Hendrik_2000
Lieutenant General
Now this is a kick a**! photo via LKJ86
J-10 Thread IV
- Thread starter Jeff Head
- Start date
Well, Eurojet *would* say that, wouldn't they
I get what they mean in theory, if you only move the divergent (=supersonic) section, there is no possibility of any disturbance from deflecting it propagating upstream to the engine turbomachinery: in supersonic flow, perturbations can propagate downstream only. It's certainly nice to eliminate any such risk from the outset, but I doubt the impact is in fact anywhere near as "big" as they claim.
For one, the LPT rotor throat is almost certainly choked with sonic flow, so any disturbance doesn't propagate very far into the engine at all. Also, *plenty* of (non-vectoring) engines have the nozzle axis tilted (typically downward) a couple of degrees from the engine centerline, among them the AL-31F. If the penalty was of a magnitude which could be remotely described as "big" I doubt these examples could afford to accept it *permanently* (rather than temporarily, when the nozzle is deflected only).
It is possible that they were considering a method of moving the whole nozzle other than the ball joint, one which changes the area of the subsonic section before the nozzle throat when deflected - that WOULD have a serious effect. In the context of Saturn's solution that is moot however, as the joint is spherical and has the same flow area no matter where the nozzle is pointing. OTOH, the ball joint means all nozzle cross sections from the LPT to the exit plane are perfectly circular, more so even than in the classical AVEN/PYBBN design in theory at least. The latter has a circular exit, but when deflected it's not perfectly perpendicular to the divergent section "boresight", so to the flow the actual cross section is very slightly elliptical.
Saturn's solution does, as I mentioned earlier, require a comparatively large number of actuators, as all functions (throat area, exit area, deflection) are performed by their own distinct set. The Eurojet TVN (split ring) gets away with 4 actuators for all 3 jobs, whereas AFAIK the AL-31FP/117S nozzle has 4 for deflection alone!
Everything is a compromise - personally, I'd tend to agree that the ball joint is too complex to be worthwhile, but it undeniably has its benefits.
When they say "current EJ200 nozzle", they mean the non-vectoring production design. Nozzles with independent A8/A9 actuation are actually pretty few and far in between so far, the only operational example I'm certain of is the RD-33, possibly also the AL-31F, NK-32 and F119. F100, F110, F404/414 and, by the looks of it, the F135 are all one-parameter nozzles (M53, WS-10 and M88 have ejectors, as discussed earlier).
Eurojet's split ring TVC design has independent A8/A9 actuation, though the lack of separate sync rings for both means the exit cross section is markedly non-circular in some positions. This is visible in the video I posted earlier (and called "ovalization" in the paper).
As the paper mentions, the split ring is the only one which they ever built and fitted to an actual engine. It improves thrust because it allows independent A9 control by tilting the ring halves against each other, making the divergent section petals pivot about the hinge with joins them to the convergent section.
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Well, Eurojet *would* say that, wouldn't they
To illustrate what I meant there, consider:
Funnily enough, no mention at all of the thrust penalty from this effect
I do like the Eurojet design for its elegance (and am an even bigger fan of the EJ200 engine in general), but you have to bear in mind that the authors of this paper aren't disinterested observers.
Well, Eurojet *would* say that, wouldn't they
I get what they mean in theory, if you only move the divergent (=supersonic) section, there is no possibility of any disturbance from deflecting it propagating upstream to the engine turbomachinery: in supersonic flow, perturbations can propagate downstream only. It's certainly nice to eliminate any such risk from the outset, but I doubt the impact is in fact anywhere near as "big" as they claim.
For one, the LPT rotor throat is almost certainly choked with sonic flow, so any disturbance doesn't propagate very far into the engine at all. Also, *plenty* of (non-vectoring) engines have the nozzle axis tilted (typically downward) a couple of degrees from the engine centerline, among them the AL-31F. If the penalty was of a magnitude which could be remotely described as "big" I doubt these examples could afford to accept it *permanently* (rather than temporarily, when the nozzle is deflected only).
It is possible that they were considering a method of moving the whole nozzle other than the ball joint, one which changes the area of the subsonic section before the nozzle throat when deflected - that WOULD have a serious effect. In the context of Saturn's solution that is moot however, as the joint is spherical and has the same flow area no matter where the nozzle is pointing. OTOH, the ball joint means all nozzle cross sections from the LPT to the exit plane are perfectly circular, more so even than in the classical AVEN/PYBBN design in theory at least. The latter has a circular exit, but when deflected it's not perfectly perpendicular to the divergent section "boresight", so to the flow the actual cross section is very slightly elliptical.
Saturn's solution does, as I mentioned earlier, require a comparatively large number of actuators, as all functions (throat area, exit area, deflection) are performed by their own distinct set. The Eurojet TVN (split ring) gets away with 4 actuators for all 3 jobs, whereas AFAIK the AL-31FP/117S nozzle has 4 for deflection alone!
Everything is a compromise - personally, I'd tend to agree that the ball joint is too complex to be worthwhile, but it undeniably has its benefits.
That applies not only to Eurojet, but also the latest Russian design, doesn't it? Otherwise how would you explain the Russian's choice for Su-50's TVC?
No, Eurojet meant TVN as well. See page 11-5 and 11-6 Baseline. I quote
The split ring is one variant based on the baseline design, but still one set of actuator only.
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To illustrate what I meant there, consider:
Funnily enough, no mention at all of the thrust penalty from this effect
Firstly, the base of your consideration may be wrong, see my other reply #2796.
Regarding thrust penalty from the split ring design. Eurojet did mention impact on thrust, not penalty but gain (over baseline) in certain condition, 7% increase, in page 11-7
There may be penalties in other condition, may be not, Eurojet did not say. But I must say you should not be easily skeptical about Eurojet's document as some sort of biased advertisement. Remember this is a internal research report, not a sales brochure.
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Sure - this caveat applies whenever a manufacturer is talking about their own product in comparison to a competitor's (whether that competitor is explicitly named or not). Saturn like to boast the weight penalty of their TVC nozzle is significantly less than 100kg per engine - a favourable value - but leave the reader to work out for himself that this is in relation to a baseline AL-31F nozzle that is already pretty complex and heavy to begin with.
As for the Su-57 & Izd.30, the jury is actually still out on what nozzle configuration it will ultimately use. The flight test engine as currently fitted to prototype #052 is has a Izd.117-like ball joint nozzle with independent exit area control and RCS reduction, NOT the AVEN/PYBBN-style Salyut design! I'm still hoping this will change for the production version, but the fact of the matter is that for all we know at the moment the ball joint might well be here to stay.
Yes, the 3 actuator TVN configuration is labeled as the "Baseline", bearing in mind however that the only TVC hardware Eurojet ever built was of the 4 actuator split-ring design with independent A9 control, "current nozzle" makes more sense if it refers to the production non-TVC nozzle. But that's arguing semantics.
Yup, that's the beauty of the split-ring layout: it gives you independent exit area control (albeit with a "squashed" exit cross section when contracted) with a single set of actuators.
That's a misquote of what I said though. The penalty of the split-ring design comes NOT from independent A8/A9 control (that's a *benefit*), but from "ovalization" (am I the only one who has to concentrate not to write "ovulation" there?!
).I.e. Eurojet's split-ring, 4 actuator configuration is better than the 3 actuator version (thanks to independent exit area control), but suffers a penalty compared to a AVEN/PYBBN-style nozzle with separate sync rings and actuator sets for throat and exit. This is due to the markedly non-circular exit cross section when the divergent section is contracted in the split-ring implementation.
As to whether the 4 actuator split-ring nozzle does in fact have independent A8/A9 control, I don't think there can be any mistake on this point:
The throat is closed/opened by all 4 actuators moving fore/aft in unison, exit area is (independently) closed/opened by symmetrical fore/aft movement of the top & bottom actuators only ("eyelid" movement by the split-ring). Pitch vectoring is performed by asymmetrical motion of the top & bottom actuators, yaw vectoring by asymmetrical motion of the left/right group.
I have absolutely no issues with what Eurojet *did* mention in that paper.
I just think they aren't 100% objective by *not* mentioning an effect (one which penalizes their own design) that is likely every bit as significant as one of the drawbacks in competing designs which they do flag prominently (calling it "big"). Better yet, I don't even necessarily fault them for the omission - it's a case of buyer beware, the intended audience should be competent enough.
Are you changing your statement?
Or simply forget what you said? To not to loose track of what we are arguing, I quote what you said in post #2792Now you are saying independent control, that can only be done by separate set of actuators.
In my reply I was telling you that A8/A9 is not independently actuated. Also the purple texts that you highlighted from the report says "It has four degrees of freedom (DOFs), namely Throat Area (A8), Exit Area (A9)..." That does not mean A8 and A9 are independently actuated, it merely means that both A8 and A9 are actuated. The sentence (I highlight in yellow), says "actuators are linked ONLY to the outer ring). What does ONLY mean to you?
Eurojet has always said that A8 and A9 has a predefined relationship but there is no place in the report saying that they are independently controlled. Show me otherwise.
Are you changing your statement?
Not at all. With hindsight, I am guilty of using "actuated" and "controlled" interchangeably, which apparently makes what I said prone to misunderstanding but I haven't moved the goal posts one bit. Allow me to explain:
That's the whole point of Eurojet's 4 actuator, split-ring configuration - it enables A8 and A9 to be controlled separately with a single set of actuators, subject to the compromise of "ovalization" in the divergent section.
Yeah, but if A8/A9 can be independently *controlled*, the net result (disregarding losses due to "ovalization" for the moment) is the same benefit, whether this is achieved by independent *actuation* (as in, two dedicated sets of actuators for each task) or not.
It absolutely does! If A9 cannot be *controlled* independently from A8 (which does NOT require it to be *actuated* by its own group of actuators!) it isn't a separate degree of freedom. That's why a (non-vectoring) nozzle with a fixed A8/A9 schedule is termed a "one-parameter nozzle".
No argument from me. Doesn't mean that, by cleverly driving the actuators individually or in conjunction, you can't change the exit/A9 separately from the throat/A8 though.
At the risk of sounding condescending, I don't think it makes sense to discuss this any further unless you can get your head around the paper's or my description of how the actuators interact to produce the various motions. We are drifting off-topic as it is.
Apart from A9 control listed as a degree of freedom in its own right, note the word "pure" in this sentence, for example:
