Sub Minimum Diameter L-2050 Build Thread

[manixFan]

I thought the discussion mentioned that off the shelf fin cans were not allowed in regards to records. Not sure if that is what track we're on at the moment. Not sure if that is even a rule.

Wow, I’m surprised that folks can’t take time to read a thread but still feel compelled to post. I clearly stated it was only my opinion, and likely an unpopular one at that. There is no such rule.

I absolutely regret bringing it up, especially since it seems some folks can’t seem to follow a thread.


Tony

 

[rfjustin]

Carbon fiber or fiberglass reinforcement (tip to tip) vacuum bagged or not is unnecessary on any minimum diameter rocket 75mm or smaller. Even some 98mm minimum diameter dont need it. It just adds weight and unnecessary costs. Using the correct epoxy, I use hysol E-120hp. With proper preparation to tube and fin you can exceed Mach 2 with absolutely no issues with a fin ripping off. Of course you have to design the rocket correctly. Yes, in the beginning of my rocket career over 10 years ago I would have said always do tip to tip because I actually did those steps. But now in the last 5 years no tip to tip for me. Now if I was using a high thrust 98mm motor in a min diameter the situation would be different.

While I do agree with you that tip-to-tip is not needed for the up part, the added strength might be needed for the down part. Especially those fin cans that get heat soaked by graphite nozzle motors. Minimum diameter is fun stuff.

 

[Rob702Martinez]

Wow, I’m surprised that folks can’t take time to read a thread but still feel compelled to post. I clearly stated it was only my opinion, and likely an unpopular one at that. There is no such rule.

I absolutely regret bringing it up, especially since it seems some folks can’t seem to follow a thread.


Tony

It's not a matter of not reading the thread before I post. I may have had the rule confused with L3 rather than records. And also stated wasnt sure if it was even a rule, but if it was, what it could have been about. No need to generalize "folks" when you're clearly referring to me. Its a discussion forum dont get all wound up.

 

[Michael Wilson]

After a bit of thought, how do you guys feel about 0.125 G10 fins, and beefy fillets (0.4-0.5 radius) with 3M DP460NS and possibly tip to tip CF with a thin layer of ablative? (I'm thinking about the Raytheon approach, Powdered cork and silicon epoxy)

 

[plugger]

why 4 fins, try 3 fins less drag, 4 does help with corkscrew but its a hit on CD

The main reasons are:
- using 4 fins allows them to be smaller for the same stability margin, this makes good structural sense
- I am told that 4 finned boosters tend to spin less during drogue descent, reducing tangling, important if you're spending a lot of time under drogue
- the intense CP shift experienced above M2.7 is less pronounced with 4 fin designs, i.e. you can start with a lower static stability margin on the pad and still retain enough margin at max V. This is seemingly confirmed by the sims and possibly also why so many military designs are 4 finned.
sauce

Carbon fiber or fiberglass reinforcement (tip to tip) vacuum bagged or not is unnecessary on any minimum diameter rocket 75mm or smaller. Even some 98mm minimum diameter dont need it. It just adds weight and unnecessary costs. Using the correct epoxy, I use hysol E-120hp. With proper preparation to tube and fin you can exceed Mach 2 with absolutely no issues with a fin ripping off. Of course you have to design the rocket correctly. Yes, in the beginning of my rocket career over 10 years ago I would have said always do tip to tip because I actually did those steps. But now in the last 5 years no tip to tip for me. Now if I was using a high thrust 98mm motor in a min diameter the situation would be different.

Gotta disagree here. For the up part up to Mach 3 it's unnecessary from my experience if you fins are appropriately designed. But if your trailing edge of your fin is swept back and could see some force applied to it on landing it could easily pop a fin. I've had this happen with a 54mm MD flight on a L935; I hit Mach 2.67 and the fins without t2t were fine but I popped a fin on landing under chute. I've done a M2245 MD flight where the nose cone/AV bay sheared off the top of the rocket at or near MaxQ at ~ Mach 3. Even with that anomoly the lower portion of the rocket (top of casing down) kept flying stably as the fins stayed on. Now I do a layer of t2t on MD birds just to provide a bit of added insurance that a fillet doesn't provide for landing. Remember for an altitude record you can't lose a fin and still claim the record.

Or on the flip side, anyone gone Mach 3.6 WITH tip to tip and had it stay intact?

Nic Lottering hit Mach 3.52 on a O3400 MD flight with a T2T fincan solely made from composites excluding the stainless steel caps he used on the fin leading edges.
sauce

They should just do away with the altitude record keeping it does not help in promoting safety

improved building methods should not be discourage by such rules

In the scheme of "safe flights" I've seen much worse from a safety perspective from odd rockets, unstable rockets, and poorly built rockets when compared to MD flights. If a MD flight fails most often it rekits itself and falls from the sky with plenty of warning in comparison to a craply built rocket landsharking towards the flight line just after ignition.

After a bit of thought, how do you guys feel about 0.125 G10 fins, and beefy fillets (0.4-0.5 radius) with 3M DP460NS and possibly tip to tip CF with a thin layer of ablative? (I'm thinking about the Raytheon approach, Powdered cork and silicon epoxy)

I think you'd be better served using CF fins when compared to G10 for above M3. I also think Nic Lottering's approach of using stainless for the leading edge makes more sense when compared to an ablative that will most likely incur more drag after burnout from ablation when compared to smooth stainless.

 

[Neutronium95]

The main reasons are:
- using 4 fins allows them to be smaller for the same stability margin, this makes good structural sense
- I am told that 4 finned boosters tend to spin less during drogue descent, reducing tangling, important if you're spending a lot of time under drogue
- the intense CP shift experienced above M2.7 is less pronounced with 4 fin designs, i.e. you can start with a lower static stability margin on the pad and still retain enough margin at max V. This is seemingly confirmed by the sims and possibly also why so many military designs are 4 finned.

One of the big reasons I've heard for four fins is that three fins can induce roll when they apply a corrective force. In most rockets that's not a big problem, but at the extreme speeds highly optimized designs can reach, a bit of roll can quickly turn into coning and possibly cause the rocket to shred or at least lose out on a lot of altitude.

 

[REK]

After a bit of thought, how do you guys feel about 0.125 G10 fins, and beefy fillets (0.4-0.5 radius) with 3M DP460NS and possibly tip to tip CF with a thin layer of ablative? (I'm thinking about the Raytheon approach, Powdered cork and silicon epoxy)

Look into these

https://www.eplastics.com/G10BLK-125X12X12
I recomend them, because someone I know shared his mach 3 flights using these have survived without any issues.

 

[ether]

The main reasons are:
- using 4 fins allows them to be smaller for the same stability margin, this makes good structural sense
- I am told that 4 finned boosters tend to spin less during drogue descent, reducing tangling, important if you're spending a lot of time under drogue
- the intense CP shift experienced above M2.7 is less pronounced with 4 fin designs, i.e. you can start with a lower static stability margin on the pad and still retain enough margin at max V. This is seemingly confirmed by the sims and possibly also why so many military designs are 4 finned.

https://forum.ausrocketry.com/viewtopic.php?f=10&t=4666&hilit=o3400#p54988

great source - thanks for pointing to it, came across it before, really great info there and awesome project and build skills

- yupp agree 4 less height, easier to handle fin flutter - however its a "circular" equation with the materials, materials that can hold up to higher velocities this can negate the point, however there is usually a con associated with the other material - principally weight

- under drouge make sense for the same reason as coning, can design around that via recovery system to make it less of an issue

- agree, again balancing with tradeoffs of higher CD of 4 fins and their weight vs 3 fins that have to be larger to compensate for CP shift - which needs to be considered also with propellant burn rate as CG is also moving during flight

military and sounding rockets not necessarily the best guidance, as Neutron95 mentions the effect of 4 fins in those scenarios helps those purpose built vehicles do what they need to do. For a pure altitude optimized flight, got to make trade-offs, look for good weather with limited wind throughout the flight.

i personally like how 4 fin rockets look and appreciate the benefits they bring, in-fact building something that will use 4 fins because i need a stable platform for doing a 360 degree video, but know that its a trade-off on other things, but this one is not about speed or altitude, looking for "verticality" over other attributes

 

[plugger]

...but this one is not about speed or altitude, looking for "verticality" over other attributes

Verticality is also a very good attribute for gaining optimized altitude.

 

[Michael Wilson]

Thank you for all of your advice, but I don’t understand where you guys are getting Mach 3.6 from, mine is simmed to just over Mach 3.1.
I’m thinking that I can just do t2t and have the leading edges coated with high temp epoxy, or possibly ablative. I think the stainless steel leading edges are a bit overkill for this project.
And as far as 4 fins over 3, Neutron95 couldn’t of said it better, with the added fact that there’s less cp shift with 4 fins in high Mach conditions

 

[conman13]

Thank you for all of your advice, but I don’t understand where you guys are getting Mach 3.6 from, mine is simmed to just over Mach 3.1.
I’m thinking that I can just do t2t and have the leading edges coated with high temp epoxy, or possibly ablative. I think the stainless steel leading edges are a bit overkill for this project.
And as far as 4 fins over 3, Neutron95 couldn’t of said it better, with the added fact that there’s less cp shift with 4 fins in high Mach conditions

It seems like you have a good grasp of what you need to do. You will want to utilize both leading edge protectant and an ablative. The ablative decreases the energy that reaches your T2T lamination during flight, protecting your epoxy system from decreasing in strength. The leading edge protectant will prevent the edges of your T2T lamination from peeling back. If you have access to Aero fin sim you can get a good grasp of the thickness material you should go with for your fin stock, if you don’t have it shoot me a PM and I can run an analysis of your fin shape.

 

[REK]

Thank you for all of your advice, but I don’t understand where you guys are getting Mach 3.6 from, mine is simmed to just over Mach 3.1.
I’m thinking that I can just do t2t and have the leading edges coated with high temp epoxy, or possibly ablative. I think the stainless steel leading edges are a bit overkill for this project.
And as far as 4 fins over 3, Neutron95 couldn’t of said it better, with the added fact that there’s less cp shift with 4 fins in high Mach conditions

I believe the Mach 3.1 sim you got is based your aluminum fin can design right?

If so, then you’d be surprised just how much weight you’d be removing if you use composites and therefore end up with higher speed numbers.

I’d would ditch the aluminum fin can for not only the weight reduction, but because you also introduce even more drag due to the fin can being a little larger in diameter than the base frame.

 

[Michael Wilson]

I believe the Mach 3.1 sim you got is based your aluminum fin can design right?

If so, then you’d be surprised just how much weight you’d be removing if you use composites and therefore end up with higher speed numbers.

I’d would ditch the aluminum fin can for not only the weight reduction, but because you also introduce even more drag due to the fin can being a little larger in diameter than the base frame.

Nope, Since i added an airframe it kinda balanced out, look:

 

[Joshua F Thomas]

Is OpenRocket accurate for flights above Mach 1? Just curious here....

 

[Rocketcamper123]

Nope, Since i added an airframe it kinda balanced out, look:
View attachment 428996

I NEVER WILL TRUST OPEN ROCKET OR ROCKSIM WITH A MACH 1+ FLIGHT NO MATTER THE SIZE OR DIAMETER. RASAERO IS THE WAY TO GO PERIOD!!!!! DONT WASTE YOUR TIME. SURE ITS OKAY TO USE TO FIGURE CALIBERS PRE FLIGHT FOR BALANCE BUT FOR ANY REAL FLIGHT INFO DO AWAY WITH EVERYTHING EXCEPT RASAERO

 

[Michael Wilson]

I NEVER WILL TRUST OPEN ROCKET OR ROCKSIM WITH A MACH 1+ FLIGHT NO MATTER THE SIZE OR DIAMETER. RASAERO IS THE WAY TO GO PERIOD!!!!! DONT WASTE YOUR TIME. SURE ITS OKAY TO USE TO FIGURE CALIBERS PRE FLIGHT FOR BALANCE BUT FOR ANY REAL FLIGHT INFO DO AWAY WITH EVERYTHING EXCEPT RASAERO

Oh don’t worry I’m checking things with Ras aero, open rocket is so much easier to design thru openrocket.

 

[Rocketcamper123]

Oh don’t worry I’m checking things with Ras aero, open rocket is so much easier to design thru openrocket.

design yes

 

[manixFan]

I NEVER WILL TRUST OPEN ROCKET OR ROCKSIM WITH A MACH 1+ FLIGHT NO MATTER THE SIZE OR DIAMETER. RASAERO IS THE WAY TO GO PERIOD!!!!! DONT WASTE YOUR TIME. SURE ITS OKAY TO USE TO FIGURE CALIBERS PRE FLIGHT FOR BALANCE BUT FOR ANY REAL FLIGHT INFO DO AWAY WITH EVERYTHING EXCEPT RASAERO

Interesting. I've used OpenRocket for several 38mm and 54mm MD rockets that have exceeded Mach 2 and it was pretty close. Maybe it's gotten better or doesn't work as well with larger diameters? The altitude and speeds have been within expected range of acceptable errors.

But I can see that approaching Mach 3 may be a different story.


Tony

 

[Rocketcamper123]

Interesting. I've used OpenRocket for several 38mm and 54mm MD rockets that have exceeded Mach 2 and it was pretty close. Maybe it's gotten better or doesn't work as well with larger diameters? The altitude and speeds have been within expected range of acceptable errors.

But I can see that approaching Mach 3 may be a different story.


Tony

i am just old school. i dont fall for what is popular. rasero works well for simulations. but true it may be better to build in openrocket and import into rasero. one thing with rasero you cant have double fins or elaborate fin shapes like in open rocket

 

[plugger]

Thank you for all of your advice, but I don’t understand where you guys are getting Mach 3.6 from, mine is simmed to just over Mach 3.1.
I’m thinking that I can just do t2t and have the leading edges coated with high temp epoxy, or possibly ablative. I think the stainless steel leading edges are a bit overkill for this project.
And as far as 4 fins over 3, Neutron95 couldn’t of said it better, with the added fact that there’s less cp shift with 4 fins in high Mach conditions

The Mach 3.6 came from another post, not yours. Just addressing it. If your sim tops out at Mach 3.1 t2t or leading edges coating or ablative aren't necessary. You can literally fly appropriate thickness CF fins with good fillets and be fine. You might pop one on landing but the up part will be fine.

 

[manixFan]

OP, If you consider carbon fiber plate for the fins, you might look into:

https://www.rockwestcomposites.com/p-t1100-125-11
It's surplus T1100 sheet. The price is very reasonable. There are other thicknesses available. Here's info on T1100:

https://www.torayca.com/en/download/pdf/torayca_t1100g.pdf
It seems to be well suited for fin material. I ordered a couple of sheets in two different thicknesses and it does seem to be stiffer than the other CF plate I have on hand. Hopefullfy someone can chime in with some real-world experience.


Tony

 

[ether]

Understand that rasaero got updated post that flight, if you sim it now, rasaero indicates instability

Using as many tools can't hurt, better to find out on the drawing board than in flight

 

[REK]

OP, If you consider carbon fiber plate for the fins, you might look into:

https://www.rockwestcomposites.com/p-t1100-125-11
It's surplus T1100 sheet. The price is very reasonable. There are other thicknesses available. Here's info on T1100:

https://www.torayca.com/en/download/pdf/torayca_t1100g.pdf
It seems to be well suited for fin material. I ordered a couple of sheets in two different thicknesses and it does seem to be stiffer than the other CF plate I have on hand. Hopefullfy someone can chime in with some real-world experience.


Tony

It is a high modulus carbon material making it very stiff. These are the components that have crazy strong properties that replace metal parts such as steel.

They make perfect sense to use as fins since they will be less likely to fin flutter due to the stiffness.

I’ve made some Intermediate modulus UNI carbon fins and the stiffness for 0.08” thick fins was impressive.

 

[ether]

Are they easy to cut out from those sheets?

 

[REK]

Are they easy to cut out from those sheets?

About the same with standard tools. I actually used a CNC router with a downcut flute to cut these.

Never the less tungsten carbide tools are your friend when cutting composites.

 

[Michael Wilson]

About the same with standard tools. I actually used a CNC router with a downcut flute to cut these.

Never the less tungsten carbide tools are your friend when cutting composites.

Hmm, Ill look into these. Thanks!

 

[Chuck Rogers]

….. I've been talking with one of the people on the Bare Necessities rocket, and while it simulated fine in Rasaero, apparently Openrocket indicated that there were problems with dynamic stability. That rocket ended up making a sharp turn at Mach 4 or so. Given that testimonial, I'm still likely to rely on Rasaero for raw altitude estimates, but also use Openrocket for design and as a second opinion for stability.

Doing a Google search, it looks like Bare Necessities was designed/flown back in 2012-2013. The Supersonic Center of Pressure (CP) issue identified in RASAero was corrected in the initial release of the RASAero II software back in 2015, five years ago.

I kind of get tired of people bringing up a RASAero issue from 8 or so years ago, which we corrected 5 years ago, and made some pretty wide announcements about the correction, and recommended that rocketeers download the new version of the software. We've had two subsequent RASAero II releases since then.

I believe that since 2015 RASAero II has the most accurate Supersonic CP predictions of any of the high power rocketry software packages.

See the RASAero II CP prediction comparisons with Supersonic CP wind tunnel data for the ARCAS sounding rocket in the following Rocketry Forum thread. In particular note the accuracy of the RASAero II Supersonic CP predictions at Mach 3 and Mach 4.
https://www.rocketryforum.com/showthread.php?130843-RASAero-II-Comparisons-with-Supersonic-CP-and-CD-ARCAS-Wind-Tunnel-Data

and the CP shift with Mach number, including my recommendation for using 2.0 calibers stability margin for all Supersonic Mach numbers, in the following Rocketry Forum thread:
https://www.rocketryforum.com/showthread.php?130690-Affect-of-mach-on-CP

Running the RASAero II software versions since 2015, and using a minimum Supersonic stability margin of at least 2.0 calibers, many rocketeers have had no stability issues with their Mach 3, and over Mach 3 flights using RASAero II.

There was one flight that had high altitude coning above 100K ft (a Jim Jarvis flight), and even on that flight from on-board flight data RASAero II was very accurately predicting velocity and altitude until the coning started.


Charles E. (Chuck) Rogers
Rogers Aeroscience

 

[CarVac]

The issues we had on Bare Necessities indeed were with the old version of RASAero.

I believe I've also mentioned this to Neutron95, but perhaps I should have emphasized it more.

That said, I haven't checked Bare Necessities's geometry in v2 to compare.

 

[Neutronium95]

Doing a Google search, it looks like Bare Necessities was designed/flown back in 2012-2013. The Supersonic Center of Pressure (CP) issue identified in RASAero was corrected in the initial release of the RASAero II software back in 2015, five years ago.

I kind of get tired of people bringing up a RASAero issue from 8 or so years ago, which we corrected 5 years ago, and made some pretty wide announcements about the correction, and recommended that rocketeers download the new version of the software. We've had two subsequent RASAero II releases since then.

Sorry about that. I've been out of the hobby for a few years, and only just jumped back in a few months ago. I will edit my original post to reflect that.

Thank you for making RASAero, it's a great tool for people making high performance rockets.

 

[Chuck Rogers]

Sorry about that. I've been out of the hobby for a few years, and only just jumped back in a few months ago. I will edit my original post to reflect that.

Thank you for making RASAero, it's a great tool for people making high performance rockets.

Really no problem. I tried to word my reply carefully. It was information you got from others, that I felt needed to be corrected.

And you're welcome on RASAero!


Charles E. (Chuck) Rogers
Rogers Aeroscience