Typhoon v Rafale Question
Rafale dihedral not so obvious especially when the foreplane is not in streamlined position.
Rafale | Flickr - Photo Sharing!
Also when loading this picture, noticed it has radar reflecting edges built into the trailing edge of the foreplane. Not immediately obvious but looking closer on the pic will show the characteristic zig-zag.
The radar reduced reflection edges | Flickr - Photo Sharing!
Rafale | Flickr - Photo Sharing!
Also when loading this picture, noticed it has radar reflecting edges built into the trailing edge of the foreplane. Not immediately obvious but looking closer on the pic will show the characteristic zig-zag.
The radar reduced reflection edges | Flickr - Photo Sharing!
Last edited by sandozer; 14th Sep 2013 at 20:45. Reason: Additional picture
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I must be sad and joining the old farts club but I am actually finding this interesting - purile and childish comments (by me) aside.....
do keep it up - I are learnding
wibble
do keep it up - I are learnding
wibble
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Many thanks chaps ...
Armed with a couple of cups of strong tea ... I've now read the material you guys posted ... what a fascinating topic
A special thanks to Courtney for the Wednesday afternoon maths workout ... which was a bit painful in places.
So in short summary ...
It would seem an important aspect of close-coupled canard/foreplanes is the production of vortices which interact/excite/energise other vortices (eg wing generated) to benefit, amongst other positives at sub/supersonic speeds, the max angle of attack achievable which in turn provides the aircraft with extensive post stall maneuvering capabilities. It would seem that the use of anhedral or dihedral applied to canard/foreplanes has a lot to do with positioning/optimising these vortices.
Some very complicated trade offs and compromises appear to be at work
For those interested ORAC's reference ... see "Aerodynamics" section which covers the topic in more depth (which I suspect is a lift from other work).
Best ...
Coff.
Armed with a couple of cups of strong tea ... I've now read the material you guys posted ... what a fascinating topic
A special thanks to Courtney for the Wednesday afternoon maths workout ... which was a bit painful in places.
So in short summary ...
It would seem an important aspect of close-coupled canard/foreplanes is the production of vortices which interact/excite/energise other vortices (eg wing generated) to benefit, amongst other positives at sub/supersonic speeds, the max angle of attack achievable which in turn provides the aircraft with extensive post stall maneuvering capabilities. It would seem that the use of anhedral or dihedral applied to canard/foreplanes has a lot to do with positioning/optimising these vortices.
Some very complicated trade offs and compromises appear to be at work
For those interested ORAC's reference ... see "Aerodynamics" section which covers the topic in more depth (which I suspect is a lift from other work).
Best ...
Coff.
Last edited by CoffmanStarter; 11th Sep 2013 at 17:38.
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ORAC -After having a quick scan through that blog article my spidey senses are screaming Top Trumps, a copy of Jane's 'All The World's Aircraft' and a combat flight sim game of some sort are his primary reference material.
Some selected gems include,
"Wikipedia puts flyaway cost at 90 million....."
An in-line reference to Wikipedia. Sweet Jesus, how to destroy any academic credibility in one simple swipe.
"Typhoon has larger radar, but that doesn’t matter because noone sane is going to use radar in air-to-air combat anyway...."
Yeah I'm sure he is right, they're just more convenient to install than a big lump of concrete.
Some selected gems include,
"Wikipedia puts flyaway cost at 90 million....."
An in-line reference to Wikipedia. Sweet Jesus, how to destroy any academic credibility in one simple swipe.
"Typhoon has larger radar, but that doesn’t matter because noone sane is going to use radar in air-to-air combat anyway...."
Yeah I'm sure he is right, they're just more convenient to install than a big lump of concrete.
The link provided by ORAC is more interesting, but still a bit limited - e.g.:
"Mid-wing vertical arrangement is more laterally stable than low-wing arrangement, especially when combined with Rafale’s wide body. As too much lateral stability can cause severe Dutch roll and excessive roll response to lateral gusts, Rafale’s wings are designed with anhedral to reduce stability."
Any fule no that, so I am surprised they put that in the article.
If I am to stick my neck out, I would say that the Rafale designers have prioritised low-speed handling characteristics to allow it to land on carriers with reasonable safety margins. This has meant optimising the airframe for non-compressible flow - hence fairly conventional lateral stability augmentation by increasing anhedral. They have probably done some clever stability augmentation to take care of the compromises in other parts of the flight envelope, particularly supersonic flight.
On the other hand, Typhoon designers have possibly aimed to optimise performance in compressible flow. Anhedral is not desirable in supersonic flight as it worsens shock wave separation from the extrados of the wing exacerbating mach tuck, and drag. So they have possibly gone for a flat wing to give good stability and range in supersonic flight and used stability augmentation to improve handling in subsonic flight.
Just guesswork - you would really have to interview the software engineers to get a proper answer.
Last edited by Trim Stab; 11th Sep 2013 at 18:17.
According to the following paper there are only two locations for the foreplane that don't cause excessive interference with the main wing and thus deterioration of lift/drag ratio in a Delta Canard configuration:
Low and far forward or high and close to the wing.
It is stated that this was found out in years of Investigation prior to finalisation of the design.
You see exactly these two layouts in the Typhoon and Rafale, respectively:
Rafale has the canard close to the main wing. Dihedral serves to move the tip of the canard high above the main plane without messing up the fuselage shape/cross section.
Typhoon has the other layout: Low canard and with anhedral they move the tip down to the level of the main plane despite the chin inlet for the engines.
Dihedral/anhedral in both designs is not related to lateral stability. It is rather used to move the foreplane higher/lower matching to the longitudinal position of the foreplane without compromising general fuselage layout.
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADP010499
ETA: The difference between both layouts points indeed as @coffman has stated to the design priorities:
The Close Coupled Canard of the Rafale will help to control airflow over the main wing at higher AoA and thus be helpful for low speed performance/lift which is crucial for Carrier operations.
Long Coupled Canard has some advantages at supersonic speeds as it allows for a more negative longitudinal static stability margin and allows the use of a somewhat smaller foreplane size.
regards,
henra
Low and far forward or high and close to the wing.
It is stated that this was found out in years of Investigation prior to finalisation of the design.
You see exactly these two layouts in the Typhoon and Rafale, respectively:
Rafale has the canard close to the main wing. Dihedral serves to move the tip of the canard high above the main plane without messing up the fuselage shape/cross section.
Typhoon has the other layout: Low canard and with anhedral they move the tip down to the level of the main plane despite the chin inlet for the engines.
Dihedral/anhedral in both designs is not related to lateral stability. It is rather used to move the foreplane higher/lower matching to the longitudinal position of the foreplane without compromising general fuselage layout.
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADP010499
ETA: The difference between both layouts points indeed as @coffman has stated to the design priorities:
The Close Coupled Canard of the Rafale will help to control airflow over the main wing at higher AoA and thus be helpful for low speed performance/lift which is crucial for Carrier operations.
Long Coupled Canard has some advantages at supersonic speeds as it allows for a more negative longitudinal static stability margin and allows the use of a somewhat smaller foreplane size.
regards,
henra
Last edited by henra; 11th Sep 2013 at 21:54.
Henra - very interesting paper - would like to see an equivalent essay on the Rafale!
I thought that this passage was quite interesting:
"The demand for linear aerodynamics for the flight control system is always present with every aircraft design. However, there is also a view that, because the FCS is clever, it can cope with very non-linear aerodynamics. The phrase often heard was "never mind, the FCS will take care of it!" In the case of Eurofighter, the level of instability that was required for the overall aircraft was such that linear aerodynamics became a much firmer requirement, together with good aerodynamics from the flying controls. "
I have to say that I thought that FCS would be able to take care of any anomalies in the aero-design.
I thought that this passage was quite interesting:
"The demand for linear aerodynamics for the flight control system is always present with every aircraft design. However, there is also a view that, because the FCS is clever, it can cope with very non-linear aerodynamics. The phrase often heard was "never mind, the FCS will take care of it!" In the case of Eurofighter, the level of instability that was required for the overall aircraft was such that linear aerodynamics became a much firmer requirement, together with good aerodynamics from the flying controls. "
I have to say that I thought that FCS would be able to take care of any anomalies in the aero-design.
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Originally Posted by Trim Stab
...would like to see an equivalent essay on the Rafale!
Download Rafale_demonstrator.pdf from FileFactory.com
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I do not believe the Eurofighter foreplane anhedral is motivated by any particular stability criteria, in this case, but simply to stay away from the pilot field of view. The paper referenced by Henra alludes to it.
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Another limiting factor is the airframe structural rigidity. The inertial sensors providing inputs to the FBW computers are ideally located at the aircraft CG, however, there will still be some input from the structure bending under load. If the FBW system has very high gains to keep up with large amounts of aerodynamic instabilities the structural response can be large enough to affect the sensor inputs. In the extreme this “feedback” can cause the system to diverge (not good). It is also very important that the actuator mounting and connection to the flight control surface be as rigid as practical as it can have a similar effect.
(Based on the subject of spelling and grammar in some threads on this forum I apologize in advance for the “American” spelling and any other grammatical errors others may find offensive.)
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Why are aircraft the shapes they are?
Somebody mentioned the Harrier.
Senior design chappie to a Hawker’s ideas man- late 50s: “You want to put an engine that is how big on the CG? Well it will need a very big hole to get it in and out. Said hole will have to be on top as the fuse will need strengthening round the hole and you might as well use the wing as a nice strong cover plate.
The wing will have to have sweep for the speed you want, so the rolling moment due to sideslip will be too big ‘cos of the sum of the sweep effects and the high wing low CG setup. So standby for some anhedral to keep the L&D gust response sensible (you did say you want to aim this thing at targets didn’t you?)
With the wing so far off the ground a pair of tricycle main legs will be stupidly long and heavy and will have to retract into pods as the wing is the only place for fuel thanks to this bloody engine you started with. As for those hot rear exhausts what do you want to use for tyres? Use a bicycle gear and it might work. Tough tit about the reduced braking effect - I thought you said it was a VTOL so who needs brakes?
Don’t forget to keep the outriggers short enough to not hit the ground until the main leg has taken the landing loads. If you don’t want it to lean after the main leg expands following touchdown well fit the main leg with an oleo that has no rebound (I’m sure you can stuff the oil somewhere until it is needed for the next landing). Go away I’ve got work to do.
Foreplanes
As to why the foreplanes on the OPs aircraft are like they are I have no insider knowledge but I would be pretty sure that the designers had two main aims:
1 Improve the wing aerodynamics - especially at high AoA by feeding it helpful vortices
2 Help longitudinal control in general and especially in unstable parts of the envelope
As to whether they have anhedral or dihedral remember they have to be positioned pretty carefully with respect to the wing because of point 1 above. If at that particular height on the side of the nose it is not easy to provide pivots and actuators then stand by to move the attachment point up and down a bit thus needing anhedral or dihedral to achieve a compromise relationship with the wing.
Aircraft design is full of such compromises and as with sex one thing always leads to another.
Somebody mentioned the Harrier.
Senior design chappie to a Hawker’s ideas man- late 50s: “You want to put an engine that is how big on the CG? Well it will need a very big hole to get it in and out. Said hole will have to be on top as the fuse will need strengthening round the hole and you might as well use the wing as a nice strong cover plate.
The wing will have to have sweep for the speed you want, so the rolling moment due to sideslip will be too big ‘cos of the sum of the sweep effects and the high wing low CG setup. So standby for some anhedral to keep the L&D gust response sensible (you did say you want to aim this thing at targets didn’t you?)
With the wing so far off the ground a pair of tricycle main legs will be stupidly long and heavy and will have to retract into pods as the wing is the only place for fuel thanks to this bloody engine you started with. As for those hot rear exhausts what do you want to use for tyres? Use a bicycle gear and it might work. Tough tit about the reduced braking effect - I thought you said it was a VTOL so who needs brakes?
Don’t forget to keep the outriggers short enough to not hit the ground until the main leg has taken the landing loads. If you don’t want it to lean after the main leg expands following touchdown well fit the main leg with an oleo that has no rebound (I’m sure you can stuff the oil somewhere until it is needed for the next landing). Go away I’ve got work to do.
Foreplanes
As to why the foreplanes on the OPs aircraft are like they are I have no insider knowledge but I would be pretty sure that the designers had two main aims:
1 Improve the wing aerodynamics - especially at high AoA by feeding it helpful vortices
2 Help longitudinal control in general and especially in unstable parts of the envelope
As to whether they have anhedral or dihedral remember they have to be positioned pretty carefully with respect to the wing because of point 1 above. If at that particular height on the side of the nose it is not easy to provide pivots and actuators then stand by to move the attachment point up and down a bit thus needing anhedral or dihedral to achieve a compromise relationship with the wing.
Aircraft design is full of such compromises and as with sex one thing always leads to another.
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Many thanks John for taking the trouble to help
Now wouldn't it be interesting to do a "fly off" between both aircraft ... but I doubt that will ever happen.
Best ...
Coff.
Now wouldn't it be interesting to do a "fly off" between both aircraft ... but I doubt that will ever happen.
Best ...
Coff.