Some help with a sim?

Would someone mind running a sim on this: a Goonified LOC Viper III? I'm most concerned about the amount of nose weight I need to make it stable.

The main BT is 7.5" and the 3 MMT tubes extend 2.25" past that. The dimensions of the three fins are in the attached picture. They are actually a little wider, but some of the fin is in the crease.

Thanks a million for the sim help.

More information would be helpful like what size of motor will you be using.

If I read it correctly your 3 MMT extends past your body tube by 2.5" into the nose cone????

I did a quick and dirty sim and with 3xC6-7, about 3 oz of weight will give you a static margin of 1.5.

Also a simulated altitude of around 1000ft.

kj

I think the MMT's extend past the AFT of the body tube by 2.25"..

I did a quick and dirty sim on it and in mine reqiures 4.5oz of nose weight:surprised: to get an UNloaded margin of 1.54..Loaded with 3xC6-7's it shows unstable at -0.02 margin but flies straight to an altitude of ~1300 ft and a Deployment Velocity of 23.25ft/sec

I did a little more tinkering with rocksim on this and got the unloaded margin up to 1.6 with 2.75oz of nose weight(I changed the nose cone to plastic from balsa)..Sims loaded with C6-7's as marginal at .99- so close enough..Flights on C6-7 take it to 1700 ft

Have attached my RS file if anyone cares to take a look at it and do their own 'tinkering'..

View attachment Goony Viper III.rkt

Ahh, you used longer motor tubes than I did. I just put in the standard BT-20 motor mount tubes of 2.75" and no CR.

View attachment Goony Viper IIIa.rkt

So what we have is two different people using Rocksim and coming up with different amounts of required nose weight.

Then consider that Rocksim's estimate of the CG may not be accurate; it may have wrong values for masses of certain items, and it certainly won't know how much glue and paint you've used. Which means that when I've used it on my own rockets, I sometimes need to add an extra mass item to move the CG to where it really is on the model.

So I'd suggest that you build the model without nose weight, use Rocksim to find its CP, then keep adding nose weight to the real model until the CG is where you want it. If you want to simulate its flight, add the nose weight into Rocksim, then add additional mass as required to get the rocket's CG and overall mass accurate.

zog43editor said:

Ahh, you used longer motor tubes than I did. I just put in the standard BT-20 motor mount tubes of 2.75" and no CR.

Click to expand...

Yeah, I figured that way the tubes would be more secure and straight...And your right Adrian, 2 RS files, 2 different nose cone weights..lol..RS does have a lot of leeway as far as component weight and such-I agree..This was just to give an 'approximation' of what the real world rocket will do..

Yeap, RockSim can be a good tool, but you have to take it with a grain of salt. Also the 1st sim I did on version 8 but didn't save it. The one I posted was built in version 7 and it came up with a different answer than what version 8 did.

kj

Thanks for your help. I'll start with the lower weights and then do some swing testing.

Ummmmm, make sure you load it with motors before doing the swing test! Empty the CG is on the nose cone..Loaded with 3 C6-7's it should be between about 5 1/4" to 5 1/2" from the tip of the nose cone...

Mine shows loaded CG at 5.2501" and KJ's shows at 5.4978"