JanRV6UK
Well Known Member
These are all good ideas being presented on how to match drill a new horizontal stab except they don't account for one critical variable.
They all assume that the holes were drilled perfectly straight and square to the structure in the beginning. It is likely that in many builds they were not. If a match drilling process is used that aids alignment during drilling, and the original holes were slightly miss-aligned, it will result in oversized hole in the fuselage portion. How much, and will it be bad enough to be a problem? It all depends how missaligned the holes were in the first place.
A slight missalignment the first time was not an issue as long as the bit wasn't wobbled... the bolts would still be a tight fit in the holes (just not quite square to the surface). If these holes are now used to match drill, but at a slightly different angle, depending on the variation, it could result in oversized holes.
I probably did not explain myself very well in my process ? I agree that problem with original holes being drilled not normal to the longeron will be a problem if you try and re-drill from the top down into the longeron. The idea with the bolt that has a hole in it is to use it as a jig in the longeron ? i.e. you inset the bolt from inside the fuselage up through the longeron (and if the hole in the longeron is not drilled perfectly perpendicular to the longeron originally ? it does not matter ..as the bolt you have inserted from the underside will be at whatever angle the hole is...) Then with the bolt sticking up from the longeron ? you put on the required spacers (I think it is 1/8 shim or something like that ) .. then you clamp in place the new HS ... Now take your angle drill .. and drill up from inside the fuselage ..... using the hole in the bolt.. as you drill guide ... the drill will never touch any of the original parts... it will drill into the new HS only...
Once you have done the #40 hole .. then change the bolt with the largest possible hole in it .. and drill again .. you only drill in the new HS .. never the longeron ...
If you screw something up .. you can always refit the old HS ! ..
To be fair ... Two things can go wrong with this method ... the machine shop that put the hole in the bolt ? does not put it in the centre of the bolt ... and / or the original hole in the longeron are so poorly drilled in the first place that the bolt you use has a sloppy fit .. Then just go back to the machine shop and get them to make a pin that does match the oversize hole you have in the longeron (not that having a oversize hole in the longeron is a good idea !!)
I have full confidence in VAN and the SB make sense to me ... I just wanted to suggest a way to drill a new HS ... if anyone wanted to do that ... The worst thing anyone could do would be to try and drill using the original hole in the longeron ( without a drill bush of some sort ...) ... the drill will for sure enlarge the hole in the longeron .. not a good idea ..