Minimum body tube length for DD

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gcanroc

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I'm about to order a payload bt for my PML Spitfire (3" diameter) There are three sizes to choose form 9",12" and 18". Is it preferred to have a longer tube for DD for the main chute then a shorter one?? I'll loose 3 inches on each end from the nose cone and the avionics bay. Any input would be most appreciated.

Geoff
 
Obviously, depends on how big a chute you use and how well it and the rest of your gear packs. If there's no compelling reason to go shorter, I'd go with the 18" although the 12" would probably work OK.

With the Spitfire's fins, I'd tend to go with a bigger chute.
 
+1 on 18", but definitely try to figure out how big your chute is when packed. Add a couple of inches for U-bolts and shock cords as well.
 
Rocketman and Fruity list packing volumes for their chutes. Volume of a cylinder is πr^2h.

9" tube (minus couplers) gives you 21.2 cu in.

12" tube (minus couplers) gives you 42.4 cu in.

18" tube (minus couplers) gives you 84.8 cu in.

So each tube sizes doubles your volume. Remember that you also need room for the harness and attachment points.
 
You want tube long enough so it's easy to pack for sport flying. All my 3in rockets use 18-20in payloads.
As you mention after remove space for coupler/Nc you are down to 12in [with 18]. Getting 15-20ft of shock cord, nomex chute protector [12in size] and a 36-48-60in chute will take up most of remaining space.

Save the shorter size for high performance flights where ya really have to fold tight and cram stuff in there for performance sake.:cool:
 
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