If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#2
|
|||
|
|||
Sailplane wing joint
On 6/26/2019 1:13 PM, Sky Surfer wrote:
Hi all, I started studying Jim Marske's Composite Design Manual to understand composite techniques generally and glider construction in particular. My current topic of interest is the best design for joining two plug-in wings for a small sailplane, say in the 13 meter class. It seems the accepted method involves two overlapping main spar tongues that are pinned together by large-diameter pins in the fuselage. Typically, each wing root also has two short pins, near the leading and trailing edges, that slide into receptacles in the fuselage sides for alignment and for imparting lifting forces to the fusefage. Jim's Manual refers to these pins as "dagger pins" and says that they transmit ALL the wings' loads. He recommends that the main spar not even touch any fuselage structure. This last idea is counterintuitive and begs for clarification for my limited understanding of the topic. I recently emailed Jim and hope to get a response, if he's willing to do so. In the meantime, I hope the very knowledgeable people on this forum can weigh in with your thoughts about the reason for structurally isolating the joined-spar from the fuselage. Is this how it's actually done (asking those who really know gliders)? I would also appreciate other details about how you would join two lightweight sailplane wings, considering structural integrity (of course), weight, ease of rigging, and maintenance. Thanks in advance. FYI: The bulk of my email to Jim follows below: "Hi Jim, I think an "overlap spar with dagger attach pins" arrangement, shown on page F7 of your manual, would be good. I'm familiar the overlapping spar design only to the extent that I've seen other pilots assemble their "glass" sailplanes. The note at the bottom of page F7 says of the dagger pins, "There are four such pins located near the leading edge and rear spar (or trailing edge). These four pins transmit all loads from the wing to the fuselage. The main spar does not touch the fuselage structure anywhere." Can you please explain the importance of isolating the main spar from the fuselage? What is the downside, for example, of passing the two spar tongues under reinforced fuselage longerons so that the wings can lift there (where the spar touches the longerons/fuselage) in addition to the four pins? This is probably my top question from the manual. So I'm hoping that you can shed light on the rationale for not touching the main spar to the fuselage structure." - - - - - - Coupla notes, Sky Surfer... 1) rec.aviation.homebuilt is moribund...maybe not quite as "indubitably dead" as Monty Python's parrot, but darned close. Has been for years. The only reason I caught your post is because my Thunderbird is set up to notify me when any posts appear in RAH. 2) rec.aviation.soaring IS still active, and at least one "does it for a living" sailplane designer lurks and occasionally posts there. (Bob Kuykendall - designer of the carbon fiber, 15-meter, HP-24.) Additionally, several people with beaucoup years' experience rebuilding/repairing plastic sailplanes regularly check/chime in. (UH - Hank Nixon; JJ - John Sinclair) 3) My 2-cents (as a NON-practicing, degreed aerospace engineer) regarding Jim Marske's guidelines is - from a structural perspective - it's difficult to design a simpler, "continuously-aerodynamic-load-distributing" wing than imagining single-spar plastic sailplane wings ONLY bearing flight loads across the span. Arguably, Jim Marske's suggested approach seeks to approach this load-bearing condition...no struts; minimal introduced point loads along the spar span (2-dagger pins/side); etc. FWIW/FYI, the 15 meter sailplane in which I have most of my time pretty much does as Marske suggests (the late George Applebay's 15 meter, 1st-generation-fiberglass, Zuni): fore/aft lift/anti-torque/"dagger" pins in each wingroot rib connecting with receptacles in each side of the fuselage structure, while the tongue-and-tongue spars both have spar-end pins connecting into similar receptacles in the opposite wing's root rib. The wings are held together with a single through-pin located on the apar's neutral-load-axis at mid-span (rather than two pins each located near the root rib along the neutral axis; some with this design dispense with the spar-end-pins). HTH, and try rec.aviation.soaring. Bob W. --- This email has been checked for viruses by AVG. https://www.avg.com |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
AK-X swept wing sailplane | Mike C | Soaring | 22 | July 21st 18 03:05 AM |
For Sale: Used Sailplane Wing & Fuselage Cover | Scott Alexander[_2_] | Soaring | 1 | December 11th 09 04:40 AM |
Sailplane wing covers | Bob Greenblatt | Soaring | 0 | July 18th 07 01:51 PM |
How did he make this joint? | Michael Horowitz | Home Built | 4 | September 16th 05 06:14 PM |
How did he make this joint? | Michael Horowitz | Instrument Flight Rules | 1 | September 10th 05 02:07 AM |