sounding rocket sorta

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Rex R

Rex R

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I wanted a low cost rocket for wind observations...so I bought/built a baby bertha. a few minor deviations from the instructions(fins papered, longer shock cord, foamed the nose). the SMH baby bertha.
rex

smhbbertha 001.jpg
 
I really like the Baby Bertha, as well as the Big Bertha. A few questions about yours:

How will you use it for wind observations?

What are the benefits of the foamed nosecone and longer shock cord? I've only used foam one time, to surround my Darkstar Mini motor mount.

Do you know the approximate weight of the foam? I've thought of using it as nose weight or in conjunction with lead nose weight.
 
send it up and see how the wind affects it(weathercocking, drift under chute). longer cord to reduce the odds of an 'Estes Dent'(the provided rubber band is about 15" long).
the foam(low expansion 'soft' foam) is mainly to provide a bit of weight (about 5g) to help with the cg...the stock BB cg ends up pretty far back.
 
The Bertha is a great design and using the baby bertha in this instance is a great idea. I recently went over to my local hobby lobby and found a baby bertha but didnt pull the trigger on it because part of the BT was crushed :(

What ive done before was to skip in a A8-3 into my starLight "Apogee" and use that as a "wind checker" with its 12" chute...
 
got to test fly it today...it went up(B6-4), it drifted quite nicely. oh right, it whistled, so it is a sounding rocket. whistling was planned, we were not able to see if it also spun. pic showing one of the whistles (2 total) made from half a bobber.

smhbbertha 002.jpg
 
Rex R said:
got to test fly it today...it went up(B6-4), it drifted quite nicely. oh right, it whistled, so it is a sounding rocket. whistling was planned, we were not able to see if it also spun. pic showing one of the whistles (2 total) made from half a bobber.
Click to expand...

How did you get a bobber to whistle?
 
Thanks chad.
well I started by cutting a bobber in half, cleaned out the tube that runs through a bobber(so they will not sink), which left a 3/16"(approx) hole. then used CA to glue the hemisphere to the fin. when air flows over the fin/whistle sound is emitted (just like blowing across the top of a soda bottle). I would guess that my bird needs to get up to 40-50mph before the whistle gets audible.
 
Rex R said:
Thanks chad.
well I started by cutting a bobber in half, cleaned out the tube that runs through a bobber(so they will not sink), which left a 3/16"(approx) hole. then used CA to glue the hemisphere to the fin. when air flows over the fin/whistle sound is emitted (just like blowing across the top of a soda bottle). I would guess that my bird needs to get up to 40-50mph before the whistle gets audible.
Click to expand...

What type of bobber did you use. Could you post a picture of it? Does 'cleaned out' the tube mean you removed it, or cleaned out the center of the tube?
 
Last edited:
'cleaned' as removed. I wanted a hollow plastic sphere, though I suppose that one could use a plastic spoon if you wanted a 'cleaner aero profile'. I used a red/white 1/2" dia plastic bobber(not foam). a bigger one should produce a lower pitch(due to a larger resonating cavity), not sure what effect the hole size has.
 
Rex R said:
'cleaned' as removed. I wanted a hollow plastic sphere, though I suppose that one could use a plastic spoon if you wanted a 'cleaner aero profile'. I used a red/white 1/2" dia plastic bobber(not foam). a bigger one should produce a lower pitch(due to a larger resonating cavity), not sure what effect the hole size has.
Click to expand...


OK, thanks.
 

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