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The Estes E12 and F15 motors combine an unusually good initial thrust spike and about 3 second burn solid right to the end, and can be flown low and slow with their shortest delay versions. I built a sort of 6" funnel-stabilized rocket that would only make it about 400' on an E12, bigger than...

One simple thing was just throwing a basic rocket model into Open Rocket and using Angle of Attack simulation to compare short and long versions of the rocket. The long rocket had much more shift of the CP forward at any angle of attack. This is because much of the mass being fins and motor...

I question that the stabilizing effect has much or anything with the base drag at all. Consider the most popular saucer rocket shape, a flattened cone. If this starts traveling at an angle, the side pitched forward becomes more square on to the air, and the other side less so, producing an...

I don't have to know what is wrong to or how to fix it to think something is fishy. Fortunately most people are cautious. I have attempted to point out some issues and theories. The Levison paper was just a first pass at this after all, so surely the BDH could be tweaked. The R2-D2 is an...

A hack that reverses one absurdity to the opposite absurdity is obviously also absurd.

Keep having to edit my reply to keep up... Any type of rocket could end up unstable, however your rockets would indicate stable using the cardboard cutout method. Meanwhile the 3D view of the R2-D2, which I presume is the unhacked version, shows a red dot in front of the entire rocket. Surely...

Clearly the CP in front of the rocket is in error. It looks probably stable to me but very unlikely as stable as with your BDH version. That Red Columbine rocket is surely stable with that CG just from looking at it. In both cases the simulator is clearly in error or picking up on something...

Yes, because it's based on normal forces. But looks to me that simple symmetrical drag can't result in an effect like the CP behind the rocket either, merely right at the back surface, even if it does something. To get that effect requires asymmetrical drag. The problem is, merging that...

I suggested this here in the past and a got a cold reception. Length of the rocket is a better measure of how large the rocket is than diameter/caliber, and therefore a better definition of what a significant margin is. With most stubby rockets, there is simply no need to explain a problem...

I consider the fins part of the shape. Rockets vary especially mine, and I used to actually use RASP, so switched to calculating equivalent diameter and used Cd .35 with good results. .7 would include a factor for how much bigger the whole thing is than what is measured. That's fine for...

In some cases in rocketry, Cd is not normal. For example RASP basic altitude and speed software asks you diameter and Cd but nothing about the fins. To be correct that has to include fin drag and a lot of other stuff not directly related to cross section area of the airframe. That's why high...

Do not attach your screecher directly at the shroud lines, the added weight will pull it into the plants unless the shrouds are really long. And be able to rely on it or them.

Tried this and difficult to get a "lot" of improvement. With tailcone got 279m. Make sure fins are thin (0 or stupid thin Airfoil) and surface is set to polished. Tends to be an ugly rocket!

Well Hobby Lobby was out of the Star when I went by and I really didn't want it anyway. Lost sight of the Vapor twice last weekend on E12s. Zero interest in putting an H180 in it.

The physics say the peak forces will always be FAR higher, all else equal, for a shock cord with almost no stretch. Real life may differ, and the trend has been against elastic, which does have a lot of failure modes. I guess a nasty zipper still beats a crash, and you can overbuild easiest with...

Not exactly, but the Star is essentially their regular rocket modified for 29 mm motors, or really intended primarily for the 29 mm BP motors. I flew my unmodded Vapor recently on an F44, OMG. For a rocket that doesn't have to be launched from a great distance, soooo fast. I built it because I...

The deployment speed is almost the same for after the apogee and before it. Except for air resistance, the rocket is deaccelerating at 32 ft/sec per second upwards motion due to gravity, and then on the way down it accelerates down at 32 ft/sec per sec. So 2 seconds late is little better than 2...

In my experience and in contradiction to this article, which includes finless but not saucer rockets, Open Rocket will correctly and accurately predict stability, or even be slightly over-optimistic, without additional compensation for short but otherwise normal rockets. Be sure to perform a...

5.5" diameter, simmed like 2.5", flew almost like it too. Also rear ejection so it came down nose first, however super cramped to pack and that was its undoing. No pictures after final paint job. Note, any reducing transition in the back half of the rocket reduces stability, must sim, the CG in...

A tool length measurement needs to be the difference between contact and drill depth. I recall the delay grain surface is maybe 1/32" below the plastic (just drilled one yesterday but it's gone now). Also don't count the first 1-2 32nds of the drill tip, as it just mashes down the material. Try...