I would even settle for : "I know it happened because I was there and it happened to someone I know personally and here are some of the details." Hard to find even this much evidence that UL look-alikes are targeted by the FAA for enforcement.The problem is that the slightly illegal ultralights were only slightly grounded, so documentation is somewhat iffy.
Whoops I forgot about that! Looks like we need to do strength and drag analysis, since an attachment to our spar tube add more weight weight but it would make our gussets straight and as you said, on the neutral axis.The problem with the U-channel bolted to the bottom of the spar is that the bolt holes through the spar remove material at the most highly stress points (top and bottom).
Should we move the spar attachment bolt in the middle of the two spar attachment, or should the strut line fall between the two spar bolts?The problem with the U-channel bolted to the bottom of the spar is that the bolt holes through the spar remove material at the most highly stress points (top and bottom). The side gussets as on the LE, OTOH, have the bolt holes on the neutral axis of the tube so its strength is not as severely impacted.
Thank you for the very informative reply! Having the strut line midpoint the bolt line is very smart! Thank you!Ideally, the strut centerline will be centered to the hole pattern (could be any number of holes) on the strut:
Here, the green hole is new, and the gusset plate can be chopped off at the red line. Now, both bolts through the spar are carrying the same load. This is only an example. You might need three holes, one on the centerline, one each side. You will need to look at the allowable bearing stress (load on the bolt at each point divided by the bearing area, which is bolt diameter times wall thickness) on the spar tube to know how many bolts, and of what size, you need.
The yellow one is taken from Les Homan's YouTube channel, and the video can be found here :I looked at all the pictures posted and could find NO pictures of Legal Eagle spars. The one wooden spar shown was close but no cigar. There are NO holes in the spar caps at the strut on any of the 4 flavors of Eagles. They are all into blocking between the upper and lower caps. if there are holes in the caps the builder needs to start another wing
If the struts on high wing airplane can't stand significant compression, the airplane may not survive the first time it hits a strong downward gust. Unless it has a kingpost and more struts or wires.A high wing will have the struts in tension during flight; this will mean they are lighter and smaller. They will also tend to cause less interference with the wing than struts on a low-winged aircraft, which will need to be in compression in flight, so their size will be determined by buckling criteria, not strength, and their intersection with the upper surface of the wing will tend to cause more drag.
In either case, the presence of a strut may permit an increase in span or decrease in root thickness for the same wing weight or a decrease in weight for the same thickness and span, due to a reduction in the bending moment that has to be withstood at the root. The design of the fuselage structure where the strut joins the wing is also important. Where to put the strut on the wing is dependent on the lift distribution along the wing, but also on considerations like getting into and out of the airplane and, for an aircraft that needs to be transported by road, how the wing is going to be folded or removed.
I'm not sure I follow your calculations.Thank you for the very informative reply! Having the strut line midpoint the bolt line is very smart! Thank you!
Our wings would be creating 1700 lb of lift max at 4g so with two bolts per attachment, 8 more connecting strut tubes, and 4 connecting the strut to the fuselage each would be withstanding 85 pounds. I doubled this for safety considering that the strut-spar bolts will probably bear a lot more of the weight. I did the calculations then compared it to the bearing strength of aluminum and look like we can use 2 bolts!
Thank you for bringing bearing strength to our attention, as it wasn’t even on our radar (which is why this response took so long, sorry about that).
Thank you again!
PS. We’re worried since bearing strength doesn’t consider thickness so we’re calculating tear out strength right now : )
we are discussing two different things. My reference is to a picture of what RESEMBLES a Legal Eagle spar but appears to be cable braced due to the fitting bolted in. Eagles use wood compression struts and diagonal braces. Not cables.The yellow one is taken from Les Homan's YouTube channel, and the video can be found here :It is a Legal Eagle XL, as far as my knowledge goes, but it could be possible that he changed the design.