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Thanks for the opinion on the Aeropack retainers.As for the shock cord mount, this method you are describing sounds a lot like the old north coast rocketry Gorilla shock mounts. My only concern is that the kevlar or nylon you…   Read more»

Let’s see, to address your questions:1) I love the EZI65, my favorite LOC kit. A very good choice.2) Aeropack retainers are the sine qua non of motor retainers in my opinion. While I’ve only used the 54mm and 98mm sizes,…   Read more»

Oh, I thought you meant diameter. Now I get it that you mean 1/16″ thickness.

You have to have something to braze the fins to – you cannot do it to the motor case. This slides right over the motor. The whole assembly (with cosmetic fillets) weighs just under 450 grams.Edward

Cool. It sounds like brazing is a valuable skill to have. How much does the fincan weigh? What’s the 1/16″ tube for?

I know all the discussion here has been on composite fincans but I wanted to give input about metal ones. I built one for my L3 – it was 2.5″ diameter with a 7″ root and 4″ span. I brazed…   Read more»

Good question. I’m glad you asked. The quickie analysis I gave was for the flat part of the fin, where the two face sheets are held apart by 0.04″ of something, where that something could be G10 or CF or…   Read more»

Keep in mind that Adrian was assuming that CF could withstand 62,500 pounds per square inch without trouble. That would require near perfect CF work – probably with a high pressure, high temperature cure and top grade epoxy. Realistically, most…   Read more»

Disclaimer: From a person with almost zero MD experience, who has absolutely no formal training, and horrible at math.Going backward in the thread a bit, it doesnt seem like this passes a sanity check…If I ignore the center layers of…   Read more»

After thinking about it some more, I realized that just compressing the fuel grains wouldn’t be a very representative test, considering the higher temperatures, internal pressure, and reduction in mass and volume of the fuel during the burn. It’d be…   Read more»

Thanks for the info.Maybe the lack of fin sweep was a contributing factor then. The shock wave would definitely be along the whole leading edge, not just the root. Worse, the rectangular-ish shape gives the tip a lot more leverage…   Read more»

John, your description of the fin failures has convinced me to be conservative in the structural design of the fins. It would be great if we can find out some more details so that we might guess as to what…   Read more»

I’ve read that the trailing edge of the fins should be one fin span in front of the truncated end of the fuselage. The idea was to have a clean airflow before the end was encountered and keep the drag…   Read more»

Wikipedia gives the stagnation temperature, for air, as Tstag/Tamb = 1 + .2M^2. So for Mach 3, the ratio of absolute temperature would be 1+ .2*9, or 2.8. So for 300K ambient temperature, the stagnation temperature would be 840 Kelvin,…   Read more»

Nice pictures, Chad. That really shows why someone might want to keep the fins swept back enough to stay within the Mach cone angle. I agree with Chris that sweeping the fins to 74 degrees would be a lower-risk structural…   Read more»

Great discussion….for the fin planform, there is the option to go with short fins with minimal sweep and as sharp a LE as you can make to reduce pressure wave. Think of an F-104 Starfighter wing or a Nike rocket…   Read more»

Neat image of rocket at M2.5.

Great discussion….for the fin planform, there is the option to go with short fins with minimal sweep and as sharp a LE as you can make to reduce pressure wave. Think of an F-104 Starfighter wing or a Nike rocket…   Read more»

It’s kind of a shame that you can’t just graph or predict dynamic pressure in rocksim though.

But you can graph density and velocity, so it’s pretty easy from there.

Oops. I just realized I forgot to convert from Newtons to lbs in the last wind shear calculations, so the 375 N converts to 86 lbs, which is right about what Chris calculated the 2nd time. I think we’re converging.