Grimace
Well-Known Member
3-view image added in post #3
In life, you can make time or you can make money, but seldom do opportunities present themselves to make both at the same time. Right now, I have more time than I'd like, so I figured I'd go back to that little airplane that's been built in my head for years (we all have a couple of those, don't we?) and try to put it onto paper, and into electrons and pixels. I've been reading through Raymer, Abbott & Doenhoff, Roskam, McCormick, and a few others for years. I have EAA magazines on CD going all the way back, and have been actively collecting articles on design for years. I have a decent amount of wet layup composite experience and a dusty A&P certificate. In the course of working through Raymer's book, I have come up with numbers, of course, but my main design criteria aren't primarily based on numbers, but rather on the things that, to me, make an aircraft appealing. Miss the target cruise speed by 5kts? Ok. Design a cramped cockpit? Unacceptable. My first order design requirements are as follows:
1. Single-seat, larger-than-standard cockpit. I'm just slightly smaller than average, but the thought of cramming myself into a tiny cross-country airplane just isn't appealing. I remember a picture of an Orange and Blue Corby Starlet in Sport Aviation. I remember seeing that cockpit and thinking to myself, "Who cares if you lose a few knots? That view is fantastic! It's something you'd be happy to spend another hour in. I believe that a lot of the fast glass kind of loses touch with that beautiful part of modern aviation, that we can build planes that are actually pleasant to spend time in. I have no intention of designing another AR-5, or a Lightning Bug. This desire to go bigger should also allow me to fit in a few extra safety features (roll-over protection, 'chute, crush space, etc). The present 3-view has a 32" wide cockpit and that seems positively drool-worthy to me (and works well with my intended range of engines, mentioned in point #3).
2. Reasonably complex systems. Ok, so I'll never fly a jumbo jet or an F-18. Even a small commuter plane or King Air is probably beyond my financial reach. However, money doesn't buy brains or dedication. The thought of a more complex aircraft, multiple fuel tanks, retractable gear, etc, actually is something I desire. I want something that pushes the pilot towards procedures, checklists, etc. Part of the fun, for me, is... for lack of a better description, that "bond" that you make with an aircraft, where tiny engineering details become promises on a checklist that you ignore at your own peril. For me, it would be part of the reward. I commute daily on a motorcycle, rain, sleet, snow, and ice. I've done it for a few years. People say it's dangerous, of course, but I say that it just forces you to really know your machine and your limits. The worst days for riding give me the greatest rewards. I've been riding 10 years, accident-free. I'm no daredevil, but the harder I have to work for my miles, the bigger my smile. And of course, there are some days that your common sense causes you to just stay home. Maybe that doesn't make sense to some, but hopefully it resonates with a few people here. There is joy to be found in that type of experience, even if just for its own sake.
3. Low Cost and flexibility in engine choice. I want the plane to accommodate everything from a VW to an O-200 (76-100hp). I don't mind paying a slight performance penalty and extending the nose for the lighter engines, nor moving the battery for the heavier ones. Ultimate performance isn't the goal here, although "high performance" (in quotes) certainly is. Looking at 2 of my favorite airplanes (KR-2 and Lancair 235), it is plain to see that any aircraft that can't accommodate a larger engine and the forces imposed by them, is limiting its appeal. I know that this means it will be "overbuilt" for the smaller engines, but since I'm not looking to design any sort of record-setter, I'm actually happy with that tradeoff. So basically, I'm running all my numbers for VW power at O-200 weights and speeds, always selecting the "worst case" scenario in my calculations, and then rerunning calculations for the as-designed VW engine, watching for any excessive performance or weight penalties. Another way to think of this is to say that when somebody does come up with a cheap, reliable, 180lb turbo-normalized 75-100hp engine for $7,500, this plane should be ready for it.
This brings me to the last of my "fuzzy criteria" which is the subject of this post.
#4. Awesome Flaps. Nose flaps are required. Why? Because they are technically feasible and yet way out there. I have spent a lot of time thinking about this, years actually, and it is a go/no-go point for my plane. If it proves impractical/unreasonable, I would just dream of building a KR-2. Hey, every homebuilt design has its quirks, right? In the next year or two, I hope to develop a wind-tunnel, Rutan Variviggen-style (car-top), to test a section of the wing for empirical optimization. This idea for a ground-test program has lead to several of my design choices for the wing...
a. Rectangular wing for simplicity, predictable stall, easier construction, and preventing decreasing Re numbers from mucking up the wind-tunnel tests on the wing section. Sure, I could design and build a tapered wing, but it's already a lot on my plate and at some point I just need to stop wing-optimization madness and remember that I want something that's easily buildable. For a homebuilt, a "Hersey bar" wing isn't going to give up too much in exchange for the extra simplicity of being able to build multiple identical parts.
b. Extendable nose flaps with fowler flaps in the back. With an AR of 9:1, even without the benefit of deflection, there can be a considerable variation of wing area, and being able to make those changes both fore and aft can mean less torsion on the spar as compared to when only rear flaps are used.
c. As per Raymer's Simplified Design book, I've come up with a 54sqft wing (AR = 9), which should give a tolerable Vs1, and allow a fairly impressive Vso for a "fast glass" plane with a ~940lb MTOW.
d. A non-laminar airfoil (GA30-215), to provide better stall performance at low Re, keep the max thickness farther forward to allow less stress from the nose flap system, and have less of a drag penalty caused from the spanwise break in the wing where the nose flap meets the rest of the structure.
e. Linked flaps. Anybody who thinks about the challenges of a design such as this will quickly realize that independent LE/TE flaps would be a mess. The plan is to integrate both ends into a single control, making deployment no more complicated than in any other light plane.
So, my first questions involve the first mechanical/technical hurdle I'm facing in deciding whether such a design can be done safely. The nose flaps. Does anyone have any suggestions as to the best/simplest way to implement extending and drooping nose flaps into a small wing? I have a few ideas, but if there's an obvious winner out there, I'm not sure I know what it is. Presently, I believe a torsion box between the front and rear spars is the way to go. This will get that "mess" away from the edges of the airfoil and free up the space for a track system fore and aft, then using a rotating torque tube to push/pull both sets of flaps along that track.
My second question is, what does anybody think of Alibre? I know Rhino is fantastic, but a thousand bucks just isn't in the budget at this moment.
In life, you can make time or you can make money, but seldom do opportunities present themselves to make both at the same time. Right now, I have more time than I'd like, so I figured I'd go back to that little airplane that's been built in my head for years (we all have a couple of those, don't we?) and try to put it onto paper, and into electrons and pixels. I've been reading through Raymer, Abbott & Doenhoff, Roskam, McCormick, and a few others for years. I have EAA magazines on CD going all the way back, and have been actively collecting articles on design for years. I have a decent amount of wet layup composite experience and a dusty A&P certificate. In the course of working through Raymer's book, I have come up with numbers, of course, but my main design criteria aren't primarily based on numbers, but rather on the things that, to me, make an aircraft appealing. Miss the target cruise speed by 5kts? Ok. Design a cramped cockpit? Unacceptable. My first order design requirements are as follows:
1. Single-seat, larger-than-standard cockpit. I'm just slightly smaller than average, but the thought of cramming myself into a tiny cross-country airplane just isn't appealing. I remember a picture of an Orange and Blue Corby Starlet in Sport Aviation. I remember seeing that cockpit and thinking to myself, "Who cares if you lose a few knots? That view is fantastic! It's something you'd be happy to spend another hour in. I believe that a lot of the fast glass kind of loses touch with that beautiful part of modern aviation, that we can build planes that are actually pleasant to spend time in. I have no intention of designing another AR-5, or a Lightning Bug. This desire to go bigger should also allow me to fit in a few extra safety features (roll-over protection, 'chute, crush space, etc). The present 3-view has a 32" wide cockpit and that seems positively drool-worthy to me (and works well with my intended range of engines, mentioned in point #3).
2. Reasonably complex systems. Ok, so I'll never fly a jumbo jet or an F-18. Even a small commuter plane or King Air is probably beyond my financial reach. However, money doesn't buy brains or dedication. The thought of a more complex aircraft, multiple fuel tanks, retractable gear, etc, actually is something I desire. I want something that pushes the pilot towards procedures, checklists, etc. Part of the fun, for me, is... for lack of a better description, that "bond" that you make with an aircraft, where tiny engineering details become promises on a checklist that you ignore at your own peril. For me, it would be part of the reward. I commute daily on a motorcycle, rain, sleet, snow, and ice. I've done it for a few years. People say it's dangerous, of course, but I say that it just forces you to really know your machine and your limits. The worst days for riding give me the greatest rewards. I've been riding 10 years, accident-free. I'm no daredevil, but the harder I have to work for my miles, the bigger my smile. And of course, there are some days that your common sense causes you to just stay home. Maybe that doesn't make sense to some, but hopefully it resonates with a few people here. There is joy to be found in that type of experience, even if just for its own sake.
3. Low Cost and flexibility in engine choice. I want the plane to accommodate everything from a VW to an O-200 (76-100hp). I don't mind paying a slight performance penalty and extending the nose for the lighter engines, nor moving the battery for the heavier ones. Ultimate performance isn't the goal here, although "high performance" (in quotes) certainly is. Looking at 2 of my favorite airplanes (KR-2 and Lancair 235), it is plain to see that any aircraft that can't accommodate a larger engine and the forces imposed by them, is limiting its appeal. I know that this means it will be "overbuilt" for the smaller engines, but since I'm not looking to design any sort of record-setter, I'm actually happy with that tradeoff. So basically, I'm running all my numbers for VW power at O-200 weights and speeds, always selecting the "worst case" scenario in my calculations, and then rerunning calculations for the as-designed VW engine, watching for any excessive performance or weight penalties. Another way to think of this is to say that when somebody does come up with a cheap, reliable, 180lb turbo-normalized 75-100hp engine for $7,500, this plane should be ready for it.
This brings me to the last of my "fuzzy criteria" which is the subject of this post.
#4. Awesome Flaps. Nose flaps are required. Why? Because they are technically feasible and yet way out there. I have spent a lot of time thinking about this, years actually, and it is a go/no-go point for my plane. If it proves impractical/unreasonable, I would just dream of building a KR-2. Hey, every homebuilt design has its quirks, right? In the next year or two, I hope to develop a wind-tunnel, Rutan Variviggen-style (car-top), to test a section of the wing for empirical optimization. This idea for a ground-test program has lead to several of my design choices for the wing...
a. Rectangular wing for simplicity, predictable stall, easier construction, and preventing decreasing Re numbers from mucking up the wind-tunnel tests on the wing section. Sure, I could design and build a tapered wing, but it's already a lot on my plate and at some point I just need to stop wing-optimization madness and remember that I want something that's easily buildable. For a homebuilt, a "Hersey bar" wing isn't going to give up too much in exchange for the extra simplicity of being able to build multiple identical parts.
b. Extendable nose flaps with fowler flaps in the back. With an AR of 9:1, even without the benefit of deflection, there can be a considerable variation of wing area, and being able to make those changes both fore and aft can mean less torsion on the spar as compared to when only rear flaps are used.
c. As per Raymer's Simplified Design book, I've come up with a 54sqft wing (AR = 9), which should give a tolerable Vs1, and allow a fairly impressive Vso for a "fast glass" plane with a ~940lb MTOW.
d. A non-laminar airfoil (GA30-215), to provide better stall performance at low Re, keep the max thickness farther forward to allow less stress from the nose flap system, and have less of a drag penalty caused from the spanwise break in the wing where the nose flap meets the rest of the structure.
e. Linked flaps. Anybody who thinks about the challenges of a design such as this will quickly realize that independent LE/TE flaps would be a mess. The plan is to integrate both ends into a single control, making deployment no more complicated than in any other light plane.
So, my first questions involve the first mechanical/technical hurdle I'm facing in deciding whether such a design can be done safely. The nose flaps. Does anyone have any suggestions as to the best/simplest way to implement extending and drooping nose flaps into a small wing? I have a few ideas, but if there's an obvious winner out there, I'm not sure I know what it is. Presently, I believe a torsion box between the front and rear spars is the way to go. This will get that "mess" away from the edges of the airfoil and free up the space for a track system fore and aft, then using a rotating torque tube to push/pull both sets of flaps along that track.
My second question is, what does anybody think of Alibre? I know Rhino is fantastic, but a thousand bucks just isn't in the budget at this moment.
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