Are Flanker Canards Actually Powered?

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collimatrix

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Unread post21 Oct 2018, 14:48

I was thinking about the canards on the SU-30/33/34, and the lack of canards on the SU-35. I don't think the canards are actually powered. A few salient facts:


-The SU-27 was designed without canards, so the strake area at the front of the aircraft probably wasn't designed to support the loads imposed by an active control surface, nor was it designed with the volume required for a big actuator. Even with some degree of re-design of the strake, the canards are probably a bit of kludge, and probably somewhat limited in what they can do.

-The Flanker series has a big honking fuel tank right behind the cockpit, in the thick part of the fuselage. Actually filling this tank robs the Flanker of much of its maneuverability, not just because of the added weight, but because this tank is rather far forward on the plane, and filling it drags the center of gravity of the aircraft far forward of the center of lift, leading to pitch stiffness.

-Flanker canards are more or less in line with the main wings, not above the main wings the way they would be if they were providing useful vortex/main wing interactions. Flankers have a big chine/blend/LERX that clearly serves as a vortex generator anyway, so it's clear that the canards aren't there to delay stall on the main wing.

-Flankers (like most fighters) are flown at extremely low fuel levels to pull airshow stunts.

-All the pictures I can find of the aircraft pulling Gs seem to show the canards at extreme nose-down attitudes, like so:

Image

Don't those canards look like they're aligned with the local airflow?

So, here's my hypothesis; the canards on Flanker variants that are equipped with them (SU-30,SU-33, SU-34 and all Chinese clones thereof) aren't actually powered, active control surfaces. They're passive devices that are either locked in place or left to weathervane and align themselves with local airflow.

The purpose of the canards isn't to provide additional control at high AOA or greater dogfight agility, at least not directly. The purpose of the canards on the Flanker is to adjust the center of lift of the aircraft and offset the pitch stiffness caused by carrying a full load of fuel in the forward fuel tank, or to offset the rearward CL shift caused by supersonic flight. If the CL needs to be brought forwards, the flight control system automatically locks the canards to an AOA where they will generate lift. If they are not needed, they are unlocked and allowed to weathervane.

The reason that the canards are always pointing down in airshow pictures of Flankers is that the planes are flying subsonic with very low fuel levels, so the CG/CL relationship is exactly where it needs to be for maximum agility. Lift from the canards is not needed (indeed, it might disturb the CG/CL relationship so much that the FBW couldn't handle it), so the canards are unlocked and left in weathervane mode.

The reason that the SU-35 does not have canards is that the FBW system is more advanced, and the radar system is a newer, lighter model. The SU-35 is less nose-heavy to begin with, and the FBW system is capable of handling a larger margin of static instability. Therefore, when the SU-35 is fully gassed up or flying supersonic, it suffers less from pitch stiffness and it can dispense with the additional weight, drag and RCS penalty of the canards.



So, that's my guess. Can anyone who knows the ins and outs of Flankers confirm or deny? Alternatively, does anyone have video of the canards doing a wiggle during a preflight or takeoff run?
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zhangmdev

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Unread post21 Oct 2018, 19:25

I think those canards are largely for leading edge extension vortex control. So they should move at different AoA. A number of photos of Su-34 show canards at different angles during takeoff and flying.

https://theaviationist.com/wp-content/u ... atakia.jpg
https://cdn.rbth.com/all/2017/06/05/su- ... _009-b.jpg
http://img.over-blog-kiwi.com/0/54/74/5 ... kes-on.jpg

And this cutaway shows canard actuator (44)
http://aviazioneaereimilitari.altervist ... SU-271.jpg
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sferrin

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Unread post21 Oct 2018, 20:05

They're powered. From "Red Star Volume 2: Flankers-The New Generation":

Capture.PNG
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collimatrix

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Unread post22 Oct 2018, 10:22

Thanks sferrin.

So why did they get rid of them on the Flanker E?
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sprstdlyscottsmn

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Unread post22 Oct 2018, 13:45

Reduce drag and weight.
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hythelday

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Unread post22 Oct 2018, 13:49

collimatrix wrote:Thanks sferrin.

So why did they get rid of them on the Flanker E?


I remember reading on some Russian forum years ago that canards were introduced because Su-30 gained so much avionics-related weight up front that they needed canards to address the issue. Seems like Su-35 was rebalanced yet again to make do without them.

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