Glider Performance Limitations or Requirements

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by jedi, Sep 24, 2018.

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  1. Sep 24, 2018 #1

    jedi

    jedi

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    The following is quoted from the "Ultralight from scratch, knowledgable and reasonable input requested" thread post #67.

    Thanks, useful info but advisory, not regulatory. Many references are made to European requirements of span loading and weights for gliders. I do not believe these limitations apply in the US.

    My search turned up the Basic Glider Criteria Handbook.The "Basic Glider Criteria Handbook" deals with guidance for design and structural issues. My concern was with regulations and requirements as has been discussed with regards to FAR 103. The Basic Glider Criteria Handbook does not refer to regulations nor contain minimum specifications for gliders such as sink rate, L/D, stall speeds, wing loading, or span loading. I'm cool here. Apparently we were discussing two different topics.

    This reply is copied to a new thread titled "Glider Performance Limitations or Requirements" for those who wish to make additional comments.
     
  2. Sep 24, 2018 #2

    radfordc

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    I seem to recall that there are standards that apply to type certified gliders, but not to experimental gliders or experimental motor gliders. There was a blog some years ago by a guy who fought the FAA to get his two place ultralight trainer (Challenger as I recall) licensed as an experimental motor glider. The FAA started out saying that he didn't meet "standards" as stated for type certified aircraft (not enough wing span/area). He eventually won the fight and got his motor glider certification. A can't remember the guy's name but at the time he had a reputation as a "pot stirrer".
     
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  3. Sep 24, 2018 #3

    blane.c

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    Well a Stemme 12 has a gross weight advertised of 1984lbs which is a 110lbs more than the glider "guidelines". So obviously at least if you have enough money the edges are fuzzy.
     
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  4. Sep 24, 2018 #4

    Topaz

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    Glider type certification in the USA is currently done through a portion of the FAR's that essentially allows the adoption of other nation's certification rules in particular cases. In the case of gliders (both unpowered and powered), EASA CS-22. I don't recall the US FAR reg number, since it's essentially just a "placeholder" and has no real content itself.

    Basic Glider Critera was a publication of the FAA Flight Standards Service. I have a copy of the 1962 edition. It is not a certification rule or standard. It is a collection of "best practices" for the time, aimed at designers of gliders and sailplanes who intended to pursue type certification for their design through the FAR's applicable at the time. It's filled with "Compliance Suggestions" for the designer. As such, there's nothing wrong with it from the standpoint of the amateur aircraft or glider designer. Particularly if you're designing to a 1962 level of technology, it can be a good "practical" guide to best practices in glider construction and testing. I think its best use today is in showing some points of detail part design and proof testing that are no longer covered in a lot of open texts. Basic Glider Criteria is not intended to be an aircraft design text, and is not adequate to that task. It basically talks about details of how a glider is built and tested, but doesn't even remotely cover design for performance, stability, and control, nor loads analysis and structural design.
     
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  5. Sep 24, 2018 #5

    jedi

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    Any additional details on problems and solutions are wanted. Was it EAB or grandfathered UL trainer? I would guess that it was under the grandfather provisions that have since expired.

    I think the biggest issue for EAB is finding a glider qualified DAR.
     
  6. Sep 24, 2018 #6

    jedi

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    Allows but does not require. That is the point. Requirements for Span loading do not exist in the US. Older primary gliders and modern floater gliders may not and need not meet the current EASA CS-22 requirements.
     
  7. Sep 24, 2018 #7

    Topaz

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    I believe the span-loading requirement that remains in the FAR's is only a limitation on what can be defined as a glider for type certification purposes. The span loading has to be beneath a certain value for the aircraft to qualify for type certification as a "glider," otherwise type certification must be for an "airplane", meaning it simply determines which certification standard - CS-22 or Part 23 - is to be used for purposes of type certification. I don't recall the reg. It has never applied to E-AB, at any time. Only applies to full-blown type certification efforts, which is why I've never really paid it much attention.

    With relation to Part 103, glider or airplane, there is no certification standard, airworthiness standard, or any other standard which applies to a vehicle which qualifies for use under Part 103. You are limited only by your imagination, your nerve, and the quality of your life insurance policy.
     
  8. Sep 24, 2018 #8

    jedi

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    Thanks, we agree. If you ever find the certification reg, please post for general interest.
     
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  9. Sep 24, 2018 #9

    Topaz

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    Actually, it took a lot less digging than I thought. FAR 21.17 establishes routes to type certification under conditions where a certification standard has not already been denoted in that part. One of the possible certification routes for "unconventional" aircraft (cited here as gliders, airships, etc.) is:

    Gliders fall into the (i) case, with referral to CS-22 (then JAR 22) specified in AC 21.17-2a. This AC provides the possible routes to type certification for gliders in the USA. The span-loading qualification is on page 5 pf that AC and, to my surprise, only applies to powered (self-launching) gliders. Unpowered gliders apparently are presumed "gliders" by virtue of their lack of engine alone. Which is remarkably "common sense" for the FAA! ;)

    I've put a copy of AC21.17-2a up on my Drive folder, and you can download it with this link.
     
    Last edited: Sep 24, 2018
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  10. Sep 24, 2018 #10

    proppastie

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    My thoughts on FAA Glider Criteria, .....it is a set of safe recommendations/standards. It is no longer acceptable as a means of certification as Topaz link states. There is a wealth of simplified information for someone starting out to design an aircraft, also as Topaz link to AC 21 17 2A says, last paragraph.....As to is it out of date compared to CS-22 ....perhaps, but every standard I have checked against CS-22 was close or exactly the same, but I have not checked all of the standards.

    https://www.homebuiltairplanes.com/forums/showthread.php?t=30325

    You will not go wrong designing an UL to these standards such as is there but Topaz is correct much is missing as regard to stress analysis or performance.
     
    Last edited: Sep 24, 2018
  11. Sep 24, 2018 #11

    blane.c

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    So you build a cub clone, mark the box for glider and it is a experimental motor glider?
     
  12. Sep 24, 2018 #12

    proppastie

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    not if it is Part 103 which was the original topic.....otherwise I do not know?
     
  13. Sep 24, 2018 #13

    radfordc

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    Essentially, yes. There isn't any legal restriction that I know of that prevents you from it. If the original Space Ship One qualified as an experimental motor glider then most anything should.
     
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  14. Sep 24, 2018 #14

    Topaz

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    Welllll... It's not quite that simple in the real world. The FAA can reject your airworthiness certificate application if they think you're abusing the motorglider rules to fly an airplane without a medical certificate, and has done so in the past. This has resulted in one case where a guy (an occasional poster here on HBA) got his Challenger defined as a Glider on its AC, and legally flew it as such with the appropriate ratings and endorsements. However, it took him a couple of years of arguing with the FAA to get "there", and the outcome was never certain. There have been other attempts that failed, and the FAA would not change its mind. The FAA is under no obligation to grant an airworthiness certificate as a Glider just because you check the box on the form. There's a certain "believability factor" involved as well.

    Also understand clearly that just denoting your airplane as a Glider on the AC does not mean you can then operate it without a medical certificate under your existing PPL-ASEL. You cannot legally fly a Glider without a Glider rating on your PPL ("PPL-G"), and you cannot fly a powered glider capable of taking off under its own power without a self-launch endorsement in your logbook from an appropriately qualified CFI-G. Obtaining a self-launch endorsement generally means at least five hours of dual instruction with a qualified CFI-G, in a powered Glider. Around here, for example, the one FBO that offers regular self-launch Glider endorsements does the training in a Stemme S-10 which rents out at $250/h, dry.

    If you're interested in flying without a medical, and you really want to fly from Point A to Point B instead of actually soaring, you're far better off going for a Sport Pilot certificate or the new deal for Private. If you cannot get a Sport PIlot certificate or don't qualify for the new PPL medical deal, then motorgliders may offer a way you can still fly powered aircraft. But understand that you have to have the proper certifications and endorsements necessary for powered gliders. It's not an "easy loophole."

    Ultralights operating under Part 103 have no design or certification standards at all. They have operating limitations and performance restrictions defined in Part 103 and clarified in AC103-7, but so long as it fits within those limitations, you don't have to prove anything to anybody about your ultralight vehicle. The FAA doesn't care, and won't come out and look at it, even if you ask. Ultralights operated under Part 103 also have no pilot training or certification requirement, although trying to teach yourself to fly in one is, IMHO, simply a complicated and expensive form of suicide.
     
  15. Sep 24, 2018 #15

    narfi

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  16. Sep 24, 2018 #16

    Topaz

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    Space Ship One was operated with an AC as a powered Glider, in the Experimental Research classification. Scaled Composites was able to demonstrate adequately to the FAA that a significant and necessary portion of the design mission was to be performed in gliding flight, and that the aircraft was not capable or intended for regular operation without gliding flight also being a major part of that regular operation. The fact that Space Ship One was incapable of being (or at least was not designed to be) operated by itself under its own power from a runway probably made the process that much easier.

    However, someone showing up with a Cub clone, claiming it's a "motorglider", under Experimental-Amateur Built, is going to get a LOT more of a skeptical eye from the FAA. If you tried to do it without already possessing a PPL-G with the appropriate self-launch endorsement, I suspect you'd have a very uphill battle indeed.
     
  17. Sep 24, 2018 #17

    blane.c

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    I am not interested in doing that, but curious about were the line is drawn. It seems like I generally know about were it is at but it is in the mist and wiggles around.
     
  18. Sep 24, 2018 #18

    proppastie

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    thought somewhere there was an aspect ratio spec......just make the wings longer and higher AR?
     
  19. Sep 24, 2018 #19

    blane.c

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    Well as has been pointed out, wingspan squared x .62 = gross weight, is for type certificate and for motor gliders. Not necessarily for experimental? Some existing gliders don't meet the formula.

    If I was building a small glider that fell outside of part 103 regs, I'd have to decide whether to ask for forgiveness after the fact or permission before the fact. And not wanting a extra large RC model, I think I'd go ask permission. But I agree with Topaz that it is most likely going to go more in your favor if you have glider with self launch ratings in your pocket first.
     
  20. Sep 24, 2018 #20

    BBerson

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    For a Light Sport Motorglider the rating isn't required, only an endorsement from a Light Sport Instructor.
    I also wonder if the self-launch procedures of 61.31 (j) could be done in an airplane if no Light Sport Motorglider is available.
    There may be some consensus standard for a Light Sport Motorglider but I don't have it.
     

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