H/S Spar Mod Slide Show from A.S.A Now Up!!!

[JanRV6UK]

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 ..

 

[mike newall]

Scott,

My man suggested this - and he has a lot of experience in race cars, bikes etc etc.

Make up 2 reference pins which essentially are a pin that is the dimensions of a bolt, a shoulder that is the thickness of the spacer and a small centre spike.

Place new HS on fuselage with thin packers at the front and the pins in the outer holes, no spacers.

Square, drill rear holes.

Square up HS wrt to tip to firewall as usual.

Secure.

Remove packers so HS lowers onto spikes.

Thump with big mallet.......

No - you know - make the mark

Remove, drill, replace with pins on the inside and packers in.

Square using bolts etc etc.

Remove packers and repeat above.

Ta Da...... You have match drilled holes again - probably better than the original when you crawled up the fuse or used a right angle drill.

As I said - it requires a little fettling on a lathe. I am sure Alan is already figuring it out...........

 

[rvbuilder2002]

Builders will have to make there own choices regarding what is the best path for them to take. I have never meant to imply it can't be done, and therefor shouldn't be done.
I have done a lot of this type of work over the years... even match drilling wing spars to an already built fuselage, so i do understand the issues involved.

My main concern is when building and installing a new stab is promoted as the easier/safer route to take. If you get nothing more from what I have posted. please get that taking this route is anything but a slam dunk.

The above two methods will work but still rely on using an angle drill and having the alignment of the drill bit stay exactly aligned with the existing holes in the fuselage, while doing the final drilling step (making it finished size). There are tons of different methods for matching the position of existing holes. Accurately doing the final drill step so that all of the holes are still a close/tight fit on the bolts is the challenge.
The hole you are aligning too is only 1/8 in deep. That is not enough to rely on it maintaining alignment for you. I personally like these hole to be a very close fit for the bolts

 

[JanRV6UK]

B
I have done a lot of this type of work over the years... even match drilling wing spars to an already built fuselage, so i do understand the issues involved.

That sounds like a proper challenge !

My last comment on the HS issue ... Order for the SB kit from VAN will be in with my next order ... No need to make it any harder ..