Date: Sat, 22 Mar 1997 09:12:01 -0500 From: Jim Hocut Subject: COZY: Adjustable NACA Scoop ? Just got the latest newsletter, I thought Vance's input was very interesting. Anyway, mention was made of an "adjustable" NACA scoop. Does anyone know enough about this to offer a brief description. Thanks, Jim Hocut jhocut@mindspring.com Date: Mon, 24 Mar 1997 08:01:13 -0500 From: william l kleb Organization: NASA Langley Research Center Subject: Re: COZY: Adjustable NACA Scoop ? Jim Hocut wrote: > > Anyway, mention was made of an "adjustable" NACA > scoop. Does anyone know enough about this to offer a brief > description. vance wrote it up for the central states newsletter a while back (i'll get the issue details tonight). as i remember, he made the scoop lip adjustable via a screw jack; allowing him to adjust the inlet area during flight. -- bil Date: Mon, 24 Mar 1997 23:44:40 GMT From: william l kleb Subject: COZY: variable naca air inlet vance introduced the topic in "control that cooling drag" in the april '91 csa newletter and provided drawing and detailed discussion in "variable naca air inlet for your cowl" in the july '91 csa newsletter. terry schubert (newsletter editor) has back issues for sale at $5 (see the link off of marc's unofficial cozy web-site for more info on csa). -- bil kleb bil Date: Mon, 19 May 1997 14:45:19 -0400 (EDT) From: AlWick@aol.com Subject: COZY: air inlet I would appreciate input on the following: I need to add an air intake to my wing at root. I have three choices as to it's placement. Opening is 6" x 3". A) Preferred. opening at leading edge. 6" from fuselage side. B) opening 3" behind leading edge (on wing bottom). C) Leading edge, 3" from fuselage. My goal is to minimize the risk of impacting the flight characteristics, while still obtaining the clean, high pressure air needed to cool radiator. So which of these three would be best? ( I understand that most would choose "D" "none of the above".) thanks for sharing your thoughts. -al Date: Mon, 19 May 1997 21:36:50 -0400 (EDT) From: SBLANKDDS@aol.com Subject: Re: COZY: air inlet Al, Have you considered an opening on the low pressure area of the cowling, to draw air up (heat likes to rise anyway)? I saw this on a long EZ once. No blockage to the airflow. No change to the wing structure or lift. Short oil run to the cooler. The less thing-a-ma-jingers in the oil plumbing the better. Oil goes so goes the engine. Maybe some one has done this??? I vote - leave the wing alone. Steve Blank Date: Thu, 22 May 1997 08:04:11 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: air inlet AlWick@aol.com wrote: > > I need to add an air intake to my wing at root. > ... > My goal is to minimize the risk of impacting the flight > characteristics... this is the big unknown. you can really only resolve these questions through extensive wind tunnel testing, flight testing, or computational modeling. of course, if you get lucky with a well focused literature search, you might find that someone has already done one of the above for a similar situation. i don't think this is such a scary mod to consider for a conventional airplane; but for a canard, one depends on the main wing -NOT- stalling under any circumstances. putting an unknown quantity at the leading edge of the main wing is a big, uncertain, scary step. > while still obtaining the clean, high pressure air needed > to cool radiator. this is more tractable. i offer the few comments i am capable of: o under optimum conditions (specific inlet/outlet mass-flow ratio, inlet aspect ratio, surrounding boundary layer thickness, lip shape, angle-of-attack, etc.) naca inlets recover 90% of the total ram pressure available due to the ingestion of the inlet's sidewall vortices. for off-nominal conditions a 70% recovery is more typical, so if you want high pressure recovery, don't go with the naca inlets. o keep the opening at least a boundary layer thickness (~3" if i remember correctly) away from the fuselage, otherwise you will have reduced pressure recovery due to ingestion of the low-energy fuselage boundary layer. o avoid putting the opening anywhere near the top side of the wing. just up from the leading edge is where the "leading edge suction peak" occurs due to the rapid expansion caused by the flow coming to a stop at the stagnation point and rapidly accelerating around to follow the top surface of the wing. this small region is a fairly large contributor to your wing's total lift and pitching moment---nevermind the fact that you would no longer have an inlet since the opening would see suction! :) thus, if i was forced at gun-point to do such a mod, i might take the gun option; but then again, i might put the opening at least 3" from the fuselage side and the top edge would start about 0.5" up from an estimated stagnation point when the wing is flying at about ~5 deg angle-of-attack. (a reasonable estimate for the stagnation point at 5 deg angle-of-attack could be done by running the readily-available unmodified 1130 eppler airfoil through one of the simple airfoil pressure prediction codes---see http:///www.uiuc.edu/ph/www/m-selig) -- bil Subject: Re: COZY: air inlet Date: Thu, 22 May 1997 09:18:48 -0400 (EDT) From: "Randy Smith" bil kleb wrote: > > AlWick@aol.com wrote: < deletia occurs > > > while still obtaining the clean, high pressure air needed > > to cool radiator. > > this is more tractable. i offer the few comments i am capable of: > > o under optimum conditions (specific inlet/outlet mass-flow > ratio, inlet aspect ratio, surrounding boundary layer thickness, > lip shape, angle-of-attack, etc.) naca inlets recover > 90% of the total ram pressure available due to the ingestion of the > inlet's sidewall vortices. for off-nominal conditions > a 70% recovery is more typical, so if you want high pressure > recovery, don't go with the naca inlets. If under optimum conditions the naca inlet recovers 90% of the total ram pressure, and 70% in non-optimum conditions, why not go with naca inlets if high pressure recovery is desired. Is there another inlet type that yields higher pressure recovery? Not being an Aero Engineer (but I'm reading more than I should! :-)) does the concept of pressure recovery include some accounting for the increased drag of the inlet? (I'm assuming not and that they are separate things.) Would a ratio of (pressure recovery)/(change in drag) be meaningful in determining which type of inlet would be best? What exactly is meant by pressure recovery? Is it the amount of the ram pressure available in the free stream that is moved into the inlet/duct at a particular point? (like just before the heat exchanger) Thus the higher the percentage the better. (I know this has a great deal to do with the duct geometry downstream of the inlet.) > o keep the opening at least a boundary layer thickness (~3" if > i remember correctly) away from the fuselage, otherwise you > will have reduced pressure recovery due to ingestion of the > low-energy fuselage boundary layer. Are boundary layers _that_ thick? Is the thickness different for laminar and turbulent flows? > -- > bil > -Randy "armchair aerodynamicist" Smith --* --- -* **-* *-** -*-- -* Watch this space for COZY progress |Cozy MkIV| NCR General Purpose Computing Randy.Smith@ColumbiaSC.NCR.COM |---( )---| Global Support Center Voice 803-939-7648, V+ 633-7648 ___o/o\o___ West Columbia, SC 29170 "I am the way, the truth, and the life..." -JC Date: Thu, 22 May 1997 13:13:29 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: air inlet Randy Smith wrote: > > If under optimum conditions the naca inlet recovers 90% of the > total ram pressure, and 70% in non-optimum conditions, why not go > with naca inlets if high pressure recovery is desired. because a simple flush inlet (hole) positioned in a stagnation region such as the nose or leading edge of the wing recovers nearly 100% of the "dynamic" pressure---the energy that arises from locally stopping, or stagnating, the flow. in fact this is the very principal that your airspeed indicator uses to determine the speed of the incoming air. partly for this reason, it doesn't make sense to put a naca inlet, generally known as a submerged inlet, on the front of anything (nose, or wing leading edges), because the submerged ducting just adds more losses (and thus lower pressure recovery and more drag). > does the concept of pressure recovery include some accounting for > the increased drag of the inlet? no. (at least not directly. as you surmised it would account for some of the internal drag depending on where you measure the "recovered" pressure.) a corrected drag coefficient is typically used to compare the net drag of various inlet types, but al was asking for maximum pressure... you can't have everything at once. the corrected drag coefficient typically used is something like, "measured drag minus available thrust of inducted air divided by inlet area and local dynamic pressure." > Would a ratio of (pressure recovery)/(change in drag) be meaningful > in determining which type of inlet would be best? sure. the real problem is that there are so many different variables that comparing apples-to-apples becomes very difficult. > What exactly is meant by pressure recovery? Is it the amount of > the ram pressure available in the freestream that is moved into > the inlet/duct at a particular point? something like that, yes. > Thus the higher the percentage the better. yes. 100% means you stopped the incoming flow, converting all the kinetic energy (energy due to speed) into internal energy (related to pressure) without any losses whatsoever. > Are boundary layers _that_ thick? Is the thickness different for > laminar and turbulent flows? i haven't run the numbers lately, but last time i did, i think i came up with an estimate of ~1.7 inches near the entrance to the naca inlet---although i certainly could be way off. > Is the thickness different for laminar and turbulent flows? yes. for ideal, flat-plate flow, the thicknesses are very roughly described by: laminar bl thickness ~= (1.7208*x-location)/(Re)^(0.5) turbulent bl thickness ~= (0.37*x-location)/(Re)^(0.2) where x-location is the distance from "the beginning" of the surface, for instance, distance from the nose. Re is the x-location reynolds number or, density*x-location*velocity/viscosity beep. outta time... -- bil ps: you don't need to cc to me, i am on the list... and i don't need two copies ;) Subject: Re: COZY: air inlet Date: Thu, 22 May 1997 14:57:36 -0400 (EDT) From: "Randy Smith" Bil Kleb wrote: > Randy Smith wrote: > > > > If under optimum conditions the naca inlet recovers 90% of the > > total ram pressure, and 70% in non-optimum conditions, why not go > > with naca inlets if high pressure recovery is desired. > > because a simple flush inlet (hole) positioned in a stagnation > region such as the nose or leading edge of the wing recovers > nearly 100% of the "dynamic" pressure---the energy that arises > from locally stopping, or stagnating, the flow. in fact this > is the very principal that your airspeed indicator uses to > determine the speed of the incoming air. > > partly for this reason, it doesn't make sense to put a naca > inlet, generally known as a submerged inlet, on the front of > anything (nose, or wing leading edges), because the submerged > ducting just adds more losses (and thus lower pressure recovery > and more drag). That makes sense. I guess if I had read Al's original question as to where he wanted to place the inlet, I never would have asked the question. The trick (with naca inlets in "normal" locations) must be to provide near optimum conditions to the inlet WRT location and inlet geometry. Otherwise the efficiency of the inlet will fall. > > Would a ratio of (pressure recovery)/(change in drag) be meaningful > > in determining which type of inlet would be best? > > sure. the real problem is that there are so many different > variables that comparing apples-to-apples becomes very difficult. bummer. :-) > yes. 100% means you stopped the incoming flow, converting > all the kinetic energy (energy due to speed) into internal > energy (related to pressure) without any losses whatsoever. Since this is rarely possible in the real world, you could have either 1. a little flow and some value of pressure that is below stagnation pressure or 2. no flow at a slightly higher pressure than in 1. Is this correct? > > Are boundary layers _that_ thick? Is the thickness different for > > laminar and turbulent flows? > > i haven't run the numbers lately, but last time i did, i think > i came up with an estimate of ~1.7 inches near the entrance to the > naca inlet---although i certainly could be way off. Does the bl thickness at the entrance determine the "optimum" depth (into the structure) of the submerged inlet? Are you the one who has the report of the naca inlet windtunnel data on your web site? > -- > bil > > ps: you don't need to cc to me, i am on the list... and i don't > need two copies ;) Sorry. I'll be more careful next time. -Randy "unarmed in the aerodynamics battle" Smith Date: Thu, 22 May 1997 17:24:14 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: air inlet Randy Smith wrote: > The trick (with naca inlets in "normal" locations) must be > to provide near optimum conditions to the inlet WRT location and > inlet geometry. Otherwise the efficiency of the inlet will fall. yes. however, another compounding problem is that there doesn't appear to be a lot of data for the low speed flows that we concern ourselves with---especially the effects of different boundary layer thicknesses. these inlets were originally developed during the advent of jet engines and were subsequently tested at high speeds (near mach 1). after they discovered that submerged inlets had problems around mach 1, interest wained. > Since this is rarely possible in the real world, you could have > either 1. a little flow and some value of pressure that is below > stagnation pressure or 2. no flow at a slightly higher pressure > than in 1. Is this correct? um, i am not sure of the question. for low speed flows, you can recover 99.999% of the kinetic energy if you bring the flow to a dead stop. > Does the bl thickness at the entrance determine the "optimum" depth > (into the structure) of the submerged inlet? yes, but unfortunately there isn't a lot of data out there (at least that i know of) for reasons outlined above. > Are you the one who has > the report of the naca inlet windtunnel data on your web site? yes, but i have since scanned the full reports and the full texts are available from the online naca repository: http://www.larc.nasa.gov/naca/naca.html go to the "what's new" link and you'll find the three reports i added in dec '96. if you have trouble reading or using the reports, _by all means_ send feedback to the site mantainer (there should be an email address in there somewhere), this is your tax money! -- bil Date: Fri, 29 Aug 1997 13:37:19 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: COZY: Re: NACA inlet help I received a personal email about naca inlets, and since i spent my whole lunch-break writing the response, i figured i should share it with the group to "run it through the mill"... Someone wrote: > > I am going to use the NACA scoop on the Cozy for cooling. ok. i'm not. i dislike the challenge of making the strange landing gear cover required and like the challenge (and flexibility) of external scoops. > I talked to a couple of people at Oshkosh and they said if > you are going to use an IO-360 engine, that you need more cooling air. hmmm...not very much more though i'd suspect. > One guy said to make the scoop 2 inches wider. that's a sizable increase as compared to the total capture area or the increase in horsepower (read cooling required) of the IO-360 over the O-360. > So I made the rear landing gear bulkhead hole for > the NACA 2 inches wider. this might not work out, here's why: you might find that you won't be able to make the landing gear cover so that it doesn't interfer with the landing gear legs. there is a newsletter warning/plans correction about this problem, you might also check marc z's online log about this. look for things like minimum/maximum landing gear mounting hole locations of 0.70" and 0.75" above the strut. recall, the landing gear strut is u-shaped, so the farther outboard you go, the closer to the bottom of the fuselage it will be... > I made the forward L.G. bulkhead hole the same > percentage wider, which I think I made it 1.4 inches wider. the "optimum" shape doesn't scale like that i don't believe, but the "optimum" wasn't really optimized in any way other that a couple random attempts at changing the shape and seeing if it worked any better. (the work on this was done in the 40's and mostly at transonic speeds (~mach 1) in support of the emerging jet-powered aircraft until they figured out that submerged inlets don't do very well at transonic speeds.) > [someoneelse said] that if I widened the scoop, it may also need > to be deepened to stay laminar. Is this true? i haven't run the numbers, but it'd be _very_ surprising if you still had laminar flow that far back on the fuselage anyway, particularly with that landing brake mess sitting just in front of the entrance to the scoop. i don't understand the reasoning, but there is some data on the effect of aspect ratio (width/depth ratio) for the inlets. see my page on naca inlets at: http://ab00.larc.nasa.gov/~kleb/naca/inlets.html look at the second one in particular. if you find the reports hard to read or use, by all means, give feedback to the naca report server people so they know what to do. if you are going for the "optimal" naca inlet, then you would probably need to change even the stock plans inlet since i don't beleive it has the right overall length for a 7 degree ramp or a 4:1 aspect ratio. one problem people were encountering was that the entrance to the duct went right up to the back of the landing brake, so if you deepened yours and wanted to maintain the optimum 7 degree angle, you might be well into your landing brake... > And if so can you help me come up with some new dimensions > for the NACA? i could do that, but you might find all you need in terry schubert's article from the central states newsletter. (i'll have to remember to look for the issue number tonight). he goes through the whole sizing issue and leads you through how to design one. -- bil Date: Sat, 30 Aug 1997 18:00:26 GMT From: william l kleb Subject: COZY: Re: NACA inlet help bil kleb wrote: > ... you might find all you need in terry schubert's > article from the central states newsletter. (i'll have to remember > to look for the issue number tonight). the issue is #17, jan 90. -- bil