Using Canards vs. Tail for aircraft control in USA and other countries

[lantinian]

When I saw the picture of F-15's CG/Lift diagram by rousseau, I went like: Way the ...?
How can someone pretend to analyze an aircraft if he gets the CG and the Lift mixed.

Ogami musashi is right. If a lot more to it than simply Flight dynamics.

If you (rousseau) have checked the first pages of this tread you would have noticed that me and Woody
went into the trouble of preparing a much more accurate and interesting diagrams than yours.
I had started to make the a diagram for all types of configurations and for all speeds when I realised what Ogami musashi just said. While flight dynamics are important, Aerodynamics are even more important.

Yes, this IS not appropriate to compare canard with horizontal tail, but someone go anywhere emphasis how better the conventional layout is than canard, I have to tell out the truth.

Thanks! I do not think I need to hear this truth. Looking at how you draw diagrams, I wander if the rest
of your post are of the same quality.

Even if canards were better than tails in every aerodynamic scenario (which they are not) there are still other factors that would have weighted in favour of the tails.
Of the 7 ATF proposals only 1 had canards and it was placed last.
Of the 3 JSF proposals none had canards.
The latest SU-35BM variant does not have canards any more.
I am allmost confused that the new Russian fighter Pak-fa will also be canardless.

Most if not all new fighter that reached production designed after the X-29 do not have canards.

So I will just like to quote one General Dynamics engineer. "The only place for the canards is on somebody Else's aeroplane"

lantinian

P.S. I do like canards, just like Boeing apparently:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960000737_1996900737.pdf
see page 58 is the attached image

 

[mrdetonator]

I am allmost confused that the new Russian fighter Pak-fa will also be canardless.

Most if not all new fighter that reached production designed after the X-29 do not have canards.

And why is that?? Just because some meaningless and irrelevant individuals lacking imagination and real aviation engineering draw a PAK-FA proposals based on the F-22 or F-35?? Let me remind most recent fighter designs: Eurofighter, Rafale, Gripen, J-10, Mig-1.44, S-37. What other reasons you have out there you believe that PAK-FA will certainly not be a canards design?

So I will just like to quote one General Dynamics engineer. "The only place for the canards is on somebody Else's aeroplane"

That is the dumbest argument I was talking about. :

 

[rousseau]

lantinian:

Here I won't come to say your drawing is wrong, oppositely, your drawing is wonderful. All I want to say is Canard layout compare with conventional layout is approximately same or just a little bit better for maneuverable when other condition is same.

 

[lantinian]

Let me remind most recent fighter designs: Eurofighter, Rafale, Gripen, J-10, Mig-1.44, S-37

Please read again

Most if not all new fighter that reached production designed after the X-29 do not have canards.

Eurofighter, Rafale and Gripen are all designed in the early 80s. I am talking about the layout.
J-10 was based on Lavi, which in turn was also designed then.

Mig-1.44 was also designed before the ATF configurations were shown. It is also a mid 80's design.
S-37 is not a real fighter. Its a technology demonstrator. Besides, neither of the rusian fighers will ever be operational.

All I want to say is Canard layout compare with conventional layout is approximately same or just a little bit better for maneuverable when other condition is same.

I agree. However, maneuverability is no longer the most important criteria in fighter design.

lantinian

 

[mrdetonator]

Let me remind most recent fighter designs: Eurofighter, Rafale, Gripen, J-10, Mig-1.44, S-37

Please read again

Most if not all new fighter that reached production designed after the X-29 do not have canards.

Please name me at least three new high performance fighters which reached production after X-29 with aft-tail design. thanks
thanks

 

[Woody]

Rousseau, I admire your passion which exceeds my own and thank you Mrdetonator and Ogami Musashi for your posts. Hood's Ray Whitford piece coincides with my own impressions quite nicely. But at the risk of going over old ground may I state the following:-

1. Angle of attach is not the same as turn rate. Think of a car getting sideways (drifting); it doesn't mean it turns a corner any faster because of the increased drag/friction. See my drawings in answer #90 of this thread to see the differences (I can't re-post them because I didn't keep them).

2. Instability doesn't always mean maneuverability, neutral stability should be better. A Porsche 911 has a rearward center of gravity and is a fast car but if the rear end swings wide it goes into a spin (and crashes).

3. Thrust vectoring is of little benefit to turn rates if it is only used to push a tail down to create an angle of attack (see point #1) instead of thrusting towards the center of the turn. Compare Youtube video of how the X-31 (canard) uses Thrust vectoring compared to the F-22 (tailed).

4. Please stop considering foreplanes the only pitch control of a canard. The elevons (rear of the main wing) are the main controls and the the foreplanes augment these. The Mirage 2000 is one of the worlds most maneuverable fighters and has neither canard or tail. By all of your reasoning it shouldn't be able to fly. Show me a canard without elevons then we can talk.

5. High angle of attack is generally a bad thing as it means high drag. If an aircraft can achieve the same turn rate at a lower angle of attack if will keep its speed and energy longer (and win). Because a canard doesn't need to push the tail down (and wide) they are better suited for this.

6. Super high angle of attack and post-stall maneuvering are acts of desperation and are suicide with more than one opponent.

And Lantinian, my knowledge friend, we can all see that recent fighter design (outside Western Europe) has favored convention tails (though the PAK-FA leaks could just be a smokescreen, like the canard ATF designs) what we are trying to find out is why.

Cheers, Woody

 

[Ogami musashi]

Just to add precisions, it doens't mean i don't agree with you on some points.

1. Angle of attach is not the same as turn rate. Think of a car getting sideways (drifting); it doesn't mean it turns a corner any faster because of the increased drag/friction. See my drawings in answer #90 of this thread to see the differences (I can't re-post them because I didn't keep them).

Well you're right fundamentally. An angle of attack is a angular difference so it is not an angular speed.
And below you point a good point by saying a greater angle of attack for one plane is not necessarily a good thing.

Now your comparison with a car is not precise enough. You should compare not the yaw angle of the car but rather the slip angle of the tires.
Tire's slip angle are really like AOA for wings.
This is not surprising since basically a tyre rubber slider behaves like a viscous fluid.

Like an AOA for a wing, as the slip angle grows the lateral force increases (to be compared with the lift), and just like a wing, there's a slip angle where the lateral acceleration decreases.

But the difference is that a car is granted to only slide if the lateral acceleartion decreases were a plane will stall also.
For that reason plane's are equiped and/or documented with max angle of attack for the max CL.

To this CL corresponds the max turning force.

The big parameter that will defines if for a given plane, the greater the AOA the greater the turn rate is the drag of course.
All depends on the L/D ratio of the plane over a course.

But as i'll explain you below, for planes with L/D close, the greater the angle of attack the faster the turn. Of course that means the L/D is close for the respective value of max AOA.
That's is for example if one plane has L/D of 5 at 30°AOA then if we want to compare another plane with it, this plane has to have the same L/D at the higher AOA.
Of course you also have to look out the thrust.

2. Instability doesn't always mean maneuverability, neutral stability should be better. A Porsche 911 has a rearward center of gravity and is a fast car but if the rear end swings wide it goes into a spin (and crashes).

Yeah but again this is a bit different; This is true one too unstable plane is dead one, but planes do not have load transferts as wide as cars because mainly their axis of forces are in line with the COG which is not the case for cars (even for Karts).

The simple rule is that, instability trades negative pitch performances for positive pitch performance, but if you make it too much you will have to have big control surfaces to offset it and will spend all the time trying to correct the attitude.

3. Thrust vectoring is of little benefit to turn rates if it is only used to push a tail down to create an angle of attack (see point #1) instead of thrusting towards the center of the turn. Compare Youtube video of how the X-31 (canard) uses Thrust vectoring compared to the F-22 (tailed).

Well you forget that the major role of thrust is to overcome drag. Thrust vectoring by being in line with the velocity vector enables to offset more of the drag.
As speed goes up, thrust vectoring's drag overcome advantage is reduced since AOA is reduced.
Still, the fact that it can free some of the control surfaces moves is quite okay.

5. High angle of attack is generally a bad thing as it means high drag. If an aircraft can achieve the same turn rate at a lower angle of attack if will keep its speed and energy longer (and win). Because a canard doesn't need to push the tail down (and wide) they are better suited for this.

Nah that's not correct. Actually the problem involves Flight dynamics a lot this time.
From a pure aerodynamic point of view, you're right if we could turn with the smallest AOA that would be great.

But The problem is that you can't turn into and towards something without pointing at it.
You seem to like cars, think about it, a car could turn around a corner without changing yaw attitude at all.
But after that it would have to point to the good direction else the driver would travel sideways.

The same applies for planes, actually one of the developpement of new planes like F-22 and Superhornet is the fact they can increase their AOA fast enough to override the lift increament frequency, then after they use their lower AOA to turn in and finish the turn by reapplying a fast AOA increase to point at target.

By the way, at a given speed, the L/D increases with AOA (until the max AOA).
The Lift Coef increases is far larger than the Drag coef one.
Thus a plane flying at 350km/h while crusing and the same plane under 7g's, the 7g's one will have the best L/D.


Now about canards, canards may be lifting devices and smaller, they also drag far more.

Again you have to look at the whole picture.

Your last remark about high AOA desperate maneuver is quite on spot.

According the situation a canard plane can have some advantages, a conventional plane can have in other cases.
The point is that what is the state of the aerodynamics in that situation and for what use?

 

[Scorpion82]

Then we going focus on the anhedral of canard on typhoon. Any anhedral really is a bad bad thing on canard as it will cause unwanted washing air flow force to the delta wing in subsonic flight, conteract a lift from frontal main wing more or less. Why an anhedral of angle present? The only reason just is designer rather impose the washing flow than a necessary downward close-coupled canard like rafale used which must bring mooore various/mulriple drag.

A test pilot of the EAP commented that the canards were placed at a position where it does not affect the wings and fin. Should be the same for Typhoon.

 

[mrdetonator]

5. High angle of attack is generally a bad thing as it means high drag. If an aircraft can achieve the same turn rate at a lower angle of attack if will keep its speed and energy longer (and win). Because a canard doesn't need to push the tail down (and wide) they are better suited for this.

Cheers, Woody

Nah that's not correct. Actually the problem involves Flight dynamics a lot this time.
From a pure aerodynamic point of view, you're right if we could turn with the smallest AOA that would be great.

It is obvious that to improve turning increasing AOA is necessary but I say it is a very good thinking from him....he ment to improve L/D without increasing much AOA, that is the same principle on which LERXs, canards, adaptive wings works, just means to improve L/D ratio. By increasing L/D you do not need to pull higher AOA, simple as that.
Not to mention that since eighties starting with F-16CCV some aicrafts have the ability to fly decoupled maneuvers, turning, climbing without increasing AOA,..etc

 

[mrdetonator]

1. I`m not sure but i do not see anhedral of canards on this CGI model. Nevermind, the graphics shows nice vortex system creating by canards over the main wing.
2. The canard anhedral on Eurofighter is there to couple both canard+wing vortice system together(multilayered lift). Do not forget that the delta wing is known for its non-linear lift behaviour even if the boundary layer detached.

 

[overscan (PaulMM)]

Not sure this discussion is going anywhere, guys, seems to be going round in circles.

 

[lantinian]

And Lantinian, my knowledge friend, we can all see that recent fighter design (outside Western Europe) has favored convention tails (though the PAK-FA leaks could just be a smokescreen, like the canard ATF designs) what we are trying to find out is why.

I good to know that you have found an empty place in you knowledge that you do not fear to fill. I have personally changed a lot my opinion thanks to the information learned from this tread. However, I have always felt I have the question answered. And here I will try again to share this enlightenment with everyone.

Looking at the Canards and Tails from as design-engineer, I have found the following.

FACT 1: Fighter aircrafts CG tends to be closer to the engines. This part of the airplane structure is naturally tougher. Hence you can attach a bigger and heavier control surfaces.

FACT 2: Aircrafts vertical stabilisers are also located at the back of the aeroplane (those who have them). Hence you have the design option to combine the two control surfaces (tails & rudder = v-tails) for simpler, more efficient and LO design.

FACT 3: Canards cannot in practice replace the rudder and the elevators (tails) at the same time. Hence, they cannot be used to control Yaw.

FACT 4: The nose shockwave of high speed fighters actually limits the span of the canards. Hence they cannot be an efficient roll control surface either.

FACT 5: The most important LO criteria for a fighter is the front and side RCS. Hence, canards + rudder can never present a smaller RCS then a well designed tail.

FACT 6: Important design criteria like Stealth and Speed demand simplicity in the design, with fewer control surfaces as possible. Hence the popularity of V-tails and 4 tails after FBW and LO were understood well.

FACT 7: Canards usually have longer moment arm to the CG then tails. Hence they are a more efficient pitch control surface.

FACT 8: Canards vortexes can increase the wing stall AoA. Hence canards are favoured in designs that work a lot in those flight regimes, like navy fighters on approach to the carrier or subsonic supermaneuvring fighters.

FACT 9: Canards have a lot less area than tails. Hence in some post stall conditions, tails have more control authority trough their sheer size.

FACT 10: 3D trust vector control is still not as reliable as flight control surfaces. Hence the fighter like the F-22 must be fully controlable with all engines out.

Conclusion: If Maneuverability is less import an major factor than LO and Speed, then the fighter design requires a fewer control surfaces. The V-tails are the most reliable and efficient configuration that can control the aircraft in pitch, row and yaw with the help of the wing.

If Maneuverability especially in low speed regime is more important than LO or Speed, then the Canard + V like rudders is the most effective solution (in my opinion)

If Maneuverability is the only important criteria, then the design should have as many control surfaces as possible: tails, canards, FSW, you name it.

If Stealth is the only criteria, the design should be a flying wing (no tails, canards, rudders or body). Ex B-2

If Speed is the only criteria, the design should should be a missile (very small tails or canards and no wing) Ex. Missile

That is my understanding of the canards / tails controversy as a concept without the geek details. And again it regarding high performace fighters.

 

[lantinian]

Not sure this discussion is going anywhere, guys, seems to be going round in circles.

Maybe, you should close it Overscan. I think everybody has expressed his opinion a few times by now.

Although I would like to invite everyone participating by now to wrap up his thought (+ and - or canard/tails) in just ONE sentence, no more than 1-2 lines long.

 

[mrdetonator]

Not sure this discussion is going anywhere, guys, seems to be going round in circles.

Excuse me please Paul, but which one on this forum is not going in circles? The PAK-FA thread maybe, where each day Mr.Paralay presents one of his faked-up proposals while these yogurts are meditating whether it is acceptable or not? Here at least one rational science like flight dynamics and control laws, aerodynamics is involved. There are discussions on this forum which suck even more than this one. That`s why I do not enter, I hope you understand me. thanks

 

[rousseau]

2. Instability doesn't always mean maneuverability, neutral stability should be better.

Hummm....
Anything exist must being a precondition, let's make a disproval, why aircraft designer did struggling endeavour for instability, since unstable jet not only danger but also useless as you considered?? Remember the condition which has never changed since first air combat appeared is more maneuverability requested more speed needed.
So the higher speed you want to remained urgently, you necessarily cudgel your brains for reducing your drage out of your jetfighter. But as you's already read my toutology by words in stead of Lantinian's picture, a stable jet like MiG-25 on which horizontal stabilizer will lead to so big trimdrag during supersonic flight by maximum deflected angle, now you, please tell me how it could be maneuvale more?
Of cource, if you order all air combat in future must keep in speed of airshow, that is an another thing we can talk ;D

3. Thrust vectoring is of little benefit to turn rates if it is only used to push a tail down to create an angle of attack (see point #1) instead of thrusting towards the center of the turn. Compare Youtube video of how the X-31 (canard) uses Thrust vectoring compared to the F-22 (tailed).

??? ??? ??? I think maybe wrongly you made a totally vague notion about what id PTV(Pitch Thrust Vector) and what is OVT(OrientedVectoringThrust). I didn't saw anyone here told you PTV like F-22 used promised a higher turn rate to you.

4. Please stop considering foreplanes the only pitch control of a canard. The elevons (rear of the main wing) are the main controls and the foreplanes augment these. The Mirage 2000 is one of the worlds most maneuverable fighters and has neither canard or tail. By all of your reasoning it shouldn't be able to fly. Show me a canard without elevons then we can talk.

May I reminds you of non-words I mentioned an aircraft being taking off? Yes, a delta wing jet could get high turn rate without foreplan or tailplan, but do you know how bad its capability of lift-land is if there is no TVC is fitted on? You may can relating think to that tailless MIG-35 why its tail is cut? the only reason just is whose designer relied on TVC so much with a strong confidence that TVC will must being very mature so no tailplan or foreplan will be needed. But in foreseeable future, this is impossible. The moving rate and deflected angle still is not satisfied......

5. High angle of attack is generally a bad thing as it means high drag. If an aircraft can achieve the same turn rate at a lower angle of attack if will keep its speed and energy longer (and win). Because a canard doesn't need to push the tail down (and wide) they are better suited for this.
6. Super high angle of attack and post-stall maneuvering are acts of desperation and are suicide with more than one opponent.

When I talk the advantage of canard, I always say two points. One is, canard is good for high AoA as a vortex will gives stable lift upon the wing surface; on the other hand, being Super AoA, canard will incidentally fall into stall. So the only abosolute advantage canard could give is two: 1) less trim drag during level flight with more lift given during taking off, 2) a potential, when canard will be designed as being differential, it will give more aeropower than prevenient.

To Lantinian:
Dear friend, post follow, I am not going to rebut you, if you think so, let's closed. All I am going to do just is thinking and telling what I think to you as I perfectly agree someone said you are a knowledgable person.

FACT 3: Canards cannot in practice replace the rudder and the elevators (tails) at the same time. Hence, they cannot be used to control Yaw.
FACT 4: The nose shockwave of high speed fighters actually limits the span of the canards. Hence they cannot be an efficient roll control surface either.

What will happen if canard is designed as differential deflection?

FACT 5: The most important LO criteria for a fighter is the front and side RCS. Hence, canards + rudder can never present a smaller RCS then a well designed tail.

What if a canard is set at same level with main wing?

Almost rest of point you made I agree. Someone told me that XueXiao which is one of layout of next generation jetfighter has been determined instead of that MengLong. So I'm wondering since Chinese insist strongly a canard must be set even tailplan already being, the foreplan will must be moving differentailly for supermaneuverability. What do you think?

 

[lantinian]

What will happen if canard is designed as differential deflection?

They could in theory be used to control roll. However as I mentioned in my previous post that is impractical. Purely from a flight dynamics point of view, they are either too close to the axis of rotation or they are too small to have adequate power. Their job is also made harther by being so far ahead of the CG.
You can move them aft, closer to the wing and make them bigger, like on the F-15 SMTD, but that will create two problems
1. You loose their advantage. They are bigger, heavier and will will be less efficient controlling the pitch.
2. Difficult integration with the wing. F-15 SMTD canards are somewhat V-Shaped to make sure the canard vortex goes on top of the wing.
Ideally you want to have the roll control surfaces on the far two sides of the CG. Hence the use of ailerons for that.

What if a canard is set at same level with main wing?

1. That will not reduce the front and Side RCS. It will probably reduce the rear RCS, but that's the last one to worry about. Canards are a overall better choice for shorter range aircraft as they are likely to fight over friendly territory, hence no need to be that stealthy.

2. I as mentioned above, integration problems. There is a reason why SU-30 canards are small.

The only successfull example that comes to my mind is the X-36 (Check the McDonnell Douglas studies in the PDF I have attached a few post back) being both stealthy and maneuverable. However, they have gone a bit futher and eliminated the tails. I believe this fighter would have relied heavily upon the software program called RESTORE, the company was also developing at the time to control the aircraft.
I do think that the X-36 design places maneuverability to be just as important as stealth, hence the design choice. In my opinion, that is valid only for shorter range fighters.

 

[lantinian]

I just realised something very important (I hope no one has mentioned it)

Canards like LEX generate powerful vortexes, that are damm difficult to integrate with anything but a single tail. Canards are more problematic as the vortexes are there even in level flight. If two tails are used, then they need to be either strait up (SU-35), or canted inward to pass the powerfull vortex generated by the canard tips (final S-37 design) on their outside. Outward spaced V-tails are therefore particularly difficult to integrate.

There are many examples as allmost all canard designs (but with no tail) are with a single vertical tail. Eurofighter, Gripen, Rafale, Lavi, J-10, Viggen

The F-18 rudders are V-shaped but are very close together and LEX are very wide, like on the MiG-29, creating vortexes that pass on the outside. Plus, this is only a high AoA concern

Recently The F-22 Vertical tails have experienced structural problems due to the vortex geneat ed by the strakes (LEX). Yet it does not have canards. The YF-23 huge V-tails are spaced wide appart and one small reason is that the vortexes generated by the LEX pass on the inside of the tails. A very unique feature.

The other interesting example I can think of is the MiG-1.44 design. Canard design with 2 V tails! What is the secret and how is the problem avoided here?
First the aircraft has tails underneath too and second and most important it has a dog tooth feature on the canards. It helps break up those vortexes. The F/A-18E/F and F-15 have it and I think it was pioneered by the CF-105 Arrow(Not sure).

Another solution to the problem is to have huge winglets (small tails mounted on the wing tips) insteat of vertical tail. I have only seen concept aircraft adopt this.

The most obvious solution of course it the one found on X-36. No tail at all.

To sum up. While canards are lighter and more efficient, they are more difficult to integrate and are less versatile control surfaces than tails. Hence in practically they see less use than tails.

 

[rousseau]

Lantinian:

If it is possible, please show me Leading Edge Extention on F-22 where is?
AoA capability of F-22 CACICALLY rely on PTV, here is nothing to do with LEX.

Another one your said rightly is concerning to the vortex influnced the vertical tail on F-18, but that is theoretic. According to some photos in airliners.net showed, vertical tail on F-18 works well even thought it was covered in vortex.

 

[Ogami musashi]

No, F-22 AOA capacities are not Due to TVC.

It can sustain 60° with or without, only rates changes.

If it was just on TVC then the plane would stall when doing 60° which is not the case, since the plane is able to do full barrel roll at 110°/Sec while at 60° AOA.

Actually the F-22 is a plane that makes a lot of use of vortex Lift.
This is not because you can't see LERX a la F-18/SU-27 etc that they're not here.

F-22 (and so was Yf-23) is a multi dynamic vortex plane.
Chine nose creates vortex than energize vortex created by the stakes, themselves energizing vortex created by the LERX just before the wing.

So F-22 experinces some buffeting at some AOA (past which it doesn't experience it anymore) because some of the vortex momentums brake into the tail at some AOA.

 

[lantinian]

Thank you Origami Musashi for answering one of the "I am too lazy to do a 5 min search on google" class of question by rousseau.

According to some photos in airliners.net showed, vertical tail on F-18 works well even thought it was covered in vortex.

To simply work is not good enough in the aircraft industry. Every piece of hardware on the aircraft has a service life. By exposing that component to any kind of stress, you are decreasing the service life. You want to put the vertical tail in the path of the canard/LEX vortex fine. It will not only work with decreased efficiency (it will be like flying in turbulence) but it may came off on the 5th flight or so.
Further while carefully designed canard can help keep the airflow attached over the wing for higher AoA, it can also do the opposite. It can detach the airflow so that the wing stalls at low AoA. A general rule could be to make sure that the tip of the canard is on a higher level than the wing, so the vortex, goes completely ever the wing, not trough it.

I mentined that the X-36 was an strange exception to the rule that canard should not be placed in line with the wing. However I just took a minute to look at a 3-view of the aircraft and I found something very interesting. The small wing span, coupled with the large canards and high sweep angles will allow for the canards and wing vortexes to merge. In other words, the canard might not affect the wing after all, in any way, positive or negative. The short wing span was only possible trough the use of the advanced wing platform - Lambda Wing.

F-22 (and so was Yf-23) is a multi dynamic vortex plane.
Chine nose creates vortex than energize vortex created by the stakes, themselves energizing vortex created by the LERX just before the wing.

I didn't know that. Thanks! Hey, another good example how the ATF designers have blended Stealth with Maneuverability without compromising either one. This effect of merging the vortexes only being possible trough the separation of the aircraft top and bottom surface by a sharp edge. Excellent stuff.

 

[robunos]

According to some photos in airliners.net showed, vertical tail on F-18 works well even thought it was covered in vortex.

To simply work is not good enough in the aircraft industry. Every piece of hardware on the aircraft has a service life. By exposing that component to any kind of stress, you are decreasing the service life. You want to put the vertical tail in the path of the canard/LEX vortex fine. It will not only work with decreased efficiency (it will be like flying in turbulence) but it may came off on the 5th flight or so.

didn't the early F-18s suffer structural problems with their fins, caused by vortex impingement at high AoAs? IIRC, this was only cured by adding a 'bolt on' vortex generator to the LERX, to modify the vortex shape.

cheers,
Robin.

 

[lantinian]

didn't the early F-18s suffer structural problems with their fins, caused by vortex impingement at high AoAs?

There was indeed such a thing. Thanks for bringing that up.

 

[danielgrimes]

Back to original question - canards go with deltas to give better low speed handling - USA's current aircraft ain't deltas so don't need canards??

Canards also give lower drag when COG moves rearwards during supercruise - I prepare to be corrected, but although the current USAF planes have high top speeds, these are more afterburning dash speeds that would burn all the fuel in seconds, so no need to pay too much attention to sustained supersonic flight?

 

[rousseau]

No, F-22 AOA capacities are not Due to TVC.
It can sustain 60° with or without, only rates changes.

The air flow will sapareted from nose to wing root roughly if there is no LERX or canard, those asymmetrical air flow will certainly lead F-22 fall into tail spin.

If it was just on TVC then the plane would stall when doing 60° which is not the case, since the plane is able to do full barrel roll at 110°/Sec while at 60° AOA.

Very well, please show me any photo of these as prove, it is better that you would heve video to display such excellent action.

Actually the F-22 is a plane that makes a lot of use of vortex Lift.
This is not because you can't see LERX a la F-18/SU-27 etc that they're not here.
F-22 (and so was Yf-23) is a multi dynamic vortex plane.
Chine nose creates vortex than energize vortex created by the stakes, themselves energizing vortex created by the LERX just before the wing.
So F-22 experinces some buffeting at some AOA (past which it doesn't experience it anymore) because some of the vortex momentums brake into the tail at some AOA.

I have no wind tunnel to prove a rhombus nose will create a stable vortex for AOA, if someone did test of this, I believe you must can upload some infromation to prove this we are glade to see.
===================

According to some photos in airliners.net showed, vertical tail on F-18 works well even thought it was covered in vortex.

To simply work is not good enough in the aircraft industry. Every piece of hardware on the aircraft has a service life. By exposing that component to any kind of stress, you are decreasing the service life. You want to put the vertical tail in the path of the canard/LEX vortex fine. It will not only work with decreased efficiency (it will be like flying in turbulence) but it may came off on the 5th flight or so.

didn't the early F-18s suffer structural problems with their fins, caused by vortex impingement at high AoAs? IIRC, this was only cured by adding a 'bolt on' vortex generator to the LERX, to modify the vortex shape.

cheers,
Robin.

Yes, so I would dare to say that vertical fin works well even was covered in Vortex. And, the tail of vortex looks like coil to outside which the direction just vertical fin slanted to.
-------------------------

Back to original question - canards go with deltas to give better low speed handling - USA's current aircraft ain't deltas so don't need canards??

Canards also give lower drag when COG moves rearwards during supercruise - I prepare to be corrected, but although the current USAF planes have high top speeds, these are more afterburning dash speeds that would burn all the fuel in seconds, so no need to pay too much attention to sustained supersonic flight?

Mainly, canard layout and conventional layout are similar as we have discussed. But, yes, somethind I didn't express so clearly cause you ask more again.
For unstable design, CoG is rear of lift of main wing, so if this is a canard aircraft, you may will see the foreplan deflect downward a little or so little that may be unseenable. A down force give by this downward deflection trim the lift by main wing, whereas on conventional layout, that tailplan will deflect up a little bit to give a lift against CoG, so that many people will think conventional layout is better than canard layout. This is true if we check the situation statically. But since aircraft is not on drawing table, the situation will be changed a little bit.

During supersonic flight, the focus of lift main wing given will moving backward to get close to the CoG, so if this is a conventional aircraft, it have to deflate the upward deflection angle leading the lift tailplan give reduced. contrarily, canard will also defalte its angle of downward deflection, hence the trim drag on canard aircraft will be reduced. At here you may ask why I didn't mention the trim drag of tailplan will aussi reduced? The reason is L/D rate changed, for conventional layout, both of lift and trim drag reduced while deflection trend to zero, but on canard, if its angle of downward deflection trend to zero, there is no lift losing out of canard but the trim drag. On the other hand, you may already found the wing area of most of canard layout is bigger than conventional layout, if the size and weight compare with are approximately equal.

So the conclusion is general L/D rate of canard layout will be better than conventional layout, especially during supersonic flight.

Integrated two quetions why USAF don't like canard and USAF need or not sustain supersonic. A possible answer of mine is:
1) The position of canard should be set well for optimized specification leaded by canard, but it is hard to compate both dogfight and Low Obvisiable, which means if the canard is going to be set for minimized RCS, its aerodynamic efficiency will be not ideality as conventional layout does.
2) Canard maybe not so good as it works in level flight while in super AoA.

If I amwrong, please correct me.

 

[Ogami musashi]

The air flow will sapareted from nose to wing root roughly if there is no LERX or canard, those asymmetrical air flow will certainly lead F-22 fall into tail spin.

Sorry i do not understand what you say, please reformulate.

Very well, please show me any photo of these as prove, it is better that you would heve video to display such excellent action.

http://66.102.9.104/search?q=cache:CW0_RMQJFd8J:www.geocities.com/capecanaveral/hangar/6846/f22structure.html+Yf-22+60%C2%B0+AOA+360&hl=fr&ct=clnk&cd=2&gl=us
AS for the photo there was a sequence taken during Yf-22 show off i don't find it on internet.
anyway looking at any F-22 video demonstration you can see the roll/yaw autority at high AOA.

I have no wind tunnel to prove a rhombus nose will create a stable vortex for AOA, if someone did test of this, I believe you must can upload some infromation to prove this we are glade to see.

http://ntrs.nasa.gov/search.jsp?R=938537&id=3&qs=N%3D4294827928
http://tbn0.google.com/images?q=tbn:39So-xBZRaEj1M:http://img73.imageshack.us/img73/7725/f22vortexqo3.jpg

 

[sferrin]

Back to original question - canards go with deltas to give better low speed handling - USA's current aircraft ain't deltas so don't need canards??

Canards also give lower drag when COG moves rearwards during supercruise - I prepare to be corrected, but although the current USAF planes have high top speeds, these are more afterburning dash speeds that would burn all the fuel in seconds, so no need to pay too much attention to sustained supersonic flight?

The F-22 is effectively a delta with a tail slapped on some booms aft of the nozzles.

 

[rousseau]

Thanks to Ogami musashi
After read your post I did some research, now I'd to say, my opinion has changed a little bit.
According to some photo I snag them from video, and a small (small enough) photo you supplied, that wing root of Raptor could engender a sort of vortex. Now the point I thought is, if the principle is same, that LEX on Tigershark could engender the vortex, then the shape of upper board of Raptor's inlet is similar to the Tigershark, if profile also is similar, then doubtless the VORTEX engendered by Tigershark also COULD be engerndered by F-22.
Sadly your picture is too small to be seen what's knid of vortex engendered by that LEX on F-22

AS for the photo there was a sequence taken during Yf-22 show off i don't find it on internet.
anyway looking at any F-22 video demonstration you can see the roll/yaw autority at high AOA.

Maybe you mean helicopter action ???

-----------
What I didn't change is I didn't find any evidence to prove that rhombus nose can engender any vortex. That file you given here didn't say that. Any stable fluid is not mean vortex.

The vortex must has two characters:
1) its shape is a taper or say conics if you see what I mean?
2) the athletic mode of vortex must be circinate.

No provable sign show me that stream leaded by F-22 nose is a vortex. So more research should be done by us

cheers.

 

[Ogami musashi]

To create of vortex you don't need a dedicated vortex generator.
Every low span/high camber device will create vortex, the thing that changes is the vector and form of the vortex

A chined nose by splitting flows does create vortex that energize the adjacent boundary layers.
To prevent the vortex to slow down and burst , creating pressure drag, a new technique is used via multiple vortex.

This is of use in Formula 1 a lot and so does the F-22.

The chine of the nose on the F-22 is nearly straight because being a Air Superiority plane Lift is necessary to come even at low AOA.

Thus the chine creates vortex from about 15-20° AOA.

On the F-35/MAKO etc since the chine is there for stealth and vortex lift less complex the chine is inclined so that vortex don't develop at small AOAs.



About the Manoeuver, no this is not the helicopter, this is a barrel roll at 60° AOA, which, at this Attitude correspond to a pure Yaw movement.


For you last part i'm sorry to say i don't understand what you write. I know english is not the native langage of everyone (it is not mine) but here i can't really understand what you mean.

 

[rousseau]

Multiple vortex!
So glade to hear this will emerged on F-22. I sincerely hope a big photo of that you linked to.
BTW, what I mean is this

 

[Woody]

Probably does me no credit to submit this but what the hey...

This analysis by Pierre M. Spey, a key member of the F-16 and A-10 design teams, cast sharp doubt on the F-35’s capabilities:

“Even without new problems, the F-35 is a ‘dog.’ If one accepts every performance promise the DoD currently makes for the aircraft, the F-35 will be: “Overweight and underpowered: at 49,500 lb (22,450kg) air-to-air take-off weight with an engine rated at 42,000 lb of thrust, it will be a significant step backward in thrust-to-weight ratio for a new fighter…. [F-35A and F-35B variants] will have a ‘wing-loading’ of 108 lb per square foot…. less manoeuvrable than the appallingly vulnerable F-105 ‘Lead Sled’ that got wiped out over North Vietnam…. payload of only two 2,000 lb bombs in its bomb bay…. With more bombs carried under its wings, the F-35 instantly becomes ‘non-stealthy’ and the DoD does not plan to seriously test it in this configuration for years. As a ‘close air support’... too fast to see the tactical targets it is shooting at; too delicate and flammable to withstand ground fire; and it lacks the payload and especially the endurance to loiter usefully over US forces for sustained periods…. What the USAF will not tell you is that ‘stealthy’ aircraft are quite detectable by radar; it is simply a question of the type of radar and its angle relative to the aircraft…. As for the highly complex electronics to attack targets in the air, the F-35, like the F-22 before it, has mortgaged its success on a hypothetical vision of ultra-long range, radar-based air-to-air combat that has fallen on its face many times in real air war. The F-35’s air-to-ground electronics promise little more than slicker command and control for the use of existing munitions.”

The JSF is going up against the next generation Grippen in the Netherlands competition - bet you can't guess which side I'm on.

Cheers, Woody

 

[sferrin]

Analysis by Pierre M. Moonbat these days.

 

[kcran567]

??? TAM you said

"Adding TVC is only for low speed maneuvering. TVC lacks the control authority you get with aerodynamic devices once speed gets high."

Nothing could be more incorrect. TVC is ESPECIALLY for high speed. Example is Mig-23 the AF tested in nevada area 51, the thing could hit mach 3 but was uncontrollable and crashed killing many pilots...the control surfaces just dont work at those speeds.

American fighters have no canard because it diminishes supersonic turn rates Period. Thrust vector greatly enhances susersonic turn rates END OF STORY. Youre wrong there buddy.

 

[overscan (PaulMM)]

kcran567, this is a bad first post. Please consult the forum rules.

If you wish to make bold statements about others being wrong, please make sure you know what you are talking about first.

 

[Sundog]

As with any aircraft, everything is a trade-off. To say one aircraft configuration is simply better than another is usually the result of someone not knowing much about how aircraft are designed. A canard aircraft is not better than a conventionally tailed aircraft and a conventionally tailed aircraft is not better than a canard aircraft.

Something many novices simply don't understand is the mission requirements define the aircraft. The mission requirements don't say the configuration has to have a conventional tail or it has to have a canard. There are pluses and minuses to both and whichever meets the mission requirements best is the one that will be chosen. End of story. The Eurofighter has a canard, because that was the best configuration to meet their needs as stated by the mission requirements. The F-22 has a conventional tail because it was the best design to meet the mission requirements.

As for TVC, it is very important for the F-22 at high speeds and helps it to maximize it's turn rate in certain areas of the supersonic envelope by allowing it to minimize trim drag. That's what worked best for the F-22. Now, I don't know if the F-22 required TVC in that area of the envelope to meet the maneuvering requirements, but the YF-23 met the same requirements without TVC. There are different approaches available to meet the requirements, but one, in and of itself, is not necessarily better than the other.

They will confer better performance in some of areas of the envelope than in others. As such, as has always happened in aerial combat before, the pilots will do their best to fight in the areas of the envelope where their aircraft is better than their opponents. That's one of the reasons DACM is so important.

This is like arguing whether or not jet engines are better than rocket engines or rocket engines are better than jet engines. The answer, obviously being, yes.

 

[ubiquitous08]

A canard might be problematic in terms of stealth. The oscillating surface ahead of most of the airframe probably alters radar creeping wave performance as it may disrupt and introduce more variables in how radar energy flows over the airframe. Tucking the surface behind the wing seems a safer bet as energy reflected will likely be rearwards over aft empendage. Also if we are using tvc for trim (which is probably far stealthier if enclosure is nestled inside booms a la F 22) then canard really offers no advantage but a very interesting forward fuselage stealth join problem we don't need. TVC likely negates the trim advantage of canards and allows for better pilot visibility less complications due to vortices (if close coupled) and i'm guessing has alot lower drag in sustained supercruise due to to avoidance of canard disrupting airflow ahead of most of the airframe. Thoughts anyone?

 

[Woody]

ubiquitous08 and Sundog I have no doubt that what you say makes perfect sense - that said how about this (below) for a maneuverable stealth plane.
From what you say it would appear to offer:-

Good stealth
Good control power
Large internal volume
Efficient high mach performance
Comfortable low-level flight
High instantaneous and sustained turn rates

By close coupling but not attaching the elevators (green) to the wing they could give the same control power as a conventional tail, as in pitching they would not be in the 'wind shadow' of the wing as on a delta, but in level flight, have it's stealth and cruise performance. Having the elevators supported both out and inboard by the wing frame, they could be bigger, stronger and lighter. I never seen this done, has anyone else?

Cheers, Woody

 

[ubiquitous08]

Every current stealth design has very tight tolerances between elevators and surrounding structure. Drag might also be an issue but very innovative. The rear flaps gap might provide a discontinuity we don't wan't if radar energy flows over the aircraft from behind or the side; but not any more than say a separate tail plane; just my 2 cents otherwise looks pretty good. However who knows? Thats why radar prediction is done on a pole to verfy this, radar flows over an airframe are far harder to predict than scatter.

 

[F-14D]

FWIW, my understanding is that TVC, as in the F-22 and other a/c does not so much increase turn rate or minimize radius of turn as much as allow for greater and safer ability to point the nose independent of the direction of flight, the ability to do certain maneuvers at lower speeds and permits a much larger post stall maneuvering envelope. All of these are significant achievements. Whether they are worth cost of TVC is up to the designer and the customer.

 

[kcran567]

Overscan,

Thanks for the advice on posting, I will take it ... but I stated my opinion, and there is still ongoing debate on canards vs. tails...I'm on the side of tails better for supersonic performance over canards, and TVC for better supersonic turn rates over conventional control surfaces.

For example the f-35 probably doesnt need a vectoring nozzle it is a transonic range fighter and its agility is good enough at slower speeds...and those mig-23s tested in nevada did crash due to high speed control problems. More than a few other pilots encountered the same high speed problem in the Mig-23. Any fighter will benefit more from TVC as speeds increase.

I'm welcome to hear you're view of where I was wrong...I realize this is an ongoing debate about canards everybody's got their opinion.

 

[kcran567]

Sorry TAM...Still alot of opinion involved in this on both sides for me to make bold statements like that....