Hybrid question

[markkoelsch]

Hi, I am trying to help a high schooler who asked for my help with a motor file for the Hypertek 54mm K240 motor. He has sent me the dry weights. This is the 835 cc tank. It has been a long time since chemistry- how much mass will a full/typical fill add mass wise? I realize this is temperature dependent.

Thanks

 

[dhbarr]

The AT 440cc tank takes 299g of nitrous, so I'd ballpark the 835cc at around 565g.

 

[mikec]

Hi, I am trying to help a high schooler who asked for my help with a motor file for the Hypertek 54mm K240 motor. He has sent me the dry weights. This is the 835 cc tank. It has been a long time since chemistry- how much mass will a full/typical fill add mass wise? I realize this is temperature dependent.

Thanks

From google searches, N2O liquid density at 70F is 0.77 g/cc, so if an 835cc tank were full it would be 643 grams. I'm sure it's much more complicated than this as the tank probably isn't full, is pressurized, is a mixture of gas and liquid, etc. Someone with more hybrid knowledge than me could give you a better answer.

 

[markkoelsch]

Thanks Gents. Just trying to help the guy. Hybrid motor files have always been a bit tricky due to the variance in fill due to a variety of factors all of which can directly effect performance.

 

[dhbarr]

Is it the 54mm or 81mm k240?

https://hypertekhybrids.com/jspecs.htm

Should be able to dial in based on the listed upper / lower weights.

EDIT: DERP! Thrustcurve has the 81mm and it says 54mm in the opening credits.

EDIT2: I'll bet a dollar the dry weight of the fuel grain by itself is about 748-567= ~180g

 

[AlphaHybrids]

Those tanks have a dip tube in them to provide some ullage space for gas for pressurization, typically this is 10%. That would leave you with ~751 cc of space. If your tank is ~850 PSI when filling getting the flight tank would probably be around 70 degrees/750 psi after filling. Using the density of 0.77 grams/cc you would have 579 grams. That would be a good starting point.

Edward

 

[dhbarr]

According to https://www.macmillen.com/rocketry/motor_nox_weight.html , it appears up to 620g ; that would only leave about 30cc's of headspace.

Personally I think that would be far too full and would stick with the 565-580 range. But what I don't know about hybrids can and does fill many books

 

[markkoelsch]

View attachment Hypertek_K240_54mm.engGents, thanks for the input. After some cyphering the attached is about the best I think I can do.