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  #1  
Old 03-27-2019, 11:05 AM
Newbomb Turk's Avatar
Newbomb Turk Newbomb Turk is offline
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Default Houston...you guys know the rest.

Had a very busy and nearly flawless day of flying Saturday at da club. I say nearly.

The one hiccup was my spanking new Mini-Comanche III, fully primed for it's maiden flight. See first picture. After barely getting off the rod, it turned hard right. It was just above horizontal when it first staged. By the second stage it was just below horizontal. The sustainer plowed under power before meekly ejecting the nose cone.

Considerable crumpling of the BT resulted, of course. The LCO immediately remarked that it didn't have enough thrust. Clearly, but it was flying A10-0T, A10-0T, A3-4T. The strongest and only available and recommended booster engine.

I know I did not build this thing particularly heavy, and I'm a fairly accomplished stager. (I consider myself to be in the top 5,000,000 model rocket stagers in Florida.)

So, how about it? Has anyone else built/flown this model? Am I the only one with such results?

I did follow up with a very successful D12-0, B6-0, C6-7 eighth flight of my regular size Comanche.
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  #2  
Old 03-27-2019, 12:18 PM
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Doug Sams Doug Sams is offline
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Default

Quote:
Originally Posted by Newbomb Turk
A10-0T, A10-0T, A3-4T
Bummer about your wreck. Is the Mini a BT-20 based kit? I've built and flown a few small 3-stagers using that motor combo, or maybe a ¼A or ½A in the upper stage. No doubt, the big thrust spike should be sufficient to get the stack moving off the rod.

The two thoughts I have on this are either nozzle erosion/flaking, or wind catching it during the long tail of the thrust curve.

Can you inspect the 1st stage motor's nozzle for any signs of it being asymmetric?

The long tail on the thrust curve presents an opportunity for wind to affect the flight, altho the more I think about it, the less I worry about. That is, if the thrust spike got it moving off the rod with decent speed, then, even with the long, low thrust tail, it shouldn't lose any speed, so it should still be tolerant of a cross wind that could impart weather cocking.

If it looked like it came off the rod with decent speed, then it's not the low thrust tail.

Besides these two things, the other thought is rod binding. How's your launch lug? Is it long enough not to bind? Was the rod clean? Did you wipe it down before loading the rocket? Again, if it came off the rod with good speed, this is not part of the problem.

Anyway, those are my thoughts. Like you, I am (or was) an avid stager - there's nothing like the rush I get when the next stage lights


Doug


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  #3  
Old 03-27-2019, 01:25 PM
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ghrocketman ghrocketman is offline
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Ah yessssss....an actual POWR-PRANGG !

My favorite flight profile of someone ELSE'S rocket.

Sounds like a defective booster engine to me. The A10-0T has plenty of thrust if it performs nominally.
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  #4  
Old 03-27-2019, 02:11 PM
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Tau Zero Tau Zero is offline
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Quote:
Originally Posted by Newbomb Turk
(I consider myself to be in the top 5,000,000 model rocket stagers in Florida.)
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  #5  
Old 03-30-2019, 07:40 AM
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Quote:
Originally Posted by Newbomb Turk
<snip>So, how about it? Has anyone else built/flown this model? Am I the only one with such results?<snip>
I've flown a stock mini-comanche 3 a few times (including drag racing with another guy in the club), and they've always been nominal flights. I fly it off a 3' 1/8" rod, but only in very low wind. IIRC, it's not terribly fast off the rod, but no hint of stability problems. All flights on A10-A10-A10.
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  #6  
Old 03-30-2019, 08:49 PM
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mwtoelle mwtoelle is offline
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I agree with PaulK, slow off-the-rod rockets should only be flown in calm conditions, especially three stagers. There are even some two stage combos that I know of that fall into that category. Remember, that one important flying skill is "Know when not to fly."
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  #7  
Old 04-03-2019, 08:25 PM
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blackshire blackshire is offline
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Quote:
Originally Posted by mwtoelle
I agree with PaulK, slow off-the-rod rockets should only be flown in calm conditions, especially three stagers. There are even some two stage combos that I know of that fall into that category. Remember, that one important flying skill is "Know when not to fly."
Not only for launch stability reasons, but also to avoid weather-cocking. (I once lost a *single-stage* rocket, a late-production Estes Quasar, to weather-cocking on a windy day over thirty years ago; it didn't get more that forty or fifty feet above the ground, and vanished into the distance flying nearly horizontally.) Also:

In marginal conditions for good stability off the pad, it might help if multi-stage models were launched using a Kuhn-type, fixed-piston/movable "blow-off" tube piston launcher, as it would give such models a significant velocity boost off the launcher. If the flying field is large enough (and the wind velocity is low enough), weather-cocking can be beneficial. The model flies upwind, and the wind blows the spent lower stage(s) and the (nose-blow, break-apart, streamer, or parachute recovery) final stage back to--and perhaps a bit farther back than--the launch pad.
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  #8  
Old 04-03-2019, 09:09 PM
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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.
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  #9  
Old 04-03-2019, 10:36 PM
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teflonrocketry1 teflonrocketry1 is offline
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I created a RockSim flight simulation for the Mini-Comanche 3 visit:

https://forums.rocketshoppe.com/sho...453&postcount=3

I have been looking at the length of the launch guide and even when I set the length to only 27 inches the rocket reaches 35mph at the tip of the launch rod with a stability margin of 8.24 calibers for the 3 stage configuration. Based on the simulations I would say the problem could have been due to a wind gust, as the large surface area of the fins and over stable design would allow for a horizontal flight path if there was a gust of wind at the moment of the launch. Another possibility would be launch rod whip. What was the launch rod made of? Carbon steel rod is more prone to rod whip than 316 stainless steel. You also cannot rule out launch lug binding which would easily cause a slow speed at the top of the launch rod. Did you wipe off the launch rod before your flight?
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Old 04-03-2019, 10:43 PM
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blackshire blackshire is offline
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Quote:
Originally Posted by teflonrocketry1
I created a RockSim flight simulation for the Mini-Comanche 3 visit:

https://forums.rocketshoppe.com/sho...453&postcount=3

I have been looking at the length of the launch guide and even when I set the length to only 27 inches the rocket reaches 35mph at the tip of the launch rod with a stability margin of 8.24 calibers for the 3 stage configuration. Based on the simulations I would say the problem could have been due to a wind gust, as the large surface area of the fins and over stable design would allow for a horizontal flight path if there was a gust of wind at the moment of the launch. Another possibility would be launch rod whip. What was the launch rod made of? Carbon steel rod is more prone to rod whip than 316 stainless steel. You also cannot rule out launch lug binding which would easily cause a slow speed at the top of the launch rod. Did you wipe off the launch rod before your flight?
The standard aluminum 1/8" launch rods are "whip-resistant," too, unlike steel ones (G. Harry Stine tested both types and measured it).
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