wood spar "caps"

D

decathalon

New member
Recently found a pine looking spar 'cap' on top of the wood spar that extends from rib to rib. It has been determined that this prevents compliance with the AD. Reviewing logs and 337's, the cover had never been off until 5 yrs ago, and the refurb A&P found the spars as is; with these 'caps'.

Is there any Bellanca retirees, or other that has seen blocks of wood on top fo the spar that extend from rib to rib [minus about an inch on each side] versus the more prevalent 1 1/2" block that was centered between ribs.

Trying to determine if this was truly a factory installation, or a missing log entry.
 
We recently rebuilt our wings and found spar "caps" between the wings. We had determined, as you did, that this prevented inspection. We thought that the last wing recoverer had "done us a favor" and put them on to help support the leading edge metal.

Just for info, we would like to know if they are factory or an add on.

I have seen the small wood blocks on a Tri-Traveler and a Champ but only on the inner 2 (or maybe 3) rib spans.

Thanks,
Charlie
 
By original type design, there were never any caps. Quite honestly they do very little to help the wing. If they have to break every 12 inches to clear a rib, it will do very little. The Bending inertia abruptly changes back to factory original at every rib is how I read it. Not good desgin technique and was never done by Bellanca/Champion. I would find they guy who did it and make him get it field approved.

As for the little blocks, those have been abused over the years as well. By the print, those are only in the tank area and the tapered wing tip rib bay. Thats like 4 per wing. If there is one in each rib bay, its actually not supposed to be there. However, I doubt you will find an issue with the extra little blocks. Technically, they are not supposed to be there. /shrug
 
The guy who put on the strips, rib to rib, for us is used up and planted, but we have thought about what the blocks might do, for several years. He had recovered 26 airplanes, including 3 for us, so he was very trusted. All of his work lasted at least 25 years.

In my opinion, and only mine, the blocks add some stiffness to the leading edge where it breaks down about 1/4 inch, over the spar. The leading edge is not attached to the spar, so any aerodynamic loads and vibrations would tend to deflect the leading edge, and therefore change the shape of the wing, slightly. Deflection on a beam is proportional to the length cubed so putting a block in the middle cuts the deflection by a factor of 8.

Milman says, with their aluminum spar kit and leading edge kit, which attaches the leading edge aluminum to the spar, that some owners (but not Milman) have claimed some added cruise speed. Maybe this is where it comes from.

Also, we owned a 7ECA several years ago and had a serious problem with the fabric retaining screws falling out of the ribs especially in the inner bays. Our current 7KCAB fabric vibrates a little, at cruise, in the inner bays on the right wing only. We don't worry about it. The 7KCAB has pop rivets holding the fabric so they won't fall out. My contention is that this vibration of the fabric contributed to the screws backing out and leaving in the 7ECA.

The bottom line to all of this is stiffening the leading edge on the top, with the little blocks, also would reduced aerodynamic vibrations and help maintain the airfoil shape.

All this might get you a free cup of coffee.....
 
Sure, but you could get near the same effect with the little rib blocks. I merely stated that they never where supposed to be there. Nor were they there from any of the factories. This says nothing to their viability or functionality. However, it does answer their legality. :p

Like I said in the edited responce that Bob picked off here, it will reduce deflection, but it wont increase strength. It might help just a little bit in the areas of peak stress, but given the abrupt change in interia just a few inches away, its not fracture mechanic / fatigue friendly.

Critical inspection areas would actually be confined to where the caps end. However, this is the 'rule' and the driving force of the AD is the 'exception.' *shrug*

Finally, for retaining the airfoil, I agree completely. New wings have little 'Z' brackets all the way down. Makes a difference.

These poor blocks nailed there? Or was a nice glue job done? I suppose either way, it was nailed through the Leading egde.
 
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