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Vintage Build: Microsonde III

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Joshua F Thomas

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I picked up this new-in-box Microsonde III Payloader kit from one of my local club members. I can't determine the age of the kit, but the styling suggests 1970s or 1980s.

The Microsonde III is a three-stage, 18mm kit with each stage having three fins. I'll be building it as it came, with perhaps some moderinzed upgrades (eg, kevlar shock cord).

microsonde_box.jpg


microsonde_outside_closeup.jpg



Inside the box: Clearly not opened for 30+ years! Note the fiberglass insulation wadding!

microsonde_inside_box.jpg



All the parts, minus the parachute and shock cord. Since I will be building a sim of this in OpenRocket, my first task will be to take precise measurements and mass of all the components.


microsonde_parts.jpg



The kit comes with an instruction book and a 'research report' suggesting a different way to connect the engines for successful staging. Note the suggested engines. Anyone know where I can get an A3-2? :)


microsonde_both_sheets.jpg


microsonde_instructions_inside.jpg



microsonde_research_report.jpg



Caught my eye on the last page of the instructions. Three engines for $1.25! What a deal! Do you think it's still available? 😂



microsonde_three_for_cheap.jpg
 

BABAR

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Cool!

Don’t worry about the A3-2.

For first flight go with A8-0 or B6-0 in the middle stage, and A8-5 (if you can find it) in sustainer, otherwise I’d go with A8-3, maybe B6-6 or B6-4 in sustainer. A long Kevlar shock cord plus some elastic if you have room for it will help you out if ejection occurs early or late. Some tape around the Kevlar at the site it abuts the sustainer tube edge when taut may reduce risk of zipper.

Resist the urge to go with Cs in the middle stage or sustainer on the first flight. This will increase the probability of a second flight.

Resist the urge to fly this in winds over 5 mph.

Hope you get three straight trails and three reasonable walks with all parts recovered safely!
 

kuririn

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The old waterslide decals may be brittle. Test a small throwaway piece first. If it breaks apart when you try sliding it off the backing then you might be able to save the rest by clear coating the sheet first.
In any event scan the decal sheet before trying to use it just in case you need a scan for home printed decals.
 

jhall1964

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The old waterslide decals may be brittle. Test a small throwaway piece first. If it breaks apart when you try sliding it off the backing then you might be able to save the rest by clear coating the sheet first.
In any event scan the decal sheet before trying to use it just in case you need a scan for home printed decals.
I certainly second this tip! Looking at this build with interest as I have one still in the box too!

Sincerely,
Jeff
 

Joshua F Thomas

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Body and MMT tubes went together without fuss. They're all minimum-diameter, and friction fit. That's going to be "fun" later in making sure I don't lose any to accidental rear ejection. The nose cone and payload tube parts were connected with CA, as they're all plastic. The transition piece did not fit the clear payload section at all, even with aggressive sending. I eventually broke out the dremel to take off enough plastic to make it fit.


microsonde_1.jpg



microsonde_2.jpg



Fins were cut from the 1/8" balsa. No pre-cuts here, just lines printed on the balsa sheets to follow.


microsonde_3.jpg



Test fitting to see how they would all line up.

microsonde_4.jpg



Finally I CWF'd all the fins to seal them. Sanding once they dry. I won't be putting any rounded edges or airfoil on these fins. Not a lot of fin to begin with and I want to save all of it for stability. Secondly, keeping them square will cut down on some of the altitude, and for three-stages that's actually a good thing, since I already lost my first two-stager into trees on recovery. Less is more?


microsonde_5.jpg
 

Ez2cDave

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Looking good, so far !

Dave F.
 

MALBAR 70

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You can still find A3-2's here and there. I just happened upon these after seeing this thread.
*Disclamer*
I do not condone purchasing rocket motors from unlicensed ebay sellers.
 

Joshua F Thomas

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Finished building the OpenRocket sim for the Microsonde. All engine options have fairly slow lift-off speeds due to all the engine mass. The parachute is totally oversized for the final stage and I will probably replace it with something smaller or a streamer, as 4 m/s is way too slow a descent rate from over 1000 ft. The sim includes 10g for primer and paint plus and additional 10g dummy payload.

The *least* high thing thing can go is 835 ft, and it tops out around 1900 ft on all C engines. Stability is never less than 4 calibers.

I also ran this simulation with only two stages. The third stage has huge diminishing returns. On a C6-5, C6-0, C6-0 setup, that third motor only gives you an additional 360 feet. An A8-5, B6-0, C6-0 is only 70 ft better than an A8-5, C6-0 two-stage. No wonder people don't do four stages...



flight_sims.png


microsonde_sim.png
 

Ez2cDave

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If you "inter-digitate" the fins ( see pic #1 ) . . . It will reduce weather-cocking.

Dave F.

20170711_175255.jpg



microsonde3_built2.jpg
 

5x7

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Can you sim A8-0,A8-0,A8-5?
 

Joshua F Thomas

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Can you sim A8-0,A8-0,A8-5?
This configuration has a dangerously low speed off the rod of 9.6 m/s. That's only 21 mph. Assuming you're not smart enough to avoid this configuration, it has an apogee just under 500 ft.
 

Joshua F Thomas

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All fins were sanded down to 220 grit and then glued on each of their respective bodies. I was excited to use my Qualman fit alignment tool, but it turns out the body tubes are slightly larger than standard BT-20. I thought the Qualman's were wrong at first, but I checked with an Estee's BT-20 tube cutter, and no, it's the kit's tube.

So I did the fin alignment by hand. There may be 1/2 or 1 degree of skew between the different sets, but it's Good Enough(tm) for me.

The shock cord was also mounted into the sustainer body tube. Because there is no motor mount, the shock cord is wall-mounted using a piece of cardstock with punched holes to wind the paper through. Not really a fan of this method, but it's what I've got. The default shock cord is 12" of elastic. I added an additional 12" of kevlar to it, and the kevlar attaches to the mount.



microsonde_fins_bare.jpg
 

kuririn

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I was excited to use my Qualman fit alignment tool, but it turns out the body tubes are slightly larger than standard BT-20. I thought the Qualman's were wrong at first, but I checked with an Estee's BT-20 tube cutter, and no, it's the kit's tube.
You will notice in the instructions that they have you sleeve fit an inner tube (they call it an "engine compartment") into each section of the booster and sustainer motor sections. That is because the MPC (and later Quest) T20 tubes are slightly larger than the standard Estes BT-20 tube. 20 mm. I believe.
Otherwise the motors will be loose in those sections.
 

Joshua F Thomas

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Launch lugs added to the Microsonde. Because of the body diameter change, they have to be put on spacers of balsa. The instructions call for 1/4", but after test fitting I found that 3/8" seemed like a better choice.

The original instructions call for one single 2" long lug, but I felt like two 1" lugs spaced apart would provide better vertical straightness and stability. The launch speed of this model is lower than most.

After this was all dry, it was time to primer. Primer coat was laid on thick, then sanded down twice; first with 320 grit and then with 500 grit.

White coat is drying now. I think I'm going to aim for the look on the box - silver body with differently colored fins. White undercoat should bring out the colors.

microsonde_lugs_1.jpg



microsone_lugs_2.jpg



microsonde_primer.jpg
 

Joshua F Thomas

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Been a while since I updated this. The Microsonde III received a layer of white, and then a coating of metallic aluminum. After this I masked the bodies and painted each section according to the box-cover color scheme. All of this painting took a while.

The masking tape lifted some of the metallic aluminum paint, but it holds up at the "10 ft" view.

The kit comes with a 12" chute, way oversized for it. I went with a 9" Estes chute with a spill-hole cut in and a swivel. The total mass of the completed kit is 70g. Decals have yet to be put on.

Club launch is tomorrow, so we'll see how she works! Starting easy on an A8-5; B6-0; B6-0. I will only launch this in low winds, as the end-of-rod speed [for 1 m rod] is no more than 26 mph. If the winds are bad, I'll only launch the upper two stages, which gives a much better launch speed.




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BABAR

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I am curious how it seems with anA8-0 in the second (superior) booster. Was thinking it would light and almost immediately burn through and stage, specifically dies sim say distance traveled between ignition and staging with that motor?

What is total ready to fly mass with C6 load vs B6-0, A8-0, and A8-5?
 

Woody's Workshop

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I have 2 or 3 of these tucked away all sealed in plastic around the boxes. I'll be watching this one closely!!!
I can say from experience, someone said to use an A8-0 first. DON'T. Use the B6-0 first. You need the trust to get off the pad, and I'm not sure if a C6-0 wouldn't be even wiser. Once it's off the pad and moving upward you can move back to the A8-0 for the mid stage. Depending on your field, and how far you can chase it down, the final stage is as you see it.
I did an A8-0 in a 2 stagger....ONCE. It did a 180 and hit the ground before the sustainer even fired.
Best wishes on the build, too!
 

BABAR

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I have 2 or 3 of these tucked away all sealed in plastic around the boxes. I'll be watching this one closely!!!
I can say from experience, someone said to use an A8-0 first. DON'T. Use the B6-0 first. You need the trust to get off the pad, and I'm not sure if a C6-0 wouldn't be even wiser. Once it's off the pad and moving upward you can move back to the A8-0 for the mid stage. Depending on your field, and how far you can chase it down, the final stage is as you see it.
I did an A8-0 in a 2 stagger....ONCE. It did a 180 and hit the ground before the sustainer even fired.
Best wishes on the build, too!
If I suggested A8 in the first stage (lowest) booster, my bad. I agree at least a B if not a C in THAT Stage, you gotta have enough oomph to get the stack off the pad and up to speed. For middle stage and sustainer, for first flight go as low as possible.

Straight trails (x3!)
 

Joshua F Thomas

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The least I will use is a B6-0, B6-0. Any other configuration has terrible launch speed due to mass.

Oddly a C6-0 bottom stage actually has less launch speed due to greater mass, but more time to build speed before the second stage.

The kit is old enough that it suggests a C9-0 booster stage, and I wish those still existed!
 

BABAR

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What are you going to put in sustainer?
I'll assume A8-5

With that in sustainer, what is mass of full stack with

C6-0. B6-0. A8-5

B6-0. B6-0. A8-5.

B6-0. A8-0. A8-5

Not sure I understand your reluctance to go A8-0 in middle stage. Its gonna burn and stage quick, even if underpowered the burn time is so short inertia should keep velocity sufficient that sustainer will still be at stable velocity.

Pluses for A in middle are

lower mass for full stack (first motor) to accelerate from zero to greater than 50 fps at the tip of the rod

Lower max altitude = less drift/shorter walk for BOTH mid stage and sustainer

Less time to weathercock

Negatives?

Less exciting mid stage flight (shorter)

Sometimes less excitement is a good thing.


Hope you have a clear windless day, great flight, and three good recoveries !
 

Joshua F Thomas

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Launch speeds are all at end of 1m rod. All launches assume 5 mph wind.

C6-0. B6-0. A8-5 - total mass 128g. Launch speed: 11.5 m/s (38 fps). Apogee 986 ft. Max V: 86 m/s
B6-0. B6-0. A8-5. - total mass 123g. Launch speed: 11.3 m/s (37 fps). Apogee 778 ft. Max V: 79 m/s
B6-0. A8-0. A8-5. - total mass 121g. Launch speed: 11.5 m/s (38 fps). Apogee 648 ft. Max V: 67 m/s

The B6-0. A8-0. A8-5 has the lowest inter-stage vertical speed at 330 fps. The B6-0. B6-0. A8-5. is slightly better at 350 fps. The C6-0. B6-0. A8-5 is *much* better at 550 fps.

For comparison, a full C-stack:

C6-0. C6-0. C6-5 - total mass 139g. Launch speed 10.7 m/s (35 fps). Apogee 1700 ft. Max V: 121 m/s. Min inter-stage speed: 630 fps. (The higher upper-stage mass is providing greater momentum.)
 

Joshua F Thomas

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Note: In all cases launch rod clearance occurs around 0.25-0.3 seconds.

Edit: I should clarify that they all have terrible launch speed. It was the A8-0, A8-0, A8-5 that particularly had a scary launch speed of 9.6 m/s.
 

BABAR

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Launch speeds are all at end of 1m rod. All launches assume 5 mph wind.

C6-0. B6-0. A8-5 - total mass 128g. Launch speed: 11.5 m/s (38 fps). Apogee 986 ft. Max V: 86 m/s
B6-0. B6-0. A8-5. - total mass 123g. Launch speed: 11.3 m/s (37 fps). Apogee 778 ft. Max V: 79 m/s
B6-0. A8-0. A8-5. - total mass 121g. Launch speed: 11.5 m/s (38 fps). Apogee 648 ft. Max V: 67 m/s

The B6-0. A8-0. A8-5 has the lowest inter-stage vertical speed at 330 fps. The B6-0. B6-0. A8-5. is slightly better at 350 fps. The C6-0. B6-0. A8-5 is *much* better at 550 fps.

For comparison, a full C-stack:

C6-0. C6-0. C6-5 - total mass 139g. Launch speed 10.7 m/s (35 fps). Apogee 1700 ft. Max V: 121 m/s. Min inter-stage speed: 630 fps. (The higher upper-stage mass is providing greater momentum.)
Note: In all cases launch rod clearance occurs around 0.25-0.3 seconds.

Edit: I should clarify that they all have terrible launch speed. It was the A8-0, A8-0, A8-5 that particularly had a scary launch speed of 9.6 m/s.
Interesting
Estes motor chart
From the chart
“ Do not fly a rocket/engine combination whose lift-off weight exceeds the recommended maximum lift-off weight.”


Doesn’t even have the A8-0 listed, but since the max lift off weight for the B6-0 and C6-0 are the same as the B6-4 and C6-5. (All four are listed as 113 grams) I suspect the max lift off weight for A8-0 would be the same as the A8-3 listed as 85 grams, so no surprise that your sim wouldn’t support that. These are of course only Estes quoted recommendations, and Estes perhaps not routinely but certainly not rarely ignores them in designs.

You use a term I am ignorant of, “inter-stage vertical speed”. I figger it is the speed either at staging (for two stage) or the speed of the midstage for three stages? More importantly, what is the relevance in low power? Seems to me that unless you have a really puny but long burn booster motor, if your rocket is stable off the rod, unless the upper stage(s) has(have) very small fins (not the case for this rocket) seems like once you get up to speed off the rail, the next challenge is successful staging (just about guaranteed for non-gap staging, pretty easy for gap staging if you do it right.). So is there some minimal “interstage vertical speed” you must sustain for successful flight? I can see that for electronic staging with air starts (where there may be a specific delay between burnout of booster and ignition of sustainer) where you might get a significant velocity drop. But with BP booster motors the burn times


For A8 = 0.73 seconds and for C6 = 1.86 seconds

Are so short I can’t see the rocket losing much if any significant velocity drop during the mid stage boost burn. So I’d be interested in this Interstage Vertical speed relevance for black powder motors

(FWIW I googled it and didn’t get much. Our recently departed Gary Byrum [just lost him 13 months ago] justifiably chastised me for asking without googling!;)so I try to avoid that!)
 
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