Open Rocket motor tube question

[qquake2k]

Can someone tell me why the motor tube is hanging out so far? I have it set as a motor tube, and the motor overhang set at zero. Also, the sims seem off. It should sim a lot higher.

View attachment Viking XL.ork

 

[Rex R]

found it, for some reason your bt is also set as a motor mount with a motor overhang of 2"...so uncheck the main body tube is a motor mount and you'll be good to go(you should redo your motor configurations and make sure the body tube is not selected). as for altitude simulations I did look into that, yet.
Rex

 

[K'Tesh]

Rex beat me to it... However, I see the motor overhang on the inner tube as .375". You might want to adjust that too.

 

[Rex R]

so I tried a few tricks and got the projected altitude up to 1434'. keep in mind that this is a heavy bird, number 1 problem is you have 5 airbrakes pretending to be fins.... 1st trick was to make the fins 10% smaller, 2nd was to reduce thickness to 0.125", this netted me 1044'(up from 834'), then rounded the edges this pushed the alt. to over 1400' (on a G64-5). for reference I include my edited version file, have fun
Rex

View attachment QViking XL_edit.ork

 

[qquake2k]

found it, for some reason your bt is also set as a motor mount with a motor overhang of 2"...so uncheck the main body tube is a motor mount and you'll be good to go(you should redo your motor configurations and make sure the body tube is not selected). as for altitude simulations I did look into that, yet.
Rex

Thanks Rex, I missed that. I downloaded the RockSim file from Rocketryreviews, and upscaled it in Open Rocket. Whoever made the file must have done it.

 

[Peter Olivola]

There are very few, if any, .rkt files that don't need to be massaged in OR. It's a good idea to start with a default assumption that nothing is correct, check everything, and smile when you only have to make a handful of changes.

Thanks Rex, I missed that. I downloaded the RockSim file from Rocketryreviews, and upscaled it in Open Rocket. Whoever made the file must have done it.

 

[K'Tesh]

Thanks Rex, I missed that. I downloaded the RockSim file from Rocketryreviews, and upscaled it in Open Rocket. Whoever made the file must have done it.

I'd strongly suggest that if it came from RocketryReviews that you find an image of the original fins with a ruler (or get someone who has one to do it for you) and upscale from there. RRs .rkt files are really prone to having "close enough" fin templates that when used directly end up looking odd (because they weren't really close enough).

 

[Rex R]

well since the Viking in its' original form is a minimum diameter bird, having the body tube as the motor mount is correct, though I am not sure about the 1/2" overhang . one of the 'gotchas' of upscaling rockets.
Rex

 

[qquake2k]

I'd strongly suggest that if it came from RocketryReviews that you find an image of the original fins with a ruler (or get someone who has one to do it for you) and upscale from there. RRs .rkt files are really prone to having "close enough" fin templates that when used directly end up looking odd (because they weren't really close enough).

I always rework the file, since it will be an upscale. First time I've seen this, though.

 

[K'Tesh]

I always rework the file, since it will be an upscale. First time I've seen this, though.

Sometimes manufacturers post there, and rework the fins to see who's been cloning them. Then there was the whole Vigilante "fins are just wrong" situation.

Here's what I found over on RR and what I was able to work out the actual fins were using a scan from JimZ's site:

While they're both 2.75" at the root, and 2" in span, I took one look at the image on RR, and knew it wasn't right. And, I hadn't ever seen one except in catalog photographs up until that point. They totally don't look the same, and at least one person built a clone based on the RR's file. This was the beginning of me working on completely accurate sims.

 

[Rex R]

I measured the fin root of a still in the matrix fin and had a difference of approx. 0.01" (which is likely an error on my part), the thickness on the other hand I got 0.04", as was mentioned earlier the motor over hang is off by 0.25". I can't say whether the nose is right since I have misplaced that part.
Rex