From: skunk-works-digest-owner@harbor.ecn.purdue.edu To: skunk-works-digest@harbor.ecn.purdue.edu Subject: Skunk Works Digest V4 #84 Reply-To: skunk-works-digest@harbor.ecn.purdue.edu Errors-To: skunk-works-digest-owner@harbor.ecn.purdue.edu Precedence: bulk Skunk Works Digest Wednesday, 8 December 1993 Volume 04 : Number 084 In this issue: airships airships Questions about "array type" radars airships Questions about "array type" radars Re: Aerofax Hypersonic Airbreathing on Display 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: I am the NRA Date: Tue, 7 Dec 93 06:54:15 PST Subject: airships (this is probably getting about too far from charter...) >>> An airship, rigid, (zeppelin, akron, macon) is just a bunch of balloons >>> tucked in an aerodynamic cover. At lift off, the individual bags are >>> usually modestly underfull. As the ship rises (statically, due to >>> bouyant lift, or dynamically, due to aerodynamic lift, if motors >>> running and ship "pitched up"), the bags "fill" as the gas expands. >>> Typically, the bags fill around 6,000 feet. [1] This is called >>> "pressure height" where the gas pressure inside balances tha outside. >>> Rise above this and the bags burst, except.... The bags are always >>> fitted with pressure safety valves to keep them from bursting. BIG >>> VALVES. >>Would/is it possible to put a compressor on the valve and stuff the >>excess gas into a can for later re-use at lower altitude? >I may be wrong, but if you compressed the gas into a can as you got higher into >the atmosphere where the air is thinner, you are still carrying the weight in >essentially the same volume "compressed the gas into a can" means same weight of lift gas in less volume. Less volume means less lift. >as you were, so the overall density (weight/volume) of the airship would be >the same while the density of the air is going down, True enough, except, if compressed, the volume occupied by the lift gas is less, so there is less lift. If the lift gas is allowed to expand due to increased altitude/decreased pressure there is an increase in lift. This is (somewhat counteracted by a _decrease_ due to the decreases density of the exterior air. (For economy of weight, the gas bag has little strength: just enough to keep the gas in. A nonrigid (blimp) has a modestly stronger gasbag.) In either case, the bag cannot forcibly retain lift gas against drastic increases in internal pressure, caused by high altitude. (neglecting the effects of temperature...) The need for the pumping sustem, if employed, is to be able to "give back" the lift gas, at lower altitude, where it is needed to provide lift as the "full" bag (at high altitude) is now part empty as the increasing outside pressure compresses the remaining lift gas. Its not the gas, per se, that supplies the lift. Its the air displaced by the gas... regards dwp ------------------------------ From: I am the NRA Date: Tue, 7 Dec 93 06:54:15 PST Subject: airships (this is probably getting about too far from charter...) >>> An airship, rigid, (zeppelin, akron, macon) is just a bunch of balloons >>> tucked in an aerodynamic cover. At lift off, the individual bags are >>> usually modestly underfull. As the ship rises (statically, due to >>> bouyant lift, or dynamically, due to aerodynamic lift, if motors >>> running and ship "pitched up"), the bags "fill" as the gas expands. >>> Typically, the bags fill around 6,000 feet. [1] This is called >>> "pressure height" where the gas pressure inside balances tha outside. >>> Rise above this and the bags burst, except.... The bags are always >>> fitted with pressure safety valves to keep them from bursting. BIG >>> VALVES. >>Would/is it possible to put a compressor on the valve and stuff the >>excess gas into a can for later re-use at lower altitude? >I may be wrong, but if you compressed the gas into a can as you got higher into >the atmosphere where the air is thinner, you are still carrying the weight in >essentially the same volume "compressed the gas into a can" means same weight of lift gas in less volume. Less volume means less lift. >as you were, so the overall density (weight/volume) of the airship would be >the same while the density of the air is going down, True enough, except, if compressed, the volume occupied by the lift gas is less, so there is less lift. If the lift gas is allowed to expand due to increased altitude/decreased pressure there is an increase in lift. This is (somewhat counteracted by a _decrease_ due to the decreases density of the exterior air. (For economy of weight, the gas bag has little strength: just enough to keep the gas in. A nonrigid (blimp) has a modestly stronger gasbag.) In either case, the bag cannot forcibly retain lift gas against drastic increases in internal pressure, caused by high altitude. (neglecting the effects of temperature...) The need for the pumping sustem, if employed, is to be able to "give back" the lift gas, at lower altitude, where it is needed to provide lift as the "full" bag (at high altitude) is now part empty as the increasing outside pressure compresses the remaining lift gas. Its not the gas, per se, that supplies the lift. Its the air displaced by the gas... regards dwp ------------------------------ From: PHARABOD@frcpn11.in2p3.fr Date: Tue, 07 Dec 93 16:28:28 MET Subject: Questions about "array type" radars It seems that there are excellent radar experts in this discussion group. I have a couple of questions about "array type" (translation from French) radars used for military air safety. There is such a military radar at Semmerzake in Belgium. It sweeps 360 degrees each 12 seconds. How many points are needed to measure the speed of an aircraft? Is it possible with only one point (Doppler shift)? If yes, what is the precision of this measurement for an aircraft flying at 650 knots, 6000 ft up, distance radar-aircraft about 90 miles? 1%, 5%, 10% or more? (the general trajectory of the aircraft is a straight line known from previous points; the craft is moving away from the radar). Also, what is the precision on the measured position? A few meters, more than 10 meters, more than 100 meters? J. Pharabod ------------------------------ From: I am the NRA Date: Tue, 7 Dec 93 06:54:15 PST Subject: airships (this is probably getting about too far from charter...) >>> An airship, rigid, (zeppelin, akron, macon) is just a bunch of balloons >>> tucked in an aerodynamic cover. At lift off, the individual bags are >>> usually modestly underfull. As the ship rises (statically, due to >>> bouyant lift, or dynamically, due to aerodynamic lift, if motors >>> running and ship "pitched up"), the bags "fill" as the gas expands. >>> Typically, the bags fill around 6,000 feet. [1] This is called >>> "pressure height" where the gas pressure inside balances tha outside. >>> Rise above this and the bags burst, except.... The bags are always >>> fitted with pressure safety valves to keep them from bursting. BIG >>> VALVES. >>Would/is it possible to put a compressor on the valve and stuff the >>excess gas into a can for later re-use at lower altitude? >I may be wrong, but if you compressed the gas into a can as you got higher into >the atmosphere where the air is thinner, you are still carrying the weight in >essentially the same volume "compressed the gas into a can" means same weight of lift gas in less volume. Less volume means less lift. >as you were, so the overall density (weight/volume) of the airship would be >the same while the density of the air is going down, True enough, except, if compressed, the volume occupied by the lift gas is less, so there is less lift. If the lift gas is allowed to expand due to increased altitude/decreased pressure there is an increase in lift. This is (somewhat counteracted by a _decrease_ due to the decreases density of the exterior air. (For economy of weight, the gas bag has little strength: just enough to keep the gas in. A nonrigid (blimp) has a modestly stronger gasbag.) In either case, the bag cannot forcibly retain lift gas against drastic increases in internal pressure, caused by high altitude. (neglecting the effects of temperature...) The need for the pumping sustem, if employed, is to be able to "give back" the lift gas, at lower altitude, where it is needed to provide lift as the "full" bag (at high altitude) is now part empty as the increasing outside pressure compresses the remaining lift gas. Its not the gas, per se, that supplies the lift. Its the air displaced by the gas... regards dwp ------------------------------ From: PHARABOD@frcpn11.in2p3.fr Date: Tue, 07 Dec 93 16:28:28 MET Subject: Questions about "array type" radars It seems that there are excellent radar experts in this discussion group. I have a couple of questions about "array type" (translation from French) radars used for military air safety. There is such a military radar at Semmerzake in Belgium. It sweeps 360 degrees each 12 seconds. How many points are needed to measure the speed of an aircraft? Is it possible with only one point (Doppler shift)? If yes, what is the precision of this measurement for an aircraft flying at 650 knots, 6000 ft up, distance radar-aircraft about 90 miles? 1%, 5%, 10% or more? (the general trajectory of the aircraft is a straight line known from previous points; the craft is moving away from the radar). Also, what is the precision on the measured position? A few meters, more than 10 meters, more than 100 meters? J. Pharabod ------------------------------ From: mangan@Kodak.COM (Paul Mangan) Date: Tue, 7 Dec 93 13:24:56 EST Subject: Re: Aerofax > To anyone interested, > > I called Aerofax AGAIN to find out why I didn't receive my book > that was supposed to be shipped a week ago Thursday (Lockheed's > Skunk-Works..The last 50 Years). He said that they still have not > received them from the printer. Again, he said hopefully by the > end of the week (I quietly snickered). > -- > ------==========**********==========------ > Douglas J. Tiffany u011.oh.vp.com > I just got off the phone with Areofax and was told that an initial shipment of 200 had been recieved and that those who had "pre-ordered" would recieve their books this week and that the bulk of the books would be shipped to Aerofax by friday and therefore most people who purchased the books would recieve them before Christmas. .......I will believe it when I see my book.....but let's hope this is accurate. Paul > > > > ------------------------------ From: larry@ichips.intel.com Date: Tue, 7 Dec 1993 11:08:45 -0800 Subject: Hypersonic Airbreathing on Display Those of you close to the AF Museum in Dayton Ohio are lucky indeed, for yet another reason! Evidently already on display, or very soon to be put on display, until some time in February, is a display of work done on Aerospaceplanes and high Mach airbreathing propulsion. I'm told this display shows the first scramjet engine to achieve supersonic combustion as well as other exhibits that show the work in this field that has been going on over the past 30+ years. I've also been told that the things in this exhibit have never been on display before. If I recall precisely, the exhibit is roughly 20ft X 40ft in size and shows a lot of hardware and models of actual vehicle shapes tested at varying Mach nos. up to Mach 20 (a shock tunnel I would expect?). If anyone has already seen this or plans on going to the AF Museum soon, please check out this exhibit and let me know how good it is. If it's good, and from what I've heard so far it certainly sounds good, my suspicion is that it I need to fly there to see it. Larry ------------------------------ End of Skunk Works Digest V4 #84 ******************************** To subscribe to skunk-works-digest, send the command: subscribe skunk-works-digest in the body of a message to "listserv@harbor.ecn.purdue.edu". 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