# how much black powder do I use?

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#### Clipper

##### Well-Known Member
I have looked in several locations, but I have not been able to determine how much black powder to use for ejection. Is their an equation? I'm going to use a Madcow Squat for my Level 1 and it has a very small cavity for the parachute.

#### MarkII

##### Well-Known Member
In my own flying, I have never had an occasion to use anything other than motor-initiated deployment. But this page includes a black powder calculator that might be helpful.

Mark K.

#### THier

##### Well-Known Member
Well,, a lot of folks use a down and dirty way to calculate ejection charges, 1gr for each inch of airframe diameter. 1" diameter = 1gr bp, 4" diameter = 4gr. ect ect ect.

Tom

#### dave carver

##### ....what hump?
Problem With the 1 gram to 1 inch formula is it really doesn't make any allowance for total volume. Guess there should be a multiplication factor for length to be pressurized.

#### THier

##### Well-Known Member
Problem With the 1 gram to 1 inch formula is it really doesn't make any allowance for total volume. Guess there should be a multiplication factor for length to be pressurized.
Like I said "down and dirty" never claimed it to be the best.

Tom

#### new2hpr

##### Well-Known Member
Well,, a lot of folks use a down and dirty way to calculate ejection charges, 1gr for each inch of airframe diameter. 1" diameter = 1gr bp, 4" diameter = 4gr. ect ect ect.

Tom
Ouch! I've only used 1.1gr for drogue and 1.5gr. for main with shear pins on my 4".

If you're using motor eject, just use what came with it. If electronic, ground test until you get just the pop you want.

-Ken

#### uwish

##### Member
In general I find most people use to much. That being said, it is better to have a little more than not enough.

I can yield my own examples. I have flown my complex air start which is a 6 in diameter and the upper airframe is about 1m in length with only 2 grams of BP. I have never had an issue with pressurizing the tube.

I always recommend a ground test in full flight configuration.

#### Clipper

##### Well-Known Member
Thanks, great information.

Eric

#### Handeman

##### Well-Known Member
TRF Supporter
Both the pages listed, EMRR and Info Central, are great for a starting point.

GROUND TEST!!!! :y:

I've use both sites and the initial calculations have been pretty good, but there were a few that were way off from what I actually needed.

GROUND TEST!!!! :y: