Anyway, I will be correcting my pic in a post later on, however I realy cannot do all exoic flight conditions all at once, thats why I started with the ones that are most important for an aircraft. By the time I got to Pitch maneuver I discovered something does not ad up.
I had a closer look at the "Modern Combat Aircraft Design" by Klaus Huenecke earlier today and I got the stable aircraft Idea a little wrong.
And
Canards and stable tails are inefficient at subsonic speed
Burt Rutan designs are stable canards and are very lift efficient and stable horizontal tail designs are not lift efficient. I will show that later on. Be patient.
For those of you that are interested Lantinian has started a new thread on this subject in the 'General Aerospace discussion' section (I thought General aviation meant light aircraft ) at:-
Under the title: 'Using Canards Vs Tail for aircraft Control", maybe a little limited and not as catchy a title as mine (if I'd spelt it right) but functional all the same. Since, I gather, this section is for specific projects I suppose 'General Aerospace' is a better place. That's where I'm putting my replies. So if you want to post comments on anything you see here try doing it there (you can still quote from here, just by having both windows/tabs open at once and cutting and pasting). So don't let the 'pro-tailys' hijack the issue and see you there. GANBATE!
Cheers, Woody
(Overscan, do you want to move this threat there or join the 2 up?, it might clean things up, just a thought)
I would like to get some opinions on these results. I used a lot of real world data and the seam to prove some real results. For example, Burt Rutan Aircraft are representative of the JAS-37 configuration and so is the XB-70. This is the stable canards design.
F-22 also ranks good in both subsonic and supersonic. The Eurofigher Typhoon results are interesting. They show a plane much more optimised for supersonic travel than subsonic. I personaly agree with that. IMHO, originaly the Eurofighter was thought to beat the SU-27/MIG-29/TU-26 combination in longe range trough kinematics (Mach 2 missile lauch at long range) and trough superior agility (turn rate) in close range.
The two comparisons prove the first point and I have another one that prooves the second if only I can get some feed back on those.
When canard wake is generating vortices its not bad. In fact, an advantage to the canards is that LERX is a lumpy draggy device in the airstream and a stable canard avoids that. In effect a canard can also be a variable LERX. Now the disadvantage is that unlike a LERX which only has solid matter behind it, there is still an empty space behind the canard forming a low pressure which will draw air, forming wake or turbulence. With a LERX, the vortices can go smoothly over the body, but the low pressure behind the canard, can alter the behavior of the vortice. The behavior and the low pressure will depend on the angle of the canard, but it may be safe to say, the higher the angle of the canard, the greater is the low pressure behind the canard and the greater the chances it may affect the flow of te vortice. To get the real picture, you would need to do more fluid dynamics simulation or wind tunnel testing.
And I agree that tailless deltas seam a bad idea especially for carrier landings (because of the massive pitch up required to counter the negative elevon lift) but the Mirage 2000 is cool maneuverable plane (because of clever leading edge slats and inherent instability(?)). I can't explain why but placing the control surfaces too far from the centre of rotation would seam to make a plane too stable or is this an illusion (like a long wheelbase on a car)?
The whole lever movement also takes some time to act too. The longer the control surfaces are from the center of rotation, the slower is the rotation. A plane that is also too long becomes too stable like an arrow.
Thanks for all your efforts on the 'Why do the Americans hate cunard wings?' thread ,particularly your table and diagram. I make no secret of the fact I like canard fighters but given enough justification I'm quite willing to change camp.
There are quite a few thing to discuss, though, from the last thread. Below you conclude various things about canards vs tails; for pitch, AoA, yaw, roll and stealth. Particularly interesting to me is the comparison between canards and YF-23 type 'V' or boat tails for yaw and roll. I have another (humble) opinion for your consideration.
You seam to like the YF-23s 'V' boat tail but unfortunately your arguments reminded me why I think they suck ;D.
YAW : to use a 'V' boat tail to yaw an aircraft requires that the tail surfaces be turned in horizontal opposition (or vertical synchron). If the plane was yawed anti-clockwise (from above), without large amounts of opposite aileron trim, the aircraft would roll in the opposite direction (clockwise from behind). If this was done with any vigor it would try to turn the aircraft flat-on to the direction of flight, top side forward (not comfortable).
ROLL: to use the 'V' boat tail to try and roll the aircraft also requires that the tail surfaces be turned in in horizontal opposition (or vertical synchrony). A roll in the clockwise (from behind) would result in anti-clockwise yaw (from above). Without large amounts of braking from the right wing (differential ailerons and flaps) again the aircraft would try and go out of control in the same way as with yaw as it uses the same tail action.
In both cases it seams the same as applying left rudder and right stick (what would that do at speed, all you pilots out there?) Having large surfaces would exaggerate this problem and their wide spacing would create an unstable roll axis far below the aircraft.
PITCH: as the surfaces on a 'V' boat tail are angled obliquely to the airflow (when pitching) and are unstably high above the roll axis so they are not as effective as they might be if they were flatter.
I think trying to use one device to perform pitch, yaw and roll at the same time is at best ineffective and at worst potentially disastrous. A boat tail is so essentially compromised that to perform anyone of these functions it either requires large amounts of drag inducing trim from other devices (where available) or it compromises the other functions (you can't wear your pants and lend them to your brother at the same time ;D). There is only so much control movement available before the surfaces are turned at 90 degrees to the airflow. Combining 2 functions happens on other aircraft (elevons) but most aircraft do not try and combine roll and yaw in a single device.
It is a credit to the Northrop/MDD designers and their FBW that they got the YF-23 to fly at all (and it is no surprise to me that most of the world thinks the YF-23 wasn't as maneuverable as the YF-22). Stealth is the only possible excuse for such a compromise and for the above reasons I don't except that 'V' boat or horizontal tail's have an inherent advantage over canards in yaw or roll.
Hope you find this interesting and I'm sure you'll help me out with any mistakes ;D I'll be posting comments on the other issues shortly.
There's no lift benefit of being positive or negative lift to trim an aircraft.
If it is done to trim an aircraft, be it positive or negative it doen't contribute to the overall lift (for cruise), it is just a rotational inducing lift and if you want to consider benefits from that then look at the drag thoses lifts occasionate, then you'll find the tail drag in form more (more surface and in case of positive lift more profile drag) and that surely the canards drags more in induced drag, you can also ask yourself what is the AOA needed to trim the aircraft.
The canards needs logicaly more autority since the plane is unstable however, the "autority" penalty has to be translated in how much drag it does, and then it does not translate to "more autority=more AOA needed" because a canard on a unstable plane has more CL than the wing (and so more than a tail)(CL is dependent on aspect ratio for most of the wing's profile we can see today, the shorter the surface, the higher the CL) so needs less AOA to provide the same lift than a tail.
However if you enter the pitching scenario, the tail will need to negative lift to make th e plane ptich up and in this case will need a greater autority through a greater AOA wich will lead to a greater drag...that why i talked about global view of the system.
If a tailed plane is more unstable than a canard then the tail won't need as much AOA as i said just above so could drag not more (maybe even less) and this is also valuable for canards.
You can't make general statements that this kind of system works better than the other.
The tomcat is a fairly good example, it has VG wing that should give him better all around aero efficiency but this is not the case because the whole plane aero and weights sometimes work against that.
However in theory, a VG wing is better than a fixed one (except for the speed the fixed one was optimized).
I agree with you on the analysis of the effects the boat V-tail has on mixing the pitch, yaw and roll all at once.
I agree 100% with you that a V-tail of a normal size would not have big enough pans for you and your brother ( I really like that) and than the FCS will be more complex than anything else..
I also want to thank you for the picture. I was about time someone followed suite. I think this way even the NON guru guys can get more of an idea what’s going on.
However I still support like the boat V- tail and the reason for that i the POINT OF VIEW.
Here is how I see its advantages.
1. There was a very interesting program in about 1996 called ACTIVE (I think). I was in response in the event that a plane like the YF-23, MDD JSF lose one or part of its fligh control surfaces. It was an FCS algorithm,(IMHO) that would allow the remainig control surfaces to compensate for the loss. An amazing idea if you as me. MDD lost the JSF and I don't know what became of this program.
SO long long are going to pretend that the FCS of an aircraft it such a challenging job. It has been at least 10 years since sensor fusion software got more complicated than FC laws. I don't sea anybody complain how it will be very expensive to achieve.
2. The F-23 tails are not your normal tail. Its as big as the F-18 outer wing !!! Therefore it should have enough control power to split between Yaw, Pitch and Roll. So you are not giving your pans to you brother(another aircraft) but you are letting him jointly wear them with you. And if they are really big enough, you can invite your sister too. After all you are going(flying) in the same direction, aren’t you?
3. Let's move away from the early 80's trend to get an flight control surface for every possible aircraft maneuver, flight condition e.t.c. There is a world wide trend to get to tailless aircraft but we can't get there if we constantly try to increase the number of control surfaces per flight.
3.Operation benefits. How much does F-23 plan to actually maneuver as part of his operational concept. Use the F-117 as an example. Stealth give you the ability to spend much more time in level flight as you don't have to bother about evading missiles, going around SAM sites or flying close to the ground. Level flight demands few or no flight control surfaces ideally for less drag. The YF-23 V-tail is operationally more effective than the F-22 four Poster design as a result of drag only. Not to mention Stealth considerations.
4. You seam to think that aircraft always do all 3 Yaw, Pitch and Roll at the same time. I do not have such observations. For example how does and aircraft turn in another bearing? It Rolls first, then Pitch the nose up. In my opinion the huge V-tails can do each maneuver faster than horizontal tail or rudder (because of their sheer size) or a mart FCS will let them perform the maneuver at one, using the side effect to an advantage.
5 YAW. Yes you are right that V-tail do more than yaw when you try to. But even if we compensate for the effect the way you have wonderfully shown in the picture, (BTW I think there is another way to do that) wouldn't it work? Wouldn't the Aircraft for a moment have more yaw turning power (at the expense of extra drag) than a conventional tail? IMHO this may be more efficient (stealthier) than having to roll first, then bank, the roll back again to change a bearing.
6. I actually don't agree that in YOUR picture you have made and a good job in counteracting the yaw in the top diagram. By dropping the entire trailing edge of the aircraft up and down you have simply added another two vector to support the roll. However you have initiated a very interesting maneuver. The aircraft in the Top diagram will simultaneously roll and yaw very. If you do it with your hand you will see it is similar to executing a 120 degrees roll followed by 60 degrees bank. Only that you do it at the same time, you roll less and you accomplish the maneuver faster.
7. Roll: Naturally, again I agree with you that if you try to roll the V-tail you will also get yaw. Unfortunately I don’t see a efficient way to only roll the aircraft using the V-tails.
If you want to do that you can use the ailerons or the whole trailing edge like in the top drawing but without help from the V-tails. However, in combat you do not always only ROLL, right. You do follow the roll with other maneuvers. I do not see your point in stating that a V-tail cannot perform separate 2 very simple maneuvers efficiently on themselves when its obvious that it can do both of them at them same time faster.
8. I also do not agree with your bottom sketch. I don’t think the YF-23 will ever use its control surfaces like that. HOWEVER, you have again given me a light on something I did not expect.
What will happen if you swing only one if the left V-tails up and you bring the whole trailing edge of the wing on the same side up? Well the V-tail upward vertical vector component will cancel out with the wing downward vector leaving drag. (This actually creates pitch force on one side of the aircraft only). This drag is a force working anticlockwise the CG. The Horizontal component of the V-tail is also anticlockwise. They will add up to beautifully yaw the aircraft. So there is you YAW with V-tails. I’am however to be honest not 100% s sure it will work
9. I did see you might have not paid attention to one of the pictures in my post (with F-22,F-23,Typhoon) where it is pretty obvious that a boat tail has a GREATER LEVERAGE than the other 2 design for Yaw, Roll or Pitch (only Yf-23 feature) compared to the horizontal tails, the canards or the rudders. More leverage, more control power.
10. Imagine yourself having to play a with the YF-23 in a gun fight and you are in a F-22. You will simply not be able to follow the YF-23 trajectory even if you keep up with the visually. The YF-23 will be performing some amazing blending maneuvers that will puzzle you which way to roll turn or bank to follow suit.
11. If you do not agree with the V-tails being overall superior to canards, just look 100 pictures of perspective fighters, bombers and even transports for that matter. You'd be surprised at the number of aerospace engineers that seam to share my point of view.
You're a nice guy but clearly from another planet . It was you who said that tails and canards could be used for yaw and roll as well as pitch, you wrote whole chart comparing them, and now you are telling me its a bad idea? I think using the same surface to yaw and roll is a total nightmare.
lantinian said:
But lets look at that else does the canards bring to the table.
Can it be used for Roll? Yes but it two engine fighters equal or closer to the rolling axes than it the tail. Hence less leverage. (blind obvious)Also, even it we all agree then in positive pitch it is better (I do) in roll you have only one of the canards doung the positive and the other the negative, and in negative pitch the tail rules.
What else. Yaw? Can canards help in yaw. Not really. Can they be made to? No because, sizing the canards to act both as yaw, roll and pitch would be...close to impossible, given pilot view requirements, affect on wing, weight impact on the forwards fuselage.
Can tails help in Yaw? Conventional ones NO. Can they be modified? YES, and the YF-23 is te perfect example of that. More on that later
Well which is it? You either move the tail surfaces vertically together (pitch) on in opposition (yaw/roll). Thats the only movement they have. My point was that a boat tail can't help but yaw and roll at the same time but in the WORST POSSIBLE opposing directions. The rudder and elevator is the same surface! I'm glad you liked my pants analogy but the point isn't the size of the pants but that they can't do 2 (or 3 yaw, roll and pitch) jobs at the same time. Pehaps a better analogy is you can't sell your pants and cook them for dinner however big they are, and they're always going to taste awful ;D.
Woody said:
Having large surfaces would exaggerate this problem and their wide spacing would create an unstable roll axis far below the aircraft.
[/quote
Its obvious that ailerons would be much better than boat tail for roll and split ailerons would be better that a boat tail for yaw. If at speed the tail tries to do anything other than pitch (which I'm not sure its any good at) you'd need to use up most of the aileron and flap movement just to stop the thing tumbling out of control and breaking up. And when you have all those surfaces fighting each other just keep it together what is that called?, well I'd call it an air-break. So much for talk of aerodynamic efficiency, eh?
Anyway getting away from 'V' boat tails and back to canards, I had a look at your 3 plane comparison and I hope you don't mind I made a few changes and comments on my version.
First of all. I feel like I have made a difference already by stimulating another member to transform his post into pictures. And I believe pictures are a much better way of showing once believes options and so on.
I can clearly see your level of understanding by looking at your pictures. I welcome your use of my pictures and I just want to explain the detail with the "0" on the Eurofighter. Its not that it has 0 but rather it had the lowest figures and all the other were given as a percentage bigger than that minimum.
NB. Wing tailing edge does not have a lift force of their own but rather influence the lift on the main wing (wich focus is elsewhere). Also you have very conveniently discarded the F-22/F-23 trailing edges as if these two aircraft do not have delta wings
This tread is about tails vs canards. Let’s don't include other control surfaces, OK. Because it seams that you bring in the flaps, ailerons and so on to support your arguments and at them same time you forget that F-22/and F-23 also have them. It’s worthless to compare two aircrafts similarities, let’s stick to the differences.
I must say however that I am very disappointed by your lack of vision and you inability to have a global picture of the things. Also
It is my now my official believe Woody, that you know so little about the F-22 :'(
You are actually trying to compare the F-22 5th generation blended wing body design with a 4th generation "wing attached to a body design"?
I will humbly continue drawing somewhat less misleading pictures
Yes, but what is it (the percentage)???? and in the other columns where are your units?
lantinian said:
NB. Wing tailing edge does not have a lift force of their own but rather influence the lift on the main wing (which focus is elsewhere). Also you have very conveniently discarded the F-22/F-23 trailing edges as if these two aircraft do not have delta wings
Throughout this discussion you demonstrated that you don't 'appreciate' how canard aircraft work. The primary control surface of a canard is the elevon (for pitch and roll). It simply has canard surfaces as well. I even deliberately included a tailless delta to try and make this point inescapable. According to your arguments the delta should not be able to fly at all! The reason I disregarded the trailing edge surfaces on the conventionally tailed aircraft is because they are not used as a significant control surface to effect pitch (as far as I know). They are MAIN one on a canard and to dismiss them is ridiculous.
lantinian said:
This tread is about tails vs canards. Let’s don't include other control surfaces, OK. Because it seams that you bring in the flaps, ailerons and so on to support your arguments and at them same time you forget that F-22/and F-23 also have them. It’s worthless to compare two aircrafts similarities, let’s stick to the differences.
When I started the Why do Americans hate Cunards thread I did it because I wanted to know the reasons why the canard configuration has been disregarded by the Americans (and know Russians?) and not the Europeans. I wanted to compare both types of aircraft not just bits of them.
lantinian said:
You are actually trying to compare the F-22 5th generation blended wing body design with a 4th generation "wing attached to a body design"?
...and so, it seams, do you when it suits you (want compare both types of aircraft not just bits of them).
RE. My rough drawings. In each one I tried to draw attention to factors your argument either had not considered or had bizaarly discounted. They are as follows.
Drawing #1 and 2: I wanted to remind you that in order to rotate a body, you need to apply force on 2 (at least) opposing points otherwise you simply accelerate the whole body off in one direction. Thought mass and inertia of a body is a factor it is not always the centre of rotation and does not represent an opposing force in itself. Tail against Wing (conventionally tailed aircraft) or elavon against wing (tailless delta) or elavon against wing and canard (canard aircraft) does. And we can see that on a canard aircraft these points are considerably further apart than on a conventionally tailed aircraft).
Drawing #3: A simple diagram, included to try and demonstrate that turning force, in a sustained pre-stall condition, is totally different from pitching force, and uses different parts of an aircraft.
Drawing #4 Another quick diagram to show that a canard aircraft has more pitch-up power near 90 degrees of AoA than a conventionally tailed aircraft and about the same pitch-down or recovery force. This something you have denied in previous answers.
I know that aircraft work as whole and not as isolated components. I know an aircraft's body provides lift and drag not just its wings and fins. I also know that the fluidic dynamics of an aircraft at super sonic speed are something we can not hope to know. I know that there are many more factors than high AoA or 'efficiency' to determine an aircraft's merits.
You seam like a nice guy and you put a lot effort into your replies but please try and address some of the points I raise about your arguments :-[.
Cheers, Woody
PS: your last diagram doesn't open, you need to fix it and re-post it.
The whole lever movement also takes some time to act too. The longer the control surfaces are from the center of rotation, the slower is the rotation. A plane that is also too long becomes too stable like an arrow.
Sorry lantinian about getting a bit stressed in my last post but your arguments drive me crazy. I look forward to seeing your last 3 diagrams when you can get them fixed and re-posted (can your view them from the site? cause I can't). They are always entertaining.
Just another small comment on one of your posts (about one of my posts).
lantinian said:
4. You seam to think that aircraft always do all 3 Yaw, Pitch and Roll at the same time. I do not have such observations. For example how does and aircraft turn in another bearing? It Rolls first, then Pitch the nose up.
I am not a fighter pilot but I've had a lot of dogfights with friends on computer, and if you can't pitch and roll at the same time (some planes can't) you are at a definite disadvantage. The Typhoon is particularly good at this, as shown in this YouTube airshow clip. Its performing pitch and roll (high alpha roll) when you see it rolling with the smoke coming up off the wing at that funny angle (ha ha). As for yaw, I heard that the Typhoon's rudder pedals are locked except for take-off and landing.
We use Jane's Fighter Anthology computer game as it allows you to choose almost any fighter and any weapon since WWII (R-77/AA-12s on a Star Fighter???). It's and old game now but it was endorsed by the Jane's organisation. It is great fun for comparisons but the thrust vectoring is very hard to use and the stealth aircraft (quite rightly) have a massive advantage. Does anyone know of a better (more accurate) dissimilar air combat simulator for the PC?
Here's an F-22 clip for balance. It seams shy about doing rolls but a pretty maneuverable plane just the same.
http://www.youtube.com/watch?v=7xyiV_Aketo
Does anyone know any dogfight exercise video clips between canards and conventionals?
I am not a fighter pilot but I've had a lot of dogfights with friends on computer, and if you can't pitch and roll at the same time (some planes can't) you are at a definite disadvantage.
There's a MASSIVE difference between a computer game, no matter how sophisticated, to real world flight. Surely you can't be serious! ("I am serious, and don't call me Shirley...")
Woody said:
As for yaw, I heard that the Typhoon's rudder pedals are locked except for take-off and landing.
Why would this be the case? This is the first I've ever heard of that- wouldn't the rudder be necessary for coordinated turns in certain flight regimes?
There's a MASSIVE difference between a computer game, no matter how sophisticated, to real world flight. Surely you can't be serious! ("I am serious, and don't call me Shirley...")
Like I said I'm not a fighter pilot so for actual hands on experience of dogfight maneuvering a PC game is as close as I can get. If any real fighter pilots know better I beg to be enlightened (but it's cool game if you haven't tried it thought the graphics are prehistoric http://www.fsrz.net/fa/fa.html).
Sentinel Chicken said:
Woody said:
As for yaw, I heard that the Typhoon's rudder pedals are locked except for take-off and landing.
Why would this be the case? This is the first I've ever heard of that- wouldn't the rudder be necessary for coordinated turns in certain flight regimes?
I'm not sure but I remember it from an old airshow video commentary (left behind in NZ). The only justification I can think of is that the FWB manages the 'care free handling' without the need for pedals, perhaps to stop potential spins near the stall (?). As above, if any Typhoon people know better etc etc.
If the plane is longer, it has a tendency to be more stable (longitudinally). Just remember the thing with arrows. Longer arrows tend to be more stable in flight, and fly straighter. Thus it requires more torque to effect a change in direction.
PS. What do think of the General Aviation version of this topic? I notice you have been quiet - probably wise.
Hi All, After a long absence, I just wanted to add something to this tread.
For those that would like to make their own decision about canard or tail mounted control surface, here are some useful conclusions, references or links.
AIAA Paper 84-2401
Forward
Past investigationsl-5 have differed on the best choice between tail and canard for future tactical aircraft employing fined, low aspect ratio wings. A previous Grumman USAF study1 of an advanced strike fighter emphasizing supersonic persistence showed the superior trim drag characteristics of a canard. Northrop argued that a tail design has lower subsonic maneuver trim drag and greater stability c.g. location flexibility and is therefore the preferred configuration for an air combat fighter. A General Dynamics study3 indicated that a canard quipped F~16d design had potential high AOA stability and control problems when balanced at negative static margins; as a must the tail arrangement had a better subsonic trimmed polar and a Similar supersonic trimmed polar. An incompressible lifting system analysis found a tail to be the better choice. The message seems to be clear: the selection of a canard YE a tail is both configuration and mission dependent.
Conclusion
Equivalent canard and tail control surfaces are compared on an advanced, carrier-based fighter/attack aircraft featuring variable wing sweep and vectorable, two-dimensional nozzles. Evaluations of stability and control characteristics, trimmed drag due to lift, minimum takeoff rotation speeds, and carrier approach speeds are presented. The results show that the canard configuration has substantially less supersonic trim drag and a lower carrier approach speed, which can yield appreciable takeoff weight savings, but the tail configuration exhibits better stability and control characteristics with less development risk.
A84-44926 22-01
An evaluation of the relative merits of wing-canard, wing-tail, and tailless arrangements for advanced fighter applications
Two sets of wind tunnel tests were performed to examine the relative merits of wing-canard, wing-tail and tailless configurations for advanced fighters. Both sessions focused on variable camber using automated, prescheduled leading and trailing edge flap positioning. The trials considered a modified F-16 tail and canard configuration at subsonic, transonic and supersonic speeds, a 60 deg delta wing sweep, a 44 deg leading edge trapezoidal wing at subsonic and supersonic speeds, vortex flow effects, and flow interactions in the canard-wing-tail-tailless variations. The results showed that large negative stabilities would need to be tolerated in wing-canard arrangements to make them competitive with wing-tail arrangements. Subsonic polar shapes for canard and tailless designs were more sensitive to static design margins than were wing-tail arrangements. Canards provided better stability at supersonic speeds. The static margin limits were a critical factor in control surface selection. Finally, a tailless delta wing configuration exhibited the lowest projected gross take-off weight and drag values.
P.S. I was making a diagram with a comparison between 5 different configurations, including triplanes and delta, however I realized that if my opinion has not make a difference even an inch, it will never do. So I left them unfinished.
Anyway, I added a pic to a diagram part of an 6 Gen ATF by MDD done in the mid 90s. It has an interesting bias and the configurations with higher stealth and maneuverability feature even nose trust vectoring and additional LO features. The X-36 is a subscale technology demonstration for the best configuration.
I also added a diagram showing the initial set of the designs that this study started with.
They built them into the XB-70, the HiMAT and the X-31, Burt Ruttan likes them and all the compeditors for the ATF/F-22 and JSF/F-35 contracts initially considered them but in the end they all rejected cunards. Why? Do they really believe they can get better maneuverability/stealth/STOL out of a conventional wing and tailplane. If you're going to tell me they were too late, like forward swept wings (not that I'm a fan), they'd both been around for decades. Somebody help me out here - it's bugged me for years.
Cheers, Woody.
Well, canards (Cunard is a shipping line) don't show up on (most) commercial aircraft because the conventional layout is actually more efficient, especially when you have to worry about stuff like where you put the landing gear and fuel, as the wing is behind the c/g.
Deltas have some advantages for combat aircraft, mostly because they can permit quite high instantaneous turn rates, thanks to large surface area and vortex lift. Otherwise, deltas suck, as they have quite high induced drag.
Canards are put on deltas because deltas have poor pitch authority, as their elevons (pitch control surfaces) have a fairly small moment arm. By adding a canard, the aircraft has increased pitch authority, which increases the rate at which it can change angle of attack, and may even permits flaps. Also, the canard probably permits more freedom in loading.
I think the Rafale and Gripen are deltas because that is what Dassault and SAAB are used to building.
On the issue of stealth? I don't think it makes a significant difference.
Lantinian, your PDF links are very interesting and probably constitutes the most scientific data so far in this discussion. The http://www.aoe.vt.edu/~mason/Mason_f/canardsS03.pdf link's data seam to be mostly in 2 graphs:
'L/D' verses 'Stability'
'Trimmed CL max' verses 'Tail off static margin'
L/D = lift to drag ratio?
Stability = what kind of stability and how do they vary it in a model fixed in a wind tunnel? - C of G wouldn't make much difference.
Trimmed CL max = Trimmed maximum coefficient of lift (instead of un-trimmed)?
Tail off static margin = what the ????
I'm sure these are very illuminating but can you explain the terms and how they demonstrate the overall merits of canards and tails? I have a basic understanding of maths and physics but if you could explain in a way that is easier to visualise that would be great.
The cranked arrow pdf is also very interesting - I've always liked them but that article will take quite a long time to read and digest.
The 2 images are also great, you do come up with some good stuff. Were these early McDonald Douglas ATF concepts? And why is the Hornet type configuration attributed with Low (2401), Medium (2402) and High (2403) manoeuverability ?
Snurg, thanks for the spelling lesson once again and I generally agree with the rest of your post. Though I think airliner designers need to use a bit more imagination and move on from what is basically an evolution of the Boeing 720 with a wider body and turbofans.
Cheers, Woody
PS. Lantinian if you could indulge me and explain why my simple diagrams in reply #91 and in error I would be appreciate it (and, no opinions are not explanations ). I really want to know.
as the wake flows over the fuselage, it affects the rudder, so this means you have to install a big rudder to compensate. We have seen so far, that canard deltas use relatively large rudders
This is only siutable to J-10 but other delta wing with foreplan jetfighter. Eurofighter for example has much smaller fin compare with J-10 in terms of the scale of airframe.
Also, I never said the canard aircraft isn't capable of high alpha flight. I said it can't trim the aircraft out at as high an alpha as a conventional tail can. Also, to correct another falsehood, the conventional tail is in clean air at high alpha, because it is below the wing, not behind it. Watch some of the high alpha test videos of the F-22 where the horizontal tails make it look like the F-22 is "duck walking" (because the tails look like webbed feet walking) and you'll see what I mean.
I see this very clearly and know exactly accurate meaning of it, thanks to woody, but the problem is why shall I rely on foreplan in high AoA when I get VTC to work for this performance, despite the air flow is clean or not. I know the foreplan will fall in stall losing speed earlier than conventional horizontal tail when aircraft fly at high AoA, but since we compare the Eurofighter with Raptor, I wonder why the EF without VTC but was designed as Canards whereas F-22 raptor with VTC which more adapt to foreplan but was designed as conventional layout?
OMG
This tread is still going. I hope you aerospace geeks do not expect to come to an universal answer to the question "canards or tails?", do you?
Because THERE ISN'T ONE.
I wonder why the EF without VTC but was designed as Canards whereas F-22 raptor with VTC which more adapt to foreplan but was designed as conventional layout?
1. The Eurofighter was not designed without VTC. Its engines were. An upgrade part of Tranche 3 (I think) is going to fix that. (I hope)
2. F-22 had MUCH higher requirement for frontal RCS than Eurofighter.
3. Consider the SU-35 from 1995 and the one they market now. The Difference: The latter swapped the canards for VTC but kept the tails. Hmm, what happened to the Russian designers. Did they suddenly start paying attention to frontal RCS. Well, that's what is said in this brosure; http://www.knaapo.ru/media/News/maks2007/35_eng.zip
If we trust the engineers who actually to the math, its obvious that there are situations that favour both. The best example is the YF-23.
The USAF version has TAILS only but the NAVY has CANARDS only. Why?
The Next best Example is the F-35 which at the time of the JAST program (1994) was a Canard design. Then suddenly the engineers switched to Tails. Why?
Well, anyone can do a search on those two planes, find out why would one design go from canards to tail or the other way round.
Here is what I learnt. The foreplan always give a lift to the aircraft, push the nose down, today, is not a work foreplan have to do. For an unstable aircraft, while it goes into supercruise, the foucs of lift will gradually moving backward, closing to centre of gravity, which lead to a higher l/d rate than conventional layout.
For roll effect, horizontal tail bigger than Canard not is due to attribution of canard's shortage but only is foreplan nowadays is not designed as differential moving.
sferrin said:
Going along with your post that's why Tomcats had the glove vane that deployed at supersonic speed. It moved the CP forward to unload the tail and keep the aircraft from becoming TOO stable. That's why it was able to pull 7+ Gs at Mach 2, something I don't think anything outside the F-22 can do. Of course they eventually pinned them shut and left them off the D's altogether because they didn't get used enough to justify their existence. . .
There is some misinterpretations? What satble or unstable is not related to subsonic or supersonic. If an aircraft was designed to be unstable, the centre of gravity initially set behind the lift of main wing, if it was designed to stable, the cg originally set front of the lift of main wing. So that's why you would see the glove vane was removed on F-14D version.
This, at least, is what I found the season why so many members here appreciate conventional layout. What a huge misunderstanding.
The picture I posted here display clearly so much an unstable aircraft, the cg always being behind the lift of main wing. So please watch video on youtube or any discovery movie carefully, aircraft say Rafale for example,level flight even in subsonic though, which leading edge of canard is downward, always!
OMG
This tread is still going. I hope you aerospace geeks do not expect to come to an universal answer to the question "canards or tails?", do you?
Because THERE ISN'T ONE.
Not his fault at all, when there is more nonsense than valuable post here. He even picked up the most dumbest post in the entire thread, no wonder that after eight pages he is still asking about those basic things.
rousseau said:
but the problem is why shall I rely on foreplan in high AoA when I get VTC to work for this performance, despite the air flow is clean or not.
You still missing the point what the TVC(thrust vector control) is being used for. Hopefully these two diagrams below will help you to understand. The first diagram depicts the F-22 TVC pitching performance, note the dependency of AOA vs Horiz. stab and TVC pitching moments. Clearly, those big horizontal stabs are loosing "breath" with increasing AOA, but it is really no wonder because aircraft speed drops down. When pointing at F-22 doing high alpha(>45deg) stunts on airshow when literally hanging in the air you can see the horiz. stabs moving up and down, but why is that?. Realize the horiz. stabs have less or no authority bcs of low speed and high AOA (see the graph above), therefore the F-22 digital FCS coupled both TVC and horizontal stabs together. Simply as that during post stall maneuvers the TVC has the authority.
First compromise regarding F-22 horizontal stabs is putting them into the main wing wake. A dumb choice but who cares when end justifies the means. It helped to lower the frontal RCS not to mention when stabs are BIG ENOUGH(and they are!!) and with help of TVC, no one ever complained about aicraft pitching performance.
The second diagram shows the TVC effectiveness dependency on the speed of a TVC equiped aircraft(Su-30MKI). Believe or not the TVC looses pitching performance with speed, or better to say, that stabilizers will always have more authority when speeds M>0.6. I`ve got that confirmed also by Mr. Pavel Vlasov, the test pilot of Mig-29OVT. The same deals for movablel foreplanes vs TVC. Anyway, this does not render the TVC completely useless at higher speeds.
rousseau said:
I know the foreplan will fall in stall losing speed earlier than conventional horizontal tail when aircraft fly at high AoA, but since we compare the Eurofighter with Raptor
OMG, who told you that nonsense? Speaking of the Eurofighter how can a movable foreplane stall when it is not even a lifting surface, rather a trimming one. The beauty about aircraft with high negative static margin like Eurofighter is that further the neutral point is ahead of CoG, then smaller movable foreplanes deflection you need to put the plane out of equilibrium state. That means the Eurofighter became very agile and high pitch performance aircraft as well as less trim drag is actually needed from movable foreplanes to trim the aicraft in cruise flight. The pitch performance of an aircraft (pitch rate and pitch acceleration) is a function of the effectiveness of the pitching controls and the resistance the aircraft presents to a pitching motion.
Well, compare the EF-2000 foreplane/delta wing size ratio with horizontal stabs/wings of the F-22. Yes, the Eurofighter needs so small pitching surfaces to achieve high pitch rate compared to F-22, not to mention the TVC helps the F-22 too. Therefore which aircraft has better pitch perfomance?
Now, let say, theoretically speaking with 5% of inherent static instability at subsonic the Eurofighter would need much greater foreplane deflections(rise trim drag) to pitch the nose up at high AOA than now with its assumed -20% static margin.
Then no matter that the movable foreplanes create a smaller amount of negative trim force during a turn, bcs their main purpose is also to glue the boundary layer to the main delta wing. Their add optimal non-linear lift at any given AOA compared to not as good F-22 vortex lift management.
Once again I repeat, it is all a matter of compromise between priorities. When you want a supermaneuverable aircraft then delta layout with movable foreplanes is the best, especially for supersonic performance. But when the frontal RCS priority prevails ahead of supermaneuverability, the movable foreplanes layout as most of ATF proposals become incompatible and you start to look for arguments. Sometimes, you read also dumb arguments....
And your "Su" diagram is absolutely wrong!!!!. The close coupled movable foreplanes always produce a small down force, but their real job is seen on the main wing. Note their deflections on these pictures.
Going along with your post that's why Tomcats had the glove vane that deployed at supersonic speed. It moved the CP forward to unload the tail and keep the aircraft from becoming TOO stable. That's why it was able to pull 7+ Gs at Mach 2, something I don't think anything outside the F-22 can do. Of course they eventually pinned them shut and left them off the D's altogether because they didn't get used enough to justify their existence. . .
There is some misinterpretations? What satble or unstable is not related to subsonic or supersonic. If an aircraft was designed to be unstable, the centre of gravity initially set behind the lift of main wing, if it was designed to stable, the cg originally set front of the lift of main wing. So that's why you would see the glove vane was removed on F-14D version.
Going along with your post that's why Tomcats had the glove vane that deployed at supersonic speed. It moved the CP forward to unload the tail and keep the aircraft from becoming TOO stable. That's why it was able to pull 7+ Gs at Mach 2, something I don't think anything outside the F-22 can do. Of course they eventually pinned them shut and left them off the D's altogether because they didn't get used enough to justify their existence. . .
Hmm, ..what`s the problem with 7G at Mach 2 I really do not understand, even the old soviet Mig-29 with air2air missiles load is still capable more than 7G at M1.7 speed. Let say when at 13km altitude and higher you should pull a bit harder bcs G is limited only by hor. stab effectiveness. So instead of allowed 10deg AOA you`ll pull 15deg. When clean config, you get 7G even at higher altitudes. My opinion is that most Mach 2 capable aircrafts like F-15, Mirage, EF-2000, Mig-29, Su-27, ...etc can do 7G at Mach2. Not to mention that delta layouts are the best in pulling G at supersonic.
Do you have a similar diagram showing 7G capable Tomcat or Raptor at Mach 2 to back-up your claims.
I know, I know, withstand 7G at Mach2 is totally different matter, but he said to PULL +7G!!! I`m just asking... I doubt that Tomcat was ever capable to sustain 7G at Mach2. Anyway, F-16 with its fixed inlet is hardly capable of Mach2, not to talk about maneuvering at those speeds.
In this picture, we can see a typical stable canard jetfighter - SAAB37.
Why this jetfighter is stable? because the CoG of it in front of the lift which was caused by main wing. Since the CoG in front of the lift out of the main wing, so the nose will fall down in level flight. Solving the nose eventually fall down, leading to a Canard being. The canard naturally give a lift to balance the lift caused by main wing, against the CoG, so that the SAAB can flight levelly without any negative or positive pitch. This is a subsonic flight.
While the SAAB 37 fly into supersonic, focus of lift by main wing will slightly move backward. The backward moving of lift lead to a longer arm of force to the rear lift. Which means the lift even without any aileron or flap flirt will be bigger than the lift canard given. So the flap on canard will be put down a little for a bigger lift requested.
Then we go to next....
Here we saw is a typical unstable delta wing with canard jet fighter: Euro-typhoon.
Before you read introducing follow, please do some search to watch video or movie in which typhoon and Rafale display flight for finding what a difference between canard on Typhoon and Rafale. You must feel the canard on rafale always being downward slightly in level flight but Typhoon not. If you wondered why this happened with thinking, let's think about this together....
The Typhoon was designed as a jet fighter with extending unstable for surpassing-Su-27 such a powerful air-dominance fighter. That's why the CoG was set behind the lift of main wing so far for air-superior. Since the unstable force is strong, designors consciously give a far-coupled canard that will lead to a longer arm of lift force. Please notice here, a longer arm of lift not directly means a stronger lift. A stronger lift must accord with some conditions. 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.
This elaborately disposing to minimize any drag could appear for supersonic maneuverability,if we understood.
While typhoon going to supersonic flight, the lift of main wing will moving toward rear, closing to the CoG. In this period, because of shock wave, that unwanted washing flow will be mitigated, an attribution of high lift out of canard will naturally occur, With the long trim arm, any slight deflection of canard could give a more powerful effect to move the direction of Typhoon's nose up or down. Besides, possible vortex via that slice aside the cockpit will be intensified for very good high AoA capability which other jet never get.
Now we can go toward to conventional layout.
A stable example will be easy from a famous phenomenon. We've known while the MiG-25 fly into supersonic especially close to M3, its horizontal stabilizer will deflect to downward so much which never occur on any other jet fighter. This large downward deflection cause huge trim drag also being one of reason why the range of MiG-25 will be reduced toughly and the controllability and maneuverability is too incorrigible. The reason source mainly come from the satble design factually, as we can see higher speed of MiG-25 is, the farther lift focus moving backward, thus cause the distance between focus of lift and CoG (Centre of Gravity) bigger and biger. Now Even foolish like me can sense what a terrible thing will appear.
This above is what we called stable layout. So we can understand quit clear, why the appearance between Vigilanter, Foxbat and Eagle is similar but first two can't take be a pure combat fighter, MiG-25 only is a high supersonic interrupter platform nothing more. But Eagle is different.....
If you can find any large photo clealy shows a F-15 Eagle flying levelly but with obviously downward deflected horizontal stabilizer you would totally overthrow all of theory I told you here. Actually any wing surface fastly scratch in air horizontally will lead to a lift somewhat. the longer arm of force will give and/or the bigger wing area will be, the more lift will being upon the tail win. Whereas the arm of force by F-15's tail wing is the longest since then 70's jetfighter, the biggest wing area of tail wing on F-14 is sth we will talk later. So needless to say, F-15 has unprecedented trim effect from horizontal tail. Of course, by the strong down washing flow out of main wing, we see a sawtooth on frontal edge of Eagle's horizontail tail because of its complex main wing profile this problem is out our topic. Till here, we have known why engineers exert their vigor extendingly to make a fighter to be unsatble. If someone tell us, canard should be put on enemy's fighter, we also can respond to hori-tail should being stay at air base the excuse is exactly same to he will give. I saw many poll-parrot following what uncle sam said. But that is stupid enough they talk before think.
Then let us back to stable layout with swing wing.
very interesting thing is the situation here is closely similar to fix wing. I beg you notice why MiG-23 doesn't like other contemporary swing wing jet such as F-111 and Su-24 which wing swing back with horizontal tail could be delta effect. Well F-111 and Su-24 actually is not a eventual fighter, so when lift far away the CoG with wing sweep back, no more controllability and maneuverability needed to care, but MiG-23 thought to be a fighter with better maneuverability than MiG-21 since it was started designed. So we can see the pic display black arrow shows direction of CoG force, thick green arrow is lift of main wing blue arrow is a direction lift force move towards and a green arrow shows a direction of trim force which also is green because it could be lift. That red line give us a deflected situation of horizo-tail surface.
At last we can go to F-14 tomcat.
My best friend don't want to see my gaffe so he imply me the swing wing F-14. Please allow me to simplified problem to three step which set to wing of Tomcat, I certainly know it is stepless control.
The minimized backward sweep angle is a situation just similar to other say F-15, 2nd angle is mid-backwards sweep, so Tomcat contain the optimized dogfight capability because the season we've said that lift will be closing to or overlapping if you insist the CoG so that maneuverability at this time is the best. Even though the angle of sweep is maximal, F-14 in this situation is a stable jetfighter, but we also see that is why there is extending leading edge stretch beside the envelop of swing wing, which give a lift against the CoG and help the trim up force balancing to both. US engineers rapidly find the effect will be same if removing the leading edge extension and its device bring an advantage of reducing the weight at frontal fuselage. That is season we saw that vane disappeared on F-14D. There is no need us to worry about the trim balance since the related area of F-14's horizontal tail is the biggest in all contemporary generation fighter, we have said the result this brought before if you remember.
summarization:
I couldn't see any advantage conventional layout would bring to me in level flight. Yes, in AoA, condition will be different but capability of TVC can resolving any problem MUUUCH MUCH stronger than LERX. Another friend of mine notice me that pic I drawing on Su-37 is absolutely wrong, yes it is abolutely wrong, because I am so lazy to combined all situation into one piece so mixed relative truth can be absolute mistake, here now I have to depict it individually. Your critique and opposition will be welcome.
To me the vast problem of this discussion is that both of you are messing Aerodynamics with Flight dynamics.
What you're talking about is Flight dynamics not aerodynamics.
A greater Arm of force doesn't give more "Lift" (Lift is a topic of aerodynamics) it give better Moment coefficient which is totally different.
It gives the ability with the same servocommand autority to pitch a plane at faster rate, that's all.
You certainly can't compare High AOA characteristics of both configurations using flight dynamics since the aerodynamics of a canarded plane and a aft tailed one are different.
And talking about supersonics isn't a good choice either until you have good knowledge of what happens there.
The first mistake is that even when starting from pure supersonic (where local flow velocity is higher than mach 1 everywhere) the boundary layer behavior changes quite a lot with the mach increase.
If flow separating occurs you can throw away all your "center of lift" theory as pressures distribution will greatly change.
That doesn't mean both of you didn't point out good points but it requires a far more detailed analysis of the problem using first aerodynamics and then knowing aerodynamics involved using flight dynamics.
Just looking at how the canard of rafale and eurofighter are used you can already sense the aerodynamics are even not the same on plane that look so alike.
So starting comparisons with F-15, F-14 or mig-25 (high supersonics aerodynamics:nothing to see with planes designed at being agile in sub and transonics.) is not appropriate here.
I clearly don't have the answer to the topic as i didn't investigate the specific configurations and as i said generalities on both configuration are not appliable to specific case.
A plane is designed as a whole, not an assemblage of canards+wing+whatever you want.
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.
An example is, for stable jet, foreplan give a positive lift during level flight, for unstable jet, tailplan gives the positive lift so that why I make green downward arrow in picture plus downward deflected red line to denote the angle of tailplan.
The advantage foreplan bring to is during supersonic flight, that lift move backward to be closed to CoG, so that even no deflection foreplan made, there is trend of up nose being, oppositely, during supersonic level flight, jetaircraft always need a deflection for lift up the tail, for balance the jet. the drawing I given didn't explain everything, logically inference is really important to understand so complicated situation mixed.
Be it Canard or Aft tail, the problem is the same.
The characteristic of pitching up or down is down to the Pitching Moment, Cm.
As you go supersonic both forplane/Aft tail and wing's separate center of pressure move aft.
Cm is given by= (Center of pressure-Cog/Lenght)*alpha here, Cog, Lenght and alpha are constant so the only variable is the Center of pressure.
Since Center of pressure moves aft the (center of pressure-Cog) difference will be less then in return Cm is less.
So "arm of force" here you're talking about is the distance of the tail/canard to the center of gravity, not the center of pressure.
The result from this is that what only matters is if the plane is stable or not.
If the plane has been designed as unstable then when going supersonic he will suffer less Cm decrease, if he's stable he will experience more and so on with a "too much" stable plane (which in fact just become an unstable plane in the pitch down axis).
So for this topic, canards or aft tail don't bring differences. You need to look at the unstability of a plane.
As far as stability is concerned the "tails" are of no importance. where it get important is onto the aerodynamics involved with both.
I like to add a little from the book 'Design for Air Combat' written by Ray Whitford who has worked on hypersonics and guided missiles as well as aircraft design both in the UK and in the USA.
In the book he breaks down the design of a fighter into all its component parts like intakes, wings, tailplanes, vertical stabilisers and canards (foreplanes). It gives a more historical perspective of aircraft design in the 1970s-early 1990s.
A foreplane is a lifting surface and in the 1960s was used as such. It was a device to enable supersonic designs to get enough lift to rotate on take-off. Whitford includes the Avro 730 as such an exmaple. Foreplanes therefore produce a nose-up moment around the CG. This can be useful to counter nose-down trim in the transonic phase, the Nord 1500 being one such example of a foreplane. The Milan 'moustache' foreplanes on the Mirage 5 were to improve take-off and landing characteristics and they produced nose lift requiring elevon down trim to give constant stability.
When placed correctly the upwash from the wing will actually increase the effectiveness of the foreplane but a forward CG is needed to maintain longitudinal stability. When combined with a high-lift wing CG range is very limted which would reduce the effectiveness of the fighter during transonic flight or shifts in loads (stores expended and fuel useage etc).
The foreplane affects the lifting capability of the main wing, SAAB got around this on the Viggen by mounting the foreplane as high as possible and the foreplane vortex flowed into the wings low-pressure fied so the vortex does not burst until it leaves the trailing edge.
When the foreplane and wing arrangement is optimised for flight at high AoA the lift generation of the wing at lower AoA is reduced. The SAAB designers found numerous problems in this area and tested a straight inboard leading edge to move the lift production to the outer wings where there was strong upwash but this led to strong shock waves adverse vortex interaction so the inboard leading edge sweep was eventally changed to 45 degrees.
A highly loaded foreplane which generates most of the lift suffers from high vortex drag. A low-altitude high-speed attack aircraft's votrex drag would only be around 5% of the total drag but for a fighter in combat it makes up 90% of the total drag and this will curtail sustained manoeuvring. However a closely coupled foreplane and wing can work well together and the foreplane acts as a strake creating a vortex field which improves the pressure distribution on the wing and can increase lift by as much as 20-30% compared to the maximum lift obtained by both in isolation. This benefits high AoA manoeuvres but will not aid take-off performance but it will reduce gust-sensitivity and drag on low-altitude aircraft.
Whitford claims the F-4 canard trials enabled the Phantom to pull 1G more at 470kmh at 9000m and had a 14kmh lower approach speed.
The five main reasons designers avoided canards in the 1970s and 1980s were;
a) Lack of experience and accurate wind-tunnel pitching moment data since the foreplane must stall first.
b)Vortices may affect the fin and cause serious buffet at high AoA (the F/A-18 suffered from this)
c) Destabilising effect on wing stores aft of CG
d)designers flet it restricted the choice of wing planform
e) a highly loaded foreplane suffers from six times greater lift-induced drag than a wing
Only FBW systems really answered these problems and there is no need for inherent stability so there is no longer a need to restrict the CG to a forward position and this in turn reduces the load on the foreplane and cuts vortex drag increasing the lift drag ratios to that of conventional aircraft. In manoeuvre the lift-drag ratio is much less than a conventional aircraft as the neutral point moves aft in supersonic flight.
The removal of the tailplane cleans up the rear fuselage and this too cuts supersonic drag.
If thrust vectoring is used a canard helps to emliminate longitudinal stability and trim changes, canards go well with FSW and the downwash spreads the loading on the wing and reduces the root stall tendancy.
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