Adrian

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»

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»

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.

Rocksim indeed lets you use a launch tower that is 5000 feet high, and enter 150 ft/sec of cross-wind. When I ran it, it predicted that such a situation would result in just under 300 N*m of torque when it…   Read more»

Ok, 76 lbs is a lot more reasonable than stacking 10 SUVs on the end of the tube. I think i’ll use rocksim to double check. It provides restoring torque as an optionin the graphs. I’ll see if it let’s…   Read more»

Well, after some calculations…Ah, the cool refreshing sound of real engineering.Very interesting results. 150 ft/sec of instant shear is a pretty conservative worst case, but it shows the margin we have here. What did you assume for the distribution of…   Read more»

Good comments on the fins; the Mach cone angle at M3.5 is about 16 degrees. So these would need to have a really long root chord and short tip length. That alone will do wonders to reduce the flutter risk….   Read more»

If one would be fun, two would be better, so tell you what. You and John make the booster, Chris and I will make the sustainer, and we’ll hit 100 kft together.

Cool. I’m interested. You would definitely want a Von Karman cone for it. I can ask my friend who did the mandrel for my 38mm VK cone to do the same thing in 75mm. The length may exceed what he…   Read more»

I think it would be good to avoid the hassle of deposits or rental fees. Normal motor case rules would apply. If you can’t return it, then replace it. The replacement cost of the altimeter would be around $70-$90, depending…   Read more»

Congratulations, John. Dang, that’s some impressive simulation.Any details for your rocket? Where did it land? Pictures?

Darn. If it opened at 11:15 I would have been covered.

Hmm…. My rocket landed stayed within the larger high-altitude cylinder, so this could be very close, depending on when the window for Ed’s flight was opened. Do you recall the time?Thanks.

Another couple of fun facts:Right after burnout, the rocket was going 1440 mph (Just under Mach 2.0), and had 14 Gs of drag. The burn time for the I600 was just under 2.0 seconds, which is the same thing that…   Read more»

Thanks Joe and Ed.I got the temperature corrected altitude from//psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdfCorrecting for the fact that the ambient temperature was warmer than assumptions used in the standard atmosphere model, the peak altitude was about 16,500 feet. But if I submit this for…   Read more»

Lots more data (cross-posted at Rocketry Planet)Here’s more data from the new Featherweight Interface program:Altitude and temperature, for the whole flight:Velocity, accel, and altitude up through apogee deploymentZoomed into the the motor burn:I did the following post-processing using the Excel…   Read more»

Yes, you are right. I remembered the dry weight wrong. My calcs show exactly 500 grams, but that still puts it over what you recommend and what Adrian’s dry weight probably was. I’ll take another look.For something that is ripping…   Read more»