Jxx photo revealed? please identify

Don't really make sense.

+ If you added weight in the rear (actuators won't add that much weight), you should be able to compensate by lightening the rear with means like using composite.

+ Canards + actuators in the front will still weigh more than yaw TVC actuators + ballast in the front. That's because to put canards in such a plane, you need to cut up the stress lines, and in order to compensate for the loss of structural integrity, you need to beef up the other lines. That's going to increase the weight in the front, and with it, your plane becomes more stable and you even actually lose some maneuverbility because of this, reducing the purported gains adding the canards supposed to give. In the front, you don't have much means of reducing weight via composite structures as you can do in the back.

+ As you make the front heavier, you have to maintain your CG by making the back heavier. The canards + actuators + structural beefing up will weigh more than the 2D TVC nozzle actuators and you have to compensate by adding weight in the back.

+ Not the least, TVC's best feature is maneuverbility in the post stall regime. However, at this regime, canards don't work as well.

+ The MiG-29OVT's late development also has something to with the fact that 3D nozzle can only be finished much later than the 2D nozzle, and the OVT project wasn't a high priority one compared to the -SMT, and -M upgrades.

A Couple of Points

crobato said:

Don't really make sense.

+ If you added weight in the rear (actuators won't add that much weight), you should be able to compensate by lightening the rear with means like using composite.

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Opportunities for reducing the weight of the rearmost fuselage are relatively few. Engine temperatures are too high to use composites on the fuselage hardware itself.

The weight problem with a production TVC nozzle stems from adding all that weight so far aft. The moment arm is so long that it becomes difficult to rebalance the airplane weight by reducing (or even adding) weight elsewhere. For a demonstrator program, this can be avoided by using a lighter-weight paddle arrangement, like that used on the X-31 and F-18 HARV. For a production fighter, however, the performance loss in other segments of the flight envelope would be unacceptable with such a crude design.

crobato said:

+ Canards + actuators in the front will still weigh more than yaw TVC actuators + ballast in the front. That's because to put canards in such a plane, you need to cut up the stress lines, and in order to compensate for the loss of structural integrity, you need to beef up the other lines.

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For the Su-27, the airframe had enough space (and existing structural integrity) to make the addition of the canard a weight-effective measure. I would agree that for the much more compact MiG-29 airframe, it may not have made sense.

crobato said:

+ Not the least, TVC's best feature is maneuverbility in the post stall regime. However, at this regime, canards don't work as well.

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The design of the X-31 (and by extension the Eurofighter Typhoon) was specifically geared to maximize its post-stall performance. This was really the brainchild of Wolfgang Herbst, the German engineer who developed the theory behind post-stall maneuvering combat back in the late 1970s and early 1980s. The canard was specifically chosen, for its ability to retain its control authority well into the post-stall envelope (as opposed to a horizontal tail, which is little better than useless under these conditions).

Given the option, the X-31 opted for both TVC with pitch and yaw authority and a canard, to maximize its control authority throughout this envelope. Remember that "post stall" is not the same as "no forward airspeed". The objective is to enter and exit the post-stall regime as needed, not to dwell there.

crobato said:

+ The MiG-29OVT's late development also has something to with the fact that 3D nozzle can only be finished much later than the 2D nozzle, and the OVT project wasn't a high priority one compared to the -SMT, and -M upgrades.

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I agree. The MiG-29 needed a lot of work to transition from a point air defense fighter, to a more multirole, longer range platform. After the end of the Cold War, the Russians lost all interest in pursuing derivatives of the MiG-29 for their own use, focusing instead on the longer-range Sukhoi product line.

I am still impressed, however, with how quickly the entire Su-30MKI/Su-35 development program came together. I know of no western developer who could have pulled off a similar feat.

Re: A Couple of Points

unknauthr said:

Opportunities for reducing the weight of the rearmost fuselage are relatively few. Engine temperatures are too high to use composites on the fuselage hardware itself.

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Not really. You can use composites in the tail rudders, ventral fins, and elevators. That will already save you more than enough.

For the Su-27, the airframe had enough space (and existing structural integrity) to make the addition of the canard a weight-effective measure. I would agree that for the much more compact MiG-29 airframe, it may not have made sense.

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I have to disagree. Regardless, adding canards would still cut up up the basic airframe stress lines. Big as the Su-27 is, there is not that much space forward of the fuselage either. This is not a plane that designed from scratch to have active canards.

To optimally compensate, you have to come up with a redesigned airframe because trying to convert an existing airframe means cutting up some spars, beefing up the remaining members and you add further weight. Every bit of a surgery not only costs money but also costs structural integrity.

Furthermore, it looks like Sukhoi has abandoned any crazy ideas about converting existing airframes to canards, such as converting the Su-30Ks into Su-30MKIs (instead the Su-30Ks are looking for a buyer).

Furthermore, the canards in the Super Flanker has a really funny arrangement of being in the same plane as the main wing. That means the canards just happen to be in the way of the airflow heading to the main wing. Not only do you block some air, but the canard wake is headed straight over the main wing.

In just about every other canard design, the canards do not share the same plane as the main wing. In the J-10, the canards are diehedral to throw the wake over the fuselage and away from the main wings, which are anhedral to further the wake seperation between the two.

The design of the X-31 (and by extension the Eurofighter Typhoon) was specifically geared to maximize its post-stall performance. This was really the brainchild of Wolfgang Herbst, the German engineer who developed the theory behind post-stall maneuvering combat back in the late 1970s and early 1980s. The canard was specifically chosen, for its ability to retain its control authority well into the post-stall envelope (as opposed to a horizontal tail, which is little better than useless under these conditions).

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It is not necessaarily because the canard has better control authority, well it does, thanks to an uninterrupted airflow, but because canards will regain control faster once the plane hits a dive. All aerofoils no matter what, have their stall limits. Remember just as what you said, going in and out of the post stall regime quicker.

Do note the canards on the Super Flanker is quite small, which is wondering why how much control it can get, but the X-31 canards is quite healthy in size to the aircraft. The canards in the X-31 is a complete elevator replacement, on the Super Flanker it is there only to augment the rear elevators. So its still sizably different.

I agree. The MiG-29 needed a lot of work to transition from a point air defense fighter, to a more multirole, longer range platform. After the end of the Cold War, the Russians lost all interest in pursuing derivatives of the MiG-29 for their own use, focusing instead on the longer-range Sukhoi product line.

I am still impressed, however, with how quickly the entire Su-30MKI/Su-35 development program came together. I know of no western developer who could have pulled off a similar feat.

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It is quite impressive how indeed it is pulled together. But Sukhoi now has other plans, and their Su-35 with TVC no longer has to use canards. This will not only save you cost, but also lets you upgrade existing airframes without changing them.

Weight Statistics for Russian TVC Nozzles

To help round-out the picture, I thought I should append a comparison of engine weights, with and without TVC nozzles. The following data was pulled from Janes' Aero Engines.

Adding pitch-only TVC to the AL-31F (to produce the AL-31FP), is reported to increase engine dry weight by 40-kg, from 1530 to 1570-kg. That makes for a 2.6% increase in the total engine weight. Also bear in mind that the Su-30 is a two-engine aircraft.

Adding a multi-axis TVC nozzle to the RD-33 (to produce the RD-133), is reported to increase the engine dry weight from 1055-kg to 1145-kg, for a 90-kg increase (8.5% of the total engine weight).

The increased complexity of the multi-axis TVC nozzle should be self evident. It as not as simple as adding on an actuator or two. An entire multi-axis pivot mechanism has to be incorporated. It's the difference between mounting the engine nozzle on a "hinge" style pivot mechanism (a single-axis pivot joint), compared to a ball-and-socket, multi-axis pivot support. There is a clear weight penalty that comes along with the multi-axis TVC.

Using the percent increase in total engine weight as a guide, an AL-31F fitted with a multi-axis TVC nozzle similar to that used on the MiG-29OVT should weigh-in at around 130-kg heavier than the baseline AL-31F.

That isn't to say that multi-axis TVC shouldn't be embraced. Given the choice, it carries a clear advantage in post-stall control. It just comes at a price.

So, you're complaining about a 130kg increase in weight? That;s like the weight of a single AAM.

Tell me what would be the weight cost of a set of two canards, plus their actuators, not to mention the structural modifications into the airframe.

:china: Any updates on the J-XX project? Anyway this is what I think about the J-XX project. Their will be two new aircrafts launched one in 2010 and one in 2013.
1) The one in 2010 will be the Super 10 which is the enlarged J-10A aircraft with double engine and vertical fin with movable foward canards. This version will be cheaper as a border 4.5 to 5th generation aircraft. It will be stealthy but not as snealthy as the F-22. It will either on par with the Eurofighter/Rafale or either surpassing in capability wise. The J-10 pilots will fly this new aircraft while the J-10 fleet will have new pilots.

2) The one in 2013 will be the expensive and stealthy aircraft near the F-22 capbailities. This aircraft will be clearly in the 5th generation of aircrafts. Though this aircraft will be produced in limited numbers compared to the Super 10. Though it is much more stealthier, capable, technology advanced. By this time the pilot training hours will be western standards. With the current aggressor squad training hours becoming the normal standard training hours for the PLAAF pilots and the aggressor squad will have further and increased training hours then the standard PLAAF pilots. Aggressor pilots will fly the new aircrafts.

Simplified Su-30 TVC Trade Study

Sorry I didn't respond sooner. Too many things to juggle these past weeks.

crobato said:

So, you're complaining about a 130kg increase in weight? That;s like the weight of a single AAM.

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Unlike adding weight to the nozzle, AAM's will not significantly alter the axial CG location of the airframe.

It is not merely a matter of how much nozzle weight is added, but where it is added. Any additional nozzle weight that is added must be moment-balanced by the addition of canards (per Su-30MKI) or ballast (if applying a 3D TVC nozzle without canards), to avoid violating the airplane's design tip-back criteria. Violating tip-back, of course, would result in a tail-strike, whenever the airplane was configured with external stores that might drive the CG to its aft-most site. Recall that moment will be defined by weight times distance, not merely weight. Adding AAM's (no matter how heavy) has relatively little impact on this calculation.

Consider the following, rough approximation for the weight and balance trade, as illustrated in the diagram below:

• Adding pitch-only TVC would add 40-kg per engine, or 80-kg total. To moment balance this weight addition, the canard and actuators must add at least 102-kg of weight, to avoid shifting the airplane's tip-back limit.
  
  
• A rough calculation for the weight of the canard surfaces on the Su-35 (using openly published methods and calibrated to published data for the American F-15 horizontal tail), would suggest a total canard weight of approximately 186-kg. The addition of canards should therefore be sufficient to counter-balance the weight of adding pitch-only TVC in the tail of the aircraft, while bringing the total weight addition (nozzles plus canards) to roughly 270-kg.
  
  
• Adding a multi-axis TVC nozzle would add roughly 130-kg per engine, or 260-kg between the two engines. Assuming that ballast was located at roughly the same axial location as the canard, a total of 333-kg of ballast weight would be required, to maintain the aft-CG of the airplane. That's a total weight addition of over 590-kg.

In sum, even a rough calculation confirms that the addition of a multi-axis TVC would not buy its way into the existing Su-30/35 airframe. This trade would not necessarily hold true, however, for an all-new design (such as the J-XX), where the location of the landing gear and structural elements can be more freely adjusted.

I don't think canards would weigh less than 200kg _each_ without actuators. What is the weight of a complete elevator?

Just the variable intakes alone on the MiG-23 vs. MiG-27 cost 300kg (or 150kg per intake) and that has a much smaller surface area and mechanisms than a complete canard plus actuators. The actuators on the canards alone would weigh as much or more than the actuators on the nozzle, and have to a much higher deflection.

To say the least.

Then you have to modify the airframe to make space for these. That means cutting one of the main full length spars, which requries you to strengthen or beef up the remaining spars. That adds weight.

Adding a multi-axis TVC nozzle would add roughly 130-kg per engine, or 260-kg between the two engines. Assuming that ballast was located at roughly the same axial location as the canard, a total of 333-kg of ballast weight would be required, to maintain the aft-CG of the airplane. That's a total weight addition of over 590-kg.

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I don't see how a second set of actuators would add 130kg per engine, perhaps 80kg. The deflection is quite limited to necessitate a rather complex actuator. For a plane like the MiG-29OVT, you can shave off the weight in the tail by changing the surfaces to composite, plus a rearrangement of the innards.

I read something a while ago that the Russians had offered China TVC for their Flankers when it was thought it was being denied intentionally. But the real reason China didn't get TVC was because they didn't like the extra ton of weight on the aircraft.

AssassinsMace said:

I read something a while ago that the Russians had offered China TVC for their Flankers when it was thought it was being denied intentionally. But the real reason China didn't get TVC was because they didn't like the extra ton of weight on the aircraft.

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Miltech reported that a actuator and other associate equipment for TVC is 120 lbs.- each!