# 1971 Centuri Design Manual Pay Dirt Fin Dimensions.

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#### K'Tesh

##### .....OpenRocket's ..... "Chuck Norris"
TRF Supporter
OK... A while back on facebook, someone asked me to do one of Centuri's 1971 Design Manual designs. The Pay Dirt. I responded, but they disappeared, and haven't answered my request for info. Still, I'd like to post this.

Problem is, I can't print .pdf files and measure them here due to the nature of Chinese paper dimensions (A4), it throws off the measurements, and there was no ruler alongside the image I found of the fin templates. However, I'm certain that my fins are too large.

Can someone measure the span of the triangular fin and pass that along to me? I could also use the span of the main fin. From there, I should be able to scale what I've got.

Thanks!
Jim

I found two copies of the Manual. The better condition of the two was found at sargrocket.org

https://sargrocket.org/documents/centuri/dm-1.pdf

https://plans.rocketshoppe.com/pubs/Centuri/cenMRDM/MRDM.pdf

OK with a little simple image analysis (using Gimp) of the nice square-on photo in the Design Manual I've got you covered:

Fin span: 2.75"
Span of strake at rear edge: 0.67"
Strake root chord: 3.50"
Main fin root chord: 1.50"
Overhang of fin past end of main tube: 0.375"

These dimensions all make sense for somebody drafting it manually. Rotation angle is about 12 degrees - you have to correct by cos(rotation). You can trace the curve directly from the photo and stretch it about 2% and it will be near perfect. Or (easier) just make a correct size print of p. 32

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I sent you a PM in Facebook a while back, not sure why it did not show up. Here is a scan of the CDM fin sheet with a ruler. (the clear ruler scanned much better than the metal ruler)

This is a pic of my build:

Thanks Cabernut, Glen

I've got the sim finished save for the graphics. It looks too plain without something. I'm thinking it needs a roll pattern. However, I've got to teach school today, starting shortly, and won't be able to get to this until tonight.

dang you Glen now I found another model with clear payload section to upscale

Bobby

I sent you a PM in Facebook a while back, not sure why it did not show up. Here is a scan of the CDM fin sheet with a ruler. (the clear ruler scanned much better than the metal ruler)

View attachment 309283

This is a pic of my build:
View attachment 309284

question on the Pay Dirt body tube length
Directions say ST1010 length 10"
but Nimfinger list for Centuri Tube ST1010 says length is 10.5"

Which is correct for the Pay Dirt ?

Thanks

Bobby

Both...

Buy a 1010 tube (a common precut size for ST-10 tubes), then cut off 1/2".

K'Tesh

How about a checker board roll pattern ?

K'Tesh

How about a checker board roll pattern ?

I'll leave that up to you.

Personally, I'm not to excited about the looks of many of the old late 60's and early 70's kits. I lean more towards the kits of the 80's and 90's liveries. Some of the new stuff (preprinted body tubes), or redeux of old stuff (Wizard)), I couldn't care less for.

BTW, the .ork file has been posted in my OR files thread... Post #350

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K'Tesh

Nice job, I like it

Bobby

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