Norman Holme's plans for Cessna O-1A Bird Dog 54" span

[Tony Harrison 2]

I wonder if anyone here has built this? It's from quite some years ago I believe. This is my first attempt at building from a plan, and I find some aspects of the plans very difficult to interpret. The fuselage is more than half assembled, next stage being to complete the wing-bearing platform above the cabin - and I'm concerned about getting it wrong. Might build the wing next instead, since that might assist in getting the fit-to-fuselage process right.

All advice welcomed - rgds Tony

[kc]

It's this one on Outerzone isn't it?  It looks pretty conventional, so what item is not clear? Have you studied the photos in the article?    (article is online too )   Your F5 looks a bit different and lacks the ply each side -so far.  I think many people would fit the wing bolt mounts to F5 and drill the dowel holes in F3 before assembling - then make the wing to fit the dowel holes and wing bolt mounts.  But it looks OK as it is so far.

[Tony Harrison 2]

26 minutes ago, kc said:

It's this one on Outerzone isn't it?  It looks pretty conventional, so what item is not clear? Have you studied the photos in the article?    (article is online too )   Your F5 looks a bit different and lacks the ply each side -so far.  I think many people would fit the wing bolt mounts to F5 and drill the dowel holes in F3 before assembling - then make the wing to fit the dowel holes and wing bolt mounts.  But it looks OK as it is so far.

Yup, the very same - and naturally I have the article, which serves as a very basic set of instructions. My F5 is cut & fitted exactly according to plan, though I cut it out as a single piece, and the side apertures for longerons aren't cut yet; perhaps you refer to the on-edge strips of ply fitted side to side across the upper edge of F5, sandwiching some trailing-edge section balsa? I haven't cut & fitted those yet. I take your point about the wing fixing bolts. My current concern is to understand fully the size, shape and exact relationship between those "1/8" hard rails", the 3/16" balsa strips, and the F4 - F5 between which they're fitted. I'll just have to take it slow and easy.

Thanks - Tony

[kc]

I would suggest cutting a ply or cardboard template from the plan  with top longeron to wing seat profile and using that to  locate the wing seating parts.

If you can obtain the wing bolt brackets as shown then it should work OK but if they are not available now then you may have to think of alternatives and that's best done at this stage.    The note about wing bolts seems to refer to Peter Miller's way of pointing bits of wing bolt in a pencil sharpener and letting them mark the exact point on the wing to place holes.   Just protruding a fraction they make indentation marks. 

I suggest cutting the 3/16 sheet spar with spar doubler and fitting them to F3 and dowels before building wing.  Then ensure it all aligns.   When it's OK build the wing onto that sheet spar and doubler.    Actually I cannot see why F3 has notches level with the dowels but there may be some reason!

[Tony Harrison 2]

17 hours ago, kc said:

I would suggest cutting a ply or cardboard template from the plan  with top longeron to wing seat profile and using that to  locate the wing seating parts.

If you can obtain the wing bolt brackets as shown then it should work OK but if they are not available now then you may have to think of alternatives and that's best done at this stage.    The note about wing bolts seems to refer to Peter Miller's way of pointing bits of wing bolt in a pencil sharpener and letting them mark the exact point on the wing to place holes.   Just protruding a fraction they make indentation marks. 

I suggest cutting the 3/16 sheet spar with spar doubler and fitting them to F3 and dowels before building wing.  Then ensure it all aligns.   When it's OK build the wing onto that sheet spar and doubler.    Actually I cannot see why F3 has notches level with the dowels but there may be some reason!

Thanks for your advice. I don't follow your closing query: F3 has a few notches, but level with the dowels...?

rgds Tony

[kc]

On the plan F3 is shown with dowel holes already drilled and there are notches level with those dowel holes.   (The top notches on your F3 which does not have the dowel holes yet )  

I cannot quite see why those notches exist -the wing is cut back at F3 so there does not appear to be anything that fits into the notches.   The 3/16 sheet spar and the 1/8 ply brace need the notches but not F3 in my view.  I may be wrong!   Worth having a trial fit of the ply brace to F3 before building wing...........

 

Frankly this is the difference between plan builds and kit builds - with kits one assumes that others have built from the parts and found them OK.  When planbuilding you need to check that the parts are corrctly drawn.  Finding errors ( all plans have some!)  before it's too late saves lots of agro!  I always measure the width and height of formers and compare them with fuselage plan.   Then I check that notches etc are at the correct height and also correct width.   Usually the errors are exactly 1/2 inch, 1/4 inch or 1/8th out ( or 10mm, 5mm etc ) never just a little bit wrong always an exact marking on a ruler!   Usually this occurs at some intermediate process  - it's not the designers fault.

[kc]

Further study of the online plan reveals that the wing dowels are not symmetrical - it could be an error or perhaps there is some reason for it that is not obvious to me.    F3, the wing plan and 1/8 brace all show this uneven spacing,  so there may be a reason.   Clearly the wing brace needs building into the wing the same way round as F3 is drilled.

[Tony Harrison 2]

6 hours ago, kc said:

Further study of the online plan reveals that the wing dowels are not symmetrical - it could be an error or perhaps there is some reason for it that is not obvious to me.    F3, the wing plan and 1/8 brace all show this uneven spacing,  so there may be a reason.   Clearly the wing brace needs building into the wing the same way round as F3 is drilled.

Thanks again KC. You guys who've been doing this for decades need to appreciate that newcomers don't share your expertise! I built a couple of balsa & tissue KeilKraft planes in my teens, but got back into this game only about 7 years ago; interpreting these plans is challenging since we lack experience. I don't understand your reference to the wing dowels not being symmetrical. I know what you mean about the upper notches on F3, and I just hope that as I continue to fiddle around, their purpose might become clearer. I'm reasonably flexible (have built two kits incorporating some personal changes, each flew well) and might just use my initiative instead of trying to follow a plan I don't understand. I'm already having to adapt this plane, since it was designed for i/c and I'm installing electric - did this with another ready-made plane I bought s/h and it flies well.

rgds Tony

[kc]

The dowel holes are shown with different distances to the edge - it's normal to have them exactly the same.   Difference is slight but I can see it on the screen!   Symmetrical they could be put in either way - 'handed' means F3 and wing brace need to go in same way around.   As you have not yet drilled F3 it will work out OK.   There could be a reason for the odd spacing, but I cannot see why.

 

The reason for the notches I mentioned yesterday could be to take the 3/16 parts shown on the fuselage side view supporting the windscreen glazing.   Not shown with all the rib shapes but should be like the front of an R1 I reckon.  

 

Edited November 17, 2022 by kc

[Tony Harrison 2]

4 hours ago, kc said:

The dowel holes are shown with different distances to the edge - it's normal to have them exactly the same.   Difference is slight but I can see it on the screen!   Symmetrical they could be put in either way - 'handed' means F3 and wing brace need to go in same way around.   As you have not yet drilled F3 it will work out OK.   There could be a reason for the odd spacing, but I cannot see why.

 

The reason for the notches I mentioned yesterday could be to take the 3/16 parts shown on the fuselage side view supporting the windscreen glazing.   Not shown with all the rib shapes but should be like the front of an R1 I reckon.  

 

Further thanks - I see what you mean re those offset dowels - like you I don't understand why the holes aren't centred exactly. Yes, I wondered about the notches and those 3/16 side pieces, hope I can figure it out!

Thanks again, Tony