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-   -   Afternoon Project (http://www.oldrocketforum.com/showthread.php?t=20352)

MarkB. 06-30-2022 08:23 AM

So,

OCD can be a bad thing. I wanted to put the Center of Pressure decal and the Center of Gravity decal in the correct locations. I found both a D12-7 and a C11-5 for use in the CG measurement

Using the Bruce Lee worksheets Dave posted in another thread, I calculated the CP of my Semroc Cherokee-D as 17.18" from the tip of the nose. With a D12-7, the CG is only .875" ahead of that and with the C11-5, 1.625" ahead.

The Semroc kit is short body (16.35") like the original and I added a hardwood dowel to the nose cone to give the screw eye something to bite into. Still need a bit more nose weight.

If anybody wants to check my math, great. I'd note that using an 18" body tube moves the CP slightly forward (1.46") but this is offset by the CG having a longer moment arm.



Addendum: For fun, I measured the CG on the old Estes Cherokee I mentioned above with the same D12-7 and I don't know if the paint is heavier or the balsa cone denser, but its CG is 1.375" ahead of the CP. So it's OK.

MarkB. 07-04-2022 09:40 AM

3 Attachment(s)
Well,

Here's the finished product. Total time decalling ended up being just over an hour mostly because of trying to do a good job cutting close to the images and lining everything up. I did it in two sessions about 45 minutes for the fins and the other bottom end decals and about 20 minutes for the wraps and the CG/CP markings.

The Semroc decals were, as usual, a little translucent, but they went on well. I used a little Walther's Solvaset decal solution. A coat of Tree House Acrylic Clear and this one's ready to go.

I was going for the original 1970 catalog look. Pic. 1 is the right side. The CG/CP decals are in their correct locations for a D12-7. It took a couple of weights under the screw eye to get that all sorted out.

Pic 2 is the other side. The decal layout seems to suggest a rocket in a cradle so the other two sides of the rocket are pretty plain. Also, I noticed that, in addition to not following that general visual layout, the "NASA" on the sheet was in two different font sizes, an error which apparently cares over from the original Estes sheet. So I cut them off and used the larger of the two to make the bottom end decal you see here. The larger NASA plus the decal sheet part number and the small numerals provided on the decal sheet make up a new marking for the bottom of this side. I used my NAR number. Lining up the individual number decals was, shall we say, challenging. The CP/CG markings on this side are farther apart as those are the measurements for a C11-5.

Pic 3 is a close up. The Semroc kit number is KV-84 whereas the Estes kit number K-47. The number on the Semroc decal sheet reflects this difference on the United States decal as well.

A fun project that came out well. Now I'm debating refinishing the eBay rescue Cherokee, but I definitely need an Estes decal sheet.

John Brohm 07-04-2022 10:00 AM

Nicely done!


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