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Thread: Microlift Glider Project....

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    Microlift Glider Project....

    Hello Everyone,

    Im new on the forum although I have been reading it for months.

    Although I'm in Iquitos, Peru, at the moment, I'll be coming back to the states this summer and will begin construction of a microlight glider.

    In preparation of building,I've been reading the messages here in the forum and other places on the internet for a few months and decided to sign up and get some advice and/or suggestions.

    My background is likeTopaz's in regards to number of flight hours and gliders. Though I haven't flown in a number of years I plan on starting again when I return to the states this summer. My first love is gliders and soaring. Flying is like boating. Some like fast, high powered, high decibel speed boats. Some like slow, silent canoes. I like canoes up a jungle river at dawn. To each their own.

    My longest soaring flight is 3hours 45 minutes. Highest altitude gain AGL 11,400 feet. Both in a 1-26. No xc. Like Topaz, longest flight would have been longer but I made a serious error in judgment. I drank a 64oz Big Gulp Coke just prior to launch. Stupid and not good.

    I've been reading about the exploits of Gary Osoba, microlift, and dynamic soaring (google all three) and want to explore this area of soaring.

    I've reached the stage in planning where I need expert advice, critiques, and suggestions. Or any combination thereof.

    My objective is light as possible for the lowest span squared loading for the lowest possible sink rate.

    And a fast build; I want to fly, not build.

    I'm not adverse to trying new ideas and methods as long as my safety is not compromised and my thin wallet is not further depleted.

    In some of the past messages I read about methods and techniques that are far more complicated than they need to be. I don't believe in re-inventing building techniques, methods or processes (though do believe in new innovative ways to save time, money and KISS). I firmly believe in KISS as long as safety is not compromised.

    I thought about building Mike Sandlin's BUG4. Though a fun and practical glider, I decided the performance isn't what I'm looking for. So I took a little from here and a little from there and designed my own microlight glider.

    Following are design particulars for a microlight glider to explore microlight and dynamic soaring I plan on building. Design weight is 155 pounds max (including fiberglass pod) for FAR 103.

    1. Wing Span 50 feet
    2. Wing Chord 48" Root and tip ribs. Rectangle. KISS. (Wing area 200 square feet)
    3. Length 18 feet
    4. 23013 Airfoil (very little, if any, pitching moment)
    5. One strut on each wing panel
    6 Marske Carbon Rod, E-glass spars. Spar located at CP of airfoil (30% if I remember correctly).
    7. 1" Foam Ribs in Warren Truss (45 degrees)
    8. Nose Ribs - 1 1/2" foam on 16 inch centers. Wooden strip leading edge. No D-tube. KISS
    9. Kevlar tape rib caps (KISS)
    9. Tyvek covered surfaces - heat shrinked. Possibly Tufflite
    10. Tail Boom 3" x 12" x 12 ' (or 13') foam, a carbon rod in each corner, plywood spar caps, phenolic blocks for wing and tail fittings, all wrapped with 2 plys of glass.
    11. Wing panel spars mounted directly to boom with simple 1/8" 6061T6 fittings
    12. Horizontal stabilizer 96" span, 36" chord (root and tip) made with 1" aluminum tubing (no airfoil). Elevator the same. KISS
    13. Vertical stabilizer 60" tall, 36" chord (root and tip) made with 1" aluminum tubing (no airfoil) Rudder the same. KISS
    14. Ailerons - 12 feet in each wing panel starting 10 feet from root rib. 12" chord (25% of wing chord). Torque tubes
    15. Cockpit 24" wide - like the Hart Ultrafloater (see photos at Hart Aero Ultralight and Light Sport Aircraft) without vertical triangle tubing at rear of cockpit area. Instead 2" alumimum tubing triangles will be part of cockpit tub like the Archaeopteryx. Top of triangles will attach to two fittings on main spar located at CP of airfoil (which is also CG of loaded aircraft). If weight of cockpit pod is suspended from CP (main spar) of airfoil and CG of aircraft is located at same point, glider would be able to accommodate a pilot of any weight without need for ballast or CG check (as long as spar will handle g load). Logic tell me anyway.
    15. Nose skid and two main wheels (no wing runner needed) one either side of cockpit pod (behind CG). Possible nose wheel if max weight limitation permits.
    16. Tow hooks on nose and rear of cockpit pod.
    17. No flaps. KISS
    18. No spoiler. (KISS). Glider should slip, and sink like a brick, with the slab tail boom. Slips are good. And fun.
    19. No dihedral. KISS
    20. Rudder bar. KISS
    21. No dihedral. KISS
    22. Droop wing tips.
    23. Vortex generators on wing to lower stall speed even more (if they would lower the stall speed even lower).
    24. Contoured foamed seat in the cockpit pod for those 10 hour flights. (I'll be returning to Tucson and 8k thermals).
    25. Built in record at Zapata, TX in FAI class. (Google Gary Osoba).


    Following is provided:

    Static Margin - 11.87% (which puts the CG (at MTOW) and the CP of airfoil at the same location).
    MAC - 48
    Sweep at MAC - 0
    Wing Root LE to AC - 12
    Wing Root LE to NP - 20.09
    Wing LE to CG - 14.41
    Tail Volume - .45

    MTOW - 330 lbs (155 empty with 175 lb pilot - me). But designed for more (see 14 above) if possible.

    Wing area - 200 square feet

    Wing loading at 330 lbs - 1.575
    Span squared at 330 lbs -.126 (Very low sink rate)

    Questions....in keeping with the spirit of "there are no dumb questions"......

    1. Since the load on the strut of a wing is determined by the wing panel load (half the MTOW) divided by the sin of the angle of strut/wing attachment (acccording to Orion in a message dated February 20th, 2008) do I make the attachment at the highest or lowest pounds on the strut? If I make it at the highest that would take most of the weight off the root attachment. To me that seems logical. Does logic apply in this case? Also, when determining the lbs on the strut with a spreadsheet comparing different angles some of the numbers are negative. See below:

    Degrees lbs 165/sin angle (330 MTOW 1G)

    30 -167.00
    35 -385.35
    40 221.44
    45 193.91
    50 -628.87
    55 -165.04
    60 -541.32
    65 199.56
    70 213.21

    Since trig was not my best subject, though not my worst, again I must resort to logic. First, logic tells me to use absolute numbers.
    If I do that, I'd make the attachment at 50 degrees, if indeed, I use the highest number. However, if I make it at 60 degrees more of the wing would be supported and there would be less stress on the outer portion of the wing with a loss of only 87.55 lbs on the strut itself.

    Where do I attach the struts and why?

    2. Will Kelvar tape be sufficient for rib caps?

    3. Will the tail boom constructed as described support all side stresses of aggressive slipping and stresses generated by the tail group with a 23013 airfoil? I do NOT want wire braces anywhere. A Skypup uses a 4x10 spar of foam with spruce spar caps and there has NEVER been spar failure in 30 odd years. However, a 50 foot span wing using the same spar would weigh to much. A 6 or 8" round tail boom of 6061T6 would probably be strong enough but the glider wouldn't slip as well as a slab sided boom. And, without spoilers to alter the glide path, landings - especially outlandings - would be touch and go. Or, at least touch.

    I thought of a tail boom made in accordance with Mark Stull's instructions in the Composite Tube Method thread. However, it's round so again, glider would have limited slip.

    I thought of making an I-beam out of plywood for the web and spruce or fir for the caps, put in carbon rods in the corners, flush out with foam and cover with a couple of plys of FG. Much to heavy.

    Ahhh...maybe the best just hit me. A Marske carbon rod spar. Sort of. 3x12" foam. Notch corners for carbon rods. Inbed hard points in foam. Wrap with 2 or 3 plys of FG.

    How many plys of what would I need to have the strength needed for the boom if I used the 12" Marske spar idea above?

    4. A 50 foot span slow speed glider will have a roll rate of exactly.......well, put it this way. I'll use a 3 minute egg timer to get the exact roll rate and let everyone know. Is there a practical limit as to how long I can/should make the ailerons to maximize roll rate? Would a small amount of dihedral help maximize roll rate? Is there a particular dihedral percent that would maximize roll rate?

    5. Can I use 3M's mylar tape for attaching ribs to spars instead of epoxy (KISS)?

    6. With the big wing I need a LOT or rudder to overcome yaw. The vertical stab is 60" tall. Suggestions for the chord of the rudder would be appreciated. Same for the elevator.

    7. My preference for the main spar is a 6061T6 tube (KISS). However, I think it would be to heavy. And, it would have to be spliced. Not good. Not practical. And probably not capable of higher g loadings for heavier pilots. Agreed?

    Suggestions, advice, and positive critique would be appreciated.

    I know one of the suggestions will be to get a few books on sailplane aircraft design and study them. I have some of the titles recommended in past messages. However, there are in storage in Tucson and it's been a while since I read them. I will study those texts again when I return to the states.

    The only access I have here in Peru for design questions is the Internet. I've downloaded almost everything online that pertains to design and have studied and exhausted that route. I think.

    I now to turn to this group and welcome any and all ideas, suggestions, positive critiques, and advice.

    On another topic, any glider pilots interested in discussing a sailplane designed to use a steam rocket to take off and climb a few thousand feet till the water is exhausted? Just think, launches for less than 50 cents (cost of water and electricity to heat the water). Aluminum scuba or oxygen tank would be mounted on the CG of aircraft so there would be no problem with weight and balance as water is exhausted. Simple. Easy. Cheap. Thrilling. Environmental friendly. KISS. And, yes, you can throttle a steam rocket.

    By the way, rockets on a glider aren't new..Google "Opel Rak". And, someplace hidden on my hard drive, is a steam rocket glider. Or, was that a dream?

    Thanks in advance to all and

    Best regards to all,

    Tom

  2. #2
    Registered User bmcj's Avatar
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    Re: Microlift Glider Project....

    Hi Tom,

    Welcome to the Forum!

    A 50' span and 155 lbs seems ambitious, but can be done with careful planning. You mentioned adding vortex generators. If you search this forum for VG's, you'll find some comments (from Orion, I believe) stating that VG's are typically added in response to an incorrect choice of airfoils. Given that you like light and slow (without the need to design for high speed), I think that you can find an airfoil optimized for what you want without the need for VG's.

    Good luck in your design and building and keep us in the loop with frequent updates.

    Bruce
    Last edited by bmcj; April 10th, 2009 at 01:38 AM.

  3. #3
    Registered User olgol's Avatar
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    Re: Microlift Glider Project....

    Quote Originally Posted by tinman View Post
    Suggestions, advice, and positive critique would be appreciated.
    Tom, this may sound too harsh, but go back to plan A, build a GOAT-4 (I think you meant GOAT, not BUG). If you are very ambitious (looks like you are), build a Carbon Dragon or ULF-1. You have way too much KISS in your project and not a lot from a micro-lift glider.

  4. #4
    Super Moderator orion's Avatar
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    Re: Microlift Glider Project....

    Regarding your paragraph labeled "#1", the fact that you got negative numbers should be your first clue that your calculations are incorrect. Furthermore, the exercise does not reflect an analysis based on a free-body diagram - that would have resolved all the loads and reactions so that you could get a proper representation of all the attachment and reaction forces based on the strut attachment position.

    Given your other questions and comments I'd probably second the opinion that you should first build a plans based design or possibly a kit, and then spend a few years studying design practices, structures and fabrication techniques before you even think of going down this road. History does not lie - too many folks have wasted a lot of time and money as a result of the belief that they could design and/or build an airplane without actually having ever done so in the past, nor having taken the time to get the proper experience or help along the way.

    Furthermore, given the limitations of the discussion board, non here can actually design your airplane for you nor give you any more in depth answers than can be covered in a few paragraphs.

    Doing this yourself is certainly possible but as I'm sure many here can attest, it can be a long road since the common experience seems to be that the more you learn, the more you begin to realize how much you actually don't know.
    "To live is to learn; to learn is to live" (author unknown)

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    Registered User BBerson's Avatar
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    Re: Microlift Glider Project....

    A D-Tube is required (or some suitable substitute) for wing torsional stiffness.
    Even with two struts.... a 50 foot wing would have a large cantilever outboard span that must have some torsion structure such as a D-Tube or tube spar or space frame structure.
    BB

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    Re: Microlift Glider Project....

    Actually, I think if he did the Warren truss right, it might take care of the torsion. But that's a big iff. I wouldn't use kevlar as rib caps with a Warren truss. You need something with a bit of depth so as not to buckle.

    If you want KISS, leave off the vortex generators and the drooped tips. Those are marketing bits unless very well done, I think.

    Suspect you would find it a lot easier to fly with a little dihedral.

    I think slipping as the only way to add a lot of drag is a bad idea. What are you going to do, slip all the way in? You'll drag one tip of that 50 foot wing! Suggest that flaps are not as complicated as you think. Or maybe spoilers, except for the structural issues, flaps are simpler. While I have VERY little time in a full size glider, my RC experience suggests that it's nice to get it on the ground reasonably quickly instead of just hovering a foot or two off the runway, in ground effect, waiting for the speed to bleed off or a gust to mess you up. If you're getting 40:1 in ground effect, it'll take 18 seconds to decelerate from 40mph to 30mph. Or about 900 feet of runway! I assume you don't want to smack the nose into the ground the way we do with RC.

    Anyway, this is a really big project just to design and you're not going to get it done in Peru working off the internet!

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    Re: Microlift Glider Project....

    Quote Originally Posted by lr27 View Post
    I think slipping as the only way to add a lot of drag is a bad idea. What are you going to do, slip all the way in? You'll drag one tip of that 50 foot wing! Suggest that flaps are not as complicated as you think. Or maybe spoilers, except for the structural issues, flaps are simpler.
    I think I would disagree with this part. Slips work fine in most aircraft for steepening (is that a word?) your descent. If you still need the slip below 50 ft, then you've got bigger problems. Even below 50 ft, you can transition to a wings level sideslip if you are trying to drop extra speed.

    Also, I think that basic spoilers would be simpler and lighter than flaps. Spoilers only need to disrupt the airflow above the wing (and below if dual surfaced) and are not subject to the same loads as those endured by flaps. Also, spoilers are very effective for glide path control. The only thing a flap can give you that a spoiler does not is an increased coefficient of lift for reduced stall speed.

    Bruce

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    Re: Microlift Glider Project....

    I'm coming into this thread late, and I'm no soaring expert, but something stikes me: for microlift and dynamic soaring, don't you need an aircraft that can maneuver quickly to take advantage of tiny areas of lift and changing conditions? That doesn't seem to jive with a 50' wingspan...

    -Dana

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    Re: Microlift Glider Project....

    If the wingtips are turned up about 30 or 40 degrees, the rudder can assist banking into a turn. This seems to work well on the RC gliders I fly that have rudder only (no ailerons).
    I bet 40 feet span is enough for an ultralight glider (155 lbs).
    BB

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    Re: Microlift Glider Project....

    Quote Originally Posted by Dana View Post
    I'm coming into this thread late, and I'm no soaring expert, but something stikes me: for microlift and dynamic soaring, don't you need an aircraft that can maneuver quickly to take advantage of tiny areas of lift and changing conditions? That doesn't seem to jive with a 50' wingspan.
    The 50 ft span is a result of designing to a high aspect ratio. It gives a more efficient wing for soaring and is quite typical of high performance sailplanes. Granted, a microlift craft may be able to forego the high aspect ratio and focus more on light wing loading. As far as maneuverability goes, sailplanes are not known for fast roll rates. However, they are known for tight turning radius in an established turn, but that is accomplished with a steep bank angle. They are also known for slow stall speeds so they can fly slow in lift (level or banked) without stalling.

    The truly high performance sailplanes also carry water ballast to increase wing loading when lift is strong (for faster dashes between lift during cross country flying). In Tinman's case, he would not carry water on a microlift craft because his ultimate goal would be minimum sink rate (through minimum wing loading) without the need to cover large distances. Local loiter is the goal here.

    Bruce

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    Re: Microlift Glider Project....

    Guess I'm missing something here. If you knock off sideslipping at 50 feet, and go to wings level, on a really clean glider that glides flat, aren't you just going to kind of drift to the side?

    As soon as you stop slipping there will be this really flat glide that'll eat up lots of runway as mentioned below. This is a problem even with models, which are strong enough to smack into the ground. Or, at least, it's a problem with the bigger models with higher aspect ratios. (I had one that was 17:1) Note, as mentioned before, if you are getting 40:1 (say, in ground effect), you want to land at 30mph (remember how light this thing is) and you are at 40mph instead, it's going to cost you 900 feet of runway! Assuming you're not landing out, in which it might cost you 900 feet of field or maybe 20 trees.

    I'm not sure how you can make spoilers simpler than flaps. In order not to ruin performance, they have to fit tightly on all sides and be sealed from air leaks, plus actuation is going to be more complicated.

    A flap might be heavier, but all you really need is a nearly triangular (or in some cases fully triangular) piece that is torsionally resistant. You might even be able to actuate it by just twisting on one end. And there's just the one hinge. The boundary layer is thicker by the time it gets that far back, and likely the flow will no longer be laminar either.

    Flaps are pretty effective for glide path control if they go down far enough. (I'm not talking about just 40 degrees or something, how about 70 or 80?)

    I'll admit that they're likely to be a little heavier, unless you end up putting in a bunch of weight to reinforce the edge of the spoiler bay.

    Suggest reading this article:
    http://www.soaridaho.com/Schreder/Stories
    Schreder_on_Flaps.htm
    Schreder on FlapsBTW, I've been in a Taylorcraft and a Cessna in some pretty good slips, where it was easier to see the runway ahead through the side window than the windshield. Or so it seemed. Works great. Those wings are much shorter and a heck of a lot higher off the runway, so you can slip until you are pretty close without clipping any runway lights. Plus once you stop slipping, their glide ratios are far worse, so they settle down ok.

    Quote Originally Posted by bmcj View Post
    I think I would disagree with this part. Slips work fine in most aircraft for steepening (is that a word?) your descent. If you still need the slip below 50 ft, then you've got bigger problems. Even below 50 ft, you can transition to a wings level sideslip if you are trying to drop extra speed.

    Also, I think that basic spoilers would be simpler and lighter than flaps. Spoilers only need to disrupt the airflow above the wing (and below if dual surfaced) and are not subject to the same loads as those endured by flaps. Also, spoilers are very effective for glide path control. The only thing a flap can give you that a spoiler does not is an increased coefficient of lift for reduced stall speed.

    Bruce

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    Re: Microlift Glider Project....

    BTW, I heard a talk by a very accomplished soaring pilot the other day. He says the new unlimited gliders are marvelous but it's really hard to make them turn with those looong wings. And that's at higher speeds with water ballast, which reduces the radius of gyration.

  13. #13
    Registered User bmcj's Avatar
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    Re: Microlift Glider Project....

    SLIPS: Though most people think of slips as a tool for altitude loss, it is really a speed control that allows you a steeper descent without gaining speed. Used properly, you can terminate your slip with your airspeed down to a point where the glider will continue to descend adequately with wings level. Also, a microlift glider will be very light with a light wing loading; penetration will not be a big factor for this type of craft.

    SPOILERS: a set of spoilers can be a simple plate on pivot arms that slides up above the wing when actuated. Actuation can be by a simple cabel pull with retraction by spring. Flaps will add drag but there is a transition phase during initial deployment where they actually create more lift and little drag, which is counter to what you are trying to use them for.

    TURNS: I have not flown a competition level sailplane, but any craft with a long wing has a tendency to steepen the bank due to the added speed of the outboard wing. At times, quite a bit of opposite aileron are required to keep from overbanking. I'm not sure if this is what soaring pilot was referring to.

    Bruce
    Last edited by bmcj; April 20th, 2009 at 12:37 PM.

  14. #14
    Registered User BBerson's Avatar
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    Re: Microlift Glider Project....

    Slips are not very effective on a high performance glider. Spoilers are required for a certified glider to bring the glide ratio down to something in the range of 7 to 1, I think.

    My G109 motorglider has huge dive brakes, the slips are ineffective.
    BB

  15. #15
    Registered User bmcj's Avatar
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    Re: Microlift Glider Project....

    Quote Originally Posted by BBerson View Post
    Slips are not very effective on a high performance glider. Spoilers are required for a certified glider to bring the glide ratio down to something in the range of 7 to 1, I think.

    My G109 motorglider has huge dive brakes, the slips are ineffective.
    BB

    I would definitely agree that spoilers/dive brakes would be hugely more effective than slips in a high performance glider (due to being designed with minimal wetted area on the fuselage). For lower performance ships such as the 2-33, slips can still be used effectively, though they may not get you down as well as spoilers would. In the case of a microlift glider, though, I think that you would still be able to use slips effectively.

    Bottom line (and I concede to you on this point) is that spoilers are probably the best option for any glider because of their effectiveness and simplicity. Slips, however, can still be used, even with spoilers deployed.

    In case anyone hasn't figured it out yet, I enjoy doing slips to landing!

    Bruce

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