Sugar rocket 23kft flight

[Cl(VII)]

That is so impressive. Thanks for sharing.

 

[Leo]

It seems, to me, that Eastern Europe countries have less restriction on motor impulse than Western Europe ?

What makes you say that?

 

[bobkrech]

Thanks guys. I was very surprised on the difference between altitude reading on Stratologger and ARTS2. GPS altitude and Stratologger altitude are preety close
(196 feet difference), but ARTS2 seems to be way off (1298 feet higher then Stratologger). It seems that Stratologger should be much more accurate with it's better baro sensor and 24 bit ADC compared to 10 bit ADC on ARTS2. Is this known issue with ARTS2 or was my unit not calibrated very well?

The 1300 feet difference at this altitude equals roughly to a difference of 20mBar air pressure. A 10bit ADC on an absolute pressure sensor with about 1050mBar range has an resolution of about 1mBar (~65ft resolution @ 23kft). The ADC alone (unless it is a horrible one with 20 LSB nonlinearity) wouldn't explain the difference. The classic Freescale sensors like the MPX4100A have an accuracy of 1,8% over the temperature range from 0°C-85°C. This alone would be nearly enough to explain the difference. In addition to that, there are many other sources for error. One notable difference, between the newer sensors from Meas Spec (probably an MS5607 on the Stratologger) is the calibration and compensation. The newer sensor offers a temperature readout and some calibration parameters (determined in the factory for each sensor) that allows the computation of a compensated pressure value that will be much more precise. The hardware temperature compensation in something like the MPX4100A works in a much simpler way and therefore is less accurate.

Finally, even the GPS system and the Stratologger have only a limited accuracy. The Stratologger uses an atmospheric model that does not exactly reflect the atmospheric conditions on your launch site. GPS on the other hand is less accurate in the vertical direction compared to the horizontal direction, because most of the visible GPS satellites are rather close to the horizon. All of the affordable (and unregulated) GPS systems are optimized for a different dynamic environment (cars, pedestrians). This will also limit the accuracy when used in rockets. Seeing that GPS and the Stratologger agree within less than 1% is quite good in my opinion, but you might have been lucky on this flight.

Reinhard

I'm comfortable saying the Stratologger is more accurate than the ARTS 2 when it comes to measuring altitude. The analog 4100 series altimeter is a 30+ year old design without smarts and is digitized with a 10-bit ADC. From graphs in the ARTS manual, it looks like the ground level resolution is 20'', reasonable for the era and very adequate for dual deployment application. The Stratologger has a current technology 24-bit digital sensor with a good atmospheric model and has temperature compensation with a resolution of better than 1' at sea level because it internally averages the sensor, has a very good atmospheric model and is temperature compensated. Regardless of precision, the accuracy in inversely proportional to pressure, so the higher you go the less accurate the altitude will become.

For contest altitude records, Tripoli uses Raven altimeters below 30 KFT and GPS above 30 KFT. A reason is the error analysis of a FAA certified altimeters indicates that a FAA certified barometric based altimeter is more accurate than a GPS based altimeter below 30 Kft most of the time. While it is possible for the GPS to be more accurate when there are multiple satellites in view and when at least 1 is overhead, there are many times when you do not have the optimum number of satellites or they are not overhead but near the horizon. The latter case gives very accurate lat-lon positioning but very poor vertical accuracy. When you exceed 30 Kft, the error analysis favors GPS almost all the time.

As a practical matter in both flights the Stratologger and the GPS are within 1% of each other, and the ARTS was not, however both the Strattologger and ARTS2 are excellent altimeters.

Bob

 

[Reinhard]

It seems, to me, that Eastern Europe countries have less restriction on motor impulse than Western Europe ?

I'm not aware of such differences. Here in Europe, if motors are restricted, it is usually by propellant weight. For example, until recently motors with more than 20g of propellant weight (this includes the mighty D12) required a permisson in Germany. There are few other reasons, why big motors aren't flown that often in Europe. The primary reason is probably the population density. Unfortunatly, we can only dream of locations like Black Rock. AT and CTI motors are also significantly more expensive here. And finally, the rocket comunity as much smaller.

Andre's flight happened at one of the few places where it is possible to fly a little higher: an area of the polish army in Torun. Now that I think of it, 3 out of 5 launch sites that I've visited over the last years, were military installations: Besides Torun there is the drop zone near Manching (Germany) and the missile test range in Biscarosse (France).

Reinhard

 

[rocketsaway]

From oversea customers correspondence , mainly France.
W/out going into details, seems 29mm-ok, 38mm-2G ok, 38mm-6G not so and definitely not 54mm.
I have seen non-public videos of West EUR launch fields were its possible to go 10k+ w/out tree probs.
Though I havnt any EUR requests for 76/98mms, I was surprised to see the 98-N motor.

out of curiosity, why all aluminum ? 1.9mach doesnt require it. CF or FG would be much lighter.

nice grains :wink:

 

[Interceptor]

Hi Andre. Congrats on your project.
Im new to rocketry so this may be a basic question but are you not taking a risk by using one chute ?
Some detailed pics of the internal workings would be great.

 

[Andre]

out of curiosity, why all aluminum ? 1.9mach doesnt require it. CF or FG would be much lighter.

You are right Ed. Mach 1.9 can certainly be done without aluminum. However this is a sort of a boilerplate rocket for future rockets that will go higher and faster and where this sort of construction will be needed. As I said in my first post this rocket was mainly built to gain some experience with larger sugar motors and to test some new (for me at least) construction techniques. Besides if you have machines available building with aluminum is usually much faster than laying numerous plys of fiberglass then curing it, sanding, painting, polishing, etc. I think it took me about 4 hours to build this fincan.

Im new to rocketry so this may be a basic question but are you not taking a risk by using one chute ?
Some detailed pics of the internal workings would be great.

Every flight possesses some degree of risk. My approach is to make things as simple as possible. That means very simple recovery scheme with one or two altimeters and a single small chute deployed at apogee. Descent rate of about 60ft/s is used to reduce drift. This may seem high but it's no problem for all aluminum rocket. Besides simplicity, single small chute requires very little space which means much shorter and more compact rocket which also means lighter rocket and better overall performance. If you look at some high power rockets more than half of the body lenght is used for electronics and dual deployment systems with huge parachutes. Off course all this adds a lot of extra weight, which makes very poor propellant mass ratio, which means that even with high specific impulse APCP propellant you won't go very high.
Right now I don't have any available photos of the recovery system but you can see the electronics bay in the video from the first flight. This electronics bay is screwed to a short lenght of aluminum tube. On top of the electronics bay is a plastic piston and a X-form parachute with kevlar/nylon shock cord. That's it- very simple.

 

[Andre]

Some detailed pics of the internal workings would be great.

Here it is: