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  #21  
Old 04-06-2019, 11:57 AM
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Something was definitely "foul" with the propellant combustion.
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  #22  
Old 04-06-2019, 06:32 PM
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Quote:
Originally Posted by mwtoelle
A piston would help, but only the only people that I know that would use them are competition fliers. If the A10 was actually labelled to reflect the actual average of the motor, it would be an A2 instead. I have actually flown 1974 vintage A10-0Ts, and even those motors had a long burn. I even put a comment in my flight log about to A10-0T burning about as long as an A3 motor. In the Estes catalogs of the time it was claimed that the A10s had a 0.26 sec. thrust duration. Current catalogs show the A10s with a 0.80 sec thrust duration. Personally, I think that the A10 has always had the longer duration listed in the newer catalogs. Even the data from S&T concurs with the longer thrust duration. As I have learned over the years, long burn, low thrust motors and windy flight conditions do not mix very well.


Interesting. Iíve only flown a 13mm stager once, my scratch-built Double Mini Max. It was A10 to A10. It flew pretty well, but not the roaring liftoff I expected. Upper stage flight angle was not perfectly vertical, but itís a gap-stager, so I suspect it may have had a bit of arc-over before upper stage ignition. Recovery was fine. If I were to build another, Iíd go 18mm booster. The extra length of an 18mm booster would be no issues since I used at least an inch of gap in the design.

A similar difference in motor average thrust exists with the 18/20 RMS D reloads. Probably a lot more examples, but I noticed this because I bought the 18/20 specifically for the Mars Lander. I thought the D24 might be too much, so I bought the D13 also.Then I looked closer at the thrust curves. The D13W is rated 12.67 N average thrust, the D24T is 14.77 N. The thrust curves are very similar. Iíll try the D24 next flight. Iíve flown it twice on D13 with excellent results.
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  #23  
Old 04-06-2019, 08:45 PM
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Quote:
Originally Posted by blackshire
Clustering the first stage of the Mini-Commanche-3 (adding three--or even two [although it would look unsymmetrical, but it would fly fine]--13 mm booster motor tubes on the sides of the center tube) would greatly increase the first stage's thrust and acceleration, although clustering the igniters must be done carefully, and it requires more juice than a four-AA battery launch controller can put out.
FWIW, I've built and flown several BP powered stagers with clusters in the 1st stage for getting it off the rod with good speed, and had good luck with all flights. I always take my time and make sure the nozzles are clean, the ignitors are seated fully in the nozzles and not shorted, and that all the ignitors are securely connected.

No doubt, you want a lot more than 4 AA's

Doug


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  #24  
Old 04-06-2019, 08:57 PM
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Quote:
Originally Posted by LeeR
Interesting. Iíve only flown a 13mm stager once, my scratch-built Double Mini Max. It was A10 to A10. It flew pretty well, but not the roaring liftoff I expected. Upper stage flight angle was not perfectly vertical, but itís a gap-stager, so I suspect it may have had a bit of arc-over before upper stage ignition. Recovery was fine. <snip>
When I got back in the hobby (almost 20 years ago, upon the release of October Sky on video), one of my first flights was my 1969 K-40 Midget, resurrected from my attic with many broken fins, and flown using an A10-0T in the booster with a 13-18mm adapter.

It seemed like that booster burned forever - finally the sustainer lit and the flight was 100% successful. I was totally psyched by it - I've been a staging fiend ever since

Doug


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  #25  
Old 04-06-2019, 09:51 PM
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Quote:
Originally Posted by jdbectec
That almost looks as though the propellant was was damp.Definitely not good combustion.


I had the same idea when I viewed the pictures of the spent first stage motor. My first thought was moisture damage after seeing the pictures of the nozzle and casing.
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  #26  
Old 04-10-2019, 04:15 AM
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Quote:
Originally Posted by Doug Sams
FWIW, I've built and flown several BP powered stagers with clusters in the 1st stage for getting it off the rod with good speed, and had good luck with all flights. I always take my time and make sure the nozzles are clean, the ignitors are seated fully in the nozzles and not shorted, and that all the ignitors are securely connected.

No doubt, you want a lot more than 4 AA's

Doug


.
Normally, yes--*but*... If you used a launcher arrangement like the Centuri Servo-Launcher (see: http://www.ninfinger.org/rockets/no...a/72cen052.html [one can do the same thing electrically with a relay launch system, so that the leads from the ignition batteries are only 6" or so long, reducing the voltage drop along them to almost nothing, for all practical purposes]), four AA batteries could probably fire three or four low-power Estes Solar Igniters and/or Quest Q2G2 Igniters with no problems at all. The Servo Launcher only needed two Photo-Flash D batteries.
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  #27  
Old 04-10-2019, 04:33 AM
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Quote:
Originally Posted by tbzep
Is the A10 nozzle eroded? That would significantly lower thrust.

Maybe some impurity got into the BP during the motor making process and lowered the thrust.
If a M.E.S.S. form submission is in order here, that would be well worth inspecting the motor for. That happened with an Omega of yours once, if memory serves (where the clay of one of the stages' D12 nozzles asymmetrically eroded, making the rocket pitch over under power and hit the ground hard--you even caught it on camera too, I think). Even perfectly symmetrical erosion of a clay nozzle (as unlikely as such an occurrence would be) would drastically reduce the motor's thrust, regardless of the motor's size and rated thrust-time curve.
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  #28  
Old 04-10-2019, 05:48 AM
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Quote:
Originally Posted by Newbomb Turk
I'm inclined, knowing the conditions at flight time, to think GH might be right. If the A10-0T does in fact have enough oompf to power the design, perhaps this particular A10 was a less than perfect product.

Our LCO is a Physics PhD. His immediate reaction was that it didn't have enough thrust.

Note the damage sustained by the second stage upon impact with the ground under power.
Well...at least you have more hardware to examine to hopefully determine the cause (pity the incident investigators who have to determine why ballistic missiles or space launch vehicles fail--while they [usually] have telemetry data, they either have no hardware at all, or--unless they're very lucky--just tiny fragments or shards to examine). Here (see: www.youtube.com/watch?v=g9Dbfa0V38s ) is another "gravity turn" Mini Commanche-3 flight. Also:

I'd check the nozzle for unusual (excessive), asymmetrical erosion, as tbzep suggested. In addition, examining the ablation on the inside walls of the motor might reveal some unusual pattern, that could point to poor or incomplete (in the usual thrust duration time) combustion of the propellant. I suppose that from time to time, a batch of black powder may be "sour" (Estes sometimes buys it from overseas suppliers, which could provide opportunities for excessive amounts of moisture, dust, or some other impurity to find its way into it, despite precautions). If a motor containing such "sour" black powder burned even 15% - 20% more slowly than it should, the amount of thrust produced each second could be low enough to result in the crash that your Mini Commanche-3 suffered. As well--to mention something more cheerful, after looking at your posted pictures:

The lower two stages' fin spans look large enough to make them gliding stages, like the Centuri Black Widow kit's gliding first stage. While two of the three fins on each Mini Commanche-3 lower stage could--like the fins on the Black Widow's first stage--be spaced either *less* than 120 degrees apart (as in the early version, see: http://plans.rocketshoppe.com/centu...B-6/cenKB-6.htm ) or *more* than 120 degrees apart (as in the later version, see: http://www.spacemodeling.org/jimz/kb-6.htm ), there is a way to space the Mini Commanche-3's lower stages' fins normally (120 degrees from each other), yet have each lower stage glide (which would be more spectacular, while also making them easier to track [because they would remain aloft longer than tumble recovery lower stages]):

The early "Mini-Bird" boost-gliders (which appeared in either the First, Second, or Third Edition of G. Harry Stine's "Handbook of Model Rocketry") were very similar to the lower stages of multi-stage model rockets. A typical Mini-Bird looked like, say, an Estes Alpha, with a body tube (usually--but not necessarily--minimum-diameter) no longer than the motor, and with a nose cone glued into the front end of the body tube. The fins were spaced 120 degrees apart, and one fin (the "bottom" or "centerboard" [as in a sailboat] fin--was either slightly longer in span than the other two fins, ^OR^:

The "bottom" fin could be of the same planform as the other two, with ballast weight applied to its tip). After the motor (or the motor mount; either could be streamer-recovered, to make Mini-Bird BGs "NAR-Kosher" for contest flying) ejected itself from the model, it settled into gliding attitude. The two lower stages of the Mini Commanche-3 could be modified slightly--in either of the two above-described ways--so that they would glide like Mini-Bird boost-gliders (in the case of minimum-diameter multi-stage models such as the Mini Commance-3, the spent motors would remain inside the lower stage airframe or airframes, as with the Centuri Black Widow's lower stage). As well:

For multi-stage models with *larger*-than-minimum-diameter body tubes, the lower stage's (or stages') motor mount tube(s) could eject themselves rearward (each lower stage's forward stage coupler would act as a thrust ring for the motor mount), and descend under steamers. The "middle" lower stage (the second stage, when all three stages are used) of the BT-50 size Estes Commanche-3 (see: https://estesrockets.com/wp-content..._COMANCHE_3.pdf ) could use the rear-ejecting, streamer-recovered 18 mm motor mount with a "Mini-Bird modified," gliding second stage (the C11-0 or D12-0 powered first stage could--like the Centuri Black Widow's gliding first stage--retain the spent C11 or D12 motor casing, and--like the Commanche-3's second stage--also incorporate the Mini-Bird modifications, so that it too would glide).
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  #29  
Old 04-10-2019, 10:16 AM
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Quote:
Originally Posted by blackshire
If a M.E.S.S. form submission is in order here, that would be well worth inspecting the motor for. That happened with an Omega of yours once, if memory serves (where the clay of one of the stages' D12 nozzles asymmetrically eroded, making the rocket pitch over under power and hit the ground hard--you even caught it on camera too, I think). Even perfectly symmetrical erosion of a clay nozzle (as unlikely as such an occurrence would be) would drastically reduce the motor's thrust, regardless of the motor's size and rated thrust-time curve.

Since that Omega Cineroc flight, I've found that off axis thrust is pretty common with BP motors, especially during that critical time of high thrust the first 25 ft or so off the rod. Nozzles normally look fine after flight, so I don't know if smeared clay nozzle material, igniter residue, or something else causes it. Many of the super slow-mo videos on Youtube show this also. With that in mind, I don't know if Estes would want to start honoring off-axis thrust as a reason for flight failures.

BTW, I used to see off-axis thrust in C-slot composite motors all the time. You'd think the nozzle would straighten it out, but a nozzle throat is just a fraction of an inch long.
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  #30  
Old 04-10-2019, 11:14 AM
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Quote:
Originally Posted by tbzep
Since that Omega Cineroc flight, I've found that off axis thrust is pretty common with BP motors, especially during that critical time of high thrust the first 25 ft or so off the rod. Nozzles normally look fine after flight, so I don't know if smeared clay nozzle material, igniter residue, or something else causes it. Many of the super slow-mo videos on Youtube show this also. With that in mind, I don't know if Estes would want to start honoring off-axis thrust as a reason for flight failures.

BTW, I used to see off-axis thrust in C-slot composite motors all the time. You'd think the nozzle would straighten it out, but a nozzle throat is just a fraction of an inch long.
I guess the high acceleration--a significant portion of whose "run" is done on the launch rod--and the quite short motor burn times (usually less than a second) of most motors might make off-axis thrust largely irrelevant in most cases. If it is that common (I don't doubt you, having seen high-speed [slow-motion] footage of model rocket launches), we don't want to risk "complaining Estes [or Quest] out of business," or eroding--no pun intended--their reputations... :-) Also:

I would never have suspected that such "off-center-burning grain" composite motors would have exhaust plumes that would actually mirror--in the rockets' flight characteristics--the internal ballistics of the burning grain inside. Maybe a sufficiently-long nozzle (or even a provided jetavator) would eliminate that, without really hurting the motor performance enough to matter.
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