Operational Performace Comparison: Viper, Beagle, and Stubby

The F-35 compared with other modern jets.
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gta4

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Unread post14 Sep 2019, 19:50

One of my friends is majored in aerodynamics and they have been doing CFD analysis on T-50/F-22 for ages, with lots of 3D reconstruction and finite element computation.

Conclusion?

F-22's features:
1. lower wing sweep
2. bigger (exposed wing aera)/(reference wing area) ratio
3. bigger wing tip twist

These features give it an edge in lift curve slope and Lift/Drag ratio at subsonic. The seemingly bigger LEX of Su-57 does not out weight these features. F-22's LEX and vortex are already very strong.

PKA-FA's features:
1. Movable upper air intake
2. Nozzle deflection along a V-shape

The first one gives it extra pitch moment, but offers little impacts on Lift/Drag. The second one gives it less pitching moment (15 deg vs 20 deg deflection, and part of the 15 deg is unusable due to its inclination) but some yaw control authority, if one nozzle pitches upward and the other pitches downward.
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sprstdlyscottsmn

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Unread post15 Sep 2019, 03:47

gta4 wrote:One of my friends is majored in aerodynamics and they have been doing CFD analysis on T-50/F-22 for ages, with lots of 3D reconstruction and finite element computation.

I would be very interested in using your friends analysis results as an input to my own analysis, if they were willing to share. I would happily cite them for all data obtained.
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southerncross

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Unread post15 Sep 2019, 12:09

gta4 wrote:According to Russian Bureau of Intellectual Properties, the thrust vectoring of Su-57 is still 2D (moving along a V trail) instead of 3D.

Yes, a far as I know this is the case. Also izd. 30 and even possible future developments still seem to consider this configuration. There was another possible design by Salut which apparently was 3D but I doubt it gathered enough attention. Current model is light with little thrust losses and has pitch, roll and yaw authority, even when not in an independent way.
6DA3Aiy.jpg
Alternative 3D nozzle

qEjfBcu.png
Izd. 30 seems to have the same joint type of 1st stage engine

Nozzle.png
Study of biomimetic construction by Sukhoi

One of my friends is majored in aerodynamics and they have been doing CFD analysis on T-50/F-22 for ages, with lots of 3D reconstruction and finite element computation.

Great, are they willing to share their work?
These features give it an edge in lift curve slope and Lift/Drag ratio at subsonic.

What is the advantage then? Design later, with a proven reference to do it worse looks a bit silly. Advantages in supersonic regime, fuel capacity?
The seemingly bigger LEX of Su-57 does not out weight these features.

You are referring the lifting body sections affected by the LEVCONs? Only to make sure we are in the same page, this would be body not LEX to my understanding, maybe you mean otherwise?
The first one gives it extra pitch moment, but offers little impacts on Lift/Drag.

I have never seen the LEVCONS deflect like canards for increased pitch authority (for instance deflect upwards to pitch up the nose) but rather deflect downwards in such situation, just like LE flaps. It is very difficult that they don't increase lift at high AoA since they will almost inevitably delay stall, maybe you were meaning no L/D improvement at low AoA?
The second one gives it less pitching moment (15 deg vs 20 deg deflection, and part of the 15 deg is unusable due to its inclination)

True, yet the deflected 2D nozzle of the F-22 will sensibly reduce the nozzle section and due to fuselage layout and engine positioning, the torque arm is notably shorter, plus the losses of the flat nozzle are bigger in general. It is a different compromise.

BTW, out of curiosity: how do people doing these comparative CFD studies manage to figure out things like the airfoil profiles? I guess that must be very difficult to ascertain from pictures but maybe there is some smart way of knowing...
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Unread post15 Sep 2019, 12:41

sprstdlyscottsmn wrote:
gta4 wrote:One of my friends is majored in aerodynamics and they have been doing CFD analysis on T-50/F-22 for ages, with lots of 3D reconstruction and finite element computation.

I would be very interested in using your friends analysis results as an input to my own analysis, if they were willing to share. I would happily cite them for all data obtained.


It is in a different language.

There is one thing I remember: At 45 deg AOA the normal force factor of F-22 is nearly 2.8-2.9
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Unread post15 Sep 2019, 14:52

There was mention of the LEVCONS and their purpose. I wanted to post these still shots from 2019MAKS video uploaded to YouTube by airguardian. I believe they act like a wing slats for body lift.
65F5502C-4A31-49C9-96D1-6B5CCA2D52FD.jpeg
4D5045D3-D202-43CC-8FC0-C5EE02113226.jpeg


When the 57 is pulling high G they seem to drop down
E317FAF7-D08C-42E8-9E11-04C2E2D017D9.jpeg


I also wonder if that’s why they were able to get away with the shorter vertical stabilizers? I would think the LEVCONS make the vertical stabilizers more effective, by smoothing out airflow over the body portion of the Su-57 during high AoA. A
08006ACC-5664-47A7-B673-C48D593EFA2A.jpeg
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gta4

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Unread post15 Sep 2019, 15:51

I have never seen the LEVCONS deflect like canards for increased pitch authority (for instance deflect upwards to pitch up the nose) but rather deflect downwards in such situation, just like LE flaps.


I believe you misunderstood how canards work. Canards also deflects to the reverse direction of pitching. It is required by trim to balance the inherit up-pitching moment created by the unstable airframe.
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Unread post15 Sep 2019, 15:55

plus the losses of the flat nozzle are bigger in general


Wrong. The thrust rating of F119 is measured with nozzle, so no need to multiply by a factor one more time.

And, flat nozzle does not have significant thrust difference compared to cylinder nozzle.
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Unread post15 Sep 2019, 16:03

gta4 wrote:
It is in a different language.

There is one thing I remember: At 45 deg AOA the normal force factor of F-22 is nearly 2.8-2.9

That didn't stop me from getting information off an old photocopied MiG-25 manual
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southerncross

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Unread post15 Sep 2019, 19:21

n3sk wrote:I also wonder if that’s why they were able to get away with the shorter vertical stabilizers? I would think the LEVCONS make the vertical stabilizers more effective, by smoothing out airflow over the body portion of the Su-57 during high AoA.

I concur here and think this is in fact a very relevant design feature :thumb:
gta4 wrote:I believe you misunderstood how canards work. Canards also deflects to the reverse direction of pitching. It is required by trim to balance the inherit up-pitching moment created by the unstable airframe.

I think I am roughly aware of how they work, even when this changes depending on the airframe and situation, canards on stable planes behaving differently than newer, unstable fighters. They would normally deflect upwards to pitch up the nose and then depending on the reaction of the plane, go back to neutral position (aligned with the wing), much like the tail of a F-16 would do, once the nose is up, since the plane has no tendency to lower the nose by itself. The deflection to counter pitch-up moment does not need to last more than some instants. At high AoA sometimes they are permanently deflected downwards in relation with the wings, but normally they don't go negative, this has IMHO more to do with smoothing the air over the body and wings than with countering pitch, at least from what I have seen. A good sequence to see them in action below, notice how the angle of the canard changes after the nose pitch-up movement but is never negative to the airflow or just really slightly:



This is not exactly what I see with the Su-57's LEVCONS nevertheless:
- They don't deflect upwards even during rotation phase, so cannot create a moment to pitch up the nose. Feel free to correct me if you have evidence in contrary but I have never seen the Su-57 pitching up the LEVCONS and I have to doubt they are even mechanically designed to do so.
- It would be simply absurd that the Su-57 tries to keep a high angle of attack (i.e. while turning) while keeping the LEVCONS constantly down as we see them doing, if they where a control surface as you say. They would just create drag and oppose the intended maneuver. On the contrary, what we see is that they are deployed together with the wing's LE flaps and almost always in the same angles. Their mission must be ensuring the airflow stays attached to the body and changing camber, thus creating lift.
Wrong. The thrust rating of F119 is measured with nozzle, so no need to multiply by a factor one more time.

I was not implying there was an additional reduction factor to apply, but that a flat 2D TVC nozzle like that on the F-22 has its intrinsic downsides and that they most probably played a role in the decision to use the current round ones.
And, flat nozzle does not have significant thrust difference compared to cylinder nozzle.

IIRC the thrust loss was in the order of 3-4% (600 kgf for a 15 tf engine), I could try to find the source if you are interested.
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Unread post16 Sep 2019, 03:52

southerncross wrote:If you notice, those high speed systems you refer are ABMs, it does not seem that the ones meant against planes do have that performance. One could argue that aircraft could carry even bigger AAMs if that was interesting, the same they carry big AGM/ASMs

I know they are ABM, my point is if missions require high speed, it is very easy to design SAM with long range and high speed. To the point that SR-71, XB-70 were abandon in favor of stealth and low altitude aircraft.

southerncross wrote:True, and as we just see the engagement zone of the missile vs, a high-flying, fast target also shrinks notably. I don't dispute that you have a point, I just don't know what of the two competing factors weights more and in general I take for granted that it will depend on the concrete case as we are seeing in the thread

According to Spurt simulation, the engagement zone is larger when target is high and fast.
Shooter and target flying at 36,000ft at 1.2M:
1.PNG

Target at 75,000 ft at 2.5 M and shooter at 1.2M and a range of altitude from 30,000-50,000ft in 5,000ft increments
2.PNG

TBH, I still want to see what the result will be when the seeker FoV of Meteor and AIM-120 is 120° but they are detected at 30 km.



southerncross wrote:Those of Container type are said to be reasonably precise (they use only one reflection on the ionosphere) and capable of detecting the launching of those CMs 3000 km away. So they can put the whole AD to intercept them straight away.

AFAIK, all OTH-B use one reflection in the ionosphere, the accuracy is still low because it operates in HF
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Unread post16 Sep 2019, 04:02

sprstdlyscottsmn wrote: would be very interested in using your friends analysis results as an input to my own analysis, if they were willing to share. I would happily cite them for all data obtained.

I also have something I want to share, I don't know whether they are accurate or not. CLmax for both model sound too low, at least compare to F-16 and Su-27:
t-50.PNG
F-22.PNG
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Unread post16 Sep 2019, 04:42

Garrya,

Careful about what you are saying. Maximum flight range of a missile improves when the target is at high altitude. Maximum engagement range also improves when the target is at high altitude. What does not improve is the missiles ability to turn. A missile will effectively never have a tighter turn radius than an aircraft. That would require it to have a stall speed lower than the aircraft. Stall speed and turn radius are tightly linked. Remember that a min radius turn occurs when an aero vehicle is at max CL. Max rate turn occurs only when Max CL and Max G meet.

Also, I think I failed to communicate something effectively (as engineers do). When I stated that in my missile sim the FoV was 60, I mean +-60, 60 from bore, or 120 total.

Also, thank you. Thank you thank you thank you. I set the conditions for a MiG-31 evading immediately at 30km from the missile (I still think the missile RCS is beneath the clutter floor, but that is another topic for which I am not a subject matter expert). I realized the exact same thing was happening. So I looked into my aimpoint calculator. The aimpoint was only ever 0.1s ahead of the target, meaning it was effectively always in Pure Pursuit! I fixed it to be based on current flight time and now the MiG-31 gets hit regardless because the missile is aiming appropriately far enough ahead of the MiG.

I am so glad when people challenge my assertions and make me second guess and re-validate my formulas.
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Unread post16 Sep 2019, 04:46

garrya wrote:I also have something I want to share, I don't know whether they are accurate or not. CLmax for both model sound too low, at least compare to F-16 and Su-27:
t-50.PNG
F-22.PNG

Thank you for sharing that as well! I agree the values are too low, but that is because with both of these aircraft every single surface is moving to make sure everything is optimally balanced. These are relatively fixed models. It does give a neat visualization.
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Unread post16 Sep 2019, 16:48

sprstdlyscottsmn wrote:Garrya,
Also, thank you. Thank you thank you thank you. I set the conditions for a MiG-31 evading immediately at 30km from the missile (I still think the missile RCS is beneath the clutter floor, but that is another topic for which I am not a subject matter expert). I realized the exact same thing was happening. So I looked into my aimpoint calculator. The aimpoint was only ever 0.1s ahead of the target, meaning it was effectively always in Pure Pursuit! I fixed it to be based on current flight time and now the MiG-31 gets hit regardless because the missile is aiming appropriately far enough ahead of the MiG.

I am so glad when people challenge my assertions and make me second guess and re-validate my formulas.

Thank you Spurt, can you please explain what do you mean with "base on current fly time"?. When you said with lead guidance logic, all AMRAAM hit Mig-31 regardless, does that also include AIM-120D launched at maximum range from a plane traveling at 1.0M at 36,000ft?
Do you think F-15 or F-16 block 60 fighting Mig-31 from BVR will end in mutual kill?, let say we ignore jamming. I wonder how much earlier R-37 from Mig-31 can reach target before it get hit in the face with AMRAAM
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Unread post16 Sep 2019, 17:23

garrya wrote:Thank you Spurt, can you please explain what do you mean with "base on current fly time"?.

Sorry. Again with the not being very clear. My original Lead Pursuit computation was incorrectly set up to only compute the position of the target aircraft one time instance (initially 1 sec, currently 0.1 sec) in the future. Now it calculates the position of the target aircraft based on estimated time to collision based on current closure rates. This is a more accurate Lead Pursuit as my previous iteration was still effectively Pure Pursuit. I still have a bit of a histeresis wobble from it not properly taking into account the missiles rotation in the apparent change of target position off the missiles nose. That seemed easy in theory but implementing it has been a pain.

garrya wrote:When you said with lead guidance logic, all AMRAAM hit Mig-31 regardless, does that also include AIM-120D launched at maximum range from a plane traveling at 1.0M at 36,000ft?


Sorry, I was looking at when the MiG began evading a missile launched from 1.4M at 49,000ft only when I said that. That said, checking a 30km detection of the AIM-120 launched from 36,000ft and 1.0M from a range of 145nm and having zero delay in MiG reaction time shows that the MiG would still be hit. It's close though.

About mutual kill, the R-37 fired against the "low and slow" AMRAAM shooter will definitely reach it's target before the AMRAAM reaches. If I assume the AMRAAM shooter is unaware until ~5-6nm when the RWR goes off the lower altitude allows for the plane to make faster heading changes meaning it can make a 90 degree turn in ~9 seconds and then make a gentle sustained turn back into the missile and the R-37 will not be able to track, having lost too much speed and thus turn rate.
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