An "R"-powered rocket build

[OverTheTop]

In the real world, split fins exist to provide steering of the rear fin set...in hobby rockets they exist for style....and when it comes to extremely high impulse levels, they don't exist at all....

Makes sense. I guess the earlier set of fins (or sometimes strakes) guide the airflow more predictably over the following set of fins.

 

[Andrew_ASC]

Here’s an example of someone not using aerofinsim or doing flutter predictions by hand at the least. Literally I would keep the fins simple and not over complicate fin design so the program can do the analysis. Bevel them if you want. Solid core flat plate single material. This is why you need a flutter analysis. You don’t want an R motor breaking fins by harmonic vibrations while under boost.

 

[Rail Dawg]

In the real world, split fins exist to provide steering of the rear fin set...in hobby rockets they exist for style....and when it comes to extremely high impulse levels, they don't exist at all....

The first thing you have to decide....is whether to build a BDR, ....a high altitude " throughbred" ...or something in between.....the thrust curve on the motor Pat designed looks more like a thoroughbred than a BDR to me....either way you go the most valuable resource you have are the guys that have " been there ...done that"...and the " techies" who can help you learn from others mistakes....and avoid making some new ones....you're already starting to attract some of the people who can help make this a successful project...as It progresses you'll undoubtably find more people willing to offer advice or help...just my opinion...

Well said Paul.

Like I've mentioned I'm eating this discussion up.

Although any rocket can fail this one is going to be built to handle the load.

Definitely watching and learning from every post.

Chuck C.

 

[jqavins]

The problem is with flutter analysis in a range of Mach 3-4 is rather important and the programs that do that assume it’s a solid material. Not honeycomb. Not airfoil. Not multi material.

OK, I get that. I have a couple of questions though, not advocacy. An EE's view of what flutter analysis would probably involve (that is to say, just enough knowledge to be dangerous) says that if you know the fin's strength and stiffness then what's inside (solid or honeycomb) which achieves those properties shouldn't matter; after all, the air doesn't go inside either way.

And this point I'm even less sanguine about: can an airfoil (or at least a bevel) ever make matters worse? That is, if the analysis is done for square edges then beveled edges are used, will it ever increase the flutter? One would think that less turbulence would be better for flutter just as it is for drag, but one knows that it does get complicated and hard to predict.

 

[Andrew_ASC]

Beveled edges will improve behavior in compressible flow by altering the oblique shock from strong blunt to weak conical behavior in theory. This may have a minor impact on flutter. The main thing about flutter is span, thickness, and material.

Let’s just leave airfoils out of this. Those are experimentally flutter tested. The tips when airfoiled can flutter before root when thickness tapers. Certain airfoils are more flutter resistant such as NACA 65A series symmetrical off of fighter jets for certain Mach ranges. The profiles airfoil or diamond are simply improving shockwave and compressibility behavior along with lower drag coefficients to the best of my knowledge as new ME. Harmonically by flutter they may be more or less prone to flutter depending on span, thickness, and material.

 

[Andrew_ASC]

In finsim there is an advanced section that allows users to flight test the airfoil in a supersonic wind tunnel and vibrate the fin to flutter experimentally then override more parameters if measured with a LVDT device or something capable of getting vibration data. This is what I assume professional companies would do for layered construction, hollow core, or complex airfoil geometry. You’ll see Langley for example flutter model airplanes in a tunnel first.

And that my friends is getting way beyond most hobbyists level. Literally on H-I range motors I’ve tested airfoils by assuming flat plate. Then flying it to see if the fins rip off. The better method is unaffordable. Would I try an airfoil or diamond or honeycomb core with an R? F*** no. Too dangerous in my opinion here based on what I know so far. A Mach 3-4 environment for a fin is no joking matter. Keep it simple please.

UTSI has a civilian Mach 4 wind tunnel with a 12” Test chamber if serious and loaded with $$$$. Other tunnels are for military use mainly or defense companies with multi million dollar budgets to answer experimentally if something flutters. Compressors costs to operate real wind tunnels are insane. Nothing replaces a real wind tunnel and real data.

 

[Andrew_ASC]

An EE's view of what flutter analysis would probably involve (that is to say, just enough knowledge to be dangerous) says that if you know the fin's strength and stiffness then what's inside (solid or honeycomb) which achieves those properties shouldn't matter; after all, the air doesn't go inside either way.

The air doesn’t have to go inside it for it to fail. It’s a vibrations problem. A honeycomb core has a outer layer skin. You have two different material modulus of elasticity values and no way to predict the flutter for it without physically destroying it on ground for real at a high Mach number. Look I’m not trying to insult you. I respect the honeycomb core makes fin lighter. There’s no way to accurately simulate and predict flutter for it achievable by hobbyist methods.

 

[jqavins]

I'm not insulted, and I'm not arguing for the honeycomb. I just find it curious (so asking if you can provide an explanation) that the separate properties of the honeycomb, face sheet, and adhesive matter if you can adequately characterize the whole. One should be able to measure the stiffness, density, whatever other characteristics of the finished fin, and it just seems weird that that's not good enough for whatever degree of simulation is possible for a solid fin.

 

[AeroAggie]

I'm not insulted, and I'm not arguing for the honeycomb. I just find it curious (so asking if you can provide an explanation) that the separate properties of the honeycomb, face sheet, and adhesive matter if you can adequately characterize the whole. One should be able to measure the stiffness, density, whatever other characteristics of the finished fin, and it just seems weird that that's not good enough for whatever degree of simulation is possible for a solid fin.

You’ve got it right. Finsim uses a single value for extensional and shear modulus, thus “seeming” to not account for anything other than a flat plate. In the real world, a structural analyst will calculate properties for the overall plate with any number of constituent materials. A hobbyist can come up with these numbers too using basic laminate theory, and input a user defined material in finsim.

 

[Ez2cDave]

"Back in the day", I did a lot of Drag Racing, both on the track and "otherwise".

My favorite "Speed Shop" had a sign up over the cash register.

It read, " Speed Costs Money . . . How Fast Do You Want To Go ? "

A lot of wisdom in those words . . .

Dave F.

 

[grouch]

Not that I have a say but I dig the ideas of big and dumb. Not snow mobile dumb but short and stubby dumb. Seems no matter how fast and high you go, somebody has already beat you but fat and stubby is always impressive. Imagine being able to keep it around 6000’ so you could see and feel the whole flight. Too cool.

 

[Rail Dawg]

Not that I have a say but I dig the ideas of big and dumb. Not snow mobile dumb but short and stubby dumb. Seems no matter how fast and high you go, somebody has already beat you but fat and stubby is always impressive. Imagine being able to keep it around 6000’ so you could see and feel the whole flight. Too cool.

Well I've got (2) 8' long 30" sonotubes in my rocket shed.

Cut out a bunch of centering rings, make it strong with all-thread stringers and figure out how to get a 100' parachute to deploy correctly.

Would like to do such a project.

Especially at an event like LDRS but the concerns for safety are well-justified.

Because it's Black Rock it's easier to build a 12" diameter G-12 rocket with off-the-shelf parts.

Trust me I'm tossing things around before an actual build begins lol.

Chuck C.

 

[BryRocket]

I have zero experience, hands on or otherwise, on such a project but it sure SEEMS to me that g12 tubes, layered internally with couplers as you mentioned, and then wrapped with 7-10 layers of CF would be strong enough for an airframe. I like the sounds of it anyway! You thinking the desert 2019? If so I hope I can make that.

 

[Rail Dawg]

I have zero experience, hands on or otherwise, on such a project but it sure SEEMS to me that g12 tubes, layered internally with couplers as you mentioned, and then wrapped with 7-10 layers of CF would be strong enough for an airframe. I like the sounds of it anyway! You thinking the desert 2019? If so I hope I can make that.

I think you're right in a G-12 build being sufficient.

And yes the desert in 2019. Love it out there.

Chuck C.

 

[Rail Dawg]

Well this is kind of interesting.

The Qu8k rocket with a Q motor weighed in at only 320 lbs.

It's a minimum diameter 8" rocket.

Flew to 121,000 ft.

The fins and nosecone were designed purely for speed and altitude.

My 12" design with less speed-efficient Nike Smoke-style fins and a weight of 520 lbs only sims to an altitude of 42,000 ft.

It's a "baby R" so not much over a "Q".

LDRS 2019 has an altitude waiver of 50,000'.

I still have a lot of tweaking to do and am still getting a handle on Open Rocket but this is actually quite encouraging.

Building a G-12 rocket is something I've done many times and I've always built these things bulletproof.

Got to keep running the simulations to see if I'm screwing something up but so far it's looking pretty darn good!

Chuck C.

 

[Andrew_ASC]

Let me know with a Mach number, nosecone length, and radius then I’ll reply with the aeroheating temp with calculation shown.

 

[Rail Dawg]

Mach 2.0

3 ft. nose cone (ogive)

6" radius

 

[Ez2cDave]

Cut out a bunch of centering rings, make it strong with all-thread stringers and figure out how to get a 100' parachute to deploy correctly.

Chuck C.

Churck,

I've been thinking about chute deployment . . . Got an idea, but need a lot of "feedback" on it.

What about using a "Pilot Chute" ( size TBD ) to pull the Main Chute out of the airframe ?

The Pilot Chute would not only pull the Main Chute out, but also help it to unfurl completely, without tangling.

Once the Pilot Chute "stretches" the Main Chute & Shroud Lines out, it should catch enough air to "blossom" the chute fully . . .

Thoughts ?

 

[BayouRat]

Back in 2011 I did get to see an actual R motor fly. I also know of one S motor that's out there ready to be flown but I'm sworn to secrecy on that project.

 

[Rail Dawg]

Churck,

I've been thinking about chute deployment . . . Got an idea, but need a lot of "feedback" on it.

What about using a "Pilot Chute" ( size TBD ) to pull the Main Chute out of the airframe ?

The Pilot Chute would not only pull the Main Chute out, but also help it to unfurl completely, without tangling.

Once the Pilot Chute "stretches" the Main Chute & Shroud Lines out, it should catch enough air to "blossom" the chute fully . . .

Thoughts ?

My thoughts exactly Dave.

Definitely want a successful recovery and focusing on getting the chute to unfurl correctly is a priority.

Thanks!

Chuck C.

 

[tbonerocketeer]

Churck,

I've been thinking about chute deployment . . . Got an idea, but need a lot of "feedback" on it.

What about using a "Pilot Chute" ( size TBD ) to pull the Main Chute out of the airframe ?

The Pilot Chute would not only pull the Main Chute out, but also help it to unfurl completely, without tangling.

Once the Pilot Chute "stretches" the Main Chute & Shroud Lines out, it should catch enough air to "blossom" the chute fully . . .

Thoughts ?

I think you're asking the wrong people...99% of the people here have never flown something this size. You need to look for the ones that have. A couple people that have this experience commented early on but have likely stopped as you seem to blow off their feedback.

 

[Andrew_ASC]

So I used an online oblique shock calculator for your wedge angle of 9.46 degrees at a entry Mach of 2.0. The exit Mach is 1.66 which I then used for your total temperature across the shock including oblique shock effect. You have a nosecone temperature of 372.35 degrees Fahrenheit assuming a room temperature starting point.

 

[Rail Dawg]

Back in 2011 I did get to see an actual R motor fly. I also know of one S motor that's out there ready to be flown but I'm sworn to secrecy on that project.

Very cool.

Now tell us more about this “S” rocket lol.

Chuck C.

 

[Rail Dawg]

View attachment 369575 View attachment 369574 So I used an online oblique shock calculator for your wedge angle of 9.46 degrees at a entry Mach of 2.0. The exit Mach is 1.66 which I then used for your total temperature across the shock including oblique shock effect. You have a nosecone temperature of 372.35 degrees Fahrenheit assuming a room temperature starting point.

Heading out but want to acknowledge your good work.

Will respond later.

Chuck C.

 

[Ez2cDave]

I think you're asking the wrong people...99% of the people here have never flown something this size. You need to look for the ones that have. A couple people that have this experience commented early on but have likely stopped as you seem to blow off their feedback.

Christopher Short
TRA #10247 L3 TAP
NAR #83000 L3CC
Prefect #38

Christopher,

So, as an L3CC / L3 TAP, what are your suggestions about getting a 100 ft cargo chute to deploy correctly ?

Dave F.

 

[tbonerocketeer]

Christopher,

So, given your "credentials", as an L3CC / TAP, what are your suggestions about getting a 100 ft cargo chute to deploy correctly ?

Dave F.

Never done it, so it is beyond my level. Point is, when I get to that kind of size chute, I'll find the people that have and ask them.

 

[Ez2cDave]

Never done it, so it is beyond my level. Point is, when I get to that kind of size chute, I'll find the people that have and ask them.

So, among the other L3CC / L3 TAP people in the USA, whom do you recommend to consult with on this ?

Dave F.

 

[tbonerocketeer]

So, among the other L3CC / L3 TAP people in the USA, whom do you recommend to consult with on this ?

Dave F.

Not sure about tap part, but maybe start with Steve eves as he flew that monster Saturn. Lance from kloudbusters also comes to mind with the monster rocket they just flew, as does wedge Oldham. Kevin trojanoski has done some monster rockets too...they exist, just need to locate them.

 

[ksaves2]

I've seen posters here in the past (been awhile though) who gave parachute advice and mentioned they were certified parachute riggers. That'd be someone to have for advice especially if they fly rockets.
I am inexperienced but I had reservations of this project of doing an R screamer but when I saw the specs above, looks nicely doable considering size and weight. Best a of luck. Kurt

 

[BayouRat]

Christopher,

So, as an L3CC / L3 TAP, what are your suggestions about getting a 100 ft cargo chute to deploy correctly ?

Dave F.

Why would you want to ask a TAP/L3CC? I was a loadmaster in the USAF. My job was to throw massive stuff out the back of a cargo plane. Half the TAP's and L3CC's can't even put their pants on the right way in the morning. How would they know anything about deploying large chutes.