Mach Speed Club

Discussions on high/extreme altitude and mach busting rockets.

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blackbird
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Postby blackbird » Thu Mar 26, 2009 7:19 am

I was thinking about it last night because I still wasn't happy with the numbers - I'm still not happy with the numbers this morning! I had changed my force due to gravity to a momentum component but I'm still getting a significant separation force from aerodynamics alone. I'm still thinking about the momentum part of it as I don't believe my calculations are right yet.

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Postby rocket_troy » Thu Mar 26, 2009 8:30 am

Well, if the part of the rocket forward of the coupler experiences the same *drag* as the part aft of the coupler and the part forward of the coupler is heavier, then it will *try* and separate.

Note: it's important to distinguish the above statement must use the accumulated momentary drag of the parts not the coefficient of drag.

TP.

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Postby rocket_troy » Thu Mar 26, 2009 8:33 am

Well, if the part of the rocket forward of the coupler experiences the same *drag* as the part aft of the coupler and the part forward of the coupler is heavier, then it will *try* and separate.


Of course, it's assumed we're talking about a decelerating rocket here

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Postby blackbird » Thu Mar 26, 2009 9:42 am

Just to confuse things again, I've been trying to find some references regarding this issue but the only thing I found so far is:

http://www.grc.nasa.gov/WWW/K-12/rocket/flteqs.html

This states that the forces acting on the rocket during the coasting phase are drag and weight force. They don't mention momentum (except in relation to propulsion).

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Postby rocket_troy » Thu Mar 26, 2009 10:07 am

This states that the forces acting on the rocket during the coasting phase are drag and weight force. They don't mention momentum (except in relation to propulsion).


Well, it's not really a force, and when I said "something like" I didn't mean to add *that* strictly to the equations. However, momentum is mass x velocity and Newton says that an object will continue along its path at constant velocity unless a force is acted upon it - which in this case is drag and gravity. The gravitation force on all the components in the vehicle are essentially the same. If the drag forces where also the same at a single moment in time, then we can simple use f = ma to gather deceleration where "a" will be negative so
a = f/m
If all the f are constant, then "a" will be proportional to "m"
ie. as you increase "m" (the denominator), "a" will decrease in its negative form. So deceleration will decrease with an increase in mass of the part.

TP

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Postby rocket_troy » Thu Mar 26, 2009 3:29 pm

The gravitation force on all the components in the vehicle are essentially the same


Via "weight" that is, which is the force of gravity x mass of the part.

TP (whilst we're buggering up terminology)

hotspot
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Postby hotspot » Fri Jul 03, 2009 10:06 pm

Any new projects on the go to break Mach.

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Postby hotspot » Mon Jul 06, 2009 10:50 am

Looks like no one has anything of interest.

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Postby rocket_troy » Mon Jul 06, 2009 11:06 am

Well, most of my larger rockets can exceed mach in the right conditions. The one I flew yesterday would have exceeded mach, but it's all a bit of a dull affair really. You can't hear a mach clap or boom from behind the direction of travel. You'll notice this with whip cracking - ie. there will be a distinct difference in sound of when the person cracking the whip is facing towards you or facing away from you as they crack the whip. If they're facing away, the chances are you'll only hear the reflection of the sonic crack/boom off opposing objects. It's very directional.
I was somewhat impressed to see a mach cloud from onboard video footage of a group project I was involved with in the late 90s -early 2000s. It's very brief (one 1 frame of video) but very distinct nevertheless.
No toilet roll airframes for this stuff.

TP

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Postby Sumo310 » Mon Jul 06, 2009 12:27 pm

I have my Cirrus Dart, and waiting on pieces for a 4" project which will break mach, but we currently don't have enough altitude to fly either of these.

They're not very interesting though, pointy tubes with a couple if fins on the back. Nothing out of the ordinary.
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Postby hotspot » Mon Jul 06, 2009 1:19 pm

Thats what i was thinking the thread is a bit like mines bigger then yours but yes all rockets are a tube nosecone and fins.

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Postby rocket_troy » Mon Jul 06, 2009 2:17 pm

Thats what i was thinking the thread is a bit like mines bigger then yours but yes all rockets are a tube nosecone and fins.


There will always be threads with a certain element of that on such forums, but (ok, I only came in late on this one) I didn't get that impression with the dialogue I was involved with.
Let's not trivialize the requirements of largish rockets that need to handle mach either. They really do need to be quite strong to handle the loads. It's not modroc, there's a distinct difference in minimum structural requirements between large rockets that need to handle mach and those that don't.

TP

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Postby hotspot » Mon Jul 06, 2009 4:04 pm

For sure thats what is interesting about this type of rocket.

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Postby Scoop1261 » Mon Jul 06, 2009 4:13 pm

I guess when I started this thread it was really to see who had done what with what sort of construction...To show documented evidence of a rocket going Mach, and not some..... "I've got a ABC Pointybird Rocket and I'm gonna stick a J500 in it and I reckon it will go Mach...coz that's wot the sim says!"

The idea was/is to show a particular design and a particular motor combo, that has exceeded Mach, so others can look and learn and perhaps adapt some of the features into their own designs!
Why Limit Yourself?

AMRS #4 - L3 |TRA #11080 - L3 |MDRA #263

Impulse: A Whole Lot ..So much I've lost count!

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Postby hotspot » Mon Jul 06, 2009 7:26 pm

Thats it pass it on make sure the next guy does not fall into the same traps.


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