KR> Drilling Holes in Spars - stress riser?
Looking at a simple vertical shear moment diagram for a wing fuselage arrangement like the KR(treating the spar as a beam) with a questionable but perhaps not unrealistic assumption that the vertical load on the two longerons is equal (this assumes the weight of the plane is centered within the fuselage including the pilot or the fuselage structure equalizes the loads) and the wing loading is symetrical, the vertical shear force on the spar inside the fuselage is zero and the bending moment is constant and at its maximum across the entire width of the fuselage. The vertical shear force is zero because of the assumption that each wing provides half the lift which is half the weight of the plane X G factor and that load is transferred to the fuselage structure at the longeron. Wesley I confess to being grossly uninformed on structural analysis and maybe at the dangerous stage of knowing only a little. I am very interested in the subject and thus read all I can and seek every opportunity to induce a discussion. As such I found your post stimulating - I made sketches as I read your post and what you say makes sense. I visualize the inverted aircraft with sandbags all over the wing - the pile getting biggest 3/4 the way out on each wing - and I am still struggling to see that the largest load is not in the centre (where left wing loads meet right wing loads) Maybe I should not see the loads opposing the weight of the fuselage as acting in the centre, but rather where the twain meet. Take care Steve J
KR> Drilling Holes in Spars - stress riser?
Stephen this is exactly how the stress and load factors are determined in the Marcel Jurca replica fighter designs. That being said however this designs have a one piece wing which is fastened to the fuselage the same as the Pazmany designs. This would be an easy enough change to make on the KR series aircraft but the purists out there are bound to flip there collective wigs at the mere mention of making structural changes even though they themselves are usually guilty of doing exactly the same changes as so well documented on the various web pages of Netters. I would also point out that many have stated over and over here that each KR is a one off machine, even if built exactly per plans. Study any and all information you can and after taking into consideration the snowball effect that any changes tend to create and what you want your aircraft to do performance wise (fast or sort field, stable enough to relax and enjoy the ride or constant attention to keeping it in the air), make your own choice. It would also be wise to get the opinion of the local FAA (or Air Ministry for those in other Countries) representative as they are the ones that shall make the final decision as to whether you will fly or have a very expensive lawn ornament. Doug Rupert
KR> Drilling Holes in Spars
The shear load is not affected. It is always the total weight that is being carried by the spar. Increasing the spacing between the spar caps does not affect the shear. + Thank you for that, advice on this level is very much appreciated. I Sometimes I see the neutral axis far away from the forces and thus the plane where loads are least - then again, logic (mine) suggests that loads must be the highest opposite forces along the NA. Where we need a 2 to 3" hole through the spar in the web surfaces (for control runs etc.) is it better to avoid the centre of the web? I am tempted to fit a filler block (extra pillar) between the ply webs in the area of the hole, but worry about creating a stress break (riser?). Pending a better solution, my intention is to place a reinforcing ring of the same ply around the hole - maybe change the grain direction. Steve J
KR> Drilling Holes in Spars
At 02:57 AM 7/3/2004, you wrote: >The shear load is not affected. It is always the total weight that is >being carried by the spar. Increasing the spacing between the spar caps >does not affect the shear. > >I Sometimes I see the neutral axis far away from the forces and thus the >plane where loads are least - then again, logic (mine) suggests that >loads must be the highest opposite forces along the NA. This is not correct. The neutral axis is very near the center of the spar and it is the best place to put holes. >Where we need a 2 to 3" hole through the spar in the web surfaces (for >control runs etc.) is it better to avoid the centre of the web? I am >tempted to fit a filler block (extra pillar) between the ply webs in the >area of the hole, but worry about creating a stress break (riser?). > >Pending a better solution, my intention is to place a reinforcing ring >of the same ply around the hole - maybe change the grain direction. A reinforcing ring is an excellent idea. I used them in the few places that I had to pierce the shear web. You should feather the edge (make it thinner) at the outer edges of the ring. This will prevent creating what is called a stress riser. Don Reid - donreid "at" erols.com Bumpass, Va Visit my web sites at: AeroFoil, a 2-D Airfoil Design And Analysis Computer Program: http://www.eaa231.org/AeroFoil/index.htm KR2XL construction: http://users.erols.com/donreid/kr_page.htm Aviation Surplus: http://users.erols.com/donreid/Airparts.htm EAA Chapter 231: http://eaa231.org Ultralights: http://usua250.org VA EAA State Fly-in: http://vaeaa.org
KR> Drilling Holes in Spars
This is not correct. The neutral axis is very near the center of the spar and it is the best place to put holes. A reinforcing ring is an excellent idea. You should feather the edge ... prevent creating what is called a stress riser. +++ Thank you Donald - much obliged Steve J
KR> Drilling Holes in Spars
It LOOKED like Steve Jacobs wrote: > to UNSUBSCRIBE from KRnet, send a message to krnet-le...@mylist.net. This is the ONLY way to unsubscribe! But I actually stuck that on the top of ALL KRnet messages, but forgot to put a space or a line under it to delineate it, so I'm the jerk, not him. I've had a few hours to cool down now, so I'll just take it off. I still really haven't cooled off enough to discuss it further though... Mark Langford, Huntsville, Alabama N56ML "at" hiwaay.net see KR2S project at http://home.hiwaay.net/~langford
KR> Drilling Holes in Spars - stress riser?
> > "A reinforcing ring is an excellent idea. You should feather the > edge ... prevent creating what is called a stress riser. " I can see where this would be needed in what I would assume would be the working part of the wing ( mostly outside the WAFs ). But not inside the fuse where we would be drilling holes for routing to the tail, or where I feel most changes should take place in jumping to the other side of the spar with controls or whatever. I would think that where the spar joins the fuse, there is one hell of a stress riser! Steve McGee EndeavoWI KR2SW
KR> Drilling Holes in Spars - stress riser?
I can see where this would be needed in what I would assume would be the working part of the wing ( mostly outside the WAFs ). + In the interest of us non-structural types getting the facts straight and not breaking our necks: I would have thought that the further outboard we go, the lower the bending loads on the spar - thus the lower all the stresses (compression, tensile and shear). Is that not why the spar can be tapered? Surely the point of max stress for any beam or truss is point where the load works through the longest moment arm - in our case, right in the centre of the airplane (for spars). I can see that the fuselage structure may have a minor influence on the spar stress analysis but I figured the fuselage is not contributing anything meaningful, it is designed for structural integrity in its own rights (mainly for/aft axis) with the gussets and doublers in the spar /fuselage area being there to keep the fuselage attached to the wing. If anything, the spar is a significant contributor to the fuselage strength. Sorry to keep tugging at this one, but it is important in my application. I want to put the elevator push-rod through the rear spar and the rudder cables down the centre through both spars. That way all the controls go down the middle, the antenna (RF) leads all go down one side (over the spars) and the electrical power supply wires have max separation by going aft way over on the other side. Hopefully that will keep the "noise" from strobes /beacons /pumps away from the antenna leads. The input from Donald R has me convinced that I will be Ok with a small hole in the centre of the front spar (Just enough for two rudder cables); plus a hole through the rear spar (enough for two cables and the push rod) both holes with tapered (feathered) reinforcing rings both sides of each spar. Take care Steve J
KR> Drilling Holes in Spars - stress riser?
Looking at a simple vertical shear moment diagram for a wing fuselage arrangement like the KR(treating the spar as a beam) with a questionable but perhaps not unrealistic assumption that the vertical load on the two longerons is equal (this assumes the weight of the plane is centered within the fuselage including the pilot or the fuselage structure equalizes the loads) and the wing loading is symetrical, the vertical shear force on the spar inside the fuselage is zero and the bending moment is constant and at its maximum across the entire width of the fuselage. The vertical shear force is zero because of the assumption that each wing provides half the lift which is half the weight of the plane X G factor and that load is transferred to the fuselage structure at the longeron. ref: section 5-8 Shear and Moment Diagrams, Mechanics of Materials, 3rd Ed. Higdon, Ohlsen, Stiles, Weese and Riley, John Wiley & Sons, NY, copyright 1976 - Original Message - From: "Stephen Jacobs" <ask...@microlink.zm> To: "'KRnet'" <kr...@mylist.net> Sent: Saturday, July 03, 2004 3:24 PM Subject: RE: KR> Drilling Holes in Spars - stress riser? > I can see where this would be needed in what I would assume would be the > working part of the wing ( mostly outside the WAFs ). > > + > > In the interest of us non-structural types getting the facts straight > and not breaking our necks: > > I would have thought that the further outboard we go, the lower the > bending loads on the spar - thus the lower all the stresses > (compression, tensile and shear). Is that not why the spar can be > tapered? > > Surely the point of max stress for any beam or truss is point where the > load works through the longest moment arm - in our case, right in the > centre of the airplane (for spars). > > I can see that the fuselage structure may have a minor influence on the > spar stress analysis but I figured the fuselage is not contributing > anything meaningful, it is designed for structural integrity in its own > rights (mainly for/aft axis) with the gussets and doublers in the spar > /fuselage area being there to keep the fuselage attached to the wing. > > If anything, the spar is a significant contributor to the fuselage > strength. > > Sorry to keep tugging at this one, but it is important in my > application. I want to put the elevator push-rod through the rear spar > and the rudder cables down the centre through both spars. That way all > the controls go down the middle, the antenna (RF) leads all go down one > side (over the spars) and the electrical power supply wires have max > separation by going aft way over on the other side. Hopefully that will > keep the "noise" from strobes /beacons /pumps away from the antenna > leads. > > The input from Donald R has me convinced that I will be Ok with a small > hole in the centre of the front spar (Just enough for two rudder > cables); plus a hole through the rear spar (enough for two cables and > the push rod) both holes with tapered (feathered) reinforcing rings both > sides of each spar. > > Take care > Steve J > > > > ___ > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html > >
