How many 2-56 nylon screws do you guys use !

[daveyfire]

I use that chute as a drogue on my 4" Jart and it's perfect. Drops straight down with enough drag to hold the nose above the body.

My Jart probably weighs close to what your Magnum does, but the sectional density is much higher. You may want a slightly larger drogue.

 

[JP Morgan]

I use that chute as a drogue on my 4" Jart and it's perfect. Drops straight down with enough drag to hold the nose above the body.

My Jart probably weighs close to what your Magnum does, but the sectional density is much higher. You may want a slightly larger drogue.

Are you saying you use the Aerocon 18" chute?

The price on the Top Flight 24" Ultra X is fantastic!

After reading a few posts on Drogue chutes it looks like the better location is about 12"-18" from the Av Bay, hopefully
placing the fin can lower than the upper half when it deploys the Main Chute. I like that idea.

So today I'm testing the fin can separation charge. Glad I got 100 E-Matches and 3 pounds of powder!

JP

 

[daveyfire]

I'd personally go with something in the 24" range on a Magnum due to the size of the booster section and fins. I always attach my drogue at or very near the base of the avbay coupler to keep the sections as far apart as possible on descent.

 

[JP Morgan]

I'd personally go with something in the 24" range on a Magnum due to the size of the booster section and fins. I always attach my drogue at or very near the base of the avbay coupler to keep the sections as far apart as possible on descent.

10-4. Thank you! At first I didn't recognize the links you put in there! Great pics of recovery and hardware.
I'll place an order for the 24" Ultra X then.

The test for the fin can got rained out today...
I suspect 2.5 grams will be plenty as there's no nylon bolts to shear off and about the same amount of friction
on the connecting parts. We'll see.

JP

 

[dixontj93060]

10-4. Thank you!
I'll place an order for the 24" Ultra X then.

The test for the fin can got rained out today...
I suspect 2.5 grams will be plenty as there's no nylon bolts to shear off and about the same amount of friction
on the connecting parts. We'll see.

JP

Personally I would use a shear pin or two on the booster also just as insurance against drag separation which is dependent on how heavy the fore of your rocket is and how loose or tight your coupler is.

 

[dixontj93060]

So if I want to protect the nose cone from coming off at apogee, does using 3 screws provide 3 times the protection of 1 screw? E.g. if I wanted to ensure 90 lbf protection I'd use 3 2-56 screws at about 30 lbf shear strength each, am I really getting 90 lbf of protection or something less

Others may answer differently, I would answer yes. Remember what you are trying to guard against is the nosecone assembly from separating from the main payload. To calculate this, you would look at the mass/weight of your nosecone assembly, lets say 3 lb (or 20 lbs, I don't know). Take that and multiple by expected "shock" during flight and most specifically during drogue separation. This may be anywhere from 5 gees to 25 gees. I typically use 20 gees just in case I get an "end of shock cord event." So the amount your shear pins need to hold against is: 3 lbs * 20 gees = 60 lbs. So two, or, to be safer, 3 pins are required.

 

[MarkH]

Others may answer differently, I would answer yes. Remember what you are trying to guard against is the nosecone assembly from separating from the main payload. To calculate this, you would look at the mass/weight of your nosecone assembly, lets say 3 lb (or 20 lbs, I don't know). Take that and multiple by expected "shock" during flight and most specifically during drogue separation. This may be anywhere from 5 gees to 25 gees. I typically use 20 gees just in case I get an "end of shock cord event." So the amount your shear pins need to hold against is: 3 lbs * 20 gees = 60 lbs. So two, or, to be safer, 3 pins are required.

Thanks. I've got the mass x acceleration part for the drogue seperation shock loading. It sounded like what Bob was saying was that the shear force required for multiple screws isn't additive but this was in the context of blowing two sections apart. I was just going the other way with it, applying the same logic to the shock loading on my screws when the payload section comes to the end of the rope. I'll just keep on going with the additive approach, in the absence of any more accurate methodology for determining how much protection the screws in the nosecone are really providing.

 

[dixontj93060]

Thanks. I've got the mass x acceleration part for the drogue seperation shock loading. It sounded like what Bob was saying was that the shear force required for multiple screws isn't additive but this was in the context of blowing two sections apart. I was just going the other way with it, applying the same logic to the shock loading on my screws when the payload section comes to the end of the rope. I'll just keep on going with the additive approach, in the absence of any more accurate methodology for determining how much protection I really need.

Actually non-additive is what Bob is saying. But absent other contributing factors which are yet unidentified and aligning with both my observation over the years and comments/contributions from a couple ME friends of mine, I find that additive fits my needs. Again, I encourage validation and conclusions from your own ground testing before flight.

 

[MarkH]

Actually non-additive is what Bob is saying. But absent other contributing factors which are yet unidentified and aligning with both my observation over the years and comments/contributions from a couple ME friends of mine, I find that additive fits my needs. Again, I encourage validation and conclusions from your own ground testing before flight.

Totally agree.

 

[JP Morgan]

Personally I would use a shear pin or two on the booster also just as insurance against drag separation which is dependent on how heavy the fore of your rocket is and how loose or tight your coupler is.

Glad you mentioned that, I hadn't thought about drag separation.
Surely one screw will do but I may do two just for insurance. My charges work just fine. I've been using Black
Electricians Tape, three strips over top of canister and one wrap around diameter to hold those, packed well
with "Dog Barf".

JP

JP