I´m 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)
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,