A rambling wing building discussion

[grdev]

on my DE I didn't raise the rear spar, frankly I was new to building and I never heard of it before. My leading edge did develop some dimples after I set the washout, but I didn't connect the dots until I built my wings for my Wagabond. I learned there it is standard practice to raise the end of the rear spar about the height of a 2x4 block under the last full rib.  I raised the rear spar and then glued all my ribs in place. I plan to do the same on my XL I will have to double check to find out just how high the rear spar should be raised

[Sam Buchanan]

on my DE I didn't raise the rear spar, frankly I was new to building and I never heard of it before. My leading edge did develop some dimples after I set the washout, but I didn't connect the dots until I built my wings for my Wagabond. I learned there it is standard practice to raise the end of the rear spar about the height of a 2x4 block under the last full rib.  I raised the rear spar and then glued all my ribs in place. I plan to do the same on my XL I will have to double check to find out just how high the rear spar should be raised

XL-58 has zero washout. The wing was assembled flat on the table.

[grdev]

I know some pilots prefer washout, some more some less and some not at all. It is my understanding washout helps during stall situations. I'm not knowledgeable enough   on the subject to recommend it one way or the other.  Looks like the drawings on page 56 call for the wing tips to be flat, just how much washout that is, I don't know.  I will have to ask Leonard what he suggest. I also didn't see how much dihedral he calls for, will have to read a little more.

[grdev]

Wing washout reduces the lift distribution across the span of the wing. this causes the wing tip to stall later than the wing root thus aiding in more aileron control in a stall situation. It also helps reduce the chances of you plane going into a spin. Now that is basically my understanding of why there is washout built into wings. Again I know very qualified pilots that built there wings with no washout at all. My one buddy claims with out washout his take offs are much shorter. I guess it all boils down to preferences

[Sam Buchanan]

I know some pilots prefer washout, some more some less and some not at all. It is my understanding washout helps during stall situations. I'm not knowledgeable enough   on the subject to recommend it one way or the other.  Looks like the drawings on page 56 call for the wing tips to be flat, just how much washout that is, I don't know.  I will have to ask Leonard what he suggest. I also didn't see how much dihedral he calls for, will have to read a little more.

If the wingtips are in exactly the same plane as the root tips, that is zero washout. But the Eagle instructions can be a little confusing because they call for the wingtips to be "flat". Flat in this instance means level with the rear top fuse longeron. this will result in 2* washout since the root ribs are set with a 2* positive incidence relative to the rear top longeron.

However, I rigged XL-58 so the tip ribs and root ribs are at the same angle, in other words, zero washout. This means the wing is "straight", no warp. Details here:

http://eaglexl-58.com/assembly-1.htm



I did use the recommended 3" of dihedral:



Dihedral gives the rudder more authority to bank the wings which makes it easier to overcome adverse yaw.

Washout is often recommended so the wingtips will stall at a slower speed than the wing root which retains aileron authority deeper into the stall.

However, stalls with the XL are non-events, the thing really doesn't stall, it just mushes even with zero washout. I prefer a straight wing if there is no aerodynamic reason driving washout. A straight wing has less drag, and that is a good thing.

[Rich Snyder]

OK, here's my 2cents on the application of varnish. First; don't use materials that will mess with your varnish. I plan to use Stewart System covering system. Their products don't melt varnish. No worries. Also; when applying my leading edge skins, I did not go to the trouble of taping off the inside  areas that would not be varnished due to the fear that T-88 would not stick to the  varnish. Instead I took an auto body filler applicator/squeegee that is smooth and stiff, to spread a THIN coat of T-88 over the entire inner side. That T-88, of course, has no inclination not to bond with the T-88 on the nose ribs. The leading edge skins are as light as varnished skins and probably as waterproof as my kayak that I built with System 3 epoxy. (They make T-88). 
As far as building in the washout as you assemble the wing: NOW YOU TELL ME. If an Eagler is thinking of having washout in the wing,  it sounds like a good way to prevent stress in the wing when tweaking it later for final assembly. Rich.

[Sparrow]

The drawing shows a 1 inch difference between the front and rear on the fuselage drawing setup for the attachment points on the wing spars. LE XL that is.


I keep trying to insert a picture and I have had no joy so far.  I have used the "Attach and other Options" below and on the left and the location of the picture chosen is shown but there is no picture showing up in the review.  It is LE-XL Sheet 6 2 degree angle shown at wing attach point.  Incidence angle.

 

 
I guestimated a 1 inch lift of the trailing edge of the rib on the outboard end would allow for the twist the plywood will have when the rear strut is pushed up or extended to twist the trailing edge back to zero degrees when the bottom of the fuselage is level.  Of course the ribs all have to be glued up and the wing basically just lacks the plywood before twisting it to accommodate the twist required when it is rigged.  Noob I am happy someone else has recognized this as a built in dimple maker if it isn’t compensated for during the glue up.
 
Thank you Sam, all instructions tell us to make it all flat.  I know someone said in a post I read that to prevent the wing leading edge plywood from dimpling a specific sequence had to be followed when twisting the wing tip to give a zero degree from fuse leveled.  I think they said the last thing to do was to extend the rear lift strut to push the trailing edge up after the front strut was set to hold the wing tip to the 3 inches of dihedral.
 
I will be putting the twist in after everything else is glued up.  The plywood is the last gluing I will do.  I will have all the diagonals (drag braces) and compression ribs in place and the wing will be square before I twist it.  It’s a plan and I guess I will find out if it works about a year from now.
 
Noob you are correct about the washout.  The main reason for it is to allow the wing to stall at the root and the stall of the wing to progress outward to the outer wing tip. What this does is allows for aileron functionality when the main part of the flying surface is stalling.  You can still control the roll as the aircraft begins to stop flying.  From the drawings the incidence angle is 2 degrees at the wing attach point on the fuse. If I am not correct regarding this, someone chime in and correct my current understanding.
 
Briefly off topic, I do intend to install VGs (vortex generators) all along the leading edge of the wing.  When I get serious about that I will start another thread to address design and placement.  There is already a vast body of work already done regarding this subject.  This also improves the low speed characteristics of the flying surfaces.
 
Thanks for the input.  John

[Sam Buchanan]

Wow....John, you must be an engineer by trade as evidenced by your drawing. Way too much thinking going on here.     There is no need to analyze angles and such, unless you just enjoy doing that sort of thing.

The XL is a very simple aircraft that only requires very simple construction techniques. Think yardstick....not protractor.

[Jlwright]

Probably a good thing John and I aren't building a plane together. We would never get it finished. Engineer and tool and die maker would not make a quick build.

[grdev]

John, you might find that if you don't assemble your wing with the 1" lift you have calculated, you may have trouble aligning your ailerons in the pockets With the eagles as you know you cut the aileron ribs after the wing is built. With the ribs, compression struts installed with the washout built in I would think you would reduce some stress in the wing structure itself. this information I was told from some guys who built Piper cones such as the Cub, and PA20. That's the way I did my Wagabond wings, of coarse I have aluminum ailerons and aluminum leading and trailing edges. This is a photo of my Wagbond wing and if you look closely towards the end you can see the 2x4 block I had under the rear spar during construction.

[Sparrow]

Hi Noob,
Thank you.  That does make sense to build the actual intended twist into the wing when everything is being glued up and the actual diagonal measurements can be kept correct to keep it square but have a slight helical angle built in.  (In actuality the wing tip will lose an apparent 0.017” from the cord length if a horizontal line is drawn through when it is twisted 2 degrees but this can and should be ignored when taking diagonal measurements.)
 
The actual shift of the top “D to the rear and the bottom “D” to the forward is calculated to be 0.120” at each point.  The helical angle along the leading edge is 0 degrees 26.7 minutes of angle.  Knowing this I understand why dimpling can occur in some cases.  The plywood is being moved from a rectangle to a parallelogram with a 1/8” displacement of the corner.
 
This thread has turned into a wing construction side discussion.  Should we open a thread to discuss the impact of adding washout to a wing tip when the incidence angle at the attach point is 2 degrees and how we build the wing with washout already in it so the structure isn’t torsioned around and put in a stress/strain and having aileron clearances changed and bearing alignment slightly made misaligned?
 
If all agree to a new thread then where should it be placed?
 
Thanks, John
 
PS: That is a beautiful piece of craftsmanship on the wing Noob.

[Sparrow]

Hi Guys,
 
I had to chuckle after reading all the responses.  Yep, I am a retired Mechanical Engineer that is used to manufacturing to 3 micron tolerances and designing equipment and measuring devices that are statistically capable to +-6 standard deviations.  This works out to no more than 5 defective parts in a million. Design a machine to do that and make 74 bearings a minute, 24 hours a day, 7 days a week and see if it doesn’t drive one a bit nutty.  We manufactured over 800,000 bearings per day on our automatic lines.
 
A small explanation is in order.
* Yes, I enjoy analyzing things.  Some people like watching sports and I enjoy watching “How Its Made and The Big Bang Theory”.
* I broke down the fuse into all the various angles to actually calculate the true theoretical length of all the members and to pull some buckling analysis on some members I thought could be reduced in cross section to additionally reduce weight.
* The main reason for my concern with the washout introduced after the structure is built is because of leading edge plywood dimpling.  I truly wanted a clear understanding about what was actually going on there and how it might be compensated for during the build so it never occurs.
* When I build, it will be with a yard stick and I will change some of the build techniques to compensate for issues that could occur after rigging.
 
Noob, we are building it together because you have given great input for my consideration.  Sam, your sage advice is always turning on my light bulb.  I intend to build once and it is correct.  It will not be too long and I will feel comfortable with the direction I choose.  I served as a Sr. Manufacturing Engineer making product and designing machines to make product for Eaton Cutler Hammer electronic switches to Cummings diesel turbo chargers and 6 cylinder head manufacture to TRW steering and suspension components and Torrington elastohydrodynamic bearing systems on bearings up to 14 feet inside diameter to lastly Federal-Mogul engine bearings and cam shaft production.  So, you get an idea of where the obsessive compulsive behavior comes from.  It is truly a freaking curse.
 
I am very appreciative of all of you helping me understand the issues you dealt with and how you resolved them.  I believe that one can learn from others and know if I stick my hand in the fire it will hurt because someone who did that told me so.  I truly trust but I always verify.  John 

John

[Steve]

For Gil Devault:

John,If you want to start a new thread it is fine with me. You will find some interested in the finer points to why things are done, and others won't. There will be mutable reasons pro and con for anyway you approach anything you do to your aircraft. Debate and discussions are a good thing to have when it comes to hanging your butt 2000 foot or more in the air.
A lot of first time builders, I would think are low time, or no time fliers. For them I would not deviate one fraction from what Leonard calls for.  For the more experienced pilots they know what stalls are and what to expect.

For me personally ,IMHO, I like to know why some things are done a certain way, as I have found what I thought was not all that important could come back to bite you hard.

SHK

[Sam Buchanan]

John, did you ever visit plants in Athens, AL? There is an abandoned Cutler Hammer plant and a running Federal Mogul plant within a mile of my keyboard.

[rockiedog2]

Hi guys
On the washout maybe this will help you decide what you wanta do
I first built mine with a stick under the rear spar outboard end to build the washout in so no strain built into it like some of you are discussing here. I flew it that way for some time. Flew fine no probs. I also installed a rodend in the butt of the rear lift strut for fine rigging adjustment which came in handy. I did/do use it and recommend that if you know what you're doing when you install it, if you don't then I don't recommend it. I later shortened that rodend and took all the washout out of it. Made it flat. Still flew fine couldn't tell any diff in roll control at stall. There may be some gain in performance due less drag/more lift but I couldn't tell it subjectively and didn't bother to do any testing. Couldn't tell any diff in the dimples after warping the wing the 2 degrees or so. Personally I don't see any reason to put any washout in the wings. It'll work just fine either way. As for the dimpling I think it's likely gonna dimple regardless of washout unless you put extra nose blocks inbetween the ribs and thats more weight/work.  I mean, it's .8MM and 15" between ribs and normal temp swings will probably be enuf to dimple it. Mine is dimpled always has been I expected it and it never bothered me still doesn't. But i dont care about show, only go. It has no noticeable effect on handling or performance.
The engineering you guys are capable of just floors me. I've found that I can eyeball 1/4", 3/8" and 1/2" as close as a pencil line width so rarely use my ruler for those anymore. Now that's a liberating feeling.