From: skunk-works-digest-owner@mail.orst.edu To: skunk-works-digest@mail.orst.edu Subject: Skunk Works Digest V5 #586 Reply-To: skunk-works-digest@mail.orst.edu Errors-To: skunk-works-digest-owner@mail.orst.edu Precedence: bulk Skunk Works Digest Sunday, 31 December 1995 Volume 05 : Number 586 In this issue: Re: diamonds 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: Mary Shafer Date: Sat, 30 Dec 1995 22:11:30 -0500 (EST) Subject: Re: diamonds We call them shock diamonds and they're caused by the reflection of the shockwave in the exhaust plume at the edge of the plume. Pretty, aren't they? Any good aerodynamics book will explain the phenomenon. They're sort of standing shocks. I suppose that you can tell how fast the exhaust plume is by counting the diamonds, but I've never heard anyone actually say that this is possible or how to do it. If you look at a really good photo or up close in real life (standing at the center taxiway for the SR-71, for example), you can see that there's actually quite a bit of structure in the plume--little diamonds inside the big diamonds, etc. Usually by the time you see a photo of a moving plume, scanned in, you get blobs instead of beautiful sharp-edged diamonds. The phenomenon is not limited to the SR-71, by the way--I've seen it on every plane with an afterburner. Regards, Mary Mary Shafer DoD #0362 KotFR shafer@ursa-major.spdcc.com URL http://www.dfrc.nasa.gov/People/Shafer/mary.html Some days it don't come easy/And some days it don't come hard Some days it don't come at all/And these are the days that never end.... On Thu, 28 Dec 1995, Greg Fieser wrote: > > > > Can someone please tell me what creates/created the "diamonds" in the > > exhaust of the SR-71? I have often seen pictures of this but I have > > never read a real explanation of how this happens. THANKS! :) > > > > These "diamonds" are visible in many augmented (afterburner-equipped) jet > powered aircraft, including the SR-71. I have heard several myths, but I do > not know the true explanation...here are some I've heard: > > 1) Sometimes called Mach Diamonds, related to the (relative) speed of the > exhaust gases; > > 2) Claims that the number of visible diamonds represent the number of reheat > (afterburner) stages in the engine; > > 3) Function of the internal engine geometry, i.e. length/diameter of AB > section, nozzle area, etc. > > 4) Phase of the moon, hair color of the pilot, etc. > > I too would be interested in an informed explanation of this phenomenon... > > > Greg Fieser ------------------------------ End of Skunk Works Digest V5 #586 ********************************* 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. Administrative requests, problems, and other non-list mail can be sent to either "skunk-works-digest-owner@mail.orst.edu" or, if you don't like to type a lot, "prm@mail.orst.edu A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace all instances of "skunk-works-digest" in the commands above with "skunk-works". Back issues are available for anonymous FTP from mail.orst.edu, in /pub/skunk-works/digest/vNN.nMMM (where "NN" is the volume number, and "MMM" is the issue number).