From: "Steve Campbell" Subject: COZY: More on Drag Reduction Date: Thu, 22 May 1997 13:37:58 I can't respond to Jim's comments, but I'll wait for someone else to pipe up. My question relates to the most recent issue of Sport Aviation. One of the articles talks about drag reduction through wing root fairings. The author indicates that this intersection produces considerable drag and that properly designed joints in which the radius of the joint increases as one moves back toward the rear of the aircraft can significantly improve performance. Has anyone tried this on canard type aircraft, either on the strake or on the canard? (This is one of those ivory tower, hypothetical type questions. I'm not about to go and risk my rear end trying it.) Steve **************************************** Stephen A. Campbell Associate Professor, EE University of Minnesota ***************************************** Date: Thu, 22 May 1997 13:38:07 -0400 From: Jim Hocut Subject: COZY: Drag Reduction - Riblets ? A fellow I know who used to work for a small airplane company in Seattle got to talking about "riblets" and their role in drag reduction. At first I thought he was nuts, but upon further investigation found that I have a lot to learn. Apparently NASA developed this concept, and it was applied to one of our America's Cup boats. What it amounts to is many V shaped "scratches" on the surface, and reduces skin drag between 5 and 10%. According to what I read the airlines are looking into applying a thin adhesive backed sheet which has riblets machined into the surface. Does anybody know anything more about this? Is it a concept which could be applied to a homebuild fiberglass airplane? How (attack our pristine paint with 60 grit ??) Thanks, Jim Hocut jhocut@mindspring.com Date: Thu, 22 May 1997 16:58:57 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: Drag Reduction - Riblets ? Jim Hocut wrote: > ... > Apparently NASA developed this concept yes. dr. ash of old dominion u, working under a grant from nasa langley, had the idea; and m walsh (of langley) developed it to fruition. later it was discovered that some stanford boys had tried a similar method in '66, but didn't go anywhere with it. later they found that sharks have `riblet' skin in some areas; _and_ they even found that fast sharks had more riblet acreage then slow ones. go figure. nature just knows this stuff. > and it was applied to one of our America's Cup boats. yes, on d conners' `stars and stripes' '87. > What it amounts to is many V shaped "scratches" on the > surface, and reduces skin drag between 5 and 10%. 4-8% is the amount i hear bandied about. > According to what I read the airlines are looking > into applying a thin adhesive backed sheet which has > riblets machined into the surface. 3m developed the method to accurately produce adhesively- backed riblet sheets---the grooves are on the order of 0.001" to 0.005". riblets do all their work in the lower 1% of the turbulent boundary layer! as of '90 boeing had tested the sheets for contamination effects and air-bus was waiting to reduce their flight data... i tried contacting m walsh to get an update, but he was out. > Is it a concept which could be applied to a homebuild > fiberglass airplane? i don't see why not, but i don't think the long-term contamination issue has been put to rest yet and i don't have any idea what 3m wants for their riblet film. i can only guess that it's not like buying post-it notes. > How (attack our pristine paint with 60 grit ??) not a chance: accurate machining is a big issue as to whether riblets work or don't. :( can you tell i am burned out after a couple months of 24hr/day, 7days/wk work? -- bil Date: Mon, 11 Aug 1997 09:29:21 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: Drag Reduction - Riblets ? i finally managed to speak with m walsh about the current status of riblets. here is a brain dump: o 6% drag reduction is typical o the v-shaped grooves are as width as they are deep o the grooves are between 0.001" and 0.005" for most applications (reynolds number dependent---see literature) o only useful for surfaces which have turbulent boundary layers o can accomodate +/- 15 degree flow misalignment o putting the riblet sheets on a large transport aircraft is not cost effective due to the small drag reduction and the low price of jet-a. o back when 3M had the tooling (mid 80's) the riblet sheet was affordable(?$), now the stocks have run dry and it would require a decent-sized order to get things going again. o it is rumored that airbus had 3M make some riblet sheets and then, as part of the contract, took the tooling. so apparently there still is interest in riblets... o frank marentic used to head the 3M riblet operation, he is now retired and is working to develop teflon-based riblet technology(?). his _home_ number is 612 738 6357. -- bil Date: Mon, 11 Aug 1997 09:50:21 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: Drag Reduction - Riblets ? one more thing: previously i mentioned that contamination (from bugs, dirt, etc) was still being investigated. this doesn't appear to be an issue. -- bil