IRIS Sounding Rocket - SCALE DATA !

[SolarYellow]

You could do some further calculation. The arrangement of the three, 8-in. Sparrow motors will start the fins farther away from centerline than the 12-in. Iris sustainer. So you could do some trig on that geometry and see if it works out that (46.5-35.6) corresponds to the difference in radius. I haven't done the math, but waving my hands in the air, it looks close.

 

[BigMacDaddy]

You could do some further calculation. The arrangement of the three, 8-in. Sparrow motors will start the fins farther away from centerline than the 12-in. Iris sustainer. So you could do some trig on that geometry and see if it works out that (46.5-35.6) corresponds to the difference in radius. I haven't done the math, but waving my hands in the air, it looks close.

Thanks, I see what you are saying... My math is rusty but I am building the whole rocket in 3D design software so easy enough to see what height fin would line up with the height of the booster fin. Currently sustainer the fin that maintains the 45 degree sweep angle is about 1.1cm taller than the scale booster fin. Not sure what is correct but my gut suggests that the 45 degree sweep is something that might be consistent across the 4 and 3 fin variation of the sustainer.

Sorry, graphic below is a bit of a mess since it is my mock-up / design space (once I get parts close to final I move them over to a neater space for my factory / printing files).

 

[SolarYellow]

Based on the photos, it looks about right to me.

 

[BigMacDaddy]

@Ez2cDave - Any information / opinion on height of sustainers fins in 3-motor booster IRIS Hydra?

Did I miss that info in all the scale data you shared or do you think the 45 degree sweep suggests the accurate fin height?

 

[Ez2cDave]

Late to the party on this question but I was also looking for better pictures of the connecting part between body tube and NC Extension. I found a couple of slightly higher-resolution picture of the IRIS at Goddard which shows the detail here a bit better (if you can turn on your LIDAR eyes to see through all the layers of paint may be able to figure out what those parts look like). Does anyone else happen to have better pictures of that transition/bracket section of the IRIS rocket.

 

[Ez2cDave]

@Ez2cDave - Any information / opinion on height of sustainers fins in 3-motor booster IRIS Hydra?

Did I miss that info in all the scale data you shared or do you think the 45 degree sweep suggests the accurate fin height?

HYDRA-IRIS . . .

 

[BigMacDaddy]

HYDRA-IRIS . . .

View attachment 596412

Yes, that is the data I am working from. However, it was not clear that the sustainer fins were the same height as the booster fins. Do you think they are?

That will significantly change the sweep angle of the sustainer fins from the 45 degrees of the 4-fin IRIS sustainer fins. The left fin is what these would look like if the booster fin height is assumed to be the same as a booster fin height given. The right is what the sustainer fins would look like if you maintain a 45 degree angle (i.e., the height is the same as the difference between the root and top fin length given).



The sustainer fins also look larger in the pictures (there is obviously some perspective distortion going on here but they still look taller).


Thanks for any advice.

Ah, also just noticed another photo from the 2nd page of the brochure above that shows the sustainer fin fairly square on. Unless some photo manipulation is going on this looks like a photo of the 3-fin sustainer. It also looks like the 45 degree sweep angle for the fin is more accurate proportion.