Why did American fighter-jet designers never go for canards?

Factual Questions
1

Starting in the 1970s-2000s, canards really caught on in Europe, Russia and China. The Rafale, Eurofighter, Gripen, Viggen, Jian-10, Jian-20, Jian-31, Su-30, Su-33, Su-34, Su-35 and Su-37 all featured canards near the nose. The Israeli Lavi would have had it too had it been mass-produced.

But this never caught on with American warplanes. (I know there were some experimental prototypes, such as the XB-70 Valkyrie bomber or X-29, and the B-1 Lancer has a little mustache, but that was it.)

Just a cultural thing?

2

Canards provide two general benefits; first is lateral stability, and the second is being able to trim the aircraft by more evenly distributing lift surfaces, particularly if the distribution of mass of the aircraft tends forward. This comes at the expensive of more weight, and for articulating canards, greater complexity. Modern American fighter jets tend to be larger than their European counterparts and (with the exception of the F-16 and F-35) dual engine with twin vertical stabilizers with little need of forward aerosurfaces for lateral stability, and if anything have difficulty in being rear heavy, so forward lift surfaces aren’t really necessary. There was an experimental version of the F-16 equipped with canards below the air intake but from what I can tell it turned out to not be that big of an advantage given the already ‘relaxed’ stability of the F-16 and its dynamic fly-by-wire control.

There are also supersonic drag and stealth compromises with canards (although they can be designed to reduce radar return off of engines), as well as issues with US doctrine on how fighter aircraft are used; canards are great for low speed maneuverability but compromise performance at high speed/high angle of attack, and at the risk of being overly simplistic US air superiority doctrine is focused on standoff engagements and low altitude flight with ability to achieve high angle of attack at high speed rather than engaging in close engagement with complex air combat maneuvers. In most modern (4 and 4-1/2 generation fighters) canards are generally something glommed onto an existing design to fix trim or stability issues.

This isn’t to discount that there are certainly “cultural” notions that permeate aircraft companies and design bureaus which lead to utilizing particular design solutions across lines of aircraft (as is quite evident looking at different aircraft where you can see the design heritage in particular characteristics) but there are good reasons to avoid using canards if they aren’t really necessary.

Stranger

3

Excellent explanation Stranger. Thinking aloud, my brother flew the F-16 and he was also a test pilot at Edwards. I wonder if asking him might add more good info.

4

Yes, great reply, much thanks.

As a layman, I was also thinking more in aesthetic terms - canards tend to make anything look rakish and daring :wink:

5

Aesthetics, huh? Were you a fan of Milli Vanilli?

6

Aesthetics seem to come into play a little with concept designs (see the marketing concepts of the Boeing Dreamliner) but the drawing board says that what worked best last time will probably work best the next time.

With aircraft, when I see little wings hanging off the fuselage in odd places (not including canards), no matter how cool they look, I can’t help wonder what aerodynamic problems they were designed to fix.

On the F16 with canards, the AFTI, it could apparently do flat turns (turns without banking). It also had advanced helmet mounted targeting systems. I remember being very intrigued with the idea when I was young (wow, you can just look at an enemy plane and shoot it down with a missile!) The canards on the F16 come from a different design space than Eurofighter type canards though, the F16 ones were to allow it to do more than what can be achieved with main wings and tail plane. The Eurofighter canards were part of a basic design choice between having the stabiliser at the front or rear of the plane.

7

I believe there might be one more advantage that Stranger did not list, but did address. I was told that canard designs make especially tactical aircraft more agile with a greater climb rate in addition to being more stable. A stable platform is vital for firing guns according to Chuck Yeager; a small wiggle in the wings while firing can cause a huge variation at a thousand yards where fighter pilots are often aiming.

As Stranger mentioned, F16’s can already make 9G turns- that is as tight as almost any pilot can endure (and more than they can sustain for very long) so additional flight surfaces are entirely wasted. The F15 and F16 for sure have a greater than one to one thrust to weight ratio (in the right configuration of course) and I have personally witnessed an F15 pivot from horizontal to vertical flight in about a nanosecond and blast into the stratosphere with full afterburner like a booster rocket. I am pretty sure the F18 Hornets and Super Hornets are also greater than a one to one ratio, but not fully loaded because they have much heavier landing gear and a large payload.

The one tactical aircraft that might have benefited from adding canards already had one of the most complex system of flight surfaces, the F14 Tomcat. They WERE front heavy, and just heavy! (They are no longer in service, retired quite some time ago.) They had a lot of thrust, but they also weighed a lot. They already had the variable geometry wings which adjusted automatically (in at least some situations if I am remembering correctly but it was still one more thing the pilot had to keep track of). They were not very agile by most accounts, but their role was as a standoff Fleet Defense weapon that carried missiles that had a range of about 135 miles with three different targeting systems as well as other shorter range missiles. They did not turn very tight and that would be a distinct disadvantage in a genuine dog fight, and as mentioned above they were very nose heavy.

Years ago I watched a training film or documentary about aviator training and all of the pilots said they trained mostly against each other and since all the similar aircraft had the same turning radius, the trick to a victorious encounter was to get your opponent pointed down while you were going up. Once that happened you could literally just get behind them and drive them into the sea as they turned in ever descending circles to stay ahead of your guns. Once you are spiraling down in aircraft that turn at the same rate, the flier who is higher and behind HAS to win the encounter.

But if one of them had canards in otherwise similar aircraft, they could out turn and out climb their opponent, a huge advantage. If you can out turn and out climb – you no longer have to spiral downward to stay ahead of his guns. Even if you are spiraling in with the other plane behind and above you- you can make a short dive to build up airspeed then pull back hard and climb at a rate that would never allow the other guys guns to be pointed at you. What is more, since you turn tighter, you could loop around and come in behind him causing the hunter to become the hunted and then he would have to perform evasive maneuvers to avoid your guns. Once you are behind the other aircraft that cannot turn as tightly as you can, you can drop back a bit and (no matter what attitude you are at) use the canard assisted lift of your wings to put a burst out where he will climb into it momentarily. As long as your wings are parallel to the other aircraft, you can pull your nose a little higher than he can and then it is just a matter of timing the burst to hit before he changes direction. The canards would also help you dive more rapidly so that could be used if he instead dives to avoid you.

The tricky thing about canards is that all three sets of control surfaces must not align in level flight or they will interfere with each other. Just like your main wings and rear stabilizers cannot be in the same slipstream, the canards must also have uninterrupted airflow that does not disturb the airflow of the other surfaces under any circumstances. That by-the-way, is why so many tactical aircraft have twin tails I am told. In a steep climb a single tail can become entirely hidden in the “shadow” of the cockpit bubble. In flat, level flight airflow streaks along the canopy and flows over the tail smoothly. But once you start jinxing around the airflow over the tail might be disturbed so they put twin tails outside the profile of the canopy so at all times one or the other (and mostly both) will have smooth airflow over the surface area.

Disclaimer: Even if I have remembered this perfectly accurately, the information is twenty years old or so. Watching aerial demonstrations of the F22 have convinced me the aircraft I so admired long ago are woefully inadequate against top of the line modern aircraft. (It is however, my opinion that any of those older planes mentioned above, any still in service, is a match for the F35 which is a dog in this guy’s view.) Ducted thrust is an amazing technology that beats even the most rakish canards in real life it would seem.

8

IIRC I read somewhere that winglets are often worthless on many planes. Certainly they have a beneficial effect on commercial planes (read “big” planes) but on small planes (think private planes) their effect is minimal and almost entirely for looks.

9

I have been told those upended wing tips were added to eliminate voritices which caused little shock waves in the flat wings that preceded the ones shown. On humid days you could see trails of round tubes of air that followed the plains before they added the up turned tips. The best way to view it was in wind tunnel tests where they would blow smoke over the flat wings-- then the up turned wings and had vastly different results. I do not recall the details, but it was determined that the extra drag was more than made up for by the lack of vortices over long level flights.

10

You are correct. That is what they are for.

But, apparently, the effect is more dramatic on bigger planes so they get more benefit from them. On small planes it happens but the effect is so minor it really is not worth the cost of a winglet. But they put them there now because they are “cool”.

It doesn’t make things worse. Maybe even a little better but, mostly, a waste of money on a small plane (again…a vague memory…I may be wrong and doubtless someone will say so if I am).

There is a reason you do not see these on most small, private planes.

11

The purpose of winglets isn’t to eliminate wingtip vortices of a cruising airliner (impossible unless your wing never terminates) but to move the vortices up away from the lift surface, thus reducing the loss of lift near the end of the wing. The amount of actual drag these add at cruising speed (460-520 kt, Ma~0.85) is minimal since they’re already in a low pressure region above the wing, and the primary cost is just the additional weight. The utility of upturned winglets on aircraft that do not have airflow over the wing at transonic speeds is negligible.

Stranger

12

I thought winglets were ALL about fuel savings. The vortices at the wingtips induced drag which equated to fuel loss. It was not a big difference but these things add up.

Take a Boeing 737 with 4,000 gallons of fuel. At a price of $1.75/gallon that’s $7,000 of gas. If that plane does it 3x per day and flies 365 days a year that’s $7,665,000/year in fuel.

If you can save 3% on that then you save nearly $230,000/year/plane. That’s not nothing.

I know planes don’t fly 24/7/365 or use all their fuel every flight. The above is just an illustration. Southwest Airlines has almost 700 planes. A 3% fuel savings across the fleet can be a substantial amount of money.

But for your little Cessna 172? Not so much.

13

Thank you both for the clarification.

14

Color me a little skeptical on the statement that canards can increase rate of climb. Can someone explain to me how that would work? I would have expected rate of climb to be a function of things like power to weight ratio and maybe L /D. Not the number or placement of control surfaces.
Thanks.

15

IANAPilot but I would be shocked if canards improved rate of climb. As long as a plane can point its nose up at a given angle the rest is up to the engines to push you up that slope. Maybe if they reduced drag a lot but I would think an extra bit in the airstream would be more likely to increase drag. But maybe they are mope efficient than elevators? (total WAG)

I can see a canard maybe making a plane more maneuverable though.

16

AIUI, canards are essentially elevators, just in front of your wings instead of behind. So if you pitch your nose up, you have canards pushing your nose up AND the tail elevators also pushing your nose up - essentially 2x the amount of control surfaces doing the same job instead of 1x, hence why you’d pitch up more quickly. Unless I’m misunderstanding the question.

17

I can see canards maybe making an aircraft more maneuverable, but a faster pitch up isn’t the same as a greater rate of climb.

18

Let me see if I can recall what I was told all those years ago.
First, the rate of climb for any aircraft with a greater than one to one thrust to weight ration would be completely unimpacted by canards or possibly negatively impacted due to drag. Rate of climb for that type of aircraft is a function of the gross weight vs. the total thrust; it can climb straight up without going into a stall. I would imagine the closer you get to weight and thrust being equal the less canards would help but no authoritative source I ever heard mentioned that.

But in an aircraft that weighs a lot but has say half the thrust as it has weight, I believe canards can have an impact on rate of climb. Perhaps due to more than one factor if I am remembering all of this correctly. If the thrust is used primarily for forward thrust (relative to the ground I mean, all thrust is forward from within the craft), canard equipped ships with less than one to one ratios can achieve a higher angle of attack without going into a stall

First, the elevators behind the wings actually push the tail down to increase attitude of attack. So to add pitch you actually have the elevators working against the main wings. Perhaps once the proper angle of attack is achieved the elevators can be adjusted to a neutral position, but that contradicts my understanding of how they work. The main lift wings are configured to achieve flat level flight, and perhaps with flaps (if they are leading edge or rear edge) could cause you to climb even during level flight but that would be painfully slow – especially when someone is shooting at you. So if you want maximum climb to avoid tragedy, you will want to pitch up to the angle of attack that maximizes climb rate and does not cause a stall. In that case the elevators are pushing down while the wings are pushing up until climb out has been achieved.

Second, canards create more surface area for lift. All tactical aircraft, and especially the F14 we were discussing has lift from pressure pushing up under the entire body of the craft (as well as the wings) which is extra wide in the Fourteen so they could (can- keep stumbling over tense since we are discussing an active flight, but they are a discontinued platform) carry four Phoenix missiles between the engines. So very ugly and poorly designed canards (lacking ANY rakish charm) that were two feet by five feet rectangles on each side up front would provide 20 square feet of surface area to gain lift from.

Third, the canards can actually lift the front rather than push down the back. As Velocity stated earlier, you could achieve that twice as fast with canards arguably. That might not be that big a consideration because achieving angle of attack in a tactical aircraft is a pretty quick process already, but it would make the process quicker. But if the canard designed aircraft can achieve an aggressive angle of attack quickly without the elevators pushing the tail down (and using that surface area for lift also), the climb rate would have to be increased. By using the canards to lift the nose instead of the elevators to drop the tail- all three airfoils would be creating lift. A distinct benefit compared to a conventional craft that has one set of surfaces providing lift (main wings) while the other pushes part of the craft down (elevators).

Fourth, with canards it is possible (theoretically and I assume literally) to sustain a higher angle of attack without going into a stall and for a longer period (until you reach the operational ceiling). I assume one can jinx up quickly without stalling as long as you go back to a sustainable angle of attack quickly, but you would lose airflow over your control surfaces and be unstable momentarily. This is what I was getting at in my previous post; if the canard equipped craft can be more nose up during a climb and it is behind the non-canard equipped craft, it can fire a burst into the air above the other craft and the slower climbing plain will simply climb into the stream of fire unless it changes direction.
(This is my own thought and I was never told it by any authoritative source. But I was reminded of it when I recalled the story of a pilot who, during the early days of supersonic flight, fired live rounds while in a steep climb, then leveled off or dove then leveled off under the falling rounds literally shooting himself down. I figured it would work in reverse if you fired right above a climbing aircraft it would eventually climb into the stream of fire.)

I agree, but I believe the above does demonstrate how canards can achieve a greater rate of climb.

19

Just so I’m understanding this correctly, is the idea that the pursued (prey) aircraft cannot climb up to avoid crashing into the sea, because doing so will mean slowing down and then he is squarely in the gunsights of the pursuing warplane?

(Although, with off-boresight helmet-cued missiles, I’m guessing this wouldn’t be as much of a factor either way anymore)

20

Canards could only improve the climb rate if they somehow improved lift-to-drag ratio at high angle of attack. Given that canards are always in front of the main wing surface and spoil the flow behind them, I would expect the opposite, i.e. that they improve stability or maneuverability at the expense of maximum potential lift.

The intuitive understanding of aircraft dynamics should start with the notion that from a purely L/D and efficiency standpoint, the ideal aircraft is all wing (of the correct camber and sweep for the flight condition) and everything else is a compromise for dynamics, stability, accommodations for payload and passengers, et cetera. The more aerosurfaces you add for any purpose other than eliminating adverse drag (e.g. wingtip devices) add weight and drag.

Stranger