From: skunk-works-digest-owner@mail.orst.edu To: skunk-works-digest@mail.orst.edu Subject: Skunk Works Digest V5 #192 Reply-To: skunk-works-digest@mail.orst.edu Errors-To: skunk-works-digest-owner@mail.orst.edu Precedence: bulk Skunk Works Digest Monday, 30 January 1995 Volume 05 : Number 192 In this issue: Tooling, Fixtures, and Jigs Re: Turing Clarification? Re: TR-3A Inlet Stuff Re: Tooling, Fixtures, and Jigs Re: SR71 spike the (cancelled) "Q" spy plane sr-71 follow on Aurora..In Thrust We Trust..? Re: Aurora..In Thrust We Trust..? video of the day Re: SR unstarts See the end of the digest for information on subscribing to the skunk-works or skunk-works-digest mailing lists and on how to retrieve back issues. ---------------------------------------------------------------------- From: murr rhame Date: Sat, 28 Jan 1995 03:39:11 -0500 (EST) Subject: Tooling, Fixtures, and Jigs On Mon, 23 Jan 1995 steveje@videocrash.tv.tek.com wrote: > Mary wrote: >>Just a titch of information--we no longer refer to the tooling as jigs. >>I don't know why this piece of jargon fell out of use, but it has. >>(I've heard a couple of hypotheses, but they sound totally improbable.) >> > > From the time I was quite young, my Dad (he worked aerospace, Army Air >Corp and Air Force) -always- correct me when ever I inadvertanly used the >term "jig" ..... He said it was a quite racist term. The terms to use were >"fixture" or "tooling". I still hear the "jig" on T.V., etc. from time to >time. I'm a machinist. Fixture is the most common term for a device that holds a workpiece for machining. Distinguished from a simple clamp or vice, a fixture is usually custom built to hold a specific part often at GREAT expense. Tooling generally refers to the actual cutting tools, for example drill bits and taps. The term tooling is sometimes used in a broader sense to include the machine tools, fixtures, cutting tools and related equipment. The term Jig is not common use in machining with two exceptions. There are precision machines called Jig Boring Machines. There is a special cutting tool know as a Jig Bore Reamer. Jig Bore Reamers are used for precision positioning of holes. Devices that hold parts in place for assembly are sometimes referred to as Jigs. As far as I know the word Jig has not been politically corrected out of the industrial world. It's hard to insult an inanimate object. Jigs are still used for fishing and some people still dance a little Jig now and then as well. In my humble opinion, Jig is a legitimate word despite the fact that some have used it as a racial slur. murr@vnet.net /\/\ |_| |~ |~ Charlotte, NC ------------------------------ From: dadams@netcom.com (Dean Adams) Date: Sat, 28 Jan 1995 03:20:45 -0800 Subject: Re: Turing Clarification? >>That to me sounds like someone seeing an aircraft TURING, which would >>both explain it seeming to "pause" briefly from certain viewing angles... >Pardon my ignorance, but what is "Turing"? The only Turing I know developed a >test for determining intelligence.... ;-) Or artifical intelligence... in this case I could probably have used a more intelligent keyboard (or something)... :), since of course what I really meant to say was _TURNING_. ------------------------------ From: dadams@netcom.com (Dean Adams) Date: Sat, 28 Jan 1995 06:23:05 -0800 Subject: Re: TR-3A >>BTW, speaking of the TR-3A, am I the only one wondering if >>"Air International", et al have borrowed some writers from the >>Enquirer or something? :) To be speaking so matter-of-factly, >>about something we have yet to get *any* hard facts yet seems\ >>a little strange to me. > >I AGREE!! >I have mentioned my curiosity over this Dr. Baker guy myself! >Since Rene Francillon is the U.S. Editor for Air International, when >I talked to Rene I figured he might know something about this guy. >So I asked him. Rene didn't know ANYTHING about him at all! I asked >about Dr. Baker's background - Rene knew nothing. I asked if the >name 'Baker' was an alias - Rene knew nothing. Rene agreed much >of what Baker wrote seemed to be speculation. > >This is not to say that some of what Baker writes might be true, >but I agree it seems to be presented not as speculation, or even >new information, but as past history or something, or as you >said, very matter-of-factly. My guess is that rather than getting any real "new information", they just collected all the previous articles and speculation on this subject and used that. They also seemed to be filling in a few gaps with speculation of their own. The biggest problem of course is that somewhere along the line all that speculation got rewritten as though it was "fact". > It would help if they explained who this guy is! It certainly does seem strange that the editor "knows nothing"... ------------------------------ From: Eric Date: Sat, 28 Jan 95 11:28:23 EST Subject: Inlet Stuff Here's my 2 cents worth about inlets and supersonic flow with regards to Ron's questions. First, supersonic flow *only* travels in a straight line, until it's forced to travel in a different direction by an object in the flow path (i.e., an inlet spike). The physics behind this is that since the flow is travelling faster than the speed of sound, no perturbations from the object in the flow path will travel upstream to "tell" the air to move out of the way. For instance, a subsonic air flow will begin to move out of the way of an object some relative distance ahead of that object because it the perturbations to the airflow are free to travel back upstream to tell it to move. Supersonic flow has to bump into an object before it can know to move. As an aside, the pictures that Ron mentioned of a normal shock wave over the center of pressure of a wing is of a wing in transonic (near M1) flight. The airflow encounters the wing near M1, is accelerated to at least M1 over the wing surface, and forms a normal shock wave. This is mixed supersonic flow (which is much more tricky to predict). The ideal flow for inlets would be well-behaved supersonic flow up until the normal shock to take it down to subsonic. In a high-speek inlet like the SR, you have a series of shock waves to do this. The reason for this, as Larry explained is that you want to slow down the supersonic flow in small steps rather than all at once because gradual compression is more thermodynamically efficient (you let the speed of the aircraft do some of the engine air comp- ression so the engine compressor doesn't have to). Ron mentioned a normal shock sitting on the inlet spike at M1.4, rather than being attached to the spike. This isn't a contradiction of shock wave theory, but just the fact that for any flow turning angle, there is a minimum Mach number at which flow will attach itself to the object. Below that mach number, the airstream is just as content to go through a normal shock and make the turn subsonically. This doesn't incurr too much thermodynamic performance penalty at lower mach numbers (say, 1.5) because normal shock waves aren't too ineff- icient at those numbers. That's why the F-18 has a normal shock inlet. For most of its operating envelope, a normal shock inlet is efficient enough, and a whole lot less complex (I believe the F-16 also went to a normal shock inlet in some later models because it was much simpler. If you have to go faster than M1.8 or son, you probably will want a ramp or wedge type inlet (as you have on the F-15). This allows you to put the air- stream through at least one oblique (an attached shock wave that allows the airflow to turn through some angle) before the normal shock inside the inlet to take the airflow down to subsonic speeds for the engine. If I remember correctly, the F-14 inlet is a multiple ramp inlet, which is scheduled by a computer algorithm to produce different flow turning angles to produce a multiple shock system in the inlet. The extra weight and complexity is of course the price you pay for the extra thermodynamic efficiency of that type of inlet. On the the SR inlet. By the time you are inside the inlet cowl, the flow is probably ready for the final normal shock (I don't know this inlet specific- ally; Some high-speed inlets have multiple internal shock patterns, which are more efficient from thermodynamic and drag penalty standpoints, but are more subject to off-design performance penalties - Given that the SR mission calls for fairly stable cruise conditions, it might have this more complex design). The slots in the spike are for inlet boundary layer bleed. Here's the problem: as the flow approaches M1, it becomes very sensitive to any kind of perturbation that might send it into a normal shock, including turbulence in the boundary layer (that layer of sluggish air next to any fixed surface in a flow stream). If you don't remove the boundary layer, the normal shock in the inlet has a tendency to "dance" around or oscillate back and forth in what is known as inlet buzz. Buzz will cause engine compressor stalls, which then result in inlet unstarts. The inlet unstarts when the shock wave system is disgorged from the inlet and a normal shock wave forms in front of the inlet. Lary discussed the loss of thrust that would result from an inlet unstart quite well. An additional problem is the extra drag that results from this. When the inlet and engine are operating properly, the inlet only slows down enough of the airstream to feed the engine. When the inlet unstarts, you hav this big normal shock wave perched out in front of the inlet stopping a lot of air. The engine will draw some of the air, but the rest gets "spilled" over around the engine nacelle. Because the normal shock wave is suddenly slowing down a lot more air than it was with the stable shock system (think of it as anti-thrust), you get big instantaneous yawing forces. In the SR, the immediate response is to advance the spike to recapture the freestream airflow ahead of the normal shock wave, and then retract it into the inlet to re-establish the flow system. Sorry for the long primer on supersonics. I hope that sheds some light on the subject. Eric ------------------------------ From: freeman@netcom.com (Jay Reynolds Freeman) Date: Sat, 28 Jan 1995 09:24:24 -0800 Subject: Re: Tooling, Fixtures, and Jigs My dictionary (Merriam Webster's Ninth New Collegiate) shows "jig" deriving from middle French _giguer_ (to dance), in turn from _gigue_ (fiddle), related to old Norse _geiga_ (to turn aside), all of which makes perfect sense for the name for a kind of dance (e.g., an Irish jig). Now we are left wondering how a word whose original meaning had to do with lively motion ever became (1) jargon for a mechanical contrivance to hold something stationary, and (2) a racial slur. Isn't language wonderful? Some day folks will similarly wonder how "aurora" got to be a synonym for "will-o'-the-wisp"... We now return to your regularly scheduled newsgroup. -- Jay Freeman ------------------------------ From: king@reasoning.com Date: Sat, 28 Jan 95 09:43:39 GMT Subject: Re: SR71 spike >> >> Okay: at 1.4 the shock wave is in the inlet (assuming it was attached >> to the tip, and not formed at the constriction where the shock trap is >> ?????). As the speed increases, the spike moves back further into the >> nacelle for the expressed purpose of holding the shock wave at the >> right point. I don't get it. Doesn't the shock wave form a _narrower_ cone as Mach number increases? Wouldn't the spike need to EXTEND? - -dk ------------------------------ From: TRADER@cup.portal.com Date: Sat, 28 Jan 95 13:51:48 PST Subject: the (cancelled) "Q" spy plane An article in the January 13, 1995 issue of 'Aerotech News and Review' provides additional information on an SR-71 follow-on. The article is titled "Was the SR-71 revived because the "Q" fell through?", and was written by John Boatman, from Janes On Defense. (Aerotech News is an aerospace industry publication from California's Antelope Valley, home of the Lockheed "Skunk Works", Edwards AFB, and other military contractors and installations.) The points of the article can be summarized as follows: * Starting in 1983, the CIA and the Air Force started to develop a SR-71 follow-on, referred to as "Q" in correspondence, because "Q" is apparently the first letter of the codeword used for the program. * Lockheed and Boeing were given contracts for a stealthy aircraft similar to, but smaller than, the B-2 stealth bomber. The program was cancelled in 1992, because it would have cost more than 1 billion dollars apiece. * In July 1994, a Senate Appropriations Committee wrote "The system which some hoped would be developed and procured as a follow-on to the SR-71 has not materialized." * Most of the questions about a SR-71 follow-on have appeared after the program was cancelled and "no questions were asked about a replacement that would be unmanned, invisible to radar, and able to fly at subsonic speeds." This is interesting if true -- it suggests that people were misled into believing in a manned, hypersonic SR-71 follow-on ("Aurora") based on the results of hypersonic research, while work proceeded on a B-2 like aircraft. Paul McGinnis / TRADER@cup.portal.com / PaulMcG@aol.com ********************************************************************** Anonymous FTP access to files dealing with excessive military secrecy is available from Internet host ftp.shell.portal.com (IP address 156.151.3.4) in the /pub/trader directory. Read the 00readme files for descriptions of the files. Writings from Glenn Campbell, author of the "Area 51 Viewer's Guide" are available in /pub/trader/secrecy/psychospy. ------------------------------ From: "Frank Schiffel, Jr." Date: Sat, 28 Jan 95 17:12:05 CST Subject: sr-71 follow on I ran across some material (not original, but secondary) that DOD was getting flooded with Aurora queries and came out and said that an SR-71 follow on was envisioned, but cancelled due to cost and problems in trying to get all the engineering bugs worked out. Seems expenditures were in the billions. I don't know if a mockup or prototype was built, but it seems that it was not. This would lend credence to the theory that there would be (or was expected to be a follow on to the SR-71). Sort of like the B-2 was a follow on to the B-52. It seems that the concept that satellites would be just as good is a smokescreen to keep people from figuring out how poorly the decisions were made at the national level. Why they don't work as well has been alluded to, and as the details...well, if you know you know, if you don't you don't. One problem that seems to crop up is the cost of these systems, especially the amount of overruns (whether being a black project or not will cut the cost is moot - its the same Congress and government). There seems to be interest in strategic UAVs (Tier II as well as Tier III+/Tier III- crop up in the searches). But it seems that they would be a subsonic loiter capability, probably stealthy at high altitude. I'm not sure going above the SR-71 envelope gets you much, i.e. there are a lot of U-2 variants, and that is definitely a subsonic aircraft. Type of sensors could be debated all across the spectrum, though I'm more interested in what types of air vehicles are doing recon (and therefore what data gets to the decision makers - had to get the pol sci PhD work in there somehow to make it relevant). Though it is strange there is not as much interest in the sensors as in the platform. IMHO what is more key is that what used to be strategic intelligence is now getting down to the theater commanders. I'll bet we'll win, but will that volume help? What's more important, winds, temperatures aloft or that the bad guy can't fly tomorrow? ------------------------------ From: DAVID WINDLE Date: Sun, 29 Jan 1995 16:57:29 Subject: Aurora..In Thrust We Trust..? >As a new subscriber to Skunk-Works, I've been reading some of the >group's thoughts on the aircraft that has become known as Aurora >i.e. a hypersonic replacement for the SR71 with great interest. >I'm a journalist- not an aeronautical engineer - though I like to >get my facts straight, so if I'm wrong please let me know! I began >researching the Aurora story some time ago, and initially the >idea of a faster SR71 replacement seemed like a logical >progression, until I put myself in front of a hypothetical >appropriations committee to argue for the case for a manned, >hypersonic spy plane. >Why replace the SR71 ?: They're getting old and they're not fast >or high enough to outfly modern enemy missiles - Perfectly true - >But ... To fly faster or higher than the SR71 in an operational >role the physics start to go against you. The SR71's integration of >airframe and engines is what make it so remarkable- It is a work of >sheer aeronautical genius on the parts of Kelly Johnson and Ben >Rich. When they designed the Blackbird family years ago there was a >definite requirement for such an aircraft - if it was possible to >build one, to resolve the shortcomings of the U2 in some >situations. At that time speed was the only way round the problem >of missile attack..The 'In Thrust We Trust' philosophy. Today we >have Stealth technology. The SR71's shape had a low RCS for it's >day, but the radar and IR signatures of those J 58s compromised the >overall RCS. Surely a hypersonic spy plane would be even more of a >giveaway, though I accept, difficult to aquire as a target. >If you fly at Mach 5+ you immediately tip your hand, because the >enemy can track you and they know that you have a Mach 5+ aircraft. >No radar - as far as I know has tracked a target travelling at that >kind of speed in any "Aurora" contacts. >What will you power this hypersonic plane with ? The X-15A-2 >fitted with drop tanks used up 14 tons of rocket fuel in it's 140 >odd second burn. A long time ago admittedly, but even with >unimaginably improved rocket engines you're going to need a very >large aircraft to carry enough fuel to fly a meaningful distance >before re-fuelling. How about air breathing rocket engines? There's >a world of difference between the kind of engine that you'd need >for an SSTO spaceplane and a strategic reconnaissance cruiser. One >is designed for acceleration, the other for fairly constant speed. >The designs that are around tend to be for SSTO application so >would be of little use in our hypersonic spy plane. Exotic >propulsion systems are often cited..but in an operational >aircraft..hard to believe unless the engines have been well and >truly tested and de-bugged. >On the other hand, if you asked that hypothetical appropriations >committee for a reconnaissance plane with low IR, radar and >acoustic signatures I think you'd find that you had a much stronger >case... >Combine that aircraft with advanced developments of the old D-21 >for high speed passes over sensitive areas, satellites and more >conventional reconnaissance aircraft and you'd have a very >adaptable and formidable aerial SR / TR capability. It's evident >that very high speed experimental aircraft are being tested at >places like the Ranch - though whether you'd need a pilot to fly >such is a vehicle is debatable - no crew-less weight-less fuel-no >life support system development etc. >Thanks for reading this - I'd be very interested to hear your >thoughts. >Best wishes >David ------------------------------ From: STEVEN SILVESTER Date: Sun, 29 Jan 1995 20:17:59 Subject: Re: Aurora..In Thrust We Trust..? > >>As a new subscriber to Skunk-Works, I've been reading some of the >>group's thoughts on the aircraft that has become known as Aurora >>i.e. a hypersonic replacement for the SR71 with great interest. > >>I'm a journalist- not an aeronautical engineer - though I like to >>get my facts straight, so if I'm wrong please let me know! I began >>researching the Aurora story some time ago, and initially the >>idea of a faster SR71 replacement seemed like a logical >>progression, until I put myself in front of a hypothetical >>appropriations committee to argue for the case for a manned, >>hypersonic spy plane. >-----------------cut 4 resources > It's evident >>that very high speed experimental aircraft are being tested at >>places like the Ranch - though whether you'd need a pilot to fly >>such is a vehicle is debatable - no crew-less weight-less fuel-no >>life support system development etc. > >>Thanks for reading this - I'd be very interested to hear your >>thoughts. > >>Best wishes > >>David > > > >Do you write for the Sunday Times ? If so I enjoyed the Blackbird >and Cyberseat articles.......steve ------------------------------ From: TRADER@cup.portal.com Date: Sun, 29 Jan 95 13:19:42 PST Subject: video of the day As I've mentioned before, the NTIS (National Technical Information Service), part of the Department of Commerce, is a great place to buy military documents. I've found an amazing video tape in their database, but I don't know whether I will be buying it, due to its $145.00 price. That video tape is listed as follows: Accession Number: AD-M000 333HDV Title: Secret City: A History of the Navy at China Lake (Video). Source of Item: NAVY (DODN) Publication Date: 1993 Document Type: Audio Visual 2 VHS videos Country of Pub: United States Language: English Abstract: This two-part video documents the establishment of China Lake, which began as an airfield in the Mojave Desert in the middle of World War II, and which became the Navy's largest research and development center where military personnel and civilian scientists and engineers would work together to develop weapons systems for the fleet. Subject Categories: Military Sciences(74); Ordnance(79); Administration & Management-Research Program Administration & Technology Transfer(70E) Key Words: Administration & Management*; China Lake(California)*; Naval research laboratories*; Weapon systems*; Civilian personnel; Engineers; History; Military personnel; Mojave Desert; NOTS(Naval Ordnance Test Station); Ordnance laboratories; Research and development; Scientists Performing Org: Naval Air Warfare Center, China Lake, CA. Weapons Div. Availability: These VHS videos are 1/2 inch in color with total playing time of 3 hr 14 min (Part 1=84min; Part 2=110 min). Price: AV$145.00. Order No. AD-M000 333HDV The thought that occurs is that since items created by the government are not usually subject to copyright protection, an entrepeneur could buy a set of these tapes, duplicate them, and sell copies at a lower price. If you are interested in ordering the tapes from NTIS, you can contact: U.S. Department of Commerce National Technical Information Service Springfield, VA 22161 USA phone: (703) 487-4650 Paul McGinnis / TRADER@cup.portal.com / PaulMcG@aol.com ------------------------------ From: larry@ichips.intel.com Date: Mon, 30 Jan 1995 03:31:47 -0800 Subject: Re: SR unstarts >If I can ask the right questions, maybe you can clear out some >cobwebs of dusty memory and enlighten me on areas I never fully >understood. >When an aircraft hits M1, the shock wave is "at right angles to the >flow." But where precisely IS the shock wave? I've seen some pictures >on tv that seem to show it at the center of pressure on a wing (i.e. >NOT on the leading edge), while others seem to show the shockwave >attached to the leading edge. I've apparently missed something here, >or could it be different based upon the type of wing? Those two sets of pictures: A. A normal shock is on top of the wing, near the region of maximum thickness, when the aircraft is at a high subsonic Mach number. B. The shock is attached to the leading edge of the wing are really two different things. Explaining the first will help you understand the difference between the two. The process that eventually forms the shock in the first phenomenon starts to appear at what is called the 'critical Mach number', defined as that freestream Mach number at which sonic flow is first obtained somewhere on the airfoil surface. At the 'critical Mach number', the freestream Mach number is less than, one. Therefore a shock won't form on the leading edge of the wing yet because the leading edge encounters a subsonic flow. However, on the top surface of the airfoil, at the point of minimum pressure, and maximum thickness, because the flow is expanding around that maximum thickness, the Mach number will be greater than the freestream Mach number. And therefore the point of minimum pressure on the top surface can be sonic where the rest of the airfoil is still subsonic. Thicker airfoils, with bigger humps, so to speak, on the top surface, have lower critical Mach numbers than thinner airfoils. Just after the freestream Mach number passes the critical Mach number (say the aircraft is accelerating), but still not quite at Mach 1, a point will be reached where the drag will suddenly greatly increase and the lift will greatly decrease, this is the drag divergent Mach number, where the drag suddenly and drastically diverges from its previous constant subsonic value. This point is where the full shock has finally formed on the top surface, because what the drag rise is saying, is that the shock is up there on top of the airfoil, not only increasing losses as the air flows through it, but also raising the pressure of the air as it passes through it, and causing flow separation on the upper surface of the wing. Obviously, it would be nice to put off this whole mess, especially for high subsonic transports, and therefore the desire to design thin airfoils, to raise critical Mach number, and airfoils with high values of drag divergence Mach number (ex: swept wings and supercritical airfoils). > As it regards >the SR, when it hits M1, is the shock wave forming and attached on the >tip of the spike, or towards the back of the spike where the >restriction inside the inlet is? (I know there's several shock waves, >but I refer to the shock wave the engine is dealing with). The engine (J-58), needs the WHOLE TRAIN of shocks that starts at the tip of the inlet spike and ends with the normal shock, hopefully in the throat (as we discussed earlier). These shocks work together to convert the velocity or kinetic energy in the freestream air, to pressure and temperature energy, used by the J-58 (there is a subsonic diffuser (divergent duct) downstream of the throat that increases the pressure of the air as well). All of those shocks are needed so that you don't have to shock the flow down with one big strong normal shock, where the losses would be excessive (which is what you'd have to do if you didn't put a spike on the front of the nacelle). At Mach 3.2, the cone shock (off the inlet spike tip) and oblique shocks (past the cowl lip - before the normal shock in the throat), and the weaker normal shock in the throat, cause smaller losses in kinetic energy TOGETHER, than one big normal shock would! The designers of the blackbird's inlet used shock wave theory to design all of those shocks into the inlet intentionally. Those spikes aren't there just for looks! :) > Also, what happens >to the flow as speed increases? I'd always believed it "bends" back >until it's in the nacelle, It does. Consider a fixed spike for a moment, in an accelerating supersonic stream. As you go faster, the surface of the cone shaped shock, off the tip of that spike, comes closer to the surface of the cone. Looking at hypersonic flow over such a cone for a moment. At hypersonic speeeds, the cone shock is so close to the surface of the cone that it is actually in the boundary layer of the cone (the boundary layer is growing outward as well-getting thicker)! This is one of the 'definitions' of hypersonic flow in fact, where shocks and boundary layers are mixing together, called the 'shock-layer'. Now the SR's inlet. The SR's inlet is designed so that at Mach 3.2, or so, when the spike is fully retracted into the inlet, the cone shock off the tip of that spike is on the lip of the cowl, or adequately inside the nacelle. This is the least draggy configuration. If you let the cone shock off the spike stay outside of the nacelle, you would have high supersonic wave drag on the nacelle, during cruise. Now, since the spike turned the flow outward from the centerline of the nacelle, once we get the flow inside the nacelle, the internal angle of the cowl, and the angle of the spike inside the nacelle, as it converges towards the nacelle at the throat, will generate oblique shocks to keep the flow headed towards the throat (the exact number depends on the exact geometry and Mach nos.). By the time we get to the constriction, or the throat, nature will generate a weak normal shock to take us subsonic. The downstream of the throat, as I said earlier, there is a subsonic diffuser to furhter pressurize the air and also slow it down. >(See, you opened a can of worms--now I want answers!!! :-) :-) I hope the above helped! >I tried to draw a side view of the spike and nacelle, but it doesn't >work well here. Let me describe it. The spike stays full forward as >everyone sees it until M1.4. If you look in the inlet of an SR you see >that the spike keeps its same shape until about 4 inches inside the >inlet where it then flattens out (and btw has a lot of open slots in it >to let air *inside* the spike, maybe boundary air flow control?). Normally, in flight, boundary layer bleed, yes. Also, the flight manual shows that on the ramp, the suction from the inlet can cause flow INTO the nacelle through these bleeds, from the spike bleed grilles on the top side of the nacelle! Interesting! Some other observations: As the airplane accelerates from supersonic to top design speed around Mach 3.2, the spike always forms a cone shock at the tip (of course). It isn't till the spike shock is inside the nacelle that full capture of all the air in front of the inlet is achieved. Also, until the spike shock is in the nacelle, the nacelle experiences the wave drag of the spike shock, mentioned earlier. Now, this is REALLY COOL! During acceleration, the Flight Manual says that the normal shock is kept in the trap, even though the spike has not been fully retracted yet. It says that the forward bypass doors control the back-pressure on the normal shock to keep the normal shock in the trap. Now, since the spike isn't retracted fully yet, I would surmise this means that the regular throat is not formed yet! This is COOL! So since the spike is forward, and the shock trap is lining up with the CONVERGENT part of the spike (the part BEHIND the widest part - towards the J-58), this means to me that the inlet automatically runs 'supercritical' while the spike is at any position forward! This makes sense!! Then, when the spike is fully retracted, the shock trap is in the true throat, at which point it is then 'critical' and achieving therefore maximum pressure recovery!!!! THIS IS COOL! Lockheed must have patented that mechanism, or attempted to. It's hard to tell axactly from the drawing in the Flight Manual, it's hard to get an idea of the angles on the back side of the spike, but the observation above may be true, it is consistent with how supersonic inlets can work. Running 'supercritical' is definitely running 'started', it just doesn't have as high a pressure recovery because the normal shock is not in the throat, per my post last week. >Thanks in advance for more insights!! I tried! If you have any more questions/observations, let me know. Regards, Larry ------------------------------ End of Skunk Works Digest V5 #192 ********************************* To subscribe to skunk-works-digest, send the command: subscribe skunk-works-digest in the body of a message to "majordomo@mail.orst.edu". If you want to subscribe something other than the account the mail is coming from, such as a local redistribution list, then append that address to the "subscribe" command; for example, to subscribe "local-skunk-works": subscribe skunk-works-digest local-skunk-works@your.domain.net To unsubscribe, send mail to the same address, with the command: unsubscribe skunk-works-digest in the body. 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