Filament-Wound NC's & Shear Pins

I'm building a Frenzy Massive with one of the 'relatively' new filament wound nose cones. In the past, I've usually gone with (3) 2-256 bolts as NC shear pins. With the additional mass of the FW NC, I was planning to move up to (3) 4-40 bolts instead. Info-Central's ejection charge size calculator shows I should be using 5 or 8 instead.

Any feedback on what has worked for you with these NC's?

Thanks in advance.

SSenesy said:

I'm building a Frenzy Massive with one of the 'relatively' new filament wound nose cones. In the past, I've usually gone with (3) 2-256 bolts as NC shear pins. With the additional mass of the FW NC, I was planning to move up to (3) 4-40 bolts instead. Info-Central's ejection charge size calculator shows I should be using 5 or 8 instead.

Any feedback on what has worked for you with these NC's?

Thanks in advance.

Click to expand...

Be careful of your interpretation. InfoCentral reports the number of shear pins equal to the lbs force you have selected. That doesn't mean you should use that number of shear pins. On a typical flight you might experience up to 50 gees (some even say 100 gees, but I use 50) of force. Multiply this by the weight of the nosecone and then you have the total that your shear pins should inhibit, e.g., 50 gees * 2 lb nosecone = 100 lbs. This would equate to a bit over two 4-40 nylon screws (40 to 45 lbs each) but you should have some "overage" so three screws should be just fine for that 5.5" airframe; personally I have gotten by with much less on a 5.5" airframe (3, 2-56 screws), but I had a lighter, plastic nosecone.

Thanks for the info!

So, if I'm reading it right..

NC weight is just over 4 pounds which at 50g's would mean 200 pounds of force. So I'd need (5) 4-40 bolts to give me about 200 - 220 lbs of resistance?

SSenesy said:

Thanks for the info!

So, if I'm reading it right..

NC weight is just over 4 pounds which at 50g's would mean 200 pounds of force. So I'd need (5) 4-40 bolts to give me about 200 - 220 lbs of resistance?

Click to expand...

Actually four is probably OK (I was a little low on the 4/40 shear which should be 50 to 76 lbs).

View attachment Shear Pin_Screw Calculations.pdf