Put some canted motors up front!
Put some canted motors up front!
Powdered Tungsten; will do wonders reducing your golf handicap and adding to your model rocketry handicap!I hear you and I believe we follow the same belief/religion/cult lol! But powdered tungsten...mind blown, but thumbs up!
I will eventually, but I have to get Rocksim or similar first and learn it. What are you looking for in the sim?
Idk if you've missed it, but I provided a 2D profile cutout just before your post with it balancing. That cutout is extremely precise...I measured the body tube dimensions and took the actual rear fin (had broken off) or a direct tracing of the front fin to make the cutout.I woud just like to know where the Cp is, so we can all stop speculating about whether this is a "stable design with the Cp forward of the Cg".
If you could post the critica dimensions - length and diameter of the body tube, nosecone, fins etc. - I could whip a sim up for you. Or, post a side-on photo of the rocket, trying to eliminated perspective as much as possible, and I can guess at the dimensions from the photo.
Great looking Tiger!
Great looking Tiger!
The tip of rocket to root of forward fins/wings is 5 - 1/16", the wings are swept at a 45 degree angle (or add on 90)... I'd forgotten what sweep I used and was happy to see it match 45 exactly!Oh, I did miss that pic; thanks. Working on your measurements instead of the cutout (I'm out of time tonight) this is what I get, first pass:
View attachment 457423
It would help to know the distance from tip of rocket to root of forward fins/wings, and also the sweep of the wings - in degrees, or inches. Ignore the Cg, because I didn't enter accurate data to calculate that.
Idk if you've missed it, but I provided a 2D profile cutout just before your post with it balancing. That cutout is extremely precise...I measured the body tube dimensions and took the actual rear fin (had broken off) or a direct tracing of the front fin to make the cutout.
Cool, thanks! What are your thoughts on this?OK, with those updates, I get this:
View attachment 457443
It shows the Cp as being 6.7" back from the tip, or maybe 1/2" back from the back edge of the root. FWIW.
Makes sense that it is conservative...I later realized that means it's more likely farther forward so you can place the CG farther forward for a safer measure.The "Cardboard Cutout" method of determining CP tends to place the CP somewhat AHEAD of its actual "mathematical location". In my experience, the Cardboard Cutout method provides a SAFE approximation of CP location, but I am curious how much it differs from Barrowman and the various "Sim" programs.
https://www.rocketryforum.com/threads/center-of-pressure-cardboard-cutout-vs-barrowman-vs-computer-sims.163511
https://apogeerockets.com/education/downloads/Newsletter18.pdf
Dave F.
Estes should make the Lacrosse! They've done much worse.I think, based on where you show the Cg, and where the sim shows the Cp is, and the flight video, that the pseudo-lacrosse is marginally stable. Still, if you have some novel stabilization mechanism, we'd love to see it.
Looking at the Gnikiv, and the flight video, it seems that this is unstable, though the extremely short flight duration keeps it from doing anything too crazy.
And the plane's not bad, either . . . LOL !
Dave F.
Covid lockdown lead to alot of building experimenting and tried a couple of WW2 designs of Winged Rockets. Both were miserable failures. But looked cool before flight!
I think, based on where you show the Cg, and where the sim shows the Cp is, and the flight video, that the pseudo-lacrosse is marginally stable. Still, if you have some novel stabilization mechanism, we'd love to see it.
Looking at the Gnikiv, and the flight video, it seems that this is unstable, though the extremely short flight duration keeps it from doing anything too crazy.
Excellent explanation!Cardboard cutouts err slightly to the side of conservative due to the fact that it correctly represents wings and fins as flat plates and incorrectly represents the body tube and nose cone as flat plates, which they are not.
When the model has a small deflection from straight flight, the flat fins and wings have a bigger effect on the airflow than the curved surface of the body tube and nose cone has on the airflow. If the deflection from straight flight gets large, the tube and nose cone start having the drag effect of a tube section with the relative wind 90 degrees to it, which starts having a very large effect.
RC model wise, aircraft of fairly normal configuration can be balanced for flight based on the wing planform only (again, CG in front of CP). However, aircraft models of things like an F-104 must take the fuselage planform into account, as it is large compared to the wing area.
Try to watch the video more... particularly 0:11-0:12. From what I can tell the rocket goes unstable and horizontal into the wind, but then stabilizes and actually shifts vertical and perpendicular to the wind...very odd, but I believe it shows it stabilizing itself.Looking at the Gnikiv, and the flight video, it seems that this is unstable, though the extremely short flight duration keeps it from doing anything too crazy.
Noris makes a V1 kit. Hostile Projectiles made a winged V2 kit.Covid lockdown lead to alot of building experimenting and tried a couple of WW2 designs of Winged Rockets. Both were miserable failures. But looked cool before flight!
Thanks! Fins forward past CG work to easily stabilze...My first build is attached to the nosecone and was pretty cool and can be moved to other rockets... making me think "Valkyrie" build. Later design I have to come would have rear fins going opposite, but more as non-flying demo first... should be cool!Well, it's intriguing. Can you describe how the weighted/pivoting fins are supposed to work? I just can't work out in my mind what this could be doing that is useful. Normally, in order to stabilize a rocket, fins need to move in the opposite direction they would tend to go naturally, which means some sort of active control is necessary.
Does the Gnikiv use this? Unfortunately, 11-12 seconds is about the entire flight, and the rocket loses speed so quickly that it's tough to determine whether it is 'stabilizing' or just 'randomly orienting' itself.
Sorry to hear about the work issues; "I need to deal with some lawyers" ranks right up there with "The government is going to help with that" in terms of phrases you never want to hear...
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