Seeking Advice on "Flying the Field"

[KerryQuinn]

I have been trying to come up with a methodical way to select engine & parachute sizes and launch rod angles and rod directions to keep rockets away from the flight line AND still on the flying field. Ted Cochran gave an excellent talk at Narcon2010 on flying safely - and that got me thinking further.

I have been running a bunch of simulations using OpenRocket to try to see how these variables interact at 10mph and 20mph winds. Here is a summary of some of my findings so far. I'm looking for feedback from the group to see if these findings make sense - and for suggestions on how to expand upon this study....

My study so far is for one of the home flying fields for the foxvalley rocketeers. All of the work below is for an AlphaIII flying on a C6-5 at this field on days with 10mph and 20mph winds with the winds blowing to the west (view in the figures is looking towards the north)

Our flightline is usually set up parallel to the southern edge of the parking lot.
In these simulations I flew with launch rod direction (LRD) pointed at 0/45/90/135/180 degrees where 0 degrees is into the wind. I also looked at launch rod angles (LRA) of 10 and 20 degrees off vertical. I studied normal deploys of an 8" and 12" chute as well as non-deploy (lawndart) flights.

My findings (see attached plots) suggest that angling the LRA 10 or 20 degrees AWAY from the flight line is a good idea (no suprise), that using a smaller chute keeps the rocket on the field (no suprise) and that flying in lower winds keeps the rockets on the field (no suprise).

The results also suggest that flying with a LRD of between 90 degrees (crosswind) and 45 degrees into the wind is optimal for our flying field. (One thing not obvious from these google_earth plots is that the area downwind of the soccer fields is a swamp.)

A problem with this type of analysis, however, is that it is all for a single rocket & engine & wind direction. I'd like to be able to generalize the analysis without having to re-run all of the cases for every rocket, engine, wind combination. Since peak altitude, stability and inertia are all significant, I don't see a way around this.... any thoughts?

-Kerry

 

[MarkII]

Sounds like a good R & D project for NARAM.

One skill that I really want to get better at is the ability to launch any of my rockets on any of the motors that I use and have them drop into a prescribed sector of the field during recovery, all with pretty good precision and predictability. My goal is to be just like a good batter in a baseball game who is able to consistently drop hits into the parts of the field "where the other side ain't." Undoubtedly this will be more art than science, but science will certainly factor into it. I'm not sure how much precision is realistically possible, but it's something that I want to work toward. I don't want to be just a good rocket builder; I want to be a skillful rocket flier, too. With the very circumscribed launch fields that we have in the eastern US, I think that it is a skill that is becoming ever more relevant.

Mark K.

 

[sylvie369]

Easily the simplest way to make sure that you land on the field near the pad is to put an expensive tracker into your rocket.

 

[TheAviator]

Sounds like a good R & D project for NARAM.

One skill that I really want to get better at is the ability to launch any of my rockets on any of the motors that I use and have them drop into a prescribed sector of the field during recovery, all with pretty good precision and predictability. My goal is to be just like a good batter in a baseball game who is able to consistently drop hits into the parts of the field "where the other side ain't." Undoubtedly this will be more art than science, but science will certainly factor into it. I'm not sure how much precision is realistically possible, but it's something that I want to work toward. I don't want to be just a good rocket builder; I want to be a skillful rocket flier, too. With the very circumscribed launch fields that we have in the eastern US, I think that it is a skill that is becoming ever more relevant.

Mark K.

We competitors have made an art out of doing exactly the opposite. The problem with precision landings is, as constant as we want it to be, the air mass on the field is always shifting and changing. The two big hindrances to landing perfectly are thermal/sink activity and variable winds. Variable winds can usually be somewhat corrected for, as an average wind velocity over the last minute will typically give you a good idea for the next minute. However, thermal/sink activity will change your decent rate and is much harder to compensate for. Thermals can can significantly decrease and even reverse your decent rate. Sink can push your rocket into the ground just as fast as the thermals can make it float away. It doesn't help that the two usually move with the wind.

That being said, just as competitors try to hit the thermals with duration models, you can deliberately miss them too. (This is an easier prospect.) Bodies of water or moisture (swamps, etc.) tend to kill thermals by absorbing the heat that creates and sustains them. Trees and other ground obstructions tend to break up the smooth flow that occurs in a thermal and collapse it. Large, flat, open spaces tend to create stronger thermals.

 

[The EGE]

Easily the simplest way to make sure that you land on the field near the pad is to put an expensive tracker into your rocket.

50% chance of a perfect landing near the pad, 50% in some unrecoverable spot, or a ditch that soaks and shorts out the tracker.

Seriously, though, that is very impressive stuff, definitely consider an R&D report. How'd you do the plots?

 

[KerryQuinn]

This is exactly some of the feedback I was looking for.
I too am wondering about what the "limit" is on being able to accurately
predict a flight - and I agree that variations in wind speed & direction make the "up" part variable and during the "down" you also have thermals to think about (at least with reasonably large chutes). I am planning to purchase a bulk pack of identical rockets, build them as similarly as I can, and then launch them one after the other from the same launch pad in succession to see what the landing distribution looks like. I am SURE lots of people must have done this before - but I don't recall seeing any tech reports on this type of research - anyone know of or can recommend one like that?

I performed these simulations using OpenRocket and then I created a utility program that translates the OpenRocket output files into trajectories you can load into Google_Earth. (Google Earth is a great program if you haven't tried it out - you can view/rotate/zoom all around your results - it is much better and more fun that these 2-D images convey. The 2D images are just screen captures of what I was seeing in Google_Earth.)

-Kerry

 

[MarkII]

We competitors have made an art out of doing exactly the opposite.

As I said, it might not be attainable, but it wouldn't hurt to at least work on improving the accuracy and predictability. I haven't flown too often when thermals were a factor (wind is a much bigger issue here) and I have never actually witnessed the classic thermal-induced phenomenon of a rocket gaining altitude while it was under 'chute.

Mark K.

 

[highpowerrocket]

Simulations are great and I applaud you for the systematic approach that you are taking. However, you can only go so far with simulations because our models rarely account for all of the variables life throws at us. The next step is keeping detailed records of your flights so you can compare them to the simulations. You may never get to the point of pin point predictions but my experience is that you will be able to meet your goal of avoiding the flight line while staying on the field.

 

[powderburner]

From a preliminary glance at your photos, there would seem to be a pattern indicating that you may want to move your launch location to another part of the field.

Other than that, have you tried using some weather-check rockets to see exactly what kind of winds you have to deal with? Those cheapo RTF POS rockets do indeed have a useful purpose. I suggest you bring one or two with simple nose-blow recovery (remove the parachute or streamer) for the first launch, and one or two more with small recovery devices (vented chute or short streamer, to deliberately obtain a high descent rate) to follow up and fine-tune your assessment of field conditions. Your "main" rockets, with full-sized recovery systems, will drift at least as far as the test rockets but you can at least get a feel for what the wind is doing right there on the spot.

You should start with small motors and build to higher-impulse motors. You may want to re-launch these test birds through the day, as weather conditions can change.

It's a lot cheaper to lose a weather-check rocket than watch a really nice one drift off the field into trees or houses. Besides, when the neighborhood kids show up you can get a couple to insert motors, load the wadding, prep the rocket, and launch.