Hatz Biplane Association

I have set up my shop and started to cut practice pieces (rib nose blocks on the router table etc.) I have gained confidence and have started to construct my rib jig. I copied the full scale rib outlined and took some measurements and the measurements were off by almost 1/2 inch. The spar measurement was .750, but the rib length etc. were off. I presume part of this error was a result of plan shrinkage and/or the rollers from copying my original set. I measured the originals and they were off as well (albiet not as much). So, I have now lost confidence on what to do.

I am not an engineer by profession and my experience working from plans is limited. My next step was to download Profili and attempt to re-print my own Clark Y airfoil.

So here are my questions:
1. Do I need to be so anal? If the spar dimensions are .750 does shrinkage of 1/4 inch or so on the Chord really matter?
2. Is the Clark Y airfoil the correct airfoil (or is it one of the many variations of the Clark Y)?
3. If I should draw the rib from coordinates on my template, what is the best way to do so? I have found the coordinates for a Clark Y on the net.
4. What about the nose blocks, trailing and leading edges?

(As an aside Makelin Corp has not responded to my emails or phone calls, so I guess I am on my own.)

Thanks in advance.

Daniel Findling
(New Hatz Biplane Association member and struggling beginning homebuilder.)

Hi Dan,

First of all, WELCOME to the Hatz family! Glad to see a new builder starting out. I'll answer what I can and I'm sure others will chime in as well.

Regarding plans shrinkage, it has been known to happen, although I, fortunately, have not had to deal with it. However, I would recommend that you get a corrected full size rib template. If you stop and think about the rest of the associated assemblies (center section, ailerons, wing struts, aileron linkage assembly, etc.) they will all be impacted in some form by changes to the chord (unless you choose to adjust them as well along the way ): for example the Center Section would have a longer (correct) chord compared to the wing and the C/S spars may not align with the wing spars depending on where the differences are (and if the spars are closer together then this may affect the dimensions of the fuel tank), Ailerons would need to be adjusted or they may have too long of a chord relative to the wing, Interplane Struts may have to be adjusted if the dimensions between the front and rear spars don't match the plans. There are a lot of ripple effects to consider - 1/2 an inch can be a lot.

I have some digital images of the drawings (including the ribs). email or PM me with a mailing address and I can get you a cd. this should solve the dimensional problem and also help with the other rib components.

Doug.

Hi Daniel. Welcome!

I faced exactly the same problem you are having. Here's what I figured out.

The really important dimensions are the outside dimensions of the rib and the distance between spars. So when I built my rib jig, I just made sure these dimensions were perfect, then fit everything else together. The precise position of each of the structural members won't make a huge difference within, say 1/8" because they're really mainly holding fabric in shape, and as long as you build them all identical, it will work out just fine.

Remember, the main concern is the distance between spars, as this is how it will hook up to your fuselage.

Plus, accept the fact that you are going to do some things over. Go ahead and make one rib just to see how it works out. You'll get the hang of it quickly and before you know it you'll have a stack of ribs.

Best Luck!

Nick

Doug,

Thank you for the kind offer. I will kindly pay you for the CD. My office address is 414 W. Fifth St. Royal Oak, MI 48067.

Daniel

My fullsize rib template from the original plans was dead-on accurate, but my attempts to copy it were fruitless. I went to a couple of different lithographic shops in the Dallas area and never found a copy that was worth bringing home. I was finding variances in the copy that were more than a quarter of an inch.

I ended up sitting down with a french curve and tracing the outline of the rib, from the original plans, onto a clean sheet of paper. THAT became my basis for my rib jig. When you are manually building a part out of an organic material (wood), there is going to be some variance from the plan - but my theory is that you need to start with an accurate guide.

Daniel,

I'll get a copy o the cd out this weekend.
Doug.

Thanks again in advance. Anxiously awaiting to get started. I cut my wing template jig out and practiced making some more bits out of scrap.

Daniel

Hi Daniel, Sorry for the delay, but I got your cd in the mail today.