Going Supersonic

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guy97
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Going Supersonic

Postby guy97 » Sat Apr 30, 2011 9:33 pm

Hello,
I am new to rocketry and have just ordered a couple of rockets(cee-yah and blue streak) and have found out that a blue streak will go supersonic if you put a D21-7t :shock: . Are there any tips or tricks about construction and flight about going over 340m/s :twisted:

Regards,
Mathew
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Lamp
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Re: Going Supersonic

Postby Lamp » Sun May 01, 2011 8:45 am

Hmmm, a rocket reaching Mach on a D21T-7.....I would have thought it unlikely but I have not simmed it. Looking at the kit, and looking at the reasonably long fins compared to their root chord length combined with their swept back design, I would think fin flutter would be an issue so if you did get it anywhere close to transonic I would think it would start losing fins and shred itself to bits.

You need a really good design, good build technique and good strong fillets to have a chance of your rocket surviving. You will probably have to reinforce your fins and fillets, but all this adds weight decreasing your chances of actually breaking mach.

The classic medium power "Mach buster" is from the same manufacturer as the "Blue Streak" and is called the "Apogee Aspire" I believe 2 or 3 guys at our club launched them on high impulse G motors (G80T-10 motors I think)....I could be wrong but I don't think any of them broke Mach and managed to survive the experience. I actually missed that particular launch but I know Krusty was there....one of the Aspire builds was his! A well built HPR can have a much better chance on a high impulse motor but you are using much stronger materials and different build techniques....

Krusty and others here would have more knowelege about the possibility of an LPR rocket actually getting to mach.....
‘It takes sixty-five thousand errors before you are qualified to make a rocket.’ — Werhner von Braun
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guy97
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Re: Going Supersonic

Postby guy97 » Mon May 02, 2011 7:04 pm

Hello,
After reading the above article and over articles I have decide to build both my rockets for strength and not to go supersonic but super high :lol:.

Regards,
Mathew
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Re: Going Supersonic

Postby Lamp » Mon May 02, 2011 7:48 pm

That sounds like a wise move to me..... :wink:
‘It takes sixty-five thousand errors before you are qualified to make a rocket.’ — Werhner von Braun
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Re: Going Supersonic

Postby rocket_troy » Tue May 03, 2011 9:04 am

That sounds like a wise move to me..


Ditto that!

I've lost count how many people I've seen put MPR motors into model rocket strength airframes simmed to go >Mach resulting in a perfect 100% record of a total destruction to the airframe. It can be done, but you really need a very carefully designed and constructed airframe to pull it off. Yes a 10-20Ns motor isn't considered MPR, but you get my point.

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Re: Going Supersonic

Postby october sky » Tue May 03, 2011 11:08 am

Fully agree with above comments from Lamp & Rocket Troy !
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Re: Going Supersonic

Postby ogivemeahome » Wed May 04, 2011 9:54 pm

There's an article about fin flutter on http://www.info-central.org/?article=138
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Re: Going Supersonic

Postby krusty » Wed May 04, 2011 10:32 pm

I had an Apogee Aspire that's billed as a 'supersonic' rocket. Came down in little pieces.... The first .8 seconds were shear awsomeness....

Krusty

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Re: Going Supersonic

Postby PK » Fri May 06, 2011 9:51 pm

krusty wrote:Came down in little pieces.... The first .8 seconds were shear awsomeness....

Just like marriage!
PK

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Re: Going Supersonic

Postby guy97 » Sat May 07, 2011 4:23 pm

Hello all,
I have just finished my two rockets but probably not going to use a d21-7t( Have to build better for that). I am preparing to paint and I am just wondering if the primer is neccessary?

Regards,
Mathew
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Re: Going Supersonic

Postby krusty » Sat May 07, 2011 5:26 pm

guy97 wrote:Hello all,
I have just finished my two rockets but probably not going to use a d21-7t( Have to build better for that). I am preparing to paint and I am just wondering if the primer is neccessary?

Regards,
Mathew


Hi Mathew,
I prime - I use the cheap grey stuff from bunnings (it's about $3.50 a can) in fact, most of my rockets get done in the cheap bunnings paint :) It also gives you something to sand down to smooth things out a bit.

If you're doing a light colour, give the rocket a coat of white over the primer.

But it's all up to you and the finish you want. On some rockets, I've primed, then sprayed with filler (you can get spray automotive filler at supercheap auto for about $15) then another primer, a coat of white and then the colours on top of that.

Krusty

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Re: Going Supersonic

Postby GDJ » Mon Jan 06, 2014 3:14 pm

Just my 2¢ here, but I found the best way for a small rocket to survive a quick slap into supersonic is to replace the balsa fins with something a little more robust, like Basswood or Birch. Basswood is considerably tougher than Balsa, but there is a weight penalty which may need some compensation at the nose cone.

Birch is slightly heavier than Basswood, but very strong. My favourite trick is to laminate a few layers of 1/32" birch (thinnest 3 ply I can find) and glue them together and clamp them overnight. Still makes a fairly light fin, but it has the rigidity approaching CF (in my opinion and what my hands tell me).

Good alternative: Slightly thinner balsa, then laminate 1/64" birch to that. The stiffness in the fin really increases, but the weight penalty is less than using Basswood entirely.

Hope this helps some on your next projects.
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