Lakeroadster's 2 Stage Alpha Variant

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lakeroadster

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Cutting Body Tubes & Couplers....... Booster, Build Day 1

Since the Body is a BT-55, and the Motor Mount is a BT-50, and since the fins are though wall, I thought this booster is a good candidate for masking tape centering rings.

001.JPG 002.JPG 003.JPG
 
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neil_w

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When cutting fin slots, if you hold a piece of aluminum angle there and use it as a cutting guide, you can get beautiful straight cuts quickly and easily with very little effort (yeah it'll all be hidden by fillets).
 

GlenP

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If you have a spent engine casing, you could also try to balance the booster alone, near the cp, before you anchor the engine block, so you have a bit of wiggle room to adjust it to tumble so you don’t have to add any weight to it to change its cg.
 
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BABAR

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All that is true, of course, and super super basic. Did you have a point here about horizontal roll recovery?
Very late answer. Main point was that for early or perfectly timed ejection horizontal spin on booster should work if you are above 50 feet. On descent, all bets would be off.

however, since this is a booster, if it is descending at staging, you’ve got a lot more to worry about than the booster coming in hot!

fortunately that is pretty unlikely.
 

lakeroadster

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When cutting fin slots, if you hold a piece of aluminum angle there and use it as a cutting guide, you can get beautiful straight cuts quickly and easily with very little effort (yeah it'll all be hidden by fillets).
Thanks Neil for adding this comment. I used it today to cut fin slots in the sustainer tube and it was easy peazy.

000.JPG
 

lakeroadster

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Booster Day 2

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_________________________________________________________________________________________________
Sustainer Day 1

Since the Body is a BT-55, and the Motor Mount is a BT-50, and since the fins are though wall, I thought this rocket is a good candidate for masking tape centering rings.

003.JPG 004.JPG 005.JPG 007.JPG
 
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Grog6

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I have been trying for months to figure out just what rocket I'd made to get one of my favorite rockets, that flew for years until it landed in an unrecoverable spot. (skunk den opening , I missed it but not that much. my nephew 'helped me put it together', so the fins ended up stuck on a longer, larger, full length piece of tubing, must have been 30".
I saw lakeroadster's post and recognized it. :)
So now I'm building a new one, with plywood ttw fins and thick cardboard. a neighbor blew up the skunks, so they aren't a problem now. :)
Stuff we go thru for rocketry. :)
 

GlenP

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Which engines did you load into the booster and sustainer for the swing test? C and C, or C and B, or B and B?
 

jqavins

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For curiosity's sake, how about putting an E12 in the booster, with the extra inch hanging out the back? Just to see what happens. In OR, I mean; really no need to swing test it that way.
 

lakeroadster

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For curiosity's sake, how about putting an E12 in the booster, with the extra inch hanging out the back? Just to see what happens. In OR, I mean; really no need to swing test it that way.
Stability goes from 0.729 cal to 0.411 cal ..... and apogee is 1642 ft

Mindsim says the E12 just may turn the rocket into skywriter.

This design is not overly stable, based on the swing test with the D12's. I've done enough swing tests that you can start to tell just how rock solid stable a rocket is. This rocket does a bit of pitching and diving during the swing test, but it's not excessive. The other thing is I didn't want to be to aggressive swinging the rocket since it has a booster... to much lateral force could uncouple the booster (I taped it to the sustainer, but I was still a bit nervous during the test)

If you run the video's at 0.25 speed, you can see the test flight orientation better.

The unknown though is the booster ring fin with all those holes in it. At speed, I'm thinking it's going to be super draggy.... which should help with stability.
 
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GlenP

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Yeah that shape looks really cool in flight in the swing test video. I didn’t realize you had a 24mm motor mount in there, that thing will really scoot. Might be pretty fast and high alt at staging with the D if you blink you might miss it.
 

lakeroadster

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Yeah that shape looks really cool in flight in the swing test video. I didn’t realize you had a 24mm motor mount in there, that thing will really scoot. Might be pretty fast and high alt at staging with the D if you blink you might miss it.
Stage separation occurs at about 137 feet, according to the exported data shown in the Excel screen grab.

But the apogee of the booster in the graph looks more like 250 ft

Perhaps from the booster coasting upwards I'm guessing, seems like a lot of coasting though. :dontknow:

2022-01-14 Ahpla 24 MM Open Rocket D12 Plot.jpg2022-01-14 Ahpla 24 MM Open Rocket D12 Data Export.jpg
 
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jqavins

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It looks like the staging event is at about 130 ft., and the booster coasts up to about 250. Which it shouldn't do unless it's stable. And it seems to be coming in ballistic, i.e. stable, because the speed when it reaches zero altitude is literally off the chart. If I were you I'd worry about that.
1642198735894.png
 

lakeroadster

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It looks like the staging event is at about 130 ft., and the booster coasts up to about 250. Which it shouldn't do unless it's stable. And it seems to be coming in ballistic, i.e. stable, because the speed when it reaches zero altitude is literally off the chart. If I were you I'd worry about that.
View attachment 499704
Cool, thanks for the enlarged enlightenment :goodjob:

No worries:
  • The booster ring has holes in it, in order to induce the Magnus Effect . Of course Open Rocket (OR) can't account for that. OR doesn't even know there is a ring fin.
  • And an OR simulation of the booster itself, as a stand alone rocket, shows it to have a negative 0.78 cal stability.
1642200591341.png
 
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GlenP

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Cool, so you even wind [tunnel] tested it!

I am not sure which config looks better in flight, the full stack or the sustainer, that thing just looks fast.
 

jqavins

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  • OR doesn't even know there is a ring fin.
  • And an OR simulation of the booster itself, as a stand alone rocket, shows it to have a negative 0.78 cal stability.
But, but, but... The unaccounted for ring tail will increase the boosters stability margin, so it will be not as negative as 0.78. Will it still be negative? It's your stuff, of course, but I'd feel better if you swing test the booster. With a spent motor (better for you) since it is spent by the time this matters.

I will now cease harping on it.
 

GlenP

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I think you have done a great job at analyzing and testing stability here, those swing tests are really a great way to see what that shape looks like in motion. Really neat to see your drawings come to life, thanks for sharing!
 

lakeroadster

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But, but, but... The unaccounted for ring tail will increase the boosters stability margin, so it will be not as negative as 0.78. Will it still be negative? It's your stuff, of course, but I'd feel better if you swing test the booster. With a spent motor (better for you) since it is spent by the time this matters.

I will now cease harping on it.
Come on Joe.. what do you think I am, your trained Monkey. :p

I loaded a spent D12 motor into the booster, and headed for my outdoor video lab...

The video in the link below is viewed best if you change the speed setting to 0.25 and the quality up to 720. You can clearly see the booster is unstable.

I also attached some screen grabs below.

Model Rocket Swing Test: Spent Booster for Scratch Design / Build Ahpla - YouTube

0A.jpg 0B.jpg 0C.jpg 0D.jpg 004.JPG

2022-01-17: Added directional arrows to the screen grab photo's
 
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jqavins

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Thanks for checking.

(For the record, mindsim says it obviously should be unstable, and I'd never have brought it up if the OR sim hadn't made it look otherwise.)
 
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