Horizontal stab incidence

[CHARLES DEBOER]

Does anyone have to keep constant foreword pressure on the stick to keep the plane from climbing while adding power?  If I keep the air speed down to 40 or 45 mph it will fly fine but as soon as I add more power I have to keep foreword pressure.  I built the Stab. level with the top longeron of the fuse.  My weight and balance indicates that I am 28 % of the wing chord.  I have added 5 washers (5/16") to the leading edge of the H. Stab. but still require foreword pressure.

[scottiniowa]

Does anyone have to keep constant foreword pressure on the stick to keep the plane from climbing while adding power?  If I keep the air speed down to 40 or 45 mph it will fly fine but as soon as I add more power I have to keep foreword pressure.  I built the Stab. level with the top longeron of the fuse.  My weight and balance indicates that I am 28 % of the wing chord.  I have added 5 washers (5/16") to the leading edge of the H. Stab. but still require foreword pressure.

Generally these angles  (wing cord line incidence and H stab incidence) are measured to the lower station line.  Where often the wing maybe +2 to +4 degrees,  and the tail a minus X something.     I am not sure how this is called out on the XL plans, but am guessing it would be related back to the lower line.

there are lots of ways to set a data point (level line) but would be much harder if you use the “top longeron” as it is NOT on a level plane with the lower one (beneath the seat) or a right angle to the fire wall.

Just thoughts.

[moserwe]

I am a new member and I know this is an old post, but I am just trying to understand the wing incidence and how it is determined on the XL.  It seems from the plans that the upper longeron is maybe the level line, and that the longerons below the seat are parallel to the upper longeron, and that these two longerons are perpendicular to the engine fire wall.  To get to the point, my main question is, it looks like the wing incidence is set at the fuse mount attach brackets at 2 degs, but the wing root fitting do not look like they are parallel to the chord line of the wing profile, I have not measured the difference, but it could add several degs to the wing incidence angle.  Am I all wet? My son tells me just build it and stop analyzing it.

[Kamcoman77]

Recommend following Son's advice noted in last sentence of your post.

[DA Miller]

I agree with Keith, but in a little gentler and kinder way there are many Legal Eagles flying that were built to plans and seem to be getting along ok

[scottiniowa]

I am a new member and I know this is an old post, but I am just trying to understand the wing incidence and how it is determined on the XL.  It seems from the plans that the upper longeron is maybe the level line, and that the longerons below the seat are parallel to the upper longeron, and that these two longerons are perpendicular to the engine fire wall.  To get to the point, my main question is, it looks like the wing incidence is set at the fuse mount attach brackets at 2 degs, but the wing root fitting do not look like they are parallel to the chord line of the wing profile, I have not measured the difference, but it could add several degs to the wing incidence angle.  Am I all wet? My son tells me just build it and stop analyzing it.

I am not sure if your wondering if you should change something here?
Or just wanting to measure something?   

Not once have I seen that someone felt that they should change something on the plans for their flying aircraft.. So I would recommend to follow the plans for all of it, attach points, wing ribs, and the works.  I don't know if they (top and bottom) longerons are parallel or not, but that wouldn't make a difference as long as ALL the mounting locations are where they are supposed to be.

Every aircraft built has "one called out line", this line dictates everything to measure to.  This line could be most anywhere in space, but almost always is the base level line as noted. To spend time wondering why the designer picked a certain location for the base line...will in now help... AS your not going to change it anyway  without lots of work.. (project stopping work)

[moserwe]

First, I'm just trying to understand why the wing root fitting locations and structure around the fittings are different between the LE and the LEXL.  The LEXL has both front and rear spar web area, around the root fittings, filled in with wood, while the LE does not.  This looks to me like added weigh for no reason, be it not a lot but then I want a Legal Eagle.  This led me to look deeper at the differences between the LE and the LEXL wing root fitting location, and I found that the wing incidence was 2 degs on the LE because the root fitting locations are parallel to wing chord, while the LEXL fitting location adds 3 degs to the wing incidence for a total of 5 degs wing incidence.  This got me to look into why planes have wing incidence anyway.  From what I found wing incidence changes the pitch attitude of the aircraft, helps you see over the nose better.  Wing incidence also effect the drag of the aircraft.  Well, there you have it.  I'm not looking to change anything yet, just trying to understand why the changes were made between the LE and the LEXL.

Also, don't know if I should tell you all this but then you will know why I ask all these questions.  I was raised on the farm (built and fixed stuff), service rep for a farm machinery company (fixed manufacturing and engineering design issues), then for the last 26 year was a structural engineer for a company that makes big yellow equipment (fixed engineering designs before they got to the field, and sometimes after they got there).  I guess I'm a fix it guy that ask a lot of questions!  Sorry, please put up with me, I do want to build an Ultralight someday that is legal!  I used to build and fly RC Sail planes and RC Power planes before kids.  Also, built an Icarus II hang glider, out of wood off the farm - no money, while I was in college before I had any engineering mechanics classes, that's scary to think about!  Just lucky there were no cliffs to fly off of around home, just hills with lot of cow pies to dodge!  Thanks for all your help, I really have enjoyed reading all the post on this site!  Also, I'm good with numbers but not with words (can't write worth a darn!
 Can't spell either!), so sorry for the poor posting skills!

[scottiniowa]

First, I'm just trying to understand why the wing root fitting locations and structure around the fittings are different between the LE and the LEXL.  The LEXL has both front and rear spar web area, around the root fittings, filled in with wood, while the LE does not. 

  I'm not looking to change anything yet, just trying to understand why the changes were made between the LE and the LEXL.

 

It would seem to me, that they are not the same as they ARE NOT the same aircraft.  

 Just like a Dakota CUB, Javron CUB and Piper CUB, while all having CUB in the name, have  differences.

[Kamcoman77]

Only Mr. Milholland knows all the ins & outs of why the LE & XL are designed differently. I think the main reason the wing fittings are located lower on the XL wing is to move the wing higher for taller pilots. The wood filler is to transfer the wing fitting load to the upper spar cap. XL definitely has a better wing fitting to fuselage setup. It took me and two other guys almost 30 minutes to mount the wings on an LE because we had to support and align both wings to fit a single bolt through the fuselage bracket. XL uses one bolt per wing. I've never tried to figure out the wing incidence since builders of both planes say they fly fine. A few builders have changed the decalage by shimming the horizontal stabilizer nose up or down to allow for hands off cruising at a specific speed with no stick back pressure.

[Vince Carucci]

I logged on tonight to ask about the pitch of the horizontal stab and found this string. I'll start with my question first and then comment on the rest. 

Ignoring the elevator, what is the height difference from the front and read horizontal stab attach points to the top longeron? I assume the front is lower than the rear as it's my understanding that the rear wings pull the tail down in cruise rather than pull it up.

I'm very interested in what others have done especially after reading Charles initial post. His is described as level with the top longeron so it sounds like he may need to raise the front a bit for level flight at higher speeds, which contradicts the way I thought it should work. [Only the front mount is adjustable on the LE, while it looks like the XL is adjustable both front and rear.]

Moserwe is correct, the top longeron is level. As is the lower longerons below the seat [between sta. 2 & 3], and all are perpendicular to the firewall. It states clearly in the text "It should be level as this is the level line for the aircraft, and is used for the adjustment of the tail and wings." I presumed as much when building my LE, and Leonard actually added the word LEVEL to the top and bottom longerons in the XL drawings. They have to be level in order to have a +2 degree inline on the main wings.

I think Moserwe misunderstood some other numbers. The LE & XL both are +2 degrees nose high on the main wings. That's it... no more. Separate from that, Leonard calls for 3 inches dihedral to the wings. This means the ends of the wings are 3 inches higher than the fuselage attach points. Separate from that, Leonard describes how to use the rear struts to add 2 degrees of washout. That essentially puts a twist in the wing so the outer ends of the wings are flatter than the wing root. That should keep your ailerons functioning even as the inner wings start to stall. Do a search on the word "washout" in this forum. You should find a lot to read.

I think the wing fittings were lowered on the XL because of complaints from larger fliers that their head was touching the wings. I'm building the LE and I moved the fittings to the bottom. I used the control stick design from the XL [I never liked the LE controls]. Another place I made changes was at the upper seat post. I widened the fuselage to 24 inches at that point for shoulder room [more complaints by fliers]. You might be able to see it in the picture. The bottom remained at 20 inches per the plans.

The LE and XL are very-very similar. The XL is just a little roomier for the big boys. The wings are a bit longer and there are a few other small changes but they're essentially the same.

Enjoy the process, ask a lot of questions, build to the plans as much as possible. As Scott often points out, "one change leads to ten."

[scottiniowa]

Very well stated Vince!  And in reading through all of yours and then going back through many of the others, I see I did miss-spoke (speak) (type) on the upper cabin longeron. being parallel, I stand corrected and admit it.     Well Done Vince!  Enjoy the journey of building! It is a grand hobby!

[moserwe]

A picture is worth a thousand words.  The picture below shows the line that the wing attach points make for both the LE and the LEXL.  The wing attach line for the LE are parallel to the airfoil chord line, while the wing attach line for the LEXL is different by 3 degrees to the airfoil chord line.  The angle of incidence is 2 degrees for the LE, while the angle of incidence for the LEXL is 5 degrees (2 degrees fuse + 3 degrees wing attach line to chord line).

Hope the attach pic come thru.

[Kamcoman77]

Very nice drawing. Scott says it looks familiar. I wonder why? Scott may not be "The Man Of Steel" but he may be the mysterious "Man Of Iron"

[scottiniowa]

Very nice drawing.

It looked familiar,