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edwinshap1
4th November 2010, 08:02 AM
i'm still conducting heavy research about my first HPR, and this question is regarding the strength gained by through the wall fins, and tip to tip. If i'm making a minimum diameter rocket, i can't through the wall, but i can tip to tip. Through the wall gives the fins more attachment and durability, but not supersonic capabilities by itself. I'm wondering, if i make a minimum diameter rocket with plywood fins, and i tip to tip without glassing the fins separately, will the strength go down a lot? I really just want to make sure those fins stay put and don't erupt off and give me a failed cert and a heap of twisted and smoldering stuff.

Gnomad
4th November 2010, 08:59 AM
For a certification flight, go low and slow with a fat body tube. Remember, you need to recover to get your cert!

o1d_dude
4th November 2010, 09:25 AM
For a certification flight, go low and slow with a fat body tube. Remember, you need to recover to get your cert!
Think Minnie Magg or Thumper Jr.

Once you get your cert you can blow the woolies out with a minimum diameter screamer.

berlinetta
4th November 2010, 01:35 PM
Even though you cannot do through the wall with a minimum diameter rocket, you can cut semi slots. What I am talking about is only going through about halfway through the tube. That way when you epoxy the fins on, the epoxy will soak into the tube. Then you can also do tip-to-tip as well. I did this with my VB Extreme 54. That kit has fiberglass fins with a tip-to-tip fiberglass job done as well. I also fiberglassed each of the tubes as well.

I agree Gnomad, low and slow is the way to go for a cert flight. After that, you can play with minimum diameter stuff and go real high.

Good luck with your cert.

karlbaum
4th November 2010, 02:27 PM
After you attatch your fins to your min diam rocket, lay fiberglass between the fins and up the fins and this will hold them rock solid.

Handeman
4th November 2010, 11:56 PM
i'm still conducting heavy research about my first HPR, and this question is regarding the strength gained by through the wall fins, and tip to tip. If i'm making a minimum diameter rocket, i can't through the wall, but i can tip to tip. Through the wall gives the fins more attachment and durability, but not supersonic capabilities by itself. I'm wondering, if i make a minimum diameter rocket with plywood fins, and i tip to tip without glassing the fins separately, will the strength go down a lot? I really just want to make sure those fins stay put and don't erupt off and give me a failed cert and a heap of twisted and smoldering stuff.

Are you flying a minimum diameter with 29mm or 38mm? It really doesn't matter too much, but I wouldn't worry too much about the fins. My thought is that you will have much more stress on the fins when landing then when flying unless you're using a 29mm min. dia. with an I200W in a 29/360 case. In most cases you would want the fins to break off on landing and not break themselves. That way you can just use some 5 min. epoxy and glue it back on, and fly again in an hour.

bobkrech
5th November 2010, 12:00 AM
i'm still conducting heavy research about my first HPR, and this question is regarding the strength gained by through the wall fins, and tip to tip. If i'm making a minimum diameter rocket, i can't through the wall, but i can tip to tip. Through the wall gives the fins more attachment and durability, but not supersonic capabilities by itself. I'm wondering, if i make a minimum diameter rocket with plywood fins, and i tip to tip without glassing the fins separately, will the strength go down a lot? I really just want to make sure those fins stay put and don't erupt off and give me a failed cert and a heap of twisted and smoldering stuff.

If you are absolutely convinced that you have to break Mach on your L1 cert flight, find a really big field and use a PML Cirrus. Just be aware that if you break mach with a rocket, your apogee exceeds 1 mile.

http://www.rocketreviews.com/reviews/all/pml_cirrus.shtml

It is a 38 mm minimum diameter rocket with surface mounted tip-to-tip glassed fins capable of breaking 2 miles with an L2 motor approaching Mach 2. Just be sure and kiss it goodbye before you push the button cause you might not see it again.

https://blastzone.com/pml/images/CirrusDartDataSheet.pdf

https://blastzone.com/pml/kits.asp?groupid=5

Bob

cbrarick
5th November 2010, 12:31 AM
Best get yourself a tracker and figure out how to use the thing because that's the onliest way you will ever see that bird again.

But seriously, why do all that? Either go with paper tube (LOC/precision has a ton of great kits, or just go all glass - see Wildman for a ton of L1 capable fully fiberglass rockets. Save the tip to tip and min. diameter for AFTER you get your cert...they are much more complex (small spaces, still needing all the stuff of a regular rocket) and easier to loose or break - not things you need to do in a cert. If you feel you must do the alpha dog cert, CTI makes a I800 vMax motor to ensure you never see it again!

good luck :cheers:

sparky
5th November 2010, 12:57 AM
If you get a cirrus dart get a tracker...get a tracker...get a tracker! I flew mine on a CTI H400 v-max and this is the last time I saw it. I covered the whole thing in carbon fiber, at apogee I saw it drift far far away.:(

JimJarvis50
5th November 2010, 02:35 AM
if i make a minimum diameter rocket with plywood fins, and i tip to tip without glassing the fins separately, will the strength go down a lot?

The answer to your specific question is no. If you use tip-to-tip construction, you don't have to start with glass fins or glass them first. My 54mm Shocklet (attached) has plywood fins with one layer of tip-to-tip carbon. It has flown on everything from an F60 to an L1030. The secrets, in my opinion, are to start with a strong tube (a fiberglass or carbon tube which you don't slot or partially slot) and to use a relatively large-radius fillet. Then, the tube and the tip-to-tip work together to make a very strong structure.

Jim

rocdoc
5th November 2010, 02:59 AM
It always amuses me how much "low and slow" and "KISS" advice you get when you start talking about cert attempts. Make sure you're safe, that you've taken a realistic look at potential failure modes and done your best to address/eliminate them, then push the button. If wicked neck-snapping minimum diameter flights get you going, go for it and make yourself happy. There are lots of reasons why people pursue this hobby, which is great because it makes for interesting builds and interesting launches.

That being said, go tip-to-tip over nice rounded fillets, put a tracker in it, and light the fuse. I've never understood the low and slow advice followed by a mach-busting attempt. Why is it preferable to lose your rocket once you're level one than on your L1 attempt? Either way, you're out the rocket (which sucks). If you lose your L1 rocket, they won't take away your birthday or anything. You'll just have to build another rocket (darn), then build another L1 motor (shoot), and then launch again (oh my!). As long as you're safe and you don't endanger anyone else, you've lost nothing and you will always have the satisfaction of getting your L1 in the style of your choosing.

Be safe, and good luck on your L1.

Bryan

edwinshap1
5th November 2010, 06:41 AM
lucerne is a fairly large field as far as i can tell, so i don't mind walking a mile or so to get the rocket, unless of course its summer and im walking in 100 degree + temps :P

I'll probably make a min diameter rocket just because i want everyone to think im insane for mach busting on an L1 attempt :D But on a slower burning H motor, i don't see mach being busted :P H73J will gimme a slow launch with a nice black trail, and then i'll probably drop in an I for my second attempt and watch it fly like crazy :D

Handeman
5th November 2010, 06:59 PM
lucerne is a fairly large field as far as i can tell, so i don't mind walking a mile or so to get the rocket, unless of course its summer and im walking in 100 degree + temps :P

I'll probably make a min diameter rocket just because i want everyone to think im insane for mach busting on an L1 attempt :D But on a slower burning H motor, i don't see mach being busted :P H73J will gimme a slow launch with a nice black trail, and then i'll probably drop in an I for my second attempt and watch it fly like crazy :D

I tend to agree with Bryan on this. Fly your L1 the way you want to and don't listen to the low and slow crowd if that's not the way you want to do your L1. As long as you're safe, if you want to bust Mach on your cert flight, go for it!

Bill P
6th November 2010, 01:41 PM
The "low and slow" and the "fly what you will be flying" concepts have their benefits.

If you want high and fast, go for it. Remember it is your flight and your cert so do it as you want. Just do it safely.