More questions about wing numbers....

[ArcticDave]

I cannot seem to cut and paste an URL lately so to see the site I use for distance / angle calculator you'd have to google search    angular size calculator   .

This it..?

http://www.1728.org/angsize.htm

Thanks for finding that Dan. Saved it to my bookmarks.

[Tom XL-7]

I was fiddling around ( good at that ) with some sketches and drew a few adaptors that would raise the front fuselage wing mount an inch. Totally reversible if desired.
Tom XL-7
 I have some changes I want to do to my build but have had a lot of good advice not to.  So example: I want to use a torque tube to operate ailerons.
But I will weld the pulley ready plates on the fuse and have the ability to change to the tested cable system. 
If some of my ideas are not so bright I want to be able to backtrack as painlesslly as possible. I have seen 3 legal eagles, A double , and Sam's XL.
Found them all pleasing. Would be proud to match any of them.

[Poorman2]

David, look on page 8 under the heading struts and you will see that the dihedral is 3 inches not 3 degrees. Also the cord line is not the bottom of the wing, so it is about 3 degrees up from the bottom if I remember correctly added to the 2 degrees built into the fuselage and it is about 5 degrees total. Also on page 34 the rear spar is called out at 5 1/4 inches not 5. My wings are drilled to the specs called out on the plans on page 35. I have no dought it will fly fine as many others have already. I hope I have helped.

[Dave Stroud]

Thanks for those clarifications, Poorman.

[Poorman2]

Your more than welcome.

[ArcticDave]

Didn't even think of the fact the wing bottom is not the chord line. If it's at or close to 5° already,  I'm not messing with it any further. Thanks Poorman!

[Dave Stroud]

While we're at it, why do you think the plans call out the wing spar to fuselage attach fitting to have it's mount hole 2" out from the end of the spar ?  The fuselage mount end of things only needs 1/2" to clear. If the 2" fitting dimension was brought down to say, 1"or 1.5", there'd be less stress on the end of the spar and still room to attach things. Just wondering if that extra space is needed for something.

[John Reinking]

DS:  Was wondering the same thing.

[Tom XL-7]

just speculation but the 2" for the spar mount hole may just be a carry over from the legal eagle. Both wings mounted to a single hole. actually two, one front and one rear. Yes, there would be an overlap and one wing would be a mount thickness in front of the other.

For those readers with the question of which one to build XL or LE keep in mind that the xl not only picked up some wing area but the drawings contain some popular builder mods and running improvements. Think about mounting both wings at once. 
Tom XL-7

[Darren C]

While we're at it, why do you think the plans call out the wing spar to fuselage attach fitting to have it's mount hole 2" out from the end of the spar ?  The fuselage mount end of things only needs 1/2" to clear. If the 2" fitting dimension was brought down to say, 1"or 1.5", there'd be less stress on the end of the spar and still room to attach things. Just wondering if that extra space is needed for something.

It's to clear the cabanes.  See the last pic.

http://www.mykitlog.com/users/display_log.php?user=ontherun&project=2554&category=0&log=233329&row=75

Darren 

[Dave Stroud]

And there's the good answer. Thanks, Darren. Not an issue with my squared up cabin so I figure I can shorten my fittings some. 

I start the fuselage next week and a couple of days ago I gaffed a real nice building table for only $120 CAD. 10 feet by 30". A heavily built, wood topped retired bakery table with SS frame, shelf rack below and on casters. When the fuselage is done, I'll dump one of my older benches in the garage and install this against the wall with the casters off.

[scottiniowa]

While we're at it, why do you think the plans call out the wing spar to fuselage attach fitting to have it's mount hole 2" out from the end of the spar ?  The fuselage mount end of things only needs 1/2" to clear. If the 2" fitting dimension was brought down to say, 1"or 1.5", there'd be less stress on the end of the spar and still room to attach things. Just wondering if that extra space is needed for something.

When straps are used in the XL fashion  from the ends of the wing spar, There is not any undo stress being applied to the spars.
When your flying, the "stress" if you want to call it that, is trying to push the center together horizontally.  Or compressing the center..

A large (although) in this case "small" reason for space it to give ample room for your fingers installing the wing attach bolts.

Certainly are those that like things tight, and consider areas best if they are cause of a battle, but I don't think you will find this area under "stress" that would change by taking out 1/4" to 3/4"

I relate this somewhat like the kingpin on a semi tractor-   One small pin, pulling for millions of miles a load of 40-45,000 pounds...  If you reduce the pins/straps/and holes for the XL to match the % reduction of the 45K load, there wouldn't hardly be anything left.  

Looks to be an area where "if it is not broke, why fix it" 

[Dave Stroud]

Thanks for that, Scott. What are the most stressed areas on a LE wing spar in flight, please ?

[scottiniowa]

Thanks for that, Scott. What are the most stressed areas on a LE wing spar in flight, please ?

I am pondering this question Dave. In the mean time I will offer this.

• if there was a problem, we would have heard about it by now
• to really get down to the nitty gritty, one would have benefited  to be at the stress test of the wing.  I was not there, and even if I was,  how the test was done, can effect where this "most stressed" area shows its face. But have never heard that it was at the compression zone of the root. In fact have never heard that of just about any wing.
• While perhaps it would be nice to know this info on just about any wing,  when good enough is good enough, I am not sure what most can/or would do about it.. Sometimes, "more better" doesn't really make a difference than good enough.

Just the thoughts for the day! 

There are all kinds of books, some really large ones that deal with this question, but that is more of a design aspect than anything else.

[Tom XL-7]

Most importantly there is no professional engineers registration number with this post.
That means this is an opinion. Perhaps an educated one but no more than an opinion.
Therein lies the problem of changing things from a proven design. This wing and slight variations of it has been flying for a very long time.  possibly 30 - 40 years.
 
In a simple world and we don't live in one, there are two types of wing structures. Not talking about materials or methods, just structure.
  The cantilever wing is the modern one. heaviest loads are at the root, which is pretty easy to understand because there is no other attachment.  Landing gear loads could exceed flight loads. They are outrageous, the gear wants to tear right off backward.
  Then there is the braced wing we have. That can be old-time, like a kingpost and cables running everywhere, or strut braced like ours.
These have more drag but can be much lighter. 
 The vast majority of the lift is carried by the brace, so your highest stress will be in and around that strut mount point.
  An attachment may help visualize. Notice in the third sketch the spar loads go from positive to negative at the attach point.
That's where the action is. 
Tom XL-7