WARNING AND DISCLAIMER: If you are underage, then consult with your parents or guardians before attempting any of this. You are on your own - I'm not responsible for your actions or harm you may bring to others because of your actions. Making the items described below can result in injury or death to you or people in your vicinity. Some things mentioned here may be illegal to make in your city, county, state, or country so check the laws that apply to you before you attempt anything described here. These notes are not complete on purpose. If you are reading them and new to pyrotechnics, then you are making a mistake. Stop now - this page is not for you. Get a beginning book on fireworks (see Skylighter or American Fireworks News (very quick shipping) for a start) and read up. You can't make any of this work without more information so read up or join a club or ask someone to help you.
Rocket Engine Sizes
'Poundage' I.D. Normal Length 2 oz 3/8" 2.75" 4 oz 1/2" 5" 8 oz 5/8" 6-1/4" 1 lb 3/4" 7-1/2" 2 lb 7/8" 8" 3 lb 1" 10" 3.5 lb (estimated) 1 1/8" 11" (estimated ) 4 lb 1-1/4" 12" 6 lb 1-1/2" 16"
Granulations of Potassium Nitrate Black Powders
as posted on rec.pyrotechnics
Engineering Design Handbook
Solid Propellants Part One
|Mil Grade of Powder||Retained Sieve||Max %||Through Sieve||Max %|
|Commercial Grades/Sporting||Retained Sieve||Max %||Through Sieve||Max %|
|Life Saving Service||6||3||12||12|
|"A" Blasting||Retained Sieve||Max %||Through Sieve||Max %|
from: Illustrated Dictionary of Pyrotechnics (shortened) and rec.pyrotechnics
The "Retained Sieve" and "Through Sieve" categories are confusing. However, the way AMCP 706-175 describes them is that the 'retained' sieve is accompanied by the percent that would be retained. The 'through' sieve is accompanied by the percent that would pass through (whew!). So for the first line:
Powder Retained Sieve percent Through Sieve percent
A1 4 3 8 5
For A1 powder and a sieve of 4, 3% would be held. For A1 powder and a sieve of 8, 5% would pass. That actually makes sense if you take a couple of cups of coffee and stand on your head. ;-}
Note that these would only be useful to the hobbyist if one were attempting to duplicate the commercial grades. Some would say that such an undertaking would not be practical since it would be easier to purchase the graded powder. However, I've done sillier things and it is good to see the specifications in print.
Dan Williams (http://www.wecreate4u.net/dwilliams/top.html - website now down) created a more practical range of sizes by not overlapping the grains. His sizes (not official!) are
|2Fg||4 to 10 Mesh|
|3Fg||10 to 20 Mesh|
|4Fg||20 to 40 Mesh|
Why would one want to make artificial sizes like this? Probably the best reason is to categorize homemade BP. It is unlikely it would be meaningful to others but it would help make loads more consistent. I like a 4Fg that includes more than just 40 mesh stuff. I run it out to about 100 just like the commercial version. The reason is that the grain is still good and hot. Anything past 100 is considered dust (thus slower) and is used for coatings or recycled and repressed.
Calculating Altitudes of Test Shells
Note that these do NOT take into account wind resistance. Wind resistance can be a huge factor in some cases so you are really just estimating with this method.
The following are approximations but are close enough for most purposes if an accurate timing mechanism is available. I use a digital camera.
If you time the flight of a shell, half the flight time is when the shell was at apogee. This helps determine the timing fuse length and lift powder adjustments. The formula for total height is:
H=1/2 x A x T2
H=Height of the shell
A=Acceleration (32.2 ft per sec2)
T=Time to maximum shell height
For example, if the total flight time is 6 seconds, the shell reaches apogee at 3 seconds and the maximum height is 1/2 * 32.2 *(3*3) or about 145 feet. Seven seconds total flight time (3.5 seconds to apogee) would be about 197 feet and eight seconds total flight time (4 seconds to apogee) would be about 257 feet.
Display Site Radius
|< 3 in.||140 ft.|
|3 in.||210 ft.|
|4 in.||280 ft.|
|5 in.||350 ft.|
|6 in.||420 ft.|
|7 in.||490 ft.|
|8 in.||640 ft.|
|10 in.||700 ft.|
|12 in.||840 ft.|
|> 12 in.||AHJ approval|
The display site radius represents the total area from which the public is not allowed to enter during setup and display of an outdoor show.
Source: NFPA 1123-1990 (through Passfire.com)
|Mortar ID (in.)||Single Break||Double Break||Up to 4-Break|
The mortar length is measured from above the bottom plug. A rule of thumb is 5 times the mortar diameter for shells under 8 inches, and 4 times the mortar diameter for shells 8 inches and up.
Source: Illustrated Dictionary of
Shell Burst Height
The height above the ground for which a shell should typically break. Rule of thumb: 100ft plus 100ft for each inch of shell diameter.
Source: Illustrated Dictionary of
2Fg Lift Charges For Common Mortar Sizes
There is a table of lift charges posted in Pyrotechnica IX that uses 2Fa powder. Generally, it recommends 1 oz of 2Fa powder for each pound up to 10 pounds and 1/2 ounce per pound thereafter. This table is often posted on the different Pyro sites as a guide to lift powder charges. Unfortunately, most of us amateurs can only easily get 2Fg which is much more powerful than 2Fa. Using the Pyrotechnica tables and 2Fg powder might result in serious overloading of the mortars.
For mines, use a 1:5 ratio of lift to weight of stars if using 2Fa. I f using 2Fg use a 1:6 or even a 1:7 ratio.
As a rough estimate, use 2Fg for lift up to about 5" shells (there are experiences posted for larger shells but over 5" is pushing it). After 5", most think cannon powder (1fg) or the Fa powders should be used. Always send up a test shell to determine the proper load.
Since it is much easier to make Benzolift than hot BP (especially if one can't get/make the reactive charcoals), I've included Benzolift in the following table. These are small diameter rules of thumb for lift quantities that I go by (your mileage and cardboard shrapnel may vary):
2Fg Lift Powder Loads (your shrapnel may vary)
Well, just to prove there are a
lot of opinions out there about this - here are some more inputs
on lift powder quantities for 2Fg. The information was taken from Passfire,
Best of American Fireworks News, United Nuclear, and David Bleser. Use this to get
a feel for the starting size of your load.
2.5 to 3 grams
Don't use Benzolift
for over 3" shells. Use BP - even poor BP will lift a 4" shell and
Benzolift would probably destroy it
2Fa powder or cannon grade or something less hot than 2Fg
Well, just to prove there are a lot of opinions out there about this - here are some more inputs on lift powder quantities for 2Fg. The information was taken from Passfire, Best of American Fireworks News, United Nuclear, and David Bleser. Use this to get a feel for the starting size of your load.
Common 2Fg Lift Powder Loads (in grams)
Round Stars and Shells (p. 62)
|John H (Passfire)||Jason Murri (Passfire)||Chinese Festival (by autopsy - 2Fg equiv. assumed)||Best of AFN II page 140 Shimizu (approximately 2Fg/3Fg - roughly converted to grams)||United Nuclear (2Fg assumed)|
|3"||17||15 round, 18 cyl (18" mortar)||20|
|4"||25||19 (24" mortar)||40||35|
|5"||45||60||36 - 45|
|6"||80||90-100||75 - 85||60|
|7"||110 - 130|
|8.5"||170 - 190|
|10"||240 - 280|
|12"||450 - 500|
|24"||4100 - 4850|
Many variables will affect the lift charge amounts. Shell type (cyl or round), weight, size (diameter), length if canister, powder grain, powder quality, tube length, loading space (distance between shell and powder charge), shell clearance, etc. (summarized from BAFN II page 138)
|Sieve Designation||Nominal Sieve Opening|
|4.76 mm||No. 4||0.187||4.76||4760|
|4.00 mm||No. 5||0.157||4.00||4000|
|3.36 mm||No. 6||0.132||3.36||3360|
|2.83 mm||No. 7||0.111||2.83||2830|
|2.38 mm||No. 8||0.0937||2.38||2380|
|2.00 mm||No. 10||0.0787||2.00||2000|
|1.68 mm||No. 12||0.0661||1.68||1680|
|1.41 mm||No. 14||0.0555||1.41||1410|
|1.19 mm||No. 16||0.0469||1.19||1190|
|1.00 mm||No. 18||0.0394||1.00||1000|
|841 mm||No. 20||0.0331||0.841||841|
|707 mm||No. 25||0.0278||0.707||707|
|595 mm||No. 30||0.0234||0.595||595|
|500 mm||No. 35||0.0197||0.500||500|
|420 mm||No. 40||0.0165||0.420||420|
|354 mm||No. 45||0.0139||0.354||354|
|297 mm||No. 50||0.0117||0.297||297|
|250 mm||No. 60||0.0098||0.250||250|
|210 mm||No. 70||0.0083||0.210||210|
|177 mm||No. 80||0.0070||0.177||177|
|149 mm||No. 100||0.0059||0.149||149|
|125 mm||No. 120||0.0049||0.125||125|
|105 mm||No. 140||0.0041||0.105||105|
|88 mm||No. 170||0.0035||0.088||88|
|74 mm||No. 200||0.0029||0.074||74|
|63 mm||No. 230||0.0025||0.063||63|
|53 mm||No. 270||0.0021||0.053||53|
|44 mm||No. 325||0.0017||0.044||44|
|37 mm||No. 400||0.0015||0.037||37|
A good reference for screen sizes: http://www.wovenwire.com/reference/mesh-locator.htm
Charcoal Tests Tables
The charcoal tests have assumed a life of their own so they now have a whole page all to themselves. See it at: charcoal_tests.html.
(from Pyrotechnica IX and Experimentation)
Make from lightweight aluminum sheet. Roll on an appropriately sized dowel or former and tape with thin strong tape. Stranded tape was used in the 1/2" version above. You can also use cardboard tubing or a couple of turns of heavy paper to make a cannula.
Shell Size Diameter 2" 1/2" 3" 3/4" to 1" 4" 1" to 1-1/4" 5" 1 1/2" to 1 3/4" 6" 1 3/4" to 2" 8" 2 1/4" to 3"
Pressures that Burst Common Rocket Tubes
(as done by Ned Gorski and posted with permission)
|Type Tube||Burst Pressure|
|1/8" wall from PGI vending||3200|
|1/4" wall from PGI vending||4500|
|1/4" wall from Skylighter||3600|
|1/4" wall from Skylighter with Minwax||4300|
|1/4" wall Precocious Pyrotechnics Tube||3400|
|1/4" wall Precocious Pyrotechnics Tube with Minwax||3900|
|1/8" wall New England Paper Tube||5700|
|1/4" wall New England Paper Tube||10000|
The following is a post from Mike Swisher on Passfire. It is reprinted here with permission.
The customary sizes are:
1-1/2" long X 5/16" ID X 1/2" OD
2" long X 5/16" ID X 1/2" OD
2-1/2" long X 5/16" ID X 1/2" OD
3" long X 5/16" ID X 1.2" OD
The above are for timed-report and hammer shell inserts and for 3" shells. The 1-1/2" length is for between breaks in 3" multi-break shells and for the tops of 3" 1-breaks. The 2" length is for the tops of 3" multi-breaks and for shorter timings in inserts. The 2-1/2" and 3" lengths are for longer timings in inserts.
2-1/2" long X 5/16" ID X 5/8" OD
3" long X 5/16" ID X 5/8" OD
4" long X 5/16" ID X 5/8" OD
The above suit shells 4" and up. The 2-1/2" length is for the tops of 4" shells and between breaks in 4", 5", and 6", unless an extremely long timing be needed. The 3" length is for the tops of 5" and 6" shells, for bottom shots in those sizes, and may be made to work between breaks in 8" and occasionally larger shells. The 4" size is for the tops of 8" shells and may be made to work for 10" shells; it also suits between breaks in 10" and 12" shells. I mostly use metal spolettes on the tops of 10" and larger shells. They can be cut to whatever length needed.
If you are ordering un-cut tubes, then, only two sizes are needed: 5/16" ID X 1/2" OD and 5/16" ID X 5/8" OD. It is better to have the OD run on the large size than on the small, so it fits tightly in the hole of a disc. I have some old red-rope tubes that are about 21/32" OD and they work nicely if one has discs that are slightly loose on 5/8" OD spolettes.