What is the upper limit of standard TTW fins?

[Issus]

Rubbish! Getting certifications is all about pushing your boundaries. I say do your cert in style If you dont learn anything on a cert and just do things exactly as you have before with a bigger motor - you need to try harder

 

[cherokeej]

Rubbish! Getting certifications is all about pushing your boundaries. I say do your cert in style If you dont learn anything on a cert and just do things exactly as you have before with a bigger motor - you need to try harder

In a word... Wrong.

Getting certified is about proving that you possess the skills and knowledge to build and fly an airframe capable of flying SAFELY on high power motors. Part of the skill set involved is understanding the limits of the materials and techniques being used.

There IS something very wrong with shredding an airframe and dropping chunks on someone's head.

The first problem is that it won't get an autograph.

I'll leave you to consider what else is wrong with it.

 

[blackbrandt]

But, in my opinion, if you already possess the skills, then why not do your cert in style? I am already planning my cert to be some crazy scheme, mostly because I have already flown a decent amount of HPR, so why do your cert on a baby H in a low and slow rocket? Why not have some FUN!

 

[CZ Brat]

But, in my opinion, if you already possess the skills, then why not do your cert in style? I am already planning my cert to be some crazy scheme, mostly because I have already flown a decent amount of HPR, so why do your cert on a baby H in a low and slow rocket? Why not have some FUN!

I think the debate is over how risky you should be with any flight. If you're going to go Mach, you should engineer it so it is highly likely to survive. 1/8" ply w/o any cloth, IMHO, does not meet the standard of "highly likely to survive" a Mach flight. Though nothing forbids Mach on an L1 flight, I think you should do one thing at a time. 1st, make your first successful HPR flight. Then your first Mach.

Combining lots of firsts into one rocket/flight, leads to higher failure rates. And that is an opinion I think most people will agree with.

 

[wsume99]

So I'm considering taking a rocket kit that I've already purchased and replacing the stock 29mm MMT with a 38mm MMT. I can do my level 1 cert with it in either configuration so that's not really the issue. What I'm trying to ensure is that if I do upgrade to a larger MMT that the rocket will be able to handle the near full range of what that motor diameter has to offer. It seems like a huge waste to me to go with a 38mm MMT but then be limited to G and baby H motors because the airframe is too weak. Others can disagree with my opinion but this is MY rocket so I'll build and fly it how I want (within safe limits). That statement is not directed specifically at anyone but instead just letting everyone know where I'm coming from. I do value everyone's input so keep the comments coming. I'm learning A LOT.

 

[blackbrandt]

I think the debate is over how risky you should be with any flight. If you're going to go Mach, you should engineer it so it is highly likely to survive. 1/8" ply w/o any cloth, IMHO, does not meet the standard of "highly likely to survive" a Mach flight. Though nothing forbids Mach on an L1 flight, I think you should do one thing at a time. 1st, make your first successful HPR flight. Then your first Mach.

Combining lots of firsts into one rocket/flight, leads to higher failure rates. And that is an opinion I think most people will agree with.

Well, I guess the difference is that I will already have flown a good 40-50 HPR flight by the time I turn 18. So, I already will have experience under my belt.

 

[wsume99]

I know where to get epoxy. What's a good place to buy some fiberglass from?

 

[blackbrandt]

uscomposites.com

 

[GregGleason]

I know where to get epoxy. What's a good place to buy some fiberglass from?

https://www.aircraftspruce.com/menus/cm/fiberglass.html

Greg

 

[blackbrandt]

Also:
https://thayercraft.com/

 

[Issus]

https://fiberglast.com
https://www.sollercomposites.com/
https://cstsales.com/

Local composites dealer?

 

[wsume99]

Any suggestions for a good peel ply?

 

[CZ Brat]

So I'm considering taking a rocket kit that I've already purchased and replacing the stock 29mm MMT with a 38mm MMT. I can do my level 1 cert with it in either configuration so that's not really the issue. What I'm trying to ensure is that if I do upgrade to a larger MMT that the rocket will be able to handle the near full range of what that motor diameter has to offer. It seems like a huge waste to me to go with a 38mm MMT but then be limited to G and baby H motors because the airframe is too weak. Others can disagree with my opinion but this is MY rocket so I'll build and fly it how I want (within safe limits). That statement is not directed specifically at anyone but instead just letting everyone know where I'm coming from. I do value everyone's input so keep the comments coming. I'm learning A LOT.

What kit are you upgrading? How big of 38mm motors you want to put in it (full I, possible baby J for L2)?

 

[wsume99]

^^You may think I'm crazy but I'm considering using an Estes Argent. If I glass the whole thing it should be fine. Only issue I can see with a large motor will be recovery. Large I and baby J motors would definitely require dual deploy. I'm trying to build a rocket that is light enough to fly on E and G yet strong enough to handle a full I.

Edit: I meant F and G not E and G

 

[John Beans]

If you're going the route of minimum diameter and using punchy (not long-burn) motors, you should consider shortening your fins. Use a sim program to make sure the rocket is stable for any motor you will put in it, but if you keep the fin tips close to the fuselage and use a trapezoidal (not swept) shape, you'll dramatically stiffen them and dramatically reduce flutter. Remember: stability is a function of airspeed. If your rocket leaps off the pad, it's really moving at the end of the rod/rail. At high speed, the fins don't need to be that large to generate strong stabilizing moment around the center of gravity.