RocketTree
Well-Known Member
In this thread, I would like to discuss ejection charge pressures, and deployment area volume limits with disposable/reloadable motors. Unlike smaller model rockets, the recovery gear volume must be optimized for sufficient deployment pressure on larger diameter models - for example 4 inch dia.
Assuming we can not add more black powder, what are the limitations of a factory deployment charge in disposable or reloadable motors?
If a disposable Aerotech G motor has 0.7g black powder and we are building a 4 inch diameter rocket:
What is the maximum recovery gear volume to achieve 10-15psi?
3.9" (ID) x 7" = 16.25psi (83.6 cu in) 194lb force
3.9" (ID) x 8" = 15psi (95.6 cu in) 179lb force
3.9" (ID) x 9" = 13psi (107.5 cu in) 155lb force
3.9" (ID) x 10" = 11.5psi (119.4 cu in) 137lb force
3.9" (ID) x 11" = 10.5psi (131.4 cu in) 125lb force
3.9" (ID) x 12" = 9.5psi (143.3 cu in) 113lb force
With a suggested 10-15psi, it looks like our maximum volume can be determined.
We should also consider the volume of the motor mount tube itself.
Motor tube 1.1" x 18" = Volume 17.11 cu in
This would drop the pressure by an additional 1psi.
From here, we know the recovery bay should optimally be 7 inches (up to a maximum of 10 inches)
How can we increase pressure without adding more black powder or reducing recovery bay size (assuming we can't add BP)
- Seal-off factory nose cone (big hole in the bottom)? (but leave a small pinhole for equalizing)
- Add solid mass? (Large styrofoam ball, etc)
- More stuffer tube and plate?
- If recovery gear itself (parachute, nomex, cord, etc) adds internal mass, reduces volume - we can assume it will cause a higher pressure than previously calculated.
How much black powder in various motor types/brands?
- Do larger disposable motors have more BP? (eg. M1350, H180 ,I205....)
- How much BP charge in Aerotech RMS vs DMS
- How much BP charge in CTI and other brand motors?
- What is the BP equivalent of an Estes A - F black powder motor ejection charge?
Should a small diameter rocket use less than 0.7 BP than included from factory?
Minimum diameter rocket 29mm (1.1") @ 24" long with Aerotech G80-13T
0.2 grams BP = 15psi and 14 lb force on the nose cone base.
0.7 grams BP = 50psi and 57lb force on the nose cone base.
If the entire BP charge is not necessary, some of that BP could instead be used on larger rockets.
Do we take a chance and reduce the amount, or just use it all?
How relevant is the lb force on the nose cone in small vs large diameter rocket?
What is the maximum amount of BP you can SAFELY use in a DMS (disposable motor system) cartridge?
Any ideas or previous experience?
----------------------------------------------------------------------
Looking for your input.
Thanks
-RocketTree
Assuming we can not add more black powder, what are the limitations of a factory deployment charge in disposable or reloadable motors?
If a disposable Aerotech G motor has 0.7g black powder and we are building a 4 inch diameter rocket:
What is the maximum recovery gear volume to achieve 10-15psi?
3.9" (ID) x 7" = 16.25psi (83.6 cu in) 194lb force
3.9" (ID) x 8" = 15psi (95.6 cu in) 179lb force
3.9" (ID) x 9" = 13psi (107.5 cu in) 155lb force
3.9" (ID) x 10" = 11.5psi (119.4 cu in) 137lb force
3.9" (ID) x 11" = 10.5psi (131.4 cu in) 125lb force
3.9" (ID) x 12" = 9.5psi (143.3 cu in) 113lb force
With a suggested 10-15psi, it looks like our maximum volume can be determined.
We should also consider the volume of the motor mount tube itself.
Motor tube 1.1" x 18" = Volume 17.11 cu in
This would drop the pressure by an additional 1psi.
From here, we know the recovery bay should optimally be 7 inches (up to a maximum of 10 inches)
How can we increase pressure without adding more black powder or reducing recovery bay size (assuming we can't add BP)
- Seal-off factory nose cone (big hole in the bottom)? (but leave a small pinhole for equalizing)
- Add solid mass? (Large styrofoam ball, etc)
- More stuffer tube and plate?
- If recovery gear itself (parachute, nomex, cord, etc) adds internal mass, reduces volume - we can assume it will cause a higher pressure than previously calculated.
How much black powder in various motor types/brands?
- Do larger disposable motors have more BP? (eg. M1350, H180 ,I205....)
- How much BP charge in Aerotech RMS vs DMS
- How much BP charge in CTI and other brand motors?
- What is the BP equivalent of an Estes A - F black powder motor ejection charge?
Should a small diameter rocket use less than 0.7 BP than included from factory?
Minimum diameter rocket 29mm (1.1") @ 24" long with Aerotech G80-13T
0.2 grams BP = 15psi and 14 lb force on the nose cone base.
0.7 grams BP = 50psi and 57lb force on the nose cone base.
If the entire BP charge is not necessary, some of that BP could instead be used on larger rockets.
Do we take a chance and reduce the amount, or just use it all?
How relevant is the lb force on the nose cone in small vs large diameter rocket?
What is the maximum amount of BP you can SAFELY use in a DMS (disposable motor system) cartridge?
Any ideas or previous experience?
----------------------------------------------------------------------
Looking for your input.
Thanks
-RocketTree