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Question for you engineers...vans support could not give an answer

Christopher Murphy

Well Known Member
Doing the horizontal stab spar SB on my RV4

Looking at the kit and the drawings specifically fig 5
It appears the only rivets through the spar are the 8 rivets in the 2 hinge brackets.

My experince tells me there should be some rivets going out into the fingers on each side of the hinge brackets going through the spar webs

Tom at vans didnt know if it was an oversight considering its not a predrilled kit.

Are the pre drilled kits drilled out there?
If I were just doing a repair i would put rivets there
Thanks
Cm
 
My pre-drilled parts don't have holes on the fingers. I had the same thoughts.. but the instructions don't show holes there.
 
The main loads come through the caps. The web carries shear, which is adequately carried in this area through the hinge rivets. Shear is a considerably smaller load than the bending.

There is also the bending at the forward face of the hinges due to the hinge load - you can think of this as the hinge load trying to pry the hinges off the spar. This transfers into the new part through the hinge rivets and out through the cap rivets.

Nomenclature - the word "cap" refers to the combination of the spar flange and skin in this area. "Web" is the vertical face of the spar to which the hinges attach.

Dave
 
Thanks

But

As I see it then, there should not be fingers designed into this piece. The fingers make that weaker than if it was just a plain channel. Ive done alot of repairs as an A&P in an airline shop and this looks pretty suspect. Im sure it will be just fine but im not putting that notch in mine if there are not rivets to in them.

The fact that the pre punch parts dont have rivet holes tells me it wasnt an oversight..

Thanks for the replies
Cm
 
Doing the horizontal stab spar SB on my RV4

Looking at the kit and the drawings specifically fig 5
It appears the only rivets through the spar are the 8 rivets in the 2 hinge brackets.

My experince tells me there should be some rivets going out into the fingers on each side of the hinge brackets going through the spar webs

Tom at vans didnt know if it was an oversight considering its not a predrilled kit.

Are the pre drilled kits drilled out there?
If I were just doing a repair i would put rivets there
Thanks
Cm

Do you mean like this? This was the 1st iteration of the fix. There has to be a good reason that is not obvious.
Screenshot 2023-05-16 at 4.42.23 PM.png
 
Do you mean like this? This was the 1st iteration of the fix. There has to be a good reason that is not obvious.
View attachment 42518

I can see why that version got tossed. Good thing.

No, the 4130 steel hinge brackets dont have the top and bottom bend to nest in the spar flange like the early version. That would be tough to make it fit in the taper of the spar.

I going to omit the fingers and just put the 7 inch piece in with only the 8 -4 rivets as shown in figure 5. And the -3 skin rivets.
 
The fingers are necessary to spread the load a bit and help avoid abrupt stiffness discontinuities, which decrease fatigue life. Follow the directions.

Dave
 
The fingers are necessary to spread the load a bit and help avoid abrupt stiffness discontinuities, which decrease fatigue life. Follow the directions.

Dave

So the fingers do all of this without being fastened to the spar web?

Is the radius of the curve tangent to the edge of the hinge bracket important? Its not shown on the drawing.

I dont have cracks but adding that .063 doubler on the front of the spar would be a major abrubt stiffness discontinuity.

I guess I will make it look like the drawing...

Thanks for the discussion
Cm
 
What David Said.

the 'fingers' just transition the web to the area of the nested flanges where there are rivets. Those nested flanges transition the load from the steel hinge brackets over a nice long portion of the spar flange and skin which as David said constitutes a spar 'cap'. Then, the web is notched out to create the fingers, partly because it is un-needed weight and partly to create a more gradual transition of stiffness.

It is a pretty well thought-out enhancement. I would not recommend installing the forward face doublers unless there are cracks in the spar. (as per instructions).
 
Steps 18-29 in SB-00036 for fitting the HS-00416 Nested Spar Doubler Blank on the RV-4 HS are very explicit.

There was no oversight by the engineers at Van's in designing the HS-00416 Nested Doubler or in the steps for installing it.

If the engineers wanted you to use additional rivets in the "fingers" of the doubler there would have been instructions on where to place them or pre-punched holes for them. Why the need to second guess the provided instructions?

Here's the official advice from Van's Tech Support - STICK TO THE INSTRUCTIONS AS PUBLISHED!
 
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