Here is the Honda's tech paper about the SHM-1 airfoil (which was designed for the Honda-Jet). The airfoil includes features which are not important on low speed low Reynolds number flight but it also has features which makes it ideal for lower speed concepts:
http://hondajet.honda.com/pdf/tech_papers/Journal_of_Aircraft_Vol40_No4_P609_P615_SHM_1_NLF.pdf
SHM-1 could be a good starting point for an airfoil for GA-use. The Re area for the SHM-1 is a lot higher than needed by GA, so it may not be directly applicable, but the ideology in the SHM-1 seems just what would be needed for also high speed high efficiency, long endurance GA aircraft, which in addition to having low drag and high Clmax also exhibits good behavior.
High transition length NLF body
I was looking Parson's high transition length body in a book and thought that maybe if I modify my body shape also so that the nose becomes sharper. By sacrificing some interior space, the flow acceleration can be kept for high transition length according the book I was reading this. My modified body looks like this.
Despite the QFLR5 algorithm is not maybe designed for simulating NLF bodies (it is designed for simulating wings), the pressure distribution looks like the same as the wind tunnel data for the Parson's body which makes me think that it might not be that much wrong.
Despite the QFLR5 algorithm is not maybe designed for simulating NLF bodies (it is designed for simulating wings), the pressure distribution looks like the same as the wind tunnel data for the Parson's body which makes me think that it might not be that much wrong.
Fuselage shape optimization
I decided to do svn up for QFLR5 and was delighted that it has progressed further. I decided to try out fuselage shapes this time because it turned out that QFLR5 now allows larger airfoil thicknesses than 20%. Therefore here is a 26% fuselage shape I created today.
Here is how I started it:
1. I took NLF414F airfoil which I know to have very low drag value at 10 million reynolds number.
2. I decambered to it to zero camber
3. I changed thickness to 26%
4. I changed leading edge radius: 30% from leading edge, 0.8 ratio.
The simulation result gives very low Cd-value. The problem in reality is that because of all intersections, and a hatch where one has to enter the craft, the transition point is not that great as predicted by the program most likely.
Here is another simulation, transition forced at 40% chord. The Reynolds number is the same, 41 million with mach 0.29:
I further adjusted the leading edge radius, from the above, I reduced it to 0.8 again.
Here is the result KSNLFFUSELAGE3:
The simulated polar for the NLFFUSELAGE3:
Obviously the fuselage is supposed to be flown at zero angle of attack on cruise flight, but for slight side slip situations it is good to know how the drag rises on the fuselage. It also affects to the stability negatively (for example because the lift slope is not at all linear).
Potential improvement idea for use in non-steady flight: widen the low drag bucket a bit.
The airfoil shape as a axisymmetric fuselage (or as a generic pod, this works also as a engine pod), 3D illustration:
And this is how it looks from inside:
Structurally the pod requires thicker boom than the optimum and unfortunately the drag will be larger than the simulated one for the pod alone.
Here is how I started it:
1. I took NLF414F airfoil which I know to have very low drag value at 10 million reynolds number.
2. I decambered to it to zero camber
3. I changed thickness to 26%
4. I changed leading edge radius: 30% from leading edge, 0.8 ratio.
The simulation result gives very low Cd-value. The problem in reality is that because of all intersections, and a hatch where one has to enter the craft, the transition point is not that great as predicted by the program most likely.
Here is another simulation, transition forced at 40% chord. The Reynolds number is the same, 41 million with mach 0.29:
I further adjusted the leading edge radius, from the above, I reduced it to 0.8 again.
Here is the result KSNLFFUSELAGE3:
The simulated polar for the NLFFUSELAGE3:
Obviously the fuselage is supposed to be flown at zero angle of attack on cruise flight, but for slight side slip situations it is good to know how the drag rises on the fuselage. It also affects to the stability negatively (for example because the lift slope is not at all linear).
Potential improvement idea for use in non-steady flight: widen the low drag bucket a bit.
The airfoil shape as a axisymmetric fuselage (or as a generic pod, this works also as a engine pod), 3D illustration:
And this is how it looks from inside:
Structurally the pod requires thicker boom than the optimum and unfortunately the drag will be larger than the simulated one for the pod alone.
High transition length NLF body
I was looking Parson's high transition length body in a book and thought that maybe if I modify my body shape also so that the nose becomes sharper. By sacrificing some interior space, the flow acceleration can be kept for high transition length according the book I was reading this. My modified body looks like this.
Despite the QFLR5 algorithm is not maybe designed for simulating NLF bodies (it is designed for simulating wings), the pressure distribution looks like the same as the wind tunnel data for the Parson's body which makes me think that it might not be that much wrong.
Despite the QFLR5 algorithm is not maybe designed for simulating NLF bodies (it is designed for simulating wings), the pressure distribution looks like the same as the wind tunnel data for the Parson's body which makes me think that it might not be that much wrong.
Fuselage shape optimization
I decided to do svn up for QFLR5 and was delighted that it has progressed further. I decided to try out fuselage shapes this time because it turned out that QFLR5 now allows larger airfoil thicknesses than 20%. Therefore here is a 26% fuselage shape I created today.
Here is how I started it:
1. I took NLF414F airfoil which I know to have very low drag value at 10 million reynolds number.
2. I decambered to it to zero camber
3. I changed thickness to 26%
4. I changed leading edge radius: 30% from leading edge, 0.8 ratio.
The simulation result gives very low Cd-value. The problem in reality is that because of all intersections, and a hatch where one has to enter the craft, the transition point is not that great as predicted by the program most likely.
Here is another simulation, transition forced at 40% chord. The Reynolds number is the same, 41 million with mach 0.29:
I further adjusted the leading edge radius, from the above, I reduced it to 0.8 again.
Here is the result KSNLFFUSELAGE3:
The simulated polar for the NLFFUSELAGE3:
Obviously the fuselage is supposed to be flown at zero angle of attack on cruise flight, but for slight side slip situations it is good to know how the drag rises on the fuselage. It also affects to the stability negatively (for example because the lift slope is not at all linear).
Potential improvement idea for use in non-steady flight: widen the low drag bucket a bit.
The airfoil shape as a axisymmetric fuselage (or as a generic pod, this works also as a engine pod), 3D illustration:
And this is how it looks from inside:
Structurally the pod requires thicker boom than the optimum and unfortunately the drag will be larger than the simulated one for the pod alone.
Here is how I started it:
1. I took NLF414F airfoil which I know to have very low drag value at 10 million reynolds number.
2. I decambered to it to zero camber
3. I changed thickness to 26%
4. I changed leading edge radius: 30% from leading edge, 0.8 ratio.
The simulation result gives very low Cd-value. The problem in reality is that because of all intersections, and a hatch where one has to enter the craft, the transition point is not that great as predicted by the program most likely.
Here is another simulation, transition forced at 40% chord. The Reynolds number is the same, 41 million with mach 0.29:
I further adjusted the leading edge radius, from the above, I reduced it to 0.8 again.
Here is the result KSNLFFUSELAGE3:
The simulated polar for the NLFFUSELAGE3:
Obviously the fuselage is supposed to be flown at zero angle of attack on cruise flight, but for slight side slip situations it is good to know how the drag rises on the fuselage. It also affects to the stability negatively (for example because the lift slope is not at all linear).
Potential improvement idea for use in non-steady flight: widen the low drag bucket a bit.
The airfoil shape as a axisymmetric fuselage (or as a generic pod, this works also as a engine pod), 3D illustration:
And this is how it looks from inside:
Structurally the pod requires thicker boom than the optimum and unfortunately the drag will be larger than the simulated one for the pod alone.
Low pitching moment NLF airfoil with low sensitivity to bugs and dirt
Here is the Honda's tech paper about the SHM-1 airfoil (which was designed for the Honda-Jet). The airfoil includes features which are not important on low speed low Reynolds number flight but it also has features which makes it ideal for lower speed concepts:
http://hondajet.honda.com/pdf/tech_papers/Journal_of_Aircraft_Vol40_No4_P609_P615_SHM_1_NLF.pdf
SHM-1 could be a good starting point for an airfoil for GA-use. The Re area for the SHM-1 is a lot higher than needed by GA, so it may not be directly applicable, but the ideology in the SHM-1 seems just what would be needed for also high speed high efficiency, long endurance GA aircraft, which in addition to having low drag and high Clmax also exhibits good behavior.
http://hondajet.honda.com/pdf/tech_papers/Journal_of_Aircraft_Vol40_No4_P609_P615_SHM_1_NLF.pdf
SHM-1 could be a good starting point for an airfoil for GA-use. The Re area for the SHM-1 is a lot higher than needed by GA, so it may not be directly applicable, but the ideology in the SHM-1 seems just what would be needed for also high speed high efficiency, long endurance GA aircraft, which in addition to having low drag and high Clmax also exhibits good behavior.
Wing droops on laminar flow section
If you have wondered why Cirrus has the discontinuity on the wings. This may answer to that to some extent. I have not found any factual information about the airfoil section used on the Cirrus other than that it is a natural laminar flow section. Cirrus VK-30 used the Jeff Viken NLF414F airfoil. I don't know if the SR20/SR22 uses the same airfoil or a different NLF section.
Anyway in this NASA tech paper it is explained how the stall resistance can be made better with the wing droop. The wing droop on the NASA test C210 actually indeed resembles the discontinuity on the Cirrus SR20/SR22 wing. Please have a look:
Wind tunnel results of the low-speed NLF(1)-0414F airfoil
Notable thing is that the Vmax-probe did not have this wing droop or any other means to prevent tip stall. And it crashed on landing possibly according to NTSB report and Bruce Carmichael's book, because of unfavorable stalling charasteristics at low Re of the airfoil caused a hard landing (which the pilot did not survive). NLF414F is not to be used without some means to prevent tip stall and to soften the otherwise very sharp stall at low Re.
Anyway in this NASA tech paper it is explained how the stall resistance can be made better with the wing droop. The wing droop on the NASA test C210 actually indeed resembles the discontinuity on the Cirrus SR20/SR22 wing. Please have a look:
Wind tunnel results of the low-speed NLF(1)-0414F airfoil
Notable thing is that the Vmax-probe did not have this wing droop or any other means to prevent tip stall. And it crashed on landing possibly according to NTSB report and Bruce Carmichael's book, because of unfavorable stalling charasteristics at low Re of the airfoil caused a hard landing (which the pilot did not survive). NLF414F is not to be used without some means to prevent tip stall and to soften the otherwise very sharp stall at low Re.
A Lancair builder has collected a list of links to tech papers, e.g. NLF215F
Link:
Interesting technical papers
There is link to the NLF215F airfoil tech paper. It was particularly interesting. Now I understood the philosophy of the profile - I was always wondering, why this profile has the low drag bucket at so high Cl (around 0.5) rather than what is realized in cruise with small aircraft (up to 0.2). But, it seems, that this airfoil is designed to be used with -10 degrees flaps. With those, the low drag bucket gets into the cruise area. Heureka.
Here is a direct link to the paper:
http://www.n91cz.com/Interesting_Technical_Reports/NASA-81-tp1865.pdf
Interesting technical papers
There is link to the NLF215F airfoil tech paper. It was particularly interesting. Now I understood the philosophy of the profile - I was always wondering, why this profile has the low drag bucket at so high Cl (around 0.5) rather than what is realized in cruise with small aircraft (up to 0.2). But, it seems, that this airfoil is designed to be used with -10 degrees flaps. With those, the low drag bucket gets into the cruise area. Heureka.
Here is a direct link to the paper:
http://www.n91cz.com/Interesting_Technical_Reports/NASA-81-tp1865.pdf
NASA NLF-115-20%
I was changing the parameters in the DesignFoil demo. And got interesting positive change for the NLF-115 airfoil: increasing the thickness to 20%, it does not effect the laminar bucket low Cl area, but it increases the laminar bucket towards higher Cl area. On other airfoils, this change usually moves the low drag bucket upwards to higher Cl, but on this airfoil, the low drag bucket seems to rather extend than move. I was trying it out with Reynolds numbers 2000000, 3000000 and 5000000.
The higher thickness (if the simulation is at all correct) would be favorable for structural reasons. The Burt Rutan's canards also use thick airfoils in the canard wing, the thickness of the original GU25 is 20%. I don't know the exact thickness of Roncz R1145MS and haven't measured (I have the Cozy MKIV plans which have the Roncz airfoil included, so I could measure it if I had time to look at it).
The larger thickness contributes to the strength achieved (only those little glass fiber spar caps are needed instead of very heavy big wing spar or alternatively a wing spar made of carbon fiber).
The higher thickness (if the simulation is at all correct) would be favorable for structural reasons. The Burt Rutan's canards also use thick airfoils in the canard wing, the thickness of the original GU25 is 20%. I don't know the exact thickness of Roncz R1145MS and haven't measured (I have the Cozy MKIV plans which have the Roncz airfoil included, so I could measure it if I had time to look at it).
The larger thickness contributes to the strength achieved (only those little glass fiber spar caps are needed instead of very heavy big wing spar or alternatively a wing spar made of carbon fiber).
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