Rib dimension discrepency

[Bitshifter]

The spar center distance is stated to be 25" but my plans are 25 1/16. I have noticed that others have had and corrected for the problem. I have not been able to find how anybody corrected for it. I am assuming that complaining to Makelan will probably not help. I am getting ready to build my jig and am not sure what is the best way to correct the problem.
Thanks

[JBMoore]

1/16" isn't enough to worry about in my opinion and I wouldn't be concerned with the difference as long as you're consistant. You don't say where the numbers come from and it's been forever since I've studied my plans. Make a note to yourself "self - all spar center distances are XX" no mater what the print says" and start cutting wood. The center section will follow suit as will the fuselage attach points. As far as the cabanes and N-struts, I built them to fit and didn't use a print dimension.

Good luck.

Jeff Moore

[PoconoJohn]

If you visit my page, http://imageevent.com//hatz you'll see the images of what I did. Basically, I took two pieces of wood, placed them side by side, and extended them until they were exactly 24 1/4" (the space between the spars). I then bolted them together. I use this 'spacer' to make sure the spars of rib #10 will match with the other spars as well as making sure the spar blocks are correctly spaced in my rib templates. Using the 'spacer' I placed spar blocks on the plans with the blocks up against both ends of the 'spacer'. I ended up placing the forward face of the aft spar on the line, not against it.

[Bitshifter]

My problem is that I have one given dimension 25" and it is wrong, do I correct for it and assume that all the other non listed dimensions are correct. It is also frustrating because it is given to 3 decimal places, usually that imparts a lot of precision importance.
When you re-spaced the spar did you move the wing forward, backwards or split the difference?
I know that its not a big deal but I don't want to build all the ribs and a year later find out that they don't fit the spar.

[mtaylor]

Basically, if you build all your ribs out of the same jig, the spars will plug into the ribs and the distance between front and rear spars will be whatever they are. Just be sure to build the center section spars and fuselage attach points to the same dimensions as the wing spars (or vice versa if you build the C section and/or fuselage first as I did). All the compression struts will be then fitted to whatever dimension that will fit inside the spars. If you were building an airplane with a wing span of 8", it might have a problem flying with a 1/8" discrepancy from the plans. With a wingspan of 11' and a chord of 53" you won't notice a 1/8" discrepancy other than if it were between the fit of one component to another. I don't mean to say that it's OK to be lackadaisical about your measurements, just that in some instances you don't need to loose any sleep over a slight discrepancy. Again, the main goal is to make all components fit to EACH OTHER.

[mtaylor]

I forgot to add that in the case of 3 decimals, the decimal for 1/8" is .125. 3/8" is .375. Doesn't mean that it is a critical tolerance necessarily unless, again, it refers to two components fitting together. I know I've seen measurements on plans that I wondered why in the world is this measurement so precise. Sometimes it heeds your precision, and sometimes it don't.

[dougm]

My problem is that I have one given dimension 25" and it is wrong, do I correct for it and assume that all the other non listed dimensions are correct. .

This particular issue has been raised in other threads. Folks have found that temp & humidity issues have generated physical differences in the paper itself. In other words, the dimension of 25.000 is correct, but the paper (or perhaps the printing process) have yielded a product (the drawing) that does not match the stated dimensions.

viewtopic.php?f=8&t=141



Mark made some excellent points. I wouldn't worry.

[PoconoJohn]

The front spar location was not changed. The forward face of the aft spar ended up ON the (forward) line on the plans, not centered. My ribs will all be exact and will also match rib #10 as I still centered the forward spar and placed the rear spar up against my spacer. Hope that helps.

[Bitshifter]

I took my rib template drawing to a Fed X copy center and had two copies made. The dimension on the copies is exactly 25 ", go figure. All the other dimensions are correct also.

[ha622]

It seems to me that similar questions come up on a regular basis.

I encountered the same problem on my CB-1 drawings (more than 10 years ago). I have redrawn the wing section using the coordinates for the ClarkY airfoil. This is the airfoil which is used on the Hatz. I have appended a pdf version of the drawing to this post. You can probably take the file and have it printed full-scale at a local printing shop and you should get an accurate drawing to work from. Since the pdf-file was converted from the original HPGL format you may want to double check that the dimensions are OK. Printing out on mylar or something similar will guarantee that there are no distortions due to humidity. I don't think that this is necessary though. I assume that you will use the printout pretty quickly to make your jig, not giving the paper time to deform. The drawing is for the CB-1 but the dimensions are the same as for the Classic. I have built my wings as CB-1 wings but have used exclusively Classic steel parts obtained from Makelan (I think I have the second fuselage built by Jeff Shoemake). I haven't encountered any problems even though I had built the wings before I received the finished compression struts.

Alternatively, you can modify the wing section drawing which you already have. The ClarkY airfoil is not a very critical airfoil. Therefore it doesn't really matter if you move the difference forward, backward or split the difference. You want to keep a smooth curve and not make any changes on the leading edge radius. Personally, I would prefer to have the 25" between spar centerlines are maintained. I think that there are less chances to make an error and later find that something doesn't fit.

Juerg, S/N-622

PS: Sorry, but it seems that the upload of a pdf file is not allowed in the forum. Is there an alternate method to include/distribute non-jpg files? Does anybody know?