Amiga500Reaaaaally? You’ll have to talk me through that one.
Leaving aside the rest as blind protection of pilots.
Attitude comes from gyroscopes, which are internal only.
Thrust, well, the FADEC does use various parameters to determine what its fuel rate should be – however the primary readings are all internal to the engine. Your not going to get icing within your compressor for instance. Its also pretty hard to hide your turbine temperature/core massflow rate relationship [from your fuel mix being lean/rich/right].
The FADEC should be cross-comparing to the aircraft-level readings, and should note the anomaly, but core fadec function will come from the local engine sensors, not aircraft. In summary, the FADEC should have a pretty good (if not quite exact) idea of the level of thrust it is producing.
If pilots are taught to rely on a pitot tube for primary flight, then the training is awful. The concept should not be about going from your complex systems to simple ones until you find what works – it should be the reverse – go from the most basic and foolproof (art. horz and thrust) back up until you find your inconsistency. Right enough, I wouldn’t be surprised if that is something so obvious the authorities have forgotten it in arrogance about the redundancies in CS-25/FAR-25.
Amiga500Agreed. I don’t know much about that particular accident, but I do know that keeping “the damn thing” straight and level can be quite difficult given enough turbulence, for instance.
As opposed to keeping it at 20-30 degrees AoA?
If they aren’t sure of keeping their stall margin due to altitude – then the solution is simple – put the nose down and accept the loss in altitude. Its a long way down from 35,000 ft.
Amiga500The authorities seem unclear as to what the circumstances were but you seem to be very sure.
Oh, no. They know. They definitely know.
But due to “politics” they cannot come out and say it.
Ignoring a stall warning for a full minute?
Catch yourselves on. The pilots screwed up – big time.
Altitude is an inferred reading and airspeed is an inferred reading – both susceptible to external effects on the aircraft.
Aircraft pitch and throttle/thrust are not. It is not unreasonable to expect people whose core damn job is knowing how to fly an aircraft to know that.
Amiga500Nobody can really criticise the crew for their actions, purely because nobody else was there, you weren’t in the flightdeck so how can you pass judgement on what it was really like?
I don’t give a damn about rubbish like “what it was like”.
Here are a bunch of people, paid obscene amounts of money – yet they cannot perform even the most basic of functions – namely keeping the damn even approximately thing straight and level.
People are making loads of excuses for them – incompetence would be a better way of looking at it.
Its like the driver of a car forgetting to turn the steering wheel to go around a corner. Ridiculous.
Maybe I am being unfair – maybe it is unfair to expect well paid long haul commercial pilots to have even the most basic understanding of what is a primary reading, what is an inferred reading, what is cause and what is effect.
The litany of excuses surrounding the whole episode is pathetic.
Amiga500And this is lower drag?
Yip.
Also, if that’s really the better solution it begs the question of why they didn’t they just go with that solution. It’s not like they couldn’t have found that modeling an F-22 airframe?
Indeed. Unless of course they aren’t aiming for an air superiority fighter…. 😉
We can probably assume they optimized the positions which the vortices are shed.
Reasonable. But the vortex strength and diameter does depend on aircraft and ambient conditions. Which makes it hard to have a ‘one-size-fits-all’ design.
Pardon my physics, but isn’t the direction your TVC is pointed towards a big contribution to your velocity vector?
No.
If the TVC is inducing a moment around the aircraft’s centre of gravity, it will turn around that centre of gravity.
If the engines are producing thrust in a vector ‘through’ the aircraft’s centre of gravity, then it will allow the wings to change the velocity vector..
Amiga500…So what’s today’s.
A cambered upper surface. With a possible vortex sheet running along it – note – this is different from the vortices from LERXs.
And what would the second set of LERXes do then?
Depends how close they are – very close and they will combine, not so close and they may mutually destroy each other, further away and they will act rather independently. Its still a high drag way of making lift though.
Your using thrust to push your nose in a direction, so not only would your nose turn in that direction, it will go forward in that direction? Anyways, it’s not like the aerofoils aren’t being used either.
Velocity vector =/= AoA.
Tailplane/TVC points your nose (AoA).
Lift from wings changes your velocity vector.
Amiga500Well, your point is that there will be flow separation from the J-20’s body at high alphas due to its shaping…but wouldn’t the vortice generated by the canards and the two pairs of lerxes prevent that?
Only over the two intakes, and not over the central fuselage.
A LERX is also a very high energy way of inducing lift. Basically, it is yesterdays technology.
The direction of your thrust is being changed whether you’re using aerofoils or TVC though. Bleed will happen regardless of which method you use.
If your using thrust to push your nose around, you are not using thrust to push forward.
The direction you are pointing does not equal the direction you are travelling.
Amiga500Ridic.
I was wrong…. its even more impressive!
It was supposedly 600 miles at Mach 2.6.
A flight of Foxhounds did a speed run into Sakhalin in 1983 just after the KAL007 shoot-down incident.
Yefim Gordon’s “Mig-25 Foxbat Mig-31 Foxhound – Russia’s Defensive Front Line” book states the MiG-31 has a range, with 4 R-33 at Mach 2.35 of 869 miles. That may include drop tanks.
The intercept range, which I assume includes the same missile load but at max attainable speed, drops to 447 miles.
Amiga500I just had a thought, wouldn’t the addition of TVC help compensate for maneuverability at lower speed envelopes?
Pointability.
I wouldn’t necessarily call it helping maneuverability as it takes away thrust from pushing you forward – so your energy bleed rate will increase.
Amiga500Amiga strikes me as ignoring body lift as a contributor to maneuverability. If you disregard body lift, the F-22 has a wing loading comparable to that of a bomber. The same applies to the J-20; if you include the body lift on the J-20 the aircraft only has about a 7% inferiority compared to the F-22 in wing area for size.
Which is of course why I have been at such pains to repeatedly point out the lift generation mechanisms over the body are very different….
Amiga500Well I was more thinking along the lines that we cannot know how the individual features of the aircraft can interact together to affect its performance as a whole.
Producing a quantitative analysis on here is not possible. Theoretical qualitative is possible.
Amiga500What’s the record on delta canards with high finnesse ratio? Also double lerxes and canards?
Record meaning?
Smallest ever?
Mass is also dependent on materials and empty space.
There is no empty space on a modern fighter.
Seeing the DMU of any modern fighter is a bit humbling in terms of the lengths gone to to get things packaged.
The F-22 is way heavier than it’s dimensions would indicate in part because of ram. A lighter ram/material/internal structure/bigger air tunnels could all affect mass.
Will affect mass.
There’s also the possibility that it looks more volumous than it is.
Always a possibility. I consider it unlikely.
Is the fuselage really longer relative to the wingspan? Or does it simply look longer due to wing positioning?
I’ve seen people try to give the j-20 the f-22’s planform, wings forward canards back, and it didn’t look that long anymore.
Proportionally yes. Compare the length:width ratio. We don’t need an absolute figure for length or width to do that.
It would be beyond cool and educational if we could stick a model of the J-20 in a simulator with different estimated parameters.
Wouldn’t matter a damn if the geometry wasn’t accurate.
Give me a CAD model, and I’ll give you CFD results.
Amiga500The same professionals that said it would take China well beyond 2020 to field its first stealth fighter?
Who, the military? Or some Lockheed marketing “guru”?
Or, did that come from engineers?
Unless you have some knowledge and information about this aircraft beyond what we know then extrapolating a role from eyeballing the physics while most people can still not agree on its length seems a little strange no?
Not really.
Quite often, design tools are used to find relative improvements rather than give absolute numbers. No different here.
We don’t need the length to 4 decimal places if the wingspan is proportionally smaller, and the 1/4 chord sweep of the wing proportionally greater than the potential contemporaries.
Amiga500More importantly how would an F-22 or an F-15 compare in terns of fuel fraction with a mig-31 when outfitted for an intercept mission.
Very poorly.
Hence why the MiG-31 is the no #1 interceptor in the world.
There has been an instance reported of MiG-31s travelling over 600 miles at Mach 2.35.
That is what big fuel fractions do for ya!
Contingent on volume of course. Just because it’s longer doesn’t necessarily mean its more volumic.
It looks to have a big enough frontal cross section. Certainly bigger than PAK-FA in cross-sectional area.
I meant in the sense of how they each achieve their manueverability. It sounds like the J-20 primarily generates body lift for level flight and relies on canards and lerxes for high alphas
No, not level flight, but the flow over the J-20 fuselage/body is much more likely to detach much earlier than over the F-22/PAK-FA at medium to high AoA.
The J-20 looks like it is designed for high speed maneuvers, whereas the F-22 and PAK-FA are designed more for medium speed maneuvers.
Which again, would be reflective of the J-20 being aimed at high speed interceptor/interdictor.
while the F-22 uses its body for lift at high alphas (as well?). To my knowledge you can’t extrapolate comparative performances from that though.
The forebody of the F-22, and the intake sides also generate vortices at very high alphas.
Same as the PAK-FA.
But their lifting bodies are designed for a different maneuvering envelope c.f. the J-20.
Amiga5001. Interceptor/Interdictor.
It’ll not be dedicated to one of those two – it wouldn’t make sense to do that. It should be capable of both. A nice extra would be “conformal” fuel tanks within the weapons bays for an interceptor load-out, which could be removed for an interdiction mission. More like an internal FAST pack I guess.
2. Finnesse.
Finnesse ratio will normally result in some loss of maneuverability – a smaller wingspan coupled with a longer – i.e. heavier fuselage. Something has to give.
3. Measurements.
While we have very little in the way of solid absolute measurements, we have relative measurements and proportions. The fuselage is long relative to the wingspan, and the fuselage internal volume looks large relative to the wingspan.
4. Accuracy
If this actually mattered, you’d be damn sure I wouldn’t be proceeding without solid numbers to start with. But it doesn’t, so I will. 😉
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