Where are the fast high wing LSA kits?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by KevinThorp, Nov 4, 2008.

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  1. Nov 26, 2008 #41

    orion

    orion

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    But then it'd be up to you to deal with the FAA. Keep in mind that by selling a "kit", the company and the builder still need to comply with the 51% rule. And this is especially true today since the FAA is coming down hard on fast-build kits and will probably shut down most if not all unapproved builder assistance centers.

    If you were to build the airplanes then you would become the "manufacturer", which would put you into a whole new category of bureaucracy. I think this may become a potential problem for the producers of these airplanes since the kit and assembled LSA products will need to be produced in such a way that there is a clear debarkation between the two product variants. Given the FAA's current aggressive stance for getting back to the "spirit" of the 51% rule, there may be some interesting and possibly painful developments in the industry in the next year or so.
     
  2. Nov 27, 2008 #42

    Topaz

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    At the risk of going off-topic, do you think that may forbode a resurgence of plans-built or 'traditional' non-quick-build kit aircraft and companies? Or will much of what is currently "quick-build" market share simply disappear, leaving the numbers for the rest of the market largely unchanged?
     
  3. Nov 27, 2008 #43

    MalcolmW

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    Hello, Double Eagle;

    well, there are lots of wood and tubing kits on the market, however, if you want a *fast* high wing LSA... well, I'm not sure that there are many that are *inexpensive* See 'Kit Planes Magazine' December issue for a listing of kits. Lots to look at, but I'm not sure that they meet your requirements. I listed the American Patriot II because it looked like a relatively inexpensive aircraft that should perform reasonably well. I've never flown one, but would love to.

    Okay, I have another question:

    This is a question about LSA aircraft. I see that there is a LSA weight limitation of 1320 lbs MTOW. Yet, I see that there are other aircraft (Cessna 150, Ercoupe, Paradise, etc.) that have 100 hp engines, yet have higher MTOW (significantly).

    Is it my imagination, or is the LSA 1320 lb MTOW a truly *artificial* weight limit which gets winked at? Or is it *real* and should never be violated? Y'know, 'gotta meet the rule' requirement. Some LSA aircraft have similar power to weight ratios equalling aircraft like the Cessna 182, but carry a far lower maximum weight ratio.

    Hmm, I wonder if the LSAs with a 100 hp engine actually are limited (performance & safety) to a true 1320 lb weight? I note that there are a number of LSA aircraft, when carrying a full fuel load, can only carry one and one-half persons (or the equivalent) - how impractical.

    I know when I do a weight and balance, I take the limitations quite seriously and fuel a plane accordingly, yet, in the back of my mind, I always wonder if I'm being overly cautious. Maybe these LSA could carry a higher weight? Maybe even another fifty or even one hundred pounds? It sure would be comforting to know that there was a *real* margin of safety.

    Does anyone know enough aeronautical engineering to give a good analytical answer?

    I'd sure appreciate comments on this.

    Thanks!

    (always fly safe)

    MalcolmW
     
  4. Nov 27, 2008 #44

    Dana

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    The gross weight is whatever the manufacturer says it is. It may be for engineering reasons, or it may be artifically low to get the airplane to comply with regulations (i.e. LSA). The question is do you know which it is?

    -Dana

    People will accept your ideas much more readily if you tell them that Benjamin Franklin said it first.
     
  5. Nov 27, 2008 #45

    orion

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    I think it may signal a resurgence of plans built airplanes, as well as raw material kits such as that commonly associated with the early RV models. However, given the popularity of some of today's kits, I'd guess that a significant amount of people will still go for the kit, even at a higher price.

    As far as the quick build option or builder assistance centers are concerned, I think that much of the former will disappear or will be substantially modified. As far as the latter is concerned, those may still survive but under much stricter control. Recently Glasair's Glastar builder assistance program was given the official green light and I think that other, equally well documented programs might survive as well.
     
  6. Nov 27, 2008 #46

    orion

    orion

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    It's definitely real and set in stone. If you violate it, it'll be simply the same as exceeding the gross weight rating of any other airplane. But there is one difference: The LSAs generally do not have the structural margins that the Part 23 aircraft have and so flying over gross might tend to put you at a significantly higher risk for structural failure. This is a particularly important consideration in connection with the airplane's fatigue characteristics - without the more generous margins of Part 23, these lighter airplanes may be more prone to issue of fatigue, which may not affect the low airframe time owner but may bite a subsequent owner some time down the line.

    As a matter of fact, the LSA category has no load rating requirements at all - it's pretty arbitrary and really up to the manufacturer. As such, even if some do claim Part 23 type structural capabilities, there is no requirement or criteria the manufacturer has to meet to demonstrate the capability and the buyer has no way of evaluating what criteria were used to establish the claim.

    Yes they are. No exceptions, except of course if it's an amphib.

    You noticed that, did you? This has a longer story than is practical to recite herein but in short, the purpose of the LSA category was to reign in the ultralight industry as they started producing the "fat" ultralights. These were either faster and heavier ultralights, or two seat versions of the basic models. The theory was that the two seat models were to be used as checkout platforms for the company's products.

    But then someone decided that these light two seaters would be good trainers so the industry sort of exploded suddenly with a gaggle of two seat models, something that was complicated further by European manufacturers who had similar aircraft although more refined, flying under their version of the ultralight category. As these started to gain market place here in the US, the FAA suddenly realized that the ultralight category no longer applied, yet placing them under "experimental" would have made them useless for commercial work like training.

    As the variants grew, the FAA decided that this was beyond the spirit of the ultralight category and so set about making a new classification for these new, heavier airplanes. They did recognize that this might be a good market for training so they were initially inclined to create the LSA classification with a 1,600 pound gross weight. This would've been very logical since decades of production had already proven that this class of airplane had sufficient structural margins for durability, even when used in a training scenario.

    But since when is a government bureaucracy logical? Turns out a single distributor of one of the European aircraft had the FAA's ear and pointed out that the lower weight category already exists in Europe so why not use their criteria. The FAA agreed with this "logic " and so set the weight limit at the 1,320 pound weight, neglecting to consider the vastly different uses we place on aircraft here as opposed to that in Europe.

    The result? A category of very marginal and somewhat overpriced airplanes that will have no greater use than simply flying within sight of their home airport. Furthermore, it also creates an unlikely training platform since what the market ended up with is structurally marginal airplanes being piloted by very low time pilots. Not a good combination.
     
  7. Nov 27, 2008 #47

    Yenn

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    One other factor stopping manufacturers selling kits is the fact that they have no control over the quality of the finished article but it will carry their name. Not necessarily giving them the right kind of publicity.
     
  8. Nov 27, 2008 #48

    BBerson

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    I thought LSA was created to allow for a kit of any stage of completion, for example 90%.
    Please correct me if I am wrong, I don't have the rule book for LSA.
    BB

    Edit: I found this online from FAA 8130.2F CHG2
    c. Kit Assembly.
    (1) Eligible aircraft must be designed in accordance with the applicable consensus standard,
    and assembled in accordance with the LSA kit manufacturer’s assembly instructions. Accordingly, the
    detailed design data, quality systems, and procedures will not necessarily be the same as that of the
    holder of a type design and PC for the production of aircraft. The components of LSA kit aircraft are
    not necessarily held to the requirements of type-certificated or supplement type-certificated aircraft, or
    those of parts manufacturer approval status.
    (2) The LSA kit does not have to meet a major portion requirement. However, the applicant
    must show evidence that the LSA is properly assembled in accordance with the manufacturer’s assembly
    instructions for that aircraft.
    NOTE: The FAA does not certify LSA manufacturer’s kits or approve the kit
    manufacturers. The FAA does not perform evaluations of LSA kits or LSA kit
    manufacturers, and no FAA listing of approved or evaluated LSA kits or
    manufacturers will be provided.
     
    Last edited: Nov 27, 2008
  9. Nov 27, 2008 #49

    orion

    orion

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    No, I haven't seen that one - if anyone has more info on this please chime in. This would significantly depart from the FAA's current policy of cracking down on quick-build kits for being too complete. But maybe that's intentional in that it differentiates the LSAs from the standard Experimental category.
     
  10. Nov 27, 2008 #50

    Midniteoyl

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    Thats what I heard also.. You can buy a 95% complete LSA and its still a 'kit'. The only caveat is you have to finish it exactly as the factory plane. No deviations allowed. (Other than paint.)
     
  11. Nov 27, 2008 #51

    Midniteoyl

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    Van's Aircraft - Aircraft Models: RV-12 Introduction




     
  12. Nov 27, 2008 #52

    BBerson

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    The LSA rules are confusing for us oldtimers.
    I was at an IA seminar last year and an FAA speaker was trying to explain the LSA laws to the old guys. She must have stopped and said "I'm confused" 25 times in 25 minutes of talking.... and the FAA gets paid to understand the rules, we don't.
    BB
     
  13. Nov 28, 2008 #53

    MalcolmW

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    Hello, Orion;

    Hmm, I’m still somewhat puzzled by your comments – maybe I’m a little slow this morning. However, the thrust of my query was about the MTOW limit for LSA aircraft. It seems to me that it is a regulatory limit that does not relate to the true MTOW (engineered capacity) of the aircraft.

    Let me give you an example of what I’m referring to: A Cessna 150 (with a 100 hp engine), has a MTOW of 1600 lbs – empty weight plus full fuel of about 1300 lbs. Some of my training was in a C150 and the combination of fuel, my instructor and myself was clearly above the legal MTOW (the instructor said, ‘ah, no problem, it’ll fly just fine). That was okay in the winter, but in the summer, I flew with just enough fuel for the lesson. Density altitude is very real.

    Er, I got off topic. Okay, in contrast to the C150 (a certified aircraft), there are many LSAs which have 100 hp engines and a MTOW of 1320 lbs. This puzzles me, for there is one LSA which has different MTOW in its country of origin (Paradise P-1, from Brazil), some 1650 lbs. This suggests to me that the LSA MTOW is an artificial limit, based solely upon the regulation.

    I hope so, for there are a number of LSAs which are, well, structurally heavy. By this I mean that when fueled, they have payload capacity for, as I said before, one and one-half adult males. Examples are the Cessna 162, Flight Design CTLS – both of which have payloads of 346 lbs. – not enough for two typical male adults of today.

    So, how does one figure out what is safe as far as the payload is concerned? I’m sure you’ll say observe the 1320 lb. MTOW limit, yet that means fly alone most of the time. And what happens when a pilot wants to get checked out in a LSA? With the average weight of adult males close to 190 lbs., this means an overweight condition, or, fly with partial fuel on board.

    I do not have the aeronautical engineering skills, nor training to make an evaluation as to the amount of ‘extra capacity’ built in the LSA aircraft. Yet it seems obvious to me that 100 hp (from an even tired forty-year old Continental engine) that can safely carry two adult males in a C150 on training flights repeatedly in an over-load condition, should be able to carry more than 1320 lbs. in a lighter aircraft.

    Incidentally, I calculated the power to weight ratio for a 100 hp LSA, and found that it was similar to that of a C182 - how about that, now?

    Your comments would be appreciated.

    Always fly safe - MalcolmW

    PS: I'm really interested in hearing more about the E-LSA regulations, and build limitations.
     
  14. Nov 28, 2008 #54

    orion

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    For the vast majority of aircraft, the maximum operational weight is the design number for which all the structural and performance characteristics are calculated and engineered. As such, exceeding that maximum weight may compromise either the structure or the operational capabilities, or both.

    Can aircraft operate over gross safely? Well, yes and no so the best answer is "it depends". Aircraft structures for instance are designed for a particular amount of G loading plus a safety factor on top of that. If we follow Part 23 for example, the Normal category operations limit load is 3.8 Gs. This means that the airplane must be able to be subject to 3.8 Gs with no permanent set (no yielding of any part of the structure - this is where the material exceeds the elastic limit and attains a permanent distortion). For metal structures we also have a 1.5 safety factor on top of that for an ultimate design load of 5.7 Gs. Between 3.8 Gs and 5.7 Gs the structure is allowed to distort but must not break or fail in any catastrophic manner.

    If an airplane takes off over gross it may fly fine but now the factors mentioned above are compromised since the G loads at which the airframe may be damaged will be lower. If you take the calculated risk of flying over gross (and most of us have at some point or another) you then must evaluate the type of flying you will do. For instance, if you fly in an area of significant turbulence, that could be sufficient to compromise said structure since abrupt gusts gets into another part of structural design, that being "impact" loading. And in most assemblies you might get through it OK but the fact is that unless you go and gauge the airplane, you really don't know if said flight caused any damage or not. As such, flying over gross is sort of the aviation equivalent of Russian Roulette.

    The second, and maybe more obvious issue then is that of performance. If someone is used to flying within the limits of the airframe's capabilities and then exceeds them, the result could provide the pilot with a nasty surprise. Don't be fooled by simplistic ratios like power-to-eight - comparisons of aircraft performance or capabilities are not all that simple nor linear. It's often a nice number to use in a brochure but generally beyond that it's relatively meaningless.

    Regarding your comment about LSAs being structurally heavy, as compared to what? Again, forget about power loading and look simply at historical precedents. Decades of flight training have pretty much proven that the old 1,600 pound designs provided good, durable airframes to the training market, airframes that regularly took a beating and still flew thousands of hours with little or no significant issues. But despite that, even at 1,600 pounds these airplanes were still relatively marginal from a performance and payload standpoint since for practical application like cross country flying or commuting, they were still beset by significant limitations of payload and fuel. Personally, I used to own one of the Grummans (an AA-1C). At 1,600 pounds, my wife and I and full fuel virtually always resulted in an airplane at gross or just a hair over - me and an instructor was definitely over gross and very near the aft CG limit.

    Now, for the LSA category I'd have to take that 1,600 pound airplane, still get two people and fuel into it, yet I'd have to shed 280 pounds from somewhere to meet the criteria. So, where to start. Well, most LSAs carry less fuel so there's a few pounds but not much since the Grumman held only 24 gallons. Most of the LSA engines also have a bit less mass than the O-235 so there's a few more pounds there. But the bottom line of this is that the only other place to loose weight is in the structure. Yes, the lower gross weight limit may not require as much structure as the 1,600 pound airplane but not by that much so to shed that amount the only realistic process here is to reduce the load capabilities of the airframe. Not good for something that's to have a life as a trainer.

    About two years ago we took a look at the category in order to see if we wanted any involvement and decided that it would be relatively difficult to come up with an airframe that met all the criteria of Part 23 and still fit into the LSA category. The only two variants we determined could do it with reasonable margins would be to do a steel tube, fabric covered airframe with a strut braced wing. In that configuration an aluminum wing would most likely work also. An all aluminum strut braced high wing airplane might work too but we estimated that the light structure would have little or no significant protection in case of a forced landing.

    A low wing airplane would be more difficult to design within said limits unless the company was willing to invest in fairly high end composites and their associated processes.

    In short, the new designs developed for and sold under this category will be generally designed to the regulatory limits of said category with absolutely no margin available for continued over-gross operation. Designing them to higher limits would make no sense since higher load factors would instill a weight penalty. But whether you keep to those limits or not is, as always, up to the owner.

    As far as the other airplanes are concerned, where they operate under a heavier weight limit outside the US, it is unlikely that the airframe sold here is identical to the one sold in its home market. I certainly would not assume the change in gross weight limits is arbitrary - most likely there is a modification of the structure in order for them to be sold here. If not, I'd be rather dubious about that airplane's capabilities for the higher weight unless the other country's load limits were somehow lower than those we impose here (this is actually possible and has happened before).

    The bottom line in all this is that it is unwise to assume that any part of aviation is arbitrary. As with a rubber band, you can stretch things a bit but only so far - you do it often enough or far enough and it will snap.
     
  15. Nov 28, 2008 #55

    MalcolmW

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    Hello, Orion,

    Thank you for your thoughtful comments about MTOW design limits. I must confess I focused upon * power * requirements to keep an aircraft flying, and assumed (ah, what a dangerous thing to do!) that the structural integrity would be enough. Obviously, that wasn't correct.

    I was led down this road due to recognizing that some LSAs can easily exceed the max cruise speed (and some by a significant margin), and have to handicap their performance with less efficient props, leaving off streamlining of landing gear, etc.

    As for aircraft from different countries having different MTOW limits, I can cite one example where the limits is far higher in the country of origin, and to meet LSA requirements, state a lower limit in that particular designation. It is the Paradise P-1, see: Paradise Aircraft for the comment where they state the structure is unchanged.

    It is items like this that raised the question about whether the 1320 lbs. MTOW is design based or a result of a regulatory requirement (y'know, oh, put down 1320 lbs., even though we know it's higher than that & would have to go the certified route if we did - God forbid... etc.).

    I have come across a couple of other examples, but don't have them at my fingertips.

    Again, thank you for your comments.

    MalcolmW
     
  16. Nov 28, 2008 #56

    orion

    orion

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    One of the problems with the company's web site is simply that based on my quick look, nowhere does it seem to list the structural design limits to which the airplane was developed. As such, trying to make a direct or meaningful comparison between their standard version and the LSA version is difficult at best since without knowing the G rating and the safety factors for either application, one can only make very general statements.

    However, based on the historical perspective, we can make a few comparative "guesses". First, the ratio of empty weight to gross weight for their standard configuration is just a hair over 49%. Looking at Part 23 historical figures, aircraft operating within the Normal Category are usually at about 55% or higher. One or two has approached 50% (although off the top of my head I don't recall which ones) but the occurrence is rare. As such, right off the top I might be tempted to say that this is a very light structure, leading to a possible guess that it might not be designed to the same limits that a standard production airplane might be designed to here in the US.

    But, at a 1,320 pound gross weight, that structural fraction goes to 61.7%, which might be indicative that for that particular gross weight as imposed by the LSA category, the structural capability "might" be on the conservative side, which would support your argument, assuming of course that their claim of no structural changes is accurate. But personally, I probably would not be willing to risk my life and that of my passengers on that assumption.
     
  17. Nov 29, 2008 #57

    MalcolmW

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    To BBerson, Midniteoyl, & others confused about E-LSAs...

    I'm still confused. I read the article posted by Midniteoyl (by Ron Wanttaja: http://www.kitplanes.com/sportplanes/0505-3740.pdf ) and I get one set of rules. Yet, when I looked at the Pipistrel website, they offer up another set of rules. See: Sinus Virus and Taurus Motorgliders by Pipistrel Mercy!

    Can anyone clarify this? If you buy an E-SLA kit, can you put in a different EFIS (that is a technology which is changing FAST), and autopilot? Or, do you have to build as specified, then rip out the stuff you don't want and replace it with the stuff you do want?

    Seems like a strange way to build an aircraft.

    Incidentally, the Pipistrel aircraft performed well in the CAFE (NASA sponsored) contests - under what seems like rigorously fair conditions. Too bad more LSAs don't enter that competition - it might give us a better idea of the relative merits of different LSA aircraft.

    (Fly safe) MalcolmW

    PS: Orion - I've asked Paradise aircraft for a clarification on the structure of their P-1 LSA and Brazilian version.
     
  18. Nov 29, 2008 #58

    BBerson

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    MalcomW,

    It looks to me that Pipistrel has not received the LSA consensus approval yet.... so they are using the old experimental rules.
    "Before the Pipistrel range are accepted as SLSA aircraft all Pipistrel aircraft will be registered in the "Experimental" category, the sub group is "amateur built" if built from a kit, or "racing and exhibition" if purchased as ready to fly. Currently ready to fly aircraft can also be registered as ELSA aircraft?"

    BB
     
  19. Nov 30, 2008 #59

    George Sychrovsky

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    Given the above number 55% empty to gross as a “normal“ ratio, that’s 726lbs and 594lbs payload. With 25 gal of fuel =150lbs you still have 444 lbs for two people, what is the problem or so undoable here.
    The CTSW has empty weight only 650lbs leaving 670 lbs for a payload , You can certainly achieve 50/50 empty to gross ratio without any strength compromise if you build the plane with modern composites as it should be built in the year 2000 instead of building it like its still 1947.
    I went to the terrafugia shop Terrafugia, Inc. last week to do some consulting on BRS installation and meet the test pilot as they are getting thing ready to fly.
    Now there, building an airplane and a car in one and that fits within 1320lbs SLSA category, that is a challenge.
     
  20. Nov 30, 2008 #60

    DaveK

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    We have yet to see if the Terrafugia guys can pull that one off. And while it maybe possible to get 50% empty to gross it is difficult, even with modern materials, and especially at a reasonable cost.
     

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