New wings for the Culver Cadet

[Dan Rhinehart]

Hi all,

As we all know a problem facing Culver owners during a wing rebuild is the partial delamination of the spruce spar caps from the plywood web. This is usually 1/8" to 1/2" deep. More often than not this is not caused from water damage but "just because".

I believe a very solid fix for this situation is to drill a 0.047" hole (the diameter of a 18g hypodermic needle) in the face of the spar cap at or slightly above the deepest area of separation (perpendicular to the top face of the spar cap). Then insert an 18g hypodermic needle in said 0.047" hole to fill (flood) the void (from the bottom up) with Hughes FPL-16A structural epoxy.

The reason for "flooding" the void from the bottom up is to eliminate air bubbles. Hughes FPL-16A epoxy has the consistency of cream and is white. In other words it is a viscous liquid rather than a jell like other epoxies, hence flows like water.

Also Hughes FPL-16A epoxy has been tested and passed the FAA prescribed boiling test unlike many other epoxies. Also due to its watery viscosity it penetrates deep into wood before drying. This stuff is flexible and is tough as steel. I once got some drops of of it on the hangar floor and had to use a hammer and chisel with a lot of elbow grease to get it off! And even then it took some of the floor with it!

[Dan Rhinehart]

Hi all,

I have been doing my homework on just what the differences are between the "hollow spar" wing and the "solid spar" wing.

I have a new spar that is dated manufactured in 1946 (written in pencil) as well as a hollow spar. To start off if you place the two over one another the holes are not an exact match for the landing gear attach points. (My landing gear hardware came out of the remains of a 1942 Culver S/N 415.) This hardware will not line up on all 4 landing gear attach points on the "hollow spar". The top inboard hole is about 1/8" off from fitting. It however fits on the solid spar perfectly.
 
Also if you place the spars over one another the attach points are slightly different causing a slight difference in dihedral between the "hollow spar" and "solid spar" wing. The "hollow spar" has slightly more dihedral.

As for what makes the "solid spar" solid. It has a 3 1/2" solid plywood block (outside grain running vertical) that runs from the root to just outboard of the 3/32" plywood doubler that extends to the landing gear attach points. It is in the center of the spar and the two main wing attach points run through the center of this plywood block. The landing gear attach points are totally inside of the spruce caps on the top and bottom of this plywood block. Also the bottom spruce spar cap is deeper on the "solid spar" wing (from the root to landing gear attach points). And the 1/4" vertical plates over the wing attach points are plywood with the outside grain going vertical.

The "hollow spar" wing has both the inboard and outboard main wing attach points are running through spruce rather than plywood and most of the holes are between joints in the wood caps. Also the 1/4" vertical plates at the main wing attach points are spruce (grain running vertical) rather than plywood.

I will send pictures asap. I used a plainer to CAREFULLY plain off the 3/32" root doublers.

[Dan Rhinehart]

Hi all,

Here is a picture of a hollow spar compared to a solid spar.
I covered the center pieces of wood with blue masking tape for the sake of being able to see the lamination lines in the hollow spar.

After further investigation I have determined that I was in error in stating that the holes in the hollow spar and solid spar do not line up. All of the hardware lines up perfectly. The solid spar is slightly 1/4" deeper at the bottom between the outboard main attach point and root. Also the lower spar cap is deeper from the root to just outside the landing gear attach point.

[Paul Rule]

I am not sure if this has been said before or not but there are no differences between the 'light' and 'heavy' spars outboard of the gear attach.  I do not know when the change was made or even if it was a consistant change.  I have a bare Helton spar and it is a 'heavy'.  I have several others but don't recall what they are.  The only advantage I can see is that the 'heavy' spar won't split in the filler wood between the two big attach bushings.   It is a good practice to push out those bushings every time the wing is off to inspect the inside bore for cracks.   On the other side of the coin, those cracks are not in the spar caps... just in the filler blocks in between the caps and probably indicate humidity expansion and contraction more then any over load or stress causes.

The helton spar I have has vertical grain plywood blocks all along the spar at each rib attach point.  I know the Culver Corp spars all had solid spruce vertical grain blocks at the same points but the large blocking was all horizonal grain.

It is possible the 'heavy' was a Helton thing or maybe a PQ-8 thing and over the years we have gotten them mixed together. 

Dan is that 'light' the spar I traded to you?

[Gregory]

Hi Neal,

I am a new Forum member, very much interested in Culver Cadet.   Do you still offer the plans for the STF?
How I can contact you?
My e-mail address is:  g.sachs@sympatico.ca.

Regards,
Gregory

[Phil Kite]

I been busy working on my wings and unfortunately many or most of the butt (90* such as rib to spar) glue joints are loose.  I’m considering removing all the ribs and starting with fresh spars.  I have a few questions to the wing building experts;
1)   Does the Culver wing have any washout?
2)   Were the original wings built in a jig, or does the steel tubing line everything up?
3)   If they used a jig, are there any drawings or old pictures?

Thank you,  Phil

[Phil Kite]

Here is a wooden wing we built over 10 years ago from ALL new spruce.  The one wing panel is almost the entire span of the Culver!  Any ideas of what it is from?

[Brett Lovett]

I been busy working on my wings and unfortunately many or most of the butt (90* such as rib to spar) glue joints are loose.  I’m considering removing all the ribs and starting with fresh spars.  I have a few questions to the wing building experts;
1)   Does the Culver wing have any washout?
2)   Were the original wings built in a jig, or does the steel tubing line everything up?
3)   If they used a jig, are there any drawings or old pictures?

Thank you,  Phil

Phil,

I'm almost certain that the Culver wing has no washout.  Washout would probably defeat the lift distribution that the elliptical taper is attempting to accomplish.  Washout would also probably have made the wing slots unnecessary.  I don't know of any airplanes that use both wing slots and washout together.  I do believe that the airfoil is a NACA 3414 at the root and tapers to a 3408 at the tip (meaning the airfoil tapers from a 12% thickness to an 8% thickness).

I've seen a picture of the fuselage assembly in the factory, but not of the wing. 

Brett

[Paul Rule]

Here (FINALLY) are those ANC-18 pages on the wing spar tests from long-long ago.

Paul R.