From: skunk-works-digest-owner@mail.orst.edu To: skunk-works-digest@mail.orst.edu Subject: Skunk Works Digest V5 #282 Reply-To: skunk-works-digest@mail.orst.edu Errors-To: skunk-works-digest-owner@mail.orst.edu Precedence: bulk Skunk Works Digest Saturday, 27 May 1995 Volume 05 : Number 282 In this issue: Helicopter Reality Re: Helicopter Reality Silent Helicopters (again) A little more helicopter stuff... sigh... 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: Charles_E._Smith.wbst200@xerox.com Date: Fri, 26 May 1995 03:10:44 PDT Subject: Helicopter Reality 1) Teetering Rotor helicopters CAN loop. The rotor has no way of knowing if the acceleration it feels is due to gravity or Vsquared/R. Yo can be upsidedown and pulling +3 G`s in almost any aircraft. This why aeodynamics students must learn all about "Euler angles" when they study flight dynamics. 2) Noise. The highest source of noise on a helo is the rotor blades. The forward speed of a helicopter is limited by i. power available ii. rotor diameter iii. rotor angular velocity. as you can see, ii &iii are "coupled". The faster you want to go, the faster the rotor tips go. (In this case I mean Vmax., design point. The rotor speed stays pretty well constant on a modern helo, contolled by the collective pitch setting. On Jet helo`s this is automaticaly controlled.) As the tip speed of the rotor reaches the critical Mach number for the airfoil used a (a function of alpha) a shock wave will develop. This is the source of the wop-wop- wop sound associated with a helicopter. So, yes you could build a very quiet helicopter, but it would a low top speed. Engine noise is a six-inch put. Schweizer has been building low acoustic signature aircraft for years. Cultural Note: Damping is the exponential change in amplitude of a periodic function. Dampening is making something moist. Chuck Smith "Aerospace Engineer to the Stars" ------------------------------ From: wizard@sccsi.com (John F. Regus) Date: Fri, 26 May 1995 07:28:05 -0500 Subject: Re: Helicopter Reality I think everyone's concern about what type of helicopters they had been seeing that were silent were laid to rest yesterday when the Army rolled out the Commanche to the public. They state the helicopter has stealth capability. It will be used for observation and will lightly armed. ******************************************************************* * STRATACOM WORLDNET *internet: wizard@sccsi.com | SYS/370/390 *internet: world@ibm.net (int'l)| Systems Software Engineering *voice: 011-1-713-960-0045 | Data and Tele-Communications *fax/data: 011-1-713-960-0015 | *WUI: REGUSHOU | John F. Regus, Consultant ******************************************************************* ------------------------------ From: MiGEater1@aol.com Date: Fri, 26 May 1995 10:05:24 -0400 Subject: Silent Helicopters (again) Wow, what great response and discussions this topic has raised. I've already learned quite a few bits of information that I did not know. Thanks to all of those in the know that keep this board humming along. Regarding the "silent " helicopter type that I (we) observed at Roving Sands. They were most certainly (x)H-60 Blackhawk types. We observed them flying out at dusk and could clearly see the sillouettes before they inserted the troops on the ground. They were not RAH-66's. Sikorsky rolled out the first prototype yesterday, May 25th, in Connecticut. There were no reports of any flying yet and Sikorsky is fairly public with its information when they are trying to get congressional approval for the Army to buy a bunch of these. And they can't carry troops the way these two helicopters did. In any case, whatever we saw was extremely effective at limiting noise output. Perfect for those late night covert operational activities. Cheers to all, John ------------------------------ From: David Lednicer Date: Fri, 26 May 1995 08:40:19 -0700 (PDT) Subject: A little more helicopter stuff... The Bo 105 WAS NOT the first helicopter to loop and roll. I have seen a video of a Sikorsky S-52 looping (this predates the Bo 105 by at least a decade) and I know that other helicopters did this before the Bo 105. As to the X wing - I worked on that damned thing at Sikorsky and it never, ever flew. If it had, we would have some more test pilot obits to look at. I think you might be getting confused by the flights NASA made with the RSRA in its various configurations. They flew it as a helicopter, as a compound helicopter and as an airplane. The trouble is that NASA/Langley originally funded RSRA and were forced to transfer it to NASA/Ames under a reorganization. Ames didn't really want it and it was never used to its potential. Finally, someone got the bright idea to put the X-wing rotor on it. This was a horrible waste of money, because we knew it wouldn't work, but they persisted. After it was all modified, THEY realized that it wouldn't work and pushed the thing into the back of the hangar and tried to forget about it. The only reason it was "black" was to hide the waste of money from the public. Interestingly enough, the guy who got X-wing going bailed out when the going was good and started up NASP. Personally, I would consider this two black marks on my resume. - ------------------------------------------------------------------- David Lednicer | "Applied Computational Fluid Dynamics" Analytical Methods, Inc. | email: dave@amiwest.com 2133 152nd Ave NE | tel: (206) 643-9090 Redmond, WA 98052 USA | fax: (206) 746-1299 ------------------------------ From: Kathryn & Andreas Gehrs-Pahl Date: Fri, 26 May 1995 13:05:01 -0400 (EDT) Subject: sigh... After I introduced the latest high-tech solution for silent helicopters - -- wrapping them in wet cloth -- and fell for the urban legend that the Bo-105 was the first helicopter capable of aerobatic flight maneuvers, (probable of German origin, ooops), I guess I will stick more to historic topics, rather than technical. :) But I have a request: Our computer here was down for a while, resulting in the loss of some email (I suppose). The last Digest I received before 5-281 was 5-278. Could someone please forward me 5-279 and 5-280? At least the first article in digest 5-281 I didn't receive before, so I am sure that some other email got lost, too. Thanks in advance, - -- Andreas - --- --- Andreas & Kathryn Gehrs-Pahl E-Mail: schnars@ais.org 313 West Court St. #305 or: gpahl@raptor.csc.flint.umich.edu Flint, MI 48502-1239 Tel: (810) 238-8469 WWW URL: http://www.umcc.umich.edu/~schnars/ - --- --- ------------------------------ End of Skunk Works Digest V5 #282 ********************************* 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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