Hi guys, time to post a serious reply now
This thread has given me quite a few thoughts to digest, particularly drag on decelleration.
When I've run sims, I allow for a fairly generous margin for error of about 25% in all my calculations/results, to make sure the rocket will be fairly capable of breaking mach. Theres no reason for your sims not to be accurate with the appropriate provisions made, as previously mentioned. My sims have been compared to actual flight data, so I know what kind of accuracy I can expect - what a shock when my first altimeter flight came in 1000ft under what rocsim said!
Aside from my Cirrus Dart, I’m building a 3metre-ish, 4inch diameter rocket using an assortment of fibreglass and metal components including 4” Extreme(TM) glass tubing, a black brandt style nosecone and a 3 fin tail, with a 98mm MMT which is basically the lower section of the rocket that has been designed to accommodate any commercial 98mm motor available today. I had great fun in messing around with rocsim, to see what impacts various components, component dimensions, shapes and weights would do to a flights performance. My final design has ended up with components that have been flight tested past Mach 2 (or so the manufacturers say
), so my build skills will be really tested if I fly this on something large. Unlike the Cirrus Dart, I intend to actually recover this rocket.
I've seen many similar rocket designs, which made me think there are certain recipes for mach and altitude flights. I've kept my build fairly simple as there will be enough going on when the rocket transitions through mach, and I reckon the less that can go wrong, the better. Time will tell if this philosophy proves right. If I'm wrong, I'm sure I'll learn the hard way.
I still haven’t figured out a way of ensuring the sections don’t drag separate without relying on shear pins alone. More thought will be spent here.
Then there is the video camera mount - I need to figure a way of filming the flight without impacting drag, or having wind pressure playing the avionics bay 'like a flute', to quote another thread.
Fin alignment will be another issue, but if Scoop is allowed to use a fincan, then why can't I? That takes 1 more variable out of the equation, as I can expect these fins to perform solidly. (See what I did there, its "reducing the number of variables", not "cheating"
Some final questions:
1. What electronics are you all using to record your flights?
I see Scoop is using a G-Wiz (amongst others), Hotspot has an rrc2? I've only used Perfectflite altimeters, and while user friendly, they don't offer anywhere near the information the G-Wiz offer.
2. Has anyone relied on GPS data alone to analyse rocket flights?