Vintage Build: Microsonde III

[Joshua F Thomas]

“ Do not fly a rocket/engine combination whose lift-off weight exceeds the recommended maximum lift-off weight.”

I assume Estes is a little conservative, but yeah, this setup is already kind of marginal. Hence my desire to fly only in calm conditions. This kit is from the 70s, so perhaps things have changed since then? I'm betting the now missing C9-0 would have been a better choice.

I would kill for a higher-thrust, black-powder motor for this bottom stage.

You use a term I am ignorant of, “inter-stage vertical speed”.

If you sim these, you will see a slight dip in vertical speed as the motors stage. It's not much, but it gives some idea of the worst case for stability issues after launch. The lowest speed there is always between bottom and middle stage. The higher this speed, the more stable - all other things equal - it should be.

 

[Joshua F Thomas]

By the way, Tim at Apogee suggests 13.8 m/s should be the lowest sane launch speed. Longer rods would be helpful here, I wonder if I can get my club to use a 1.5m or 2.0 m rod.

https://www.apogeerockets.com/education/downloads/Newsletter498.pdf [page 3, right side].

[Edit]: More sim shows that,

1.5m rod: Launch speed 12.0-13.2 m/s
2.0m rod: Launch speed 13.1-14.1 m/s

 

[Ez2cDave]

I assume Estes is a little conservative, but yeah, this setup is already kind of marginal. Hence my desire to fly only in calm conditions. This kit is from the 70s, so perhaps things have changed since then? I'm betting the now missing C9-0 would have been a better choice.

I would kill for a higher-thrust, black-powder motor for this bottom stage.

The B14-0 would have been nice . . . I really miss the B14's !

Dave F.

 

[Joshua F Thomas]

The B14-0 would have been nice . . . I really miss the B14's !

Dave F.

*cries*

 

[Joshua F Thomas]

Is there no one who makes black-powder 18mm motors with higher thrust than an Estes' C?

 

[Joshua F Thomas]

Anyone have a B14, B8 or C9 they want to sell me?

 

[BABAR]

This is really outside the box, but if you could build some really LIGHT 18mm to 13mm adapters, you could put A10-0T and A3-4T in mid stage and sustainer respectively. Not sure how much mass the adapter would cost you, but might do two things if it shaves off a few grams

https://www.rocketreviews.com/compare-estes-a8-to-estes-a10t.html
1. Drops your lift off mass.

2. Because the mass dropped is in the tail, should move CG FORWARD. on the other hand that may be bad as it will make the rocket MORE stable and more likely to weathercock. Hmmmm.

 

[Ez2cDave]

Is there no one who makes black-powder 18mm motors with higher thrust than an Estes' C?

There is the Estes "C5" . . .

https://www.nar.org/SandT/pdf/Estes/C6.pdf

https://www.nar.org/SandT/pdf/Estes/Estes_C5_2019.pdf

Dave F.

 

[Joshua F Thomas]

There is the Estes "C5" . . .

https://www.nar.org/SandT/pdf/Estes/C6.pdf

https://www.nar.org/SandT/pdf/Estes/Estes_C5_2019.pdf

Dave F.

It doesn't help me without a -0 variant tho

 

[Joshua F Thomas]

This is really outside the box, but if you could build some really LIGHT 18mm to 13mm adapters, you could put A10-0T and A3-4T in mid stage and sustainer respectively. Not sure how much mass the adapter would cost you, but might do two things if it shaves off a few grams

https://www.rocketreviews.com/compare-estes-a8-to-estes-a10t.html
1. Drops your lift off mass.

2. Because the mass dropped is in the tail, should move CG FORWARD. on the other hand that may be bad as it will make the rocket MORE stable and more likely to weathercock. Hmmmm.

Interesting idea!

Assuming a theoretical zero-mass 13mm to 18mm adaptor, here's what we get with a configuration of B6-0; A10T-0; A3T-4:

Launch speed: 13.8 m/s. Apogee: 729 ft. Deployment velocity: 6 m/s. Max V: 63 m/s. Total mass with motors: 94.4g. Stability: 5.31 cal -> 6.08 cal -> 5.37 cal (per stage).

If I spec two 13-to-18mm adaptors at 3g each, I still get 13.4 m/s launch and about 720 ft apogee.

This looks promising. It saves considerable mass (14-20g) over the next-best option, the B6-0; B6-0; A8-5, and has much better launch speed. Stability is high, but it's already above 4.0 cal for every possible engine choice. This kit seems to have been designed with very high stability. I think the designer must have been worried about change in trajectory when staging.

As a bonus, the apogee is lower than any other choice I have (excepting the awful A8-0; A8-0; A8-5), which is really a bonus for me, I don't like losing things into trees. The deployment velocity is also lower than any other motor option, meaning less shock on cord and chute.

One interesting thing (see the plots below) is that the A10T-0 is an oddball motor. According to the thrust curve, the engine burns almost entirely in 0.2 seconds, with a sharp spike up to 12 N; and then it burns for another 0.6 seconds at a tiny 1 N of thrust! The result is an average of barely over 2 N for the entire 0.8 second burn time. In practice this causes the upward speed on this rocket to noticeably decrease during the middle stage.

If I can build myself some 13-to-18 adaptors this is a real option.



Here are the plots for each of the stages on the above configuration:

B6-0 stage (bottom):




A10T-0 stage (middle):

(Open rocket has issues trying to model the tumbling of this stage)



A34T-0 (sustainer):

 

[Woody's Workshop]

Quest needs to come out with a zero delay 18 mm D!

I give that a BIG 2nd!!!

 

[BABAR]

Fun story about an Estes Apogee II launch in the 70s with a B6-0 in the booster.

Dad and I launched it, quick off the pad, flight in clear view to apogee (no pun intended.). Parachute deployed, tracked descent to ground...........

We looked at each other.....Where was the booster? We never saw the staging event, and definitely didn’t see the booster come down. It wasn’t windy, so where did it go.

Finally looked ON THE PAD. The booster had fired, accelerated the rocket to the end of the rod, successfully staged and ignited the sustainer, and then slid down the rod back onto the pad. It happened so fast Dad and I (he’s 95 now) just tracked the sustainer on its upward trajectory and never noticed in real time the separation. Too bad cheap video cameras or cell phone video cams weren’t around then, wish I had a video to post.

Definitely set (or at least equaled) the shortest recovery walk for a booster in history!

 

[BABAR]

The A8-3 and the A10-3 have nearly identical performance characteristics, aside from the first being 18 mm and the second 13, and the first 16.2 grams net weight and the second 7.9 grams per Estes chart (Rocket reviews has 16.35 and 5.25 grams respectively)

https://www.rocketreviews.com/compare-estes-a8-to-estes-a10t.htmlhttps://estesrockets.com/wp-content/uploads/Educator/Estes_Engine_Chart.pdf
Interestingly the above don’t agree on a couple of things, not only mass but also total newton thrust , Rocket reviews has the A8-3 as 2.32 N vs 2.0 for A10, confusing as the Estes chart says the A10 has (slightly) more propellant. I’d be curious as to the mass assigned by Open Rocket.

In any case, assuming a lightweight (less than 8 grams) adapter, the A10 essentially at least is the equal of the A8 in performance, and since it is 4 to a pack, a bit cheaper (always a plus!)

Hope you get a clear day, light winds, at least two extra pairs of sharp eyes (designate a spotter for each segment, the natural inclination is for ALL eyes to follow the sustainer), three straight (VERTICAL!) trails, three short walks and soft landings!

 

[Ez2cDave]

It doesn't help me without a -0 variant tho

True . . . I forgot that Estes hasn't made a Booster version of the C5 yet. Hopefully, they will, soon !

Dave F.

 

[Ez2cDave]

I loved "core-burner" motors, back in the day !

Dave F.

 

[Joshua F Thomas]

Finally put decals on the upper section of the Microsonde III. Kept it simple - flight tracking bars and a USA flag.

I'm waiting on 13-to-18 motor adaptors to do a full stage flight, but I'm going to try just the single stage later today, on an A8-3.

 

[SCooke123]

Looks good with the decals applied. Good luck with your single stage flight!

 

[BABAR]

I loved "core-burner" motors, back in the day !

Dave F.

View attachment 428710

Interesting. Looks like the delay INCLUDES the burn time, rather than is AFTER the burn time. Is this correct? I had always assumed “Delay” meant time blowing smoke but no significant propulsion AFTER the thrust propellant was exhausted.

 

[BABAR]

True . . . I forgot that Estes hasn't made a Booster version of the C5 yet. Hopefully, they will, soon !

Dave F.

Seems like a natural progression. OTOH how long was the A10-3T out before they released the A10-0?

 

[Ez2cDave]

Interesting. Looks like the delay INCLUDES the burn time, rather than is AFTER the burn time. Is this correct? I had always assumed “Delay” meant time blowing smoke but no significant propulsion AFTER the thrust propellant was exhausted.

That's a good question . . . I always have believed that the Delay Time started after Burn Time, too.

Dave F.

 

[Joshua F Thomas]

Interesting. Looks like the delay INCLUDES the burn time, rather than is AFTER the burn time. Is this correct? I had always assumed “Delay” meant time blowing smoke but no significant propulsion AFTER the thrust propellant was exhausted.

Those burn times are short enough that rounding to the upper number for time is “close enough” for the advertising shown. Plus, olden days before simulation.

Delay doesn’t include burn time.

 

[Joshua F Thomas]

Microsonde first stage flew successfully on an A8-3. It weathercocks *hard* from the high stability. Moderate breeze and it just nosed right over into it. Chute deployed a little slower than I expected. Otherwise all good.

If anyone else builds this model I would suggest it only be used on totally calm days. Also perhaps shorten the body tube to drive the CG and CP closer to each other and reduce the overstability.

 

[Ez2cDave]

Plus, olden days before simulation.

Simulations are only as good as the data plugged into them.

Dave F.

 

[Ez2cDave]

Seems like a natural progression. OTOH how long was the A10-3T out before they released the A10-0?

They were introduced together, in 1973. ( Data per the Ninfinger website )

https://www.ninfinger.org/rockets/catalogs/estes73/73estcat.html

https://www.ninfinger.org/rockets/catalogs/estes73/73est54.jpg



Dave F.

 

[BABAR]

They were introduced together, in 1973. ( Data per the Ninfinger website )

https://www.ninfinger.org/rockets/catalogs/estes73/73estcat.html

https://www.ninfinger.org/rockets/catalogs/estes73/73est54.jpg

View attachment 429201

Dave F.

Thanks. I did a search but obviously not a good enough one. When did they have their first two stage 13 mm rocket?

 

[BABAR]

Microsonde first stage flew successfully on an A8-3. It weathercocks *hard* from the high stability. Moderate breeze and it just nosed right over into it. Chute deployed a little slower than I expected. Otherwise all good.

If anyone else builds this model I would suggest it only be used on totally calm days. Also perhaps shorten the body tube to drive the CG and CP closer to each other and reduce the overstability.

Congrats. Wondering if smaller (perhaps less swept and more durable) fins might be helpful AND more efficient.

 

[Joshua F Thomas]

Congrats. Wondering if smaller (perhaps less swept and more durable) fins might be helpful AND more efficient.

The swept back wings do most of it. The rocket has a stability of 4.0-4.5 on just the first stage!

A few adjustments can be made:
1) Cut the payload bay from 10 cm to 6 cm
2) Reduce the body tube from 9 in to 6 in, which is probably as small as you can get and still stuff everything inside

This knocks it down to 3.0 - 3.5 calibers of stability. It would also knock a little mass off.

Pushing the fins up the body by 2 cm reduces the stability down to 2.0 - 2.5. This is all just for the sustainer stage.

For the full three stage setup, these changes give a stability of 1.75-3.0 (heaviest configuration) to 2.6 - 3.75 (lightest configuration).

 

[Joshua F Thomas]

The simulated effect of doubling fin thickness from 1/8 to 1/4 isn't much - balsa is very light. On the other hand, just changing from balsa to plywood drops stability by nearly a whole caliber.

 

[Ez2cDave]

When did they have their first two stage 13 mm rocket?

1972 . . . Midget & Beta. ( from Ninfinger )

Dave F.

 

[Joshua F Thomas]

Hm, adding some stubby fins all the way up the body also helps the overstability problem a fair bit. This may be the easiest fix for me....