SundogJust a quick question, since I’ve only been following this program off and on. Has SAAB specified a rollout date, yet, for the actual E/F? Thanks.
SundogThe more compact boxy type fuselage puts more of the mass near the cg, so it reduces the required forces to change direction due to lower inertial forces and requires less damping, all of which helps agility. However, it also increases structural weight by putting more of the mass in one place. Aerodynamically, it minimizes surface area and thereby parasite drag. It also makes engine out control on a twin engine design much easier to deal with since the thrust lines are so close to the cg. However, the engines close together require more protection between them to prevent a fire or failure in one engine spreading to/damaging the other engine.
The spread out podded engine type of layout can have some benefits of how they help lift, in that the fuselage of this type may produce more lift than the boxy type. However, the podded engine design has much more surface area and therefore more parasite drag. Also, spreading the engines out increases rolling inertia so you need more control power in general. They do tend to allow better engine protection in the sense that if one engine is damaged it’s less likely to damage the other, but you will also have higher control forces (trim drag) in the engine out configuration due to the thrust line being further from the cg. This design can be more efficient structurally because the loads are more distributed across the span, so you get a slightly span loaded design.
SundogAre you guys trying to re-write history ?
The X-32 was a modern take on the Harrier ?If I recall, the Harrier can take off vertically, while the X-32 failed miserably, even over the pit, ie out of ground effect.
Don’t tell me what the X-32 would have been able to do and how well, as I’m sure a lot of developement troubles would have come up with it also. Don’t forget, the F-35, or X-35, was going to do all sorts of wonderful things also, and for a very low price. How did that work out ?
The X-32 was a much more compact and dense design and as such, had less growth capability. Its original design with a delta had to be modified to swept with a tail for a more horizontal attitude for carrier landings. And although Boeing assured everyone that its RCS and flying qualities would be unchanged, I don’t think anyone wanted the extra insecurity.
I also don’t think its RCS was in the same class as the F-35. That big opening at the front had to expose compressor blades and even if a screen were used as a shield ( so I’ve heard ), it would only work for a certain range of wavelengths.I suggest you guys re-read the IAPR article in issue #1, and I remember seeing a NOVA program on the JSF competition on TV. It may be available online.
Go back and read the original post, it proposed the question about how this would have worked out if it had just been the CTOL variant. I think most of the people here are familiar with how the actual program proceeded. Also, the X-32 is the ultimate derivative of the Harrier program as redesigned by McDonnell-Douglas and all of the experience they gained with AV-8B. You can see how that transformed into the Macair model 279 to the X-32.
Also, it’s a well known fact that Boeing was going to use a fan blocker at the from of the engine, the design of which is still classified. As such, the people who ran the program had every reason to believe it would meet the RCS requirements as they never brought up any misgivings about its RCS. Also, the fan blocker would only work for certain wavelengths in much the same sense that the F-35s inlets only work for certain wavelengths.
Now, comparing the Harrier to the X-32 is comparing Apples and Oranges. The Harrier was nowhere near as capable in the over all mission profile and it sure as hell wasn’t supersonic. Boeing knew their VTOL performance was going to be marginal at best and the reason they had to add horizontal tails, IIRC, was due to the bring brack weight of the Navy version increasing during the program.
SundogTurbine Aerostars, though one is a highly modified one off conversion.;)
SundogA few points. One, when aircraft are being developed many tails are tested on them. I’ve yet to see any evidence that the McD-Northrop design switched to the four tails for the production variant, it was just one of the many variations tested.
Two, the reason the X-32 went with the conventional tail instead of the Pelikan tail was due to the design team leader being conservative, since they knew what to expect from the four tailed design more so than the Pelikan tail design; I.e., it was less risky.
Three, the YF-23 had a butterfly tail, not a Pelikan tail. The production version also had the butterfly tail.
The difference between the butterfly tail and the Pelikan tail is the butterfly tail has the standard actuator at a pinion mounting into the side of the fuselage. Where as the Pelikan tail uses a trunion mount at the trailing edge portion of the fuselage where part of the control surface is also horizontal on the trailing edge behind the trunion mount. You can see this kind of mounting used on the F-35 and T-50 PAK-FA stabilators. It handles the loads better by distributing them more which should, theoretically, lead to a lower weight solution.
SundogIn regards to some of the statements posted above it should be noted that the “boxy” angled fuselage is actually a plus at high alpha, not a detriment. Also, with regard to the ventral fins, many are assuming they’ve been added for high alpha purposes, which may not and most likely isn’t the case. The canards could be used to stabilize the aircraft at high alpha, so I would be willing to bet the ventral fins are there to provide more stability at high speeds, especially given the small size of the vertical tails.
SundogIIRC the X-32 CTOL variant had a top speed quite a bit higher than the X-35 and was also more maneuverable. However, there was no way the X-32 was going to win the STOVL requirement unless the shaft driven lift fan failed massively.
That said, if there had been no STOVL requirement, I think the X-35 would have still looked very much as it does now, but the X-32 most likely would have been longer with the engine a little further back since it wouldn’t need to be so far forward for cg/lift nozzle reasons and the nose probably would have been a little longer as in some of the earlier design iterations for a better fineness ratio. In fact, it would have probably looked more like their (Boeings) F-24 design studies.
What impressed me most about the X-32 was its single piece composite wing design. But being as short and slab sided as it was I couldn’t help looking at it and thinking, “Saunders-Roe.”
SundogEven USAF dont replace their a/c every 20 years, better assume 30 year life.
It is unclear just how much ‘stealth’ skin cost to maintain,
but other than that, F-35 should be cheaper to operate than EF
The F-35 will cost somewhere between 1.5 to 1.7 times what it costs to operate the SuperHornet per flight hour. At least, that’s what the U.S. Navy was told with regard to the F-35C. Needless to say, they weren’t very happy about it.
SundogThis is pretty laughable. You simply don’t just “download” the blueprints of a modern 5th generation fighter off a server. At best they had access to some design discussion memo’s or emails. I doubt lockheed-martin would network anything sensitive in a position where it can be “hacked” through the internet.
You fail to understand I’m simply reporting actual news that was covered in Aviation Week. It was an extreme lack of network security on L-M’s part. There wasn’t anything laughable about it.
SundogIt’s one thing to “copy” some aspects related to shape which can be dirived from the photos available on the net… It’s an entirely different matter to copy the avionics, software, etc which would require deep penetration cyber attacks (or a good spy) and industrial capability to accomplish.
Considering China hacked Lockheed-Martins servers, looking for information on a still classified program, and downloaded everything on the F-22 and F-35 while they were at it, you’re not far off. Of course, we (The public) never found out if they got the information on the classified program they were trying to get the tech on.
SundogMore ADVENT info, including a more up to date cut away of what the integrated propulsion system may look like.
SundogI’m not really sure about this at all, other than i’ve read of a phenomena of ‘nose heaviness’ at supersonic flight.
Do you know the root to the phenomena ?
i would guess on a change in air flow myself inducing a pitch down moment, but why and how ?
In your experience, how much of an impact did it have on turn sub vs supersonic ?
Basically, at subsonic speeds, the center of pressure of a wing is 1/4 of the way back from the leading edge at the 1/4 chord line. However, at supersonic speeds it moves back to approximately 50% of the 1/4 chord line.
Now, the tail of the airplane is what keeps the moment generated by the wing, wrt to the center of mass, in balance. If the aircraft is naturally stable, the center of mass is usually in front of the center of lift, the nose of the plane being “forward.” So the center of lift is back from the center of mass and this generates a nose down moment which is compensated for by the tail pushing down to keep the nose up. However, as the airplane becomes supersonic and the center of lift moves back from the center of mass the moment becomes larger. Therefore the tail has to be designed to create even more power to keep the nose up. That is assuming the controls and control surfaces are designed for supersonic flight. Early WW2 planes were designed before they understood this phenomena and the tails were generally too small to pull the nose up and the tail design wasn’t really any good for control at supersonic speeds, due to how the shock waves effect the pressure distribution. Generally the elevators were ineffective, so the only way to recover was to throttle back and hope prop drag would slow you down before anything broke/came off or you hit the ground.
Having said that, you also have to take into account instability and control configured vehicles. I specifically add the latter, because there were early fighters that were intentionally designed to be unstable for good turning performance, but that also made them a pain to fly straight and level for any length of time. Also, those aircraft didn’t have near the instability margins modern CCV aircraft have because it still had to be controlled by the pilot and not a computer. Some of those early aircraft were the Hawker Hurricane and the F4D Skyray. I think some WWI aircraft were as well. Of course, the P-51 and the F-4 could be unstable under certain heavy fuel loads, but that was done at the behest of range, not to enhance maneuverability.
Anyway, with an unstable aircraft, the center of lift is ahead of the center of mass. This allows the tail to provide lift at subsonic speeds, which means the wing can also be smaller, to an extent. However, at supersonic speeds, when the aerodynamic center moves aft, at least in the case of the F-16, it becomes naturally stable at supersonic speeds and the nose now gets a nose down moment, but nowhere as near as much for the stable designs. I should also point out, that with regard to tail volume (The tail area x the distance of it’s center of pressure to the center of mass), usually the greatest factor in it’s sizing is in being able to rotate the nose up under full load at take off. That’s another area where TV can come in handy, because you don’t need to make the tail too large. Which saves weight, but I doubt it saves as much as what the weight of the TV adds.
With regard to the Typhoon and the Rafale, i don’t know if they remain unstable, even at supersonic speed or if they become stable, but it shouldn’t be too hard to figure out based on the info I’ve provided here. If you need to figure out the approx location of the center of mass, just draw the tail scrape angle between the main gear and the tail, draw a line perpendicular to it from the main gear and rotate it two or three degrees forward and that will get you in the ball park.
Sundogthe Naval YF-23 proposal also had fixed canards
You’re incorrect, the Northrop NATF has all moving canards as can be seen by the fixed stubs in the drawing you reference. Not to mention, the detailed drawings clearly show the actuators for them in the internal views.
SundogI have a subscription and received two volumes of the four and never received another. Haven’t seen anything of vol 27, much less vol 28.
SundogFirst a few quick corrections to some mis-conceptions here.
Myth 1) Stealth makes designers pay an aerodynamic penalty compared to standard aircraft. This is patently false. In fact, both Northrop and Lockheed pointed out that their ATF’s were much more aerodynamically clean than previous aircraft and had better aerodynamics than other aircraft of the period. People tend to confuse the penalty the F-117 paid aerodynamically with it’s faceted approach and apply it to all stealth aircraft.
Myth 2) Because of internal weapons carriage, aircraft pay a wave drag penalty. This would only be true if aircraft designers didn’t know what the hell they are doing. As long as you follow the basic fundamentals of aircraft design and try to optimize to match for a Sears_Haack body of revolution, and watch your fineness ratio, wave drag will not be any higher than a conventional design in the same weight class. Now, you do have more internal volume and more wetted area, but that’s also with a full weapons load. Put the same load on a conventional design and you also run into increased surface area, much greater interference drag, and possible problems with seeker head life due to exposure to the elements.
– It should also be pointed out that one of the main factors in giving the ATF engines their thrust levels was their increased mass flow when compared to previous engines, especially with regard to dry thrust.
– As for cost, stealth does add cost, but much more of the cost is in the systems themselves, which have to have stealthy modes of operation, etc, as opposed to the “mechanical” stealth built into the design. Mechanically, where they seem to pay the biggest price mechanically is in terms of maintaining their surfaces. In fact, that’s one of the biggest gripes with the F-35; it’s higher operational costs as a result of stealth maintenance.
– England demonstrated their ability to build a stealth aircraft with their Replica design study. However, “stealth” has been something designers have looked for since World War I, when they tried to use the transparent covering back then to “hide” the aircraft in the sky.
– With regard to Horten and the B-2, it’s mostly non-sense, as the Northrop flying Wings of the 40’s actually flew a number of times, and although they weren’t designed to absorb RADAR energy the way the Horten design was, in flight testing they learned the wing itself was difficult to detect.
– Also, you’ll find serious stealth development in the U.S. goes to the late 40’s early 50’s, especially if you look at the development of UAV’s/unmanned vehicles and recon vehicles back then.
– Having said that, it really does just come down to money. If a country has enough money to spend developing these systems, they’ll develop the technology. It really becomes a cost vs capability mentality. In terms of aircraft that weren’t designed for stealth from the ground up, BAe claims the stealthiest is the F/A-18E/F. The Eurofighter and Rafale did have some stealth technology applied to them, especially from the front aspect, to reduce their signatures. In fact, IIRC, that was why the Eurofighter went from the original rectilinear inlet design to the slightly curved variation on the production model.
– It should also be noted, that in terms of capability, the U.K. was looking at buying a squadron or two of F-22’s, even while buying the Typhoon, but they realized they simply couldn’t afford them.
– Also, although internal carriage leads to a larger aircraft, the larger it is the less of a penalty it pays for internal carriage. Large aircraft, also, have been shown to have more advantages than smaller aircraft over their lifetimes, as they tend to have more volume for upgrading/ adding capability, when compared with smaller designs.
– In terms of the ATF (F-22 & F-23) you have to consider their size is also a fall out of the supercruise requirements. IIRC, you ideally don’t want a fuel weight fraction less than .25. It’s in Picarillo’s book on ATF development, but I’m not sure that was the exact number. But that also was a major design driver for the ATF.
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