O3400 Min Diameter L3

[Dustin Lobner]

That checks, I would hate to lose a $1,000+ build trying to save $50 on epoxy... Do you normally trust the mixing that that nozzle does or do you mix it extra to be sure?

-Tony

Use the long mixing tips and you're good. I actually learned back in school (I'm a Materials Engineer) how to calculate what you have to do for those nozzles to "fully mix" things. As stated above, use the long ones and you're good.

 

[airforcetp1991]

Use the long mixing tips and you're good. I actually learned back in school (I'm a Materials Engineer) how to calculate what you have to do for those nozzles to "fully mix" things. As stated above, use the long ones and you're good.

This is my first time using this epoxy mix gun setup, what would be a long vs short nozzle? the ones I have are about 3" long.

-Tony

 

[Dustin Lobner]

This is my first time using this epoxy mix gun setup, what would be a long vs short nozzle? the ones I have are about 3" long.

-Tony

Long is about 6-8", you have shorts.

 

[airforcetp1991]

Long is about 6-8", you have shorts.

Thank you!

 

[David Schwantz]

I actually prefer mixing in a dixie cup. Squirted right out of the gun, no tip. That way I can put it into a syringe if needed, or just apply with pop stick or whatever is needed.

 

[DAllen]

Wait...you're NOT going to use the 5 minute LocTite epoxy they have on sale at Wally World????

 

[David Schwantz]

I love Wally World

 

[airforcetp1991]

Wait...you're NOT going to use the 5 minute LocTite epoxy they have on sale at Wally World????

You could build the whole rocket in 1 day....

 

[DAllen]

You could build the whole rocket in 1 day....

I want to meet the L3 TAP that would sign off on that nonsense.

Methinks said TAP does not exist.

 

[jimzcatz]

Not that anyone would heed my advice,advice based on my opinion. This a a BAD idea. I cannot in good conscience wish you good luck. Get your cert, fly a few M motors and then go stupid crazy. Which this project is most definitely.

 

[jimzcatz]

I want to meet the L3 TAP that would sign off on that nonsense.

Methinks said TAP does not exist.

Gawd I hope you are right.

 

[airforcetp1991]

Not that anyone would heed my advice,advice based on my opinion. This a a BAD idea. I cannot in good conscience wish you good luck. Get your cert, fly a few M motors and then go stupid crazy. Which this project is most definitely.

I very much respect your opinion, advice and experience. I'm not naïve to the difficulty of what I am proposing or the possibility of failure for any number of reasons, it's not my intent to challenge your position but I would like to explain more of my thinking. If this is just a dumb L2 guy speaking out of turn well then I am sure everyone will ignore it appropriately...

What I would say is that at the end of the day no hobby rocketry project will ever come close to what is truly possible (SpaceX, NASA...etc) and so I think the question becomes why do it, why spend the money and risk the failure of all your hard work. For me the answer to that question is that I am passionate about the scientific and engineering challenge that has to be overcome to make a project like this succeed and find real enjoyment in seeing it (hopefully) succeed. So is this project a bad idea, yes, in many ways it probably is, I'd be much better off investing the money but that isn't going to give me the same sense of accomplishment and fulfill that passion. If I am able to/allowed make this attempt and end up picking up a bunch of shredded pieces of carbon fiber I'll take the "I told you so" gladly, from more than one direct I'm sure, but I will be happy knowing I followed what I am passionate about.

-Tony

 

[watheyak]

Are people forgetting that some VERY notable and popular people in the community have done level 3 projects very similar to this?

Tony isn't the first and won't be the last to do a 4" minimum diameter Level 3 cert.

What if most of what you've done prior is minimum diameter high performance rockets, and that's all you intend to do in the future? Why on Earth would you do a big carboard rocket with an M? Seems like THAT would be a really bad idea.

So good luck, and don't put any stock in the nay-sayers paranoias.

 

[jimzcatz]

Not minimum diameter O to 85k. I would pass a cardboard rocket on an M before this. In fact my L3 was just that. 7.5 inch paper on 3"M

 

[watheyak]

Not minimum diameter O to 85k. I would pass a cardboard rocket on an M before this. In fact my L3 was just that. 7.5 inch paper on 3"M

I stand corrected. Multiple minimum diameter N level 3 projects. One, an N5800. All successful.

 

[ChuckH]

Not that anyone would heed my advice,advice based on my opinion. This a a BAD idea. I cannot in good conscience wish you good luck. Get your cert, fly a few M motors and then go stupid crazy. Which this project is most definitely.

Are we doing this again? lol

 

[jimzcatz]

Evidently

 

[watheyak]

Evidently

Correct me if I'm wrong, but I'm pretty sure we'd prefer YOU didn't take us down this road.

Enjoy your popcorn.

Can we please get on with the build thread without the carboard rocket police, please?

 

[plugger]

I am designing a L3 build for this summer, for a BALLS launch or locally if the waiver is approved. The overall concept is a 60" carbon airframe from Wildman with a 2" switch band and a 24" VK nosecone. Redundant Raven4 altimeters and Raptors for the drogue deployment. It is a head-end dual deployment concept with a Sim max altitude of ~85,000 according to RASAero II (rounded fin edge for a conservative estimate) with a max Mach of ~3.6. Planning on 3 or 4 #6 shear pins for each section.

I'd revisit that sim if I were you. I don't believe you'll get anywhere near 85k on a O3400 in an aluminum casing. Nic Lottering hit just shy of 66k on an O3400 and Greg Morgan hit just over 70k with MD designs. It's possible you have some incremental optimisations but I find it hard to believe that either one of those guys left 15-20k feet on the table, especially when you look at their builds. If I were you I'd ensure a healthy stability margin.

And FTR I flew a baby M (M2250) in a MD airframe for my L3. I probably would have gone harder if I had the ceiling to support it. I'm not sure I would have considered the O3400 though...

 

[airforcetp1991]

I'd revisit that sim if I were you. I don't believe you'll get anywhere near 85k on a O3400 in an aluminum casing. Nic Lottering hit just shy of 66k on an O3400 and Greg Morgan hit just over 70k with MD designs. It's possible you have some incremental optimisations but I find it hard to believe that either one of those guys left 15-20k feet on the table, especially when you look at their builds. If I were you I'd ensure a healthy stability margin.

And FTR I flew a baby M (M2250) in a MD airframe for my L3. I probably would have gone harder if I had the ceiling to support it. I'm not sure I would have considered the O3400 though...

I agree the SIM is very optimistic and I will not bet my life on the altitude it predicts... SM will be at least 2 calibers throughout for sure.

I have looked at both their build threads extensively and I see 2 key differences.

1) They used a 4 fin rather than 3 fin design and as we all know the drag penalty is high at >Mach 3

2) There was a step in the design where the top of the fin can met the case and I believe that will have a significant affect at the speeds we are talking about.

Both of these differences I feel are further magnified by the ~50 secs of coast time post burn out. Again this is not to say the SIM is perfect, it most certainly is not but I do think there is evidence that the design differences are valid. I have looked into the build below which achieved a 70,500' flight on an O3400 with a 3 fin design. My fins are smaller which will make some difference but I do think this supports the idea that the "sub min diameter" design, though very impressive, may not be optimal.

 

[plugger]

1) They used a 4 fin rather than 3 fin design and as we all know the drag penalty is high at >Mach 3

4 fin designs are more stable when compared to 3 fins. To my understanding that's the main reason why MD designs have shifted to 4 fin designs instead of 3 over recent years. Also, 4 fins allows you to have less span/height and still be stable, which helps with reducing both drag and fin flutter.

2) There was a step in the design where the top of the fin can met the case and I believe that will have a significant affect at the speeds we are talking about.

That's just not the case when you look at Nic Lottering's design. He hit Mach 3.52 max V which is very similar to your sim prediction.

I 100% agree that fin can designs induce drag at the top of the fin can, but I don't believe they're so draggy that you'd leave that much margin on the table. Furthermore the fin can step would have a positive impact on stability which is very beneficial in flights this aggressive.

...I do think this supports the idea that the "sub min diameter" design, though very impressive, may not be optimal.

I, like you, don't believe sub min diameter is the answer for more altitude. And for the record Nic doesn't either (I've spoken to him at length about this in the past). With that said I don't believe they are more inefficient when compared to a 'classic' min dia design. My expectation is that all that effort comes out in the wash.

Finally, your NC is less efficient/more draggy at 6:1 that Nic's was given he made his own 7.5:1 design. That's going to negatively impact your post boost coast time when compared to his flight.

 

[AeroAggie]

I'd recommend you keep minimum 2 calibers stability at Mach 3, not just sitting on the pad. You may need 4 calibers on the pad.

 

[Rocketjunkie]

I'm still waiting for a TAP that will witness and sign off on the flight.

 

[airforcetp1991]

4 fin designs are more stable when compared to 3 fins. To my understanding that's the main reason why MD designs have shifted to 4 fin designs instead of 3 over recent years. Also, 4 fins allows you to have less span/height and still be stable, which helps with reducing both drag and fin flutter.



That's just not the case when you look at Nic Lottering's design. He hit Mach 3.52 max V which is very similar to your sim prediction.

I 100% agree that fin can designs induce drag at the top of the fin can, but I don't believe they're so draggy that you'd leave that much margin on the table. Furthermore the fin can step would have a positive impact on stability which is very beneficial in flights this aggressive.



I, like you, don't believe sub min diameter is the answer for more altitude. And for the record Nic doesn't either (I've spoken to him at length about this in the past). With that said I don't believe they are more inefficient when compared to a 'classic' min dia design. My expectation is that all that effort comes out in the wash.

Finally, your NC is less efficient/more draggy at 6:1 that Nic's was given he made his own 7.5:1 design. That's going to negatively impact your post boost coast time when compared to his flight.

If the fins are the same size yes I would agree that the 4 fin design is more stable but you can achieve the same Cp location and SM with 3 fins if they are sized and located properly. At high speed there is going to be an optimal point where the span length and surface area of the fins balance out and it may be that a 25% increase in span with 3 fins is less net drag than a 4 fin design with a smaller span. From the SIMs I have run it seems that the 3 fin design gives the best balance. The flutter is a concern I agree.

I was looking at Nic Lottering's O3400 build on the Tripoli Records page which does appear to show a step but I will not claim to know him better than you by any means. To be fair that step will also create another oblique shock which would reduce fin stress/drag so it may very well wash out.

I agree the 7.5:1 is more efficient however from what I can tell based on this article (https://www.apogeerockets.com/education/downloads/Newsletter376.pdf) there is a point of diminishing returns past about a 5:1 ratio. Does that check, I am not an expert on this, but it would seem that at some point the increased surface area will create enough drag to overcome the more optimal shape?

 

[airforcetp1991]

I'd recommend you keep minimum 2 calibers stability at Mach 3, not just sitting on the pad. You may need 4 calibers on the pad.

I completely agree and the SIMs I have run so far in RASAero II support that.

 

[3stoogesrocketry]

I want to meet the L3 TAP that would sign off on that nonsense.

Methinks said TAP does not exist.

I'm still waiting for a TAP that will witness and sign off on the flight.

over here......

Show me you know what your talking about and let's do it. Why should we all say no to the OP simply because we will never do it or it has not been done ?

 

[THarrison]

I built a similar 98mm minimum diameter rocket and made the FWFG airframe 2” shorter than the casing. The nosecone then fit right over the top end of the case. I didn’t trust any unsupported sections of airframe tubing. I mounted a sled in the tip of the nosecone with a Big Red Bee GPS and a Raven. In the middle area of the cone I stuffed a tight packing Spherachute with a cable cutter release. I’ve seen a lot of 98mm airframes fail, so you might want to consider this approach since your design is already pretty short. Just some food for thought.

Todd Harrison

 

[airforcetp1991]

I built a similar 98mm minimum diameter rocket and made the FWFG airframe 2” shorter than the casing. The nosecone then fit right over the top end of the case. I didn’t trust any unsupported sections of airframe tubing. I mounted a sled in the tip of the nosecone with a Big Red Bee GPS and a Raven. In the middle area of the cone I stuffed a tight packing Spherachute with a cable cutter release. I’ve seen a lot of 98mm airframes fail, so you might want to consider this approach since your design is already pretty short. Just some food for thought.

Todd Harrison

That is a big concern I have as well and I liked the elegance of the Sub-min diameter builds in how everything was contained in the nosecone. That also eliminated the need for one of the joints at the switch band in my current design. I liked the Parana cable cutter for that concept a lot but the big thing that worried me was the use of BP at such a high altitude. I have read a lot of threads of people using the charge cannons successfully but it is something I have no experience with.

Did you have any issues with the fit of the nosecone on the case? Also maybe I am just not imagining it right, but where did you place the shear pins or equivalent if the NC was over the case?

-Tony

 

[OverTheTop]

Have a look at some of the builds by cryoscum. He held the Tripoli O class commercial record for altitude and speed. O3400 to 66k' and M3.6 IIRC

Here are a couple of his threads on the Australia forum:
https://forum.ausrocketry.com/viewtopic.php?f=10&t=4666https://forum.ausrocketry.com/viewtopic.php?f=10&t=4253https://forum.ausrocketry.com/viewtopic.php?f=10&t=3659
There should be some useful information there .

Enjoy the build!

 

[watheyak]

I built a similar 98mm minimum diameter rocket and made the FWFG airframe 2” shorter than the casing. The nosecone then fit right over the top end of the case. I didn’t trust any unsupported sections of airframe tubing. I mounted a sled in the tip of the nosecone with a Big Red Bee GPS and a Raven. In the middle area of the cone I stuffed a tight packing Spherachute with a cable cutter release. I’ve seen a lot of 98mm airframes fail, so you might want to consider this approach since your design is already pretty short. Just some food for thought.

Todd Harrison

I agree. My recent 90g flight was built similar to this. As few joints and as little unsupported airframe as possible with a very, very strong coupler.

My 4" N project that's in the works for Balls is built exactly as you describe. Which, full disclosure, is also my level 3 project. Hence my interest I your build, Tony. I've already got multiple TAPs, so it's definitely not out of the question.

Did you have any issues with the fit of the nosecone on the case? Also maybe I am just not imagining it right, but where did you place the shear pins or equivalent if the NC was over the case?

My solution to this is a Delrin disc that sits on top of the forward closure. It has a very slight taper to match the interior of the nosecone, adds stability to the joint and gives you a place for the shear pins.