I've made and flown several split fin rockets. All have flown straight but no whistle. I've been trying to make a rocket whistle for a while.
Puzzling problem with flight path stability
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I've used spin stabilization before;One of my 3 stage efforts.
It was really windy that spring, and my neighbor told me it would make weathercocking go away.
"If it doesn't, spin it faster."
Dude was a cool old guy that was part of the Manhatten Project WBW.
He also managed to teach me to make NG,NC, and some other cool stuff that ended up with my chemistry set getting traded for an electronics set, lol.
I learned Trig to know how high they went,and derivatives so I could figure out the optimum weight for a given engine /rocket combo.
It's been very helpful in life, lol.
It was really windy that spring, and my neighbor told me it would make weathercocking go away.
"If it doesn't, spin it faster."
Dude was a cool old guy that was part of the Manhatten Project WBW.
He also managed to teach me to make NG,NC, and some other cool stuff that ended up with my chemistry set getting traded for an electronics set, lol.
I learned Trig to know how high they went,and derivatives so I could figure out the optimum weight for a given engine /rocket combo.
It's been very helpful in life, lol.
You talk about non-axisymmetric weight and drag, what about boost gliders? And even my beloved Pigasus, it is clear that both weight and drag are offset from the center axis in the same direction, and if flies accordingly, with a graceful arch. Not a dangerous arch, but not straight up, either. Just sayin'... it can be real, and if there is a weight (or mass...) concentration on one side of a vehicle, it will create a moment with the thrust vector that will tend to turn the rocket off-vertical.
billdz
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I've launched 4" diameter rockets that flew straight up with a 20 gram keychain camera taped to the outside of the airframe. I'm no expert but it seems a rocket would have to be really light for the course to be affected by an internal battery or a gob of epoxy. I'd fly it a couple of more times before rejecting Steve's "rockets just do some weird things" theory.
Agree. It would have to be a helluva lot of epoxy to screw it up. My keychain fob is 27g and can affect the stability of a LPR. The cube SQ11 is 17g and works well. The Astrocam cam is the lightest.
On second thought, most cams are not near the motor so doesn't take a lot of epoxy to mess up the stability.
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Tad
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Sooner Boomer
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I saw this a lot at Airfest this year. I don't think it is due to wind, but I don't know what caused it. Looking at the smoke trail left by the rocket, most maintained the same shape/angle as the smoke drifted away. If the deviation were due to wind (higher wind aloft than at the surface) the angle would increase as the upper winds carried the smoke further than at the surface.
Probably overpowered until enough propellant burned off, guessing…
Thingiverse. Arrow Whistle
https://www.thingiverse.com/thing:1626416or
https://www.thingiverse.com/thing:5140145
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Since only two points make a line, if there are three, one of the three is not helping, unless they are perfect.
This may be hair splitting, but, if the effective guides were the front and rear, when the front slips off the guide, now the rocket is guided by the middle and rear buttons. I can see this as a way to induce a wiggle as the rocket leaves the rail. A button induced wiggle would be more likely if the three buttons had the rocket in a bind, and it "un-binds" when the top button leaves.
I suspect it more likely that a nose-heavy rocket is just making a couple of weather cock adjustments to varying wind while still at low speed. I have a few 4" rockets with nose weight for a short 75mm. They are very nose heavy when flying a long 38mm or 54mm. When on a smaller motor (especially lower thrust), they do tend to follow the wind, but it is more of a tendency than a turn. I would expect this to get worse if your rail exit speed is low.
gldknght
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Because split fins are way cool.
And a bit more of a build challenge compared to a simple 3 or 4fnc rocket. I have a Pml Small Endeavor and a 4" Wildman Darkstar. They all fly great.
gldknght
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I've flown a lot of rockets over the 40+ years I've been in the hobby. This includes Estes, Centuri (that tells you how far back I go), Single use and AT RMS, and Cti motors. I've never once, not a single time, had a rocket motor fly off course due to thrust vectoring. I know it happens, have seen video of it. But it has never happened to me, which leads me to think it is a very very rare thing. When it does happen, I suspect it's due to a damaged or partially blocked (most likely by a chunk of igniter, but could be any debris from inside the motor) nozzle. I've never seen a damaged nozzle either when doing my preflight inspection or motor assembly. I HAVE had to drill out a couple nozzles that still had flash in them from casting. I'm also thinking that a damaged nozzle would adversely affect the entire flight.
On the RMS and Cti motors I've built, the nozzle fits very tight when installed properly. Of course, that means the user MUST install of the the RMS components correctly.
But again, an improperly built motor probably isn't going to burn right for the first part of the flight, have a momentary off axis thrust vector, then continue with a correct burn.
I think Steve S. had it right in his post mentioning that what happened here is the result of an over stable rocket hitting variable winds at altitude and weathercocking.
On the RMS and Cti motors I've built, the nozzle fits very tight when installed properly. Of course, that means the user MUST install of the the RMS components correctly.
But again, an improperly built motor probably isn't going to burn right for the first part of the flight, have a momentary off axis thrust vector, then continue with a correct burn.
I think Steve S. had it right in his post mentioning that what happened here is the result of an over stable rocket hitting variable winds at altitude and weathercocking.
Sooner Boomer
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I've had it happen *several* times. I think Aerotech had a bunch of SU motors that had nozzles that burned off-center. They replaced the first pack, but the second pack had the same problem. It was obvious when you looked at the burned motor. Both launched resulted in damage to rocket.
gldknght
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Yeah, defective nozzles, right?
And I'm betting as long as the motor burned, the rockets were going in circles, if they didn't hit the ground first?
Split fins, don't airfoil the edges on both sides of the gap, model gap size based on a Phoenix or Mystic Buzz, etc. AND use a high and heavy quick boost so that the rocket will coast for a while at high speed (you usually can't hear the whistle when it's drowned out by the sound of thrust).
Sooner Boomer
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You couldn't tell by looking at the unburned nozzle if it was good or not. When fired, it looked like someone had run a drill across the nozzle; the erosion left a groove. The rockets arced over instead of going up. This meant the delay was too long for the altitude achieved. One hit just after ejection, but before the parachute to deploy, the other damaged from the hard jerk the frame got when the parachute opened under high (downward) speed.
gldknght
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Right. In other words, the rocket didn't fly straight for a bit, change it's flight path, then fly straight again, true?
Sooner Boomer
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Correct.
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