DE elevator area modification

[Gjsteube]

I'm about to build my DE Elevators and from what I'm reading it could use a little more elevator authority. Piper J3 has approximately 11.7 sq ft area. Any thoughts about building mine to same area as cub?

[Tom H]

We built DE Stubby tail feathers as per plans.  In our experience, any deficiencies in the elevator effectiveness is due to a too forward flying CG.  Recent discussion concludes that CG should be located at about 30% of the wing cord back from the leading edge.  Stubby's CG is somewhere around 26%, and we think that leads to up elevator being not as effective as desired (this is all during power off, low speed, as during a stall or at landing).  During flight testing, we modified the elevator linkage to allow about 45 degrees up elevator deflection, which helped.  We also adjusted the nose of the horiz stab down as far as it will go, which also helped.  We would like to get the flying CG nearer to 30%, but there are no desirable ways for us to do that.   Another change that would help would be to raise the horiz stab spar a bit, but that requires changing the support wires.  We may eventually try that.

I don't know, but it seems that increasing the elevator area may increase its authority, but may decrease vertical stability, i.e., make it more sensitive.  The airplane seems to fly well at anything above near-stall speeds.

[MrG]

Tom is smack on the money - the only thing need doing to the Horizontal is its angle of attach to the main plan (Horizontal decalarge)
If you look here there are some photos https://goo.gl/photos/j87cSBW8Z3zVkQge6 of my mod were the nose was taken down to the
fuse and the rear post was about 1.25 inches high (i can get my measurements if you need)
The drawings do not show this in the build for the fuse  and the mount posts - also take into account when build the Hor.Stabilizer
that the mount points will be out as you add/make it all on a flat surface - this keeps the bolts holes in both straight and the distance
if measured flat and after dropping the nose shortens (bolt hole to bolt hole) about 1/8inch which will cause stress if then bolted up

That will fix the amount of down force to counteract the natural roll in the main wing to were it got me hands off flying at cruse - we still
have to address the COG issues for the plane and like Tom would like to get our COG back and wish i shortened the nose about 2 inches
knowing what i know now. I dont think i have as much weight up front as Tom and speaking to Bubba Flairs he is also cutting the front of
his fuse 5 inches to do the same

Drawing of Hoz Mods

[Gjsteube]

Awesome, so what did you end up with on the horizontal stabilizer angle of incident?

[rfeenstra]

I built  mine with 2 degrees negative incidence on the stab, 2 degrees down thrust on the engine, and approximately 5 degrees positive incidence on the wing.  Do note that in the plans, the wing incidence is set to, i believe, 2 degrees positive using the flat bottom of the wing as the reference line.  The normally used reference is the line from leading edge to trailing edge.  That comes out to the  approximately 5 degrees positive incidence I mentioned.  With these settings, and the CG at about 30%,  I was able to flare and land nicely dead stick.  A lot of guys have expressed the need to have a little throttle in to get the plane to flare.

[MrG]

@Gjsteube Its about 1 1/4 over 23 inches ( centre of bolt to bolt ) don't have CAD installed to give you that angle - but the 1:60 rule converted to metric here is about 2.5 ?
mine wing is as per drawings. , i think my CofG is about 25/26% slowly adding weigh and hope to re-weigh plane next week - cant wait to be able to land with out a bit of 
power,  unless you come in fast - have to say thou it flies so nice now the Empennage is correct. Not sure why the Emp mod has not been added to the  drawings. 
its pretty important info to make the plane fly correctly and is totally seperate to the CofG issue

[Gjsteube]

Thanks again for all the input, I do appreciate it.