Aurora 38mm MD rocket

[blackbrandt]

Nate.... did you check stability? The extra amount of weight in the back of the rocket with the fillets may affect your stability. Balance the loaded rocket and override the CG in OpenRocket.

 

[conman13]

Nate.... did you check stability? The extra amount of weight in the back of the rocket with the fillets may affect your stability. Balance the loaded rocket and override the CG in OpenRocket.

Hes fine.

 

[nute]

Nate.... did you check stability? The extra amount of weight in the back of the rocket with the fillets may affect your stability. Balance the loaded rocket and override the CG in OpenRocket.

When I was doing preliminary sims, I added an estimated fillet mass. I have yet to balance it, but I've been updating the sun
Sim as I go. Once I've got a final weight and cg with recovery, I'll put it in.

Nate

 

[conman13]

Alrighty then, I got my telemetrum back from Landru the other day. I had sent it to him so that he could make all the new telemetrum sleds and in return he sent me a couple of his 3d printed sleds. One of the sleds he sent me was a 38mm telemetrum sled. I got it all configured in my AVbay and I'm going to epoxy the nosecone and AV-bay in. After that all thats left to do is fillets and a clear coat!

 

[conman13]

first fillets done. Unlike the usual way of doing one side of 2 fins at once I did both fillets on one fin because i wanted to get the epoxy around the leading and trailing edge of the fin. They came out pretty nice but the leading and trailing edges need a bit of sanding. Other then that I'm happy. Pictures soon. I guess I will also mention I epoxied my nosecone and AV-Bay in the payload tube and got my electronics sled assembled. In addition I drilled 3 1/8" vent holes.

 

[codysmith]

I want pictures NOW!!!!! :gavel::gavel::gavel::rant::rant::rant::rant:

 

[conman13]

well still no pictures but all of the external fillets are done and sanded smooth. Now I just need nice weather in order to give it a couple coats of clear. Now to buy the rest of my telemetrum stuff.....

 

[codysmith]

Well, Why no pics???

 

[conman13]

Ok so I've been thinking about the motor I will fly it on. I am now going to fly this on the new Loki K, It is LDRS so go big or go home I'm now expecting mach 2.5 and 19,000ft. Of course with this new velocity I'm thinking I'm going to have to do a T2T of carbon on the fins. What do you all think?

 

[codysmith]

It may or may not be needed however it would look cool as heck if left unpainted!

 

[conman13]

It may or may not be needed however it would look cool as heck if left unpainted!

Either way fins and body are already carbon so won't look much different. Only thing being painted is cone.

 

[REK]

Ok so I've been thinking about the motor I will fly it on. I am now going to fly this on the new Loki K, It is LDRS so go big or go home I'm now expecting mach 2.5 and 19,000ft. Of course with this new velocity I'm thinking I'm going to have to do a T2T of carbon on the fins. What do you all think?

Its a K motor? Only Mach 2.5? How much power does that baby K have? I am sure its going to go faster, at this point I will recommend T2T.

 

[conman13]

Its a K motor? Only Mach 2.5? How much power does that baby K have? I am sure its going to go faster, at this point I will recommend T2T.

well its not really a K. it's 0% K.. I;m thinking T2T would be smart to.

 

[RocketHunter]

It depends on how stiff your fins are and how tall they are. On my 38mm flying case I'm looking at just under M3 on the K1127 or J1026. My fins are small and only 1.5" tall, are ~0.1" thick and constructed mostly with unidirectional CF perpendicular to the AF, so they are stiff as heck. If your fins are stiff/short enough to resist any flutter, and on straight, the forces trying to pull your fins off are not extreme and good sturdy epoxy fillets should be plenty strong enough. On the other hand, if your fins aren't stiff enough, T2T will add stiffness and increase your attachment stength. How thick/tall are your fins?

 

[conman13]

It depends on how stiff your fins are and how tall they are. On my 38mm flying case I'm looking at just under M3 on the K1127 or J1026. My fins are small and only 1.5" tall, are ~0.1" thick and constructed mostly with unidirectional CF perpendicular to the AF, so they are stiff as heck. If your fins are stiff/short enough to resist any flutter, and on straight, the forces trying to pull your fins off are not extreme and good sturdy epoxy fillets should be plenty strong enough. On the other hand, if your fins aren't stiff enough, T2T will add stiffness and increase your attachment stength. How thick/tall are your fins?

Fins are just under 2" tall, .1" unidirectional carbon crazy stiff, 5/8" JB Weld fillets. I think I'm just going to do the T2T for he heck of it. I'd rather slowdown a little then shred.

 

[REK]

Fins are just under 2" tall, .1" unidirectional carbon crazy stiff, 5/8" JB Weld fillets. I think I'm just going to do the T2T for he heck of it. I'd rather slowdown a little then shred.

What are you using for fillets? Lets face it everytime there is a shred its not due to fins being destroyed, its more due to the fillets giving up from all the forces that fin flutter causes.

Still I'm all for doing a T2T, better be safe than sorry.

 

[RocketHunter]

Fins are just under 2" tall, .1" unidirectional carbon crazy stiff, 5/8" JB Weld fillets. I think I'm just going to do the T2T for he heck of it. I'd rather slowdown a little then shred.

Yeah your fins aren't big and they sound quite stiff so you probably don't need T2T, but like you say, if you'd rather do it for some extra security, it can't hurt

 

[flynfrog]

T2T can hurt. It adds mass at the rear of the rocket that can cause it to be under stable. We are talking less than a 2 inch span here. If the fin shape is well designed and the bonding was done properly and the matl choice is correct T2T is not needed for a mach 2.5 flight

https://www.aerorocket.com/finsim.html

as we say in engineering Do Math

If you are going to do a Min diameter rocket why would you not try to maximize its performance.

Its easy to build a bridge that doesn't fall down. Its very hard to build a bridge that just barely does not fall down.

 

[A5tr0 An0n]

T2T can hurt. It adds mass at the rear of the rocket that can cause it to be under stable. We are talking less than a 2 inch span here. If the fin shape is well designed and the bonding was done properly and the matl choice is correct T2T is not needed for a mach 2.5 flight

https://www.aerorocket.com/finsim.html

as we say in engineering Do Math

If you are going to do a Min diameter rocket why would you not try to maximize its performance.

Its easy to build a bridge that doesn't fall down. Its very hard to build a bridge that just barely does not fall down.

THIS.

 

[markkoelsch]

Personally, I would ask what amendment did you use in your fillets? Epoxy by itself is not as strong.

 

[conman13]

Personally, I would ask what amendment did you use in your fillets? Epoxy by itself is not as strong.

As I used JB Weld nothing else was added.

 

[conman13]

I will do the math when I get home today and see what happens.

 

[markkoelsch]

It will likely be fine, but I think amendments make for a better/stronger fillet.

 

[REK]

As stated eariler the fillets are the ones that give in, not the fins. Flynfrog was right to check the stats using finsim to calculate whether or not the fillets will be enough.

I still need to learn how to use that software lol.

 

[flynfrog]

As stated eariler the fillets are the ones that give in, not the fins. Flynfrog was right to check the stats using finsim to calculate whether or not the fillets will be enough.

I still need to learn how to use that software lol.

Truth be told I used a spreadsheet I just cant find the link to it at the moment

If you are using Finsim use this walkthrough
https://www.aerorocket.com/FinSim_Supersonic_Flutter.html

It will likely be fine, but I think amendments make for a better/stronger fillet.

This depends if you are using neat resin like aeropoxy or west systems then yes adding some long fiber will help. If it is a paste adhesive made for bonding like EA9394 then adding anything will most likely weaken the fillet.

JB weld Im not sure

 

[RocketHunter]

I will do the math when I get home today and see what happens.

I've been playing around with the software for a while, checking both the fins on my project and yours. Using the weakest CFRP material (these are non-professional layups so best to assume the worst), for your fins I get 2.47 mach flutter velocity and 3.25 mach divergence velocity. Using the strongest CFRP material I get 2.91 mach flutter velocity and 3.86 mach divergence velocity. For additional comparison, if they were G10, flutter is at M1.6 and divergence at M2.01. (FYI, to get your fins CG, I copied 1 fin, put it on a mass-less BT in a new OR simulation, and used the calculated CG. Much easier and more accurate than doing the cutout technique.)

The last rocksim file you posted was pretty out of date it seemed; I added the conical NC, changed the finish to smooth paint, fins to rounded, and weight at 20oz.. With these parameters you're looking at M2.3 and 16-17,000'.

Overall then, I would say that you're probably just fine w/o T2T as long as your AOA stays low to keep the fin bending stress down.

Its amazing how the height of the fin changes the results - for my fins which are 1.5'' tall (vs yours @ 2''), using the weakest CFRP, flutter is @ M3.75 and divergence @ M5.97. Even using G10, flutter is at M2.27 & divergence at M3.7.

 

[conman13]

I've been playing around with the software for a while, checking both the fins on my project and yours. Using the weakest CFRP material (these are non-professional layups so best to assume the worst), for your fins I get 2.47 mach flutter velocity and 3.25 mach divergence velocity. Using the strongest CFRP material I get 2.91 mach flutter velocity and 3.86 mach divergence velocity. For additional comparison, if they were G10, flutter is at M1.6 and divergence at M2.01. (FYI, to get your fins CG, I copied 1 fin, put it on a mass-less BT in a new OR simulation, and used the calculated CG. Much easier and more accurate than doing the cutout technique.)

The last rocksim file you posted was pretty out of date it seemed; I added the conical NC, changed the finish to smooth paint, fins to rounded, and weight at 20oz.. With these parameters you're looking at M2.3 and 16-17,000'.

Overall then, I would say that you're probably just fine w/o T2T as long as your AOA stays low to keep the fin bending stress down.

Its amazing how the height of the fin changes the results - for my fins which are 1.5'' tall (vs yours @ 2''), using the weakest CFRP, flutter is @ M3.75 and divergence @ M5.97. Even using G10, flutter is at M2.27 & divergence at M3.7.

Thanks. I'm going to run some myself as there are some differences from the parameter you used however it gives me a great start. Speaking of Files, Here is the final Open rocket file:

View attachment Aurora.ork

 

[RocketHunter]

Thanks. I'm going to run some myself as there are some differences from the parameter you used however it gives me a great start. Speaking of Files, Here is the final Open rocket file:

View attachment 259987

Ok thanks. So it looks like your fins are a bit shorter now, that should raise the flutter and divergence velocity to well over your predicted maximum speed, so as long as you're confident in the strength of your fillets I think you're safe.

 

[conman13]

Done!!

 

[conman13]