Winged and forward winged designs unstable for rockets?

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neil_w

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curious, i would agree that pivoting fins would alter CP much less than fixed fins, but I would expect just from a drag standpoint they would have some effect on CP. Am I out to lunch on this, @neil_w ?
Sorry but I honestly have no clue about the behavior of pivoting fins, or how to approximate it in OR.
 

KenECoyote

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curious, i would agree that pivoting fins would alter CP much less than fixed fins, but I would expect just from a drag standpoint they would have some effect on CP. Am I out to lunch on this, @neil_w ?
I'd agree it has drag...at the very LEAST similar to a rod, but more than that since the cross section isn't always only the front and with weight it may be more.
 

KenECoyote

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You might want to try eliminating the weights. Allowing the forward fins to pivot more freely may make the system work better since it will reduce their effect on the CP.
Hey Roger! (I love you guys at Jon Rocket!)
Thanks for the suggestion, but maybe that should be a separate thread since my idea is adding weights to allow fins or wings ahead of the CG to help stabilize the rocket. Without the weights, it's just flowing along. I'm using pendulum weights to try to keep the path straight (influence vs. follow).
Based on my observations of my substantially winged Tomahawk, I don't think removing the weights would make it better since it already flew better than I would've expected and I have yet to see another model like it fly so consistently well and in wind.
Again, I still have a LOT more testing, so please be patient with me... I've already planned out a version where I can add and remove weights and also hope to do a drag race at my club next month to compare side-by-side. Right now I can't build fast enough since many steps take a lot of figuring out and very custom building (see the locking system pic on video cover in post #85 above). :)
 

KenECoyote

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Actually this thread is about winged rockets, not my system, so if any others are up for the challenge, please do try building some with freely pivoting forward wings/fins...would be great to get additional info/reports and the help would definitely be appreciated!
 

jadebox

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I've been considering building a full-scale AMRAAM missile and using the pivot technique to reduce the effect of the forward fins. It's, unfortunately, just one item on a long list of todos. :)
 
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DrewW

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I've been considering building a full-scale AMRAAM missile and using the pivot technique to reduce the effect of the forward fins. It's, unfortunately, just one item on a long list of todos. :)
@jadebox a free spinning “canard can” may be an easier approach. I’m experimenting with this on some LPR rockets
 

DrewW

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I am not sure what you mean. Can you describe it in more detail? Thanks.

BTW, I originally got the idea of allowing the forward fins to pivot from this:

@jadebox Yeah the Python is ridiculous, that front set of canards I believe are called “destabilizers” if that tells you anything about the design.
I’m working on a scratch build of the Thales Starstreak. The image was my first prototype made with a clear tube to show what was going on inside. The orange circles are bearings on a hollow axel which allows free rotation and canards were not attached...which requires some imagination. Canards spinning about the missile long axis should average out their CP contributions, but also add gyroscopic stability.

IMG_9049.JPEG
 

KenECoyote

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Wow, very cool stuff! I love those designs! The Python is REALLY out there with it 3 calibers unstable. o_O
 

KenECoyote

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BTW, I originally got the idea of allowing the forward fins to pivot from this:

That one is great info...I had heard about pivoting forward fins on something like an AMRAAM but thought it was more to reduce the CP effect of small forward fins, but that design is saying it almost negates it.
This really gets me thinking...
However I wonder about how much it can affect flight, how forward they have to be, and flight when there is wind.
My first designs do have to be forward of the CG to work (I've thought of another that can be on the rear fins).
 

KenECoyote

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Also many of these winged suggestions probably may not fit/work the same since the wings aren't forward enough. More testing!
 

KenECoyote

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@jadebox Yeah the Python is ridiculous, that front set of canards I believe are called “destabilizers” if that tells you anything about the design.
I’m working on a scratch build of the Thales Starstreak. The image was my first prototype made with a clear tube to show what was going on inside. The orange circles are bearings on a hollow axel which allows free rotation and canards were not attached...which requires some imagination. Canards spinning about the missile long axis should average out their CP contributions, but also add gyroscopic stability.

View attachment 459979
That Thales Starstreak project is really cool! I think I read a bit about it in FB?
I love spinning rocket parts! At one point I was building spinning rear fin cans, but had limited success before I left rocketry for a bit. I like your idea of spinning forward fins...so would the front canards be angled?
Fyi one if my long range & long term projects is to build a dual prop rocket similar to the Dornier DO 335, so this may be similar in how it can work.
 

DrewW

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I like your idea of spinning forward fins...so would the front canards be angled?
Yes, though I'm still working to figure out how little is necessary. I have several replaceable canard cans ready to get on the bench for final assembly to see what I can get away with in cant angle and static stability to 0.75 or lower depending on flight results.
 

KenECoyote

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Yes, though I'm still working to figure out how little is necessary. I have several replaceable canard cans ready to get on the bench for final assembly to see what I can get away with in cant angle and static stability to 0.75 or lower depending on flight results.
One issue I had when trying my "spin can" build was that it was very hard to find the correct bearings for the rear because there's forces on two axes...downward from the thrust as well as laterally (?) from the spin. I figured I'd need both thrust and roller bearings (got the roller bearings, but not the thrust ones...one day). The set up you have looks fantastic!
Only thing I can offer based on my experience is that the rocket body during flight has a lot less resistance to spinning in the air vs. the bearing spinning, so you will still see some rotation of the rocket itself (if built true) unless you do something to counter it such as angling the leading edge of the rear fins, etc.
 
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