Rocksim not showing a rocket in (Flight Simulation) to launch.

[Sterk03]

First I am new to rocksim and learning so go easy on me. I have an Estes Saturn Skylab file and When I first opened it and added an engine it would show a flight sim with results. I wanted to use the Estes F15-4 as advertised by Estes for the rocket. I had a launch or two with results but they showed it weather cocking with 8mph and 0 mph wind. I notice that the 12.31 overstable with the engine loaded?
Seems hight to me for looking at the diagram it shows maybe a little over the diameter of the body tube so why 12 and then I notice they have 30g of the 60 grams mass loaded in the front of the nose cone? I want to then enter my weight and cg and do a mass overide to see what engine I need as my rocket comes in at 625G and CG 24.0 I wanted to see what size I would need for that weight. It would not display any engines or I could enter an engine but no rocket would show up again in the Flt Sim display? I am going back to reference the Rocksim file weights vs my actual weights and see why the huge difference but I am baffled if it is so overstable why add 30 of the 60grams recomended in the nose to increase stability and increase the weight. I checked that there was no hidden mass overide but I don't understand why it will not show any rocket to flight test in Flight Sim. I will try to re-install Rocksim just incase I messed something up but it was working just fine for other rockets prior?
Thanks in advance for any insight.

Sterk03

 

[aerostadt]

I am looking at your RocSim and I don't see anything immediately wrong. I am not familiar with this model, so I am amazed at the low model weight (12 oz). I see 2.11 oz ( or 60 gm ) nozzle clay weight, which seems to me to be a lot. The margin of stability with no motor is shown as 30, which seems very high. No wonder when a motor is inserted the stability margin comes down, but is still in the low 20's. I do not see E12-4 on the RocSim recommended motor list. You might want to ask Apogee your questions.

 

[aerostadt]

Your 625 g (or 22.04 oz) is considerably higher than the RocSim weight of 12 oz.

 

[aerostadt]

My thinking is that your measured weight is higher than the RocSim weight. I have found over the years that often a "design" RocSim file weight will differ considerably from the actual weight. I think this is what you are stating in your first post. In this case I would ake the actual weight (say 625 g or 22 oz) and subtract the best Design RocSim weight, say 12 oz. In the current case the RocSim model needs 10 more ounces. I would then place an "added mass" of 10 oz in the RocSim model and iterate moving it until I get a RocSim model that has a c.g. location that is close to your measured c.g. You now have a RocSim model that has the correct gross mass and c.g. location. It will not have a correct component-by-component weight, but should be good on giving altitude performance and margin of stability predictions.

 

[Sterk03]

I was thinking it had something to do with the high overstable number and I was questioning the same why add weight and you have plenty of cg when the weight is removed. The last coment is sort of like me just putting in mass overide of my present weight and my present cg which I have tried and it willnot produce any engines as recommended. I just tried to enter the design file I attached into a new install of rocksim n another computer. It will not show a flight sim after I select the F15-4 engine. its just a blank blue sky, I then tried a a Saturn V Estes not the Skylab version and it will not show a Flt sim either after an engine is sellected so I have no clue. I could rebuild one and use my weights for each part and see if that works.

Thanks for info and I'm still open for answers.

Sterk03

 

[bobbyg23]

So the weight without motor seems low to me. I only have open rocket and it shows 2.43 cal for stability without motor and 1.6 cal with motor so right on.

 

[bobbyg23]

Do you know what your finished weight is?

 

[aerostadt]

I think the RocSim and Open Rocket models are about the same. I loaded the RocSim file into Open Rocket and the weight is 353 grams or 12.45 oz. This is essentially the same as RocSim weight of 12.43 oz. The stability margin is high in RocSim because the reference diameter is the nose cone, which gives a margin of 30.35 for the empty rocket. Multiplying 30.35 by the nose cone diameter .36", I get a distance of 10.93" (again, for empty rocket). Open rocket is probably using the base diameter 3.938" for the stability margin 2.43 cal . If I multiply 2.43 x 3.938", I get 9.57" for the margin of safety distance for an empty rocket, similar to RocSim.

I am not understanding the flight simulation issues. I loaded in an E-9 in RocSim and got a flight simulation, but it was only around 150'.

 

[kalsow]

I notice that the 12.31 overstable with the engine loaded?
Seems hight to me for looking at the diagram it shows maybe a little over the diameter of the body tube so why 12

On the "Rocket design attributes" tab, for the "Static margin reference" you have the default "The nose cone base diameter" selected. Your defined nose cone is just the tiny tip with a diameter of 0.36 inches. For the static margin reference, select "The user reference diameter below", then enter the diameter of your main tube, 3.938 inches, in the box below. You static margins will look much better.

I don't know why the simulations are failing. RockSim is pretty terrible about reporting inconsistencies, divide-by-zero faults, etc. Usually there's a single component with zero thickness walls or zero mass, or something else it doesn't like. My go-to debugging strategy is to start deleting components until things start working. I would start with the fin faring pods. Is a pod that consists of just a transition really allowed? Changing the transitions to conical nose cones might help. If it doesn't, delete the farings and the associated pods. Does it work then? I dunno.

Good luck.

 

[Sterk03]

Yes I was going to go through each item I did once just to make sure no mass overide but have not sat down to check weight of each item. I really did not think my rocket was that heavy but I'm not really sure how it could be that much difference. The margin was way to much and having built the simular Saturn V it was not adding up. My newness to rocksim would not catch the nose cone diameter but that makes sense in this issue. I will need to go to open rocket to se what you said about the nose cone and also just go through each segment again. The added mass they show in the nose cone does not add up with the stability numbers so I knew somewhere it was not correct. The rocket comes with clay for adding up to 60g in the nose cone so I feel it will take some weight but I first need to address the nosecone diameter. Thanks to all and I will let you know the outcome. All I could think about the no rocket in the flt sim was with the non normal stability issue the selected rockets were not adding . From the Saturns I know it will need more then a E estes motor but I thought for the first flight a F-15 might be ok. It really needs an AT E30 or F32 to get the speed off the pad which I probably will use.
Weight without engines is 526g and cg 22.5 the instructions have the cg marked at about 24/25 so with a ATE30-4T I'm around 628g. I'm sure its my amount of epoxy and paint making it higher then it should be. I'm trying for a launch Saturday but now 3 inches of snow and then rain will make a mess. UGH
Thanks to all again I do appreciate it, will let you know.

Sterk03

 

[Sterk03]

My Sat V Skylab is 629g and 24.0 cg as mentioned above. I realize it is much heavier then the rocksim and I'm not sure why, that is why I'm wondering if the rocksim file is correct. I will go through each item and check weights against each other. I thin the stability margin is like someone said the difference in the diameter of the nose cone. I will have to look at that and it makes sense there is no way it can be that much overstable when the Saturn V 100 scale is always needing nose weight to ???? Thanks to al and todays launch is cancelled so it will be a month until I see how she flies!

Sterk03

 

[aerostadt]

Thanks to al and todays launch is cancelled so it will be a month until I see how she flies!

If you see things on the simulation that you don't like and, especially, if a bad flight is predicted, it is good to delay the flight until things are resolved to have a good flight.

 

[PhlAsh]

discontinuity between tube sizes with cause things to go pear-shaped as well.