JF-17 Thunder Multirole Fighter [Thread 5]

[Munir]

@Munir

Aerodynamically unstable, DFBEWCS aided canard cropped deltas fly much better and sustain high Gs much better than the previous generation of similar wing designs. Gripen NG is a good example.

I agree that unstable systems are extremely more reactive but that does not mean you eliminate drag by being unstable. It is the same idea that many posters think that TVC is magic. Just look at the drag you create...

Quoting H Khan from Pakdef.....

I think the tiny, small conventional wings have lowest drag when forced into turning... Even a failed turboprop can outturn a delta if that one lost all its kinetic energy... The golden rule by all pilots is that the first turn against a delta is the most important. After that you can have fun cause it just cannot get back to speed as fast as you will.

 

[Rajput_Pakistani]

@Munir @Dazzler

AFAIK, Delta wing configuration is ideal for high-speed, high altitude. Delta wing gave more lift, more wing-loading and fuel storage. At low speeds and low altitude, the aircraft with Delta wing configuration is hard to fly as the wing create more drag then lift. So the Canard concept was introduced to balance out the drag and create more lift. So at high-altitude and BVR, may be Mirage-2000 have an advantage over JF-17 but at WVR i dont think Mirage stand a chance against fighters like F16 or JF17.
Either it will over-shoot or bleed energy at tight turns in WVR dog fight.

 

[Munir]

@rajput
The wingloading is lower. You get essential a lot more wing so the weight is better distributed. And there is less power needed to get higher speeds cause the delta bleeds less energy when flying straight.

In WVR range... When the delta has kinetic energy it will win anywhere. The moment it trades that it will begin struggling. But... When flying at high altitudes the delta gains back its advantage of turning against even F16. This pretty much shows that PAF uses F16 at medium altitude, JF17 at low altitude and the FC20 at high altitudes... It does not take rocket scientist to figure out the tactics on both sides.

Good Stuff! Masha'Allah

So this means the JFT is cleared to use SD-10 BVR by the Air Force ?

§block 2 has indeed the WVR SD10 as standard weapon. It means that all the previous blocks need software upgrade.

 

[SQ8]

When they say Block 2 would have improved avionics, what does improved means ? Cockpit layout suggest avionics are already up to date

Extra Radar modes...optimized processing.. improved ECM.. additional protocols for weapons.

 

[Manticore]

by Irfan Baloch

 

[razgriz19]

so what are the plans for 5th generation short range missile?
Will PAF go for A-Darter or the PL-10?

A darter

 

[nomi007]

 

[Dazzler]

MAA-1B piranha 2 was ordered back in 2011, it is better than R-73 xx in general perofrmance. Piranha 1 were given for weapon system familiarization purpose, even MAA-1 has a higher off boreshight angle than AIM-9Ps

 

[Tempest II]

A few months ago, somewhere, appeared an article quoting CATIC or AVIC on the JF-17 GPS/INS system and how much time it needs to calibrate/align/reboot (something like that). It was somewhere around two minutes. Anyone remembers/recalls/knows the article and where I can find it? … … One of those things one reads and takes little notice until later.

 

[Tempest II]

I found the info. It is on the slide below.

Now does anyone know when you would use the 4-min compass alignment routine, or when you should/could use the 30-sec quick or when one would do the alignment when airborne?
Thanks.

 

[Tempest II]

Finding some answers slowly: http://www.honeywell.com/sites/serv...t?docid=D1A8786B5-5658-438B-AB93-7B37E787F29A

Strapdown inertial navigation systems require an initialization process that establishes the relationship between the aircraft body frame and the local geographic reference. This process, called alignment, generally requires the device to remain stationary for some period
of time in order to establish this initial state.
This paper describes an alignment process where the initialization occurs while the device is moving. This is possible because an accurate determination of the aircraft motion is available based on measurements obtained from GPS.
Align In Motion allows initialization of a Strapdown Inertial Navigation System while an aircraft is moving, in the air or on the ground. This is accomplished using Civilian grade GPS and an inertial reasonableness test, thereby allowing commercial data integrity requirements
to be met. Align In Motion has been FAA certified to recover pure INS performance equivalent to stationary align procedures for civilian flight times up to 18 hours.
This Align In Motion capability allows the removal of dedicated backup batteries on aircraft resulting in weight, cost, and reliability improvements. Align In Motion also has benefits for aircraft operations on the ground, on board ship, and in the air such as reduced turn backs,
quicker dispatch, and world-wide alignment including polar regions.

 

[SQ8]

I found the info. It is on the slide below.


Now does anyone know when you would use the 4-min compass alignment routine, or when you should/could use the 30-sec quick or when one would do the alignment when airborne?
Thanks.

Peacetime flight, normal routine for the 4 minute timeframe. Alert status, scramble for the 30-sec alignment. Most fighters of the cold war(and some even today) have the quickstart button that bare-bones starts the jet and aligns the INS on the go.

 

[gambit]

Peacetime flight, normal routine for the 4 minute timeframe. Alert status, scramble for the 30-sec alignment. Most fighters of the cold war(and some even today) have the quickstart button that bare-bones starts the jet and aligns the INS on the go.

True...But the old mechanical gyros based INS absolutely hated that method of start up.

Each INS system, old or modern, prefers to start up where it is allowed to locate its current position DESPITE memory of its previous location prior to shut down, and every system does have that memory. That does not mean the previous location is not used. It is used to provide a quick reference after the gyro completely spooled up to full rpm. But if the jet is moved, even from the front to most rear row on the flightline, the longer the physical distance, the longer it will take to recalculate or discover the (new) current position. Ring laser gyros do have this issue but the time difference is negligible while the old mechanical gyros may require up to an extra minute to align to the new location.

Here is an example...

Micro-electro-mechanical-sensor inertial navigation system-assisted global navigation satellite system receiver acquisition scheme and performance evaluation - Springer

Abstract

When an aircraft moves under a low carrier-to-noise ratio (CNR) or at a high speed, increasing the sensitivity of global navigation satellite system (GNSS) receiver is a goal quite hard to achieve. A novel acquisition scheme assisted with micro-electro-mechanical-sensor (MEMS) inertial navigation system (INS) is presented to estimate the Doppler caused by user dynamics relative to each satellite ahead of time. Based on tightly coupled GNSS/INS estimation algorithm, MEMS INS Doppler error that can be achieved is first described. Then, by analyzing the mean acquisition time and signal detection probability, the MEMS INS-assisted acquisition capabilities in cold, warm and hot starts are quantitatively determined and compared with the standard GNSS acquisition capability. The simulations and comparisons have shown that: the acquisition time in cold start can be shortened by at least 23 s, the time in warm start can be shortened to 1 s and the acquisition capability is improved 95%, and the reacquisition time in hot start can be shortened by around 0.090 s and the capability can be enhanced 40%. The results demonstrate the validity of the novel method.

Note the highlighted.

The article talked about using an external source such as GPS to assist in reducing the alignment time and was between 'cold' and 'warm' start. Back in my F-111 days, we did not have such options. The INS was mechanical gyros based and while an INS cold start take-off was theoretical, the base must have bombs exploding all around in order for any aircrew to fly from an INS cold start.

An INS cold start is essentially you tell the INS to use its previous calculated position then constantly changing aircraft physical location while the INS tries to align itself. The position changes as detected by the gyros must be kept in memory while the INS computer try to compensate for the constant changes based upon that previous location, which may or may not be true. The lower the memory capacity, the greater the degradation of that update capability and most assuredly will not give the aircrew accurate INS data from simple A-to-B navigation to complex bombing runs.

There are plenty of band-aid fixes and patches to allow increased INS cold start accuracy, such as this mathematical mean...

On-the-move alignment for strap-down inertial navigation system - ResearchGate

ABSTRACT The initial alignment of the terrestrial vehicle borne strap-down inertial navigation system (SINS) is investigated. An on-the-move alignment algorithm using the information provided by an odometer, whose scale factor may have an unknown constant bias, is proposed. This algorithm is designed to take the place of the stationary-based fine alignment. The vehicle, during the fine alignment phase, is not necessarily to be kept in stationary state. It can leave for the destination after the stationary-based coarse alignment, and accomplishes fine alignment in the moving state. The alignment formulation of the new algorithm is derived. On the basis of the formulation, a Kalman filter is designed, which uses the difference of the SINS positioning result and the odometer dead reckoning result as the measurement. The results of a nonlinear Monte Carlo simulation show that this algorithm can accomplish initial alignment and odometer scale factor calibration jointly within 10 minutes.

An INS cold start, meaning on-the-move (OTM) alignment, can actually produce hardware failures, from the gyros themselves such as lockups, or voltage spikes that will cause internal failures of electronic components such as resistors or programmable logic controller modules. Backshops hate INS cold starts and good shops will be able to tell what happened.

 

[razgriz19]

True...But the old mechanical gyros based INS absolutely hated that method of start up.

Each INS system, old or modern, prefers to start up where it is allowed to locate its current position DESPITE memory of its previous location prior to shut down, and every system does have that memory. That does not mean the previous location is not used. It is used to provide a quick reference after the gyro completely spooled up to full rpm. But if the jet is moved, even from the front to most rear row on the flightline, the longer the physical distance, the longer it will take to recalculate or discover the (new) current position. Ring laser gyros do have this issue but the time difference is negligible while the old mechanical gyros may require up to an extra minute to align to the new location.

Here is an example...

Micro-electro-mechanical-sensor inertial navigation system-assisted global navigation satellite system receiver acquisition scheme and performance evaluation - Springer

Note the highlighted.

The article talked about using an external source such as GPS to assist in reducing the alignment time and was between 'cold' and 'warm' start. Back in my F-111 days, we did not have such options. The INS was mechanical gyros based and while an INS cold start take-off was theoretical, the base must have bombs exploding all around in order for any aircrew to fly from an INS cold start.

An INS cold start is essentially you tell the INS to use its previous calculated position then constantly changing aircraft physical location while the INS tries to align itself. The position changes as detected by the gyros must be kept in memory while the INS computer try to compensate for the constant changes based upon that previous location, which may or may not be true. The lower the memory capacity, the greater the degradation of that update capability and most assuredly will not give the aircrew accurate INS data from simple A-to-B navigation to complex bombing runs.

There are plenty of band-aid fixes and patches to allow increased INS cold start accuracy, such as this mathematical mean...

On-the-move alignment for strap-down inertial navigation system - ResearchGate

An INS cold start, meaning on-the-move (OTM) alignment, can actually produce hardware failures, from the gyros themselves such as lockups, or voltage spikes that will cause internal failures of electronic components such as resistors or programmable logic controller modules. Backshops hate INS cold starts and good shops will be able to tell what happened.

I'm not an expert on INS, but my prof (ex RCAF Aviantech) once mentioned this "time" problem is with the hornets as well. However he also mentioned that Mechanical gyros are not being used on newer platforms, everyone's moving to Laser or Solid state gyros.
If that is the case then why is Jf-17 is using mechanical gyros? is there an advantage of some sort?
As far as i know they're not cheap as well, $50K a pop.

 

[gambit]

I'm not an expert on INS, but my prof (ex RCAF Aviantech) once mentioned this "time" problem is with the hornets as well. However he also mentioned that Mechanical gyros are not being used on newer platforms, everyone's moving to Laser or Solid state gyros.
If that is the case then why is Jf-17 is using mechanical gyros? is there an advantage of some sort?
As far as i know they're not cheap as well, $50K a pop.

None worth...

I have been on both types and RLG is far superior. Nothing is perfect but for the precision, accuracy, and speed, they outweighs any weaknesses an RLG system has.

For a practical real world example...

When you shut down an INS, assuming a 'military grade' system, the latest known position is stored. When you start it up again, the gyros spools and as the system powers up to find the current position, the previous location is called -- as a reference. The closer, or smaller, the difference between the two values, the sooner the INS can start declare itself 'hot'.

Now...There is a switch position labeled 'STOR' and here is where the system deviate. Upon shut down, if you engage 'STOR', the latest known position is stored away as normal, but upon re-start, instead of the calculating the current position, the system recognized the 'STOR' switch position and immediately transfer that value as the current position. There is no verification like the normal process. If the aircraft is moved 100 meters away while the INS was sleeping, upon re-start, the system WILL NOT recognize that 100 meters difference because of the 'STOR' command. The need to use the 'STOR' option is when an aircraft is on alert duty, as in take-off ASAP when called. So when an alert jet is shut down with the 'STOR' option engaged, it should not be moved, but if it must, even from one hangar to the one next door, the entire INS system must be realigned again.

With an RLG, the need to use the 'STOR' option is dramatically reduced precisely because of how fast the system align and ready for work. An RLG system alignment will outrun engine start, whereas on a mechanical gyros based INS, you would be sitting in the cockpit with engines fully running while waiting for the INS to spool up and align itself -- up to 15 minutes.