from the engine(s) downward in order to lift the nose up in the pitch axis.

Since I've read that the F135 that powers the F-35 can produce 3,700 pounds of thrust from the roll posts, how would a similar amount of thrust in such a "pitch post" affect the pitch rate of the aircraft? Surely it would increase the rate at which the aircraft could pitch up.

What drove me to think of this is the fact that canard foreplanes are said to give a better sustained turn rate than horizontal tailplanes because they "lift the nose up" instead of "pushing the tail down". However, since I've also heard that carnard foreplanes have worse RCS characteristics than horizontal tailplanes, that makes canards less useful.

Now put thrust-vectoring into the picture. Modern thrust-vectoring technology used for in-flight manuevering "pushes the tail down" just like a horizontal tailplane does. Thus, it might be more useful if a thrust-vectoring system could "lift the nose up" like canards do instead of "pushing the tail down". That's what the "pitch post" would be used for.

Now, I must ask: how practical would this "pitch post" idea be? What if it was used in conjunction with already-existing thrust-vectoring technology that work on the main engine nozzles to increase pitch rate even further? Would it be cost-effective? Would it be too mantainence-intensive? Would similar "yaw posts" be practical either?

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I think you have pure thrust vectoring as used on the Harrier confused with that derived from exhaust deflection. The Harrier uses the very concept you describe.

I know how the Harrier's TVC works. I was wondering if it could be used to increase a jet's pitch rate and thus enhance its manueverability in a dog fight.

Well I believe it's been previously established the LiftFan/3-Bearing Nozzle of the F-35B won't be able to Vector in Forward Flight (VIFF)

"VIFFing" is what I think you're getting at, and the Harrier could do it.

Lesson: Never try to knife fight a Harrier, and especially don't go inverted in said fight. Big No No

(See attached graphics)

The roll ducts of the F135-PW-600 are rather short, but on the other hand for better/more pitch control the ducts would have to exit very near the ends of the aircraft. This takes up critical internal volume, complicates design, and adds the weight of insulated ducting running through your aircraft. (Hardly what the JSF/F-35 is about.) Two Cents

If anything they could give the nozzle a few degrees of pitch authority without LiftFan engagement? Giving a little thrust vector? (But I doubt it) Shrug

Keep 'em flyin' Thumb

TEG

Wow, that was quite an interesting and informative post. I don't remember ever hearing of "viffing" before.

Do you think that the X-32 was capable of viffing, seeing how it had TVC nozzles which it used for STOVL?

The Harrier, particularly the AV-8A, was a very, very high wing loaded aircraft from the get go, and the overall effect of any VIFF’ing was only to bring them up to a less limited level of capability in a turning fight. I’ve fought ‘em in two different lower wing loaded aircraft and VIFF’ing served only to decrease their inherent disadvantage, not to provide some magical advantage. It also cost them energy. They were better off when they kept their energy up and used the vertical.

The first two diagrams are somewhat bogus, in that the "eager", “mindless” adversary that is depicted, if flown correctly, would probably have opted for something other than just continuing to fly into a convenient position for the VIFF’ing AV-8 to shoot him. Contrary to what the diagram says about no option. If you're above the guy whose falling out of the sky, you quarterplane or hang and come down when you're ready with good nose-tail separation. Most fighters, if not all, can fly well below 200 knots.

When the Harrier started from an offensive, or even a neutral position, he was a tough customer with the AIM-9L. But an extended turning fight was not his strong suit. I don’t think the Brits even attempted to really turn with the Daggers, although they reportedly did do some VIFF'ing, probably to point the nose to shoot the Lima. I wonder if any of it was really decisive?

BTW, if you were to rotate those nozzles the full 98 degrees in high speed forward flight to use as a brake, I wonder what that DOES to the airflow in the engine?

OL

outlaw162 wrote:

The Harrier, particularly the AV-8A, was a very, very high wing loaded aircraft from the get go, and the overall effect of any VIFF’ing was only to bring them up to a less limited level of capability in a turning fight. I’ve fought ‘em in two different lower wing loaded aircraft and VIFF’ing served only to decrease their inherent disadvantage, not to provide some magical advantage. It also cost them energy. They were better off when they kept their energy up and used the vertical.

The first two diagrams are somewhat bogus, in that the "eager", “mindless” adversary that is depicted, if flown correctly, would probably have opted for something other than just continuing to fly into a convenient position for the VIFF’ing AV-8 to shoot him. Contrary to what the diagram says about no option. If you're above the guy whose falling out of the sky, you quarterplane or hang and come down when you're ready with good nose-tail separation. Most fighters, if not all, can fly well below 200 knots.

When the Harrier started from an offensive, or even a neutral position, he was a tough customer with the AIM-9L. But an extended turning fight was not his strong suit. I don’t think the Brits even attempted to really turn with the Daggers, although they reportedly did do some VIFF'ing, probably to point the nose to shoot the Lima. I wonder if any of it was really decisive?

BTW, if you were to rotate those nozzles the full 98 degrees in high speed forward flight to use as a brake, I wonder what that DOES to the airflow in the engine?

OL

1. Yes, it was very effective when used correctly. To avoid getting into an extended encounter it was good practice to get the other guy to stay high on power and burn up their gas reserve.

2. Nothing to the engine performance but your thrust vector does strange things, ask General Blott (Assassin) USMCR how he got the scar on his forehead.

Forum: Technology

How effective would a "pitch post" be?