---------------------------------------------------------- Kolb-List Digest Archive --- Total Messages Posted Mon 03/10/14: 9 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:38 AM - Drag Reduction Paradox (KIRBY, DENNIS T GS-13 USAF AFMC AFNWC/ENS) 2. 10:24 AM - Re: Drag Reduction Paradox (John Hauck) 3. 10:27 AM - Re: Drag Reduction Paradox (WhiskeyVictor36@aol.com) 4. 11:20 AM - Re: Drag Reduction Paradox (Dennis Rowe) 5. 06:36 PM - Re: Drag Reduction Paradox (Larry Cottrell) 6. 07:56 PM - Re: Drag Reduction Paradox (Rick Neilsen) 7. 08:17 PM - Re: Drag Reduction Paradox (John Hauck) 8. 09:40 PM - Drag reduction (Richard Girard) 9. 09:58 PM - Re: Drag reduction (John Hauck) ________________________________ Message 1 _____________________________________ Time: 08:38:44 AM PST US From: "KIRBY, DENNIS T GS-13 USAF AFMC AFNWC/ENS" Subject: Kolb-List: Drag Reduction Paradox Kolb Friends - Since it's been somewhat slow on the List lately, here's a bizarre flight report outcome that I thought I would share. In my quest to reduce aerodynamic drag on my Mark-III, it has become apparent that the more I attempt to clean up the airframe, instead of seeing my Kolb go faster, the results are making my airplane SLOWER! My top speed is unchanged. The typical cruise speed for my 912 Mark-III has always been between 70 and 75 mph true airspeed (at 4800 rpm). But over the last couple of years, as I've added aerodynamic fairings on my gear legs, fairings on the sides of the upper-rear pod area, and a fairing over the top-of-windshield-to-wing juncture, I kept expecting to see my cruise speed pick up a couple of mph. But no. What's actually happening is my slowest speed just keeps getting slower. Prior to installing the windshield-to-wing fairing, the lowest power setting at which I could fly without losing altitude was 3800 rpm. Any slower, and the Kolb would sink. Now, I can fly at 3400 rpm and still maintain straight and level flight. On my cross-country flights now, I'm not going any faster than before, but I'm burning two-tenths of a gallon less per hour at the same power setting. A couple of years ago, Thom Riddle posted a flight report where he stated that aerodynamic clean-ups on a Kolb seem to contribute more toward lower fuel burn instead of higher airspeeds, due to improved efficiency. I believe that's what I'm seeing here. Fine with me. Since most of my flying is local, I'm OK to putter around at low power settings, burning as little fuel as possible. The scenery around the mountains of central New Mexico is always interesting! Dennis Kirby Mark-3 / 912ul / Powerfin-72 Sandia Park, NM do not archive ________________________________ Message 2 _____________________________________ Time: 10:24:12 AM PST US From: "John Hauck" Subject: RE: Kolb-List: Drag Reduction Paradox Dennis K/Kolbers: I am strictly an amateur and what I share here is strictly my own personal opinion. Having built three of my own Kolb aircraft, three different models, I always shrink the fabric to what I consider the limit, just before it breaks the airplane. I have always felt that I should try to keep the same shape airfoil in air as it is on the ground, at rest. Because we are dealing with a fabric covered wing, it depends on its shape by inner structure and tautness of the fabric. Loose fabric makes a lot different airfoil that tight fabric. As tight as the fabric is on my wing, I still get a concave lower wing surface in flight, but not much. The more concave that surface, the slower the airplane will fly, but probably kill a lot of top and cruise speed. My MKIII has always cruised at 80 mph, or more, calibrated air speed, at 5,000 rpm with a 912, 912ULS, and at 5,800 rpm with a 582. Most Kolbs don't cruise that fast. I know of only one other MKIII that will, and it is configured identical to mine. James Trip and I made an 800 sm trip together a couple years ago. We flew side by side for much of that flight, confirming that both aircraft were performing identically at cruise. Basically, we all build a Kolb to nearly identical specification for size and shape. What makes the difference in performance is how that shape changes once in the air. Again, my own opinion, based on a lot of time on a lot of cross country flights to think about it. ;-) john h mkIII Titus, Alabama -----Original Message----- From: owner-kolb-list-server@matronics.com [mailto:owner-kolb-list-server@matronics.com] On Behalf Of KIRBY, DENNIS T GS-13 USAF AFMC AFNWC/ENS Sent: Monday, March 10, 2014 10:28 AM Subject: Kolb-List: Drag Reduction Paradox --> AFNWC/ENS" Kolb Friends - Since it's been somewhat slow on the List lately, here's a bizarre flight report outcome that I thought I would share. In my quest to reduce aerodynamic drag on my Mark-III, it has become apparent that the more I attempt to clean up the airframe, instead of seeing my Kolb go faster, the results are making my airplane SLOWER! My top speed is unchanged. The typical cruise speed for my 912 Mark-III has always been between 70 and 75 mph true airspeed (at 4800 rpm). But over the last couple of years, as I've added aerodynamic fairings on my gear legs, fairings on the sides of the upper-rear pod area, and a fairing over the top-of-windshield-to-wing juncture, I kept expecting to see my cruise speed pick up a couple of mph. But no. What's actually happening is my slowest speed just keeps getting slower. Prior to installing the windshield-to-wing fairing, the lowest power setting at which I could fly without losing altitude was 3800 rpm. Any slower, and the Kolb would sink. Now, I can fly at 3400 rpm and still maintain straight and level flight. On my cross-country flights now, I'm not going any faster than before, but I'm burning two-tenths of a gallon less per hour at the same power setting. A couple of years ago, Thom Riddle posted a flight report where he stated that aerodynamic clean-ups on a Kolb seem to contribute more toward lower fuel burn instead of higher airspeeds, due to improved efficiency. I believe that's what I'm seeing here. Fine with me. Since most of my flying is local, I'm OK to putter around at low power settings, burning as little fuel as possible. The scenery around the mountains of central New Mexico is always interesting! Dennis Kirby Mark-3 / 912ul / Powerfin-72 Sandia Park, NM do not archive ________________________________ Message 3 _____________________________________ Time: 10:27:55 AM PST US From: WhiskeyVictor36@aol.com Subject: Re: Kolb-List: Drag Reduction Paradox Mr Kirby & Other Kolbers Quite a few years ago, someone on this list was attempting to accomplish the same thing as you are. Another wise lister responded by saying, " You can't make a Butterfly go Fast". I assume he was insinuating that Kolbs are like butterflies. Bill Varnes Original Kolb FireStar Audubon NJ Do Not Archive In a message dated 3/10/2014 11:38:49 A.M. Eastern Daylight Time, dennis.kirby.3@us.af.mil writes: In my quest to reduce aerodynamic drag on my Mark-III, it has become apparent that the more I attempt to clean up the airframe, instead of seeing my Kolb go faster, the results are making my airplane SLOWER! ________________________________ Message 4 _____________________________________ Time: 11:20:33 AM PST US Subject: Re: Kolb-List: Drag Reduction Paradox From: Dennis Rowe John, I also wonder if your enclosed rear fuselage helps you and Mr Tripps speeds. I often Think of closing mine up like yours but the wife is against it. I think once I get a bigger fuel tank installed I might over rule her and give it a try. Dennis "Skid" Rowe Mk3, 690L-70, Leechburg, PA > On Mar 10, 2014, at 1:23 PM, "John Hauck" wrote: > > > Dennis K/Kolbers: > > I am strictly an amateur and what I share here is strictly my own personal > opinion. > > Having built three of my own Kolb aircraft, three different models, I always > shrink the fabric to what I consider the limit, just before it breaks the > airplane. I have always felt that I should try to keep the same shape > airfoil in air as it is on the ground, at rest. Because we are dealing with > a fabric covered wing, it depends on its shape by inner structure and > tautness of the fabric. Loose fabric makes a lot different airfoil that > tight fabric. As tight as the fabric is on my wing, I still get a concave > lower wing surface in flight, but not much. The more concave that surface, > the slower the airplane will fly, but probably kill a lot of top and cruise > speed. > > My MKIII has always cruised at 80 mph, or more, calibrated air speed, at > 5,000 rpm with a 912, 912ULS, and at 5,800 rpm with a 582. Most Kolbs don't > cruise that fast. I know of only one other MKIII that will, and it is > configured identical to mine. James Trip and I made an 800 sm trip together > a couple years ago. We flew side by side for much of that flight, > confirming that both aircraft were performing identically at cruise. > > Basically, we all build a Kolb to nearly identical specification for size > and shape. What makes the difference in performance is how that shape > changes once in the air. > > Again, my own opinion, based on a lot of time on a lot of cross country > flights to think about it. ;-) > > john h > mkIII > Titus, Alabama > > > > -----Original Message----- > From: owner-kolb-list-server@matronics.com > [mailto:owner-kolb-list-server@matronics.com] On Behalf Of KIRBY, DENNIS T > GS-13 USAF AFMC AFNWC/ENS > Sent: Monday, March 10, 2014 10:28 AM > To: kolb-list@matronics.com > Subject: Kolb-List: Drag Reduction Paradox > > --> AFNWC/ENS" > > Kolb Friends - > > Since it's been somewhat slow on the List lately, here's a bizarre flight > report outcome that I thought I would share. > > In my quest to reduce aerodynamic drag on my Mark-III, it has become > apparent that the more I attempt to clean up the airframe, instead of seeing > my Kolb go faster, the results are making my airplane SLOWER! > > My top speed is unchanged. The typical cruise speed for my 912 Mark-III has > always been between 70 and 75 mph true airspeed (at 4800 rpm). But over the > last couple of years, as I've added aerodynamic fairings on my gear legs, > fairings on the sides of the upper-rear pod area, and a fairing over the > top-of-windshield-to-wing juncture, I kept expecting to see my cruise speed > pick up a couple of mph. But no. > > What's actually happening is my slowest speed just keeps getting slower. > Prior to installing the windshield-to-wing fairing, the lowest power setting > at which I could fly without losing altitude was 3800 rpm. Any slower, and > the Kolb would sink. Now, I can fly at 3400 rpm and still maintain straight > and level flight. On my cross-country flights now, I'm not going any faster > than before, but I'm burning two-tenths of a gallon less per hour at the > same power setting. > > A couple of years ago, Thom Riddle posted a flight report where he stated > that aerodynamic clean-ups on a Kolb seem to contribute more toward lower > fuel burn instead of higher airspeeds, due to improved efficiency. I > believe that's what I'm seeing here. > > Fine with me. Since most of my flying is local, I'm OK to putter around at > low power settings, burning as little fuel as possible. The scenery around > the mountains of central New Mexico is always interesting! > > Dennis Kirby > Mark-3 / 912ul / Powerfin-72 > Sandia Park, NM > do not archive > > > > > > > > > > ________________________________ Message 5 _____________________________________ Time: 06:36:36 PM PST US Subject: Re: Kolb-List: Drag Reduction Paradox From: Larry Cottrell Dennis, I have no idea what your enclosure looks like, so I can't make any guess as to what can help. However when I made my trip with Arty several years ago, I used Kolb's "full enclosure" on my Firestar II so that I could stuff it full of camping stuff. I had the wrap around lexan, and the "convertible" type of flexible fabric that went behind the rear jump seat and in front of the tanks. That configuration cost me 3 MPH. When I got back I took off the fabric leaving the windshield and making the plane look like a "shuttlecock", but it was faster. The square fabric was causing the drag. I put streamlined fairings on both my struts and gear legs, and gained about 3 mph each. Then I put bigger wheels on the plane and lost a couple. I do believe that John's enclosure would give you less drag, I guess its whether it is worth the extra speed is what you will have to decide. I had a Mark III with a full windshield that was open at the back. With a 582 I could never get much more than 63 MPH out of it, and it burned 5 gph. I sold the plane and the guy came over and flew with me, and I had to fly S's patterns in order to not fly off and leave him. Larry On Mon, Mar 10, 2014 at 9:28 AM, KIRBY, DENNIS T GS-13 USAF AFMC AFNWC/ENS < dennis.kirby.3@us.af.mil> wrote: > AFNWC/ENS" > > Kolb Friends - > > Since it's been somewhat slow on the List lately, here's a bizarre flight > report outcome that I thought I would share. > > In my quest to reduce aerodynamic drag on my Mark-III, it has become > apparent that the more I attempt to clean up the airframe, instead of > seeing my Kolb go faster, the results are making my airplane SLOWER! > > My top speed is unchanged. The typical cruise speed for my 912 Mark-III > has always been between 70 and 75 mph true airspeed (at 4800 rpm). But > over the last couple of years, as I've added aerodynamic fairings on my > gear legs, fairings on the sides of the upper-rear pod area, and a fairing > over the top-of-windshield-to-wing juncture, I kept expecting to see my > cruise speed pick up a couple of mph. But no. > > What's actually happening is my slowest speed just keeps getting slower. > Prior to installing the windshield-to-wing fairing, the lowest power > setting at which I could fly without losing altitude was 3800 rpm. Any > slower, and the Kolb would sink. Now, I can fly at 3400 rpm and still > maintain straight and level flight. On my cross-country flights now, I'm > not going any faster than before, but I'm burning two-tenths of a gallon > less per hour at the same power setting. > > A couple of years ago, Thom Riddle posted a flight report where he stated > that aerodynamic clean-ups on a Kolb seem to contribute more toward lower > fuel burn instead of higher airspeeds, due to improved efficiency. I > believe that's what I'm seeing here. > > Fine with me. Since most of my flying is local, I'm OK to putter around > at low power settings, burning as little fuel as possible. The scenery > around the mountains of central New Mexico is always interesting! > > Dennis Kirby > Mark-3 / 912ul / Powerfin-72 > Sandia Park, NM > do not archive > > -- *If you forward this email, or any part of it, please remove my email address before sending.* ________________________________ Message 6 _____________________________________ Time: 07:56:47 PM PST US Subject: Re: Kolb-List: Drag Reduction Paradox From: Rick Neilsen I have a VW powered MKIIIC with a full enclosure like Johns. Flying in Michigan I felt it would be warmer. The nicest feature is I can stuff a weeks worth of clothes and food in that enclosure. I put all my camping gear in the passenger seat along with a aux fuel tank and I'm good to go. My MKIIIC likes to fly at 75 MKH. Yes it will fly faster but it isn't happy. I have flown cross country with four other MKIIICs, two 80HP without enclosures were happy app. 5 MPH faster and one was just a tad slower. John's MKIIIC with enclosure is also faster with 100HP. My big VW hangs out in the wind and may slow it down a bit so is the enclosed Kolb faster???? Rick Neilsen Redrive VW powered MKIIIC On Mon, Mar 10, 2014 at 9:36 PM, Larry Cottrell wrote: > Dennis, > I have no idea what your enclosure looks like, so I can't make any > guess as to what can help. However when I made my trip with Arty several > years ago, I used Kolb's "full enclosure" on my Firestar II so that I could > stuff it full of camping stuff. I had the wrap around lexan, and the > "convertible" type of flexible fabric that went behind the rear jump seat > and in front of the tanks. That configuration cost me 3 MPH. > > When I got back I took off the fabric leaving the windshield and making > the plane look like a "shuttlecock", but it was faster. The square fabric > was causing the drag. > > I put streamlined fairings on both my struts and gear legs, and gained > about 3 mph each. Then I put bigger wheels on the plane and lost a couple. > > I do believe that John's enclosure would give you less drag, I guess its > whether it is worth the extra speed is what you will have to decide. I had > a Mark III with a full windshield that was open at the back. With a 582 I > could never get much more than 63 MPH out of it, and it burned 5 gph. I > sold the plane and the guy came over and flew with me, and I had to fly S's > patterns in order to not fly off and leave him. > > Larry > > > On Mon, Mar 10, 2014 at 9:28 AM, KIRBY, DENNIS T GS-13 USAF AFMC AFNWC/ENS > wrote: > >> AFNWC/ENS" >> >> >> Kolb Friends - >> >> Since it's been somewhat slow on the List lately, here's a bizarre flight >> report outcome that I thought I would share. >> >> In my quest to reduce aerodynamic drag on my Mark-III, it has become >> apparent that the more I attempt to clean up the airframe, instead of >> seeing my Kolb go faster, the results are making my airplane SLOWER! >> >> My top speed is unchanged. The typical cruise speed for my 912 Mark-III >> has always been between 70 and 75 mph true airspeed (at 4800 rpm). But >> over the last couple of years, as I've added aerodynamic fairings on my >> gear legs, fairings on the sides of the upper-rear pod area, and a fairing >> over the top-of-windshield-to-wing juncture, I kept expecting to see my >> cruise speed pick up a couple of mph. But no. >> >> What's actually happening is my slowest speed just keeps getting slower. >> Prior to installing the windshield-to-wing fairing, the lowest power >> setting at which I could fly without losing altitude was 3800 rpm. Any >> slower, and the Kolb would sink. Now, I can fly at 3400 rpm and still >> maintain straight and level flight. On my cross-country flights now, I'm >> not going any faster than before, but I'm burning two-tenths of a gallon >> less per hour at the same power setting. >> >> A couple of years ago, Thom Riddle posted a flight report where he stated >> that aerodynamic clean-ups on a Kolb seem to contribute more toward lower >> fuel burn instead of higher airspeeds, due to improved efficiency. I >> believe that's what I'm seeing here. >> >> Fine with me. Since most of my flying is local, I'm OK to putter around >> at low power settings, burning as little fuel as possible. The scenery >> around the mountains of central New Mexico is always interesting! >> >> Dennis Kirby >> Mark-3 / 912ul / Powerfin-72 >> Sandia Park, NM >> do not archive >> >> >> ========== >> arget="_blank">http://www.matronics.com/Navigator?Kolb-List >> ========== >> http://forums.matronics.com >> ========== >> le, List Admin. >> ="_blank">http://www.matronics.com/contribution >> ========== >> >> >> >> > > > -- > *If you forward this email, or any part of it, please remove my email > address before sending.* > > * > > > * > > ________________________________ Message 7 _____________________________________ Time: 08:17:44 PM PST US From: "John Hauck" Subject: RE: Kolb-List: Drag Reduction Paradox Rick N, Kolbers: I think it is. My MKIII cruised 80 mph with all three different engines, 912, 912ULS, and the 582. 80 mph is the sweet spot for my airplane. I can cruise 86-88 mph at 5200 rpm and usually fly long cross country flights at that speed. Some of those flights get plenty boring and I get a little anxious to get where I am going. I think the reason my MKIII flies as well as it does is because of the modifications we made to it, the small frontal area of the 912 series and 582 engines. I think another little trick that helps is the keel fabric fairing which forms a V, instead of the flat belly on the standard MKIII. Also the configuration of my landing gear. There is only 18" of gear leg protruding from the main gear sockets. Braces on the main gear are streamlined 4130. I couldn't tell any difference from flying with 6.00X6 and 8.00X6 tires, and I flew each on individual flights to Alaska. Don't forget my fabric tension. I still think that alone makes a lot of difference over a Kolb that is not as tight. john h mkIII Titus, Alabama From: owner-kolb-list-server@matronics.com [mailto:owner-kolb-list-server@matronics.com] On Behalf Of Rick Neilsen Sent: Monday, March 10, 2014 9:56 PM Subject: Re: Kolb-List: Drag Reduction Paradox I have a VW powered MKIIIC with a full enclosure like Johns. Flying in Michigan I felt it would be warmer. The nicest feature is I can stuff a weeks worth of clothes and food in that enclosure. I put all my camping gear in the passenger seat along with a aux fuel tank and I'm good to go. My MKIIIC likes to fly at 75 MKH. Yes it will fly faster but it isn't happy. I have flown cross country with four other MKIIICs, two 80HP without enclosures were happy app. 5 MPH faster and one was just a tad slower. John's MKIIIC with enclosure is also faster with 100HP. My big VW hangs out in the wind and may slow it down a bit so is the enclosed Kolb faster???? Rick Neilsen Redrive VW powered MKIIIC On Mon, Mar 10, 2014 at 9:36 PM, Larry Cottrell wrote: Dennis, I have no idea what your enclosure looks like, so I can't make any guess as to what can help. However when I made my trip with Arty several years ago, I used Kolb's "full enclosure" on my Firestar II so that I could stuff it full of camping stuff. I had the wrap around lexan, and the "convertible" type of flexible fabric that went behind the rear jump seat and in front of the tanks. That configuration cost me 3 MPH. When I got back I took off the fabric leaving the windshield and making the plane look like a "shuttlecock", but it was faster. The square fabric was causing the drag. I put streamlined fairings on both my struts and gear legs, and gained about 3 mph each. Then I put bigger wheels on the plane and lost a couple. I do believe that John's enclosure would give you less drag, I guess its whether it is worth the extra speed is what you will have to decide. I had a Mark III with a full windshield that was open at the back. With a 582 I could never get much more than 63 MPH out of it, and it burned 5 gph. I sold the plane and the guy came over and flew with me, and I had to fly S's patterns in order to not fly off and leave him. Larry On Mon, Mar 10, 2014 at 9:28 AM, KIRBY, DENNIS T GS-13 USAF AFMC AFNWC/ENS wrote: Kolb Friends - Since it's been somewhat slow on the List lately, here's a bizarre flight report outcome that I thought I would share. In my quest to reduce aerodynamic drag on my Mark-III, it has become apparent that the more I attempt to clean up the airframe, instead of seeing my Kolb go faster, the results are making my airplane SLOWER! My top speed is unchanged. The typical cruise speed for my 912 Mark-III has always been between 70 and 75 mph true airspeed (at 4800 rpm). But over the last couple of years, as I've added aerodynamic fairings on my gear legs, fairings on the sides of the upper-rear pod area, and a fairing over the top-of-windshield-to-wing juncture, I kept expecting to see my cruise speed pick up a couple of mph. But no. What's actually happening is my slowest speed just keeps getting slower. Prior to installing the windshield-to-wing fairing, the lowest power setting at which I could fly without losing altitude was 3800 rpm. Any slower, and the Kolb would sink. Now, I can fly at 3400 rpm and still maintain straight and level flight. On my cross-country flights now, I'm not going any faster than before, but I'm burning two-tenths of a gallon less per hour at the same power setting. A couple of years ago, Thom Riddle posted a flight report where he stated that aerodynamic clean-ups on a Kolb seem to contribute more toward lower fuel burn instead of higher airspeeds, due to improved efficiency. I believe that's what I'm seeing here. Fine with me. Since most of my flying is local, I'm OK to putter around at low power settings, burning as little fuel as possible. The scenery around the mountains of central New Mexico is always interesting! Dennis Kirby Mark-3 / 912ul / Powerfin-72 Sandia Park, NM do not archive ========== arget="_blank">http://www.matronics.com/Navigator?Kolb-List ========== http://forums.matronics.com ========== le, List Admin. ="_blank">http://www.matronics.com/contribution ========== -- If you forward this email, or any part of it, please remove my email address before sending. get="_blank">http://www.matronics.com/Navigator?Kolb-List tp://forums.matronics.com _blank">http://www.matronics.com/contribution ________________________________ Message 8 _____________________________________ Time: 09:40:31 PM PST US Subject: Kolb-List: Drag reduction From: Richard Girard Dennis, Have you ever heard of the Pareto Principle? To generalize using it we could say that 80% of the drag of a Kolb is caused by 20% of the drag producers. So, we start by listing all the things that produce drag on the Kolb and tackle the big hitters first, those 20%er's. Speculation, don't yell at me or cry HERESY, please, on the big hitters of drag that keep the Mk III from going faster. 1. The pod shape. When Kolb created the IIIX based upon suggestions from Barnaby Wainfan (see Kitplanes Magazine, "Windtunnel" monthly column to get his bonafides as to why he might know a thing or two about aerodynamics) where did they make modifications? They tried to reduce the included angles between the forward and aft surfaces of the pod, the idea being that when air is forced to change its direction, if you change it more than 14 to 16 degrees the flow can't follow and separation occurs. What's the stall angle of attack of almost all airfoils? Yep, 14 to 16 degrees. On YouTube there's a video I made a few years ago where I tufted up the aft side surface of my Mk III's pod. Look under Rick51076. Watch what the tufts do at all air speeds. Surprised by what you see? I was. Notice the tuft right behind the strut intersection. That little guy had a big story to tell. 2. The wing. There's a reason why NACA pretty much stopped investigating airfoil sections with flat bottoms along about 1925. They are high drag. You don't have to go crazy and jump to the ultra modern natural laminar flow (NLF) airfoil or any of the laminar flow airfoil sections for that matter. IMHO you can look at what are called the five digit series. A great variety of airplanes have flown with airfoils from this series. My friend, Dick, who retired from Cessna's engineering department always points me there when we start talking about airfoils. I have a NACA report about this series of airfoil sections, TR 460, from 1935. Matronics keeps regurgitating it due to size. I'll be happy to send it to anyone interested or you can get it from the NASA technical report server. 3. The empennage. There are big and small drag producers here, but one that really gets me is the open boom tube. I once put an extra air speed indicator with a long pitot tube into the boom tube facing aft. The airplane was going about 70 mph south and that airspeed indicator was reading 28 mph from the north. So the air was making a 98 mph change in direction. Someday I'd like to tuft up the upper and lower vertical stabilizer and the rudder and video what the flow looks like around the end of the boom tube. I'll bet that they will tell a very interesting story, but for now it's just speculation. Putting a symmetrical airfoil section on the horizontal and vertical stabilizers might be interesting, too, but I suspect we're getting into the 80% of drag producers that only produce 20% of the drag. The things to tackle after 1 and 2 are dealt with. Just some things to ponder. I love my Mk III and really miss flying it, but since I have an opportunity to try some things when I rebuild her.....I'll report back when I know more. Rick Girard do not archive -- Zulu Delta Mk IIIC Thanks, Homer GBYM It isn't necessary to have relatives in Kansas City in order to be unhappy. - Groucho Marx ________________________________ Message 9 _____________________________________ Time: 09:58:36 PM PST US From: "John Hauck" Subject: RE: Kolb-List: Drag reduction Let me add a couple bits of info. First, you don't need tufts to see the dead air. Simply fly in the rain. The area between the leading edge of the center section and the windshield is dead. Easy to see air flowing forward when it hits the rear half of the cockpit. I call them rear quarter windows. Back when Brother Jim and I were much younger we decided to fabricate a fairing similar to the rear fuselage fairing of the OH-58 or Bell Jet Ranger helicopters. I believe that was what those fairings were for, to straighten up the air flow. We never got around to it. Now I have been flying the MKIII so long like it is, I'm too lazy to experiment. Having the fairing right by the rear of the door opening was put it in a position to get knocked around and would probably be a pain in the butt. Like washing a wing with VG's. ;-) Another note on the bottom of the wing. Everyone says the bottom of the Kolb wing is flat. It is flat on sitting on the ground. Soon as it gets loaded up in flight, it becomes a concave bottom. That is the reason I shrink the fabric as tight as I think I can get away with to keep the bottom of the wing as flat as possible. A lot of airspeed is lost the more concave the bottom of the wing. If I am patient I can go anywhere I desire at 80 mph. My airplane is draggy, but I love to fly it. Oh yea.there is a lot of air coming forward in the boom tube. One notices it much more in the winter when that cold air hits the back of your neck. john h mkIII Titus, Alabama From: owner-kolb-list-server@matronics.com [mailto:owner-kolb-list-server@matronics.com] On Behalf Of Richard Girard Sent: Monday, March 10, 2014 11:40 PM Subject: Kolb-List: Drag reduction Dennis, Have you ever heard of the Pareto Principle? To generalize using it we could say that 80% of the drag of a Kolb is caused by 20% of the drag producers. So, we start by listing all the things that produce drag on the Kolb and tackle the big hitters first, those 20%er's. Speculation, don't yell at me or cry HERESY, please, on the big hitters of drag that keep the Mk III from going faster. 1. The pod shape. When Kolb created the IIIX based upon suggestions from Barnaby Wainfan (see Kitplanes Magazine, "Windtunnel" monthly column to get his bonafides as to why he might know a thing or two about aerodynamics) where did they make modifications? They tried to reduce the included angles between the forward and aft surfaces of the pod, the idea being that when air is forced to change its direction, if you change it more than 14 to 16 degrees the flow can't follow and separation occurs. What's the stall angle of attack of almost all airfoils? Yep, 14 to 16 degrees. On YouTube there's a video I made a few years ago where I tufted up the aft side surface of my Mk III's pod. Look under Rick51076. Watch what the tufts do at all air speeds. Surprised by what you see? I was. Notice the tuft right behind the strut intersection. That little guy had a big story to tell. 2. The wing. There's a reason why NACA pretty much stopped investigating airfoil sections with flat bottoms along about 1925. They are high drag. You don't have to go crazy and jump to the ultra modern natural laminar flow (NLF) airfoil or any of the laminar flow airfoil sections for that matter. IMHO you can look at what are called the five digit series. A great variety of airplanes have flown with airfoils from this series. My friend, Dick, who retired from Cessna's engineering department always points me there when we start talking about airfoils. I have a NACA report about this series of airfoil sections, TR 460, from 1935. Matronics keeps regurgitating it due to size. I'll be happy to send it to anyone interested or you can get it from the NASA technical report server. 3. The empennage. There are big and small drag producers here, but one that really gets me is the open boom tube. I once put an extra air speed indicator with a long pitot tube into the boom tube facing aft. The airplane was going about 70 mph south and that airspeed indicator was reading 28 mph from the north. So the air was making a 98 mph change in direction. Someday I'd like to tuft up the upper and lower vertical stabilizer and the rudder and video what the flow looks like around the end of the boom tube. I'll bet that they will tell a very interesting story, but for now it's just speculation. Putting a symmetrical airfoil section on the horizontal and vertical stabilizers might be interesting, too, but I suspect we're getting into the 80% of drag producers that only produce 20% of the drag. The things to tackle after 1 and 2 are dealt with. Just some things to ponder. I love my Mk III and really miss flying it, but since I have an opportunity to try some things when I rebuild her.....I'll report back when I know more. Rick Girard do not archive -- Zulu Delta Mk IIIC Thanks, Homer GBYM It isn't necessary to have relatives in Kansas City in order to be unhappy. - Groucho Marx ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message kolb-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Kolb-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/kolb-list Browse Digests http://www.matronics.com/digest/kolb-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.