General design question

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epicvalor

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Unread post12 Sep 2011, 07:11

Some of you might find this a silly question, but I'd really like to know why something like has never officially been in a fighter jet design.

It has to do with thrust vectoring; Why couldn't there be some way to port some thrust to various points on the aircraft to provide better maneuverability, as well as using the tail nozzle? Something in addition to the control surfaces.

I mean, if you really wanted to keep a stealthy design, and make it competitive enough dogfighting, wouldn't having the ability to maneuver better if needed be helpful?

It seems to me that you could make a fighter, with no rudder, in kind of a diamond shape, and make tighter sliding turns...with less stress on the frame.

It would all have to be heavily computer controlled, of course.


Eventually we'll reach the point of designing the most maneuverable plane a human can survive...without finding some way to dampen inertia, and then we'll have nothing but electronics, and weapons to improve.

It's sad we humans still have to make machines of war.

Anyway, I'm a noob at this. I just happened to see a show on the history channel a couple of months ago, and just now thought about again.
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haavarla

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Unread post12 Sep 2011, 07:56

Not sure whay your idea is..
But if you thinkin about some additional small control thruster placed around the aircraft aka on the space shuttle.
Then this is a no go.

It would steal a lot of space and add extra weight, then you have the extra IR-signatur spots all over the fuselage..

And keep in mind, any control surfaces you take away, the more unstable an aircraft become.
The Flight Control Computer/system can add up some of that, but a golden rule, the less aerodynamic relaxed stability, you get less 'supermanuverbility' on a aircraft in the first place.
Nothing comes for free, the laws of physics still apply.
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epicvalor

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Unread post12 Sep 2011, 08:09

They'd be more like fixed, recessed vents that got a redirected thrust from the main engine as needed while in dogfighting mode. You obviously don't need stealth in a turn fight. Not something that was always on, I meant.

They do have that unmanned tester x-plane with no rudder. I have no idea how maneuverable it is.
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em745

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Unread post12 Sep 2011, 11:12

You're talking about ports akin to the maneuvering "puffer ports" used on VTOL/STOVL like the Harrier and F-35B?

For that to work you'd need to produce a HELLUVA lot of thrust from those ports to even come close to the moment arms (i.e. force) produced by flight surfaces--a lot more than what's typically produced by puffer ports, which are only used for positional maneuvering while VTOL jets are hovering.

For instance, at max deflection (20°) the F-22's TVN's can produce a pitching force (vector) in excess of 20,000 lb. How feasible do you think it would be for ducted "maneuvering ports" to produce that level of force (i.e. thrust), necessary for high-energy maneuvering? :wink:
Last edited by em745 on 12 Sep 2011, 16:08, edited 1 time in total.
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southernphantom

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Unread post12 Sep 2011, 13:11

epicvalor wrote:They'd be more like fixed, recessed vents that got a redirected thrust from the main engine as needed while in dogfighting mode. You obviously don't need stealth in a turn fight. Not something that was always on, I meant.

They do have that unmanned tester x-plane with no rudder. I have no idea how maneuverable it is.


Well, you'd still have regular control surfaces in that case, and possibly 2d/3d TVC on the actual nozzles. I also wouldn't even want to THINK about maintaining an aircraft-wide duct system with 20 different doors. If it would be feasible to create a 'LO Harrier thrust duct' that was vectorable, I could see your point, and have conducted simulations to this effect. It was highly effective and drastically reduced landing speed.
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epicvalor

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Unread post12 Sep 2011, 19:24

Yes, through a internal duct system. I imagine it would be hard to maintain now that you mention it, and probably some exotic, or expensive material to deal with the heat, and pressure.

It looks like it would have too many drawbacks on a fullsize aircraft.

I have plans for a 4 port RC model to test the yaw, 2 in front, and 2 near the rear, on a wedge shaped body that should provide decent lift even while moving sideways. Theoretically, allowing it to face a single point, and circle it for a period of time. 8 ports in an x-formation in both front/rear would be ideal, but one step at a time.

I just stumbled upon this forum, and noticed that some of you are probably actual aero engineers, and maybe find the concept interesting.
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delvo

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Unread post12 Sep 2011, 20:01

You'd have to add ducts, with mechanisms to open & close the outer ports of each one, plus possibly other doors where the ducts meet the engine. The ducts would add only a small amount of weight, but a lot of volume, which gets in the way of other stuff that could be put in the same space instead, unless you just make the plane bigger and thus increase its drag and its field/hangar/deck requirements.

The door mechanisms would add not only weight and volume, but also more places for stuff to go wrong and need maintenance/repairs (especially given how much force they'd have to resist and how often and quickly they'd have to do it). They'd also add new edges to have to deal with radar return from and still possibly have radar return increase when they're open anyway. Effective maneuvering response would also be slow once they were opened, unless the plane routinely flew with the ducts already heavily pressurized at all times just waiting to blow out the outer doors for a maneuver, which brings along its own special complications.

Also, a more elaborate air flow path inside the plane slows down the air at every turn, which reduces the air's effectiveness at pushing the plane when it gets out. It sucks away some of the energy your engine is working to produce and use to move the air in the first place (converting it to unnecessary air compression & heating inside the ducts instead). That's part of the reason why OV-8B is slower than F-35B; when flying forward, the latter has a very straight, simple air flow path (same as in models A and C) while the former's path is still split and serpentine.
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munny

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Unread post12 Sep 2011, 22:58

If you could work out a way to dramatically and quickly shift an aircraft's centre of lift while maintaining a VLO RCS, and combine it with existing TVC, then you'll be onto something.
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Shaken

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Unread post13 Sep 2011, 01:09

What you are describing is just another form of thrust vectoring, with slight variation in directions of push and implementation.

Thrust vectoring seems really cool, but it doesn't actually do a lot to turn the aircraft. Seriously. The lift generating surfaces (wings and body) can generate oodles of G's... often more than the pilot can take. The engine can generate less than 1.5 G, and you can only use a fraction of this for turning (a basic trigonometry problem) and when doing so you give up a substantial amount of thrust that is better used maintaining the aircraft's energy state.

So why use thrust vectoring? You only want to do so when the uses justify the added weight, cost, volume and complexity. Thrust vectoring is used to provide control authority when aerodynamic controls are limited or ineffective. This could be because the air is thin (like for a Raptor, floating along at 60,000 ft), when you are really slow (for air shows, or if you've really made a huge set of errors in a dogfight) or when you want to replace or supplant conventional control surfaces (helping when control surfaces are removed by damage, or if you want to remove control surfaces to reduce an aircraft's signature).

On the topic of using thrust vectoring to eliminate control surfaces, this was reportedly part of what was looked at with X-36 and the main focus of the X-44. Fluidic thrust-vectoring (using gas ports inside the exhaust nozzle to shape and steer the main engine's thrust) was mentioned around these aircraft. It sounds like a cool solution to me, although I'm sure there are plenty of .



So I've heard about VIFFing and how it made the Harrier a boss dogfighting machine...

VIFFing allows a pilot to add between a half- and full- G of turning acceleration, in exchange for ALL of the forward thrust. Since most airframes can exceed the pilot's capacity for G's when moving, the only advantages of this change is to slow down a huge amount (aided by the Harrier's significant frontal area for its size) or to turn when going so slow that its wings generate insufficient turning-G. VIFFing could be used to get an opponent to overshoot, if they were unaware of the Harriers great capacity for deceleration; but once opposing pilots learned about this trick, all they had to do is idle-boards and lag outside or into a high yo-yo above the VIFFing Harrier's turn circle. The Harrier quickly renders itself out of energy and options... a grape ready for the picking. (Many Harriers still perform well in ACM, but I believe this is more a product of quality piloting than the attributes of the machine.)

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That_Engine_Guy

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Unread post13 Sep 2011, 01:35

It would be easier to just use 360* vectoring nozzles. (Like NASA did)

PW and GE both had nozzles like this for the F100/F110 respectively.

Research F-15 ACTIVE, or F-16 MATV or ACTIVE

Keep 'em flyin' :thumb:
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Must be pretty good directional power when you have to bolt the entire aircraft down to the ground!?!
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Shaken

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Unread post13 Sep 2011, 02:09

epicvalor wrote:It seems to me that you could make a fighter, with no rudder, in kind of a diamond shape, and make tighter sliding turns...with less stress on the frame.


Short of some sort of anti-gravity / inertia-dampning bit of science fiction, I know of no way to generate less stress on an airframe for a given turn rate (at a given speed). The G-forces are simply the turning acceleration force. For a given circle flown at a given speed, the same G is produced no matter what aircraft (or bird of skateboarder or whatever) is flying around that circle.

I'm having a hard time picturing tighter sliding turns. Fighters turn by rolling so their target is along the (conceptual) line between their nose and canopy and then pulling back on the stick. In other words, they rotate around in PITCH to turn. This is rather different than the "bank-to-turn" approach used by airliners and civil aviation, but is necessary to generate the high-turning rates needed in air-to-air combat.

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That_Engine_Guy

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Unread post13 Sep 2011, 03:17

Shaken wrote:I'm having a hard time picturing tighter sliding turns. Fighters turn by rolling so their target is along the (conceptual) line between their nose and canopy and then pulling back on the stick. In other words, they rotate around in PITCH to turn. This is rather different than the "bank-to-turn" approach used by airliners and civil aviation, but is necessary to generate the high-turning rates needed in air-to-air combat.


The F-16 CCV and AFTI demonstrators did just these sorts of things back in the late 70's and early 80's.

Flight Global wrote:The Fighter CCV YF-16 pioneered "the new way to fly" between March 1976 and June 1977—with a nine month break following a landing accident. The aircraft demonstrated direct lift and sideforce control, independent fuselage pointing and translation, manoeuvre quickening and gust alleviation. Principal changes were two intake-mounted vertical canards and the provision for symmertical upwards deflection of the flaperons.


http://www.flightglobal.com/pdfarchive/ ... 01132.html

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geogen

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Unread post13 Sep 2011, 05:10

Now if we can only get an F-16 CCV + 360 degree F110 TVC worked up over at NASA and into the airshows.

Seriously though, a note to Shaken... thanks for that description and indeed, many if not all fighter pilots could find themselves in a position making a series of dogfight errors as you say - at least once in the phone booth, so to speak. And as you say... when aircrafts are maneuvering at the upper limits of their effective operating altitudes and when their respective speeds decrease after sustained ACM, or when ACM demands an aircraft be flown in maximal angles of attack, or if there is some form of control surface damage, etc, true, TVC would enable an effective advantage. And definitely, when an aircraft equipped with TVC might be conducting rapid directional nose-pointing maneuvers, it is an aircraft more effectively in control of the flight envelope's advantage - e.g., in it's ability to maximize the direction of the nose pointing in a minimum sequence of time and G loads.

Perhaps the optimal compromise to the thread's theme would be generated from some sort of combined rapid center-of-lift manipulating airframe lay-out, combined with a Thrust-reversing, Fluidic Thrust vectoring nozzle ;) Yes please, for the F-16XXL :thumb:
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energo

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Unread post13 Sep 2011, 19:49

Epicvalor,

Sounds like some form of fluidic actuation or thrust vectoring might fit your bill. Was even researched for the JAST/JSF. Certainly a potential in terms of lower observablity, complexity, maintenance and so on. Do a Google and Youtube for the BAE FLAVIIR or "flapless vehicle" program and for instance Yaw vectoring for exhaust nozzle and
SUMMARY OF FLUIDIC THRUST VECTORING RESEARCH CONDUCTED AT NASA LANGLEY RESEARCH CENTER

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wrightwing

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Unread post13 Sep 2011, 20:28

geogen wrote:Now if we can only get an F-16 CCV + 360 degree F110 TVC worked up over at NASA and into the airshows.

Seriously though, a note to Shaken... thanks for that description and indeed, many if not all fighter pilots could find themselves in a position making a series of dogfight errors as you say - at least once in the phone booth, so to speak. And as you say... when aircrafts are maneuvering at the upper limits of their effective operating altitudes and when their respective speeds decrease after sustained ACM, or when ACM demands an aircraft be flown in maximal angles of attack, or if there is some form of control surface damage, etc, true, TVC would enable an effective advantage. And definitely, when an aircraft equipped with TVC might be conducting rapid directional nose-pointing maneuvers, it is an aircraft more effectively in control of the flight envelope's advantage - e.g., in it's ability to maximize the direction of the nose pointing in a minimum sequence of time and G loads.

Perhaps the optimal compromise to the thread's theme would be generated from some sort of combined rapid center-of-lift manipulating airframe lay-out, combined with a Thrust-reversing, Fluidic Thrust vectoring nozzle ;) Yes please, for the F-16XXL :thumb:


Why not a Block IV cranked arrow Super Hornet, with EPE engines, CFTs, etc...? 8)
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