Hello all,
Norman reminds me that I’ve changed my plans without really saying anything about it to you folks, so some of what I’ve been mentioning about my own project may be a bit confusing. Those of you who have been around for a bit will recall that I was working upon a two-seat flying-plank pusher LSA. Here’s the last report on that airplane.
Two things happened in the meantime: 1) I redid the cost estimate for that airplane after increasing the engine power to 100hp. 2) I took my sideline business full-time last July, as my sole source of income. Needless to say, the two budgets weren’t mutually compatible! :speechles
I still want to design and build, and sooner rather than later. Heck, I’ve been dreaming about this for years now. So how do you reduce the cost of an airplane project? Radically, as in cut it to a third of the former value?(!) Well, you lose the engine and drop the passenger, of course! It helps that my flying lessons have been in sailplanes, as you’ve heard me talking about. The ultimate plan will add an SEL rating to the PPL-G license and rating, but for now, it’s motorless flight for me. My best flight so far is just under three and a half hours in duration, and could’ve been longer – oh, for a relief tube when you want one! :nervous:
So, what you see here is what I’ve been working upon since October. It’s a single-seat medium-performance sailplane. The performance goal is to match or slightly better that of a Schweizer SGS 1-26, an airplane I’ve flown with my soaring club. This will let me to thermal on weak-lift days when higher-wing-loading machines are doing sled rides, but still allow me to do some basic cross-country flying when my flight training progresses to that point. The storage and trailerability requirements are the same for my earlier LSA design – build and store in a one-car garage while still using the garage for a car. This is one of the rules of my condo complex. You have to park a car in your garage; you can’t use as a storage space. So, the wings have to come off and the fuselage has to be less than sixteen feet long. That pretty much says “tailless”, and my (lack of) skills as an aircraft designer (especially in structures) says “flying plank” and not “swept flying wing.” I’m pretty sure I’m not ready to tackle aeroelasticity on the level a high aspect-ratio swept wing would require!
With my two-seat LSA as a starting point, various factors slowly converged the design on a similar formula as Jim Marske’s ‘Pioneer’ series of tailless sailplanes, and the final airplane is broadly similar. One thing I have consistently read in pilot reports of the Pioneer II is an apparent lack of yaw stability and yaw control power, something I told myself I would not tolerate in my own airplane. Thus, the rather large vertical tail, set well aft. Right now it’s sized by a simple tail-volume-coefficient method, but my task this week is to size the vertical tail, rudder, and ailerons with real static stability and control-power methods to a specific cross-wind specification from JAR-22, plus some others from Raymer’s books. I’m hoping the vertical tail will get a little smaller for reasons of weight and wetted area, but if it doesn’t, then no big deal. I think I can meet my performance goals with everything as you see it here. This also reflects my design philosophy – there will be no ‘magic’ in this design, just because it’s tailless. I want to meet all the same specs as ‘regular’ airplanes, using the same design methods. Just because it’s tailless doesn’t mean it can get away with some different kind of physics than any other airplane! I’m generally using JAR-22 for my design criteria, and FAR-23 where the former doesn’t say anything on a particular subject.
I’ve already done full pitch-axis (Edit: static) stability and control numbers, so it's got enough control power for the worst-case (forward) CG and flight condition, and still has about 8.5% static margin at aft CG and just shy of 9% at design CG. I’ve also run cases for ground effect (long story) both under tow and for landing, and rotation at 0.8*Vs0 under tow. The pilot weight can only vary by 25lbs. (that’s total, not twenty-five on either side of the design value), but that’s the price you pay for a flying plank. The landing gear is a single fixed main wheel and nose skid, with tip wheels, as is common in sailplanes in this performance range. As of now, maximum L/D is coming out at 24:1, and the minimum sink is 163fpm. Since the 1-26’s numbers are 23:1 and 162fpm, respectively, I’m happy with my results so far. Length overall is 14ft., and the span is 41ft.
I should stress that, even as you see it here, this is a very preliminary design and may still change in various respects. I think overall what you see is very close to my final product, but only time will tell on that. I’ve learned a lot along the way to this point, and I’ve got a lot still to learn. Expect that I’ll be burning up the electrons with loading and structural questions for you folks in a very few weeks! :gig:
As always, your questions, comments, and encouragement are more than welcome.
Okay, back to work for me, or I won't be able to afford even this! :roll:
Norman reminds me that I’ve changed my plans without really saying anything about it to you folks, so some of what I’ve been mentioning about my own project may be a bit confusing. Those of you who have been around for a bit will recall that I was working upon a two-seat flying-plank pusher LSA. Here’s the last report on that airplane.
Two things happened in the meantime: 1) I redid the cost estimate for that airplane after increasing the engine power to 100hp. 2) I took my sideline business full-time last July, as my sole source of income. Needless to say, the two budgets weren’t mutually compatible! :speechles
I still want to design and build, and sooner rather than later. Heck, I’ve been dreaming about this for years now. So how do you reduce the cost of an airplane project? Radically, as in cut it to a third of the former value?(!) Well, you lose the engine and drop the passenger, of course! It helps that my flying lessons have been in sailplanes, as you’ve heard me talking about. The ultimate plan will add an SEL rating to the PPL-G license and rating, but for now, it’s motorless flight for me. My best flight so far is just under three and a half hours in duration, and could’ve been longer – oh, for a relief tube when you want one! :nervous:
So, what you see here is what I’ve been working upon since October. It’s a single-seat medium-performance sailplane. The performance goal is to match or slightly better that of a Schweizer SGS 1-26, an airplane I’ve flown with my soaring club. This will let me to thermal on weak-lift days when higher-wing-loading machines are doing sled rides, but still allow me to do some basic cross-country flying when my flight training progresses to that point. The storage and trailerability requirements are the same for my earlier LSA design – build and store in a one-car garage while still using the garage for a car. This is one of the rules of my condo complex. You have to park a car in your garage; you can’t use as a storage space. So, the wings have to come off and the fuselage has to be less than sixteen feet long. That pretty much says “tailless”, and my (lack of) skills as an aircraft designer (especially in structures) says “flying plank” and not “swept flying wing.” I’m pretty sure I’m not ready to tackle aeroelasticity on the level a high aspect-ratio swept wing would require!
With my two-seat LSA as a starting point, various factors slowly converged the design on a similar formula as Jim Marske’s ‘Pioneer’ series of tailless sailplanes, and the final airplane is broadly similar. One thing I have consistently read in pilot reports of the Pioneer II is an apparent lack of yaw stability and yaw control power, something I told myself I would not tolerate in my own airplane. Thus, the rather large vertical tail, set well aft. Right now it’s sized by a simple tail-volume-coefficient method, but my task this week is to size the vertical tail, rudder, and ailerons with real static stability and control-power methods to a specific cross-wind specification from JAR-22, plus some others from Raymer’s books. I’m hoping the vertical tail will get a little smaller for reasons of weight and wetted area, but if it doesn’t, then no big deal. I think I can meet my performance goals with everything as you see it here. This also reflects my design philosophy – there will be no ‘magic’ in this design, just because it’s tailless. I want to meet all the same specs as ‘regular’ airplanes, using the same design methods. Just because it’s tailless doesn’t mean it can get away with some different kind of physics than any other airplane! I’m generally using JAR-22 for my design criteria, and FAR-23 where the former doesn’t say anything on a particular subject.
I’ve already done full pitch-axis (Edit: static) stability and control numbers, so it's got enough control power for the worst-case (forward) CG and flight condition, and still has about 8.5% static margin at aft CG and just shy of 9% at design CG. I’ve also run cases for ground effect (long story) both under tow and for landing, and rotation at 0.8*Vs0 under tow. The pilot weight can only vary by 25lbs. (that’s total, not twenty-five on either side of the design value), but that’s the price you pay for a flying plank. The landing gear is a single fixed main wheel and nose skid, with tip wheels, as is common in sailplanes in this performance range. As of now, maximum L/D is coming out at 24:1, and the minimum sink is 163fpm. Since the 1-26’s numbers are 23:1 and 162fpm, respectively, I’m happy with my results so far. Length overall is 14ft., and the span is 41ft.
I should stress that, even as you see it here, this is a very preliminary design and may still change in various respects. I think overall what you see is very close to my final product, but only time will tell on that. I’ve learned a lot along the way to this point, and I’ve got a lot still to learn. Expect that I’ll be burning up the electrons with loading and structural questions for you folks in a very few weeks! :gig:
As always, your questions, comments, and encouragement are more than welcome.
Okay, back to work for me, or I won't be able to afford even this! :roll:
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