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By: - 5th June 2004 at 07:09 Permalink - Edited 1st January 1970 at 01:00
Looks interesting, similar to the F-29 concept (wonder if Argentina is interested in that secretly).
The twin missile rails on the tips is interesting, wouldn't that be rather heavy for the tips in high AoA? I can see that it's not exactly a stealth a/c due to the mid fusalage fin. Most of the frame looks like it has been a redevlopment of the basic Hornet frame, leading me to think that there maybe some US involvment in it.
By: - 5th June 2004 at 18:00 Permalink - Edited 1st January 1970 at 01:00
Aerodynamically there are no cons to this design. Structurally its a nightmare, and is a huge problem trying to find ways to make the wing strong enough to prevent wing twist (or as you say flutter). The Grumman X-29 was the US´s stab at this type of design.
By: - 5th June 2004 at 18:51 Permalink - Edited 1st January 1970 at 01:00
Looks great, but did they develop some new kind of super-stiff and light material ? If not, those wingtip rails would reduce manouverability of the aircraft drastically.(Since you had a very low g-limit) Or you would get some weight problems, making the wing durable enough. And for what reason they placed this fin right in front of the airbrake (near the center of gravity) ? Next thing are the rudders. They are placed behind the canards. I would assume that those turbulences generated by the canards would reduce the effectiveness of those rudders. Further more this could cause some problems with vibrations. So again you would need a very strong (and heavy) structure...
:confused:
By: - 5th June 2004 at 19:30 Permalink - Edited 1st January 1970 at 01:00
"Looks great, but did they develop some new kind of super-stiff and light material ?"
Yeah, carbon fiber
"If not, those wingtip rails would reduce manouverability of the aircraft drastically.(Since you had a very low g-limit) "
No, that type of wing planeshape increases maneuverability.
"Or you would get some weight problems, making the wing durable enough."
The technology is just not there to make a forward swept wing structurally equal to a normal swept wing.
"And for what reason they placed this fin right in front of the airbrake (near the center of gravity) ?"
Im guessing for making the rudders more effective or for spin recovery
"Next thing are the rudders. They are placed behind the canards. I would assume that those turbulences generated by the canards would reduce the effectiveness of those rudders. "
No, the turbulence (vorcities) actually improve wing lift. They would only have an effect on the rudders at high AOA, and then less so than the wings.
"Further more this could cause some problems with vibrations. So again you would need a very strong (and heavy) structure... "
I dont see why the canards would cause vibrations anymore than any other canard fighter.
By: - 5th June 2004 at 20:21 Permalink - Edited 1st January 1970 at 01:00
Yeah, carbon fiber
The young modulus of carbon fiber is not endless high. It is possible to produce a forward swept wing with it. But with those rails you got extra momentums to counter. So you would need a material with a higher young's modulus or you had to increase the size of your structural elements,but there are limits given by the aerodynamic and weight. An other solution would be a lower g-limit. Lets say 4.5 instead of 9 or so. That is what I meant with decraesed manouverability caused by this rail-construction. Even if you use Si-Si-C (silicon infiltrated silicon carbide), you will have a problem with the limited dimensions.
I dont see why the canards would cause vibrations anymore than any other canard fighter.
Have a look at any other canard/delta. None of them has the canards placed in that way. Most of them have only one rudder, so no problem with the turbulences caused by the canards. The MiG 1.42 has the canards in a position, the don't effect the rudders, too. Now let's have a look at this design: those canards are placed pretty high. The turbulent airstream produced by the canards hits directly the rudders. That means they are less effective, additionally turbulences will cause vibrations. Vibrations mean you need a stronger structure, to counter them. This means weight.
My conclusion is: it is an great looking aircraft. It is limited to 5 g. It has a damn short range, because it's structure is pretty heavy and provides not much space for fuel.
But it should have a good low speed handling. It is the perfect .... heli-buster !
By: - 5th June 2004 at 21:18 Permalink - Edited 1st January 1970 at 01:00
Very nice!
I see a potential center of gravity problem with weapons and external fuel loaded. Also the landing gear position (main) might be too far aft which may increase take off distances and aerobraking on landing may not be possible either.
Looks great though any more pictures?
By: - 5th June 2004 at 21:21 Permalink - Edited 1st January 1970 at 01:00
Very nice!I see a potential center of gravity problem with weapons and external fuel loaded. Also the landing gear position (main) might be too far aft which may increase take off distances and aerobraking on landing may not be possible either.
Looks great though any more pictures?
there's tons here and a link to more on that same page
http://www.starshipmodeler.org/gallery8/gc_pampa.htm
great analysis Mixtec and Aurel, very interesting reads. I do agree that it is quite odd to add a fin near the airbrakes though.
By: - 5th June 2004 at 21:46 Permalink - Edited 1st January 1970 at 01:00
There was an other design from this guy, even more exotic. Didn't found it on your link Wachenroder, but I'm shure you know what I mean. It had big canted inlets with blinds in front of it, on the upper side of the fuselage. It sports a green camouflage. :confused:
By: - 5th June 2004 at 22:26 Permalink - Edited 1st January 1970 at 01:00
I tend to agree with Aurel on this one; those canards will cause problems for the rudders. (Remember those problems that were caused by the small lex:es on F-18. Now that was small lex:es, this is pretty big canards...)
And when it comes to flutter - a forward swept wing means that you are getting serious flutter effects (divergence!) at lower speed than you would get with an aft swept wing. In order to dampen out flutter effects you could add point masses at the maximum displacement positions - but in this case they've actually added more mass (ie two missiles) to the wingtip which acts as a node. This will make flutter effects even worse!
And at last, I don't see the point in having this fin behind the cockpit glas. When you get a few degrees of AoA, it will have zero effect on the yaw stability.
Castor
By: - 5th June 2004 at 23:22 Permalink - Edited 1st January 1970 at 01:00
totally agree woth flutter and that canard and double rudder problems... Same thoughts here. Added to that. Double missiles so close to eachother is not practical. Releasing one and maneuvring... That will be dangerous. Just like the fact that the smoke will make the other screen dirty...
And those flaps on the front of the forward swept wing... pretty impossible...
refueling just behind the canard? Wow.. must be difficult to handle for a boom operator...
Those inlets are not possible with that front gear...
By: - 6th June 2004 at 00:16 Permalink - Edited 1st January 1970 at 01:00
The young modulus of carbon fiber is not endless high. It is possible to produce a forward swept wing with it. But with those rails you got extra momentums to counter. So you would need a material with a higher young's modulus or you had to increase the size of your structural elements,but there are limits given by the aerodynamic and weight. An other solution would be a lower g-limit. Lets say 4.5 instead of 9 or so. That is what I meant with decraesed manouverability caused by this rail-construction. Even if you use Si-Si-C (silicon infiltrated silicon carbide), you will have a problem with the limited dimensions.Have a look at any other canard/delta. None of them has the canards placed in that way. Most of them have only one rudder, so no problem with the turbulences caused by the canards. The MiG 1.42 has the canards in a position, the don't effect the rudders, too. Now let's have a look at this design: those canards are placed pretty high. The turbulent airstream produced by the canards hits directly the rudders. That means they are less effective, additionally turbulences will cause vibrations. Vibrations mean you need a stronger structure, to counter them. This means weight.
My conclusion is: it is an great looking aircraft. It is limited to 5 g. It has a damn short range, because it's structure is pretty heavy and provides not much space for fuel.
But it should have a good low speed handling. It is the perfect .... heli-buster !
the modulus is not the problem as forward swept wings have already been made using composite materials.
These materials are used in mil and civil applications i.e. T300 (torayca/Toray of japan) and IM7/8552 (hexcel composites USA as used in F/A-18's EFA etc etc. (T300 being lesser of the two).
the problem is the compression strength, and delamination resistance fracture toughness modes I+II.
in the end though to cut it short, the wing structure thickness would be/is so high that you would not be able to store any fuel in them as can be done with conventional wings.
and you cant use Si-Si-C in a structure thats going to be pounded constantly thats suicidel! and do you mean Silican coated carbon carbon? ceramics ?
XN-70 garnoc!
By: - 6th June 2004 at 00:54 Permalink - Edited 1st January 1970 at 01:00
I tend to agree with Aurel on this one; those canards will cause problems for the rudders. (Remember those problems that were caused by the small lex:es on F-18. Now that was small lex:es, this is pretty big canards...)And when it comes to flutter - a forward swept wing means that you are getting serious flutter effects (divergence!) at lower speed than you would get with an aft swept wing. In order to dampen out flutter effects you could add point masses at the maximum displacement positions - but in this case they've actually added more mass (ie two missiles) to the wingtip which acts as a node. This will make flutter effects even worse!
And at last, I don't see the point in having this fin behind the cockpit glas. When you get a few degrees of AoA, it will have zero effect on the yaw stability.
Castor
Thats certainly not true, when you say flutter, again I assume you mean vorcities. And at lower speed the vorcities instead of seperating and pulling off the wingtips to create huge drag inducing wing tip vortexes as on a normal reaward swept plane, instead stay on the wing and adhere to the wing to improve lift, especially to the upper rear part of the wing where airflow becomes sluggish.
And as for the fin on the back of the plane losing lift at AoA, if that were true, it would be true for the rudder also.
BTW, I hope you guys have noticed that the guy who made this model just by cutting out different parts from different models and just molded them together with putty. The forward part of the fuselage is an F-15 with Rafale canards stuck on it and the rear part of the the fuselage is an F-18, with F-22 rudders and reversed F-16 strakes under them. Wings could be Su-27 wings reversed, who knows what else.
By: - 6th June 2004 at 06:21 Permalink - Edited 1st January 1970 at 01:00
the modulus is not the problem as forward swept wings have already been made using composite materials.
Yes, but without the additional stress of those wingtip railes. We all know that torque is the nastiest stress. In the end we all speak about the same problem: to make the wing strong enough for these railes you have to design oversized structural elements. And as aerodynamics limit your possibilities you can't design those structural elements optimal, which means even more material if you don't want to change the wing's thickness. Ergo, it is heavy and provides not much room for fuel. If you streamline this aircraft a little bit, reduce unnaccesary control surfaces, use a wing that stores more fuel and eblarge the fuselage for additional fuel, you got: oups an Rafale. But this would of course be boring. This design looks much better. Maybe this little fin is inspired by the AFTI 16 ? Just a quick shot...
By: - 6th June 2004 at 09:23 Permalink - Edited 1st January 1970 at 01:00
"Thats certainly not true, when you say flutter, again I assume you mean vorcities."
- No. Flutter is NOT the same thing as vortices. Flutter is when the wing starts to twist and bend in different mode shapes. If you increase the speed further divergence will occur, and divergence means that the wing will bend up (or downwards) until it breaks into pieces.
"And as for the fin on the back of the plane losing lift at AoA, if that were true, it would be true for the rudder also."
- Yes, the real rudder suffers from the same kind of problems. But this is solved by making the rudder longer (and bigger).
By: - 6th June 2004 at 12:37 Permalink - Edited 1st January 1970 at 01:00
Yes, but without the additional stress of those wingtip railes. We all know that torque is the nastiest stress. In the end we all speak about the same problem: to make the wing strong enough for these railes you have to design oversized structural elements. And as aerodynamics limit your possibilities you can't design those structural elements optimal, which means even more material if you don't want to change the wing's thickness. Ergo, it is heavy and provides not much room for fuel.
Rails??? do you seriously believe that wingtip rails would provide more aerodynamic force then the wing itself ??
If the problems are similar to those of conventionaly swept wings then the rails would actually help evleviate some of the prblems of wing tip bleed.
compared to the wing area and torques generated by it the rails do nothing.
I have already pointed out the fuel capacity issue why restate it?
By: - 6th June 2004 at 12:42 Permalink - Edited 1st January 1970 at 01:00
canards are not large enough.
By: - 6th June 2004 at 14:52 Permalink - Edited 1st January 1970 at 01:00
The elevons on the rear edge of the wing don't seem big enough for me to give good pitch and roll authority unless they can extend backward.
It's just molded from different pieces of different aircraft like a Frankenstein.
By: - 6th June 2004 at 17:22 Permalink - Edited 1st January 1970 at 01:00
Rails??? do you seriously believe that wingtip rails would provide more aerodynamic force then the wing itself ??
You are right. The railes are no big problem. Only if missiles are attached you need a stronger structure.
By: - 6th June 2004 at 18:03 Permalink - Edited 1st January 1970 at 01:00
You are right. The railes are no big problem. Only if missiles are attached you need a stronger structure.
compared to the weight of the aircraft ?? because thats the load on the wings.
By: - 6th June 2004 at 18:39 Permalink - Edited 1st January 1970 at 01:00
compared to the weight of the aircraft ?? because thats the load on the wings.
Pulling high g's certainly means a lot to wing loading, but the wing stiffnes must also be able to deal with the dynamic effects that occurs on a wing. These dynamic effects, or flutter effects, are highly dependent on where you put your masses - which in this case is the missiles, bombs etc - and even worse on a forward swept wing than they would have been on a conventional wing.
Normally you don't want to put masses at the points where you'll get displacement maximas in the wings first bending modes, but in this design they've actually added twice the amount of mass (two missiles that is) on a point where most of the bending modes will have a displacement maxima - namely the wing tip. This will create huge dynamic effects - and stress - on the structure and ultimately (if the speed is high enough) divergence where the wing will break into pieces.
You may want to check out this movie:
http://www.airspacemag.com/asm/Web/Site/QT/A6Flutter.html
regards,
Castor
Posts: 669
By: WACHENR0DER - 5th June 2004 at 06:37
This seems to be a popular fictional concept of an attack aircraft for Argentina (found the pic through gdcdreams and starshipmodeler) sites,
in general, FSW wings give the following advantages
-better transsonic performance
-rumored to give better lift
-higher angle of attack
along with these problems
-wingtips tend to flutter.. but this is supposedly rectified by using composites
-drag
-perhaps RCS increases?
was wondering what your thoughts on this design are :)