Thorp Air Command - T18.net

Supporting Owners, Builders and Pilots of the Thorp T-18 and its variants.
It is currently Fri Mar 29, 2024 2:30 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 5 posts ] 
Author Message
Rv3maker
PostPosted: Thu Feb 29, 2024 6:28 pm 
Newbie
Newbie

Joined: Sun Oct 15, 2023 9:06 am
Posts: 25
Images: 0
Location: Halstead, KS (Wichita area)
All,

I have read through the posts, references and newsletters and I am about to final drill to size the attachment lock pin holes in the 215 and 315 fittings. My fittings came pre-drilled to 1/2" hardened and plated with only a very slight offset in one of the holes on the RH wing side (likely from heat treating). My plan is to step drill to 17/32, 35/64, possibly ream to .5615 and then final ream the holes up to the .5625/9/16" pin size.

My set up for drilling and final reaming is going to be similar to ljkrume's shown from his gallery album, shown below during drilling.

I am struggling to see any other way to do this. Everything I have read and the references I see say to "ream to final size on assembly". Well, once inner and outer wings are assembled it will be very difficult to final drill/ream. This would have to be done by hand . . .not my idea of fun. If I go ahead with assembling the 315 to the outer spars which are built minus the 315/rib mounting holes then I will kind of lose any way to do a slight adjustments when drilling/mounting the 315 to the spare and doing dihedral checks as they are already assembled. These 215/315 fittings seem so close to the correct angles when clamped together and temp assembled (they are tight!) and sitting on the catches that I believe they will be good to go.

My set up was going to be with my smaller bench drill press on top of my work table, but I am going to use my larger standing press as it will be more stable and is a better drill press than the smaller one. I will just clamp things together and level the inner spar and shim/clamp the pieces together.

Any recommendations from anyone who has built a T-18C or S-18 wing that has some words of advise or a better approach to this other then as done by ljkrume or how I am suggesting? I think it will be fine as long as everything is level and clamped tight when drilled/reamed. I am just a nervous item to do as it is not an area you want to screw up on. I am finding out on some of this stuff you just have to read everything you can, ask questions in hopes of getting some advice . . . but in the end you just do it and learn as you go . . not a lot of T-18 builders around in my area to consult with.

I am asking as there will bound to be someone who is building a new project from Jim at Thorp Central that will have the same questions!

Rob

Image
Image


Top
 Profile Personal album  
 
James Grahn
PostPosted: Fri Mar 01, 2024 12:39 am 
Hero Member
Hero Member

Joined: Sat Oct 24, 2009 7:16 pm
Posts: 1434
Images: 0
Location: USA
That should work. Be advised that there is slop in how the brackets mount to the spar caps. So if those have been drilled, you need to tak that into account.
Cubes


Top
 Profile Personal album  
 
Rv3maker
PostPosted: Fri Mar 01, 2024 10:24 am 
Newbie
Newbie

Joined: Sun Oct 15, 2023 9:06 am
Posts: 25
Images: 0
Location: Halstead, KS (Wichita area)
Hey Cubes,

I thought about that realizing that the dimensions/tightness of the two 215 pieces do change slightly as you install/torque down the AN4 bolts. My inner spar 215 cap holes have been drilled. So, I am thinking as long as I put in 2-4 AN4 bolts top and bottom to hold the 215's in place on the caps I could drill/ream the locking pin holes to size and then when doing the final install of the 215's on to the inner spar I could do it with the pins securely installed in the holes and the 315's temp installed. I believe this should keep alignment for the final install of all the AN4 bolts in the 215's. Agree?

Alternative would be to install every mount bolt on the 215's permanently and then drill/ream the pin holes to final dimensions. I was going to delay the final install the 215's to be able to get a bucking bar on the top and bottom spar caps rivets for the skins. Then slide the 215's/spacers in place (supposed to be installed "wet") and complete the install and final torque of the AN4's (I may have a few AN174's in lieu of AN4's). This is where I would install the pins in then 215/315 to keep that tight alignment.

Does this make sense?

Rob


Top
 Profile Personal album  
 
fytrplt
PostPosted: Fri Mar 01, 2024 7:49 pm 
Hero Member
Hero Member
User avatar

Joined: Tue Oct 20, 2009 8:07 pm
Posts: 1140
Images: 2
Location: Lakeland, Florida, USA
I built a seven degree jig to clamp the two top spars. Then built everything around that.

_________________
Bob Highley
N711SH
SN 835
KLAL


Top
 Profile Personal album  
 
James Grahn
PostPosted: Fri Mar 01, 2024 8:50 pm 
Hero Member
Hero Member

Joined: Sat Oct 24, 2009 7:16 pm
Posts: 1434
Images: 0
Location: USA
That will work. But you also need to think about the sweep of the wing. I have seen wings built that do not match inner to outer because the spar cap bolts were not taken into account.
In other words, you not only have dihedral to think about, but also do the leading edges of the inner and outer line up and is there any unintended wing sweep. Do that by eliminating as many variables as possible. Measure the distance from the inner wing fittings to the leading edge. Then compare that with the outer.
Are the aft spars drilled? If not, you can account for sweep back there. You can also account for any unintended twist there as well. Lee Walton came up with a beautiful cam setup to adjust twist via the trailing edge attachment fitting.
Cubes


Top
 Profile Personal album  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron

[ Time : 0.229s | 14 Queries | GZIP : On ]