delta22
Well-Known Member
- Joined
- Jan 21, 2009
- Messages
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patelldp,
There are many relevant issues your previous comments fail to consider:
1) For relatively slow rockets, the relationship between altitude and impulse is very far from linear. For example my son's LOC Viper 4 flies 650ft on 4x D12 and 320 ft on 3x D12. This is with 7 oz rocket weight per D12, for the Thunderbird at 10 oz per D12, the proportional reduction in altitude is greater.
2) Estes motors have a substantial thrust spike at the beginning of the burn that I counted on to successfully to achieve a straight vertical flight off the 6 ft rail.
3) There were very light winds on the field at the time of launch.
4) The rocket is precisely modeled in RockSim 9.0 to confirm stability and the ability of these motors to lift this rocket.
5) CG was confirmed to be proportionally further forward than on the FlisKits Thunderbird.
6) Estes engine chart rates a lifting capacity of 10 oz per D12-5 motor, so if all motors had fired the ejection charges would have fired near apogee.
7) Estes engine chart rates a lifting capacity of 14 oz for the D12-3 motor, so concerns about not flying straight off a 6 ft rail would only come into play in the event of a very high ignition failure rate.
8) An H cluster requires a 200 ft safety distance, which was observed as it always is at CMASS. This creates a very large safe area around the launch for a flight that was expected to reach 480 ft and achieved a perfectly straight flight to about 120 ft.
9) I chose to err on the side of assured stability by using only less heavy D motors for the first flight. This increased the risk of low overall altitude but gained stability margin. Future flights will include some BP E's and an AP F or G as noted previously. I wanted and got a straight up flight off the rod.
Additionally, in over 50 cluster flight firing more than 300 motors, I have averaged well over 95% of loaded motors fired. In more than 30 of those flights I fired all engines. I have never had any rocket ever approach spectators under power, clustered or single-motor.
If every rocket that failed to recover well was judged to be a mistake in the first place, we would all be building model trains...
There are many relevant issues your previous comments fail to consider:
1) For relatively slow rockets, the relationship between altitude and impulse is very far from linear. For example my son's LOC Viper 4 flies 650ft on 4x D12 and 320 ft on 3x D12. This is with 7 oz rocket weight per D12, for the Thunderbird at 10 oz per D12, the proportional reduction in altitude is greater.
2) Estes motors have a substantial thrust spike at the beginning of the burn that I counted on to successfully to achieve a straight vertical flight off the 6 ft rail.
3) There were very light winds on the field at the time of launch.
4) The rocket is precisely modeled in RockSim 9.0 to confirm stability and the ability of these motors to lift this rocket.
5) CG was confirmed to be proportionally further forward than on the FlisKits Thunderbird.
6) Estes engine chart rates a lifting capacity of 10 oz per D12-5 motor, so if all motors had fired the ejection charges would have fired near apogee.
7) Estes engine chart rates a lifting capacity of 14 oz for the D12-3 motor, so concerns about not flying straight off a 6 ft rail would only come into play in the event of a very high ignition failure rate.
8) An H cluster requires a 200 ft safety distance, which was observed as it always is at CMASS. This creates a very large safe area around the launch for a flight that was expected to reach 480 ft and achieved a perfectly straight flight to about 120 ft.
9) I chose to err on the side of assured stability by using only less heavy D motors for the first flight. This increased the risk of low overall altitude but gained stability margin. Future flights will include some BP E's and an AP F or G as noted previously. I wanted and got a straight up flight off the rod.
Additionally, in over 50 cluster flight firing more than 300 motors, I have averaged well over 95% of loaded motors fired. In more than 30 of those flights I fired all engines. I have never had any rocket ever approach spectators under power, clustered or single-motor.
If every rocket that failed to recover well was judged to be a mistake in the first place, we would all be building model trains...