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By: - 17th April 2010 at 13:16 Permalink - Edited 1st January 1970 at 01:00
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By: - 17th April 2010 at 13:26 Permalink - Edited 1st January 1970 at 01:00
Well. Here is a few snippets from a NASA sponsored study on tailess fighters (conducted by Boeing):Notice that canard designs are labeled "Moderate observables"
http://bayimg.com/kaLeNAACPLow/Moderate observables are defined here:
http://bayimg.com/kAlEpaacPI.e. according to them, to get yf-22/yf-23 level of stealth, canards are ok.
Do you have the whole article? Sounds interesting.
By: - 17th April 2010 at 13:37 Permalink - Edited 1st January 1970 at 01:00
Well, perfect stealth fighter is still a flying wing with any unnecessary surface eleminated.
Real question is if canards are really worse as tailerons for overal rcs.
By: - 17th April 2010 at 13:53 Permalink - Edited 1st January 1970 at 01:00
Do you have the whole article? Sounds interesting.
It should be available here: http://naca.larc.nasa.gov/search.jsp
The title is "Investigation into the impact of agility in conceptual fighter design"
The multi-role aircraft from this study supposedly became the x-36
By: - 17th April 2010 at 14:38 Permalink - Edited 1st January 1970 at 01:00
It should be available here: http://naca.larc.nasa.gov/search.jsp
The title is "Investigation into the impact of agility in conceptual fighter design"The multi-role aircraft from this study supposedly became the x-36
Which contributed to the McD/NG JSF proposal (wherein they eventually ditched the canard).
By: - 17th April 2010 at 15:40 Permalink - Edited 1st January 1970 at 01:00
I notice that Moderate observables is taken to describe vehicles similar to YF-22/YF23 airplanes, As is those with canards.
A superior fighter would be a B-2, but do away with control surfaces altogether replaced with jets, agile like Bruce Lee, accelerate like a 220 swift, and with the speed of light. Or at least trying to combine some measures of those attributes, like the F-22 did.
By: - 17th April 2010 at 15:45 Permalink - Edited 1st January 1970 at 01:00
I notice that Moderate observables is taken to describe vehicles similar to YF-22/YF23 airplanes, As is those with canards.A superior fighter would be a B-2, but do away with control surfaces altogether replaced with jets, agile like Bruce Lee, accelerate like a 220 swift, and with the speed of light. Or at least trying to combine some measures of those attributes, like the F-22 did.
The only thing that bugs me about getting rid of control surfaces altogether is it means you lose the engine, you eject.
By: - 17th April 2010 at 15:59 Permalink - Edited 1st January 1970 at 01:00
The only thing that bugs me about getting rid of control surfaces altogether is it means you lose the engine, you eject.
Or you can engineer in an augmented system as a reserve, preferably one that doesn't act as a weight penalty. I don't think engineers should limit themselves by sticking to the box.
By: - 17th April 2010 at 16:03 Permalink - Edited 1st January 1970 at 01:00
Or you can engineer in an augmented system as a reserve, preferably one that doesn't act as a weight penalty. I don't think engineers should limit themselves by sticking to the box.
Augmented system such as what?
By: - 17th April 2010 at 16:25 Permalink - Edited 1st January 1970 at 01:00
Augmented system such as what?
Circulation control perhaps? I'm totally clueless about it though :) But I remember reading about it some years ago
Edit: found a link about a BAE UAV using Circulation control + fludic thrust vectoring instead of usual control surfaces
By: - 17th April 2010 at 16:28 Permalink - Edited 1st January 1970 at 01:00
Circulation control perhaps? I'm totally clueless about it though :) But I remember reading about it some years agoEdit: found a link about a BAE UAV using Circulation control + fludic thrust vectoring instead of usual control surfaces
How about Iondrive thrusters:eek:
We're not there quite yet...:)
Thanks
By: - 17th April 2010 at 16:48 Permalink - Edited 1st January 1970 at 01:00
Circulation control perhaps? I'm totally clueless about it though :) But I remember reading about it some years agoEdit: found a link about a BAE UAV using Circulation control + fludic thrust vectoring instead of usual control surfaces
Fluidic goes with the engine. It's just a different form of vectoring.
By: - 17th April 2010 at 17:58 Permalink - Edited 1st January 1970 at 01:00
Take a good look at the YF-23 landing attitude, in video or photos. It seems quite steep. Now imagine trying to land on a rolling and heaving aircraft carrier.
You could get a flatter landing attitude by increasing the authority of the tailpane ( ie make it bigger ), but that is even worse for RCS and subtracts from overall lift since tailplanes produce downforce. An obviously better approach would be foreplanes, or canards, since they can be sized smaller, and they contribute to overall lift by producing upforce when it is most needed; as you're trying to land on that rolling, heaving carrier.
By: - 17th April 2010 at 19:14 Permalink - Edited 1st January 1970 at 01:00
Augmented system such as what?
There's no limit to the choices, once you lose your main powerplant you either have a spare power source, or a second redundant powerplant. Quite a few single-engine fighters carried an APU to power their electronics. Imagine if you could divert those resources in an emergency to extend flight control on a flameout.
By: - 17th April 2010 at 19:26 Permalink - Edited 1st January 1970 at 01:00
You could get a flatter landing attitude by increasing the authority of the tailpane ( ie make it bigger ), but that is even worse for RCS and subtracts from overall lift since tailplanes produce downforce.
That's only true with stable wing-tails, not unstable ones. In unstable wing-tails (like the F-16, F-22 & F-35), the stabs produce lift to prevent the nose from overpitching. In stable wing-tails (like the F-15), the stabs do indeed produce downforce to keep the nose from drooping in level flight.
An obviously better approach would be foreplanes, or canards, since they can be sized smaller, and they contribute to overall lift by producing upforce when it is most needed
That's only true with stable canard-deltas, not unstable ones. ;) In unstable canard-deltas (like the EF), canards produce downforce to keep the nose from overpitching.
As to why canards make for poor VLO designs, a major reason is canards having to be precisely sized, positioned and shaped for optimum aerodynamics and airflow interactions with the main wing. With rear-mounted stabs, engineers have much more leeway when it comes to VLO optimized shaping. Look at the shaping of the F-22's stabs:
Also look at the F-22 head-on--the stabs and wings are on the same plane. Not so with any of the canard-deltas:
By: - 17th April 2010 at 19:42 Permalink - Edited 1st January 1970 at 01:00
There's no limit to the choices, once you lose your main powerplant you either have a spare power source, or a second redundant powerplant. Quite a few single-engine fighters carried an APU to power their electronics. Imagine if you could divert those resources in an emergency to extend flight control on a flameout.
What would you use to provide thrust needed to control the aircraft? You going to pipe APU exhaust through the main engine nozzle? What if the nozzle is damaged, as is typical with a MANPADS shot? Also, APU thrust is TINY compared to the main engine and unlikely to have enough power to matter even if you did expend the internal volume to provide the ducting from the APU to the main engine nozzle (not to mention little details like a hole in the engine for APU exhaust entry and some way of ensuring the exhaust doesn't simply go out BOTH ends of the engine). As for hauling second engine just in case the first one is damaged, how are you going to get the air to and from the second engine? Where would the engine reside? How much fuel and internal volume would you give up for it and it's ducting? I think you'll find hauling around a secondary powerplant "just in case" is a non-starter. Consider how many fighters back in the day toyed with the idea of auxiliary rocket packs for added acceleration. How many made it into service? I think "none" is the answer IIRC. Then you have the problem of maintainablity. Now you have TWO engines in your maintenance chain to deal with. That was the main reason the McD/NG JSF entry got the axe.
By: - 18th April 2010 at 02:25 Permalink - Edited 1st January 1970 at 01:00
While its true thatmost new generation canards are unstable, they are only marginally so, such that as the CoL moves back from quarter chord as the aircraft becomes supersonic, they actually require a slight up-trim.
Also are you sure the F-22 \nd F-35 are unstable? I've never actually looked into that aspect of their designs. One thing that strikes me, is the size of the tailplanes on both aircraft. They are large compared to the wing. I would imagine that canards on either aircraft would have been less than half the size (?).
I don't see the reason for comparing edge alignments of F-22 and Typhoon. If the typhoon had been designed for stealth, like the X-36 for example, it would have had edge alignment. I would suggest that tailplane positioning is much more critical than a canard on the Typhoon (since its not close-coupled),simply because it has to live in the downwash of the wing.
I only stated the US NAVY's preference for a flat landing attitude because I know the Boeing X-32 was re-designed to incorporate large tail surfaces and a swept wing instead of the original delta for just such a reason.
By: - 18th April 2010 at 04:38 Permalink - Edited 1st January 1970 at 01:00
While its true thatmost new generation canards are unstable, they are only marginally so, such that as the CoL moves back from quarter chord as the aircraft becomes supersonic, they actually require a slight up-trim.
Most tight, dogfighting breaking turns occur well below sonic speeds, where ustable wing-tails are lift-lift, and unstable canard-deltas are downforce-lift.
Regardless of how you spin it, the unstable wing-tail is the more efficient design.
Also are you sure the F-22 \nd F-35 are unstable?
All US fighters after--and including--the F-16 are unstable. The only "stable" ones (gen. 4 and above) are the Eagle and the Tomcat.
One thing that strikes me, is the size of the tailplanes on both aircraft. They are large compared to the wing. I would imagine that canards on either aircraft would have been less than half the size (?).
So?
I don't see the reason for comparing edge alignments of F-22 and Typhoon. If the typhoon had been designed for stealth, like the X-36 for example, it would have had edge alignment.
If they could've incorporated planform alignment into the design, they would've.
I would suggest that tailplane positioning is much more critical than a canard on the Typhoon (since its not close-coupled),simply because it has to live in the downwash of the wing.
The fact that the canards' downwash is ahead of the wings is precisely why their design is critical, aerodynamically speaking.
Rear-mounted stabs don't affect the wings at all with their downwash. You have more leeway as to shape, position and size for a lower RCS, and to offset whatever negative effects produced by wing downwash.
Also note that wing-tails are better suited for vortice management (via LERXs), enabling better AoA performance.
By: - 18th April 2010 at 06:47 Permalink - Edited 1st January 1970 at 01:00
All US fighters after the F-16 are noi unstable. The F-18 and its newer E version are not, fly-by-wire does not mean unstable. Although I admit I don't know about F-22/35.
The downwash of the wing is huge compared to the downwash of a canard and the reason so much experimentation was done in the 50s and 60s with tailplane positioning. The downwash of the Typhoon is almost non-existant except at extreme AoA.
Canards are used (close coupled) as substitutes for LERXs to generate high AoA vortices and stick the boundary layer to the wing but LERXs provide little benefit at low or no AoA.
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By: sferrin - 17th April 2010 at 12:39
From here:
http://up-ship.com/blog/
Of course some will immediately jump on the "see, canards are totally compatible with stealth" bandwagon, BUT consider that Northrop didn't want it when they didn't HAVE to have it. They only added it to deal with the low speed carrier requirement. Same with swing-wings (someone mentioned those). They aren't great for stealth either. Why? Edge alignment. Do you align it for slow speed or high speed, or somewhere in between? Also it introduces more seams and all your high lift devices would introduce more gaps to deal with. The F-23 NATF would have (apparently) used a canard whilst the F-22 NATF would have used a swing-wing. Again, I stress (not that it'll even register to some) that if canards or swing-wings were a superior solution for stealth the USAF versions of the ATFs would have had them. Neither did.